Waveform measuring device, waveform measurement method, and waveform measurement program

Abstract

To provide a waveform measuring device or the like capable of reducing measurement time of the waveform of an electromagnetic wave pulse, such as a terahertz wave pulse.SOLUTION: A waveform measuring device 1 comprises: an electromagnetic wave oscillation section 23 for oscillating an electromagnetic wave pulse EMP with essentially the same frequency on the basis of an oscillation pulse OP; an electromagnetic wave detection section 24 for detecting the electromagnetic wave pulse EMP on the basis of a detection pulse DP having essentially the same frequency as that of the oscillation pulse OP; a route length changing section 25 for changing route length of the detection pulse DP; a waveform measurement section 3 for measuring a sample waveform of an electromagnetic wave pulse EMP' by allowing the electromagnetic wave detection section 24 to detect the electromagnetic wave pulse EMP' after being applied to a sample S while changing the route length by the route length changing section 25; and an initial route length setting section 42 for adjusting the route length in a direction for reducing time delay of the sample waveform relative to a reference waveform of the electromagnetic wave pulse EMP in a state without any samples S and setting initial route length when starting to measure the sample waveform.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a waveform measuring device and the like. [Background technology]

[0002] Patent Document 1 states that Terra (10 12 An example of so-called terahertz time-domain spectroscopy (THz-TDS) is disclosed, which inspects a sample using terahertz waves, which are electromagnetic waves having a frequency in the 100 Hz range. In general terahertz time-domain spectroscopy, a detection pulse (hereinafter also referred to as probe light or probe pulse) having substantially the same frequency as a terahertz wave pulse is used to measure the temporal waveform (time waveform) of the terahertz wave pulse after it is irradiated onto a sample. By sequentially changing the path length or optical path length along which the probe light propagates, the terahertz wave pulse to be detected can be substantially scanned in the time domain by the probe light, and the time waveform of the terahertz wave pulse can be obtained.

[0003] In terahertz time-domain spectroscopy, a reference waveform, which is the waveform of a terahertz wave pulse in the absence of a sample, may be used in addition to a sample waveform, which is the waveform of a terahertz wave pulse in the presence of a sample. Changes in the amplitude and phase of the sample waveform from the reference waveform provide useful information about the sample. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2009-150873 A Summary of the Invention [Problem to be solved by the invention]

[0005] Generally, a terahertz wave pulse is subject to a time delay when passing through a sample due to the influence of the thickness and refractive index of the sample, etc. Therefore, the sample waveform appears later in time than the reference waveform obtained under the same measurement conditions. In order to reliably capture the reference waveform and sample waveform that appear with a time difference in this way, it was necessary to set a large waveform measurement range in the time domain (if the waveform measurement range is small, for example, the rear part of the sample waveform that appears later than the reference waveform will be cut off). Increasing the waveform measurement range in the time domain is equivalent to increasing the total change distance of the optical path length of the probe light during waveform measurement, which leads to a longer waveform measurement time.

[0006] The present disclosure has been made in consideration of these circumstances, and has an object to provide a waveform measuring device and the like that can shorten the measurement time of the waveform of an electromagnetic wave pulse such as a terahertz wave pulse. [Means for solving the problem]

[0007] In order to solve the above problems, a waveform measuring device of one aspect of the present disclosure is a waveform measuring device that measures the waveform of an electromagnetic wave pulse generated based on an oscillation pulse, and includes a path length changing unit that changes the path length of at least one of the oscillation pulse and the detection pulse, a waveform measuring unit that measures a sample waveform, which is the waveform of the electromagnetic wave pulse, by detecting the electromagnetic wave pulse after it has been irradiated to a sample based on the detection pulse while changing the path length by the path length changing unit, and an initial path length setting unit that adjusts the path length in a direction that reduces the time delay of the sample waveform relative to a reference waveform, which is the waveform of the electromagnetic wave pulse in a state where a sample is not present, and sets an initial path length at the start of measurement of the sample waveform.

[0008] In this embodiment, the initial path length at the start of measurement of the sample waveform is set so as to reduce the time delay of the sample waveform relative to the reference waveform. As a result, the time difference between the reference waveform and the sample waveform is reduced, so that the measurement range of the sample waveform in the time domain (the total change distance of the path length of the path length change unit when measuring the sample waveform) can be set smaller than before, and the measurement time of the sample waveform can be shortened.

[0009] Another aspect of the present disclosure is a waveform measurement method, which includes: oscillating an electromagnetic wave pulse based on an oscillation pulse, detecting an electromagnetic wave pulse based on a detection pulse, changing a path length of at least one of the oscillation pulse and the detection pulse, detecting the electromagnetic wave pulse after it is irradiated to a sample while changing the path length, thereby measuring a sample waveform which is the waveform of the electromagnetic wave pulse, and adjusting the path length in a direction to reduce a time delay of the sample waveform with respect to a reference waveform which is the waveform of the electromagnetic wave pulse in a state where there is no sample, and setting an initial path length at the start of measurement of the sample waveform.

[0010] Any combination of the above components, or any conversion of these components into a method, device, system, recording medium, computer program, or the like, is also encompassed by the present disclosure. Effect of the Invention

[0011] According to the present disclosure, it is possible to reduce the time required to measure the waveform of an electromagnetic wave pulse such as a terahertz wave pulse. [Brief description of the drawings]

[0012] [Figure 1] 1 shows a schematic configuration of a waveform measuring device. [Diagram 2] 3 shows examples of a sample waveform and a reference waveform measured by a waveform measurement device. [Diagram 3] 1 is a flowchart illustrating an example of polarization measurement. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] In the following, a form for carrying out the present disclosure (hereinafter also referred to as an embodiment) will be described in detail with reference to the drawings. In the description and / or drawings, identical or equivalent components, members, processes, etc. will be given the same reference numerals, and duplicated descriptions will be omitted. The scale and shape of each part shown in the drawings are set for convenience in order to simplify the description, and are not to be interpreted as being limiting unless otherwise specified. The embodiment is an example, and does not limit the scope of the present disclosure in any way. All features and their combinations presented in the embodiment are not necessarily essential to the present disclosure. The embodiment is presented for convenience, decomposed into components for each function and / or each functional group that realizes it. However, one component in the embodiment may actually be realized by a combination of multiple components as separate entities, and multiple components in the embodiment may actually be realized by one component as an integrated entity.

