JP6485624B2 - Measuring device - Google Patents

Description

  The present invention relates to a measuring device.

  In recent years, terahertz waves, which are electromagnetic waves having a frequency of 100 GHz to 30 THz, have attracted attention. The terahertz wave can be used for various measurements such as imaging and spectroscopic measurement, non-destructive inspection, and the like.

  For example, as a measurement apparatus using a terahertz wave, a measurement apparatus using a terahertz time-domain spectroscopy (THz-TDS) is known. For example, in the measurement apparatus using THz-TDS disclosed in Patent Document 1, first, an optical pulse emitted from a femtosecond laser is divided into two paths by a beam splitter. One light pulse (pump light) is irradiated to a photoconductive element in which an antenna is formed on LT-GaAs to generate a terahertz wave. The generated terahertz wave is applied to the target object, and the terahertz wave transmitted through the target object is incident on the photoconductive element for detection. The other light pulse (probe light) is applied to the photoconductive element for detection through the delay means. The other light pulse is used as a gate signal when detecting the terahertz wave transmitted through the target object in the photoconductive element for detection.

  In such a measuring apparatus using THz-TDS, when imaging a target object, a time waveform of a terahertz wave transmitted through the target object is required. In order to acquire the time waveform, it is necessary to give a slightly different time difference to the terahertz wave incident on the detection photoconductive element and the optical pulse (probe light). For example, in the measurement apparatus of Patent Document 1, a delay unit that mechanically moves a mirror is used to make the optical path length of the probe light variable so as to create a time difference between the terahertz wave and the optical pulse (probe light). Yes.

JP 2010-156664 A

  Here, in the measurement apparatus of Patent Document 1, as described above, the mirror is mechanically moved to change the optical path length of the probe light. However, when the optical path length of the probe light is changed by mechanically moving the mirror, there is a problem that it takes time and the measurement time becomes long. In particular, in imaging using THz-TDS, the measurement time for each pixel becomes long, so the influence is great.

  One of the objects according to some aspects of the present invention is to provide a measuring device that can shorten the measurement time.

The measuring device according to the present invention is
An optical pulse generator capable of generating a plurality of optical pulses of different wavelengths;
An optical pulse branching unit that branches the optical pulse generated by the optical pulse generation unit into a first optical pulse and a second optical pulse;
A terahertz wave generator that generates a terahertz wave by being irradiated with the first light pulse;
A terahertz wave detection unit that is irradiated with the second light pulse and the terahertz wave that is irradiated to the sample to be measured and transmitted or reflected;
A delay optical system configured so that an optical path length of the second optical pulse from the optical pulse branching unit to the terahertz wave detecting unit changes according to a wavelength of the second optical pulse;
including.

  In such a measurement apparatus, the optical pulse generation unit generates a plurality of optical pulses having different wavelengths, and the delay optical system uses a second optical pulse from the optical pulse branching unit to the terahertz wave detection unit according to the wavelength of the second optical pulse. Since the optical path length of the second optical pulse is changed, the optical path length of the second optical pulse can be changed electrically. Therefore, in such a measurement apparatus, for example, the measurement time can be shortened as compared with a case where the delay optical system mechanically moves the mirror to change the optical path length of the probe light.

In the measuring device according to the present invention,
The delay optical system may include a prism pair.

  In such a measuring apparatus, the delay optical system can change the optical path length according to the wavelength of the second optical pulse by using a prism pair. In addition, the prism pair has a smaller light loss than other optical elements such as a diffraction grating pair. Therefore, in such a measuring apparatus, the second optical pulse can be delayed efficiently.

In the measuring device according to the present invention,
The delay optical system may include a reflection mirror that returns the second light pulse that has passed through the prism pair to the prism pair.

  In such a measuring apparatus, the delay optical system can change the optical path length according to the wavelength of the second optical pulse by using a prism pair.

In the measuring device according to the present invention,
The delay optical system may include two prism pairs.

  In such a measuring apparatus, the delay optical system can change the optical path length according to the wavelength of the second optical pulse by using two prism pairs.

In the measuring device according to the present invention,
The delay optical system may include a diffraction grating pair.

  In such a measuring apparatus, the delay optical system can change the optical path length according to the wavelength of the second optical pulse by using a diffraction grating pair. In addition, the diffraction grating pair is easier to align than, for example, a prism pair.

