JP2010038809A - Terahertz spectroscopic device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a terahertz spectroscopic device capable of solving the problem of a light condensing optical system, improving the S/N ratio in measurement, expanding a dispersible measurement frequency range without largely changing conventional optical systems. <P>SOLUTION: The terahertz spectroscopic device 1 includes a first reflector 6, a sample holder 7, and an aperture 20. The first reflector 6 condenses terahertz waves transmitted from a silicon lens 5. The sample holder 7 holds a sample on the center axis of the beam line of the terahertz waves condensed. The aperture 20 is arranged between the first reflector 6 and the sample holder 7 so that the opening making a part of the light fluxes of the terahertz waves pass through may be overlapped with the center axis of the beam line at the center of the opening. The terahertz spectroscopic device 1 receives the terahertz waves having penetrated through the sample to perform the spectral analysis of the sample. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a terahertz spectrometer that analyzes physical properties of a sample by terahertz time domain spectroscopy (THz-TDS method) using electromagnetic waves in a terahertz band.

  The THz-TDS spectroscopic device performs physical property analysis such as complex dielectric constant and complex refractive index of a sample using a wide band frequency component contained in a short-time pulse laser beam of femtosecond or picosecond order ( For example, refer nonpatent literature 1.).

  FIG. 1 is a diagram illustrating a configuration example of a conventional THz-TDS spectroscopic device.

  The terahertz spectrometer 101 includes a pulsed laser light source 102, a beam splitter 103, a photoconductive antenna 104, a silicon lens 105, a first reflection unit 106, a sample holding unit 107, a second reflection unit 108, a silicon lens 109, and a photoconductive antenna. 110, an optical delay unit 111, a DC voltage source 112, a chopper 113, a lock-in amplifier 114, a current amplifier 115, and an analysis unit 116.

The pulsed laser light source 102 emits laser light as a short-time pulse of femtosecond or picosecond order with a period of several MHz. The beam splitter 103 branches the pulse laser beam. The photoconductive antenna 104 receives the first pulse laser beam branched by the beam splitter 103 and irradiates the terahertz band electromagnetic wave pulse from the silicon lens 105. The first reflecting unit 106 collimates the electromagnetic wave pulse radiated from the silicon lens 105 with a reflecting mirror such as a parabolic mirror or an ellipsoidal mirror. The sample holder 107 holds the sample on the beam line of the electromagnetic pulse. The second reflecting unit 108 is disposed symmetrically with the first reflecting unit 106 and guides the electromagnetic wave pulse transmitted through the sample to the silicon lens 109. The photoconductive antenna 110 detects the electromagnetic wave pulse incident on the silicon lens 109 as the probe light using the second pulse laser beam branched by the beam splitter 103. The optical delay unit 111 includes an optical system having a variable optical path length, and detects the signal by time sweeping by the photoconductive antenna 110 by shifting the propagation time of the second pulse laser beam. The current amplifier 115 amplifies the output of the photoconductive antenna 110. The lock-in amplifier 114 performs synchronous detection of the output signal of the current amplifier 115 based on the reference signal input from the chopper 113. The chopper 113 modulates the voltage supplied from the DC voltage source 112 to the photoconductive antenna 104 based on the reference signal for synchronous detection. The analysis unit 116 acquires the entire time waveform of the electromagnetic wave pulse based on the output signal of the lock-in amplifier 114, and analyzes the transmission spectrum of the sample.
Terahertz Technical Directory, NGT, 2007, P106, P107, P406

  The wavelength of the terahertz wave is located between infrared and millimeter waves and cannot be visualized using an infrared camera or the like. For this reason, the optical axis of the spectroscopic device is adjusted by removing the photoconductive antennas 104 and 110 on the transmitting side and the receiving side and the silicon lenses 105 and 109 and using the pulse laser beam (for example, red visible light having a wavelength of 800 nm) as it is. Irradiation to the optical system is performed by adjusting the first reflecting unit 106 and the second reflecting unit 108 so that the pulsed laser beam is focused at the position of the sample. However, when the photoconductive antenna 104 or the silicon lens 105 is actually attached, the focal position of the femtosecond pulse laser beam and the focal position of the terahertz wave do not completely coincide. Furthermore, the wavelength of the terahertz wave is extremely long, on the order of several hundred μm, compared to the wavelength of the femtosecond pulse laser beam (for example, 800 nm). It is difficult to obtain a complete coherent terahertz wave with the same phase.

