JP3914553B2 - Time-series conversion pulse spectroscopic measurement apparatus and method capable of detecting weak time-series signals - Google Patents

Description

  The present invention relates to a time-series conversion pulse spectroscopic measurement apparatus and method capable of detecting a time-series weak signal.

  In recent years, with the practical application of ultrashort pulse laser technology, the radiation technology and detection technology of coherent pulsed electromagnetic waves in the far-infrared region (particularly in the terahertz band) have made significant progress. As a result, time-series conversion pulse spectroscopy using pulsed electromagnetic waves in the far-infrared region has become possible, and in Japan, development of a practical device for time-series conversion pulse spectrometry has been pioneered.

  Time-series conversion pulse spectroscopy is a technique for measuring the time-dependent electric field strength of a pulsed electromagnetic wave and Fourier-transforming the time-dependent data (time-series data) so that each frequency component forming the pulse This is a spectroscopic method for obtaining electric field strength and phase. One of the features of this spectroscopic method is that the measurement wavelength region is a boundary region between light and radio waves, which has conventionally been difficult to measure. Therefore, the spectroscopic method is expected to elucidate the properties of new materials and new phenomena. In addition, only the electric field strength of electromagnetic waves can be obtained with conventional spectroscopy, but with this time-series conversion pulse spectroscopy, only the electric field strength (amplitude) of electromagnetic waves is directly measured because the time variation of the electric field strength of electromagnetic waves is directly measured. Not only that, it has the unique feature of being able to obtain its phase. Therefore, a phase shift spectrum can be obtained by comparing with the case where there is no sample. Since the phase shift is proportional to the wave vector, the dispersion relationship in the sample can be determined using this spectroscopy, and the dielectric constant of the dielectric material can also be obtained from this dispersion relationship (Japanese Patent Laid-Open No. 2005-249867). 2002-277394 gazette).

  FIG. 1 shows a schematic configuration diagram of a time-series conversion pulse spectroscopic measurement apparatus. FIG. 2 shows a schematic configuration diagram of a photoconductive element used for emitting and detecting pulsed electromagnetic waves in the spectroscopic measurement apparatus of FIG. FIG. 3 is a cross-sectional view taken along the broken line AA 'in FIG.

  The time-series conversion pulse spectroscopic measurement device includes a light source 1 that generates pulse laser light having a predetermined time width at a predetermined frequency, a beam splitter 2 that splits the pulse laser light into pump pulse light and sampling pulse light, Radiation photoconductive element 5 that emits pulsed light by irradiation of pump pulse light, optical elements 6 and 7 that guide pulse electromagnetic waves radiated from the radiation photoconductive element 5 to the sample 8, and sampling pulse light as the pump pulse A pair of electrode films having an optical delay unit 13 for delaying light and antenna units 23a and 24a, respectively, and arranged so that the antenna units 23a and 24a are separated from each other with a minute gap to form a dipole antenna. A photoconductive element for detection 12 comprising a photoconductive film 22 with 23 and 24, which is delayed with respect to pump pulse light. When the photoconductive film 21 is irradiated with light, a photocarrier is generated between the antenna portions D, and a pulse electromagnetic wave reflected or transmitted from the sample is detected by measuring the photocarrier that has moved to the electrode. And a photoconductive element 12 for detection.

  The light source 1 is, for example, a titanium sapphire pulse laser having a center wavelength of 800 nm, a pulse width of 80 fs, and a repetition frequency of 80 MHz. The femtosecond pulsed laser light emitted from the light source 1 is demultiplexed by the beam splitter 2 into pump pulse light (pulse excitation light) L1 and sampling pulse light L4. The pump pulse light L1 is sent by the optical chopper 3 after being modulated at a frequency of 2 kHz, for example, focused by the objective lens 4 and applied to the radiation photoconductive element 5. In the radiation photoconductive element 5, carriers are generated only when the pump pulse light L1 is irradiated, current flows instantaneously, and a pulse electromagnetic wave L2 is emitted. This pulsed electromagnetic wave L2 is collimated by parabolic mirrors (optical elements) 6 and 7 and irradiated onto the measurement sample 8. The transmitted or reflected pulsed electromagnetic wave L3 (here, transmitted pulsed electromagnetic wave) L3 of the sample 8 is condensed by the parabolic mirrors 10 and 11 and guided to the photoconductive element 12 for detection.

  On the other hand, when the sampling pulse light L4 is guided and irradiated to the detection photoconductive element 12, the photoconductive element 12 generates optical carriers only at that moment as in the case of the radiating element, and these photocarriers are sampled. 8 moves to the electrode by the electric field of the transmitted pulse electromagnetic wave L3 and is detected as a current. The time until the sampling pulse light L4 reaches the detection photoconductive element 12 from the beam splitter 2 is delayed by the optical delay units 13 and 14, and each portion of the time waveform of the electric field strength of the transmitted pulse electromagnetic wave L3 is sequentially measured. Thus, the entire time waveform of the transmitted pulse electromagnetic wave L3 transmitted through the sample can be obtained.

  More specifically, the detection photoconductive element 12 detects a current corresponding to the electric field strength of the transmission pulse electromagnetic wave L3 from the sample 8 while the sampling pulse light L4 is being radiated. When the electric field intensity of the electromagnetic wave acts as a bias voltage between the minute antennas 23a and 24a of the electrodes 23 and 24 of the detection photoconductive element 12 with respect to the optical carrier, the optical carrier moves, and a current proportional to the electric field intensity flows. The magnitude and sign of this current are detected. The time width of the sampling pulse light L4 is considerably shorter than the time width of the transmitted pulse electromagnetic wave L3 by several tenths. In other words, the irradiation time of the sampling pulse light L4 is shorter than the time that the entire time waveform (from the first part to the last part) of the electric field intensity of the transmitted pulse electromagnetic wave L3 arrives. Therefore, the current flowing through the detection photoconductive element 12 during the irradiation of the sampling pulse light L4 has a very short irradiation time of the electric field of the transmitted pulse electromagnetic wave L3, and the optical delay portion of the electric field of the transmitted pulse electromagnetic wave L3. Only the irradiation time portion determined by the time delay due to 13 is measured as a current, and by further shifting the time delay, other portions of the electric field of the transmitted pulse electromagnetic wave L3 are also measured, and the time waveform of the electric field of the transmitted pulse electromagnetic wave L3 is measured. You will get the whole thing.