[0014] FIG. 1 is a schematic diagram showing a configuration of a waveform measuring device 1 according to an embodiment of the present disclosure. The waveform measuring device 1 measures the waveform of an electromagnetic wave pulse after being irradiated to a sample S in order to inspect the characteristics and internal state of a sample S and / or an object (not shown) of the same type as the sample S (hereinafter, collectively referred to as the sample S, except when it is necessary to distinguish between the sample S and the object). As shown in the figure, the electromagnetic wave pulse before being irradiated to the sample S is represented as EMP, and the electromagnetic wave pulse after being irradiated to the sample S is represented as EMP'. Typically, the electromagnetic wave pulse EMP' is an electromagnetic wave pulse EMP that has passed through or penetrated the sample S. In the following, the electromagnetic wave pulse EMP before being irradiated to the sample S and the electromagnetic wave pulse EMP' after being irradiated to the sample S are collectively referred to as the electromagnetic wave pulse EMP, except when it is necessary to distinguish between them.

[0015] In this embodiment, a terahertz wave pulse having a frequency in the terahertz range is used as the electromagnetic wave pulse EMP. Terahertz waves have intermediate properties between low-frequency radio waves and high-frequency light, and can, for example, pass through polymeric materials that ordinary light cannot pass through, like radio waves. Terahertz waves are also subject to strong effects such as absorption due to the inherent vibrations of biomolecules and other polymeric materials. Due to these characteristics, terahertz waves are suitable for use in spectroscopic measurement (spectral measurement) of polymeric materials. However, the waveform measurement device according to the present disclosure can also measure any light with a higher frequency than terahertz waves or any radio wave with a lower frequency than terahertz waves (for example, in the range of 10 giga (100 Hz)). 9 ) Gigahertz waves, which have frequencies in the hertz range, can be used instead of or in addition to terahertz waves.

[0016] According to terahertz time-domain spectroscopy, which uses a terahertz wave pulse as the electromagnetic wave pulse EMP, various characteristics and internal states of the sample S can be measured through waveform measurement of the electromagnetic wave pulse EMP'. For example, the refractive index anisotropy, dielectric constant anisotropy, absorbance, residual stress, distortion, orientation, internal structure, deterioration, and the like in the sample S can be measured by terahertz time-domain spectroscopy. Note that, as described later, for example, in order to measure the refractive index anisotropy and dielectric constant anisotropy of the sample S, polarization measurement is performed using multiple types of electromagnetic wave pulses EMP having different polarizations (for example, horizontal polarization and vertical polarization), whereas, for example, in measuring the absorbance of the sample S, a single electromagnetic wave pulse EMP is used.

[0017] 1 is a schematic diagram showing a configuration for a preliminary measurement performed by a waveform measuring device 1 on a sample S. Here, the preliminary measurement is a spectroscopic measurement performed preliminarily on the sample S in order to appropriately set various measurement parameters to be used in a main measurement on a typically large number of objects (not shown) of the same type as the sample S. As will be described later, in this embodiment, various measurement parameters in the waveform measurement range setting unit 4 are appropriately set through a preliminary measurement on the sample S via the waveform measurement unit 3. In a main measurement on an object of the same type as the sample S, the waveform of an electromagnetic wave pulse EMP' after being irradiated to the object is measured by the waveform measurement unit 3 based on various parameters in the waveform measurement range setting unit 4 set through the preliminary measurement.

[0018] In addition, the sample S and the object being "same type" means that they are similar to the extent that a meaningful measurement can be performed using common parameters in the waveform measurement range setting unit 4. For example, if the sample S and the object are made of substantially the same material and are formed to have substantially the same shape and thickness (dimensions through which the electromagnetic pulse EMP passes), the two can be said to be "same type". Similarly, for example, if the sample S and the object are substantially the same product (e.g., resin molded product) manufactured by substantially the same manufacturing device (e.g., injection molding machine) and / or substantially the same manufacturing method, the two can be said to be "same type". In this way, the sample S and the object may belong to the same product group. Also, the sample S may be one or more small products extracted from the product group for preliminary measurement.

[0019] In Fig. 1, the waveform measuring device 1 includes an electromagnetic wave spectroscopy measurement unit 2, a waveform measuring unit 3, a waveform measurement range setting unit 4, and a user input unit 5. Some of these functional blocks can be omitted as long as the waveform measuring device 1 can achieve at least some of the actions and / or effects described below. These functional blocks may be realized by the cooperation of hardware resources such as a central processing unit of a computer, a memory, an input device, an output device, and peripheral devices connected to the computer, and software executed using these. Regardless of the type of computer or the location where the computer is installed, each of the above functional blocks may be realized by the hardware resources of a single computer, or may be realized by combining hardware resources distributed among multiple computers.

[0020] The electromagnetic wave spectroscopic measurement unit 2 is a terahertz wave spectroscopic measurement unit that performs physical spectroscopic measurement in terahertz time-domain spectroscopy. The electromagnetic wave spectroscopic measurement unit 2 includes a basic pulse generating unit 21, a pulse dividing unit 22, an electromagnetic wave oscillator 23, an electromagnetic wave detector 24, and a path length changing unit 25.

[0021] The basic pulse generating unit 21 generates a basic pulse BP of a constant frequency (repetition frequency). The basic pulse generating unit 21 may have any configuration or method, but in this embodiment, the basic pulse generating unit 21 is configured by a pulse laser device capable of generating a laser pulse of a constant frequency as the basic pulse BP.

