DE102021133714B3 - Arrangement and method for mark-free 3D imaging - Google Patents

Abstract

The invention relates to an arrangement and a method for mark-free 3D imaging, in particular for examining biological objects with a spatial resolution in the sub-micron range. The object of the present invention is an arrangement and a method for mark-free 3D imaging, in particular quantum imaging with high-energy radiation is achieved in that the arrangement uses a laser-controlled / -driven light source in the form of an ultra-short, high-power laser for generating high harmonics in a gas environment with a wavelength in the range from 1 nm to 124 nm, with laser radiation from an optical parametric amplifier ( 1) in an argon gas jet (2) and the generated HGG radiation passes through a thin metal foil (3), a toroidal mirror (4) which focuses the HHG radiation (5) onto an intermediate focus (51) and from which this then reaches a single photon detector in the form of an SNSPD (6) and a sample holder (7) for the precise positioning of a sample to be examined in the intermediate focus (51), the SNSPD (6) having at least one straight, elongated superconducting nanowire (8) on one Supporting and forming a cryogenic sNSPD, this nanowire (8) is embedded in a coplanar waveguide connected to a bias tee that separates the bias and sense lines and reads out voltage pulses V1 and V2 at the two ends of the nanowire (8), a closed-cycle cryocooler (9) is provided for cooling the linear straight-elongated superconducting nanowire (8) in the temperature range of 1 K to 4 K, with ultra-high vacuum conditions at the position of the cryogenic sSNPD's to to prevent residual gas from the HHG source from freezing out at the position of the nanowire (8), a current source for applying the bias current to the linear, straight, elongated, superconducting nanowire (8) is provided, and a readout amplifier (10) is provided with an evaluation unit (11) for measuring the voltage pulses V1 and V2, which arise as a result of the impact of a photon on the linear, straight, elongated, superconducting nanowire (8) at the two ends of the nanowire (8).

Description

The invention relates to an arrangement and a method for mark-free 3D imaging (i.e. for 3D imaging), in particular for examining biological objects with a spatial resolution in the sub-micron range.

The examination of biological 3D objects with a spatial resolution in the sub-µm range has so far been carried out by transmission electron microscopy (TEM) with a spatial resolution in the nm range (currently from 0.045 nm), by X-ray diffraction / X-ray diffraction (XRD) with a spatial resolution in the sub- µm range (up to 10 nm) and by label-free imaging using photon-induced force microscopy (PiFM).

The disadvantage of transmission electron microscopy (TEM) is that the original in vivo structures of the 3D biological objects have to undergo extensive sample preparation. For example, the biological 3D objects are embedded in complex preparation and divided into thin slices and then cut into ultra-thin layers on an ultramicrotome, since the object must be sufficiently thin for the electrons to be able to radiate through it. TEM is therefore particularly well suited for the direct imaging of cell structures (i.e. cell sections) of prokaryotes and eukaryotes.

The disadvantage of X-ray diffraction / X-ray diffraction (XRD) is that the biological material has to be crystallized in a time-consuming process, since the diffraction of X-rays only takes place on ordered structures (e.g. crystals) and during crystallization usually the original in vivo structures of the biological 3D objects are destroyed. XRD is therefore particularly well suited for investigating the structure of DNA or the structure of proteins, such as enzymes from prokaryotic and eukaryotic cells.

The disadvantage of photon-induced force microscopy (PiFM) is that only information in the 10 to 20 nm range about the surface can be obtained, but no depth information of the biological 3D objects and no label-free detection of individual molecules or atoms is possible. The PiFM is therefore particularly suitable for the 3D examination of cell surfaces and similar structures, whereby non-conductive samples can also be examined.

In addition, it is known that light detectors are inherently critical components of optical imaging and telecommunications systems.

Electronic components are referred to here as light detectors/photosensors/optical detectors/optoelectronic sensors, which convert light into an electrical signal using the photoelectric effect or exhibit an electrical resistance that is dependent on the incident radiation.

For example, single photon detectors in the form of photomultipliers or photodiodes have been known as light detectors for decades.

An ultimate photon detector must be able to detect the elementary excitation of the incident radiation (= a single photon). Such a photon detector has been implemented for several years in the form of a superconducting nanowire single photon detector (SNSPD or SSPD).

The Superconducting Nanowire Single Photon Detector (SNSPD or SSPD) is a type of optical and near-infrared single photon detector based on a current-fed superconducting nanowire that enables photon counting.

The superconducting nanowire single photon detector (SNSPD) consists of a thin superconducting film on an insulating substrate. The superconducting film is formed into a meandering nanowire by nanofabrication processes. This geometry of the single photon detector makes it possible to cover a large surface area on the insulating substrate, collect all the incident radiation, which is coupled into the SNSPD, e.g. via an optical fiber, and at the same time create a single path for the current flow when current is applied. The detectors in the form of the SNSPD are mainly operated in the range from 1 to 4 Kelvin and a constant current (quiescent current = so-called bias current) below the critical current of the superconducting material in nanogeometry is fed into the SNSPD. The nanoscale cross-section gives the SNSPD extremely high sensitivity, allowing detection of absorption of just a single photon.

Once a single photon is absorbed in the meandered nanowire of the SNSPD, the nanowire is heated in a small area, locally breaking the superconductivity and locally inducing electrical resistance in the SNSPD. When the bias current is present, this temporary resistance generates a voltage pulse that is registered by the connected amplification electronics. Within a few nanoseconds, the heated area cools down again and the SNSPD is ready to detect the next photon.

Compared with other types of single photon detectors, the superconducting nanowire single photon detector has very high detection efficiency, very low dark count rate, and very low temporal jitter.

• • sehr hohe Detektionseffizienz auf Grund niedrige Totzeit, (d.h. Zeitintervall nach einem Detektionsereignis, in dem der Detektor nicht empfindlich ist) in der Größenordnung von einigen Nanosekunden. Diese kurze Totzeit führt zu sehr hohen Sättigungszählraten, was zu einer sehr hohen Detektionseffizienz führt.
• • niedrige Dunkelzählraten (das Auftreten von Spannungsimpulsen auf der Verstärkungselektronik in Abwesenheit eines detektierten Photons)
• • niedriger Jitter (d.h. die Unsicherheit in der Ankunftszeit der Photonen) im Bereich von Pikosekunden. Der Timing-Jitter ist eine äußerst wichtige Eigenschaft für Anwendungen der zeitkorrelierten Einzelphotonenzählung (TCSPC).

To explain these three terms / properties:

• • very high detection efficiency due to low dead time, (ie time interval after a detection event in which the detector is not sensitive) in the order of a few nanoseconds. This short dead time results in very high saturation count rates, resulting in very high detection efficiency.
• • low dark count rates (the occurrence of voltage pulses on the amplification electronics in the absence of a detected photon)
• • low jitter (ie the uncertainty in the arrival time of the photons) in the picosecond range. Timing jitter is an extremely important property for time-correlated single photon counting (TCSPC) applications.

• Der supraleitende Nanodraht-Einzelphotonendetektor besteht aus einem dünnen (≈ 5 nm bis ≈ 100 nm) supraleitenden Nanodraht, dessen Länge in der Regel Hunderte von Mikrometern beträgt, wobei der Nanodraht in einer kompakten Mäandergeometrie strukturiert ist, um ein quadratisches oder rundes Pixel mit hoher Detektionseffizienz auf dem isolierenden Trägermaterial zu erzeugen.