  Here, since the detection signal (current) detected by the photoconductive element 12 is weak, the current amplifier 15 converts the current into a voltage. Further, the excitation light is modulated by the optical chopper 3 controlled by the chopper controller 18, and only the voltage synchronized with the modulation frequency is picked up by the frequency filter by the lock-in amplifier 16 to reduce the influence of the background noise and the signal. Is detected.

  Each time-resolved data of the electric field strength of the transmitted pulse electromagnetic wave L3 of the sample 8 is processed by the signal processing means. That is, after being transmitted to the computer 17 via the lock-in amplifier 16, it is sequentially stored as time-series data, and the series of time-series data is subjected to Fourier transform processing by the computer 17 and converted into a frequency (frequency) space. By doing so, the spectrum of the amplitude and phase of the transmitted pulse electromagnetic wave L3 of the sample 8 is obtained. That is, the electric field amplitude and amplitude of the transmitted pulsed electromagnetic wave from the sample are recorded in time series as the magnitude and direction of the current between the micro-antennas of the photoconductive element, and Fourier transformed to obtain the amplitude and amplitude of the transmitted pulsed electromagnetic wave L3. Obtain the phase spectrum.

  2 and 3, a photoconductive film 22 is formed on a semiconductor substrate 21, for example, a gallium arsenide (GaAs) substrate, as shown in the figure, and a small antenna is formed at the center of each film. It is produced by vapor-depositing a pair of electrode films 23 and 24 having portions 23a and 24a. The antenna portions of the electrode film are arranged so as to form a dipole antenna separated from each other by a minute gap, and each antenna portion is located between the antenna portions (minute gap portion) D when a DC bias voltage is applied to the pair of electrode films. In such a shape, a uniform electric field can be formed. The photoconductive film is required to have a carrier lifetime of 1 ps or less, high carrier mobility, and high withstand voltage, and currently, a gallium arsenide (LT-GaAs) film grown at a low temperature is often used.

  In the photoconductive element, a laser pulse light of about 100 fs is irradiated to a region near the gap of the micro-antenna portion of the photoconductive film, and photocarriers (electrons and holes) are generated. Current flows when the optical carrier moves to the electrode by a bias voltage applied between the electrodes. The photoconductive element is usually used with a high-resistance silicon super hemisphere (or hemispherical) lens disposed on the substrate side of the photoconductive element. For example, when used for radiation, a pulsed electromagnetic wave radiated from a minute dipole antenna is usually used. The super hemispherical lens 18 is sent to a parabolic mirror while suppressing the spread of light. The pulsed electromagnetic wave is collimated by a parabolic mirror, and then squeezed by an objective lens to irradiate the sample.

When a photoconductive element is used as a detection element, since the detection current flowing between the minute antennas of the electrodes is weak, it is usually used with a low noise current amplifier. That is, when a region near the minute gap of the minute antenna portion in the photoconductive film is excited by the sampling pulse light, a light carrier is generated, and this light carrier biases the electric field intensity of the pulse electromagnetic wave reflected or transmitted from the sample. Go as a voltage to the electrode, thus a weak current flowing is detected is amplified about 10 ⁷ times the low-noise current amplifier. Thus, the electric field strength including the sign of the pulse electromagnetic wave is detected as a current flowing between the minute antennas.
JP 2003-131137 A JP 2003-121355 A JP 2003-83888 A JP 2003-75251 A JP 2003-14620 A JP 2002-277393 A JP 2002-277394 A JP 2002-257629 A JP 2002-243416 A JP 2002-98634 A JP 2001-141567 A JP 2001-66375 A JP 2001-21503 A JP 2001-275103 A Q. Wu and X.-C.Zhang, Appl. Phys. Lett. 67 (1995) 3523) M. Tani, S. Matsuura, K. Sakai, and S. Nakashima, Appl. Opt. 36 (1997) 7853 Sakai Kiyomi: Spectroscopic Studies, 50 (2001) 261 Seiji Kojima, Seiji Nishizawa, Mio Takeda: Spectroscopic Research, 52 (2003) 69

  In the detection of this current in the conventional photoconductive element for detection, the pulse interval of the pulsed laser beam is sufficiently short, and the measurement is performed assuming that it is continuous light. At this time, in the titanium sapphire pulse laser, the pulse interval is about 10 ns, and the time width of each pulse is about 100 fs, so that a signal that exists only about 100 fs is measured as a signal that exists for 10 ns. Therefore, there is a problem that the signal intensity is reduced to 1/100000 times.

  In the case of a method that amplifies and detects the weak current flowing between the electrodes of the photoconductive element, such as a conventional time-series conversion pulse spectroscopic measurement device equipped with a photoconductive element, the background noise is also amplified as it is. There is a problem that the S / N ratio becomes worse.

  In addition, when considering integrated measurement over a certain period of time, it is necessary to obtain a signal synchronized with the repetition of the laser light pulse in order to obtain an accurate time for the repetition of the pulse laser light. Has a problem that it cannot be detected because its pulse width is as short as 100 fs.

  Furthermore, since the detected signal intensity depends on the intensity of the pulsed laser beam, there is a problem that even when the intensity of the pulsed laser beam is changed, the signal intensity is measured as having changed.