In the measuring device according to the present invention,
The delay optical system may include a reflection mirror that returns the second optical pulse that has passed through the diffraction grating pair to the diffraction grating pair.

  In such a measuring apparatus, the delay optical system can change the optical path length according to the wavelength of the second optical pulse by using a diffraction grating pair.

In the measuring device according to the present invention,
The delay optical system may include two diffraction grating pairs.

  In such a measuring apparatus, the delay optical system can change the optical path length according to the wavelength of the second optical pulse by using two diffraction grating pairs.

In the measuring device according to the present invention,
The delay optical system may include a chirp mirror.

  In such a measurement apparatus, the delay optical system can change the optical path length according to the wavelength of the second optical pulse by using a chirp mirror. The chirped mirror can easily change the optical properties by adjusting the film thicknesses of the high refractive index layer and the low refractive index layer, for example. Therefore, in such a measuring device, the degree of freedom in design can be increased by using a chirp mirror as the delay optical system.

The figure which shows typically the structure of the measuring device which concerns on this embodiment. The top view which shows typically the terahertz wave generation part of the measuring device which concerns on this embodiment. The top view which shows typically the terahertz wave detection part of the measuring device which concerns on this embodiment. The figure for demonstrating the structure of the optical pulse generation part of the measuring device which concerns on this embodiment. The perspective view which shows typically the light source of the multiwavelength output part of the measuring device which concerns on this embodiment. Sectional drawing which shows typically the light source of the multiwavelength output part of the measuring device which concerns on this embodiment. Explanatory drawing of the acquisition method of the terahertz wave time waveform of the measuring device which concerns on this embodiment. The figure which shows typically the measuring device which concerns on the 1st modification of this embodiment. The figure which shows typically the measuring device which concerns on the 2nd modification of this embodiment. The figure which shows typically the measuring device which concerns on the 3rd modification of this embodiment. The figure which shows typically the measuring device which concerns on the 4th modification of this embodiment. Sectional drawing which shows a chirp mirror typically.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. The embodiments described below do not unduly limit the contents of the present invention described in the claims. In addition, not all of the configurations described below are essential constituent requirements of the present invention.

1. Measurement Device First, the configuration of the measurement device 100 according to the present embodiment will be described with reference to the drawings. FIG. 1 is a diagram schematically illustrating a configuration of a measurement apparatus 100 according to the present embodiment.

  In the measurement apparatus 100, measurement is performed using terahertz time domain spectroscopy (THz-TDS). Terahertz time-domain spectroscopy is a method in which a terahertz wave is incident on a sample S, a waveform of a terahertz wave after being transmitted or reflected by the sample S is time-resolved measurement, and the waveform is subjected to Fourier transform to thereby determine the amplitude and phase for each frequency. Is a spectroscopic method of obtaining Here, the terahertz wave means an electromagnetic wave having a frequency of 100 GHz to 30 THz, particularly an electromagnetic wave of 300 GHz to 10 THz.

  As illustrated in FIG. 1, the measurement apparatus 100 includes an optical pulse generation unit 10, an optical pulse branching unit 20, a terahertz wave generation unit 30, a delay optical system 40, and a terahertz wave detection unit 50. Measuring device 100 further includes mirrors 60, 62, 64, 66, 68, 70, 72.

The optical pulse generator 10 can generate a plurality of optical pulses (laser light) having different wavelengths. The optical pulse generation unit 10 sequentially emits optical pulses having different wavelengths at predetermined time intervals. Here, the light pulse refers to light whose intensity changes sharply in a short time. The pulse width of the optical pulse generated by the optical pulse generator 10 is, for example, 1 fs (femtoseconds) or more and 800 fs or less. The configuration of the optical pulse generator 10 will be described later. The light pulse emitted from the light pulse generation unit 10 enters the light pulse branching unit 20.

  The optical pulse branching unit (beam splitter) 20 branches the optical pulse generated by the optical pulse generating unit 10 into pump light (first optical pulse) L1 and probe light (second optical pulse) L2. That is, the optical pulse generated by the optical pulse generation unit 10 is divided into the pump light L1 and the probe light L2 by the optical pulse branching unit 20. In the illustrated example, the optical pulse branching unit 20 reflects a part of the optical pulse emitted from the optical pulse generation unit 10 as the pump light L1, and converts a part of the optical pulse emitted from the optical pulse generation unit 10. The probe light L2 is transmitted.

