JP2009075069A - Apparatus and method for obtaining information related to terahertz wave - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus capable obtaining a temporal waveform of a terahertz wave transmitted through or reflected by a sample in a set region. <P>SOLUTION: A delay unit 14 changes timing at which a detection unit 13 detects a terahertz wave 11 transmitted through a sample 19, which is originated from the terahertz wave 10 generated by a generation unit 12. A waveform obtaining unit 15 obtains a temporal waveform of the transmitted terahertz wave which is obtained by using the delay unit. The delay units 14 and 24 are controlled so that the detection unit 13 detects the transmitted terahertz wave in an area related to the temporal waveform set on the basis of information related to the sample 19 that is stored in the storage unit 16 in advance. Then, a temporal waveform of the transmitted terahertz wave in the area is obtained. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an apparatus and method for acquiring information related to a terahertz wave transmitted or reflected by a sample.

  A terahertz wave is an electromagnetic wave having an arbitrary frequency band from 0.03 THz to 30 THz. In the terahertz wave band, there are characteristic absorptions originating from structures and states of various substances including biomolecules. Taking advantage of these features, inspection techniques have been developed to analyze and identify substances in a non-destructive manner. In addition, it is expected to be applied to safe imaging technology and high-speed communication technology instead of X-rays.

  In addition, as a characteristic of the terahertz wave, there is moderate transparency with respect to the sample. For example, a technique for measuring the film thickness of a multilayer film using such a permeable property is disclosed (Patent Document 1). Patent document 1 converts the film thickness of a multilayer film from a plurality of pulse responses of terahertz waves. This pulse response is obtained by sampling a time response waveform of a terahertz wave with probe light. Such an acquisition method performs sampling over all measurement time regions.

  In recent years, as an application destination using such terahertz wave permeability, a technique for measuring the quality of a tablet in a non-destructive manner or a technique for inspecting has attracted attention. For example, it is expected to be applied to a technique for measuring and inspecting the coating film thickness of sugar-coated tablets and film-coated tablets. These coating film thicknesses affect the disintegration and solubility of tablets. A tablet is formed by mixing a powdered drug and an additive. Therefore, application to a technique for measuring and inspecting the uniformity of the content of the drug with respect to the additive is expected.

These properties directly affect the drug efficacy of the tablet. Therefore, a technique for maintaining and managing the quality of tablets is important. Currently, in order to maintain and manage this quality, some of the produced tablets are extracted and subjected to destructive inspection.
Japanese Patent Laid-Open No. 2004-28618

  In Patent Document 1, a method for shortening the time for measuring the thickness of the multilayer film is required.

  In addition, when performing quality control of drugs, it is desired in the future to always inspect this state in the production process rather than sampling inspection. In order to perform such a process inspection, a method for measuring and inspecting a sample in a non-destructive manner is desirable, but it has not been established yet. In particular, for the tablet process inspection, a method of monitoring the state in a shorter time is preferable from the viewpoint of handling a large amount of sample in a short time.

  An object of the present invention is to provide an apparatus capable of acquiring a time waveform of a terahertz wave transmitted or reflected from a sample in a set region. In addition, by using the time waveform in the region, it is possible to provide a device capable of shortening the time required to acquire information (film thickness and the like) on the sample as compared with the case of acquiring the entire region of the time waveform. It is.

  In view of the above problems, the terahertz wave detection device of the present invention has the following configuration. A detection unit that detects terahertz waves from the sample and an information storage unit that stores in advance internal information serving as a standard for the sample. A delay optical unit that adjusts the timing at which the detection unit operates by changing the delay time of the probe light incident on the detection unit with respect to the pump light. A measurement region to be measured is determined based on information serving as a standard of the information storage unit, and a delay time adjustment unit that adjusts the delay time in the measurement region. A processing unit configured to reconstruct the internal information of the sample based on the output of the detection unit and the adjustment amount of the delay time by the delay time adjustment unit;

The terahertz wave detection method of the present invention includes the following steps (a) to (e).
(A) Information storage step for preliminarily storing internal information as a standard of the sample (b) Delay optical step for adjusting the timing for detecting the terahertz wave in the detection step by the delay time of the probe light with respect to the pump light (c) Information storage A measurement region to be measured is determined based on information serving as a standard for the step, a delay time adjustment step for adjusting a delay time in the delay optical step in the measurement region (d) a detection step for detecting a terahertz wave from the sample (e) detection Processing step for reconstructing internal information of sample based on output in step and adjustment amount in delay time adjustment step

  The inspection system of the present invention has the following configuration. A detection unit that detects terahertz waves from the sample and an information storage unit that stores in advance internal information serving as a standard for the sample. A delay optical unit configured to adjust a delay time of the probe light incident on the detection unit with respect to the pump light; A measurement region to be measured is determined based on information serving as a standard of the information storage unit, and a delay time adjustment unit that adjusts the delay time of the probe light is provided in the measurement region. A processing unit configured to reconstruct internal information of the sample based on an output of the detection unit and an adjustment amount of the delay time by the delay time adjustment unit; A comparison unit that compares the internal information of the sample obtained by the processing unit with the internal information that is a standard of the sample stored in the information storage unit; According to the comparison result of the comparison unit, the apparatus has a device control unit that performs screening of the sample or adjustment of production conditions of the sample.

An apparatus for acquiring information related to a terahertz wave transmitted or reflected from another sample according to the present invention,
A generator for generating terahertz waves;
A detection unit for detecting a terahertz wave in which the terahertz wave generated by the generation unit is transmitted or reflected by the sample;
A delay unit for changing the timing detected by the detection unit;
A storage unit for storing information about the sample in advance;
A waveform acquisition unit for acquiring a time waveform of the transmitted or reflected terahertz wave obtained using the delay unit;
The delay unit is controlled so that the detection unit detects the terahertz wave in a region related to the time waveform set based on information about the sample stored in advance in the storage unit,
A time waveform of the transmitted or reflected terahertz wave in the region is acquired.

A method for obtaining information on a terahertz wave transmitted or reflected by another sample according to the present invention is as follows:
Generate terahertz waves,
Detecting the terahertz wave transmitted or reflected by the terahertz wave,
By changing the timing to detect, to acquire the time waveform of the transmitted or reflected terahertz wave,
In the region related to the time waveform set based on the time waveform of the terahertz wave that has been transmitted or reflected from the sample acquired in advance, the timing is changed so as to detect the transmitted or reflected terahertz wave,
A time waveform of the transmitted or reflected terahertz wave in the region is acquired.

  According to the present invention, a measurement reference relating to internal information serving as a standard for a sample is stored in the information storage unit in advance, and the arrival time of the terahertz wave reaching the detection unit is predicted based on the measurement reference. In the present invention, the delay time adjustment unit adjusts the delay time by switching the delay time of the probe light for operating the detection unit discontinuously so as to correspond to the arrival time of the terahertz wave. Therefore, it is possible to efficiently detect a terahertz wave (for example, a peak of a reflected terahertz wave pulse) necessary for acquiring internal information of the sample. Based on the output of the detection unit and the adjustment amount of the delay time adjustment unit, the processing unit calculates and reconstructs the internal information of the sample. Since it is a form which detects only a required location based on a measurement standard, the internal information of a sample can be acquired efficiently.

  An apparatus and method according to this embodiment will be described with reference to the drawings. It should be noted that the present invention is not limited to these embodiments and is not excluded as long as it does not depart from the spirit of the present invention.