  Accordingly, the present invention has been made in view of the above circumstances, and an object of the present invention is to provide a time-series conversion pulse spectroscopic measurement apparatus capable of performing an accurate and high SN ratio measurement without being affected by the pulse interval of the excitation laser. And

  In addition, the present invention provides a time series that can be detected even when the laser itself does not output a signal synchronized with the repetition of the laser light pulse, which is necessary to obtain an accurate time with respect to the repetition of the pulse laser light. An object of the present invention is to provide a conversion pulse spectroscopic measurement apparatus.

  Still another object of the present invention is to provide a time-series conversion pulse spectroscopic measurement apparatus in which the influence of the intensity change of the pulse laser beam on the detected signal intensity is small.

In order to achieve the above object, the present invention employs the following configuration.
The time-series conversion pulse spectroscopic measurement device according to claim 1 comprises a photoconductive element for detection comprising a pair of electrode films and a photoconductive film that generates a photocarrier when receiving sampling pulse light, and a laser. The pulse laser beam generated from the light source is demultiplexed into a plurality of pulse laser beams, one of which is used as the pump pulse beam that irradiates the radiation photoconductive element, and the other is the sampling pulse that irradiates the detection photoconductive element. In a time-series conversion pulse spectroscopic measurement device used as light, a current signal that flows between the electrode films and is sent from the detection photoconductive element in response to the electric field intensity of a reflected or transmitted electromagnetic wave from a sample is sequentially used as a charge. Charge accumulation detection means for accumulating and detecting the amount of accumulated charge, and at the time of photometry for allowing a current signal sent from the detection photoconductive element to pass through the charge accumulation detection means A photometric time division signal generating means for generating division signals, characterized by comprising a.

The “charge accumulation detection means” according to claim 1 is a cycle (hereinafter referred to as “charge accumulation detection means”) that sequentially accumulates the charges sent from the photoconductive element for detection, detects the accumulated charge amount, and discharges the accumulated charges after the detection. "Detection cycle") can be performed and this cycle can be repeated.
The charge accumulation in each photometric time segment may be started at any time after the discharge in the detection cycle of the previous photometric time segment.
The detection of the accumulated charge amount may be performed after the photometric time division signal is turned off or may be performed without being turned off. The accumulated charge amount may be detected only once during each detection cycle, or continuously or intermittently.
The charge accumulation detection means may include a memory that stores the value of the accumulated charge amount.

  The photometric time division signal generated by the “photometric time division signal generating means” according to claim 1 is for applying a gate action to the current signal from the photoconductive element for detection to the charge accumulation detecting means. The photometric time section corresponds to the “integrated time” of the electromagnetic wave signal reflected or transmitted from the sample. Since the “integrated time” of the electromagnetic wave signal corresponds to the amplification factor of the signal, the time-series conversion pulse spectroscopic measurement device according to claim 1 determines the amplification factor of the electromagnetic wave signal reflected or transmitted from the sample by the photometric time division. It can be said that it is a structure to decide. The photometric time division signal can be generated intermittently, and the generation interval may or may not be constant.

  As for the generation of the “photometric time division signal” according to the first aspect, it is possible to employ a conventional configuration for generating various gate signals.

  The time-series conversion pulse spectroscopic measurement device according to claim 2 is a clock for generating a clock signal synchronized with the period of the pulse laser beam generated from the laser light source in the time-series conversion pulse spectroscopic measurement device according to claim 1. Signal generating means, and the photometric time division signal is generated based on the number of pulses of the clock signal.

  The configuration of the “clock signal generating means for generating a clock signal synchronized with the period of the pulsed laser beam generated from the laser light source” according to claim 2 can adopt a configuration for generating various conventional clock signals. .

“The photometric time division signal is generated using the number of pulses of the clock signal” according to claim 2 is that the length of the photometric time division is set by the number of pulses of the clock signal. Setting a large value means that the photometry time section becomes long, and setting a small value means shortening. Therefore, according to this configuration, the integration time of the electromagnetic wave signal from the sample can be changed by changing the setting of the number of pulses of the clock signal corresponding to the photometric time section.
For example, when measurement is performed by continuous scanning in a configuration in which the position of the optical delay means is determined using a laser interference signal, photometry is performed at the rising edge of the first pulse of the clock signal pulse when the predetermined position of the optical delay means is exceeded. The photometric time segment is generated using the number of pulses of the clock signal, such as by a configuration in which the photometric time segment signal is generated so that the time segment signal becomes active and becomes inactive at the fall of a set number of pulses from that pulse. be able to.

  The “clock signal synchronized with the period of the pulse laser beam generated from the laser light source” according to claim 2 may be configured to use the pulse signal of the laser pulse light output from the laser source, When there is no pulse signal output, a configuration may be adopted in which a pulse signal of laser light is once detected and then generated.

  The time-series conversion pulse spectroscopic measurement device according to claim 3 is the time-series conversion pulse spectroscopic measurement device according to claim 1 or 2, wherein the photometric time segment signal generating means performs photometry for each photometric time segment. The length of the time segment can be set, and the charge accumulation detecting means can normalize the detected accumulated charge amount by the length.

  The length of each photometric time segment may be set automatically or manually, and can be set using software and / or hardware. The configuration may be such that the setting of the length of each photometric time segment can be programmed in advance. Here, the length of the photometric time segment can be easily changed, for example, by increasing the number of pulses of the clock signal that determines the photometric time segment.

  The "length of photometry time section" corresponds to the charge accumulation time or the signal integration time, and the charge accumulation time or the signal integration time corresponds to the signal amplification factor. According to the present invention, the amplification factor can be changed independently for each photometric time segment. For example, when signals are acquired by setting the photometry time division as N clock pulses, 2N, 3N,..., 2N and 3N signals are in the stage of signal processing. Is normalized by setting it to 1/2 and 1/3 of the case of N.