  The terahertz wave generation unit 30 is irradiated with the pump light L1 branched by the optical pulse branching unit 20 to generate a terahertz wave. In the illustrated example, the pump light L <b> 1 branched by the optical pulse branching unit 20 is reflected by the mirror 60 and enters the terahertz wave generation unit 30. The terahertz wave generation unit 30 is, for example, a photo conductive antenna (Photo Conductive Antenna, PCA). FIG. 2 is a plan view schematically showing the terahertz wave generation unit 30. The terahertz wave generation unit 30 is a dipole photoconductive antenna in the example of FIG.

  The terahertz wave generation unit 30 includes a substrate 32 and a pair of electrodes 36 and 38 provided on the substrate 32. The substrate 32 includes, for example, a semi-insulating GaAs (SI-GaAs) substrate and a low temperature growth GaAs (LT-GaAs) layer provided on the SI-GaAs substrate. The pair of electrodes 36 and 38 are disposed to face each other with the gap 34 interposed therebetween. The distance between the pair of electrodes 36 and 38 is appropriately set, and is, for example, 1 μm or more and 10 μm or less. The material of the electrodes 36 and 38 is, for example, Au.

  In the terahertz wave generating unit 30, free electrons are excited by irradiating the gap 34 with the pump light L <b> 1. The free electrons are accelerated by applying a voltage between the electrodes 36 and 38. Thereby, a terahertz wave is generated.

  The mirrors 62 and 64 are optical elements for guiding the terahertz wave generated by the terahertz wave generating unit 30 to the sample S as shown in FIG. The mirrors 62 and 64 are, for example, elliptical mirrors, parabolic mirrors, and the like.

  The mirrors 66 and 68 are optical elements for guiding the terahertz wave that has been irradiated and transmitted through the sample S to the terahertz wave detection unit 50. The mirrors 66 and 68 are, for example, an elliptical mirror, a parabolic mirror, and the like.

  The delay optical system 40 is configured such that the optical path length of the probe light L2 from the optical pulse branching unit 20 to the terahertz wave detecting unit 50 changes according to the wavelength of the probe light L2. In the delay optical system 40, the optical path length of the probe light L2 is changed according to the wavelength to cause an optical time delay in the probe light L2, and the timing at which the probe light L2 enters the terahertz wave detection unit 50 is controlled. To do.

  In the illustrated example, the delay optical system 40 is an optical system including two prism pairs (prism pairs) 42 and 44. The two prism pairs 42 and 44 are arranged symmetrically (plane symmetry).

  The first prism pair 42 includes a first prism 42a and a second prism 42b. The second prism pair 44 includes a third prism 44a and a fourth prism 44b.

  The first to fourth prisms 42a, 42b, 44a, 44b have the property of being largely refracted (diffracted) as the wavelength of incident light is shorter. The optical properties (shape, refractive index, etc.) of the first to fourth prisms 42a, 42b, 44a, 44b are equal, for example.

In the delay optical system 40, the probe light L2 passes through the first prism 42a, the second prism 42b, the third prism 44a, and the fourth prism 44b in this order, so that the probe light L2 corresponds to the wavelength of the probe light L2. The optical path length (so-called optical distance) changes. For example, in the delay optical system 40, the optical path length when the wavelength of the probe light L2 is λ1 (the optical path length from entering the first prism 42a to exiting from the fourth prism 44b) is L _λ1 , and the probe light the wavelength of L2 is an optical path length when the λ2 (λ1 <λ2) and L _.lambda.2, holds the relationship of _L λ1 <L λ2. In the delay optical system 40, the optical path difference is given to the probe light L2 having different wavelengths by utilizing the wavelength dependence of the refraction angle by the two prism pairs 42 and 44.

  Specifically, in the first prism 42a, the short wavelength probe light L2 (λ1) is refracted more than the long wavelength probe light L2 (λ2). In the second prism 42b, similarly to the first prism 42a, the short wavelength probe light L2 (λ1) is refracted more than the long wavelength probe light L2 (λ2). Thus, the traveling direction of the short wavelength probe light L2 (λ1) and the traveling direction of the long wavelength probe light L2 (λ2) are the same direction.