(Device for acquiring information about terahertz waves)
An apparatus according to this embodiment will be described with reference to FIG. Here, FIG. 17 is an apparatus for acquiring information related to the terahertz wave transmitted through the sample. The present invention is not limited to reflection, and may be an apparatus that acquires information about transmitted terahertz waves as in the first embodiment and FIG.

  Reference numeral 12 denotes a generator for generating terahertz waves. Reference numeral 13 denotes a detection unit for detecting the terahertz wave 11 transmitted through the sample 19 by the terahertz wave 10 generated by the generation unit 12. Details of the generation unit 12 and the detection unit 13 will be described in Example 1 described later.

  Reference numeral 14 denotes a delay unit for changing the timing detected by the detection unit 13. As shown in FIG. 17A, the delay unit 14 can be configured to change the interval between the generation unit 12 and the detection unit 13 in order to change the distance that the generated terahertz wave 10 propagates. For example, by providing a stage for moving the generation unit 12 and moving the stage to change the distance between the generation unit 12 and the detection unit 13, the distance that the terahertz wave 10 propagates can be changed.

  Here, like the delay unit 24 in FIG. 17B, the refractive index of the propagation region can be changed in order to change the propagation speed of the generated terahertz wave 10. For example, the refractive index of the propagation region can be changed by bringing a member (such as a dielectric) having a refractive index close to a terahertz wave that passes through the sample.

  Thus, the time for the terahertz wave to reach the detection unit 13 can be delayed.

  As will be described later, the delay unit can also be configured by changing at least one of the timing for generating the terahertz wave and the timing for detecting it. As an example of this, there is a mirror (corresponding to the delay optical unit 104 in FIG. 1) that moves in the optical axis direction for optical delay. At this time, a laser unit (corresponding to 101 in FIG. 1) for irradiating the generation unit 12 and the detection unit 13 with laser (light) is used. Further, a beam splitter for dividing the laser irradiated by the laser unit is used. The laser beams divided by the beam splitter are irradiated to the generation unit 12 and the detection unit 13, respectively. The laser irradiated to the detection unit 13 passes through a delay unit (the mirror that moves in the optical axis direction).

  Further, the delay unit can be configured to be electrically delayed. For example, it can be configured by delaying the time of a signal to be generated for mixing with the detected terahertz wave signal.

  Reference numeral 16 denotes a storage unit that stores information related to the sample 19 in advance. Here, it is preferable that the information regarding the sample 19 stored in advance in the storage unit 16 is a time waveform of a terahertz wave transmitted through the sample acquired in advance. Moreover, the information regarding the sample 19 is a sample size (thickness), a refractive index, a transmittance, a reflectance, an absorptivity, and the like, for example. Furthermore, for example, the moisture content such as the physical properties, crystal structure, and composition of the sample 19 that can be derived from these may be used. However, the present invention is not limited to this, and will be specifically described in Examples.

  Reference numeral 15 denotes a waveform acquisition unit (corresponding to the processing unit 107 in FIG. 1) for acquiring the time waveform of the terahertz wave obtained using the delay unit 104. Here, the waveform acquisition unit 15 acquires the time waveform of the transmitted terahertz wave by sampling the terahertz wave detected by the detection unit 13 based on the timing changed by the delay units 14 and 24. can do.

  The delay units 14 and 24 are controlled so that the detection unit 13 detects the terahertz wave in a region related to the time waveform set based on information about the sample 19 stored in the storage unit 16 in advance. . The control may be performed by the waveform acquisition unit 15. Then, the time waveform of the transmitted terahertz wave in the region can be acquired. Thereby, the information regarding the sample 19 can be acquired. In addition, by obtaining the time waveform of the region, the time until the information about the sample 19 is acquired can be shortened compared to the case where the entire region of the time waveform is acquired.

  Here, as the region related to the time waveform, pulses (for example, (1), (2), (3), and (4) in FIG. 2) of the time waveform can be considered. Moreover, the peak which the said pulse has as the area | region regarding the said time waveform is also considered. Further, a place where the absolute value of the pulse gradient is large is also conceivable.

  Since the pulse is a characteristic region in the time waveform of the transmitted terahertz wave, information on the sample can be known by acquiring the pulse. For example, the thickness of the sample 19 can be derived from the interval between pulses. However, the region is not limited to the pulse, and an arbitrary region to be acquired may be set in the time waveform of the transmitted terahertz wave.

(Get sample information or sample status)
Information about the sample can be acquired from the time waveform of the transmitted terahertz wave in the region. The information regarding the sample includes, for example, the size (thickness) of the sample, the refractive index, the transmittance, the reflectance, and the absorption rate. From these, for example, the moisture content such as the physical properties, crystal structure, and composition of the sample can be derived.

  In addition, the time waveform of the transmitted terahertz wave in the region (or the pulse included in the time waveform of the transmitted terahertz wave in the region) and information stored in the storage unit in advance (for example, acquired in advance) It is preferable to compare the pulse with the time waveform of the terahertz wave transmitted through the sample. Thereby, the state of the sample can be derived.

  Here, the state of the sample is a difference in the physical properties, crystal structure, composition, etc. of the sample with respect to information acquired in advance (such as the pulse included in the time waveform).

  Note that the information on the sample and the state of the sample are not limited to these, and will be specifically described in the first embodiment.

(Counting the number of measurements and integrating)
It is preferable that the number of times the sample is measured is counted, the terahertz waves detected by the measured detection unit are integrated, and an average intensity of the terahertz wave is obtained using the integrated value and the number of times. Details of these will be described in Example 6 to be described later.

(Fiber laser)
It is preferable to have a fiber laser for generating a pulsed laser. An optical fiber can be used as a laser oscillation medium.

  Moreover, it is preferable that the said generation | occurrence | production part is a photoconductive element for generating a terahertz wave by irradiating the said pulse laser. Furthermore, it is preferable that the detection unit is a photoconductive element for detecting a terahertz wave by irradiating the pulse laser. As the photoconductive element, GaAs or InGaAs grown at a low temperature can be used.

  The details of the fiber laser will be described in Example 7 to be described later.

(Method for obtaining information on terahertz waves)
A method for acquiring information related to a terahertz wave transmitted or reflected from a sample according to another embodiment will be described.

  First, a terahertz wave is generated.

  Next, the terahertz wave transmitted or reflected by the terahertz wave is detected. Here, the reflected terahertz wave is preferably a pulse reflected at the refractive index interface of the sample coated with the coating film. The details of the coating film will be described in Example 1 and FIG.

  Further, the time waveform of the terahertz wave is acquired by changing the detection timing.

  In addition, the region related to the time waveform is set based on the time waveform of the terahertz wave that has been transmitted or reflected by the sample acquired in advance. Then, the timing is changed so that the transmitted terahertz wave is detected in the region. Thereby, the time waveform of the transmitted terahertz wave in the region can be acquired.

  Here, information about the sample can be acquired from the time waveform of the transmitted terahertz wave in the region. The information regarding the sample includes, for example, the size (thickness) of the sample, the refractive index, the transmittance, the reflectance, and the absorption rate. From these, for example, the moisture content such as the physical properties, crystal structure, and composition of the sample can be derived.

  Further, the time waveform of the transmitted terahertz wave in the region (or the pulse included in the time waveform of the transmitted terahertz wave in the region) is compared with the pulse included in the time waveform of the terahertz wave transmitted through the sample acquired in advance. It is preferable to do. Thereby, the state of the sample can be derived.