  The “the charge accumulation detection means can normalize the amount of accumulated charge detected by the length” includes a configuration in which the charge accumulation detection means normalizes by a computer after detection by the charge accumulation detection means.

  The time-series conversion pulse spectroscopic measurement device according to claim 4 is the time-series conversion pulse spectroscopic measurement device according to claim 3, wherein the setting of the length of each photometric time segment is detected in the photometric time segment. It can be performed according to the intensity of the current signal sent out from the photoconductive element.

“According to the intensity of the current signal” means, for example, a configuration in which each photometry time segment is set to be long in advance when the intensity of the current signal is known to be weak, or a current signal detected during measurement. A configuration in which the photometry time section can be automatically set longer when the intensity of the light is weak is also included. That is, a case where the setting is made before the measurement and a case where the setting is made or changed during the measurement are included. The length of the photometry time section may be set manually or automatically.
In addition, there may be a case where the amount of accumulated charge does not reach a constant value even if the signal intensity is weak (substantially 0) and accumulated for a long time. For example, in such a case, the portion where the signal intensity is weak determines the photometric time segment by time, and the other portion determines the photometric time segment by the intensity, that is, each photometry by time (for example, the number of pulses). It is also included in “depending on the intensity of the current signal” to use a combination of the setting of the time section and the setting of each photometric time section depending on the intensity.

  According to a fourth aspect of the present invention, the amplification factor can be changed for each photometric time segment according to the intensity of the current signal transmitted from the detection photoconductive element in the photometric time segment.

  The time-series conversion pulse spectroscopic measurement apparatus according to claim 5 is the time-series conversion pulse spectroscopic measurement apparatus according to claim 3, wherein the length of each photometry time section is set in the measurement in each photometry time section. The current signal is passed through the charge accumulation detecting means until the accumulated charge amount exceeds a predetermined value.

  “To allow accumulation of charge until the amount of accumulated charge exceeds a predetermined value” means that, in measurement in each photometric time segment, the photometry time segment signal is turned off until the accumulated charge amount exceeds a predetermined value. (The gate is not closed and remains active), and the charge accumulation is continued. Therefore, the length of each photometric time segment is automatically set.

According to the fifth aspect of the present invention, it can be said that the amplification factor in each photometric time segment is determined during measurement by the intensity of the current signal sent from the detection photoconductive element.
In addition, there may be a case where the amount of accumulated charge does not reach a constant value even if the signal intensity is weak (substantially 0) and accumulated for a long time. For example, in such a case, the portion where the signal intensity is weak determines the photometric time segment by time, and the other portion determines the photometric time segment by the intensity, that is, each photometry by time (for example, the number of pulses). It is also possible to use a combination of the setting of the time section and the setting of each photometric time section depending on the intensity.

  The time-series conversion pulse spectroscopic measurement apparatus according to claim 6 is the time-series conversion pulse spectroscopic measurement apparatus according to any one of claims 1 to 5, wherein the pulse width expansion unit expands a pulse width of the sampling pulse light. It is provided with.

The time-series conversion pulse spectroscopic measurement device according to claim 7 is the time-series conversion pulse spectroscopic measurement device according to any one of claims 1 to 6, wherein the pulse laser beam generated from the laser light source is demultiplexed. Further, another one of the plurality of pulsed laser beams is used for correcting the signal intensity of the reflected or transmitted pulsed electromagnetic wave from the detected sample.
As a correction method, it is possible to make a difference from the signal intensity of the reflected or transmitted pulse electromagnetic wave, to normalize by dividing the signal intensity, or to make a difference from a signal estimated from one of the demultiplexed pulse laser beams. Conceivable.

  The time-series conversion pulse spectroscopy according to claim 8 divides a pulse laser beam generated from a laser light source into a plurality of pulse laser beams, one of which is used as a pump pulse beam for irradiating a radiation photoconductive element. In time-series conversion pulse spectroscopy, the other is used as sampling pulse light that irradiates a photoconductive element for detection provided with a pair of electrode films and a photoconductive film that generates a photocarrier when receiving sampling pulse light. The current signal sent from the photoconductive element for detection flowing between the electrode films in response to the electric field intensity of the reflected or transmitted electromagnetic wave from the sample is sequentially accumulated as charges, and the accumulated charge amount is detected. At this time, the photometric time division signal generated using the number of pulses of the clock signal synchronized with the period of the pulse laser beam generated from the laser light source is gated. And detecting for each photometric time classified by.

  The time-series conversion pulse spectroscopy according to claim 9 divides a pulse laser beam generated from a laser light source into a plurality of pulse laser beams, one of which is used as a pump pulse beam for irradiating a radiation photoconductive element. The other one is used as sampling pulse light for irradiating a detection photoconductive element having a pair of electrode films and a photoconductive film that generates a photocarrier when receiving sampling pulse light, and an optical delay means In time-series conversion pulse spectroscopy that measures the electric field intensity of reflected or transmitted electromagnetic waves from a sample by giving a delay time difference to the pump pulse light to the sampling pulse light while continuously scanning, reflected or transmitted electromagnetic waves from the sample. In response to the electric field strength, current signals sent between the photoconductive elements for detection flowing between the electrode films are sequentially accumulated as electric charges, A charge amount is detected, and at this time, a photometric time segment signal generated by using the number of pulses of the clock signal synchronized with the period of the pulse laser beam generated from the laser light source is used for each photometric time segment as a gate. In this case, the start and end of the photometric time segment are performed using a clock signal.

