CN2874476Y - Terahertz time domain spectral instrument based on optical rectification - Google Patents

Abstract

The utility model discloses a terahertz time-domain spectrometer based on optical rectification, which belongs to the improvement of the terahertz time-domain spectrometer. The spectrometer includes a femtosecond pulse laser, a terahertz emitter placed in a vacuum system, a terahertz detector, and a computer-controlled data acquisition and processing system. The utility model has the advantages of: using the computer-controlled data acquisition and processing system to measure the terahertz time-domain electric field signal of the permeable material and display it on the computer screen, which is convenient for data analysis; the time-domain signal of the permeable material can be obtained. Spectrum, the spectral resolution accuracy reaches 0.03-0.001; the vacuum system incorporates the terahertz emission and detection part, avoiding the influence of water in the air on the terahertz absorption, and improving the measurement accuracy of the material spectrum; installing a lens on the pump optical path To change the power density of the pumping light to control the radiation efficiency of the terahertz wave.

Description

Terahertz time-domain spectrometer based on optical rectification

technical field

The utility model relates to a terahertz time-domain spectrometer based on optical rectification, which belongs to the improvement of the terahertz time-domain spectrometer.

Background technique

The terahertz (THz, 1THz=10 ¹² Hz) frequency band refers to the electromagnetic radiation region with a frequency from 0.1 THz to 10 THz, between millimeter waves and infrared light. For a long time, there has been a lack of effective methods for the generation and detection of terahertz radiation pulses, resulting in very limited understanding of the nature of electromagnetic radiation in this band, so that this band is called the THz gap in the electromagnetic spectrum, and it is also an area that needs to be fully investigated in the electromagnetic spectrum. The last frequency window studied.

Terahertz waves generated by coherent femtosecond laser pulses through the optical rectification effect have high temporal and spatial coherence. The current terahertz time-domain spectroscopy (THz-TDS) is a very effective electromagnetic radiation phase coherence test technology jointly developed by AT&T, Bell Laboratories and IBM in the 1980s; the THz wavelet transform we created Domain Spectroscopy (THz-WTDS) can directly measure the amplitude and phase of the oscillating electromagnetic field and the distribution characteristics of the frequency spectrum in the time domain. This feature makes THz science and technology have great advantages in the study of transient coherent dynamics of materials. . THz time-domain spectroscopy technology has a high detection signal-to-noise ratio and a wide detection bandwidth, and can be widely used in the detection of characteristic spectra of various samples.

Contents of the invention

The purpose of this utility model is to provide a terahertz time-domain spectrometer based on optical rectification, which measures the terahertz time-domain spectrum of permeable substances. 0.0001.

The utility model is realized through the following technical scheme, a terahertz time-domain spectrometer based on optical rectification, characterized in that the spectrometer includes a femtosecond pulsed laser 1, a beam splitter 2 arranged at the output end of the pulsed laser and an optical A delay device 3, a terahertz emitter 10-1 and a terahertz detector 10-5 arranged in the vacuum system; and a data acquisition and processing system 11; sequentially between the beam splitter 2 and the terahertz emitter 10-1 A chopper 6, a plane reflector 7, and a plano-convex lens 9 are arranged, and an off-axis parabolic emitter 10-2 is arranged behind the Hertz emitter 10-1; a femtosecond pulse laser 1, a beam splitter 2, a chopper 6, and a plane Reflector 7, plano-convex lens 9 and terahertz emitter 10-1 constitute the pumping optical path; between optical delay device 3 and terahertz detector 10-5, planar reflectors 4, 5, plano-convex lens 8 and off-axis A parabolic mirror 10-4, a pumping optical filter 10-3 is arranged between the terahertz emitter 10-1 and the terahertz detector 10-5; a femtosecond pulse laser 1, a beam splitter 2, and an optical delay device 3. Plane reflectors 4, 5, plano-convex lenses 8, off-axis parabolic mirrors 10-4 and terahertz detectors 10-5 constitute the detection optical path; the data acquisition and processing system 11 includes planar reflectors 11-1 in turn, Plano-convex lens 11-2, quarter wave plate 11-3, Wollaston prism 11-4, balanced detector 11-5, lock-in amplifier 11-6, computer 11-7.

The utility model has the advantages of: using the computer-controlled data acquisition and processing system to measure the terahertz time-domain electric field signal of the permeable material and display it on the computer screen, which is convenient for data analysis; the time-domain spectrum of the permeable material can be obtained , the spectral resolution accuracy is 0.03-0.001; the vacuum system incorporates the terahertz emission and detection part, which avoids the influence of water in the air on the terahertz absorption, and improves the measurement accuracy of the spectrum of permeable substances; in the pump light path A lens is installed to change the power density of the pumping light to control the radiation efficiency of the terahertz wave.