On the principle of how a superconducting nanowire single photon detector works:

• The superconducting nanowire single photon detector consists of a thin (≈ 5 nm to ≈ 100 nm) superconducting nanowire, typically hundreds of microns in length, where the nanowire is structured in a compact meander geometry, around a square or round pixel with high detection efficiency to generate on the insulating carrier material.

The nanowire is cooled below its critical (strain) temperature and subjected to a constant direct current (bias current) that is close to, but less than, the critical current of the superconducting nanowire.

A photon hitting the nanowire breaks Cooper pairs and reduces the local critical current below that of the bias current. This leads to the formation of a localized non-superconducting area or hot spot of increased electrical resistance. This resistance is typically larger than the sense amplifier's 50 ohm input impedance, so most of the bias current is shunted to the amplifier. This creates a measurable voltage pulse approximately equal to the bias current multiplied by 50 ohms.

The time it takes for the current to return to the nanowire is typically determined by the inductive time constant of the nanowire, which is equal to the kinetic inductance of the nanowire divided by the impedance of the readout circuit. For proper device self-reset, this inductive time constant must be slower than the intrinsic cooling time of the nanowire hotspot.

Most currently known superconducting nanowire single photon detectors are made of sputtered niobium nitride (NbN), which has a relatively high superconducting critical temperature (≈ 10 K) that allows SNSPD operation in the temperature range of 1 K to 4 K (compatible with liquid helium or modern closed circuit cryocoolers). The intrinsic thermal time constants of NbN are short, resulting in very fast cooling after photon absorption (<100 picoseconds).

Current and emerging applications of superconducting nanowire single-photon detectors include imaging of infrared photoemission, characterization of single-photon emitters, and high-time-resolution photon detection.
(https://en.wikipedia.org/wiki/Superconducting_nanowire_single-photon_detector)

WO 2015/139361 A1 discloses a method and apparatus for reducing the extrinsic dark number of a nanowire single photon detector, wherein a multilayer film filter is provided on a superconducting nanowire single photon detector, and the multilayer film filter is dielectric and has a bandpass filter function.

A substrate is bonded to a surface of the multilayer filter, the substrate having an upper surface bonded to an upper anti-reflection layer and a lower surface bonded to a lower anti-reflection layer and forming an optical cavity structure bonded to a surface of the the top anti-reflective layer of the substrate, the superconducting nanowire being located between the top anti-reflective layer of the substrate and the optical cavity structure, and a reflector connected to a surface of the optical cavity structure.

A mark-free 3D imaging, especially for examining biological objects ten with a spatial resolution in the sub-micron range is not possible with this arrangement and this method.

WO 2020/127927 A1 discloses a photodetector comprising a microcell array and an output module configured to collect an output signal from each microcell upon photon detection by that microcell and to combine the collected output signals into at least one output line. Each microcell consists of a first device and a second device, at least one of the devices being a photosensitive device capable of detecting the photon, a temporal resolution module connected to this photosensitive device(s) and configured to provide a trigger signal to said photosensitive device(s) to activate them, and a reader module configured to receive when the photon arrives at the activated photosensitive device(s), a corresponding signal from the(s). activated photosensitive device(s) and based on the received signal to provide the output signal to the output module.

At the same time, she teaches WO 2020/127927 A1 that both the first device and the second device are single-photon diodes, and the gate signal is used to reverse-bias (the so-called reverse or bias voltage) across the first photosensitive device and the second photosensitive device from bottom to modulate above via a breakdown voltage thereof. The readout module is a differential readout circuit configured to detect a current/voltage change in the first device or in the second device caused by the detection of the photon and to provide the output signal indicative of this photon detection .

A mark-free 3D imaging, in particular for examining biological objects with a spatial resolution in the sub-micron range, is not possible with this arrangement and this method.

Laser-controlled and/or -driven light sources [ultra-short, high-power lasers for generating high harmonics (so-called HHG) in gases] in the extreme ultraviolet range (EUV with a wavelength of 10-124 nm) and in the soft X-ray range (SXR with a wavelength of 1-10 nm) enable nanoscopic Imaging by lensless imaging methods with unique mark-free elementary contrast. However, in order to take full advantage of the unique properties of these new light sources, novel detection methods must be provided.

In current EUV/SXR imaging applications, silicon-based back-illuminated thinned CCD detectors are typically used as detectors. The quantum efficiency of these detectors can reach values of more than 90% in the EUV range [I. Moody, M Watkins, R Bell, M Soman, J Keelan, and A Holland, CCD QE in the Soft X-ray Range. (2017)]. However, the SNR is limited by read noise and dark counts and is therefore not ideal for EUV/SXR imaging with minimized photon throughput.

In addition, due to their integrating measurement principle in connection with the very different illumination of different regions on the detector, which is typical for lensless imaging, these detectors cannot use the very high repetition rate of several 100 kHz of high-flux HHG sources, since the readout times are typically in on the order of milliseconds to seconds.

Photon counting in the SXR and EUV range has hitherto usually been carried out using electron multiplier multichannel plates (MCP). The efficiency of the MCPs and thus also their use is limited due to the open area ratio of the MCPs, the high dark count rate and the low count rate.

CCD cameras can detect individual photons of harder X-rays and can therefore be used as counting detectors. CCD cameras have limited readout times of the order of milliseconds up to seconds.

For low-energy photons, counting with CCDs is not possible due to readout noise.

There are a number of semiconductor detectors for photon counting, such as B. Avalanche photodiodes [p. Cova, M. Ghioni, A. Lacaita, C. Samori, and F. Zappa, Avalanche photodiodes and quenching circuits for single photon detection. appl. Opt. 35, 1956 (1996 )] or electron multiplier CCD detectors [ DJ Denvir and E. Conroy, Electron-multiplying CCD: the new ICCD. in proc. SPIE, vol. 4796 CB Johnson, D. Sinha, and PA Laplante, eds. (2003 ), p. 164], but mostly for the infrared and optical wavelength range. Therefore, these devices typically have no or very low detection efficiency for EUV and SXR photons, and their count rates are typically much lower than the repetition rate of high-flux HHG sources.

Fuchs, S. et al., Optical coherence tomography with nanoscale axial resolution using a laser-driven high-harmonic source. Optica, 4, 903-906, 2017 discloses nanoscale axial resolution coherence tomography, ie, non-invasive cross-sectional imaging, with high harmonics using a laser-driven high-harmonic source. A depth resolution of 24 nm and a very good material contrast are achieved. Overly demanding optics for extreme ultraviolet radiation are avoided and artifacts due to elementary geometry are suppressed with a three-stage one-dimensional phase retrieval algorithm. The images are recorded in reflection geometry, which allows the analysis of e.g. B. of semiconductor samples with the help of tabletop devices for microscopy in the extreme ultraviolet range.

Knehr, E. et al., Nanowire single-photon detectors made of atomic layer-deposited niobium nitride, Supercond. science technol. 32, 125007, 2019 discloses superconducting nanowire single photon detectors fabricated from atomically deposited (ALD) NbN layers. In order to assess the suitability of these layers as detector material, the transport properties of bare layers and of bridges with different dimensions and thicknesses were examined. Similar relationships between the measured critical current and the vent current were found for microbridges made of ALD and sputtered NbN layers. Furthermore, the single photon response was characterized for 5 and 10 nm thick nanowire detectors.