  Therefore, in the condensing optical system of the terahertz spectrometer, stray light is likely to be actually generated, and it is difficult to form a complete condensed beam of terahertz waves. The spectral range that can be handled as is naturally limited. In particular, the measurement data of the spectrum on the high frequency side deviates greatly from an accurate value.

  Further, when analyzing the sample in a cryogenic state, the sample is placed in the cryostat 117 as shown in FIG. The cryostat 117 includes a window portion 117A, a vacuum chamber 117B, and a cryogenic chamber 117C. The sample is disposed in the cryogenic chamber 117C, and the sample is irradiated with the terahertz wave through the window portion 117A. The window 117A is made of a material that is transparent to terahertz waves such as quartz and silicon. However, the optical path of a light beam that is incident on the window 117A with an inclination is shifted due to a refraction phenomenon in the window 117A. The focal position of the terahertz wave deviates from the sample holding position and the position of the photoconductive antenna on the receiving side. Therefore, the measurement accuracy deteriorates due to the insertion of the cryostat 117.

  FIG. 2 (B) shows an alumina plate (1.8 mm thick) at the time of normal transmission measurement and when a cryostat (window crystal, thickness: 2 mm, total of 4) is inserted in a conventional concentrating spectroscopic optical system. It shows the difference in transmission spectrum. This material originally shows a gentle attenuation characteristic with respect to the frequency (horizontal axis), but when the cryostat is inserted, an abnormal drop in transmittance is observed at a specific frequency, and accurate measurement cannot be performed. Even when the sample is thick, the measurement accuracy similarly deteriorates due to the refraction phenomenon in the sample.

  As a measure for avoiding the above problem, it is conceivable to irradiate the sample with a terahertz wave not by a condensing optical system but by a parallel optical system.

  However, in the parallel optical system, the beam diameter is wider than the beam diameter at the focal point in the condensing optical system (generally about φ2 mm), and is expanded to about 10 to 20 times, for example. If the size of the sample is about this enlarged beam diameter (about φ20 to 40 mm), there is no problem, but the size of the sample actually handled is generally about φ8 to 15 mm, which is smaller than the beam diameter. In many cases, the effective irradiation area of the beam by the parallel optical system is significantly smaller than the actual beam diameter. For example, if the sample size is 10 mm and the beam diameter is 30 mm, the effective irradiation area is about 11% of the area of the beam diameter. In particular, when the cryostat is inserted, the effective irradiation area of the beam by the parallel optical system is also reduced due to the restriction of the sample size that can be arranged in the cryostat. Further, for example, when the condensed light beam is converted into a parallel light beam by a reflecting mirror, the beam diameter is further increased to several centimeters to several tens of centimeters, and the effective irradiation area of the beam is also significantly smaller than the area of the beam diameter. .

  Since the irradiation intensity of terahertz waves is on the order of μW in a GaAs-based photoconductive antenna that is generally used at present, it is necessary to perform detection with extremely high sensitivity in order to analyze a transmission spectrum. However, in the parallel optical system, the effective irradiation area of the beam tends to be narrowed, the detection intensity of the terahertz wave is significantly reduced, the S / N ratio of the measurement is greatly reduced, and the transmission spectrum cannot be analyzed for a sample having a large absorption coefficient. become.

  For example, in the terahertz spectrometer 121 shown in FIG. 3, the focused light beam is converted into a parallel light beam by the concave lenses 118 arranged before and after the sample holder. In this case, since the transmittance of the concave lens 118 is not 100% but at most about 80%, when the front and rear concave lenses 118 are combined, the reception intensity of the terahertz wave is about 60% at most. Therefore, the detection intensity of the terahertz wave is further reduced from the above 11% to about 7%.

  For example, when a collimation type silicon lens attached to a photoconductive antenna is used to irradiate a terahertz wave as a parallel light flux, the spherical aberration of the collimation type lens is extremely large compared to a spherical lens. Therefore, it is necessary to adjust the position of the photoconductive antenna and the optical axis with extremely high accuracy. Specifically, the terahertz wave generator itself composed of a photoconductive antenna and a silicon lens is to be replaced, which requires significant modification and adjustment of the entire spectroscopic device. As a result, it requires extremely high expertise, technical experience, time and cost as compared with the past.

  The present invention provides a terahertz spectrometer that solves the above-mentioned problems, improves the S / N ratio of measurement, and expands the spectral frequency range that can be measured without making major changes to the conventional optical system. There is to do.