[0022] As described later, a part of the basic pulse BP becomes an oscillation pulse OP directed to the electromagnetic wave oscillator 23. The optical characteristics such as the frequency of such a basic pulse BP or oscillation pulse OP are determined so that the electromagnetic wave oscillator 23 appropriately oscillates an electromagnetic wave pulse EMP. In an example of this embodiment in which the electromagnetic wave oscillator 23 oscillates a terahertz wave pulse as the electromagnetic wave pulse EMP, for example, a laser pulse (also called a femtosecond laser) with a repetition frequency of several tens of MHz to 100 MHz by a laser beam with a wavelength of about 800 nm (e.g., 780 nm) suitable for oscillating a terahertz wave is used as the basic pulse BP and the oscillation pulse OP (and the detection pulse DP).

[0023] In this specification, "the frequencies are substantially the same" means that the repetition frequencies of various pulses are substantially the same. Specifically, as described later, the fundamental pulse BP, the oscillation pulse OP, the detection pulse DP, and the electromagnetic wave pulse EMP have substantially the same frequency (for example, a repetition frequency of several tens of MHz).

[0024] The pulse division unit 22, which is constituted by a beam splitter or the like, divides the basic pulse BP generated by the basic pulse generation unit 21 into an oscillation pulse OP directed to the electromagnetic wave oscillation unit 23 and a detection pulse DP directed to the electromagnetic wave detection unit 24. Therefore, the basic pulse BP, the oscillation pulse OP, and the detection pulse DP have substantially the same optical characteristics including frequency, wavelength, and polarization. The oscillation pulse OP may be expressed as a pump pulse or pump light, and the detection pulse DP may be expressed as a probe pulse or probe light.

[0025] In addition, instead of the basic pulse generating unit 21 and the pulse dividing unit 22, an oscillation pulse generating unit and a detection pulse generating unit capable of generating an oscillation pulse OP and a detection pulse DP, respectively, having substantially the same optical characteristics (particularly, repetition frequency) may be provided as another femtosecond laser device or the like.

[0026] The electromagnetic wave oscillator 23 oscillates an electromagnetic wave pulse EMP having substantially the same frequency as the oscillation pulse OP based on the oscillation pulse OP provided from the fundamental pulse generating unit 21 and the pulse dividing unit 22. As described above, in this embodiment, the electromagnetic wave oscillator 23 as a terahertz wave oscillator oscillates a terahertz wave pulse as the electromagnetic wave pulse EMP based on the oscillation pulse OP. As is known in terahertz time domain spectroscopy, the electromagnetic wave oscillator 23 is composed of a nonlinear optical crystal such as zinc telluride or N,N-diethylaminosulfur trifluoride (DAST), or a photoconductive switch also called a photoconductive antenna.

[0027] Here, the oscillation pulse OP (and the detection pulse DP and fundamental pulse BP substantially the same as the oscillation pulse OP) which is the input to the electromagnetic wave oscillation unit 23, and the electromagnetic wave pulse EMP which is the output of the electromagnetic wave oscillation unit 23 have substantially the same repetition frequency (for example, several tens of MHz). Note that the physical frequency of the laser light itself constituting the oscillation pulse OP (approximately 384 THz in the case of a laser light with a wavelength of 780 nm) is different from the physical frequency of the terahertz wave itself constituting the electromagnetic wave pulse EMP (for example, 1 THz (corresponding to a wavelength of approximately 300 μm)).

[0028] The electromagnetic wave pulse EMP, which is a terahertz wave pulse oscillated or generated by the electromagnetic wave oscillator 23, is irradiated onto the sample S. Then, the electromagnetic wave pulse EMP' after being irradiated onto the sample S is detected by the electromagnetic wave detector 24 as a terahertz wave detector. The electromagnetic wave detector 24 may be configured as a photoconductive switch or a photoconductive antenna, similar to the electromagnetic wave oscillator 23. Such an electromagnetic wave detector 24 detects the electromagnetic wave pulse EMP' based on the detection pulse DP having substantially the same frequency (e.g., a repetition frequency of several tens of MHz) as the oscillation pulse OP and the electromagnetic wave pulse EMP. Specifically, the electromagnetic wave detector 24 detects a point in the time waveform of the electromagnetic wave pulse EMP' as a terahertz wave pulse at the timing (or the moment) when the detection pulse DP is input.

[0029] In this way, the electromagnetic wave detection unit 24 can detect one point in the time waveform of the electromagnetic wave pulse EMP' at one time. The path length change unit 25 as a time delay stage provided in front of at least one of the electromagnetic wave oscillation unit 23 and the electromagnetic wave detection unit 24 (and behind the pulse division unit 22) changes the path length or optical path length along which at least one of the oscillation pulse OP and the detection pulse DP propagates, thereby continuously moving the point (detection point) detected by the electromagnetic wave detection unit 24 in the time waveform of the electromagnetic wave pulse EMP'. The path length change unit 25 includes, for example, a fixed mirror 251 and a movable mirror 252 as a mechanism for changing the path length of at least one of the oscillation pulse OP and the detection pulse DP. The fixed mirror 251 is substantially fixed in the electromagnetic wave spectroscopic measurement unit 2, and the movable mirror 252 is provided movably relative to the fixed mirror 251 (two positions 252, 252' are illustrated in FIG. 1).

[0030] In the example of FIG. 1 in which the path length change unit 25 is provided in front of the electromagnetic wave detection unit 24, the detection pulse DP divided by the pulse division unit 22 is incident on the input side mirror of the fixed mirror 251 and reflected toward the movable mirror 252. This detection pulse DP is substantially inverted by a pair of reflecting mirrors in the movable mirror 252 and returned to the output side mirror of the fixed mirror 251. The output side mirror outputs the detection pulse DP to the electromagnetic wave detection unit 24. By gradually changing the distance of the movable mirror 252 from the fixed mirror 251, the timing at which the detection pulse DP enters the electromagnetic wave detection unit 24 shifts. Specifically, when the distance of the movable mirror 252 from the fixed mirror 251 is increased, the timing at which the detection pulse DP enters the electromagnetic wave detection unit 24 becomes later, and when the distance of the movable mirror 252 from the fixed mirror 251 is decreased, the timing at which the detection pulse DP enters the electromagnetic wave detection unit 24 becomes earlier. In this way, by changing the path length using the path length change unit 25, the timing of the detection pulse DP entering the electromagnetic wave detection unit 24 can be freely changed, and therefore the point on the time waveform of the electromagnetic wave pulse EMP detected by the electromagnetic wave detection unit 24 based on the detection pulse DP can be freely changed.