  Similarly, in the second prism pair 44, in the third prism 44a, the short wavelength probe light L2 (λ1) is refracted more than the long wavelength probe light L2 (λ2). In the fourth prism 44b, similarly to the third prism 44a, the short-wavelength probe light L2 (λ1) is refracted more than the long-wavelength probe light L2 (λ2). Thus, the traveling direction of the short wavelength probe light L2 (λ1) and the traveling direction of the long wavelength probe light L2 (λ2) are the same direction, and the short wavelength probe light L2 (emitted from the fourth prism 44b) λ1) and the long-wavelength probe light L2 (λ2) take the same optical path.

  Here, the long-wavelength probe light L2 (λ2) has a larger geometric distance on the optical path propagating through the second prism 42b than the short-wavelength probe light L2 (λ1). Similarly, the long-wavelength probe light L2 (λ2) has a larger geometric distance on the optical path propagating through the third prism 44a than the short-wavelength probe light L2 (λ1). For this reason, the geometric distance on the optical path in the delay optical system 40 is larger for the short-wavelength probe light (λ1) than for the long-wavelength probe light L2 (λ2). Is shorter for the short-wavelength probe light (λ1) than for the long-wavelength probe light L2 (λ2).

  In this way, in the delay optical system 40, the optical path length is changed by the two prism pairs 42 and 44 in accordance with the wavelength of the probe light L2. For example, in order to increase the optical path difference according to the wavelength, the optical distance between the first prism 42a and the second prism 42b (the optical distance between the third prism 44a and the fourth prism 44b) is set. Just make it bigger.

  In the present embodiment, the delay optical system 40 is provided on the optical path of the probe light L2 to control the timing of incidence on the terahertz wave detection unit 50. In other words, the delay optical system 40 changes the relative optical path length difference between the probe light L2 and the pump light L1. However, the configuration of the present embodiment is not limited as long as the relative optical path length difference between the probe light L2 and the pump light L1 can be changed. That is, the delay optical system 40 may be provided on the optical path of the pump light L1, and the optical path length of the pump light L1 may be changed. Further, the delay optical system 40 may be provided on both the optical path of the probe light L2 and the optical path of the pump light L1, and the difference between the relative optical path lengths may be changed while changing the optical path lengths of both. .

  The mirrors 70 and 72 are optical elements for guiding the probe light L <b> 2 delayed by the delay optical system 40 to the terahertz wave detection unit 50.

  The terahertz wave detection unit 50 is irradiated with the terahertz wave that has been irradiated and transmitted through the sample S to be measured and the probe light L2. The terahertz wave detection unit 50 is, for example, a photoconductive antenna. FIG. 3 is a plan view schematically showing the terahertz wave detection unit 50. The terahertz wave detection unit 50 is a dipole photoconductive antenna in the example of FIG.

  The terahertz wave detection unit 50 includes a substrate 52 and a pair of electrodes 56 and 58 provided on the substrate 52. The substrate 52 includes, for example, a semi-insulating GaAs (SI-GaAs) substrate and a low temperature growth GaAs (LT-GaAs) layer provided on the SI-GaAs substrate. The pair of electrodes 56 and 58 are arranged to face each other with a gap 54 interposed therebetween. The distance between the pair of electrodes 56 and 58 is appropriately set, and is, for example, 1 μm or more and 10 μm or less. The material of the electrodes 56 and 58 is, for example, Au.

  In the terahertz wave detection unit 50, a terahertz wave that has passed through the sample S is irradiated to the gap 54 from the surface (surface on which the electrodes 56 and 58 are formed) side of the substrate 52, and the gap 54 is probed from the back surface side of the substrate 52. Light L2 is irradiated. Since the carriers generated in the substrate 52 by the probe light L2 are accelerated by the oscillating electric field accompanying the terahertz wave, a current proportional to the oscillating electric field of the terahertz wave flows. That is, in the terahertz wave detection unit 50, when the terahertz wave and the probe light L <b> 2 are simultaneously irradiated between the electrodes 56 and 58, a current corresponding to the intensity (oscillation electric field) of the irradiated terahertz wave is generated. Flowing into. By measuring this current with an ammeter connected to the electrodes 56 and 58, the intensity of the oscillating electric field of the terahertz wave can be measured.

  Note that the above-described terahertz wave generation unit 30 and terahertz wave detection unit 50 are not limited to a photoconductive antenna (PCA). For example, the terahertz wave generation unit 30 and the terahertz wave detection unit 50 may be a system using a nonlinear optical crystal.