A 100 nm wide, straight nanowire with a length of 5 µm shows a saturated dependency of the count rate on the bias current and a cut-off wavelength in the near infrared range. ALD technology opens up the possibility of manufacturing NbN-based detectors on a wafer scale and also conformally coating non-planar surfaces for novel device concepts.

The object of the present invention is to specify an arrangement and a method for mark-free 3D imaging, in particular for examining biological objects with a spatial resolution in the sub-micron range, which avoids the aforementioned disadvantages of the prior art, in particular quantum imaging with high-energy radiation, such as quantum ghost imaging with nanoscale resolution, whereby the sensitivity of the provided EUV/SXR detector for the lensless imaging methods is as high as possible.

According to the invention, this object is achieved by an arrangement according to claim 1 and a method according to claim 7. Further advantageous configuration options of the invention are specified in the dependent claims.

An elongated superconducting nanowire single photon detector (sSNSPD) is provided and used for label-free 3D imaging, in particular for examining biological objects with a spatial resolution in the sub-micron range, which does not, as is customary, have a meandering nanowire made of superconducting material with a nanoscale cross-section on a carrier substrate (= SNSPD), which is current-fed and is operated in the range of 1 to 4 Kelvin with a constant current below the critical current of the superconductor, but as a straight, elongated nanowire made of superconducting material (=superconductor) with a nanoscale cross-section on an electrically insulating support substrate to provide a single straight path for the current. A voltage pulse V1 and V2 is measured at each end of the nanowire. The spatial resolution of the nanowire is limited in one spatial direction of the plane by the width of the nanoscale cross section and in the other spatial direction of the plane perpendicular to the width by the time resolution when measuring the voltage pulses V1 and V2.

This straight superconducting nanowire is cooled well below its superconducting critical temperature (in the range of 1 to 4 Kelvin) and operated at a constant DC current close to, but less than, the nanowire's superconducting critical current.

• - eine lasergesteuerte und/oder -getriebene Lichtquelle in Form eines ultrakurzen Hochleistungslasers für die Erzeugung hoher Oberwellen (HHG) in einer Gasumgebung mit einer Wellenlänge im Bereich von 1 nm bis 124 nm, wobei Laserstrahlung eines optischen parametrischen Verstärkers (OPA) in einem Argon-Gasstrahl fokussiert und die im Fokus erzeugte HHG- Strahlung durch eine dünne Metallfolie (bspw. Aluminiumfilterfolie) verläuft,
• - einen Toroidspiegel, welcher die HHG- Strahlung auf einen Zwischenfokus fokussiert und von dem diese dann zum Einzelphotonendetektor in Form des sSNSPD gelangt,
• - eine Probenaufnahme zum ortsgenauem Positionieren einer zu untersuchenden biologischen Probe im Zwischenfokus,
• - zumindest ein gerader, langgestreckter supraleitender Nanodraht, welcher auf einem Träger (bspw. aus Saphirsubstrat) aufgebracht ist (bspw. durch Sputtern oder Atomlagen-Abscheidung), wobei der Nanodraht bspw. eine Niobnitrid-Schicht (NbN-Schicht) ist, welche auf ein Substrant, bspw. ein Saphirsubstrat, aufgesputtert ist und den Einzelphotonendetektor ausbildet, wobei dieser Nanodraht vorteilhaft in einen koplanaren Wellenleiter eingebettet ist, der mit einem Bias-Tee verbunden ist, das die Bias- und Ausleseleitungen trennt und das separate Auslesen von Spannungspulsen an den beiden Enden des sSNSPD ermöglich,
• - einen Kryokühler mit geschlossenem Kreislauf zum Kühlen des linear, gerade langestreckt verlaufenden, supraleitenden Nanodrahts im Temperaturbereich von 1 K bis 4 K, wobei Ultrahochvakuumbedingungen an der Position des kryogenen sSNSPD's bestehen, um das Ausfrieren von Restgas aus der HHG- Quelle an der Position des Nanodrahts zu verhindern,
• - eine Stromquelle für das Einspeisen des Bias- Stroms in den linear, gerade langestreckt verlaufenden, supraleitende Nanodraht und
• - einen Ausleseverstärker mit Auswerteeinheit zum Messen der Spannungsimpulse V1 und V2 an den beiden Enden des sSNSPD vorgesehen ist, welche in Folge des Auftreffens eines Photons auf dem linear, gerade langestreckt verlaufenden, supraleitenden Nanodraht (durch lokale Reduktion des kritischen Stroms unter den Bias- Stroms, was zur Bildung eines lokalisierten nicht-supraleitenden Bereichs mit begrenztem elektrischem Widerstand führt. der größer als die Eingangsimpedanz des Ausleseverstärkers ist, so dass der größte Teil des Bias- Stroms zum Verstärker abgeleitet wird, was zu dem messbaren Spannungsimpuls führt) erzeugt.

The arrangement for label-free 3D imaging, which includes this straight, superconducting nanowire, includes the following components:

• - A laser controlled and/or driven light source in the form of an ultrashort, high power laser for the generation of high harmonics (HHG) in a gaseous environment having a wavelength in the range 1 nm to 124 nm, using optical parametric amplifier (OPA) laser radiation in an argon gas jet is focused and the HHG radiation generated in the focus runs through a thin metal foil (e.g. aluminum filter foil),
• - a toroidal mirror, which focuses the HHG radiation onto an intermediate focus and from which it then reaches the single photon detector in the form of the sNSPD,
• - a sample holder for precise positioning of a biological sample to be examined in the intermediate focus,
• - At least one straight, elongated superconducting nanowire, which is applied (e.g. by sputtering or atomic layer deposition) to a carrier (e.g. made of sapphire substrate), the nanowire being e.g. a niobium nitride layer (NbN layer) which is a substrate, e.g. a sapphire substrate, is sputtered on and forms the single photon detector, with this nanowire advantageously being embedded in a coplanar waveguide which is connected to a bias tee which separates the bias and readout lines and enables the separate reading out of voltage pulses at the both ends of the sNSPD allow
• - a closed-cycle cryocooler for cooling the linear, straight-elongated, superconducting nanowire in the temperature range from 1 K to 4 K, with ultra-high vacuum conditions at the position of the cryogenic sSNPD's to freeze out residual gas from the HHG source at the position of the to prevent nanowire
• - a current source for injecting the bias current into the linear straight-elongated superconducting nanowire and
• - A readout amplifier with an evaluation unit is provided for measuring the voltage pulses V1 and V2 at both ends of the sSNPD, which as a result of the impact of a photon on the linear, straight, elongated, superconducting nanowire (by local reduction of the critical current below the bias current , resulting in the formation of a localized non-superconducting region of limited electrical resistance that is greater than the sense amplifier's input impedance, so that most of the bias current is shunted to the amplifier, resulting in the measurable voltage pulse).

In order to ensure spatial resolution when detecting the transmitted single photons, at least one straight superconducting nanowire, but particularly advantageously a matrix of several straight superconducting nanowires running parallel to one another, which are applied to a carrier, is used as an ultrafast single photon detector (sSNPD).