[0031] On the other hand, although not shown, when the path length change unit 25 is provided in front of the electromagnetic wave oscillator 23, the oscillation pulse OP divided by the pulse divider 22 is incident on the input side mirror of the fixed mirror 251 and reflected toward the movable mirror 252. This oscillation pulse OP is substantially inverted by a pair of reflecting mirrors in the movable mirror 252 and returned to the output side mirror of the fixed mirror 251. The output side mirror outputs the oscillation pulse OP to the electromagnetic wave oscillator 23. By gradually changing the distance of the movable mirror 252 from the fixed mirror 251, the relative timing at which the detection pulse DP enters the electromagnetic wave detector 24 with respect to the electromagnetic wave pulse EMP derived from the oscillation pulse OP is shifted. Specifically, when the distance of the movable mirror 252 from the fixed mirror 251 is increased, the timing at which the oscillation pulse OP enters the electromagnetic wave oscillator 23 is delayed, and the relative timing at which the detection pulse DP enters the electromagnetic wave detector 24 with respect to the electromagnetic wave pulse EMP derived from the oscillation pulse OP is advanced. Conversely, when the distance of the movable mirror 252 from the fixed mirror 251 is reduced, the timing at which the oscillation pulse OP enters the electromagnetic wave oscillation unit 23 becomes earlier, and the relative timing at which the detection pulse DP enters the electromagnetic wave detection unit 24 becomes later with respect to the electromagnetic wave pulse EMP derived from the oscillation pulse OP. In this way, since the timing of the oscillation pulse OP entering the electromagnetic wave oscillation unit 23 can be freely changed through the change in path length by the path length change unit 25, the point on the time waveform of the electromagnetic wave pulse EMP detected by the electromagnetic wave detection unit 24 can be freely changed based on the detection pulse DP that moves relatively to the electromagnetic wave pulse EMP derived from the oscillation pulse OP.

[0032] The waveform measurement unit 3 measures the time waveform of the electromagnetic pulse EMP based on the above-mentioned principle. That is, the waveform measurement unit 3 measures the waveform of the electromagnetic pulse EMP by having the electromagnetic wave detection unit 24 continuously detect the electromagnetic pulse EMP while changing the path length of the detection pulse DP and / or the oscillation pulse OP by the path length change unit 25. As described above, the electromagnetic wave detection unit 24 detects only one point on the time waveform for one electromagnetic pulse EMP, but the entire time waveform can be measured by performing continuous detection while gradually shifting the detection timing for continuous electromagnetic pulses EMP (while gradually changing the path length in the path length change unit 25).

[0033] The waveform measurement unit 3 includes at least a sample waveform measurement unit 31 that measures a sample waveform, which is the time waveform of the electromagnetic wave pulse EMP', by having the electromagnetic wave detection unit 24 detect the electromagnetic wave pulse EMP' after it has been irradiated to the sample S, while changing the path length of the detection pulse DP and / or the oscillation pulse OP by the path length change unit 25. The waveform measurement unit 3 may also include a reference waveform measurement unit 32 that measures a reference waveform, which is the time waveform of the electromagnetic wave pulse EMP, by having the electromagnetic wave detection unit 24 detect the electromagnetic wave pulse EMP in a state where the sample S is not present, while changing the path length of the detection pulse DP and / or the oscillation pulse OP by the path length change unit 25.

[0034] FIG. 2A shows an example of a sample waveform WFs and a reference waveform WFr obtained under the same measurement conditions. The main measurement conditions in this example are the measurement start position Ps' and the measurement end position Pe' of the movable mirror 252 in the path length change unit 25. That is, in the example of FIG. 2A, the sample waveform measurement unit 31 and the reference waveform measurement unit 32 use a common measurement start position Ps' and a common measurement end position Pe' (i.e., a common waveform measurement range ΔP'=Pe'-Ps') when measuring the sample waveform WFs and the reference waveform WFr, respectively. As shown in the figure, the minimum value or origin of the horizontal axis in FIG. 2A (i.e., the waveform start time "0 ps") corresponds to the measurement start position Ps', and the maximum value of the horizontal axis in FIG. 2A (i.e., the waveform end time "24 ps") corresponds to the measurement end position Pe'. In other words, when the sample waveform measurement unit 31 and the reference waveform measurement unit 32 measure the sample waveform WFs and the reference waveform WFr, respectively, they continuously move the movable mirror 252 over the waveform measurement range ΔP' from the measurement start position Ps' corresponding to the waveform start time "0 ps" to the measurement end position Pe' corresponding to the waveform end time "24 ps."

[0035] In general, an electromagnetic wave pulse EMP' such as a terahertz wave pulse is delayed in time when passing through a sample S due to the influence of the thickness and refractive index of the sample S. Specifically, the thicker the sample S is, or the higher the refractive index of the sample S is, the greater the delay. For this reason, the sample waveform WFs appears later in time than the reference waveform WFr obtained under the same measurement conditions (in the example of FIG. 2(A), there is a delay ΔT of about "3 ps"). In order to reliably capture the reference waveform WFr and the sample waveform WFs that appear with a time difference in this way, it was necessary to set a large waveform measurement range in the time domain (for example, the sum of the pre-measurement period Ta before the peak of the reference waveform WFr and the post-measurement period Tb' after the peak of the reference waveform WFr). For example, a short post-measurement period Tb as described later is sufficient to capture the reference waveform WFr, but a long post-measurement period Tb' was required to be set to capture the sample waveform WFs that appears later than the reference waveform WFr. Increasing the waveform measurement range (Ta+Tb') in the time domain in this manner is equivalent to increasing the total change distance of the optical path length of the probe light DP in the path length changing unit 25 (or the total movement distance (waveform measurement range) ΔP'=Pe'-Ps' of the movable mirror 252), which results in a longer waveform measurement time.

