WO2017163349A1

WO2017163349A1 - Measurement device

Info

Publication number: WO2017163349A1
Application number: PCT/JP2016/059259
Authority: WO
Inventors: 小林　秀樹
Original assignee: パイオニア株式会社
Priority date: 2016-03-23
Filing date: 2016-03-23
Publication date: 2017-09-28

Abstract

A measurement device (1) is provided with an emission unit (13) that emits electromagnetic wave pulses onto a subject by having a bias voltage applied thereto and having pump light irradiated thereon, a detection unit (16) for detecting electromagnetic wave pulses from the subject, a generation unit (22) for generating an electromagnetic wave pulse time waveform on the basis of the detection data of the detection unit, and a control unit (23) for continuously applying a first voltage to the emission unit as the bias voltage during a first period during which the detection unit detects detection data and applying a second voltage that is the inverse of the first voltage to the emission unit during at least a portion of a second period that is different from the first period.

Description

measuring device

The present invention relates to the technical field of a measuring apparatus that measures a specimen using electromagnetic waves such as terahertz waves.

As this type of device, for example, a terahertz pulse spectrometer using a pump-probe method has been proposed (see Patent Document 1).

JP 2014-222157 A

In the technique described in Patent Document 1, a lock-in amplifier is used to improve a signal-to-noise ratio (S / N ratio). In recent years, it has been desired to increase the speed of data acquisition in this type of apparatus. However, there is a technical problem that it is extremely difficult to design a lock-in amplifier that can realize high-speed data acquisition.

The present invention has been made in view of the above-described problems, for example, and an object of the present invention is to provide a measuring apparatus capable of realizing high-speed data acquisition by a relatively simple method.

In order to solve the above-described problems, the measurement apparatus of the present invention is configured to apply a bias voltage and irradiate pump light, thereby emitting an electromagnetic wave pulse to the subject, and the electromagnetic wave from the subject. A detection unit for detecting a pulse; a generation unit for generating a time waveform of the electromagnetic wave pulse based on detection data of the detection unit; and a first voltage during a first period in which the detection unit detects the detection data. A control unit that continuously applies a bias voltage to the emission unit and applies a second voltage having an attribute opposite to the first voltage to the emission unit in at least a part of a second period different from the first period; .

The operation and other advantages of the present invention will be clarified from the embodiments to be described below.

It is a conceptual diagram which shows the structure of the terahertz wave measuring device which concerns on an Example. It is the top view which looked at the optical delay part which concerns on an Example from the upper direction. It is a figure which shows an example of the time change of the bias voltage which concerns on an Example. It is a figure which shows an example of the time change of the bias voltage which concerns on a 1st modification. It is a figure which shows an example of the time change of the bias voltage which concerns on a 2nd modification.

Embodiments of the measuring apparatus according to the present invention will be described.

The measurement apparatus according to the embodiment includes an emission unit that emits an electromagnetic wave pulse to a subject, a detection unit that detects an electromagnetic wave pulse from the subject, and a detection when a bias voltage is applied and pump light is irradiated A generator for generating a time waveform of the electromagnetic wave pulse based on the detection data of the unit, and a first voltage as a bias voltage continuously applied to the emitting unit during a first period in which the detection unit detects the detection data; A control unit that applies, to at least a part of the second period that is different from the first period, a second voltage having a reverse attribute to the first voltage.

When a lock-in amplifier is used as in the technique described in Patent Document 1 described above, a sinusoidal voltage modulated based on a reference signal used for lock-in detection is used as a bias voltage in the emission unit during the measurement period. Applied.

On the other hand, in the measuring apparatus according to the present embodiment, the control unit continuously applies the first voltage having a predetermined voltage value (that is, the DC voltage) as the bias voltage to the emission unit during the first period. . For this reason, it is not necessary to perform demodulation processing based on the reference signal on the signal output from the detection unit (that is, the signal resulting from the detected electromagnetic wave pulse) (that is, no lock-in amplifier is required). Therefore, according to the measuring apparatus according to the present embodiment, it is possible to realize high-speed data acquisition. Further, the control unit applies a second voltage having an opposite attribute to the first voltage to the injection unit in at least a part of the second period different from the first period, thereby suppressing the life deterioration of the injection unit. be able to.

In one aspect of the measurement apparatus according to the embodiment, the control unit may apply the second voltage to the emission unit such that the time average value of the bias voltage applied to the emission unit becomes zero.

According to this aspect, since the bipolar bias voltage is evenly applied to the emitting part, it is possible to more suitably suppress the life deterioration of the emitting part.

In another aspect of the measurement apparatus according to the embodiment, the detection unit detects an electromagnetic wave pulse from the subject by being irradiated with the probe light. The measurement apparatus further includes a delay unit that changes the optical path length of the probe light and changes the detection timing of the detection unit. The delay unit changes the optical path length by a length corresponding to the time waveform during the first period.