  Here, the state of the sample is a difference in the physical properties, crystal structure, composition, etc. of the sample with respect to information acquired in advance (such as the pulse included in the time waveform).

  Note that the information about the sample and the state of the sample are not limited to these, and will be described more specifically in the first embodiment.

  In the present invention, a sample from which internal information can be estimated is targeted. This internal information is used as standard information and is used as a measurement standard. For example, referring to a measurement standard based on the standard information, a measurement region in the depth direction of the sample (for example, the vicinity of the refractive index interface, a region where contamination easily occurs, a material having desired physical properties, etc.) is selected. Only the selected area is measured, the standard information is updated for the measurement location, and reconstruction is performed.

  In the present invention, the time response waveform of the terahertz wave can be reconstructed from these measurement results and the standard information of the selected measurement region. Using this response waveform, spectroscopic analysis and imaging of the sample are performed. Further, by comparing this response waveform with the standard information of the reference sample, sample screening and device adjustment are performed.

  Hereinafter, more specific embodiments will be described with reference to the drawings.

(Example 1: Reflective type)
The present embodiment shows an embodiment relating to the terahertz wave detection device of the present invention. FIG. 1 shows an example of the configuration relating to the terahertz wave detection device of the present invention. As shown in FIG. 1, the terahertz wave detection apparatus according to this embodiment includes a laser unit 101, a generation unit 102, a detection unit 103, a delay optical unit 104, a delay time adjustment unit 105, an information storage unit 106, and a processing unit 107. . In FIG. 1, the sample 109 is illustrated as being transported by the transport unit 108. However, the sample 109 is not necessarily transported.

  The laser unit 101 is a part that drives the generation unit 102 and the detection unit 103 with laser light. Hereinafter, the laser light that drives the generation unit 102 may be referred to as pump light, and the laser light that drives the detection unit 103 may be referred to as probe light. In this embodiment, the laser unit 101 uses a titanium sapphire laser having a pulse width of 50 fsec, a center wavelength of 800 nm, and a repetition frequency of 76 MHz.

  The generation unit 102 is a part that generates terahertz waves by pump light incident from the laser unit 101. In this embodiment, a photoconductive element in which an antenna pattern is formed on a semiconductor thin film is used as the generation unit 102. Specifically, as a semiconductor thin film, a low-temperature grown GaAs formed by molecular beam low-temperature epitaxial growth (250 ° C.) on a semi-insulating gallium arsenide (SI-GaAs) substrate (specific resistance;> 1 × 10 7 Ω · cm). (LT-GaAs) is used. Then, a dipole antenna (antenna length 30 μm, conductor width 10 μm) having a 5 μm gap at the center made of gold (Au) is formed on LT-GaAs. When terahertz waves are generated, pump light is irradiated with a 10 V bias applied between the gaps. As a result, a pulsed terahertz wave having a half width of about 200 fsec is generated. The antenna shape is not limited to this. For example, a general bow tie antenna or a spiral antenna may be used as the broadband antenna. Further, the semiconductor thin film is not limited to this, and for example, a semiconductor material such as indium gallium arsenide (InGaAs) may be used. Further, the semiconductor material itself may be used as the generation unit 102. For example, a mirror-polished GaAs surface is irradiated with pump light, and a terahertz wave is generated by a temporal change of instantaneous current generated at this time. Alternatively, an organic crystal such as a DAST (4-dimethylamino-N-methyl-4-stilbazolium Tosylate) crystal may be used.

  The detection unit 103 is a part that detects a terahertz wave using probe light incident from the laser unit 101. The detection unit 103 irradiates the probe light at the timing when the terahertz wave enters, and detects the generated current. With such a configuration, a terahertz wave is obtained. As the detection unit 103, a photoconductive element or the like in which an antenna pattern is formed on the same semiconductor thin film as the generation unit 102 is used.

  The delay optical unit 104 is a part that optically adjusts the delay interval (delay time) of the probe light with respect to the pump light. By measuring the terahertz wave detected by the detection unit 103 while changing the delay time, so-called terahertz time domain spectroscopy (THz-TDS, Terahertz Time Domain Spectroscopy) is performed. By changing the delay time and plotting the response of the terahertz wave obtained from the detection unit 103 for each delay interval by the processing unit 107, the time response of the terahertz wave can be acquired. In FIG. 1, for simplification, description of a chopper necessary for THz-TDS is omitted. In this embodiment, as shown in FIG. 1, the sample 109 has a reflective optical system.

  The present embodiment is characterized in that the THz-TDS further includes a delay time adjustment unit 105 and an information storage unit 106.

  The information storage unit 106 is a part that stores in advance the internal information of the sample 109 as standard information. For example, the position of the refractive index interface with respect to the inside of the sample 109 and the response waveform of the terahertz wave are stored. The information stored here is obtained from the specifications when the sample 109 is manufactured. Further, a time response waveform of a standard sample or a sample arbitrarily selected from a sample group may be measured in advance (also referred to as pre-measurement), and the measurement result may be used as standard information. For example, the position of the refractive index interface is determined from the reflected waveform of this time response waveform, and the physical properties are acquired.

  The delay time adjustment unit 105 is a part responsible for controlling the delay optical unit 104. Here, referring to the standard information inside the sample stored in the information storage unit 106, the delay time of the probe light is adjusted in order to detect the terahertz wave from a predetermined measurement region in the depth direction such as the refractive index interface. To do. When the measurement region to be detected exists discontinuously, the delay time of the probe light is changed discontinuously. And the terahertz wave regarding a measurement area | region is detected by changing delay time continuously only in the measurement area | region which exists discontinuously. That is, the time for the terahertz wave to reach the detection unit 103 is predicted based on the internal information of a known sample, and the delay time of the probe light for operating the detection unit 103 is adjusted.

  In the terahertz wave signal obtained from the detection unit 103 in this way, the concept of the time axis is partially lost because the delay optical unit 104 is discontinuously changed (see FIG. 2 (signal of the detection unit). )). For example, as shown in FIG. 2, the delay time of the delay optical unit 104 is discontinuously selected by the delay time adjustment unit as t1 → t2 → t3 → t4, and the response of the terahertz wave at each delay time (1) (2) (3) Obtain (4). Therefore, time information between measurement areas is missing. In the present embodiment, the processing unit 107 is used to correct this missing portion. For example, the processing unit 107 refers to the adjustment amount of the delay time performed by the delay time adjustment unit 105 and reconstructs the response of the terahertz wave obtained from the detection unit 103 into an actual time response of the terahertz wave (see FIG. 2 (Operation of processing unit)). More specifically, the time interval of the terahertz wave responses (1), (2), (3), and (4) in each delay time is adjusted, and a terahertz wave response corresponding to the internal information of the sample is acquired.