Description of drawings

Fig. 1 is a structural block diagram of the utility model.

In the figure, 1-femtosecond pulsed laser, 2-beam splitter, 3-optical delay device, 3-1, 3-2-plane mirror, 4, 5, 7-plane mirror, 6-chopper, 8, 9-plano-convex lens, 10-terahertz emission and detection body, 10-1-terahertz emitter, 10-2, 10-4-off-axis parabolic reflector, 10-3-pump light filter, 10 -5-terahertz detector, 11-data acquisition and processing system, 11-1-plane mirror, 11-2-plano-convex lens, 11-3-quarter wave plate, 11-4-Wollaston Prism, 11-5-balance detector, 11-6-lock-in amplifier, 11-7-computer.

Detailed ways

Below in conjunction with accompanying drawing, utility model is described further.

The utility model uses a high repetition rate femtosecond laser pulse as an excitation source, and the femtosecond pulse light source can be a titanium-doped sapphire self-mode-locked femtosecond pulse laser 1 or a femtosecond laser amplifier, the output pulse repetition frequency is greater than 1KHz, and the pulse width is less than 100 Femtosecond, linearly polarized light with a wavelength of 820nm, whose polarization direction is parallel to the bottom plate of the device. The femtosecond laser is divided into two beams by the beam splitter 2: one beam is 70% light, and the other beam is 30% light, which are respectively used as pump light and probe light. The pump light passes through the 1050Hz chopper 6, and then is focused by the plano-convex lens 9 onto the terahertz emitter 10-1, and generates terahertz radiation waves according to the principle of optical rectification. The plano-convex lens 9 is placed on a high-precision platform movable along the direction of the pump beam, and the spot size of the pump light irradiated on the terahertz emitter is changed by moving the plano-convex lens 9 . The generated terahertz radiation waves pass through the 4f system composed of two off-axis parabolic mirrors 10-2 and 10-4, and focus on the terahertz detector 10-5. In order to avoid the influence of the remaining pump light on the detection of terahertz radiation waves, a pump light filter 10-3 needs to be arranged between the two off-axis parabolic mirrors 10-2 and 10-4. The computer 11-7 controls the motor-driven optical delay line with an accuracy of 0.1 μm. The terahertz radiation wave and the detection beam are collinearly coupled to the terahertz detection crystal 10-5. Using the linear electro-optic effect, electro-optic sampling is performed on the electric field of the terahertz wave to detect the time-domain signal of the measured THz wave. Balance the detector 11-5 to eliminate exogenous noise. In the case of no additional THz signal to be measured, the 1/4 wave plate 11-3 is rotated to make the output of the balanced detector zero, so that the balanced detector can be pre-biased in the linear region. The terahertz emission and detection body 10 is placed in a vacuum system, which avoids the influence of water in the air on terahertz absorption, and improves the measurement accuracy of material spectra. The detected THz wave time-domain signal can be obtained by using THz time-domain spectroscopy technology to obtain the spectrum signal of the measured material, and can also be processed by wavelet transform technology to obtain the time-domain distribution characteristics of the material characteristic spectrum.

Claims (1)

1. terahertz time-domain spectroscopy instrument based on optical rectification, it is characterized in that, this spectrometer comprises femtosecond pulse laser (1), be arranged on the beam splitter (2) and the optical delay device (3) of pulsed laser output terminal, be arranged on terahertz transmitter (10-1), terahertz detector (10-5) in the vacuum system; And data acquisition and disposal system (11); Between beam splitter (2) and terahertz transmitter (10-1), set gradually chopper (6), plane mirror (7) and plano-convex lens (9), off-axis parabolic mirror (10-2) is set afterwards at hertz transmitter (10-1); Constitute the pumping light path by femtosecond pulse laser (1), beam splitter (2), chopper (6), plane mirror (7), plano-convex lens (9) and terahertz transmitter (10-1); Between optical delay device (3) and terahertz detector (10-5), set gradually plane mirror (4), (5) and plano-convex lens (8) and off-axis parabolic mirror (10-4), between terahertz transmitter (10-1) and terahertz detector (10-5), pump light wave filter (10-3) is set; Constitute the detection light path by femtosecond pulse laser (1), beam splitter (2), optical delay device (3), plane mirror (4), (5) and plano-convex lens (8), off-axis parabolic mirror (10-4) and terahertz detector (10-5); Described data acquisition and disposal system (11) comprise planar transmit mirror (11-1) successively, plano-convex lens (11-2), quarter-wave plate (11-3), wollaston prism (11-4), balance detection device (11-5), lock-in amplifier (11-6), computing machine (11-7).