  Next, the configuration of the optical pulse generator 10 will be described.

  FIG. 4 is a diagram for explaining the configuration of the optical pulse generator 10. As illustrated in FIG. 4, the optical pulse generation unit 10 includes a multi-wavelength output unit 12, an optical switching unit 16, and a control unit 18.

  The multi-wavelength output unit 12 outputs a plurality of optical pulses having different wavelengths. The multi-wavelength output unit 12 includes a plurality (n (n is a natural number of 2 or more)) of light sources (first light source 12-1, second light source 12-2, third light source 12-3,..., Nth Light source 12-n). The n light sources 12-1 to 12-n output optical pulses having different wavelengths. For example, the n light sources 12-1 to 12-n are in the order of the first light source 12-1, the second light source 12-2, the third light source 12-3,. The wavelength of the generated light pulse is long. That is, among the first to nth light sources 12-1 to 12-n, the wavelength of the light pulse output from the first light source 12-1 is the longest, and the wavelength of the light pulse output from the nth light source 12-n. Is the shortest. The pulse width of the pulsed light output from the n light sources 12-1 to 12-n is, for example, not less than 1 fs and not more than 800 fs. For example, the pulse widths of the pulses output from the light sources 12-1 to 12-n are equal. The configuration of each of the light sources 12-1 to 12-n will be described later.

The optical switching unit 16 is connected to the light sources 12-1 to 12-n constituting the multi-wavelength output unit 12. The optical switching unit 16 selects and outputs one of the n light sources 12-1 to 12-n based on the wavelength control signal input from the control unit 18. As the optical switching unit 16, for example, an N × 1 optical switch based on an electro-optic effect or an acousto-optic effect is used. In the optical pulse generation unit 10, the optical switching unit 16 can electrically switch and output the wavelength of the optical pulse.

  The control unit 18 sends a wavelength control signal to the optical switching unit 16 so that the wavelength of the optical pulse output from the optical pulse generation unit 10 continuously changes. For example, the control unit 18 includes the first light source 12-1, the second light source 12-2, the third light source 12-3,..., And the nth light source 12-n in the order of the light sources 12-1 to 12-n. The optical switching unit 16 is controlled so as to select and output the optical pulse. As a result, the optical pulse generator 10 sequentially outputs optical pulses having different wavelengths.

  Here, the light sources 12-1 to 12-n constituting the multi-wavelength output unit 12 will be described. Each of the light sources 12-1 to 12-n includes a short light pulse generator. FIG. 5 is a perspective view schematically showing an example of the short optical pulse generator 1 that becomes each of the light sources 12-1 to 12-n of the multi-wavelength output unit 12. 6 is a cross-sectional view taken along the line VI-VI in FIG. 5 schematically showing the short optical pulse generator 1.

  As shown in FIGS. 5 and 6, the short optical pulse generator 1 includes a pulse source 2 that generates an optical pulse, a frequency chirp unit 4 that applies a frequency chirp to the optical pulse, and an optical pulse that is provided with a frequency chirp. And a group velocity dispersion unit 6 for generating a group velocity difference corresponding to the wavelength.

  The pulse source 2 generates an optical pulse. The pulse width (full width at half maximum FWHM) of the optical pulse generated by the pulse source 2 is not particularly limited, and is, for example, 1 ps (picoseconds) or more and 100 ps or less. The pulse source 2 is, for example, a semiconductor laser having a quantum well structure (first core layer 108), and is a DFB (Distributed Feedback) laser in the illustrated example. The pulse source 2 may be a semiconductor laser such as a DBR laser or a mode-locked laser, for example. Further, the pulse source 2 is not limited to a semiconductor laser, and may be a super luminescent diode (SLD), for example. The optical pulse generated by the pulse source 2 propagates through the optical waveguide 8 composed of the first cladding layer 106, the first core layer 108, and the second cladding layer 110.

  The frequency chirp unit 4 imparts a frequency chirp to the optical pulse generated by the pulse source 2. The frequency chirp portion 4 is made of, for example, a semiconductor material and has a quantum well structure. In the illustrated example, the frequency chirp portion 4 includes a first core layer 108 having a quantum well structure. When the optical pulse propagates through the optical waveguide 8 of the frequency chirped portion 4, the refractive index of the optical waveguide material changes due to the optical Kerr effect, and the phase of the electric field changes (self-phase modulation effect). Due to this self-phase modulation effect, a frequency chirp is imparted to the optical pulse. Here, frequency chirp refers to a phenomenon in which the frequency of an optical pulse changes with time.

