JP2006052948A - Method of spectrometry and spectrometer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and apparatus for measurement including information of amplitude intensity and phase information of the terahertz pulse reflected by a measurement specimen without being limited by the shape of the specimen, its physical properties, and the method of its mounting. <P>SOLUTION: The spectrometer is constituted of: a spectroscopic system for irradiating the measurement object with the terahertz light pulse generated by the laser pulse and detecting the reflected light from the measuring object; and a position measurement apparatus for detecting the relative position between the measurement object and the spectro-optical system. A delay device of the spectroscopic system is corrected by using the detected relative positional information. Thereby, the measurement including the information of amplitude intensity and the phase information of the terahertz light pulse reflected by the measurement specimen is enabled without being limited by the shape of the specimen, physical properties, and the method of its mounting. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a time-resolved reflection measurement method and a terahertz time-resolved reflection measurement apparatus that detect and measure pulse light reflected by a sample.

  Electromagnetic waves having components in a frequency range from 10 GHz to 10 THz or a wide frequency range (referred to as a terahertz band) including the frequency range are collectively referred to as terahertz light. In particular, a spectroscopic device and an imaging device in a time domain using pulsed terahertz light (referred to as terahertz pulse light) have been proposed.

  These devices irradiate various measured samples such as semiconductors and dielectrics with terahertz pulse light and transmit the measured sample or reflect the measured sample, and then change the electric field intensity of the pulsed light over time. And the electric field strength and phase information of each frequency are obtained by Fourier transform. As a result, for example, it is possible to obtain non-destructive physical property data of various measured samples that could not be obtained or was difficult to obtain with a Fourier spectrometer.

  In order to obtain information about samples using the terahertz pulse light, a reference time-series waveform is required in addition to the time-series waveforms from these samples. As the reference waveform, in the case of the transmission type, a waveform detected when the sample is removed is used, and in the case of the reflection type, a mirror that can be regarded as having a reflectance of 100% is provided instead of the sample, The waveform detected at that time is used. The reference waveform is also Fourier transformed to obtain the amplitude intensity and phase information of the electric field for each wavelength. From the ratio of the amplitude intensity of the waveform to the sample and the amplitude intensity of the reference waveform, the transmittance or reflectance of the sample can be obtained, and the phase difference can be obtained from the phase of the sample and the phase of the reference waveform. Time domain spectroscopy-"Sakai Kiyomi, Spectroscopic Research, Japan Spectroscopic Society, 2001, Vol. 50, No. 6, pp. 261-273 (Non-Patent Document 1).

  In the case of the transmission type, the sample position does not affect the phase information. However, it is impossible or difficult to measure a sample in which the amplitude intensity of the terahertz pulse light is attenuated to 1/500 or less because the terahertz pulse light is transmitted through the sample. For example, it is difficult to measure a highly doped semiconductor sample or a living body.

  In the reflection type, the sample position affects the phase. Therefore, in order to use the phase information, it is necessary to arrange the sample and the reference mirror at the same position. The position accuracy required at this time is about several micrometers at 1 THz, and the higher the frequency, the higher the position accuracy is required.

Measurement of optical properties of
highly doped silicon by terahertz time domain reflection "S. Nashima, 3 others, Applied Physics Letters, (USA), December 10, 2001, 79, 24, pp. 3923-3925 (Non-patent Document 2) describes a method in which a silicon plate is placed in close contact with a sample as a method of performing a reflection type measurement including phase information without requiring positional accuracy. Japanese Patent Application Laid-Open No. 2004-198250 (Patent Document 1) describes a measurement method using terahertz pulse light in which a sample is limited to a parallel plate, and the sample incident surface included in the time-series waveform of the reflected light is described. The reflected pulse light is used as a reference signal, and a differential signal obtained by removing the reflected pulse light from the time-series waveform of the reflected light is used as a sample signal for measurement.