Here, “the start and end of the photometric time segment are performed using the clock signal” in claim 9 is, for example, that the photometric time segment signal is activated at the rising edge of the clock signal, and a predetermined number of pulses after the clock signal It is meant to be inactive at the rising edge of the clock signal. Needless to say, inactivation is also included when the clock signal falls.
Also, “the start of photometric time segmentation” is “performed using a clock signal”, for example, when the position of the optical delay means is determined using a laser interference signal, the predetermined position of the optical delay means is exceeded. This is the case, for example, when the photometric time segment starts at the rise of the first pulse of the clock signal pulse.

According to the pulse spectroscopic measurement apparatus of the first aspect, the following operational effects are obtained.
Since detection by the photoconductive element is detected not by current but by electric charge, more accurate measurement is possible without the intensity of the detected signal being affected by the pulse interval of the laser pulse light.
The detection of the pulsed light to be measured reflected or transmitted from the sample by the photoconductive element is not detected by amplifying the weak current flowing between the electrodes of the photoconductive element, but by detecting the charge, so the background noise is amplified. The signal-to-noise ratio is significantly improved.
A more accurate measurement can be performed by appropriately setting the measurement time division for accumulating charges. For example, when the measurement by the step scanning method, that is, when the optical delay means is moved to a predetermined position and then the optical delay means is stopped to perform measurement and then moved to the next predetermined position and measurement is repeated, By setting the measurement time section to be long, not only the detection of the signal from the photoconductive element, that is, the measurement of the electric field intensity of the reflected or transmitted electromagnetic wave from the sample is facilitated, but the accuracy is improved. In addition, since the variation for each pulse is smoothed, more accurate measurement is possible.
There is no need to use an optical chopper that modulates the laser pulse light, a lock-in amplifier for detecting the detected weak current, and a current amplifier.

According to the time-series conversion pulse spectroscopic measurement apparatus of the second aspect, the following operational effects are obtained.
By changing the number of set pulses of the clock signal, the charge integration time can be easily changed. For example, when the intensity of the electromagnetic wave reflected or transmitted from the sample is weak, by increasing the number of set pulses, the amount of accumulated charges to be detected can be increased to facilitate detection.
Since the clock signal is synchronized with the period of the pulse laser beam, a malfunction of erroneously counting the pulse laser beam is prevented, and the pulse laser beam can be accurately counted.

According to the time-series conversion pulse spectrometer of the third aspect, the following operational effects are obtained. Since the length of the photometric time segment can be set independently for each photometric time segment, the signal can be amplified with an amplification factor suitable for each photometric time segment.
In the photometry time section where the intensity of the current signal is weak, the photometry time section can be set longer than in the strong photometry time section. This improves the detection accuracy when the signal is weak, and enables measurement independent of the strength of the current signal.
Depending on the state and type of the sample, the intensity of the reflected or transmitted electromagnetic wave signal from the sample may be weak, but in such a case, setting each photometric time segment long will enable high-precision measurement. It becomes possible.
It is possible to easily set a measurement mode with a desired measurement accuracy such as a high-speed measurement mode in which the length of the photometric time section is set short and a precision measurement mode in which the length is set long.
The length of the appropriate photometric time section can be set in accordance with the temporal change in the intensity of the reflected or transmitted electromagnetic wave signal from the sample.

According to the time-series conversion pulse spectroscopic measurement apparatus of the fourth aspect, the following operational effects are obtained.
Based on the intensity of the reflected or transmitted electromagnetic wave signal from the sample or the intensity of the current signal transmitted from the photoconductive element for detection, measured in the actual measurement stage, the signal can be amplified with an optimum amplification factor. . For example, when the intensity of the current signal is weak, it can be automatically set in real time during measurement, and each photometry time segment can be set longer or changed longer.

According to the time-series conversion pulse spectrometer of the fifth aspect, the following operational effects are obtained.
In the conventional apparatus, since the intensity of the signal to be detected is not known before the measurement, the optimum amplification factor in the actual measurement could not be set. However, in the present invention, the accumulated charge amount has a certain level. Since the integration is stopped when the value is reached, the optimum amplification can be measured automatically in real time during the actual measurement. This makes it possible to efficiently amplify and detect with high accuracy.

  According to the time-series conversion pulse spectroscopic measurement device of claim 6, in order to obtain an accurate time with respect to repetition of the pulse laser beam even when the pulse signal of the laser pulse beam is not output from the laser light source. A signal synchronized with the repetition of the required laser light pulse can be easily detected.

  According to the time-series conversion pulse spectrometer of claim 7, the signal intensity of the reflected or transmitted pulse electromagnetic wave from the sample to be detected can be corrected by subtracting the excitation pulse laser beam. The influence of the intensity change of the pulse laser beam is small.

According to the time-series conversion pulse spectroscopy of the eighth aspect, the following effects are obtained.
Since detection by the photoconductive element is detected not by current but by electric charge, more accurate measurement is possible without the intensity of the detected signal being affected by the pulse interval of the laser pulse light.
The detection of the pulsed light to be measured reflected or transmitted from the sample by the photoconductive element is not detected by amplifying the weak current flowing between the electrodes of the photoconductive element, but by detecting the charge, so the background noise is amplified. The signal-to-noise ratio is significantly improved.
A more accurate measurement can be performed by appropriately setting the measurement time division for accumulating charges. For example, when the measurement by the step scanning method, that is, when the optical delay means is moved to a predetermined position and then the optical delay means is stopped to perform measurement and then moved to the next predetermined position and measurement is repeated, By setting the measurement time section to be long, not only the detection of the signal from the photoconductive element, that is, the measurement of the electric field intensity of the reflected or transmitted electromagnetic wave from the sample is facilitated, but the accuracy is improved. In addition, since the variation for each pulse is smoothed, more accurate measurement is possible.
There is no need to use an optical chopper that modulates the laser pulse light, a lock-in amplifier for detecting the detected weak current, and a current amplifier.
By changing the number of set pulses of the clock signal, the charge integration time can be easily changed. For example, when the intensity of the electromagnetic wave reflected or transmitted from the sample is weak, by increasing the number of set pulses, the amount of accumulated charges to be detected can be increased to facilitate detection.
Since the clock signal is synchronized with the period of the pulse laser beam, a malfunction of erroneously counting the pulse laser beam is prevented, and the pulse laser beam can be accurately counted.