[0036] In order to solve the above problems, this embodiment is provided with a waveform measurement range setting unit 4. The waveform measurement range setting unit 4 includes a peak search unit 41, an initial path length setting unit 42, and a waveform measurement length setting unit 43.

[0037] The peak search unit 41 measures a sample peak SP, which is a peak of a sample waveform WFs, through a preliminary measurement of the sample waveform WFs by the waveform measurement unit 3 (particularly, the sample waveform measurement unit 31). The peak search unit 41 may also measure a reference peak RP, which is a peak of a reference waveform WFr, through a preliminary measurement of the reference waveform WFr by the waveform measurement unit 3 (particularly, the reference waveform measurement unit 32). As a result of such preliminary measurement, a time delay ΔT of the sample peak SP relative to the reference peak RP is detected. Note that, here, the time delay ΔT can be efficiently detected by focusing on the peaks RP and SP, which are representative shape features of each waveform WFr and WFs, but the time delay ΔT of both waveforms WFr and WFs may also be detected based on a comparison of any shape features other than the peaks RP and SP of both waveforms WFr and WFs.

[0038] Sample waveform measurement initial path length setting unit 421 in initial path length setting unit 42 adjusts the path length in path length changing unit 25 in a direction that reduces the time delay ΔT of the sample waveform WFs relative to the reference waveform WFr detected in the preliminary measurement, and sets the initial path length at the start of measurement of the sample waveform WFs. Here, as described above, the path length in path length changing unit 25 is determined by the position of movable mirror 252. Therefore, sample waveform measurement initial path length setting unit 421 sets the initial position of movable mirror 252 at the start of measurement of the sample waveform WFs.

[0039] As shown diagrammatically in FIG. 2(B), the sample waveform measurement initial path length setting unit 421 sets a measurement start position Ps different from the measurement start position Ps' of the movable mirror 252 in FIG. 2(A) for measuring the sample waveform WFs (and / or for the actual measurement of the waveform of the electromagnetic wave pulse EMP' after it is irradiated to an object (not shown) of the same type as the sample S: the same applies below).

[0040] 2, where the path length change unit 25 is provided to change the path length of the detection pulse DP, the sample waveform measurement initial path length setting unit 421 adjusts the path length of the detection pulse DP in the path length change unit 25 to be shorter, and sets the initial position Ps of the movable mirror 252 at the start of measurement of the sample waveform WFs (to the left of the initial position Ps' in FIG. 2(A)). On the other hand, although not shown, when the path length change unit 25 is provided to change the path length of the oscillation pulse OP, the sample waveform measurement initial path length setting unit 421 adjusts the path length of the oscillation pulse OP in the path length change unit 25 to be longer, and sets the initial position Ps of the movable mirror 252 at the start of measurement of the sample waveform WFs (to the right of the initial position Ps' before the change).

[0041] Note that reference waveform measurement initial path length setting section 422 in initial path length setting section 42 may set the initial path length at the start of measurement of reference waveform WFr, which is the same as in Fig. 2(A), i.e., the initial position Ps' of movable mirror 252 at the start of measurement of reference waveform WFr. In this way, according to initial path length setting section 42 of this embodiment, the initial path length at the start of measurement of reference waveform WFr (initial position Ps' of movable mirror 252 in Fig. 2(A)) may be set to be different from the initial path length at the start of measurement of sample waveform WFs (initial position Ps of movable mirror 252 in Fig. 2(B)).

[0042] As a result of setting the initial path length (initial position Ps of movable mirror 252) by sample waveform measurement initial path length setting unit 421 as described above, the sample waveform WFs, which was significantly delayed from the reference waveform WFr in FIG. 2(A) before the setting, approaches the reference waveform WFr, as shown in FIG. 2(B). Preferably, as shown in FIG. 2(B), as a result of appropriate setting by sample waveform measurement initial path length setting unit 421, the time distance ΔT between both waveforms WFr, WFs (particularly peaks RP, SP) becomes approximately zero. In this case, in the sample waveform WFs and reference waveform WFr (FIG. 2(B)) measured by waveform measurement unit 3, both peaks SP, RP and / or both waveforms WFs, WFr entirely overlap or approximately match.

[0043] As described above, in FIG. 2A before the setting by the sample waveform measurement initial path length setting unit 421, in order to capture the sample waveform WFs that appears later than the reference waveform WFr, it was necessary to set the post-measurement period Tb' after the reference peak RP long. In contrast, in FIG. 2B after the setting by the sample waveform measurement initial path length setting unit 421, the time delay ΔT between the reference waveform WFr and the sample waveform WFs is significantly reduced, so that the post-measurement period Tb of the reference peak RP and the sample peak SP that approximately coincide with each other can be significantly shorter than the post-measurement period Tb' in FIG. 2A. In this way, the waveform measurement range (Ta+Tb) in the time domain of the sample waveform WFs and the reference waveform WFr by the waveform measurement unit 3 can be made smaller than FIG. 2A (Ta+Tb') (in the example of FIG. 2, it is possible to shorten by about "3 ps" equivalent to ΔT). This is equivalent to reducing the total change distance of the path length in the path length changing unit 25 (or the total movement distance (waveform measurement range) ΔP=Pe-Ps of the movable mirror 252 in Figure 2 (B)), and the measurement time of each of the reference waveform WFr and the sample waveform WFs can be shortened.

[0044] As shown in FIG. 2B, the measurement time "Ta+Tb" of the reference waveform WFr and the sample waveform WFs is substantially the same. This measurement time may be set by the waveform measurement length setting unit 43 as the sum of a common pre-measurement period Ta before the reference peak RP and / or sample peak SP detected by the peak search unit 41 and a common post-measurement period Tb after the reference peak RP and / or sample peak SP detected by the peak search unit 41. The waveform measurement length setting unit 43 may include a pre-measurement period setting unit 431 that sets the pre-measurement period Ta individually, and a post-measurement period setting unit 432 that sets the post-measurement period Tb individually. The pre-measurement period setting unit 431 and / or the post-measurement period setting unit 432 may automatically set the pre-measurement period Ta and / or the post-measurement period Tb that can appropriately capture the reference waveform WFr and the sample waveform WFs, but in the example of FIG. 1, they are set manually through the user input unit 5 that is configured by a computer or the like that can be operated by the user.