In addition, a method that is not easily affected by misalignment is described in International Publication No. WO00 / 079248 (Patent Document 2). This method changes the vibration by driving the movable reflector of the variable optical delay device at a predetermined vibration frequency, and frequency analysis is performed on the detection signal obtained as a result of the periodic vibration change using the spectrum analyzer of the spectral processor. To obtain information on the amplitude intensity of the terahertz pulse light
JP 2004-198250 A International Publication Number WO00 / 079248 “Review: Terahertz Time Domain Spectroscopy”, Kiyomi Sakai, Spectroscopic Research, The Spectroscopical Society of Japan, 2001, Volume 50, No. 6, pp. 261-273 “Measurement of optical properties of highly doped silicon byterahertz time domain reflection” S. Nashima, 3 others, Applied Physics Letters, (USA), December 10, 2001, 79, 24, pp. 3923-3925

  The method of installing the silicon plate in close contact described in Non-Patent Document 2 is that the silicon plate having a known physical property is placed in close contact with the front surface of the sample (the surface on the terahertz pulse light incident side), and the reflection spectrum at that time Is a method that corrects the position of the sample so that it agrees with the calculation result. In addition to the sample being limited to a flat contact surface, the advantage of non-contact measurement is one of the features of terahertz spectrometry. There was a problem of being damaged.

  In the method described in Patent Document 1, as described above, the sample is limited to a parallel plate, and the amplitude intensity of the terahertz pulse light is attenuated to 1/500 or less by transmitting the terahertz pulse light through the sample. There was a problem that measurement was impossible or difficult.

  Furthermore, these conventional methods require that the sample be stationary during measurement of the time-series waveform (usually several minutes to several tens of minutes), particularly in the direction perpendicular to the terahertz pulse incident surface of the sample. It is assumed that the position of the sample is not displaced, and there has been a problem that the tolerance of displacement of this position needs to be 1 micrometer or less at 1 THz.

  As described above, the method described in Patent Document 2 changes the vibration by driving the movable reflector at a predetermined vibration frequency, and frequency-analyzes the detection signal with a spectrum analyzer of a spectral processing unit to generate terahertz pulse light. Information on amplitude intensity is obtained. However, the information obtained by this apparatus is only amplitude intensity information, and there is a problem that information on the phase cannot be obtained.

  As described above, the conventional method or apparatus can perform measurement including amplitude intensity information and phase information of the terahertz pulse light reflected by the measurement sample without limiting the shape and physical properties of the measurement sample and the installation method. There was no problem.

  Accordingly, the present invention provides a method and apparatus for performing measurement including amplitude intensity information and phase information of a terahertz pulse reflected by the measurement sample without limiting the shape and physical properties of the measurement sample and the installation method.

  The present invention has been proposed in order to solve the above-mentioned problems. In the first embodiment of the present invention, the measurement sample is irradiated with pulsed light, a response signal from the measurement sample is detected, and the measurement sample is detected. In the spectroscopic measurement method for measuring the characteristics, the relative position between the measurement sample and the spectroscopic optical system is detected, and the time axis of the response signal is corrected based on the relative position.

  A second aspect of the present invention is a spectroscopic measurement method in which the pulsed light is terahertz pulsed light in a terahertz band.

  A third aspect of the present invention is a spectroscopic measurement method that performs time-resolved measurement of the response signal.

  The fourth aspect of the present invention is a spectroscopic measurement method in which the measurement of the relative position is performed by irradiating the measurement sample with laser light.

  According to a fifth aspect of the present invention, in a spectroscopic measurement device that irradiates a measurement sample with pulsed light, detects a response signal from the measurement sample, and measures the characteristics of the measurement sample, the spectroscopic optics is applied to the measurement sample. This is a spectroscopic measurement apparatus provided with a position measuring means for arranging a system and detecting a relative position between the spectroscopic optical system and the measurement sample.

  A sixth aspect of the present invention is a spectroscopic measurement device in which the pulsed light is terahertz pulsed light in a terahertz band.

  A seventh aspect of the present invention is a spectrometer that performs time-resolved measurement of the response signal.

  8. The spectroscopic measurement apparatus according to claim 5, wherein the position measuring means is a laser position sensor using laser light.

  According to a ninth aspect of the present invention, there is provided a spectroscopic measurement apparatus in which the spectroscopic optical system includes the pulsed light delay unit and derives the delay amount of the pulsed light by the delay unit based on the relative position.