According to the time-series conversion pulse spectroscopy of the ninth aspect, the following effects are obtained.
It is possible to prevent a decrease in measurement accuracy due to an error in the moving speed of the optical delay means, which has been a problem in the past.
For example, in a continuous scanning method in which optical delay means (for example, a movable mirror) is continuously moved and measured, the repetition frequency of the pulse laser light from the laser light source is 100 MHz, and the interference of the He-Ne laser at 632.8 nm wavelength In the configuration in which the position of the optical delay means is determined using a signal, when there is an error of ± 1% at the moving speed of the optical delay means of 1 mm / sec, during the time corresponding to the interference signal of one wavelength, An error of about ± 300 pulsed laser beams will occur. The measurement error based on the error of the moving speed of the optical delay means can be reduced.

  FIG. 4 shows a block diagram of an embodiment of the characteristic part of the time-series conversion pulse spectroscopic measurement apparatus according to the present invention. In addition, about the component equivalent to FIG. 1, it shows with the same code | symbol.

  This time-series conversion pulse spectroscopic measurement device charges a current signal sent from the detection photoconductive element 12 flowing between the electrode films 23 and 24 corresponding to the electric field intensity of the reflected or transmitted electromagnetic wave L3 from the sample 8. Charge accumulation means 54 for sequentially accumulating as follows, charge detection means 51 for detecting the accumulated charge amount, clock signal generation means 52 for generating a clock signal synchronized with the period of the pulsed laser light generated from the laser light source 1, and detection And a photometric time segment signal generating means 53 for generating a photometric time segment signal for accumulating the current signal sent from the photoconductive element 12 for use. In the present embodiment, the combination of the charge accumulation means 54 and the charge detection means 51 corresponds to the “charge accumulation detection means” recited in the claims.

  Here, when the clock signal generation means 52 generates a clock signal synchronized with the period of the pulsed laser light generated from the laser light source 1, if there is a signal output from the laser light source body, the output signal can be used. When there is no signal output, a pulse laser beam is detected and a clock signal is generated. At this time, the response speed of the detector is very small as compared with the pulse width of the pulse laser beam, so that it is difficult to detect the detector as it is. In view of this, for example, the pulse width expanding means 41 using the diffraction grating pair as shown in FIG. For example, the pulse expanded by the pulse width expanding means 41 is detected by the photodetector 42 and counted by a pulse counter. Needless to say, such a pulse width extending means 41 can also be provided in a conventional pulse spectroscopic measurement apparatus.

  FIG. 6 shows a timing chart regarding the operation of the time-series conversion pulse spectroscopic measurement apparatus according to the present invention. 6 (a) to 6 (e) respectively show sampling pulse light, instantaneous current between electrodes in the photoconductive element, clock signal synchronized with the period of the pulse laser light generated from the laser light source, photometry time division signal, and charge accumulation. The signal output accumulated in the detection means is shown.

  A process in which the electric field strength of the electromagnetic wave transmitted or reflected from the sample (corresponding to the current between the electrodes of the photoconductive element) is detected as the accumulated charge amount by the charge accumulation detecting means will be described using this timing chart.

  When the photoconductive element is irradiated with the sampling pulse light with the period as shown in FIG. 6A, photocarriers are generated in the photoconductive film of the element only at that moment. The frequency of the sampling pulse light is, for example, about 80 MHz. In this case, photocarriers are generated in the photoconductive film every about 10 ns. The generated optical carrier moves between the device electrodes by the instantaneous electric field of the electromagnetic wave transmitted or reflected from the sample. FIG. 6B shows the timing of movement of the optical carrier between the electrodes (instantaneous current between the element electrodes). This instantaneous current is obtained for each sampling pulse irradiation only when the photometric time segment signal generated by the photometric time segment signal generating means 53 as shown in FIG. 6D is active as a gate signal. As shown in (e), the charges are accumulated in the charge accumulating means 54. Then, the photometric time division signal becomes inactive, but the amount of accumulated charge at that time is detected before or after being inactive, and then discharged. This is one cycle of detection, and this cycle is repeated by the step scan method or the continuous scan method, and the entire time waveform of the electric field intensity of the transmitted or reflected electromagnetic wave from the sample is reproduced.

  Here, the photometric time section is preferably set using the number of pulses of the clock signal synchronized with the period of the pulse laser beam generated from the laser light source as shown in FIG. For example, the photometry time segment can be set to the number of pulses N, 2N, 3N, and so on. The detected signal (accumulated charge amount) can be normalized by dividing by the number of pulses. In addition, the start and end of the photometric time segment can be performed, for example, at the rising or falling timing of the clock signal.

  In the mode of FIG. 6, the lengths of the photometric time sections A to C shown in FIG. 6D are equal time widths corresponding to the same number of pulses, but as another mode, FIG. As in the embodiment, the photometric time sections A to C... Can be independently set to different photometric time section lengths (for example, different pulse numbers). In the photometric time segment where the electric field of the electromagnetic wave transmitted or reflected from the sample is small and the instantaneous current flowing between the electrodes of the photoconductive element is small correspondingly, by setting the photometric time segment longer, other in the photometric time segment This is a mode in which measurement is performed at a higher amplification factor than the above-mentioned category.

