JP2005172774A - Method and apparatus for measuring physical properties based on catoptric characteristics - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a measuring instrument having high detection sensitivity and high positional resolving power in terahertz spectrometry, and a measuring method using it. <P>SOLUTION: This terahertz wave spectrometric instrument is constituted so that the arbitrary place of a sample 2 is irradiated with a frequency variable terahertz wave 5 and the reflected terahertz wave 6 or the like is detected to obtain a terahertz spectrum. The measuring result is analyzed to investigate the physical properties or composition of the sample. The measuring result is obtained as a terahertz imaging image at every measuring frequency. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a physical property measuring apparatus and a measuring method using a coherent terahertz wave.

  Conventional methods for measuring physical properties or compositions are mainly GC-MS (gas chromatograph mass spectrometer), LC-MS (liquid chromatograph mass spectrometer), NMR (nuclear magnetic resonance method), FT-IR (organic substance analysis) in organic matter analysis. Fourier transform infrared spectrophotometer) is used. In inorganic analysis, ICP-MS (inductively coupled plasma mass spectrometer), ICP-AES (inductively coupled plasma emission spectrometer), FLAA (frameless atomic absorption spectrometer) are mainly used. ) Etc. are used. Also, SIMS (secondary ion mass spectrometer), XPS (ESCA) (X-ray photoelectron spectrometer), etc. are used for local analysis of the surface. However, these all require large-scale devices such as a high vacuum device and a light-shielding unit, and are not simple.

  The natural vibration frequency of various molecules such as molecules and gas molecules constituting the living body exists in the terahertz band. If an absorption spectrum in this terahertz region is measured, it can be used for substance identification and composition analysis. As a wavelength tunable terahertz spectral light source, for example, a terahertz wave generator using a polariton mode in a semiconductor GaP crystal is known. That is, the pump light and the signal light are incident on the GaP crystal at a minute angle so as to satisfy the angle phase matching condition, and a coherent terahertz wave is generated by the difference frequency generation. By narrowing the line width of the pump light and the signal light by injection seeding technology or etalon insertion, the line width of the obtained terahertz wave is narrowed, and a larger output can be obtained, making it a light source suitable for a spectroscopic device. A spectroscopic measurement apparatus using such a terahertz wave generation apparatus is nondestructive measurement, and can obtain an absorption spectrum of an arbitrary measurement object over a wide frequency band with high resolution.

  When measuring a terahertz transmission spectrum, for example, in order to measure a substance having a low transmittance, it is necessary to adjust the transmittance by reducing the thickness of the sample, which is troublesome. That is, when it is difficult to cut or thin a part of the sample, it is difficult to apply terahertz transmittance measurement.

  Further, for example, in a living tissue, information having different materials and compositions depending on the location is important for detecting a lesion. Physical properties and composition detection at specific points are desired.

  The sample is irradiated with a variable frequency terahertz wave, and the reflected wave is received by a detector. By measuring the frequency dependence of the terahertz wave reflectivity, the physical properties are examined from the reflectivity spectrum unique to the material. At the same time, the location is scanned to examine the physical properties and composition of a particular location.

  The present invention relates to a terahertz wave spectrometer, and provides an apparatus for obtaining a terahertz spectrum by irradiating a sample with an arbitrary terahertz wavelength at an arbitrary place and detecting a reflected wave spectrum or the like, and analyzing the result. Thus, the physical properties and composition of the sample can be examined. The measurement result is also obtained as a terahertz imaging image for each frequency.

  It can be used as a simple and highly accurate physical property analyzer.

  The generation of terahertz is performed by, for example, irradiating a GaP crystal, which is a nonlinear optical crystal, with two pump laser beams obtained from a YAG laser and a YAG laser-pumped optical parametric oscillator (OPO) so as to satisfy the angle phase matching condition. There is a method to generate. In this method, an arbitrary terahertz wave is obtained with a large output in the range of 0.3 to 7.3 THz.

  As shown in FIG. 1, a coherent single-frequency irradiation terahertz wave 5 is supplied from a terahertz wave generator 1. This beam is essentially circular with a diameter of about 3 mm, but can be further condensed by a lens system, resulting in a diameter of about 300 μm. The terahertz wave generator 1 can select an arbitrary frequency or can sweep a frequency at an arbitrary speed.

  The sample 2 is fixed to an XZ stage 3 installed at an angle of 45 ° with respect to the irradiated terahertz wave, and the irradiated terahertz wave 5 is reflected by the sample 2 to become a reflected terahertz wave 6. The angle formed by the irradiation terahertz wave 5 and the reflection surface on the sample 2 can be set from approximately 0 ° to approximately 90 °. At this time, if the unevenness of the reflecting surface of the sample 2 becomes about the wavelength of the irradiated terahertz wave 2, the influence of scattering becomes large and the efficiency is lowered. Therefore, an optically flat material is bonded to the sample surface with less terahertz wave absorption. Also good. The intensity of the reflected terahertz wave 6 is measured by the detector 4.

  By moving the XZ stage 3 to which the sample 2 is fixed, the terahertz wave irradiation point on the sample 2 moves, and the reflectance at each point can be measured. Thereby, a two-dimensional reflection terahertz image can be obtained. If the lens system is designed to focus on the sample, the resolution can be increased.