  The operation of the terahertz detection device according to this embodiment will be described. In FIG. 1, the terahertz wave pulse generated from the generation unit 102 is applied to the sample 109. The structure of the sample 109 at this time is assumed to be the structure of FIG. For convenience of explanation of the operation, the structure of the sample 109 is described here assuming that the thickness of the coating film 202 is 300 μm (d1 and d3) and the thickness of the powder 201 is 3 mm (d2). Further, in order to simplify the explanation of the operation, the refractive index of each material is assumed to be 1, and the wavelength shortening effect (propagation length change) due to the refractive index of these materials is not considered. The terahertz wave incident on the sample 109 is reflected, for example, at the refractive index interface existing in the sample 109. In the sample 109 of FIG. 2, terahertz waves are reflected on the surface of the coating film 202 constituting the sample 109 and the refractive index interface between the coating film 202 and the powder 201. These reflected waves are incident on the detection unit 103 with a certain time difference according to the reflection position of the terahertz wave. In FIG. 1, the reflection pulse from the surface of the coating film 202 is (1), and the reflection pulse from the interface between the coating film 202 and the powder 201 is (2). Here, in order to simplify the description, the description of the reflection pulse (3) from the interface between the coating film 202 and the powder 201 and the reflection pulse (4) from the interface between the coating film 202 and the outside is omitted. . As described above, assuming that the film thickness of the coating film 202 is 300 μm, the time difference between the reflected pulses (1) and (2) is approximately 2 picoseconds (psec).

Information relating to the inside of the sample 109 is stored in advance in the information storage unit 106 as standard information. As described above, this standard information is obtained from specifications for producing a sample and pre-measurement of an arbitrarily selected sample. For example, the position on the time axis where the reflected pulse (1) and the reflected pulse (2) are generated, and the intensity and pulse width of each reflected pulse are stored. For example, when the position on the time axis where the reflected pulse is generated is stored in the information storage unit 106, the following setting is made. The position of the reflected pulse (1) varies depending on the setting of the measurement system of the apparatus, but here it is assumed to be 5 psec.
Reflected pulse (1) ... t1 = 5 psec
Reflected pulse (2) ... t2 = 7 psec
Reflection pulse (3) ... t3 = 27 psec
Reflection pulse (4) ... t4 = 29 psec
The position on the time axis of each reflected pulse is used as a measurement standard for determining the delay time of the delay time adjustment unit 105. Further, as will be described later, when this apparatus is used for screening of the sample 109, the standard information may be used as information for comparison.

  In the conventional THz-TDS, response waveforms from these reflection pulses (1) to (4) are continuously acquired. However, in this embodiment, the delay time adjustment unit 105 controls the delay optical unit 104 with reference to the time intervals of the reflected pulses (1) and (2) stored as standard information in the information storage unit 106. For example, when the time interval between the reflected pulses (1) and (2) is 2 psec, the delay optical unit 104 adjusts the optical length by 0.6 mm. Similarly, the reflection pulses (2) and (3) are adjusted to 6.0 mm, and the reflection pulses (3) and (4) are adjusted to 0.6 mm.

  For example, first, the delay time adjustment unit 105 refers to the measurement standard obtained from the standard information stored in the information storage unit 106, and acquires the delay time at which the reflected pulse (1) occurs. Here, the delay time adjustment unit 105 acquires 5 psec as the delay time of the reflected pulse (1) from the information storage unit 106. The delay time adjustment unit 105 moves the delay optical unit 104 to change the distance that the probe light reaches the detection unit 103, and gives a desired delay time to the apparatus. In this measurement position, in order to measure the reflected pulse (1), the delay optical unit 104 continuously changes the delay time of the probe light. For example, when it is desired to acquire a waveform having a pulse width of 1 psec, the delay optical unit 104 is moved by about 0.3 mm. Here, “continuous” means that the delay optical unit 104 is moved to a target distance at a predetermined interval. For example, when the predetermined interval is 100 μm, the delay optical unit 104 moves at a constant speed until it moves 0.3 mm. The processing unit 107 plots the signal of the detection unit 103 with respect to the continuously changing delay time, and obtains a response waveform corresponding to the reflected pulse (1).

  Thereafter, the delay time adjustment unit 105 refers to the measurement standard obtained from the standard information stored in the information storage unit 106, and acquires the delay time at which the reflected pulse (2) occurs. Here, the delay time adjustment unit 105 acquires 7 psec as the delay time of the reflected pulse (2) from the information storage unit 106. Then, the delay time adjustment unit 105 moves the delay optical unit 104 by 0.6 mm so that the reflection pulse (2) is generated again, and starts the measurement operation of the reflection pulse (2).

  As described above, in the present embodiment, the delay optical unit 104 includes a process in which the delay time adjustment unit 105 adjusts discontinuously. The response waveform of the terahertz wave obtained by the processing unit 107 is a time waveform in which the reflected pulses (1) and (2) appear continuously as shown in FIG. As described above, this response waveform lacks information on the pulse interval of each reflected pulse. Therefore, as shown in FIG. 15B, the processing unit 107 refers to the measurement criteria for the non-continuous delay time performed by the delay time adjustment unit 105, and determines the time difference between the measurement criteria as the reflected pulse (1). Apply to reflected pulse (2) to reconstruct the response waveform. Here, a time interval of 2 psec corresponding to the movement of the delay optical unit 104 is given between the reflected pulse (1) and the reflected pulse (2).

  As described above, in this embodiment, the information storage unit 106 is used to specify a rough measurement position and acquire a terahertz wave response only at a predetermined measurement position. As a result, it is not necessary to continuously measure the terahertz wave over the entire measurement time as in the conventional THz-TDS, so that the measurement time of the time difference of each measurement reference can be shortened. It becomes easy.

  FIG. 2 shows a cross-sectional view and operation of the sample 109 when a tablet is assumed as the sample 109. As shown in FIG. 2, the sample 109 has a form in which a powder 201 is hardened and coated with a coating film 202. The powder 201 is obtained by mixing and solidifying a powdery drug and an additive. Examples of the coating film 202 include sucrose, a water-soluble polymer, and an insoluble polymer. Depending on the case, there is a form without the coating film 202 (bare tablet). In this example, a sugar-coated tablet coated with sugar is assumed. At this time, the thicknesses d1 and d3 of the coating film 202 are often several 10 to several 100 μm, and the thickness d2 of the powder is often several mm. As shown in FIG. 2, the terahertz wave irradiated to the sample 109 becomes a reflected pulse (1) reflected from the surface of the coating film 202. Further, the light is reflected at the refractive index interface such as the reflection pulses (2) and (3) reflected at the interface between the coating film 202 and the powder 201 and the reflection pulse (4) reflected again at the surface of the coating film 202. In general, it is difficult to clearly distinguish this refractive index interface in measurement using a short wavelength such as visible light or X-ray. This is because the particle size of the drug is generally several tens of μm, and the shape of the interface changes in a complicated manner according to the particle size distribution of the powder 201 at the refractive index interface. However, the value of the particle size is equivalent or sufficiently smaller than the wavelength of the terahertz wave. That is, since the wavelength of the terahertz wave is reasonably large, the shape of the interface is not detected as clearly as the measurement of a short wavelength. That is, an unclear interface shape for a short wavelength can be recognized as a relatively clear interface shape for a terahertz wave. Further, since the terahertz wave has an appropriate permeability with respect to the powder 201, it is suitable for acquiring information on the interface of the powder as compared with measurement using a short wavelength.

  In the present embodiment, information on these interfaces is stored in the information storage unit 106, and the delay time adjustment unit 105 selects the locations (1), (2), (3), and (4), and sequentially Measure. For example, when each pulse is converted to a time axis and a waveform corresponding to 2 psec is acquired, a total measurement time of 8 psec is required. However, since the response detected by the detection unit 103 sequentially measures the interface information as shown in FIG. 2, the thickness information is not accurately reflected. In the present embodiment, the processing unit 107 converts the adjustment amount of the delay time of the probe light adjusted by the delay time adjustment unit 105 and reflects it in the response waveform. As a result, accurate film thicknesses (d1 ', d2', d3 ') can be measured.