According to this aspect, while the delay unit is changing the optical path length of the probe light in order to generate a time waveform having a predetermined time width, the first voltage is continuously applied to the emission unit. The electromagnetic wave pulse is continuously emitted to the specimen, and the detection unit continues to detect the electromagnetic wave pulse from the subject. As a result, the measurement time can be shortened.

In this aspect, the delay unit has a rotating body in which a plurality of retroreflecting mirrors are arranged on the same circumference, and changes the optical path length of the probe light by rotating the rotating body.

According to this aspect, the optical path length of the probe light can be changed relatively quickly, and as a result, the measurement time can be shortened.

Embodiments according to the measuring apparatus of the present invention will be described with reference to the drawings. In the following examples, a terahertz wave measuring device is given as an example of the measuring device of the present invention. An example of the “electromagnetic wave” according to the present invention is “terahertz wave”.

(Configuration of terahertz wave measuring device)
The configuration of the terahertz wave measuring apparatus according to the embodiment will be described with reference to FIG. FIG. 1 is a conceptual diagram illustrating a configuration of a terahertz wave measuring apparatus according to an embodiment.

1, the terahertz wave measuring apparatus 1 includes a laser light source 11, a terahertz (THz) wave transmitting unit 13, an optical delay unit 14, a terahertz wave receiving unit 16, and a control / arithmetic processing unit 20. The terahertz wave measuring apparatus 1 is configured to be able to execute terahertz time spectroscopy using a pump-probe method in which the optical path length is changed using the optical delay unit 14.

The laser light source 11 can repeatedly output an ultrashort pulse laser beam of sub-picosecond order or less. During the operation of the terahertz wave measuring apparatus 1, pulse laser light emitted from the laser light source 11 is divided into pump light and probe light by the beam splitter 12.

The terahertz wave transmitting unit 13 includes a terahertz wave generating element (not shown) including a photoconductive antenna having a dipole antenna or the like on a semiconductor substrate formed of, for example, GaAs (Gallium Arsenide). In addition, since various well-known aspects can be applied to the terahertz wave generating element, a detailed description thereof will be omitted.

A gap is formed at the center of the photoconductive antenna. When a bias voltage is applied to the gap and the gap is irradiated with pump light, carriers are generated in the semiconductor by photoexcitation. Sub-picosecond current is generated. As a result, a pulsed terahertz wave having an amplitude proportional to the time derivative of the generated current is emitted. The terahertz wave generated by the terahertz wave generating element is emitted from the terahertz wave transmitting unit 13 as a terahertz wave beam through, for example, a silicon collimator lens or the like (not shown).

During the operation of the terahertz wave measuring apparatus 1, the terahertz wave beam emitted from the terahertz wave transmission unit 13 is irradiated onto the target measurement object 50 via the beam splitter 15. The terahertz wave beam reflected by the measurement object 50 is reflected by the beam splitter 15 and enters the terahertz wave receiving unit 16.

The terahertz wave receiving unit 16 includes a terahertz wave detecting element (not shown) having the same configuration as the terahertz wave generating element. In addition, since various well-known aspects are applicable to a terahertz wave detection element, the description about the detail is omitted.

When the probe light having passed through the optical delay unit 14 is incident on the terahertz wave detection element, carriers are generated in the semiconductor of the terahertz wave detection element. As a result, a current proportional to the amplitude of the terahertz wave beam incident on the terahertz wave detection element at the moment when the carrier is generated is generated. The terahertz wave receiving unit 16 converts the generated current into a current-voltage conversion by, for example, an IV conversion unit (not shown), and uses a control / arithmetic processing unit as a detection signal of the terahertz wave reflected by the measurement target 50 20 output.

Here, the optical delay unit 14 will be described with reference to FIG. FIG. 2 is a plan view of the optical delay unit according to the embodiment as viewed from above.

2, the optical delay unit 14 includes a rotating body 141 and a plurality of retroreflecting mirrors 142. The rotating body 141 is configured to be rotatable around a rotation axis by a driving mechanism (not shown) such as a motor, for example.

The plurality of retroreflecting mirrors 142 are arranged on the same circle around the rotation axis of the rotating body 141. The retroreflector 142 retroreflects the probe light incident on the retroreflector 142 (that is, reflects in a direction parallel to the incident direction of the probe light). In FIG. 2, there are four retroreflecting mirrors 142, but the present invention is not limited to this.

During the operation of the terahertz wave measuring apparatus 1, the position of the retroreflecting mirror 142 varies with the rotation of the rotating body 141 of the optical delay unit 14. As a result, the optical path length of the probe light is changed. However, since the angle of the retroreflector 142 with respect to the incident probe light changes as the rotating body 141 rotates, the period during which the retroreflector 142 can retroreflect the probe light is limited.