  A tenth aspect of the present invention is a spectroscopic measurement apparatus in which a terahertz pulsed light generating element that emits the pulsed light is installed.

  An eleventh aspect of the present invention is a spectroscopic measurement apparatus in which the spectroscopic optical system and the position measuring means are housed in a box, and a movable means for allowing the box to move is attached.

  A twelfth aspect of the present invention is a spectroscopic measurement apparatus in which a laser pulse light generator is installed outside the box, and the laser pulse light generator and the box are connected by an optical fiber.

  A thirteenth aspect of the present invention is a spectroscopic measurement apparatus in which driving means for correcting a deviation of the measurement sample based on the relative position is installed.

  According to the first aspect of the present invention, the relative position between the measurement sample and the spectroscopic optical system is detected, and the time axis of the response signal is corrected based on the relative position, so the time axes of the measurement data are matched. be able to. Therefore, the response signal is captured by the trigger based on the time when the pulsed light is incident on the measurement sample. Therefore, by synchronizing with the repetition of the pulsed light, it is possible to detect a response signal with less error and noise with high efficiency.

  According to the second aspect of the present invention, since the characteristics of the measurement sample are measured using the terahertz pulse light in the terahertz band, the optical response in the photon energy region of the terahertz light can be measured. The terahertz pulse light according to the present invention can be generated by irradiating an ultra-short pulse laser onto an electro-optic crystal, a semiconductor, a quantum well, or a high-temperature superconducting thin film.

  According to the third aspect of the present invention, highly accurate amplitude and phase information of the response signal can be simultaneously measured by time-resolved measurement of the response signal. In the spectroscopic measurement apparatus according to the present invention, the position measurement apparatus is installed as described above, and the time series is detected from the response signal while measuring the relative position between the spectroscopic optical system and the measurement sample during the time-resolved measurement. You can adjust the timing. When the relative position is shifted, the optical path length from the measurement sample to the detector is shifted, so that the propagation time of the response signal changes. Since the present invention can adjust the timing for detecting the response signal based on the change in the propagation time, it is possible to realize time-resolved measurement without time axis deviation. The measurement accuracy of the position measuring device needs to be 300 micrometers or less, and desirably 10 micrometers or less. Furthermore, it becomes possible to perform optimal measurement by setting it as 1 micrometer or less.

  According to the fourth aspect of the present invention, since the relative position is measured by irradiating the measurement sample with laser light, highly accurate position measurement can be performed. The position measuring means according to the present invention can set the measurement accuracy to 1 micrometer or less, and can provide a highly accurate spectroscopic measurement.

  According to the fifth aspect of the present invention, since the spectroscopic optical system is arranged with respect to the measurement sample and the position measuring means for detecting the relative position between the spectroscopic optical system and the measurement sample is provided, The time axis can be matched. Therefore, the response signal is captured by the trigger based on the time when the pulsed light is incident on the measurement sample. Therefore, by synchronizing with the repetition of the pulsed light, it is possible to detect a response signal with less error and noise with high efficiency.

  According to the sixth aspect of the present invention, since the pulsed light is terahertz pulsed light in the terahertz band, the optical response in the photon energy region of the terahertz light can be measured. As the terahertz generator that emits the terahertz pulse light, an electro-optic crystal, a semiconductor, a quantum well, a high-temperature superconducting thin film, or the like can be used. The terahertz generator can emit terahertz pulsed light by irradiating an ultrashort pulse laser, and the ultrashort pulsed laser light is terahertz pulsed light with a pulse laser light of several fs to sub-ps. Can be generated.

  According to the seventh aspect of the present invention, highly accurate amplitude and phase information of the response signal can be simultaneously measured by time-resolved measurement of the response signal. The spectroscopic measurement apparatus according to the present invention includes the position measurement apparatus as described above, and detects the time series from the response signal while measuring the relative position between the spectroscopic optical system and the measurement sample during time-resolved measurement. You can adjust the timing. When the relative position is shifted, the optical path length from the measurement sample to the detector is shifted, so that the propagation time of the response signal changes. Since the present invention can adjust the timing for detecting the response signal based on the change in the propagation time, it is possible to realize time-resolved measurement without time axis deviation. While detecting the time-series waveform of the pulsed light, the distance deviation between the measurement sample and the position measuring device set in the spectroscopic optical system is measured. The discrete signal sequence can be corrected based on the detected distance d information. Furthermore, the amplitude intensity information and phase information of the terahertz pulse reflected by the measurement sample can be measured without limiting the shape and physical properties of the measurement sample and the installation method.