  When the above operation is performed with a conventional THz-TDS, a measurement time of about several hundred psec is required. On the other hand, in the configuration of the present embodiment, a rough measurement position is designated, and only the waveform response at that position is acquired and reconstructed. Therefore, a sugar-coated tablet (sample) is obtained in a measurement time of several psec. Internal information can be acquired. Therefore, it is easy to increase the measurement speed as compared with the conventional method.

  In this embodiment, the film thickness in the depth direction of the sample 109 has been described, but the present invention is not limited to this. As shown in conventional THz-TDS, using terahertz wave intensity and delay information at selected measurement positions, changes in physical properties, differences in crystal structure, mixing ratio, composition, powder density A material having desired physical properties can also be measured. For example, as a method for obtaining physical properties, a complex refractive index is obtained from the intensity of the reflected pulse and the delay time, and desired physical properties are converted therefrom. An embodiment for measuring the change in physical properties is also possible. It is also possible to determine the difference in crystal structure by verifying the difference in fingerprint spectrum in the terahertz wave region. In addition, assuming that the acquired fingerprint spectrum is composed of fingerprint spectra related to a plurality of substances, it is also possible to predict the mixture ratio from an operation for separating the spectra or the intensity and spread of each spectrum. Alternatively, the determination may be made using a calibration curve of each spectrum according to the thickness and concentration of the sample. It is also possible to verify the density of the powder based on the transmittance and reflectance, or the spectral information thereof. By the same method, it is possible to verify the composition of what kind of molecule the substance is. These methods are appropriately combined or selected according to the purpose.

  In the present embodiment, a tablet is shown as the sample 109, but this is not restrictive. Any sample may be used as long as the internal information of the substance can be acquired efficiently.

(Example 2: Transmission type)
The present embodiment shows an embodiment relating to the terahertz wave detection device of the present invention. More specifically, this is a modification of the terahertz wave detection apparatus according to the first embodiment. In addition, description of the part which is common in the said Example is abbreviate | omitted.

  FIG. 3 shows an example of a configuration related to the terahertz wave detection device according to the present embodiment. As shown in FIG. 3, in the terahertz wave detection device according to the present embodiment, the propagation path of the terahertz wave is a transmissive optical arrangement with respect to the sample 109.

  The operation of the terahertz wave detection device according to the present embodiment will be described. In the description of the operation, description of common parts is omitted. Here, the sample 109 is assumed to be the same as in the first embodiment. That is, the structure of the sample 109 assumes that the thickness of the coating film 202 is 300 μm and the thickness of the powder 201 is 3 mm. Further, in order to simplify the explanation of the operation, it is assumed that the refractive index of each material is 1, and the wavelength shortening effect (propagation length change) due to the refractive index of these materials is not taken into consideration. Here, the transmission pulse detected by the detection unit 103 is assumed to be the transmission pulse shown in FIG. As shown in FIG. 16, the transmission pulse (1) is a pulse that passes through the sample 109. The transmission pulse (2) and the transmission pulse (3) are pulses that are once reflected at the surface of the coating film 202 and at the interface between the coating film 202 and the powder 201. The transmitted pulse (4) is a pulse that is once reflected between the surfaces of the coating film 202.

  For example, the information storage unit 106 stores a position on the time axis at which these transmission pulses are generated. Note that the transmitted pulse includes pulses other than those described above. For example, there are a transmission pulse reflected twice at the interface and a transmission pulse reflected at an interface different from the above-described interface. In addition to the transmission pulses necessary for the inspection, the detection unit 103 arranges and detects these pulses mixed in the time axis. In this embodiment, by limiting the positions on the time axis stored in advance in the information storage unit 106, it is possible to perform inspection by filtering pulses that are not used for inspection, so that inspection efficiency is improved.

In this embodiment, the position of the transmission pulse on the time axis is set as follows. Although the position of the transmission pulse (1) varies depending on the setting of the measurement system of the apparatus, it is assumed here to be 5 psec.
Transmission pulse (1) ... t1 = 5 psec
Transmission pulse (2) ... t2 = 7 psec
Transmission pulse (3) ... t3 = 27 psec
Transmission pulse (4) ... t4 = 29 psec
The position on the time axis of each transmitted pulse is used as a measurement standard for determining the delay time of the delay time adjustment unit 105. The adjustment amount of the delay optical unit 104 for these delay times is as follows.
Transmitted pulses (1) to (2) ... 0.6mm
Transmitted pulses (2) to (3) ... 6.0mm
Transmitted pulses (3) to (4) ... 0.6mm
By taking such an optical arrangement, the terahertz wave is transmitted through the sample 109. Therefore, the terahertz wave propagating through the sample 109 has a response reflecting the rough characteristics of the sample 109 in the depth direction. For example, assuming the drug shown in FIG. 2 as the sample 109, the density of the entire sample 109, the absorption amount of the terahertz wave, the composition, and the like can be estimated from the absorbance of the first transmission pulse (1). Further, by monitoring the phase shift amount (or time delay amount), the thickness of the entire sample 109 can be estimated.

  In this way, by adopting the transmission type arrangement, it is possible to easily estimate the overall characteristics of the object to be measured.

(Example 3: Comparison part)
FIG. 4 shows an embodiment relating to the inspection system of the present invention. As illustrated in FIG. 4, the inspection system according to the present embodiment has a configuration in which a comparison unit 410 and a device control unit 411 are added to the configuration of the terahertz wave detection device according to the first embodiment. The description of the parts common to the first embodiment is omitted.

  The comparison unit 410 refers to the internal information of the sample 109 acquired by the processing unit 107 and the internal information that is the standard of the sample 109 stored in advance in the information storage unit 106. Then, the difference between the signal of the processing unit 107 obtained by actual measurement and the information of the information storage unit 106 is monitored to determine whether a sample 109 in a desired state is obtained.

  For example, when a sugar-coated tablet is assumed as the sample 109, the information storage unit 106 stores information on the thickness of the sugar-coated tablet and information on the interface between the coating film and the tablet (thickness, etc.). This information is acquired from the manufacturing conditions of the sample 109. Alternatively, a sample 109 serving as a reference may be selected, and measurement data using a terahertz wave for the sample 109 may be used as standard internal information. The comparison unit 410 sets an allowable error range for the information stored in the information storage unit 106. When the comparison unit 410 monitors the coating film thickness of the sample 109, an allowable error range of the coating film thickness is set in a range in which a desired amount of the medicinal component reaches the target affected part. In this embodiment, the allowable error range is set by the comparison unit 410, but the setting place is not limited to this. For example, the information storage unit 106 may provide the allowable error range together with the information of the sample 109.

  In the present embodiment, the information to be compared does not necessarily need to be a response waveform of a terahertz wave. For example, it is possible to use only the intensity of the terahertz wave in a predetermined measurement region as a comparison reference, and it is possible to monitor whether the intensity of the measurement location is within the set allowable error range. More specifically, the signal intensity at the apex of each pulse in FIG. 2 is measured. The temporal position of the response waveform of the terahertz wave is estimated from the change in signal intensity at the measurement location. As described above, the embodiment in which only the intensity of the measurement location is measured and inspected can be applied to the embodiments described above.