  The present invention relates to a terahertz spectrometer that receives a terahertz wave transmitted from a transmitter and transmitted through a sample by a receiver and performs spectral analysis of the sample. A shielding plate. The condensing unit condenses the terahertz wave transmitted from the transmitter. The sample holding unit holds the sample on the central axis of the terahertz beam line focused on the light collecting unit. The shielding plate is disposed between the light condensing unit and the sample holding unit so that the opening through which a part of the light beam of the terahertz wave passes overlaps the central axis of the beam line at the center of the opening.

  In this configuration, only the light beam transmitted at an incident angle near the vertical to the sample near the central axis of the beam line passes through the opening of the shielding plate and is irradiated to the sample. On the other hand, the light beam deviating from the central axis of the beam line is shielded by the shielding plate. Therefore, the light beam applied to the sample can be regarded as pseudo parallel light, and the terahertz wave can be transmitted through the sample in a quasi-coherent state in which the phases of the light beams are almost uniform. At this time, the light beam shielded by the shielding plate shields the light beam and stray light incident in an oblique direction, but the transmission loss in this case can be kept relatively low at 50% to 70%. Broadband spectroscopic analysis is possible with a high / N ratio.

  The shielding plate is disposed at a position away from the light collecting unit by a distance that is 1/10 to 1/3 of the f value of the light collecting unit, and the diameter of the opening is equal to the beam diameter of the terahertz wave at the sample holding unit. It is suitable that it is 2 to 8 times. Accordingly, it is possible to shield light flux and stray light incident from an oblique direction greatly deviated from the optical axis while maintaining the transmission loss relatively low at 50% to 70%.

  The shielding plate preferably includes a diaphragm mechanism that changes the diameter of the opening. If the aperture diameter is small, only the linear transmission component can be extracted. However, the transmission loss increases, and the component with a particularly long wavelength increases the ratio of being cut by the shielding plate. On the contrary, if the aperture diameter is large, the transmission loss is small, but a large amount of light flux and stray light incident from an oblique direction pass. Therefore, by providing a diaphragm mechanism that can adjust the aperture diameter to the shielding plate and adjusting it, it is possible to perform measurement under the optimum spectral condition according to the wavelength band to be measured and the non-measurement object. For example, when measuring a sample with large absorption or when it is desired to accurately measure the long wavelength side (low frequency side), it is preferable to increase the aperture diameter. Conversely, when measuring a sample whose characteristics vary greatly depending on the incident angle of the light wave, such as a photonic crystal or a polarizer, reducing the aperture diameter and improving the accuracy of the linear transmission component even at the expense of transmittance. Is preferred.

  The shielding plate preferably includes an absorber that absorbs terahertz waves. By sticking an absorbing material that absorbs terahertz waves to the surface of the shielding plate, stray light can be effectively absorbed by the shielding plate, and interference with incident light can be further prevented.

  The absorber may be ferrite. By using ferrite as the absorber, stray light can be absorbed more efficiently.

  The sample holding part is a container including a window part, and the window part may be arranged on the central axis of the beam line. When a container containing window material such as a cryostat is introduced, a terahertz wave close to a linear component can be made incident from the window portion by installing a shielding plate in front of the window material. Can be avoided.

  According to the present invention, the sample is irradiated with only a light beam that can be regarded as a pseudo parallel light beam by the shielding plate, so that the S / N ratio of the measurement is increased while suppressing transmission loss without changing the configuration of the light source or the like. Maintains broadband spectral analysis. Therefore, even a sample having a large absorption coefficient can be spectrally analyzed. When a container including a window material such as a cryostat is inserted, normal measurement can be performed without special adjustment of the existing spectroscopic optical system.

  A terahertz spectrometer according to an embodiment of the present invention will be described.

  FIG. 4 is a diagram illustrating the terahertz spectrometer 1 according to the present embodiment. The terahertz spectrometer 1 includes a pulsed laser light source 2, a beam splitter 3, a photoconductive antenna 4, a silicon lens 5, a first reflection unit 6, an aperture 20, a sample holding unit 7, a second reflection unit 8, a silicon lens 9, and light. A conductive antenna 10, an optical delay unit 11, a DC voltage source 12, a chopper 13, a lock-in amplifier 14, a current amplifier 15, and an analysis unit 16 are provided.