The linear, straight, elongated nanowire (sSNSPD) consists of a superconducting layer, particularly advantageously a niobium nitride (NbN) layer, which is deposited on a carrier (e.g. 3 to 20 nm thick, advantageously 10 nm thick and 50 to 200 nm wide, advantageously 100 nm wide NbN layer) and which has a relatively high critical superconductivity temperature (≈ 10 K), which enables sSNSPD operation in the temperature range from 1 K to 4 K, the carrier being made of a suitable substrate , e.g. sapphire substrate. It is particularly advantageous in the detection of the transmitted single photons from biological material that the sSNPD in 1D pixel arrays with m = 1, .... M pixels of sSNPD's or as 2D pixel arrays with M × N pixels, each pixels formed by a sNSPD are arranged and the optimal coverage of the pixels is 50%.

In order to ensure 3D imaging of biological samples to be examined, the geometry of the elongated superconducting nanowire single photon detector (sSNPD) is designed in such a way that it is constructed as a 1D pixel detector array and as a 2D pixel detector array, where the high spatial resolution in one spatial direction of the detector surface is limited by the width of the nanoscale cross-section of the nanowires and in the other spatial direction of the detector surface perpendicular to the width of the nanowires by the time resolution when measuring the voltage pulses V1 and V2 at the ends of the nanowires.

• Die Anordnung zum markierungsfreien 3D- Imaging, welche mindestens einen gerade verlaufenden, supraleitenden Nanodraht (sSNSPD) auf einem Trägersubstrat umfasst, ermöglicht die Photonenzählung von EUV/SXR- Strahlung aus lasergesteuerten hochharmonischen Quellen, welche auf biologisches Material treffen.

The procedure for label-free 3D imaging using this arrangement with at least one straight nanowire is as follows:

• The arrangement for label-free 3D imaging, which comprises at least one straight superconducting nanowire (sSNSPD) on a carrier substrate, enables photon counting of EUV/SXR radiation from laser-controlled high-harmonic sources that impinge on biological material.

Laser radiation from an optical parametric amplifier (OPA) is focused into an argon gas beam. The EUV radiation is generated and filtered out of the laser light by a thin metal foil (e.g. aluminum filter foil) (= filter for separating the EUV radiation from the remaining infrared laser light in order to generate HHG radiation = HHG source). The filter has a transmission window of 15 -72 eV, which determines the bandwidth of the photons hitting the sSNSPD.

The HHG source is operated with laser pulses with a central wavelength in the range of 1300 nm, a pulse energy in the range of 2 mJ, a pulse duration in the range of ~50 fs and a repetition rate in the range of 1 kHz.

These pulses are generated by the optical parametric amplifier (OPA) pumped with a Ti:Sa laser (35 fs pulse duration, 9 mJ pulse energy, center wavelength 790 nm).

The HHG process is triggered by focusing the linearly polarized laser pulses from the OPA into an argon gas jet, resulting in a mixture of EUV radiation with the typical harmonic comb structure and the remaining infrared laser light. In the process, EUV photons are generated up to an energy of ~ 100 eV.

EUV radiation with the typical harmonic comb structure is separated from the remaining infrared laser light by thin metal foils. Aluminum, for example, is used as the filter material (foil), which lets through EUV radiation in the range from 15 to 72 eV, or zirconium, which lets through radiation above ~60 eV.

In addition to spectral filtering, the foils are also used for differential pumping of the residual gas load from the gas jet in the HHG chamber.

The ultra-high vacuum conditions at the position of the cryogenic sSNPD are crucial to avoid freezing out of residual gas from the HHG source at the position of the deployed nanowire or 1D pixel detector array or 2D pixel detector array.

The HHG beam is focused by a toroidal mirror onto an intermediate focus, in which the biological sample to be examined is arranged, and then travels from this to the cryogenic sSNPD, so that individual photons can be detected with spectral and polarization resolution and the high resolution through the Evaluation of the transit time differences of the signals triggered by the photons is generated.

The single photon detector is designed as a straight, elongated, superconducting nanowire single photon detector (sSNSPD), whose spatial resolution in one spatial direction of the detection area is determined by the width of the nanoscale cross-section and in the other spatial direction of the detection area perpendicular to the width by the time resolution in the Measurement of the voltage pulses V1 and V2 is limited.

The sSNSPD is illuminated with EUV/SXR radiation from an HHG source, with the sSNPD being particularly advantageously arranged in 1D or 2D pixel arrays in order to examine biological samples.

In order to ensure spatial resolution in the sub-micron range, the biological material is irradiated with electromagnetic radiation with wavelengths between 0.1 and 121 nm.

In order to prevent damage to the biological material, the biological material is irradiated with low photon fluxes.

In order to ensure spatial resolution when detecting the transmitted single photons, at least one straight nanowire, but particularly advantageously a matrix of several straight, elongated parallel nanowires, is used as an ultrafast single photon detector (sSNPD).

It is particularly advantageous that the sSNPD's are formed in 1D pixel arrays with m=1, . . the optimal degree of pixel coverage is 50%.

In order to ensure 3D imaging, the geometry of the single photon detector is designed in such a way that it can be set up as a 1D pixel detector array and as a 2D pixel detector array.

By recording the voltage pulses V1 and V2 pixel by point, an image of the sample surface can be generated like in a digital photo, with the spatial resolution in one direction being determined by the width of the nanowires and in the spatial direction perpendicular thereto by the time resolution when measuring the voltage pulses V1 and V2 is limited at the end of the nanowires.

Each individual pixel (single photon detection) then stands for location information of a structural element within the biological material to be examined.

In addition, a mirror can be placed in the focal area and moved to direct the beam into an XUV spectrometer. The SNSPD signal is amplified with a room temperature amplifier (Mini-Circuits ZX60-33LN-S+) and measured with an oscilloscope.

If the elongated superconducting nanowire single photon detector (sSNPD) is irradiated with broadband EUV radiation, for example, the detector registers single photon events, e.g. at 3.0 K and a bias current of 62 µA, which are detected in the form of pixels.

The amplitude of the voltage pulses of about 100 mV after amplification for the case of EUV photon detection corresponds to the pulse height for the case of photon detection in the visible range, with the amplitude of the voltage pulses themselves also not enabling an energy resolution of the detected individual photons.

The decay time for a concrete example is about 4 ns and is determined by the kinetic inductance of the nanowire, which is about ≈42 nH, where in this concrete example the vacuum permeability µ=0, the magnetic penetration depth λNbN ≈ 550 nm and the total length of the nanowire 1 = 110 µm, the width w = 100 nm and the thickness d = 10 nm.

In the concrete example for the case of EUV photon detection, it takes about 50 - 100 ns until the output signal of the measuring system fully converges. Note that this does not affect the recovery time of the sSNPD, nor does it affect the detection efficiency or the dark count rate of the system.

With a bias current of 62 µA, the count rate is 940 events per minute, well below the source's 1 kHz repetition rate, ensuring that the detection events are due to single incident photons.

To prove that the detected events are actually caused by EUV photons, a control measurement can be performed with the infrared drive laser off to show that the events are neither dark counts nor caused by residual light in the chamber.

In a second control measurement, the gas supply can be turned off while the laser radiation is maintained to prove that the events are not triggered by infrared photons that may have penetrated the aluminum filter.

As an additional control measurement, a photodiode that detects the incoming IR pulses can be used to determine the time delay between the incoming laser pulse and a detected event.

For imaging purposes with laser-based high-harmonic light sources in coherent imaging, EUV quantum optics and quantum imaging, a pixelated array with multiple cryogenic elongated superconducting nanowire single photon detectors (sSNPD's) with straightened superconducting nanowires is required to visualize biological structures. Or, alternatively, by measuring the position of the event on the straightened superconducting nanowire by evaluating the delay between the signals at the two ends, a pixel must be generated.