In this embodiment, a period in which the retroreflecting mirror 142 can retroreflect the probe light, in other words, a period in which the optical path length of the probe light can be changed by the optical delay unit 14 is referred to as a “mirror effective period”.

1 again, the control / arithmetic processing unit 20 includes an optical delay unit driving / control unit 21, a data processing / display unit 22, a bias generation unit 23, and a data acquisition unit 24.

The optical delay unit driving / control unit 21 controls the optical delay unit 14. In this embodiment, in particular, the optical delay unit driving / control unit 21 specifies a mirror effective period based on, for example, the rotational phase of the optical delay unit 14, and outputs a signal indicating the specified mirror effective period as a bias generation unit. 21, transmit to the data acquisition unit 24 and the laser light source 11.

The bias generating unit 23 applies a DC bias voltage to the terahertz wave generating element of the terahertz wave transmitting unit 13. A specific description of the bias voltage will be described later.

The data acquisition unit 24 detects a time waveform signal caused by the terahertz wave from the detection signal output from the terahertz wave receiving unit 16. Here, the data acquisition unit 24 may detect the time waveform signal only during the period corresponding to the mirror effective period based on the signal indicating the mirror effective period.

The data processing / display unit 22 temporarily captures (that is, stores) the detected time waveform signal in a storage device or the like. The data processing / display unit 22 generates a unique spectrum of terahertz waves reflected by the measurement object 50 or an imaging image by performing Fourier transform or the like on the captured time waveform signal. That is, a time waveform having a time width corresponding to the mirror effective period can be generated and displayed. In addition, about the process of the time waveform signal which concerns on a terahertz wave, since well-known various aspects are applicable, the description about the detail is omitted.

The terahertz wave measuring apparatus 1 shown in FIG. 1 is a reflective terahertz wave measuring apparatus, but the present invention is also applicable to a transmissive terahertz wave measuring apparatus.

(Bias voltage)
Next, the bias voltage applied to the terahertz wave generating element of the terahertz wave transmitting unit 13 will be described with reference to FIG. FIG. 3 is a diagram illustrating an example of a time change of the bias voltage according to the embodiment. In FIG. 3, the period t1 is the same as the mirror effective period tmir.

Based on the signal indicating the mirror effective period, the bias generator 23 applies a positive DC voltage (here, “+ Vb1”) as a bias voltage to the terahertz generating element only during the period t1 corresponding to the mirror effective period tmir. .

The bias generator 23 applies a negative DC voltage (here, “−Vb2”) as a bias voltage to the terahertz wave generating element only during the period t2 after the mirror effective period tmir has elapsed. Here, the period t2 is the product of the absolute value of “+ Vb1” and the period t1 (ie, | Vb1 | × t1) and the product of the absolute value of “−Vb2” and the period t2 (ie, | Vb2 | × It is desirable that t2) is set to be equal. If comprised in this way, lifetime deterioration of a terahertz wave generation element can be suppressed.

The laser light source 11 emits pulsed laser light only during a period corresponding to the mirror effective period tmir based on a signal indicating the mirror effective period. Accordingly, the terahertz wave generating element is irradiated with the pump light only during the period corresponding to the mirror effective period tmir. For this reason, although the bias voltage is applied to the terahertz wave generating element also in the period t2, the pump light is not irradiated, so that the terahertz wave is not radiated from the terahertz wave generating element in the period t2.

As shown in FIG. 3, the bias voltage applied to the terahertz wave generating element in this embodiment is a DC voltage (that is, not a modulated sine wave voltage). For this reason, the data acquisition unit 24 only has to detect the time waveform signal caused by the terahertz wave from the detection signal output from the terahertz wave reception unit 16 for a period corresponding to the mirror effective period tmir (that is, lock-in). No detection is required).

Alternatively, the laser light source 11 may emit pulsed laser light during a period other than the mirror effective period tmir. That is, the pulse laser beam may continue to be emitted regardless of the mirror effective period tmir. Outside the mirror effective period tmir, retroreflection is impossible by the retroreflecting mirror 142, so that probe light does not enter the terahertz wave detecting element of the terahertz wave receiving unit 16, and therefore no detection signal is output from the terahertz wave receiving unit 16. . For this reason, the data acquisition unit 24 can acquire the detection signal of the terahertz wave reception unit 16 only during a period corresponding to the mirror effective period tmir. (Technical effect)
In this embodiment, as described above, a DC voltage is applied as a bias voltage to the terahertz wave generating element during the mirror effective period tmir. For this reason, it is not necessary to consider the modulation frequency as in the case where lock-in detection is performed. Furthermore, since the modulation frequency is not used, it is not necessary to consider occurrence of aliasing of the modulation frequency. That is, when designing a circuit constituting the terahertz wave measuring apparatus 1, it is not necessary to consider the modulation frequency and the sideband signal band (that is, it is not necessary to widen the band). As a result, since a lock-in amplifier is not particularly required, the circuit can be simplified and the cost can be reduced. In addition, the speed of data acquisition can be increased.