  As shown in FIG. 4, in this embodiment, there are a plurality of samples 109, and each sample is transported one after another by the transport unit 108. The comparison unit 410 compares the measurement data of the sample 109 obtained from the processing unit 107 with the standard information in the information storage unit 106 for these samples 109, and monitors whether the measurement data is within the allowable error range. To do. Then, the comparison unit 410 determines that the sample 109 that exhibits characteristics deviating from the allowable error range is a defective product. The device control unit 411 is a part that receives the comparison result of the comparison unit 410 and controls the apparatus. For example, when the sample 109 transported by the transport unit 108 is screened, control is performed so as to perform an operation of removing the sample 109 determined to be defective. The sample 109 to be excluded may be only the sample 109 determined to be a defective product, or may be a group of nearby samples 109 determined to be defective. Further, the device control unit 411 may receive the result of the comparison unit 410 and feed back the manufacturing conditions of the manufacturing process of the sample 109 to desirable conditions. For example, when a sugar-coated tablet is assumed as the sample 109, the coating film thickness is adjusted. In addition, when the physical properties of the interface between the coating film and the tablet exceed an allowable error due to a change in the mixing ratio of the drug and the additive or a change in the crystal structure of the drug, these production conditions are adjusted.

  By having such a configuration, the inside of the object to be measured can be inspected nondestructively. Further, similarly to the first embodiment, the measurement range is limited with reference to information inside the reference sample, and the response of the terahertz wave is reconfigured. Therefore, high-speed measurement is facilitated. In particular, it is suitably used as a medicine inspection system.

  In the present embodiment, the inspection portion using the terahertz wave has a reflection type configuration, but is not limited thereto. For example, the transmissive configuration shown in the second embodiment may be used. With this configuration, as described above, the overall characteristics of the sample can be easily estimated. Therefore, for example, it is possible to add a primary screening function such as examining the presence or absence of foreign matter in the sample or the presence or absence of cracks from the amount of terahertz wave absorption or phase shift. Thereafter, only the sample confirmed to have no macro structural defect needs to be inspected inside, so that the inspection can be performed more efficiently.

(Example 4: a plurality of delay optical units)
The present embodiment shows a modification of the above-described terahertz wave detection device. Specifically, the present invention relates to an optical system for acquiring a terahertz wave. In addition, description of the part which is common in the said Example is abbreviate | omitted.

  FIG. 5 is a diagram showing another form of the delay optical unit 104 for the apparatus described so far. As shown in FIG. 5, the delay optical unit 104 of this embodiment includes a plurality of delay optical units 504 a and 504 b. Each delay optical unit is adjusted to the measurement position selected by the delay time adjustment unit 105.

  For example, consider the case where the terahertz wave propagating from the sample 109 has pulses (1) and (2) as described in the above embodiment. In the embodiments so far, the delay optical unit 104 is sequentially moved to the position corresponding to each pulse by the delay time adjusting unit 105. In this embodiment, as shown in FIG. 5, the delay optical unit 504a is assigned to the position corresponding to the reflected pulse (1), and the delay optical unit 504b is assigned to the position corresponding to the reflected pulse (2), and the response of the terahertz wave is obtained. It is to be measured.

  Here, the two delay optical units need only have a predetermined optical length, and the positional relationship between the two delay optical units is not particularly limited.

  In this embodiment, the delay optical unit is associated with each reflected pulse of the terahertz wave propagating from the sample 109. However, the present invention is not limited to this configuration. For example, terahertz wave pulses may be set as a plurality of pulse groups, and a delay optical unit may be assigned to each reflected pulse group. In this case, the delay time adjustment unit 105 performs an operation of setting an observation position for each reflected pulse group and sequentially moving the assigned delay optical unit.

  Thus, by using a plurality of delay optical units and operating them in parallel, the time for measuring the response of the terahertz wave can be shortened. Therefore, the apparatus of the present invention can be operated at higher speed. Further, as shown in FIG. 10, a configuration in which a plurality of detection units are assigned to each delay optical unit is also possible. In this case, since the waiting time for measuring each reflected pulse is reduced as compared with the case where processing is performed by a single detection unit, it is easy to increase the speed of the apparatus.

(Example 5: Multiple detection units)
The present embodiment shows a modification regarding the above-described terahertz wave detection device. Specifically, it relates to the arrangement of the detection unit 103. In addition, description of the part which is common in the said Example is abbreviate | omitted.

  FIG. 9 is a diagram showing another form of the detection unit 103 for the apparatus described so far. As shown in FIG. 9, the present embodiment is characterized in that a plurality of detection units 103 are provided.

  For example, it is assumed that the propagation direction of each pulse of the terahertz wave propagating through the sample 109 differs depending on the state inside the sample 109. Specifically, it is assumed that the propagation directions of the terahertz wave pulses (1) and (2) are different. When the plurality of refractive index interfaces of the sample 109 have different angles with respect to the incident direction of the terahertz wave, the propagation directions of the terahertz wave pulses (1) and (2) are different. For the detection unit 103, an arrangement that can acquire the terahertz wave with the highest sensitivity is a configuration in which the detection unit 103 is arranged in the propagation path of the terahertz wave. Here, the arrangement with good sensitivity means an arrangement in which the intensity of the terahertz wave detected by the detection unit 103 is the strongest. If there are pulses with different propagation directions, for example, the sensitivity to the pulse (1) is good, but the intensity of the terahertz wave that reaches the detection unit 103 is small for the pulse (2), and the detection sensitivity is lowered. May occur. Therefore, for each pulse, a plurality of detection units 903a and 903b are arranged at positions where the terahertz wave can be acquired with the highest sensitivity. In this embodiment, the detector 903a is assigned to the pulse (1), and the detector 903b is assigned to the pulse (2). Then, corresponding to the observation position selected by the delay optical unit 104, the probe light (1) and (2) are allocated to the detection units 903a and 903b by the optical path switching unit 914, respectively. For each pulse, measurement and inspection are performed with the most sensitive arrangement.

  As described in the fourth embodiment, the detection unit is associated with each pulse of the terahertz wave propagating from the sample 109 in the present embodiment, but the present invention is not limited to this configuration. For example, for a terahertz wave pulse, pulses having substantially the same propagation direction may be set as one pulse group. At this time, each detection unit is assigned to each pulse group.

  By adopting such a configuration, the detection unit can be optimized with respect to the propagation direction of each pulse, so that an improvement in detection sensitivity can be expected. Further, as shown in FIG. 10, instead of the optical path switching unit 914, a plurality of delay optical units described in the fourth embodiment may be used. At this time, each delay optical unit is assigned a pulse having substantially the same propagation direction. In this case, since the standby time for measuring each pulse is reduced as compared with the case where processing is performed by the single delay optical unit 104, it is easy to increase the speed of the apparatus.

(Example 6: Counting the number of measurements and integration processing)
The present embodiment shows a modification regarding the above-described terahertz wave detection device. Specifically, the present invention relates to a method for acquiring a terahertz wave. In addition, description of the part which is common in the said Example is abbreviate | omitted.