  If the terahertz wave frequency is changed and a two-dimensional terahertz image is obtained for each frequency, it is possible to determine what substance is present in which part of the sample. At this time, terahertz spectrum patterns of various substances may be stored in advance and compared with measurement results.

  The frequency change of the terahertz wave can be irradiated selectively for a full frequency automatic sweep or a specific frequency. For example, spectrum measurement is performed on a certain sample, and only the frequency at which the differential coefficient is 0 is selected and set to be measured. At this time, since the terahertz spectrum becomes a peak or dip at the irradiation frequency, only the characteristic frequency can be measured efficiently.

  Of course, at this time, as shown in FIG. 2, the detector 4 can be arranged behind the sample 2. With this configuration, a transmission terahertz image is obtained, and the physical properties of each part of the sample can be examined in the same manner as the reflection terahertz image. At this time, the XZ stage may be made of a material that transmits terahertz waves, or only the back surface of the sample may be hollow. Of course, the reflection terahertz image and the transmission terahertz image may be measured simultaneously.

  As shown in FIG. 3, the half mirror 20 is installed on the half mirror transmission terahertz wave 21 irradiated on the sample 2. The half mirror transmission terahertz wave 21 is transmitted through the half mirror 20 with about half the intensity, and is irradiated onto the sample 2. At this time, similarly to the first embodiment, the irradiation point can be further reduced by the lens system. If the focal point of the lens system is on the sample, the size of the focal point becomes the resolution. However, the spot system can be further reduced by a pinhole, a condenser horn or the like, and the resolution can be further increased. The light reflected by the sample 2 returns to the half mirror 20 again, and about half the intensity is reflected and guided to the detector 4. If the sample is moved in the plane perpendicular to the half mirror transmission terahertz wave 21 by the XZ stage 3, the terahertz irradiation point on the sample 2 changes, and the reflectance of the terahertz wave at each point can be measured.

  As shown in FIG. 4, a condenser mirror 30 is disposed near the sample 2. A reflected terahertz wave 6 and a scattered terahertz wave 31 are generated by the irradiated terahertz wave 5 irradiated to the sample 2. In particular, when the surface of the sample is uneven, such as a biological tissue, most of them are scattered terahertz waves. The reflected terahertz wave 6 is further reflected by the condenser mirror and introduced into the detector 4. At the same time, the scattered terahertz wave 31 is also reflected by the condensing mirror 30 and condensed on the detector 4, thereby enabling highly sensitive measurement. At this time, the reflected terahertz wave 6 may be directly introduced into the detector 4.

  An integrating spherical condensing system as shown in FIG. 5 may be used. An irradiation terahertz wave 5 is incident from a terahertz wave incident port 41 provided in a very small size in a sealed container 40 whose inner surface is made of a material that reflects terahertz waves with high efficiency, and is emitted from a terahertz wave emitting port 43, and the surface of the sample 2 Is irradiated. The reflected terahertz wave 6 and the scattered terahertz wave 31 generated at this time are returned to the sealed container 40 from the terahertz wave exit port 43 and reflected directly or within the sealed space 40, and then introduced into the detector 4 from the minute detector port 42. Is done. In this case, since most of the reflected terahertz wave 6 and the scattered terahertz wave 31 are in the detector 4, the sensitivity is very high. At this time, the reflected terahertz wave 6 may be directly introduced into the detector 4.

  These techniques are particularly effective for measurement of biological tissues or the like having many irregularities on the surface.

  1 is a diagram illustrating a configuration of a reflective terahertz image measuring device in Embodiment 1. FIG.   1 is a diagram illustrating a configuration of a transmission terahertz image measurement apparatus in Example 1. FIG.   FIG. 6 is a diagram illustrating a configuration of a reflective terahertz image measurement device according to a second embodiment.   FIG. 6 is a diagram illustrating a configuration of a reflection and scattering terahertz image measurement apparatus in Example 3.   FIG. 6 is a diagram illustrating a configuration of a reflection and scattering terahertz image measurement apparatus in Example 3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Terahertz wave generator 2 ... Sample 3 ... XZ stage 4 ... Terahertz detector 5 ... Irradiation terahertz wave 6 ... Reflection terahertz wave 10 ... Transmission terahertz wave 20 ... Half mirror 21 ... Half mirror transmission terahertz wave 22 ... Sample reflection Terahertz wave 23: Half mirror re-reflection wave 30 ... Condensing mirror 31 ... Scattered terahertz wave 40 ... Sealed container 41 ... Terahertz wave entrance 42 ... Detector port 43 ... Terahertz wave exit port

Claims (3)

  With respect to measurement using terahertz waves, the terahertz wave frequency sweep can also limit the range, or has a function of irradiating terahertz waves designating at least one arbitrary single frequency, and at least in the sample to be measured, A measuring apparatus and method for identifying physical properties and analyzing a composition from a spectrum of a reflected terahertz wave.   For terahertz wave measurement, sweeping terahertz wave frequency that can specify the range, function to irradiate terahertz wave with at least one arbitrary single frequency, and terahertz wave irradiation position scanning function A measuring apparatus characterized in that, by measuring at least a reflected terahertz wave in a sample to be measured, physical property identification and composition analysis of each position from information on the position and frequency spectrum in the sample to be measured, and Method.   3. The measuring apparatus according to claim 1, wherein the measuring apparatus has a structure for collecting a reflected wave, a transmitted wave, or a scattered wave of an irradiation terahertz wave.

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