[0045] In the measurements of the reference waveform WFr and the sample waveform WFs, the measurement time (Ta+Tb) after optimization in Fig. 2(B) is substantially the same, but the initial positions of the movable mirror 252 are different as described above. That is, the initial position of the movable mirror 252 at the start of measurement of the reference waveform WFr is "Ps'" shown in Fig. 2(A) (however, the total movement distance is "ΔP" shown in Fig. 2(B) rather than "ΔP'" shown in Fig. 2(A)), and the initial position of the movable mirror 252 at the start of measurement of the sample waveform WFs is "Ps" shown in Fig. 2(B).

[0046] As described above, in this embodiment, the waveform measurement range setting unit 4 or the initial path length setting unit 42 sets an initial path length (initial position "Ps" for the sample waveform WFs and initial position "Ps'" for the reference waveform WFr) such that measurement of the sample waveform WFs and the reference waveform WFr is started a common pre-measurement period Ta before the sample peak SP and the reference peak RP that approximately coincide with each other. Then, the sample waveform measurement unit 31 measures the sample waveform WFs from the common pre-measurement period Ta before the sample peak SP to the common post-measurement period Tb after the sample peak SP, and the reference waveform measurement unit 32 measures the reference waveform WFr from the common pre-measurement period Ta before the reference peak RP to the common post-measurement period Tb after the reference peak RP.

[0047] According to the present embodiment as described above, the initial path length (initial position Ps of movable mirror 252) at the start of measurement of the sample waveform WFs is set so as to reduce the time delay ΔT of the sample waveform WFs relative to the reference waveform WFr. As a result, the time difference between the reference waveform WFr and the sample waveform WFs becomes small (preferably, becomes substantially zero), so that the measurement range of the sample waveform WFs and the reference waveform WFr in the time domain (Ta+Tb in FIG. 2B) or the total change distance of the path length of path length change unit 25 when measuring the sample waveform WFs and the reference waveform WFr (ΔP in FIG. 2B) can be set smaller than before, and the measurement time of the sample waveform WFs and the reference waveform WFr can be shortened.

[0048] In addition, in the example of FIG. 2(A), although both the reference waveform WFr and the sample waveform WFs are included in the waveform measurement range (Ta+Tb'), the peaks RP and SP are shifted from each other, so that the measurement period (Tb') after the reference peak RP is relatively long in the reference waveform WFr, and the measurement period before the sample peak SP is relatively long in the sample waveform WFs. In this way, the measurement ranges of the reference waveform WFr and the sample waveform WFs do not completely match, which may hinder a strict comparison between the two, and may not capture useful information of the sample waveform WFs that may be included after the waveform measurement range (Ta+Tb'). In contrast, in the example of FIG. 2(B), the reference peak RP and the sample peak SP are approximately matched, so that the waveforms WFr and WFs can be measured over substantially equal periods (Ta and Tb) before and after the peaks RP and SP. This enables a strict comparison of both waveforms WFr and WFs, and also makes it possible to avoid a situation in which useful information is missing from only one of the waveforms (particularly the sample waveform WFs).

[0049] As is known in terahertz time-domain spectroscopy, various characteristics and internal states of the sample S (and / or an object of the same type as the sample S, not shown) can be measured based on a comparison between the sample waveform WFs measured by the sample waveform measuring unit 31 (and / or the waveform related to the actual measurement of the electromagnetic wave pulse EMP' after it is irradiated to an object of the same type as the sample S, not shown) and the reference waveform WFr measured by the reference waveform measuring unit 32 (which is substantially the same as the waveform of the electromagnetic wave pulse EMP before it is irradiated to the sample S).

[0050] For example, in the graph shown in FIG. 2(B), information on the phase change between the reference waveform WFr and the sample waveform WFs (corresponding to the time delay ΔT in FIG. 2(A)) is seemingly lost, but information on the amplitude change remains. For example, based on this amplitude change (typically, the decrease from the reference peak RP to the sample peak SP), the absorbance of the sample S or the like is measured, and the characteristics and internal state of the sample S are estimated. In addition, the information on the phase change between the reference waveform WFr and the sample waveform WFs, which is seemingly lost in FIG. 2(B), can still be used because it is stored as the initial path length set by the sample waveform measurement initial path length setting unit 421 (the difference between the measurement start position Ps in FIG. 2(B) and the measurement start position Ps' in FIG. 2(A).

[0051] Also, for example, in measuring the refractive index anisotropy or dielectric constant anisotropy of the sample S, multiple types of electromagnetic wave pulses EMP or oscillation pulses OP having different polarizations (for example, horizontal polarization and vertical polarization) are used. In this case, the optimization in FIG. 2B is performed for the electromagnetic wave pulse EMP of one polarization (for example, horizontal polarization). Therefore, for the electromagnetic wave pulse EMP of the one polarization, waveforms WFr, WFs in which the reference peak RP and the sample peak SP are approximately the same as shown in FIG. 2B are obtained. On the other hand, although not shown, for the electromagnetic wave pulse EMP of another polarization (for example, vertical polarization), in typical cases, the reference peak RP and the sample peak SP appear slightly shifted due to the anisotropy of the sample S (shift smaller than the time delay ΔT in FIG. 2A). Based on the slight shift of the waveforms WFr, WFs for such an electromagnetic wave pulse EMP of another polarization, the refractive index anisotropy, dielectric constant anisotropy, etc. of the sample S are measured, and the characteristics and internal state of the sample S are estimated.

[0052] Fig. 3 is a flowchart showing an example of the above-mentioned polarization measurement. In this figure, for convenience, a preliminary measurement of a sample S and a main measurement of an object (not shown) of the same type as the sample S are shown as a series of processes in one flowchart. However, the preliminary measurement and the main measurement may be executed as separate processes at separate dates and times, for example. Note that "S" in the flowchart means a step or process. S1 to S7 are processes related to the preliminary measurement of the sample S, and S8 to S16 are processes related to the main measurement of the object.