The laser controlled and/or driven extreme ultraviolet (EUV) and soft X-ray (SXR) light source based on high harmonic generation (HHG) enables nanoscopic imaging with unique label-free elementary contrast and the provided detector array and with These detection methods to be carried out allow these unique properties of these new sources to be fully exploited.

The provided elongated superconducting nanowire single photon detectors (sSNSPD) enable the detection and counting of single photons, whereby these detectors do not detect dark current and enable very high count rates and thus high readout speeds (event-based after each laser pulse), which is a perfect complement for HHG sources with a high repetition rate and enables a high SNR, which is only limited by the photon shot exchange.

In addition to the advantages of sNSPDs for classical imaging applications with laser-driven EUV sources, the ability of sNSPDs to detect and count single photons paves the way for promising applications in quantum optics and quantum imaging with high-energy radiation, such as quantum ghost imaging nanoscale resolution.

The sensitivity of an EUV detector for lensless imaging methods is very high, with the resolution scaling directly with the number of photons detected, i.e. the signal-to-noise ratio (SNR), and a high SNR usually results from a high photon flux, a high quantum efficiency and long exposure times over which the photon flux is integrated is achieved.

On the other hand, it is advantageous to limit the incident photon flux on the sample. After all, EUV and SXR light are ionizing radiation that causes damage

• Zum einen liegt die Erholungszeit im Bereich von wenigen Nanosekunden oder sogar Pikosekunden, so dass sogar sSNSPD-Zählraten von bis zu mehreren GHz erreicht werden, wobei die sSNSPDs perfekt zu den Wiederholraten moderner Hochfluss-HHG-Quellen passen, welche mit einer Wiederholrate von mehreren 100 kHz betrieben werden.

The use of EUV radiation and sSNPDs has two main advantages:

• For one, the recovery time is in the range of a few nanoseconds or even picoseconds, allowing even sNSPD count rates of up to several GHz to be achieved, with the sNSPDs perfectly matching the repetition rates modern high-flux HHG sources, which are operated with a repetition rate of several 100 kHz.

On the other hand, sSNPDs have an extraordinarily low dark count rate, which enables detection with a high SNR.

• 1: eine schematische Übersichtsdarstellung einer Ausführungsform einer Anordnung,
• 2: eine schematische Darstellung der Bestimmung des Auftreffpunktes eines Einzelphotonens gemäß dem Stand der Technik,
• 3: eine schematische Darstellung der Bestimmung des Auftreffpunktes eines Einzelphotonens unter Verwendung der Anordnung gemäß 1,
• 4: eine schematische Darstellung einer Ausführungsform eines 1D-Pixel-Arrays,
• 5: eine schematische Darstellung einer Ausführungsform eines 2D-Pixel-Arrays,
• 6a: eine schematische Darstellung zur Ortsinformation durch die Rotation eines biologischen Objekts mit λ kleiner als das Objekt,
• 6b: eine schematische Darstellung zur Ortsinformation durch die Rotation eines biologischen Objekts mit λ größer als das Objekt,
• 7a: eine schematische Darstellung zur Ortsinformation durch die Verschiebung eines biologischen Objekts mit λ kleiner als das Objekt,
• 7b: eine schematische Darstellung zur Ortsinformation durch die Verschiebung eines biologischen Objekts mit λ größer als das Objekt,
• 8a: eine schematische Darstellung zur Ortsinformation und spektralen Information durch Rotation des biologischen Objekts und Beleuchtung mit Photonen unterschiedlicher Wellenlängen mit λ kleiner als das Objekt,
• 8b: eine schematische Darstellung zur Ortsinformation und spektralen Information durch Rotation des biologischen Objekts und Beleuchtung mit Photonen unterschiedlicher Wellenlängen mit λ größer als das Objekt,
• 9a: eine schematische Darstellung zur Ortsinformation und spektralen Information durch Verschiebung des biologischen Objekts und Beleuchtung mit Photonen unterschiedlicher Wellenlängen mit λ kleiner als das Objekt,
• 9b: eine schematische Darstellung zur Ortsinformation und spektralen Information durch Verschiebung des biologischen Objekts und Beleuchtung mit Photonen unterschiedlicher Wellenlängen mit λ größer als das Objekt,
• 10: eine schematische Darstellung der Integration von integrierten Strukturen aus 1D-Pixel-Arrays gemäß 4,
• 11: eine schematische Darstellung der Integration von integrierten Strukturen aus 2D-Pixel-Arrays gemäß 5,
• 12: eine schematische Darstellung zum labelfreien 3D-Imaging, zur Spektroskopie oder zur Polarisationsauflösung Verwendung von SNSPD mit einem dispersives Element und den Wellenlängen λ₁, λ₂, ....,_λN-1 λ_N),
• 13: eine schematische Darstellung der Bestimmung der Polarisation eines Einzelphotonens unter Verwendung von SNSPD mit einem Knickwinkel α von optimal 90° und
• 14: eine Darstellung des zeitabhängigen Analogsignals eines sSNSPD's bei Bestrahlung mit drei verschiedenen Wellenlängen λ₁=810 nm > λ₂=520 nm > λ₃=385 nm.

The invention is explained in more detail below with reference to the schematic drawings and the exemplary embodiments. It shows:

• 1 : a schematic overview of an embodiment of an arrangement,
• 2 : a schematic representation of the determination of the impact point of a single photon according to the prior art,
• 3 : a schematic representation of the determination of the impact point of a single photon using the arrangement according to FIG 1 ,
• 4 : a schematic representation of an embodiment of a 1D pixel array,
• 5 : a schematic representation of an embodiment of a 2D pixel array,
• 6a : a schematic representation of the location information through the rotation of a biological object with λ smaller than the object,
• 6b : a schematic representation of the position information by the rotation of a biological object with λ larger than the object,
• 7a : a schematic representation of the location information through the displacement of a biological object with λ smaller than the object,
• 7b : a schematic representation of the location information by the displacement of a biological object with λ larger than the object,
• 8a : a schematic representation of the spatial information and spectral information by rotation of the biological object and illumination with photons of different wavelengths with λ smaller than the object,
• 8b : a schematic representation of the spatial information and spectral information by rotation of the biological object and illumination with photons of different wavelengths with λ larger than the object,
• 9a : a schematic representation of the location information and spectral information by displacement of the biological object and illumination with photons of different wavelengths with λ smaller than the object,
• 9b : a schematic representation of the location information and spectral information by displacement of the biological object and illumination with photons of different wavelengths with λ larger than the object,
• 10 : a schematic representation of the integration of integrated structures from 1D pixel arrays according to 4 ,
• 11 : a schematic representation of the integration of integrated structures from 2D pixel arrays according to 5 ,
• 12 : a schematic representation for label-free 3D imaging, for spectroscopy or for polarization resolution using SNSPD with a dispersive element and the wavelengths λ ₁ , λ ₂ , ...., _λN-1 λ _N ),
• 13 : a schematic representation of the determination of the polarization of a single photon using SNSPD with a kink angle α of optimally 90° and
• 14 : a representation of the time-dependent analog signal of an sNSPD when irradiated with three different wavelengths λ ₁ =810 nm > λ ₂ =520 nm > λ ₃ =385 nm.