The “terahertz wave transmitting unit 13”, “terahertz wave receiving unit 16”, “optical delay unit 14”, “data processing / display unit 22”, and “bias generating unit 23” according to the present embodiment are respectively included in the present invention. It is an example of the “injection unit”, “detection unit”, “delay unit”, “generation unit”, and “control unit”.

<First Modification>
Next, a first modification of the terahertz wave measuring apparatus 1 according to the embodiment will be described with reference to FIG. FIG. 4 is a diagram illustrating an example of a temporal change in the bias voltage according to the first modification.

In the first modification, of the bias voltage applied to the terahertz wave generating element of the terahertz wave transmitting unit 13, the negative DC voltage (−Vb2) is obtained after the elapse of one mirror effective period tmir as shown in FIG. It may be applied at an arbitrary timing before the start of the next mirror effective period tmir. That is, the period t3 and the period t4 change according to the period t2.

<Second Modification>
Next, a second modification of the terahertz wave measuring apparatus 1 according to the embodiment will be described with reference to FIG. FIG. 5 is a diagram illustrating an example of a time change of the bias voltage according to the second modification.

In the second modification, among the bias voltages applied to the terahertz wave generating element of the terahertz wave transmission unit 13, the period t1 during which the positive DC voltage (+ Vb1) is applied is a mirror effective period as shown in FIG. It may be longer than tmir. Note that the period t2 is desirably set so that | Vb1 | × t1 = | Vb2 | × t2.

As described above, if the terahertz wave generating element is irradiated with the pump light only during the period corresponding to the mirror effective period tmir, a positive DC voltage is applied to the terahertz wave generating element even after the mirror effective period tmir has elapsed. In the period t1, the terahertz wave is not radiated from the terahertz wave generation element after the mirror effective period tmir elapses in the period t1 (the same applies to the period t2). Alternatively, even if the terahertz wave generating element is irradiated with pump light during a period other than the mirror effective period tmir, the retroreflecting mirror 142 cannot retroreflect the probe light outside the mirror effective period tmir. Since no probe light is incident on the detection element, no detection signal is output from the terahertz wave receiving unit 16.

In the above-described embodiments, the optical delay unit 14 is a rotary optical delay device. However, the present invention is not limited to this. For example, an optical delay device that linearly reciprocates along the incident direction of the probe light is used. May be used. In this case, the period during which the optical delay unit 14 changes the optical path length within the range of the optical path length of the probe light corresponding to the time width of the time waveform to be acquired is regarded as the “mirror effective period”, and is the same as the above-described embodiment. Is performed.

The present invention is not limited to the above-described embodiments, and can be appropriately changed without departing from the spirit or idea of the invention that can be read from the claims and the entire specification, and a measuring apparatus with such a change can also be used. It is included in the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 1 ... Terahertz wave measuring device, 11 ... Laser light source, 13 ... Terahertz wave transmission part, 14 ... Optical delay part, 16 ... Terahertz wave detection part, 20 ... Control / arithmetic processing part, 21 ... Optical delay part drive / control part, 22 ... Data processing / display unit, 23 ... Bias generation unit, 24 ... Data acquisition unit

Claims

An emission unit that emits an electromagnetic wave pulse to a subject by applying a bias voltage and irradiating pump light; and
A detection unit for detecting the electromagnetic wave pulse from the subject;
Based on detection data of the detection unit, a generation unit that generates a time waveform of the electromagnetic wave pulse,
During the first period in which the detection unit detects the detection data, the first voltage is continuously applied to the emission unit as the bias voltage, and at least in a second period different from the first period. A control unit for applying a second voltage having a reverse attribute to the first voltage to the injection unit;
A measuring apparatus comprising:
2. The measuring apparatus according to claim 1, wherein the control unit applies the second voltage to the emission unit such that a time average value of a bias voltage applied to the emission unit becomes zero.
The detection unit detects the electromagnetic wave pulse from the subject by being irradiated with probe light,
Further comprising a delay unit that changes an optical path length of the probe light and changes a detection timing by the detection unit;
The measuring apparatus according to claim 1, wherein the delay unit changes the optical path length by a length corresponding to the time waveform during the first period.
The delay unit includes a rotating body in which a plurality of retroreflecting mirrors are arranged on the same circumference, and changes the optical path length of the probe light by rotating the rotating body. 3. The measuring device according to 3.