[0053] In S1, the electromagnetic wave pulse EMP oscillated by the electromagnetic wave oscillator 23 is set to a first polarization (for example, horizontal polarization). Specifically, the electromagnetic wave pulse EMP irradiated to the sample S is set to the first polarization by a sample pre-polarization unit (not shown), such as a wire grid polarizer, which is arranged downstream of the electromagnetic wave oscillator 23 (and upstream of the sample S) in a desired attitude (or direction) corresponding to the first polarization. The electromagnetic wave pulse EMP of the first polarization, which is linearly polarized, typically changes to elliptically polarized light when passing through the sample S. On the other hand, since the downstream electromagnetic wave detection unit 24 can detect only linearly polarized light, a sample post-polarization unit (not shown) is provided that changes the elliptically polarized light of the electromagnetic wave pulse EMP' after passing through the sample S to linearly polarized light. In S2, the reference waveform measurement unit 32 measures the reference waveform WFr of the electromagnetic wave pulse EMP of the first polarization set in S1. In the preliminary measurements (S1 to S7), since it is sufficient to detect the reference peak RP in S5 described below, it is not necessary to measure the entire reference waveform WFr as shown in Fig. 2 in S2. For example, a partial waveform of the reference waveform WFr from the origin (corresponding to the initial position Ps' of the movable mirror 252) in Fig. 2(A) to the detection of the reference peak RP may be measured.

[0054] In S3, a sample S is placed. In S4, the sample waveform measurement unit 31 measures the sample waveform WFs of the electromagnetic wave pulse EMP' of the first polarization set in S1. In the preliminary measurements (S1 to S7), it is sufficient to detect the sample peak SP in S5, which will be described later, so there is no need to measure the entire sample waveform WFs as shown in FIG. 2 in S4. Here, if the basic configuration of the sample S, such as the material, thickness, and refractive index, is known to some extent, the time delay ΔT as shown in FIG. 2(A) can be predicted to some extent, so that only a part of the sample waveform WFs may be measured in S4, limited to a range where the sample peak SP is likely to appear (near the predicted time delay ΔT).

[0055] In S5, peak search unit 41 searches for or identifies a reference peak RP in reference waveform WFr measured in S2 and a sample peak SP in sample waveform WFs measured in S4. In S6, sample waveform measurement initial path length setting unit 421 adjusts the path length in path length change unit 25 in a direction that reduces the time difference ΔT between reference peak RP and sample peak SP identified in S5, and sets an initial path length at the start of main measurement of sample waveform WFs (S10 and S15 described later). As described above, in the example of FIG. 2(B), sample waveform measurement initial path length setting unit 421 sets an initial position (Ps) of movable mirror 252 at the start of main measurement of sample waveform WFs. In addition, the reference waveform measurement initial path length setting unit 422 sets the initial path length at the start of the preliminary measurement of the reference waveform WFs in S2 (corresponding to the initial position Ps' of the movable mirror 252 in Figure 2 (A)) as the initial path length at the start of the main measurement of the reference waveform WFr (S8 and S13 described below).

[0056] In S7, as the final step of the preliminary measurement, the sample S is removed. In this manner, the preliminary measurement only needs to be performed for the first polarization set in S1, and the preliminary measurement does not need to be performed for the second polarization (e.g., vertical polarization) different from the first polarization.

[0057] In S8, the reference waveform measurement unit 32 measures the reference waveform WFr of the first polarized electromagnetic wave pulse EMP set in S1 based on the initial path length set in S6 (initial position Ps' of the movable mirror 252). Note that since S8 is substantially the same as S2 in the preliminary measurement, if the entire reference waveform WFr is measured in S2, it is not necessary to execute S8 redundantly.

[0058] In S9, an object to be inspected of the same type as the sample S is placed. In S10, the sample waveform measurement unit 31 measures the sample waveform WFs of the first polarized electromagnetic wave pulse EMP' set in S1 based on the initial path length (initial position Ps of the movable mirror 252) set in S6. As a result of the waveform measurement of the first polarized electromagnetic wave pulse EMP in S8 and S10, a reference waveform WFr and a sample waveform WFs overlapping each other as shown in FIG. 2(B) are obtained. In S11, the object to be inspected is temporarily removed.

[0059] In S12, the electromagnetic wave pulse EMP oscillated by the electromagnetic wave oscillator 23 is set to a second polarization (for example, vertical polarization) different from the first polarization. Specifically, the electromagnetic wave pulse EMP irradiated to the sample S is set to the second polarization by a pre-sample polarization unit (not shown), such as a wire grid polarizer, which is arranged downstream of the electromagnetic wave oscillator 23 (and upstream of the sample S) in a desired attitude (or direction) corresponding to the second polarization. Note that the electromagnetic wave pulse EMP of the second polarization, which is linearly polarized, typically changes to elliptically polarized light when passing through the sample S. On the other hand, since the downstream electromagnetic wave detection unit 24 can detect only linearly polarized light, a post-sample polarization unit (not shown) is provided that changes the elliptically polarized light of the electromagnetic wave pulse EMP' after passing through the sample S to linearly polarized light.

[0060] In S13, the reference waveform measurement unit 32 measures the reference waveform WFr of the second polarized electromagnetic wave pulse EMP set in S12, based on the initial path length (initial position Ps' of the movable mirror 252) set in S6.

[0061] In S14, the inspection object once removed in S11 is reinstalled. In S15, the sample waveform measurement unit 31 measures the sample waveform WFs of the second polarized electromagnetic wave pulse EMP' set in S12 based on the initial path length (initial position Ps of the movable mirror 252) set in S6. As a result of the waveform measurement of the second polarized electromagnetic wave pulse EMP in S13 and S15, a reference waveform WFr and a sample waveform WFs (not shown) are obtained.

[0062] In S16, the characteristics and internal state of the object to be inspected are inspected or evaluated from multiple angles based on a comparison of the amplitude, etc., of the reference waveform WFr and sample waveform WFs (Figure 2(B)) of the electromagnetic pulse EMP of the first polarization obtained in S8 and S10, and / or a comparison of the amplitude, phase, etc., of the reference waveform WFr and sample waveform WFs (not shown) of the electromagnetic pulse EMP of the second polarization obtained in S13 and S15.