• - eine lasergesteuerte und/oder -getriebene Lichtquelle in Form eines ultrakurzen Hochleistungslasers für die Erzeugung hoher Oberwellen (HHG) in einer Gasumgebung mit einer Wellenlänge im Bereich von 1 nm bis 124 nm, wobei Laserstrahlung eines optischen parametrischen Verstärkers -OPA- (1) in einem Argon-Gasstrahl (2) fokussiert und durch dünne eine Metallfolie (3) (bspw. Aluminiumfilterfolie) verläuft,
• - einen Toroidspiegel (4), welcher die HHG- Strahlung (5) auf einen Zwischenfokus (51) fokussiert und von dem diese dann zum Einzelphotonendetektor SNSPD (6) gelangt,
• - eine Probenaufnahme (7) zum ortsgenauem Positionieren einer zu untersuchenden biologischen Probe (71) im Zwischenfokus (51),
• - zumindest ein gerader supraleitender Nanodraht (8), welcher auf einen Träger aufgebracht ist (bspw. durch Sputtern), wobei der Nanodraht (8) bspw. eine Niobnitrid-Schicht (NbN-Schicht) ist, welche auf den Träger aus Saphirsubstrat aufgesputtert ist und den Einzelphotonendetektor in Form des SSNSPD (6) ausbildet,

wobei dieser Nanodraht (8) vorteilhaft in einen koplanaren Wellenleiter eingebettet ist, der mit einem Bias-Tee verbunden ist, das die Bias- und Ausleseleitungen trennt,

• - einen Kryokühler (9) mit geschlossenem Kreislauf zum Kühlen des linear, gerade langestreckt verlaufenden, supraleitende Nanodrahts (8) im Temperaturbereich von 1 K bis 4 K, wobei Ultrahochvakuumbedingungen an der Position des kryogenen SNSPD's bestehen, um das Einfrieren des Nanodrahts zu verhindern,
• - eine Stromquelle für das Anlegen des Bias- Stroms an den linear, gerade langestreckt verlaufenden, supraleitende Nanodraht (8)

und

• - einen Ausleseverstärker (10) mit Auswerteeinheit (11) zum Messen des Spannungsimpulses, welcher in Folge des Auftreffens eines Photons auf dem linear, gerade langestreckt verlaufenden, supraleitenden Nanodraht (8) (durch Reduktion des lokalen kritischen Stroms unter den Strom des Bias- Stroms, was zur Bildung eines lokalisierten nicht-supraleitenden Bereichs mit begrenztem elektrischem Widerstand führt, der größer als die Eingangsimpedanz des Ausleseverstärkers (10) ist, so dass der größte Teil des Bias-Stroms zum Ausleseverstärkers (10) abgeleitet wird, was zu dem messbaren Spannungsimpuls führt) entsteht.

In the 1 arrangement shown includes:

• - a laser-controlled and/or -driven light source in the form of an ultra-short, high-power laser for the generation of high harmonics (HHG) in a gaseous environment with a wavelength in the range from 1 nm to 124 nm, using laser radiation from an optical parametric amplifier -OPA- (1) in an argon gas jet (2) and runs through a thin metal foil (3) (e.g. aluminum filter foil),
• - a toroidal mirror (4) which focuses the HHG radiation (5) onto an intermediate focus (51) and from which it then reaches the single photon detector SNSPD (6),
• - a sample holder (7) for precisely positioning a biological sample (71) to be examined in the intermediate focus (51),
• - At least one straight superconducting nanowire (8) which is applied to a carrier (e.g. by sputtering), the nanowire (8) being, for example, a niobium nitride layer (NbN layer) which is sputtered onto the sapphire substrate carrier and forms the single photon detector in the form of the SSNSPD (6),

this nanowire (8) advantageously being embedded in a coplanar waveguide connected to a bias tee separating the bias and readout lines,

• - a closed-loop cryocooler (9) for cooling the linear, straight-elongated, superconducting nanowire (8) in the temperature range from 1 K to 4 K, with ultra-high vacuum conditions at the position of the cryogenic SNSPD's in order to prevent freezing of the nanowire,
• - a current source for applying the bias current to the linear, straight, elongated superconducting nanowire (8)

and

• - a readout amplifier (10) with an evaluation unit (11) for measuring the voltage pulse which, as a result of the impact of a photon on the linear, straight, elongated, superconducting nanowire (8) (by reducing the local critical current below the current of the bias current , resulting in the formation of a localized non-superconducting region with limited electrical resistance that is greater than the input impedance of the sense amplifier (10), so that most of the bias current is diverted to the sense amplifier (10), resulting in the measurable voltage pulse leads) arises.

The 2 shows a schematic representation of the determination of the impact point of a single photon according to the prior art by means of a superconducting nanowire single photon detector with a meandering nanowire made of superconducting material (=superconductor). One sees the determination of the impact point x of the single photon on the meandered single photon detector.

mit s₁, s₂: Länge der Zuleitungen im Mikrowellenleiter und v: Ausbreitungsgeschwindigkeit der Einzelphotonen im Einzelphotonendetektor
wobei gilt: x=L*t1/(t2+t1) und dy=10 µm sowie dx=10 µm und
x mit Genauigkeit dx~1 sowie y mit Genauigkeit dy~H.The point of impact of the single photon is determined by measuring the runtime difference in signal V1 (contact point 1) and signal V2 (contact point 2), where the following applies: $$\text{L}\ddot{\text{a}}\text{length in x}-\text{Direction L}={\text{n}}_{\text{M}}\ast /2\ast 1+{\text{<figure-callout id="1" label="s" filenames="DE102021133714B3\_0002.png,DE102021133714B3\_0004.png" state="{{state}}">s</figure-callout>}}_1+{\text{<figure-callout id="2" label="s" filenames="DE102021133714B3\_0002.png,DE102021133714B3\_0006.png" state="{{state}}">s</figure-callout>}}_2$$

with s ₁ , s ₂ : length of the feed lines in the microwave conductor and v: propagation speed of the single photons in the single photon detector
where: x=L*t1/(t2+t1) and dy=10 µm as well as dx=10 µm and
x with precision dx~1 and y with precision dy~H.

The first disadvantage of this technical solution is the low spatial resolution in the detection plane along the x-direction and along the y-direction, which leads to a low spatial resolution of the impact point of the single photon. The second disadvantage is the poor integration capability of the meandered structure.

The 3 shows a schematic representation of the determination of the impact point of a single photon using the arrangement according to 1 with a straight superconducting nanowire single photon detector [sSNPD (straight SNSPD, sSNSPD)].

• s₁, s₂: Länge der Zuleitungen im Mikrowellenleiter
• v: Ausbreitungsgeschwindigkeit der Einzelphotonen im Einzelphotonendetektor

wobei:

• t_1. =x/v, t₂= (L-x)/v und x=L·t₁ /(t₂+t₁) sowie dy<100 nm und dx~Wellenlänge λ sowie
• x mit Genauigkeit dx~∅~Wellenlänge des Photons und y mit Genauigkeit dy~H der Breite des Nanodrahtes.

You can see the determination of the impact point x of the single photon on a straight single photon detector (straight SNSPD, sSNPD) by measuring the difference in transit time (Δt=t ₂ -t ₁ ) in signal V1 (contact point 1) and signal V2 (contact point 2), where the expansion of the impact point corresponds to ∅∼ wavelength of the single photon, where the following applies:

• s ₁ , s ₂ : length of the feed lines in the microwave conductor
• v: propagation speed of the single photons in the single photon detector

whereby:

• t _1. =x/v, t ₂ = (Lx)/v and x=L t ₁ /(t ₂ +t ₁ ) as well as dy<100 nm and dx~wavelength λ as well
• x with precision dx~∅~wavelength of the photon and y with precision dy~H the width of the nanowire.