  The pulse laser light source 2 emits laser light as a short-time pulse of femtosecond or picosecond order with a period of several MHz. The beam splitter 3 branches the pulse laser beam. The photoconductive antenna 4 receives the first pulse laser beam branched by the beam splitter 3 and irradiates the terahertz band electromagnetic wave pulse from the silicon lens 5. The photoconductive antenna 4 and the silicon lens 5 correspond to a transmitter, and an electromagnetic wave pulse corresponds to a terahertz wave transmitted from the transmitter. The first reflecting unit 6 collimates the electromagnetic wave pulse radiated from the silicon lens 5 with a reflecting mirror such as a parabolic mirror or an ellipsoidal reflecting mirror. The aperture 20 is a shielding plate made of, for example, a metal material that shields terahertz waves such as aluminum, iron, and copper, and an opening is provided so that the opening center coincides with the central axis of the terahertz wave beam line. Yes. The opening of the aperture 20 transmits only the light beam that is transmitted at an angle close to perpendicular to the sample. The sample holder 7 holds the sample on the central axis of the terahertz wave beam line that has passed through the opening of the aperture 20. The second reflecting portion 8 is disposed symmetrically with the first reflecting portion 6 and guides the electromagnetic wave pulse transmitted through the sample to the silicon lens 9. The photoconductive antenna 10 detects an electromagnetic wave pulse incident on the silicon lens 9 as probe light using the second pulse laser beam branched by the beam splitter 3. The photoconductive antenna 10 and the silicon lens 9 correspond to a receiver that receives terahertz waves. The optical delay unit 11 includes an optical system having a variable optical path length, and performs signal detection by time sweeping by the photoconductive antenna 10 by shifting the propagation time of the second pulse laser beam. The current amplifier 15 amplifies the output of the photoconductive antenna 10. The lock-in amplifier 14 performs synchronous detection of the output signal of the current amplifier 15 based on the reference signal input from the chopper 13. The chopper 13 modulates the voltage supplied from the DC voltage source 12 to the photoconductive antenna 4 based on the reference signal for synchronous detection. The analysis unit 16 acquires the entire time waveform of the electromagnetic wave pulse based on the output signal of the lock-in amplifier 14, and spectroscopically measures the transmission spectrum of the sample.

  FIG. 5A is a diagram illustrating the amplitude intensity (dynamic range) frequency spectrum of a transmitted terahertz wave when alumina (thickness 1.8 mm) having relatively small absorption in the terahertz band is used as a sample. . In this figure, the intensity is normalized by the noise level (4.5 THz or more). A solid line in the figure indicates a measurement result of the terahertz spectrometer 1 of the first configuration example. The broken line in the figure shows the measurement result of the conventional terahertz spectrometer 101 without an aperture as Comparative Example 1. The dotted line in the figure shows the measurement result with the conventional terahertz spectrometer 121 in which a concave lens is provided without providing an aperture as Comparative Example 2.

  In general, the upper limit frequency at which spectroscopy is possible is uniquely determined by the value of the dynamic range. In the case of alumina measured in this example, the lower limit of the dynamic range is about 27. In Comparative Example 1 in which no aperture is provided, the strength sharply decreases at 2 THz or more, and the upper limit frequency is around 2.6 THz. On the other hand, in this configuration example 1, there is no such drop in the spectrum. The intensity on the high frequency side is larger than that of Comparative Example 1, and the upper limit of the spectroscopic band is around 3.5 THz.

In Comparative Example 2 in which a concave lens is provided in place of the aperture, the sample size is φ8 mm and the beam diameter of the parallel light beam is φ30 mm. In Comparative Example 2, the use of a concave lens does not cause a sharp drop in strength as in Comparative Example 1 at 2 THz or more, but the overall strength is greatly reduced compared to Comparative Example 1 and Configuration Example 1. The upper limit frequency is around 3.1 THz. The amplitude peak intensity of Comparative Example 2 is reduced to about 27% when Comparative Example 1 is 100%. When this is converted into power, (0.27) ² ≈7%, and a loss of 93% actually occurs. This coincides with the calculation result in which the intensity when the transmittance of the concave lens is calculated as 80% in the description of FIG. 3 is about 7%. On the other hand, in the present configuration example 1, the fluctuation of the amplitude peak intensity is about several percent compared to the comparative example 1, and the spectrally possible band can be expanded while maintaining the intensity. As described above, in the first configuration example, it is possible to expand the spectroscopic band by only inserting the aperture without substantially reducing the dynamic range of the terahertz wave that is originally emitted with low intensity.