  According to the 8th form of this invention, since the said position measurement means is a laser position sensor using a laser beam, a highly accurate position measurement can be performed. As the laser light detector, a photomultiplier tube or a CCD camera can be used.

  According to the ninth aspect of the present invention, since the spectroscopic optical system is provided with the delay means, it is possible to easily adjust the optical path length of the pulsed light and correct the time axis of the detector. Furthermore, since the delay amount of the pulsed light is derived based on the relative position, the time axis can be corrected accurately.

  According to the tenth aspect of the present invention, since the terahertz pulse light generating element is installed as the terahertz generator that emits the pulsed light, the terahertz pulsed light can be emitted stably with high efficiency.

  According to the eleventh aspect of the present invention, the spectroscopic optical system and the position measuring means are housed in a box, and movable means for making the box movable is attached. By correcting, the response signal can be measured with high accuracy. Further, as the movable means, a three-axis movable stage of X-axis, Y-axis, and Z-axis is attached to the box, and an example of the installation is shown in FIG.

  According to the twelfth aspect of the present invention, a laser pulse light generator is installed outside the box, and the laser pulse light generator and the box are connected by an optical fiber. The box position can be arbitrarily moved regardless of the output direction of the laser.

  According to the thirteenth aspect of the present invention, since the driving means for correcting the deviation of the measurement sample is installed based on the relative position, it is possible to irradiate a desired position on the surface of the measurement sample with pulsed light. . Furthermore, the measurement sample can be imaged from the response signal by moving the measurement sample in the two-dimensional direction by the driving means.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic view of a spectroscopic measurement apparatus using terahertz pulsed light according to the present invention. In the spectroscopic measurement apparatus using the terahertz light according to the present embodiment, the laser pulse generator 1, the half mirror 2, the terahertz generator 12, the terahertz detector 6, the delay device 3, and four non-axial parabolic mirrors 7, It comprises a reflection type spectroscopic device comprising 8, 10, 11 and a laser position sensor 14.

  In FIG. 1, a laser pulse L1 output from a pulse laser 1 is branched into two laser pulses L2 and L3 by a half mirror 2. One of the divided laser pulses L3 is irradiated to the terahertz generator 12. The terahertz light L5 generated as a result is condensed on the measurement sample 9 by the non-axial parabolic mirrors 10 and 11. The terahertz light L4 reflected by the measurement object is condensed on the terahertz detector 6 by the non-axial parabolic mirrors 7 and 8. In this embodiment, there are three mirrors used to change the direction of the laser pulse: mirror 4, mirror 5, and mirror 13. However, when the arrangement of each component is changed, the number of mirrors is further increased. May be increased.

  As the terahertz generator 12, a terahertz pulse generating element capable of generating terahertz pulse light by irradiating a laser pulse can be used.

  In FIG. 1, the laser pulse L <b> 2 divided by the half mirror 2 passes through the delay device 3 and is condensed to the terahertz detector 6. The time series waveform of the terahertz pulse light is reproduced by detecting the amplitude intensity of the terahertz light L4 incident on the terahertz detector 6 while changing the time for the laser pulse L2 to reach the terahertz detector 6 by the delay device 3. Is possible.

  FIG. 2 is a schematic diagram of a spectroscopic measurement apparatus using the compound semiconductor 15 as the terahertz generator 6 according to the present invention. In FIG. 1, a low-temperature grown gallium arsenide photoconductive switch is used, but a compound semiconductor 15 such as an indium arsenide example can be used. In this case, as shown in FIG. 2, the surface on which the laser pulse L3 is incident on the compound semiconductor 15 and the surface on which the terahertz light L5 is emitted are set to the same surface. That is, by irradiating the surface of the compound semiconductor 15 with the laser pulse L3, the terahertz pulse light is generated. At this time, the incident angle φ of the laser pulse L3 with respect to the compound semiconductor 15 must be other than 90 degrees and 0 degrees.