  As shown in FIG. 6, the apparatus according to the present embodiment is configured to further include a counter unit 612 that records the number of times the terahertz wave response is measured. In the present embodiment, the counter unit 612 sets the number of times of measurement, and counts the number of samples 109 measured until the number of times of measurement is reached. In the configuration described so far, one measurement is performed for one sample 109 with respect to the sample 109 transported by the transport unit 108. If a plurality of samples 109 transported by the transport unit 108 are the same, the measurement results obtained from each sample 109 are substantially the same. In the present embodiment, the processing unit 107 performs an integration process on the plurality of measurement results as many times as the number of measurements recorded in the counter unit 612, and acquires an average measurement result. That is, here, not the measurement results of the individual samples 109 but the average measurement results of the plurality of sample 109 groups are acquired. The measurement form may be a form in which adjacent samples 109 are continuously measured, or a form in which measurements are made discretely at certain number intervals.

  In FIG. 6, the processing unit 107 performs integration processing according to the number of samples 109 to be measured, but is not limited to this form. For example, as shown in FIG. 7, the counter unit 712 that divides the measurement time may integrate data measured by the detection unit 103 within a predetermined measurement time.

  In the embodiments described so far, the mode in which the individual samples 109 are sequentially irradiated with the terahertz waves has been shown, but this is not restrictive. For example, as shown in FIG. 8, the irradiation region of the terahertz wave may be expanded and the plurality of samples 109 may be irradiated in a lump.

  Thus, by having the structure which integrate | accumulates the response of a several to-be-measured object, the influence of the noise depending on a measurement system or measurement environment can be reduced, and the improvement of the detection accuracy of a signal can be anticipated.

(Example 7: Fiber laser)
The present embodiment shows an embodiment relating to the terahertz wave detection device of the present invention. Specifically, the present invention relates to a modification of the laser unit 101. The description of the parts common to the above embodiment is omitted.

  In the embodiments so far, a titanium sapphire laser is used as the laser unit 101, but in this embodiment, a fiber laser is used.

A fiber laser is a small and stable ultrashort pulse laser source composed almost of an optical fiber. A configuration example of the fiber laser is shown in FIG. As shown in FIG. 11, the fiber laser is implemented by including the following components.
Femtosecond fiber laser 1101
Half-wave plates 1102 and 1106
Amplifier 1103
Isolator 1104
Dispersion compensation unit 1105
Polarizing beam splitter 1107
PPLN (Periodically Polled Lit), a highly efficient wavelength conversion element
high Niobate) 1108
Green cut filter 1109
Dichroic mirror 1110
The femtosecond fiber laser 1101 uses an optical fiber as a laser oscillation medium. The center wavelength is 1558 nm, the average intensity is 5 mW, the pulse width is 300 fsec, and the repetition frequency is 48 MHz. Such a fiber type femtosecond fiber laser 1101 is smaller and more stable than a solid-state laser. The half-wave plates 1102 and 1106 are used to adjust the polarization. The amplification unit 1103 is a part that amplifies the intensity of the optical pulse of the femtosecond fiber laser 1101. The optical pulse whose intensity has been amplified by the amplifier 1103 is shortened by the dispersion compensator 1105. The PPLN 1108 is a part that generates a 780 nm component, which is a second harmonic component, for an optical pulse that has been shortened. Thereafter, the green cut filter 1109 and the dichroic mirror 1110 are used to output the harmonic component 780 nm together with the reference wave component 1550 nm at a desired branching ratio. This harmonic component corresponds to the absorption wavelength of LT-GaAs, and is used as excitation light for the photoconductive element in this embodiment. When InGaAs is used as a semiconductor thin film used for the photoconductive element, a reference wave component can be used as excitation light for exciting carriers. In this case, an optical system that generates and extracts harmonics can be omitted.

  Hereinafter, a more detailed description of the amplification unit 1103 and the dispersion compensation unit 1105 will be given.

FIG. 12 shows a configuration example of the amplifying unit 1103. As shown in FIG. 12, the amplification unit 1103 is realized by the following components.
Three laser diodes (denoted LD in the figure)
Single mode fiber 1201
WDM (Wavelength Division Multiplexing) couplers 1202 and 1205
Polarization controller 1203
Er (erbium) doped fiber 1204
Polarized beam combiner 1206
The single mode fiber 1201 has a second-order group velocity dispersion of −21.4 ps 2 / km, a mode field diameter of 9.3 μm, a nonlinear coefficient of 1.89 W−1 km−1, and a fiber length of 4 for a wavelength of 1.56 μm. .5m. The Er-doped fiber 1204 has a second-order group velocity dispersion of 6.44 ps2 / km, a mode field diameter of 8.0 μm, and a nonlinear coefficient of 2.55 W-1 km−1 with respect to a wavelength of 1.56 μm. 0 m. The three LDs have a wavelength of 1480 nm and an intensity of 400 mW. As shown in FIG. 12, one of the LDs is used for forward excitation and two are used for backward excitation.

  The pulse width of the optical pulse incident from the femtosecond fiber laser 1101 is expanded in the single mode fiber 1201 due to the influence of group velocity dispersion. Thereby, the peak intensity of the light pulse is temporarily suppressed. As a result, an excessive nonlinear effect when an optical pulse propagates through the Er-doped fiber 1204 can be suppressed, so that efficient energy amplification is possible. According to this configuration, the average intensity of the light pulse can be expected to be about 20 dB.

  FIG. 13 shows a configuration example of the dispersion compensation unit 1105. The dispersion compensation unit 1105 has a dispersion characteristic opposite to the dispersion characteristic generated in the amplification unit 1103. The optical pulse output from the amplifying unit 1103 tends to have a wide band due to the influence of self-phase modulation generated in the Er-doped fiber 1204. Therefore, the dispersion compensation unit 1105 acquires a pulse shorter than the pulse width of the femtosecond fiber laser 1101 by compensating for dispersion at each wavelength. As shown in FIG. 13, in this embodiment, a dispersion compensating fiber 1301 is used as the dispersion guarantee unit 1105. Specifically, a large-diameter photonic crystal fiber is used as the dispersion compensation fiber 1301. The dispersion compensating fiber 1301 used in this example has a second-order group velocity dispersion of −30.3 ps 2 / km, a mode field diameter of 26 μm, and a nonlinear coefficient of 0.182 W−1 km−1 for a wavelength of 1.56 μm. The length is 0.42 m. According to this configuration, it is possible to expect a pulse width of the obtained optical pulse of about 55 fsec and an average intensity of about 280 mW.

  As described above, when LT-GaAs is used as the semiconductor thin film of the photoconductive element, the second harmonic is generated by the PPLN 1108 and used as excitation light. In PPLN 1108, since a reference wave component (1550 nm) is output in addition to the harmonic component (780 nm), separation is performed using dichroic mirror 1110. Further, the PPLN 1108 is configured to be removed by the green cut filter 1109 because the green light that is the third harmonic is slightly generated in addition to the second harmonic. According to such a configuration, it is possible to expect a pulse width of an optical pulse in the 780 nm band of about 58 fsec and an average intensity of about 60 mW. Further, the pulse width of the optical pulse in the 1550 nm band can be expected to be about 64 fsec, and the average intensity can be expected to be about 170 mW.

  In some cases, it is possible to perform pulse compression using a highly nonlinear fiber as shown in FIG. FIG. 14A shows a configuration diagram for compressing an optical pulse in the 1550 nm band. FIG. 14B shows a configuration diagram for compressing a light pulse in the 780 nm band. In addition, these structures are only one form, and the method of performing pulse compression is not limited to this.