  FIGS. 5B and 5C are diagrams for explaining the analysis results of the complex curvature analyzed based on the above-described amplitude intensity frequency spectrum and phase spectrum. Since the frequency at which phonon absorption occurs in alumina exists in 13 to 14 THz, the complex refractive index n and κ should increase gradually in the region of several THz lower than 10 THz, but in the frequency region where accurate measurement cannot be performed. From the data, a dispersion curve greatly deviating from the accurate numerical value is obtained. In Comparative Example 1 in which no aperture is provided, measurement is possible only up to an upper limit of about 2.5 THz. However, in Configuration Example 1, a region that can be measured up to about 3.5 THz is widened.

  FIG. 6 is a diagram illustrating a result of confirming the relationship between the aperture diameter of the aperture, the distance from the light collecting portion to the aperture, and the measurable frequency. In this measurement, the upper and lower limits of the frequency and the spectroscopic capability that can provide the necessary dynamic range (DR = 27) when it is assumed that the above-mentioned alumina is measured under the conditions of a focused beam diameter of 2 mm and a reflector f value of 210 mm. The range of the band was measured. As a result, as shown in FIG. 6A, if the aperture diameter is too small, the light on the low frequency side is difficult to transmit, and the light on the low frequency side is difficult to transmit even if the distance is too far from the light collecting portion. became. On the other hand, as shown in FIG. 6B, if the aperture diameter is too large, the measurable upper limit frequency is lowered, and the upper limit frequency is lowered even if the distance from the light condensing part is too close. Therefore, in this measurement, as shown in FIG. 6C, when the aperture diameter is 4 to 15 mm and the aperture distance is 20 to 70 mm from the light converging part, the spectral band is widened. In particular, when the aperture diameter was 6 to 11 mm and the distance from the condensing part was 50 to 65 mm, the upper limit of measurement on the high frequency side was particularly high.

  In this measurement, the focused beam diameter is 2 mm. However, the aperture diameter of the aperture may be determined based on the beam diameter. Therefore, it is preferable to determine the aperture diameter in the range of 2 to 8 times the beam diameter, and particularly in the range of 3 to 5.5 times, the upper limit of measurement on the high frequency side is particularly high. Moreover, since the divergence angle of the condensed beam from the condensing unit is determined by the f value of the curved reflecting mirror, the position where the aperture is installed may be determined based on the f value of the reflecting mirror. Based on this, it is preferable to determine the distance from the light converging part in the range of f / 10 to f / 3, and in particular, in the range of f / 4.2 to f / 3.2, the higher frequency side The measurement upper limit of becomes particularly high. By setting the aperture as described above, the present invention can be implemented particularly effectively. The optimum range of the aperture diameter of the aperture and the aperture distance from the condensing part shown in the present embodiment is merely one embodiment, and the scope of the present invention is not limited to the above numerical values.

  FIG. 7 shows a configuration example of the aperture 20, FIG. 7A is a front view, and FIG. 7B is a side sectional view. The aperture 20 of this configuration example includes a diaphragm mechanism 21, an operation lever 22, and a ferrite sheet 23. By adjusting the diaphragm of the diaphragm mechanism 21 by operating the operation lever 22, the aperture diameter can be changed. Therefore, in the terahertz spectrometer 1, the aperture diameter of the aperture 20 is controlled according to the measurement purpose.

  As described above, the spectral band changes greatly depending on the aperture diameter.For example, if you want to increase the sensitivity on the low frequency side, increase the aperture diameter. Conversely, if you want to increase the sensitivity on the high frequency side, decrease the aperture diameter. Good. In addition, as the aperture diameter is reduced, only components that are incident perpendicular to the sample can be extracted. Therefore, a sample whose characteristics greatly vary depending on the incident angle of the electromagnetic wave, such as a photonic crystal or a polarizer, is measured. In this case, the measurement accuracy can be increased by reducing the aperture diameter.

  The ferrite sheet 23 is an absorbing material in the present invention, and is affixed to the surface of the aperture 20 on the side facing the first reflecting portion, and absorbs terahertz waves. When the aperture 20 is made of metal, stray light is reflected on the metal surface unless the ferrite sheet 23 is provided, and may return to the photoconductive antenna side that generates the terahertz wave, causing interference and generating noise. Therefore, this problem can be avoided by attaching a ferrite sheet 23 that absorbs terahertz waves to the surface of the aperture 20. The ferrite sheet 23 has particularly good efficiency for absorbing terahertz waves, and therefore can effectively prevent the generation of interference noise.

  FIG. 8 is a diagram for explaining an example in which a cryostat 17, which is a container having a window portion, is inserted into the terahertz wave optical path with respect to the terahertz spectrometer 1. The cryostat 17 includes four window members, and the aperture 20 is disposed in front of the window member.