  In FIG. 7, the photometry time sections A to C shown in FIG. 7B are time widths corresponding to the number of pulses of the clock signal shown in FIG. Have In this case, the photometry time sections B and C are measured at a gain twice or three times that of the photometry time section A, respectively. In this case, as shown in FIG. 7D, the movement of the optical carrier (instantaneous current) per one irradiation of the sampling pulse light in the photometric time section B corresponding to the electric field of the transmitted or reflected electromagnetic wave from the sample. ) Is smaller than the movement of the optical carrier in the photometric time section A (thus, the amount of charge stored in the charge storage means is small per irradiation), and is smaller in the photometric time section C than the photometric time section B Accordingly, the photometry time section is set longer correspondingly. As a result, the amount of charge at the time of detection in the charge storage means can be amplified to a size suitable for measurement, and measurement becomes easy. However, in the case of measurement by the step scan method, the longer the photometry time section is set, the higher the measurement accuracy is. However, in the case of the measurement by the continuous scan method, the longer the photometry time section is set, the more the electric field of transmitted or reflected electromagnetic waves. The portion to be measured in one photometric time section of the entire time waveform of the intensity becomes wide, and the error from the instantaneous electric field intensity becomes large, so this point must be noted.

  While the photometric time division signal as shown in FIG. 7B is active, the optical carrier generated by the irradiation of the sampling pulse light as shown in FIG. 7C is transmitted or reflected from the sample. The electric field moves between the electrodes of the photoconductive element. The carriers are accumulated in the charge accumulating means as shown in FIG. 7D, and the accumulated charge amount is measured before or after the photometric time division signal becomes inactive and discharged. In this case, the accumulated charge amount detected in each of the photometric time sections A to C is normalized by the number of pulses of 10, 20, and 40, whereby the entire time waveform of the transmitted or reflected electromagnetic wave from the sample is obtained. Can be reproduced.

  The size of each photometric time segment may be determined in advance before the measurement, or the photometric time segment signal may be configured to be active during the measurement until, for example, the accumulated charge exceeds a predetermined value. . In the latter case, a configuration is provided in which the number of pulses corresponding to each photometric time segment is detected and normalized.

  FIG. 8 is a diagram for explaining an aspect of generation of a photometric time division signal in continuous scan measurement.

In FIG. 8A, the x-axis indicates the position of the optical delay means, and x ₁ , x ₂ and x ₃ indicate the positions where measurement is started. This position can be determined using, for example, an interference signal with a wavelength of 632.8 nm of a He—Ne laser. For photometric time division signals A, the rise of the optical delay means is continuously moved at a predetermined moving speed, reached x _1, beyond which pulse P ₁ of the first clock signal _(FIG. 8 (b)) At this timing, the photometric time division signal becomes active (FIG. 8C). In this example, the number of pulses of the clock signal is set to ₁₀ for the photometric time segment, and the photometric time segment signal becomes inactive at the falling timing of the _tenth pulse P10 (FIG. 8 (c) )).

Similarly, for the photometric time division signal B, and the optical delay means is continuously moved at a predetermined moving speed reaches x _2, the first clock signal Beyond that pulse Q _{1 (FIG.} 8 (b) ) At the rise timing, the photometric time segment signal becomes active (FIG. 8C). In this case as well, the number of pulses of the clock signal is set to 10 as in the case of the photometric time division signal A, except that the photometric time division signal becomes inactive at the rise timing of the _eleventh pulse Q11. (FIG. 8C).

In the configuration in which the position of the optical delay means is determined by using a laser interference signal in continuous scanning, even when measurement is started at equal intervals with respect to the position of the optical delay means (x ₂ −x ₁ = x ₃ −x ₂ ) Since the time for moving the equal interval is not equal (t ₂ −t ₁ ≠ t ₃ −t ₂ ) due to the error of the moving speed of the optical delay means, the same one wavelength (or an integral multiple thereof) Although the number of pulses of the sampling pulse light included during the movement differs even at a distance corresponding to the interference signal, according to the time-series conversion pulse spectroscopic measurement device according to the present invention, the moving speed of the optical delay means It is possible to suppress a decrease in measurement accuracy due to the error of.

  FIG. 9 shows a flowchart for explaining an aspect of the time-series conversion pulse spectroscopic measurement method according to the present invention.

  In this aspect, first, the length of the photometric time section is set. The charge storage means is initialized and charge storage is started. The charge accumulation is continued until the photometric time section is exceeded, and when the photometric time section is exceeded, the charge accumulation is stopped, and the accumulated charge amount is read as, for example, an output voltage by the charge detection means. Normalize the amount of stored charge read by the length of the photometric time segment. Move to the next measurement point (photometry time section) (for example, move the optical delay means) to start the next measurement. When all the measurement points have been measured, the measurement is finished. In the case of measurement by continuous scanning, this flow is performed while moving the optical delay means.

  FIG. 10 is a flowchart for explaining another aspect of the time-series conversion pulse spectroscopic measurement method according to the present invention.

This mode is a combination of the setting of each photometric time segment by time and the setting of each photometric time segment by intensity.
In this mode, the charge accumulation means is initialized and charge accumulation is started. If the accumulated charge amount exceeds a predetermined value (reference value) before the predetermined photometric time section is finished, the charge accumulation is stopped and the accumulation at that time is stopped. The charge amount is normalized by the storage time until then (for example, the number of pulses of the clock signal). That is, this accumulation time is an actual photometric time segment. On the other hand, if the accumulated charge amount does not exceed the predetermined value (reference value) even after the predetermined photometric time segment, the accumulation of charge at the measurement point (photometric time segment) is stopped at that time. In this case, the amount of accumulated charge at this measurement point is zero. Move to the next measurement point (photometry time section) (for example, move the optical delay means) to start the next measurement. When all the measurement points have been measured, the measurement is finished. In the case of measurement by continuous scanning, this flow is performed while moving the optical delay means.