  In FIG. 14A, a single mode fiber 1401 and a highly nonlinear fiber 1402 are used to perform pulse compression in the 1550 nm band. The single mode fiber 1401 has a second-order group velocity dispersion of −21.4 ps 2 / km, a nonlinear coefficient of 1.89 W−1 km−1, and a fiber length of 0.115 m for a wavelength of 1.56 μm. The highly nonlinear fiber 1402 has a second-order group velocity dispersion of −14.6 ps 2 / km, a nonlinear coefficient of 4.53 W−1 km−1, and a fiber length of 0.04 m for a wavelength of 1.56 μm. In addition, the optical pulse output from the fiber is collimated using a normal mirror to avoid pulse spread due to dispersion in the lens. According to such a configuration, it is possible to expect a pulse width of the obtained optical pulse of about 22 fsec and an average intensity of about 120 mW.

  In FIG. 14B, a highly nonlinear fiber 1402 and a chirped mirror 1403 are used to perform pulse compression in the 780 nm band. The chirp mirror 1403 is a negative dispersion chirp mirror, and a dispersion of approximately −35 fs 2 is added each time the mirror is reflected once. The pulse compression is performed by reflecting the light pulse between the chirp mirror 1403 a plurality of times. Here, 1 m of highly nonlinear fiber 1402 is used. According to such a configuration, the pulse width of the obtained optical pulse can be expected to be about 37 fsec, and the average intensity can be expected to be about 30 mW. In this embodiment, this light pulse is used as excitation light for the photoconductive element. The specific configuration and parameters of the fiber laser are not limited to this, and are appropriately selected according to various purposes.

  In this embodiment, a photoconductive element is used as the generation unit 102. As described above, by using a semiconductor substrate or an organic crystal having no electrode, it is possible to suppress the limitation of the band of the terahertz wave due to the electrode structure, and a wider response waveform (narrow pulse width) can be expected. Specifically, a DAST crystal (4-dimethylamino-N-methyl-4-stilbazolium Tosylate) is used as the generation unit 102, and a photoconductive element using LT-GaAs is used as the detection unit 103. At this time, by irradiating the fiber laser with 1550 nm band light as the probe light and 780 nm light as the probe light, a terahertz wave with a half width of about 200 fs (band to about 7.5 THz) can be generated.

  As described above, by using a fiber laser as the laser unit 101, stabilization, downsizing, and low cost of the apparatus can be expected.

1 is a schematic configuration diagram of an apparatus according to Embodiment 1. FIG. The figure explaining the operation | movement which acquires the internal information which made the tablet an example. FIG. 3 is a schematic configuration diagram of an apparatus according to a second embodiment. FIG. 6 is a schematic configuration diagram of an apparatus according to a third embodiment. An example of the delay optical part of the apparatus in the present invention. FIG. 10 is a schematic configuration diagram of a part of an apparatus according to a sixth embodiment. FIG. 10 is a schematic configuration diagram of a part of an apparatus according to a sixth embodiment. The figure explaining the example of the irradiation form of a terahertz wave. FIG. 10 is a schematic configuration diagram of a part of an apparatus according to a fifth embodiment. FIG. 10 is a schematic configuration diagram of a part of an apparatus according to a fifth embodiment. The figure explaining the structure of a fiber laser. The figure explaining the amplification part of a fiber laser. The figure explaining the dispersion compensation part of a fiber laser. The figure explaining the structure which performs pulse compression. FIG. 3 is a diagram for explaining the operation of the apparatus according to the first embodiment. FIG. 10 is a diagram illustrating an example of a propagation path of a transmitted pulse wave in the second embodiment. The schematic diagram for demonstrating the apparatus which concerns on this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Laser part 102 Generation | occurrence | production part 103 903a 903b 1003a 1003b Detection part 104 504a 504b Delay optical part 105 Delay time adjustment part 106 Information storage part 107 Processing part 108 Transport part 109 Sample 201 Powder 202 Coating film 410 Comparison part 411 Equipment control part 612 712 Counter unit 813 Irradiation region 1101 Femtosecond fiber laser 1102 1106 Half wave plate 1103 Amplifying unit 1104 Isolator 1105 Dispersion compensation unit 1107 Polarizing beam splitter 1108 PPLN
1109 Green Cut Filter 1110 Dichroic Mirror 1201 Single Mode Fiber 1202 1205 WDM Coupler 1203 Polarization Controller 1204 Er-Doped Fiber 1206 Polarization Beam Combiner 1301 Dispersion Compensation Fiber 1401 Single Mode Fiber 1402 Highly Nonlinear Fiber 1403 Chirped Mirror

Claims (12)

An apparatus for acquiring information about a terahertz wave transmitted or reflected from a sample,
A generator for generating terahertz waves;
A detection unit for detecting a terahertz wave in which the terahertz wave generated by the generation unit is transmitted or reflected by the sample;
A delay unit for changing the timing detected by the detection unit;
A storage unit for storing information about the sample in advance;
A waveform acquisition unit for acquiring a time waveform of the transmitted or reflected terahertz wave obtained using the delay unit;
The delay unit is controlled so that the detection unit detects the terahertz wave in a region related to the time waveform set based on information about the sample stored in advance in the storage unit,
An apparatus for acquiring a time waveform of the transmitted or reflected terahertz wave in the region.   The apparatus according to claim 1, wherein the information related to the sample stored in advance in the storage unit is a time waveform of a terahertz wave transmitted or reflected from the sample acquired in advance by the waveform acquisition unit.   The apparatus according to claim 1, wherein the region is a pulse included in the time waveform.   The waveform acquisition unit acquires a time waveform of the transmitted or reflected terahertz wave by sampling the terahertz wave detected by the detection unit based on the timing changed by the delay unit. The apparatus according to any one of claims 1 to 3.   5. The apparatus according to claim 1, wherein the delay unit changes at least one of a timing for generating the terahertz wave and a timing for detecting the terahertz wave. 6.   6. The apparatus according to claim 1, wherein information related to a sample is acquired from a time waveform of the transmitted or reflected terahertz wave in the region.   6. The sample state is derived by comparing a time waveform of the transmitted or reflected terahertz wave in the region with information stored in the storage unit in advance. The device according to item.   Counting the number of times the sample has been measured, integrating the measured terahertz waves detected by the detection unit, and using the integrated value and the number of times to obtain an average intensity of the terahertz waves The device according to any one of claims 1 to 7. Having a fiber laser for generating a pulsed laser;
The generator is a photoconductive element for generating a terahertz wave by irradiating the pulse laser,
The apparatus according to claim 1, wherein the detection unit is a photoconductive element for detecting a terahertz wave by irradiating the pulse laser. A method for obtaining information about a terahertz wave transmitted or reflected from a sample,
Generate terahertz waves,
Detecting the terahertz wave transmitted or reflected by the terahertz wave,
By changing the timing to detect, to acquire the time waveform of the transmitted or reflected terahertz wave,
In the region related to the time waveform set based on the time waveform of the terahertz wave that has been transmitted or reflected from the sample acquired in advance, the timing is changed so as to detect the transmitted or reflected terahertz wave,
A method of obtaining a time waveform of the transmitted or reflected terahertz wave in the region.   11. The state of the sample is derived by comparing the pulse of the terahertz wave detected in the region with the pulse of the time waveform of the terahertz wave that has been transmitted or reflected through the sample acquired in advance. the method of.   The method according to claim 10 or 11, wherein the reflected terahertz wave is a pulse reflected at a refractive index interface of a sample coated with a coating film.

Images