The speed of propagation is reduced by using the carrier (increase in the conduction capacitance CK of the nanowire) and reducing the cross section of the nanowire (increase in the kinetic inductance LK).

The advantages of this technical solution are the high spatial resolution in the detection plane both in the x-direction and in the y-direction and the resulting high spatial resolution of the impact point of the individual photons and the high level of integrability.

4 shows the design as an ID pixel array with m=1,..,M pixels, where each pixel is formed by an sNSPD and the optimal degree of coverage is 50%.

5 shows the embodiment as a 2D pixel array with MxN pixels, each pixel being formed by an sSNPD and the optimal degree of coverage of the M pixels: 50%, optimal degree of coverage of the N pixels: 50%.

The 6a shows the acquisition of the location information through the rotation of the biological object, where λ is smaller than the object. The beam path along the optical axis, starting from the EUV/XUV source, leads through the biological object, which is embedded in a cylinder (z axis of rotation, z axis of displacement). the sNSPD (bucket detector), where the monochromatic illumination occurs with photons of a wavelength λ, which is smaller than the object.

The 6b shows the acquisition of the location information by rotating the biological object, where λ is larger than the object. The beam path along the optical axis leads from the EUV/XUV source through the biological object, which is embedded in a cylinder (z-axis of rotation, z-axis of displacement) to the sSNSPD (bucket detector), with the monochromatic illumination being included Photons of a wavelength λ occurs, which is larger than the object.

7a shows the acquisition of location information by moving the object, where λ is smaller than the object. The beam path along the optical axis leads from the EUV/XUV source through the object, which is embedded in a cuboid (x-displacement axis, z-displacement axis, y-displacement axis) to the sSNSPD (bucket detector), with the monochromatic illumination with photons of wavelength λ, which is smaller than the object.

7b shows the acquisition of location information by moving the object, where λ is larger than the object. The beam path along the optical axis leads from the EUV/XUV source through the biological object, which is embedded in a cuboid (x-displacement axis, z-displacement axis, y-displacement axis) to the sNSPD (bucket detector), where the monochromatic illumination occurs with photons of wavelength λ, which is larger than the object.

8a shows the acquisition of location information and spectral information by rotating the object and illuminating it with photons of different wavelengths, where λ is smaller than the object. The beam path along the optical axis leads from the EUV/XUV source through the biological object, which is embedded in the cylinder (z axis of rotation, z axis of displacement) to the sSNSPD (bucket detector).

This occurs with a normal dispersion dn/dλ<0 with n ₂ (λ ₁ )>n ₂ (λ _i )n ₂ (λ _N ) and n ₁ <n ₂
where: the illumination is performed with photons of wavelength λ ₁ <λ ₂ ,...λ _i ,...λ _{N- 1} <λ _N .

8b shows the acquisition of location information and spectral information by rotating the object and illuminating it with photons of different wavelengths, where λ is larger than the object. The beam path along the optical axis leads from the EUV/XUV source through the object, which is embedded in the cylinder (z-axis of rotation, z-axis of displacement) to the sSNSPD (bucket detector), with the illumination using photons of the wavelength λ ₁ <λ ₂ ,...λ _i ,...λ _N-1 <λ _N takes place.

9a shows the acquisition of location information and spectral information by moving the biological object and illuminating it with photons of different wavelengths, where λ is smaller than the object. The beam path along the optical axis leads from the EUV/XUV source through the object, which is embedded in a cuboid (x-axis of displacement, z-axis of displacement, y-axis of displacement) to the sSNSPD (bucket detector).

This occurs with normal dispersion dn/dλ<0 with n ₂ (λ ₁ )>n ₂ (λ _i )>n ₂ (λ _N ) and n ₁ <n ₂ , where the illumination is with photons of wavelength λ ₁ <λ ₂ ,...λ _i ,...λ _N-1 <λ _N takes place.

9b shows the acquisition of location information and spectral information by moving the biological object and illuminating it with photons of different wavelengths, where λ is larger than the object. The beam path along the optical axis leads from the EUV/XUV source through the object, which is embedded in a cuboid (x-displacement axis, z-displacement axis, y-displacement axis) to the sSNSPD (bucket detector), with the Illumination with photons of wavelength λ ₁ <λ ₂ ,...λ _i ,...λ _N-1 <λ _N takes place.

In the 10 is the integration of a multiplicity of arrangements of the 1D pixel arrays with M pixels into a sNSPD structure consisting of A×B 1D pixel arrays 1DPA (i,j), i=1...A and j=1. ..B shown.

In the 11 is the integration of a variety of arrangements of 2D pixel arrays with MxN pixels with sSNPD structure consisting of AxB 2D pixel arrays [2DPA (i,j), i=1...A and j =1.. .B]

12 shows the use of a dispersive element, eg Fresnel zone plate, for label-free 3D imaging, for spectroscopy and for polarization resolution. The beam path along the optical axis leads from the EUV/XUV source through the object, a dispersive element to the sSNSPD (bucket detector), with the illumination using photons of wavelength λ ₁ <λ ₂ ,...λ _i , ...λ _{N- 1} <λ _N takes place.

13 shows the detection of the polarization of the single photon using sSNPD with at least one kink and a kink angle α of optimal α=90°

The laser-controlled and/or -driven light source in the extreme ultraviolet range (EUV) and in the soft X-ray range (SXR) with high harmonic generation (HHG), enables nanoscopic imaging with unique label-free elementary contrast and a provided detector arrangement.

The provided superconducting nanowire single photon detectors (SNSPD) enable the detection and counting of single photons, whereby these detectors are dark-count-free and enable very high count rates and thus high readout speeds (event-based after each laser pulse), which is a perfect complement to HHG -represents high repetition rate sources and enables high SNR, limited only by photon shot noise.

In addition to the advantages of SNSPDs for classical imaging applications with laser-driven EUV sources, the ability of the provided arrangement to detect and count single photons paves the way for promising applications in quantum optics and quantum imaging with high-energy radiation, such as quantum ghost imaging with nanoscale resolution.

The advantage here is that the sensitivity of the EUV detector for lensless imaging methods is very high, with the resolution scaling directly with the number of photons detected, i.e. the signal-to-noise ratio (SNR), and a high SNR usually through a high photon flux, a high quantum efficiency and long exposure times over which the photon flux is integrated is achieved.

Furthermore, it is advantageous that the recovery time of the arrangement is in the range of a few nanoseconds or even picoseconds, so that even SNSPD count rates of up to several GHz can be achieved, with the SNSPDs perfectly matching the repetition rates of modern high-flux HHG sources , which are operated with a repetition rate of several 100 kHz, and the SNSPDs have an extremely low dark count rate, which enables background-free detection.

14 shows an example of a time-dependent analog signal of an sSNSPD at its maximum in the time range from 0 to 110 ns ( 14a ) and from 14 to 30 ns ( 14b ) and at the minimum in the time range from 0 to 110 ns ( 14c ) and from 37 to 84 ns. It is advantageous that both the value of the analog signal at maximum ( 14b ) as well as the value of the analog signal at minimum ( 14d ) depend systematically on the wavelength. The value of the analog signal at maximum ( 14b ) increases with increasing wavelength. The value of the analog signal at the minimum ( 14d ) decreases with increasing wavelength.