It is a schematic block diagram of the conventional time series conversion pulse spectroscopy measuring device. It is a schematic block diagram of the photoconductive element used for the radiation | emission and detection of a pulse electromagnetic wave in the time series conversion pulse spectroscopy measuring apparatus of FIG. FIG. 3 is a sectional view taken along a broken line AA ′ in FIG. 2. It is a block diagram which shows one Embodiment of the characteristic part among the time series conversion pulse spectroscopy measuring devices which concern on this invention. It is a schematic block diagram of the time series conversion pulse spectroscopy measuring apparatus containing the pulse width expansion means using the diffraction grating pair which concerns on this invention. It is a timing chart figure of the measurement in the time series conversion pulse spectroscopy measuring device concerning the present invention. It is a timing chart figure in the other aspect of the measurement in the time series conversion pulse spectroscopy measuring device concerning the present invention. It is a timing chart for demonstrating the one aspect | mode of the production | generation of a photometry time division signal, when measuring by a continuous scan system using the time series conversion pulse spectroscopy measuring device which concerns on this invention. It is a flowchart for demonstrating the one aspect | mode of the time series conversion pulse spectroscopy measurement method which concerns on this invention. It is a flowchart for demonstrating the other aspect of the time series conversion pulse spectroscopy measuring method which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laser light source 8 Sample 12 Photoconductive element for detection 13 Optical delay means 21 Photoconductive film 23,24 Electrode film 41 Pulse width expansion means 51 Charge detection means 52 Clock signal generation means 53 Photometric time division signal generation means 54 Charge accumulation means

Claims (8)

It has a photoconductive element for detection that includes a pair of electrode films and a photoconductive film that generates photocarriers when receiving sampling pulsed light, and splits the pulsed laser light generated from the laser light source into a plurality of pulsed laser lights. In the time-series conversion pulse spectroscopic measurement apparatus using one of them as pump pulse light for irradiating the radiation photoconductive element and using the other as sampling pulse light for irradiating the detection photoconductive element,
Charge accumulation detection for sequentially accumulating current signals sent from the photoconductive element for detection flowing between the electrode films corresponding to the electric field intensity of reflected or transmitted electromagnetic waves from the sample as charges, and detecting the accumulated charge amount Means,
A photometric time division signal generating means for generating a photometric time division signal for passing the current signal sent from the detection photoconductive element to the charge accumulation detection means;
Equipped with a,
Furthermore, it comprises a clock signal generating means for generating a clock signal synchronized with the period of the pulse laser beam generated from the laser light source,
The time-series conversion pulse spectroscopic measurement apparatus, wherein the photometric time division signal is generated using the number of pulses of the clock signal . The photometry time segment signal generation means can set the length of the photometry time segment for each photometry time segment, and the charge accumulation detection means normalizes the detected accumulated charge amount by the length. The time-series conversion pulse spectroscopic measurement apparatus according to claim 1 , wherein The setting of the length of each of the photometry time segment of said, according to claim 2, characterized in that it is possible to perform in accordance with the intensity of the current signal in the metering time segment is sent from the detection light conducting element Time-series conversion pulse spectrometer. The setting of the length of each photometric time segment is performed so that the current signal passes through the charge accumulation detecting means until the accumulated charge amount exceeds a predetermined value in the measurement in each photometric time segment. The time-series conversion pulse spectroscopic measurement device according to claim 2 . Time series conversion pulse spectrometer measurement apparatus according to any one of claims 1 to 4, characterized in that it comprises a pulse width extension means to widen the pulse width of the sampling pulse light. Using another one of the plurality of pulsed laser beams obtained by demultiplexing the pulsed laser beam generated from the laser light source to correct the signal intensity of the reflected or transmitted pulsed electromagnetic wave from the detected sample. time series conversion pulse spectrometer measurement apparatus according to any one of claims 1 to 5, wherein. A pulse laser beam generated from a laser light source is split into a plurality of pulse laser beams, one of which is used as a pump pulse beam for irradiating a radiation photoconductive element, and the other is a pair of electrode films and a sampling pulse beam. In time-series conversion pulse spectroscopy used as sampling pulse light for irradiating a photoconductive element for detection provided with a photoconductive film that generates a photocarrier upon receiving,
Corresponding to the electric field strength of the reflected or transmitted electromagnetic wave from the sample, the current signal sent from the photoconductive element for detection flowing between the electrode films is sequentially accumulated as a charge, and the accumulated charge amount is detected. In this case, a time series characterized in that a photometric time segment signal generated using the number of pulses of the clock signal synchronized with the period of the pulse laser beam generated from the laser light source is detected for each photometric time segment as a gate. Conversion pulse spectroscopy. A pulse laser beam generated from a laser light source is split into a plurality of pulse laser beams, one of which is used as a pump pulse beam for irradiating a radiation photoconductive element, and the other is a pair of electrode films and a sampling pulse beam. And used as a sampling pulse light for irradiating a photoconductive element for detection having a photoconductive film for generating a photocarrier when received, and the pump pulse to the sampling pulse light while continuously scanning an optical delay means In time-series conversion pulse spectroscopy that measures the electric field strength of reflected or transmitted electromagnetic waves from a sample by giving a delay time difference to light,
Corresponding to the electric field strength of the reflected or transmitted electromagnetic wave from the sample, the current signal sent from the photoconductive element for detection flowing between the electrode films is sequentially accumulated as a charge, and the accumulated charge amount is detected. In this case, the photometric time segment signal generated by using the number of pulses of the clock signal synchronized with the period of the pulse laser beam generated from the laser light source is detected for each photometric time segment using the gate as the photometric time segment signal. Time series conversion pulse spectroscopy characterized in that start and end of segmentation are performed using a clock signal.

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