  FIG. 3 is a diagram showing the relationship between the terahertz pulse light L4 incident on the terahertz light detector 6 according to the present invention and the discrete signal sequence. When the terahertz pulse light L4 incident on the terahertz light detector 6 is as shown in FIG. 3A, the time until the laser pulse light L2 reaches the terahertz detector 6 is determined by the delay device 3. A plurality of pulse lights L3 having different delay times are made incident on the terahertz light detector 6. As a result, discrete signal sequences I (τ1), I (τ2), I (τ3),. . . , (Τn) is obtained. τ1, τ2, τ3,. . . , Τn represents a delay time.

  While detecting the time-series waveform of the terahertz pulse light L4, the distance deviation d between the measurement sample 9 and the position measurement device 14 set in the spectroscopic measurement device is measured. However, d is a direction perpendicular to the surface of the measurement sample 9 irradiated with the terahertz pulse light. The measurement accuracy of the position measuring device needs to be 300 micrometers or less, and desirably 10 micrometers or less. Furthermore, it becomes possible to perform optimal measurement by setting it as 1 micrometer or less.

  By correcting the delay amount of the delay device 3 based on the detected information on the deviation d, the discrete signal sequences I (τ1), I (τ2), I (τ3),. . . , (Τn) can be corrected. For example, if the incident angle of the terahertz pulse light L4 is θ and the speed of light is c, the correction delay time t is t = d / (cos θ × c).

  In the above correction process, the positional deviation in the sample surface is not corrected, but the positional deviation is about the vertical distance deviation d, and the deviation d is smaller than the radius of the irradiation surface of the terahertz pulse light. Alternatively, there is no problem if the sample information does not depend on the location.

  The radius W of the irradiation surface of the terahertz pulse light L5 on the measurement sample 9 is determined by the characteristics of the frequency f of the terahertz pulse light, and the well-known relational expression 2 × W = {( 4 × c) / (f × π)} × (F / D). However, (pi) represents the circumference and the focus F and the diameter D represent the focus and diameter of the non-parabolic mirror used for irradiation, respectively. If the frequency f is 1 THz, the focal point F is 10 cm, and the diameter D is 2.5 cm, the radius of the irradiated surface is 1.6 mm. Similarly, if the frequency is 100 GHz, it is 1.6 cm.

  FIG. 4 is a schematic view of a spectroscopic measurement apparatus in which the spectroscopic optical system and the position measuring means 14 according to the present invention are housed in a box 17. When measuring a measurement sample in which the deviation d is greater than or equal to the radius of the irradiated surface, or a measurement sample whose physical property data changes greatly due to a slight deviation in the sample surface, the laser pulse generator 1 as shown in FIG. It is desirable to house other structural members in the box 17 and connect the laser pulse generator and the box 17 using an optical fiber 16.

  FIG. 5 is a schematic perspective view of a spectroscopic measurement apparatus in which the spectroscopic optical system and the position measuring means 14 according to the present invention are housed in a box 17. With this arrangement, the position of the box 17 can be arbitrarily moved regardless of the output direction of the laser output from the laser pulse generator 1. Further, by attaching a three-axis movable stage 18 of X axis, Y axis, and Z axis to the box 17, and correcting the positional deviation in the sample surface, it is possible to measure with high accuracy.

  FIG. 6 is a schematic diagram of a spectroscopic measurement apparatus having position sensors 14a and 14b for detecting a positional shift in the sample plane. As shown in the figure, position sensors 14a and 14b for detecting displacement in the sample plane are arranged in the box 17, and the detected signals are used to correct the X-axis, Y-axis, and Z-axis three-stage movable stage 18. By determining the amount, it is possible to correct a deviation in the sample plane that is impossible or difficult to predict. This method is effective for measuring the skin of an active mouse or human.

  The detection accuracy of the position sensors 14a and 14b for detecting the positional deviation in the sample plane may be about 1 mm to 5 mm. In this case, the position sensors 14a and 14b are not limited to sensors using a laser, and a measurement target can be observed with a CCD camera or the like, and a positional shift can be derived from an image.