  FIG. 8B is a diagram for explaining an amplitude intensity (dynamic range) frequency spectrum when the above-described alumina is used as a sample. In this figure, the intensity is normalized by the noise level (4.5 THz or more). A solid line in the figure indicates a measurement result of the terahertz spectrometer 1 of the present configuration example 2 in which a cryostat and an aperture are inserted. The broken line in the figure shows the measurement result in Comparative Example 3 in which a cryostat is inserted but no aperture is provided. The dotted line in the figure shows the measurement result of Comparative Example 4 in which the cryostat and the concave lens are inserted but the aperture is not provided.

  In Comparative Example 3 where no aperture is provided, the strength sharply decreases at 2 THz or more, and the upper limit frequency is around 2.8 THz. Moreover, although the comparative example 4 which provides a concave lens does not show the sharp fall of intensity | strength like the comparative example 3 in 2 THz or more by using a concave lens, the whole intensity | strength is compared with the comparative example 3 and this structural example 2. The upper limit frequency is around 2.4 THz. On the other hand, this configuration example 2 does not have such a drop in the spectrum, has a high intensity on the high frequency side, and the upper limit frequency at which spectroscopy is possible is around 3.1 THz.

  FIG. 8C is a diagram for explaining the transmittance spectrum of alumina. The configuration example 2 with the cryostat inserted has a measurement error suppressed to about several percent compared to the configuration example 1 with the aperture not provided and no cryostat inserted, and the measurement can be performed with almost the same accuracy. ing. On the other hand, the cryostat is inserted in the same manner as in the configuration example 1, but in the comparative example 3 in which no aperture is provided, the spectrum shape is greatly distorted.

  As described above, in the present configuration example 2 in which the aperture is provided and the cryostat is further provided, the same wide spectroscopic band as in the present configuration example 1 can be maintained, and high-precision measurement can be performed.

It is a figure which shows the structural example of the conventional terahertz spectroscopy apparatus. It is a figure explaining the example which inserts a cryostat. It is a figure which shows the structural example of the conventional terahertz spectroscopy apparatus using a concave lens. It is a figure which shows the structure of the terahertz spectroscopy apparatus which concerns on embodiment of this invention. It is a figure which shows the example which performed the measurement of the alumina board by embodiment of this invention. It is a figure explaining the relationship between the aperture diameter of an aperture, the aperture distance from a condensing part, and a measurable frequency. It is a figure explaining the structural example of an aperture. It is a figure explaining the example at the time of inserting a cryostat in the terahertz spectroscopy apparatus which concerns on embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,101,121 ... Terahertz spectrometer 2 ... Pulse laser light source 3 ... Beam splitter 4 ... Photoconductive antenna 5 ... Silicon lens 6 ... 1st reflection part 7 ... Sample holding part 8 ... 2nd reflection part 9 ... Silicon lens 10 ... Photoconductive antenna 11 ... Optical delay unit 12 ... DC voltage source 13 ... Chopper 14 ... Lock-in amplifier 15 ... Current amplifier 16 ... Analysis unit 20 ... Aperture

Claims (6)

A terahertz spectrometer that receives a terahertz wave transmitted from a transmitter and transmitted through a sample by a receiver, and performs spectral analysis of the sample,
A condensing unit that condenses the terahertz wave transmitted from the transmitter;
A sample holding unit for holding a sample on the central axis of the beam line of the terahertz wave focused on the light collecting unit;
A shielding plate disposed between the light collecting unit and the sample holding unit so that an opening through which a part of the light beam of the terahertz wave passes overlaps a central axis of the beam line at the center of the opening. , Terahertz spectrometer.   The shielding plate is disposed at a position away from the light collecting part by a distance that is 1/10 to 1/3 of the f value of the light collecting part, and the diameter of the opening is the same as that of the sample holding part. The terahertz spectrometer according to claim 1, wherein the terahertz spectrometer is 2 to 8 times the beam diameter of the terahertz wave.   The terahertz spectrometer according to claim 1, wherein the shielding plate includes a diaphragm mechanism that changes a diameter of the opening.   The terahertz spectrometer according to claim 1, wherein the shielding plate includes an absorbing material that absorbs the terahertz wave.   The terahertz spectrometer according to claim 4, wherein the absorber is ferrite.   The terahertz spectrometer according to claim 1, wherein the sample holding unit is a container including a window unit, and the window unit is disposed on a central axis of the beam line.

Images