• - Kinetische Induktivität des sSNSPD, die nur vom Material und von der Geometrie des sSNSPD abhängt, und von der Abhängigkeit des Analogsignals von dem Bias-Strom, z.B. wenn der Bias-Strom 80%, 85%, 90% oder 92,5% des kritischen Stromes beträgt, bestimmt wird.
• - Thermische Kapazität des sSNSPD, die nur vom Material und von der Geometrie des sSNSPDs abhängt, und aus der Abhängigkeit des Analogsignals von dem Vorspannungsstrom, z.B. wenn der Vorspannungsstrom 80%, 85%, 90% oder 92,5% des kritischen Stromes beträgt, bestimmt wird.
• - Widerstand des sSNSPD zum Zeitpunkt, wenn die Temperatur im Hot spot des sSNSPD nach Absorption eines Einzelphotons der Wellenlänge λ ihr Maximum durchläuft. Der Widerstand im Maximum des Analogsignals hängt von der Wellenlänge des Einzelphotons ab.

The parameters are derived from an analysis of the time-dependent analog signal for an sSNSPD

• - Kinetic inductance of the sSNPD, which depends only on the material and the geometry of the sNSPD, and on the dependence of the analog signal on the bias current, e.g. when the bias current is 80%, 85%, 90% or 92.5% of the critical current is determined.
• - thermal capacitance of the sSNPD, which depends only on the material and the geometry of the sNSPD, and from the dependence of the analog signal on the bias current, e.g. when the bias current is 80%, 85%, 90% or 92.5% of the critical current, is determined.
• - Resistance of the sNSPD at the time when the temperature in the hot spot of the sNSPD passes its maximum after absorption of a single photon of wavelength λ. The resistance at the maximum of the analog signal depends on the wavelength of the single photon.

The advantage here is that the kinetic inductance, the thermal capacity and the wavelength-dependent resistance at the maximum of the analog signal can be determined in a calibration measurement and that an analysis of the analog signal provides spectral information about the wavelength of the absorbed single photon.

Reference List

1

optical parametric amplifier (OPA)

2

Argon gas jet

3

metal foil

4

toroidal mirror

5

electron beam

51

intermediate focus

6

Single photon detector in the form of a SNSPD = Superconducting Nanowire Single Photon Detector

7

sampling

8th

nanowire

9

cryocooler

10

readout amplifier

11

evaluation unit

V1, V2

Voltage pulses at the two ends of the sSNSPD

sNSPD

straight superconducting single nanowire photodetector

Claims (9)

Arrangement for mark-free 3D imaging with a spatial resolution in the sub-µm range, comprising - a laser-controlled and/or -driven light source in the form of an ultra-short high-power laser for generating high harmonics in a gas environment with a wavelength in the range from 1 nm to 124 nm, whereby laser radiation from an optical parametric amplifier (1) is focused in an argon gas jet (2) and the high harmonics generated in the gas in the focus, hereinafter also referred to as HHG radiation (5), pass through a thin metal foil (3), - a Toroidal mirror (4), which focuses the HHG radiation (5) onto an intermediate focus (51) and from which it then reaches a single photon detector in the form of a superconducting nanowire single photon detector, also referred to below as SNSPD (6), and - a sample holder (7) for the precise positioning of a sample to be examined in the intermediate focus (51), characterized in that - the SNSPD (6) is at least one straight, elongated superconducting nanowire (8) on a carrier and forms a cryogenic sNSPD, wherein - the nanowire (8) embedded in a coplanar waveguide connected to a bias tee that separates the bias and readout lines and allows separate readout of voltage pulses at both ends of the sSNPD, - a cryocooler (9) closed-loop circuit for cooling of the nanowire (8) is present in the temperature range of 1 K to 4 K, with ultra-high vacuum conditions at the position of the cryogenic sNSPD's to prevent freezing of residual gas from the light source at the position of the nanowire (8), - a power source for application of the bias current to the nanowire (8) is present, and - a readout amplifier (10) with an evaluation unit (11) for measuring voltage pulses (V1 and V2) at both ends of the sSNSPD, which are present as a result of the impact of a photon arise on the nanowire (8). Arrangement for mark-free 3D imaging according to claim 1 , characterized in that the nanowire (8) is a superconducting layer which is applied to the carrier and forms the sNSPD. Arrangement for mark-free 3D imaging according to claim 2 , characterized in that the support consists of a sapphire substrate and the superconducting layer is a niobium nitride layer sputtered onto the sapphire substrate. Arrangement for mark-free 3D imaging according to claim 3 , characterized in that the niobium nitride layer (3) is up to 20 nm thick and 50 to 200 nm wide. Arrangement for mark-free 3D imaging according to claim 1 , 2 , 3 or 4 , characterized in that the metal foil (3) is an aluminum filter foil with a transmission window of 15 -72 eV. Arrangement for mark-free 3D imaging according to one of Claims 1 until 5 , characterized in that the sSNSPD are formed in 1D pixel arrays with m = 1, .... M pixels of sSNPD's or as 2D pixel arrays with M × N pixels, each pixel being formed by an sSNPD, and the optimal coverage of the pixels is 50%. Method using an arrangement according to one of Claims 1 until 6 In which - the laser radiation of the optical parametric amplifier (1) in the argon gas beam (2) is focused to generate EUV radiation, - the EUV radiation generated is guided through the thin metal foil (3), the so formed HHG source is operated with laser pulses with a central wavelength in the range of 1300 nm, a pulse energy in the range of 2 mJ, a pulse duration in the range of 50 fs and a repetition rate in the range of 1 kHz, so that an HHG process is triggered , resulting in a mixture of EUV radiation with a harmonic comb structure and the remaining infrared laser light and generating EUV photons with an energy of up to 100 eV, - the EUV radiation is separated from the remaining infrared laser light by thin metal foils, whereby EUV photons in the range from 15 to 72 eV are passed through an aluminum foil and above 60 eV through a zirconium foil and differential pumping of a residual gas load from the gas jet (2) takes place in the HHG chamber, - the HHG radiation (5) is focused by the toroidal mirror (4) onto the intermediate focus (51), in which a biological sample to be examined is stored and irradiated with wavelengths between 0.1 and 121 nm, - the HHG radiation (5) from there then reaches the cryogenic sSNPD with the nanowire (8) to which the bias current is applied, - a voltage pulse (V1, V2) measured with the readout amplifier (10) with evaluation unit which arises as a result of the impact of a photon on the nanowire (8) and - finally, the voltage pulses (V1 and V2) are represented graphically. procedure according to claim 7 , characterized in that an analog signal of the sSNPD is analyzed by - the voltage pulse (V1), the voltage pulse (V2) or the voltage pulses (V1 and V2) leading to an extraction of a kinetic inductance and a thermal capacitance of the sSNPD, which only material and on the geometry of the sSNSPD, and - the voltage pulse (V1), the voltage pulse (V2) or the voltage pulses (V1 and V2) for extracting a resistance of the sSNSPD at a time when a temperature at the hot spot of the sNSPD is its maximum passes through, can be used to finally make a determination of a wavelength of an absorbed single photon from an analysis of the resistance. Use of the arrangement according to one of Claims 1 until 6 and the procedure according to Claims 7 or 8th for mark-free 3D imaging by means of photon counting of EUV/SXR radiation from laser-controlled high-harmonic sources that hit biological material.

Images