  The spectroscopic measurement apparatus according to the present invention can provide amplitude intensity information and phase information from a response signal of terahertz pulse light without limiting the shape and physical properties of the measurement sample and the installation method. Therefore, amplitude intensity information and phase information can be obtained from measurement samples in various states such as gas, liquid, solid, or a mixed state thereof, and various samples such as biomolecules and harmful substances in the atmosphere can be measured. it can.

1 is a schematic diagram of a spectroscopic measurement apparatus using terahertz band pulsed light according to the present invention. 1 is a schematic view of a spectroscopic measurement apparatus using a compound semiconductor as a terahertz generator according to the present invention. It is a related figure of the terahertz pulse light L4 which injects into the terahertz photodetector which concerns on this invention, and a discrete signal sequence. 1 is a schematic view of a spectroscopic measurement apparatus in which a spectroscopic optical system and position measurement means according to the present invention are housed in a box. 1 is a schematic perspective view of a spectroscopic measurement apparatus in which a spectroscopic optical system and position measurement means according to the present invention are housed in a box. It is the schematic of the spectroscopic measurement apparatus which has a position sensor which detects the position shift in a sample plane.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laser pulse generator 2 Half mirror 3 Delay device 4 Plane mirror 5 Plane mirror 6 Terahertz photodetector 7 Non-axis paraboloid mirror 8 Non-axis paraboloid mirror 9 Measurement sample 10 Non-axis paraboloid mirror 11 Non-axis paraboloid Mirror 12 Terahertz light generator 13 Flat mirror 14 Laser position sensor 14a Laser position sensor 14b Laser position sensor 15 Compound semiconductor 16 Optical fiber 17 Storage case 18 Three-axis movable stage L1 Laser pulse L2 Laser pulse L3 Laser pulse L4 Terahertz pulse light L5 Terahertz pulse Light L6 Laser light for position detection L6a Laser light for position detection L6b Laser light for position detection

Claims (13)

  In a spectroscopic measurement method in which a measurement sample is irradiated with pulsed light and a response signal from the measurement sample is detected to measure the characteristics of the measurement sample, the relative position between the measurement sample and the spectroscopic optical system is detected, and the relative position is detected. And a time axis of the response signal is corrected based on the spectral measurement method.   The spectroscopic measurement method according to claim 1, wherein the pulsed light is terahertz pulsed light in a terahertz band.   The spectroscopic measurement method according to claim 1, wherein time-resolved measurement of the response signal is performed.   The spectroscopic measurement method according to claim 1, wherein the relative position is measured by irradiating the measurement sample with laser light.   In a spectroscopic measurement apparatus that irradiates a measurement sample with a pulsed light, detects a response signal from the measurement sample, and measures the characteristics of the measurement sample, a spectroscopic optical system is arranged for the measurement sample, and the spectroscopic optical system And a position measuring means for detecting a relative position of the measurement sample.   The spectroscopic measurement apparatus according to claim 5, wherein the pulsed light is terahertz pulsed light in a terahertz band.   The spectroscopic measurement apparatus according to claim 5, wherein time-resolved measurement of the response signal is performed.   The spectroscopic measurement apparatus according to claim 5, wherein the position measurement unit is a laser position sensor using laser light.   The spectroscopic measurement apparatus according to claim 5, wherein the spectroscopic optical system includes a delay unit for the pulsed light, and derives a delay amount of the pulsed light by the delay unit based on the relative position. .   The spectroscopic measurement apparatus according to claim 5, wherein a terahertz pulsed light generating element that emits the pulsed light is installed.   The spectroscopic measurement apparatus according to any one of claims 5 to 10, wherein the spectroscopic optical system and the position measuring means are housed in a box, and movable means for allowing the box to move is attached.   The spectroscopic measurement apparatus according to claim 11, wherein a laser pulse light generator is installed outside the box, and the laser pulse light generator and the box are connected by an optical fiber. The spectroscopic measurement apparatus according to claim 5, further comprising a driving unit that corrects a deviation of the measurement sample based on the relative position.