[0063] The present disclosure has been described above based on the embodiments. Various modifications are possible to the combinations of the components and processes in the exemplary embodiments, and it will be obvious to those skilled in the art that such modifications are included within the scope of the present disclosure.

[0064] The configuration, action, and function of each device and method described in the embodiments can be realized by hardware resources or software resources, or by the cooperation of hardware resources and software resources. For example, a processor, ROM, RAM, and various integrated circuits can be used as hardware resources. For example, programs such as an operating system and applications can be used as software resources. [Explanation of symbols]

[0065] 1 Waveform measurement device, 2 Electromagnetic wave spectroscopy measurement unit, 3 Waveform measurement unit, 4 Waveform measurement range setting unit, 5 User input unit, 21 Basic pulse generation unit, 22 Pulse division unit, 23 Electromagnetic wave oscillation unit, 24 Electromagnetic wave detection unit, 25 Path length changing unit, 31 Sample waveform measurement unit, 32 Reference waveform measurement unit, 41 Peak search unit, 42 Initial path length setting unit, 43 Waveform measurement length setting unit, 251 Fixed mirror, 252 Movable mirror, 421 Sample waveform measurement initial path length setting unit, 422 Reference waveform measurement initial path length setting unit, 431 Pre-measurement period setting unit, 432 Post-measurement period setting unit.

Claims

1. A waveform measuring device that measures a waveform of an electromagnetic wave pulse oscillated based on an oscillation pulse, a path length changing unit that changes a path length of at least one of the oscillation pulse and the detection pulse; a waveform measurement unit that detects the electromagnetic wave pulse after it is irradiated onto a sample based on the detection pulse while changing the path length by the path length change unit, and measures a sample waveform that is a waveform of the electromagnetic wave pulse; an initial path length setting unit that adjusts the path length in a direction to reduce a time delay of the sample waveform with respect to a reference waveform, which is a waveform of the electromagnetic wave pulse in a state in which the sample is not present, and sets an initial path length at the start of measurement of the sample waveform; A waveform measuring device comprising:

2. an electromagnetic wave oscillator that oscillates the electromagnetic wave pulse having substantially the same frequency as the oscillation pulse based on the oscillation pulse; an electromagnetic wave detection unit that detects the electromagnetic wave pulse based on the detection pulse having substantially the same frequency as the oscillation pulse; Equipped with the path length changer is provided upstream of at least one of the electromagnetic wave oscillator and the electromagnetic wave detector, the waveform measurement unit measures the sample waveform by causing the electromagnetic wave detection unit to detect the electromagnetic wave pulse after it is irradiated to the sample while changing the path length by the path length change unit. The waveform measuring device according to claim 1 .

3. 3. The waveform measuring device according to claim 2, wherein the waveform measuring unit measures the reference waveform, which is the waveform of the electromagnetic wave pulse, by causing the electromagnetic wave detection unit to detect the electromagnetic wave pulse in a state where the sample is not present while changing the path length using the path length changing unit.

4. 4. The waveform measurement device according to claim 3, wherein the initial path length setting section sets an initial path length at the start of measurement of the reference waveform to be different from an initial path length at the start of measurement of the sample waveform.

5. the waveform measurement unit measures a sample peak that is a peak of the sample waveform and a reference peak that is a peak of the reference waveform; the initial path length setting unit sets the initial path length such that measurement of the sample waveform is started a predetermined pre-measurement period before the sample peak, and sets the initial path length such that measurement of the reference waveform is started the same pre-measurement period before the reference peak. The waveform measuring device according to claim 4.

6. The waveform measurement unit is measuring the sample waveform from the pre-measurement period before the sample peak to a predetermined post-measurement period after the sample peak; measuring the reference waveform from the pre-measurement period before the reference peak to the same post-measurement period after the reference peak; The waveform measuring device according to claim 5 .

7. the waveform measurement unit measures a sample peak that is a peak of the sample waveform and a reference peak that is a peak of the reference waveform; the initial path length setting unit sets the initial path lengths such that the sample peak and the reference peak overlap in the sample waveform and the reference waveform measured by the waveform measurement unit. The waveform measuring device according to claim 4.

8. a basic pulse generating unit that generates a basic pulse of a constant frequency; a pulse division unit that divides the basic pulse into the oscillation pulse and the detection pulse; The waveform measuring device according to claim 1 , further comprising:

9. The waveform measuring device according to claim 8 , wherein the basic pulse generating section generates a laser pulse as the basic pulse.

10. The waveform measuring device according to claim 1 , wherein the electromagnetic wave pulse is a terahertz wave pulse.

11. Oscillation of an electromagnetic wave pulse based on the oscillation pulse; detecting the electromagnetic wave pulse based on a detection pulse; Changing a path length of at least one of the oscillation pulse and the detection pulse; measuring a sample waveform, which is a waveform of the electromagnetic wave pulse, by detecting the electromagnetic wave pulse after it is irradiated onto a sample while changing the path length; adjusting the path length in a direction to reduce a time delay of the sample waveform with respect to a reference waveform, which is a waveform of the electromagnetic wave pulse in a state in which the sample is not present, and setting an initial path length at the start of measurement of the sample waveform; A waveform measurement method that performs

12. Oscillation of an electromagnetic wave pulse based on the oscillation pulse; detecting the electromagnetic wave pulse based on a detection pulse; Changing a path length of at least one of the oscillation pulse and the detection pulse; measuring a sample waveform, which is a waveform of the electromagnetic wave pulse, by detecting the electromagnetic wave pulse after it is irradiated onto a sample while changing the path length; adjusting the path length in a direction to reduce a time delay of the sample waveform with respect to a reference waveform, which is a waveform of the electromagnetic wave pulse in a state in which the sample is not present, and setting an initial path length at the start of measurement of the sample waveform; A waveform measurement program that causes a computer to execute the above.

Images