  Since the frequency chirp portion 4 is made of a semiconductor material, the response speed is slow with respect to an optical pulse having a pulse width of about 1 ps to 100 ps. Therefore, in the frequency chirp unit 4, a frequency chirp (up chirp or down chirp) proportional to the intensity of the optical pulse (the square of the electric field amplitude) is given to the optical pulse. Here, up-chirp means that the frequency of the optical pulse increases with time, and down-chirp means that the frequency of the optical pulse decreases with time. In other words, up-chirp refers to the case where the wavelength of the optical pulse decreases with time, and down-chirp refers to the case where the wavelength of the optical pulse increases with time.

The group velocity dispersion unit 6 generates a group velocity difference corresponding to the wavelength (frequency) for the optical pulse to which the frequency chirp is applied. Specifically, the group velocity dispersion unit 6 can generate a group velocity difference such that the pulse width of the optical pulse is reduced with respect to the optical pulse to which the frequency chirp is applied (pulse compression). For example, the group velocity dispersion unit 6 can reduce the pulse width by causing negative group velocity dispersion (abnormal dispersion) in the up-chirped optical pulse.

  Further, the group velocity dispersion unit 6 can reduce the pulse width by causing positive group velocity dispersion in the down-chirped optical pulse. The pulse width of the light pulse compressed by the group velocity dispersion unit 6 is not particularly limited, but is, for example, 1 fs (femtosecond) or more and 800 fs or less.

  The group velocity dispersion unit 6 has two optical waveguides 8 and 9 arranged at a distance for mode coupling. That is, the two optical waveguides 8 and 9 constitute a so-called coupled waveguide. Note that the mode coupling distance is a distance at which light propagating through the optical waveguide 8 and the optical waveguide 9 can travel back and forth. In the group velocity dispersion unit 6, a large group velocity difference can be generated by mode coupling in the two optical waveguides 8 and 9.

  Next, the structure of the short light pulse generator 1 will be described. In the short optical pulse generator 1, a pulse source 2, a frequency chirp unit 4, and a group velocity dispersion unit 6 are provided on the same substrate 102.

  The short optical pulse generator 1 includes a substrate 102, a buffer layer 104, a first cladding layer 106, a first core layer 108, a second cladding layer 110, a cap layer 112, a second core layer 114, The third clad layer 116, the cap layer 118, the insulating layers 120 and 122, the first electrode 130, and the second electrode 132 are configured.

  The substrate 102 is, for example, a first conductivity type (for example, n-type) GaAs substrate. The substrate 102 has a first region 102a where the pulse source 2 is formed, a second region 102b where the frequency chirp portion 4 is formed, and a third region 102c where the group velocity dispersion portion 6 is formed. Yes.

  The buffer layer 104 is provided on the substrate 102. The buffer layer 104 is, for example, an n-type GaAs layer.

  The first cladding layer 106 is provided on the buffer layer 104. The first cladding layer 106 is, for example, an n-type AlGaAs layer.

  The first guide layer 108 a is provided on the first cladding layer 106. The first guide layer 108a is, for example, an i-type AlGaAs layer.

  The MQW layer 108b is provided on the first guide layer 108a. The MQW layer 108b has a multiple quantum well structure in which, for example, three quantum well structures each composed of a GaAs well layer and an AlGaAs barrier layer are stacked. In the illustrated example, the MQW layer 108b has the same number of quantum wells (the number of stacked GaAs well layers and AlGaAs barrier layers) above the first to third regions 102a to 102c. Note that the number of quantum wells of the MQW layer 108b above the first region 102a, the number of quantum wells of the MQW layer 108b above the second region 102b, and the number of quantum wells of the MQW layer 108b above the third region 102c are as follows. , May be different.

The second guide layer 108c is provided on the MQW layer 108b. The second guide layer 108c is, for example, an i-type AlGaAs layer. The second guide layer 108c is provided with a periodic structure constituting a DFB type resonator. The periodic structure is provided above the first region 102a. The periodic structure is composed of two layers 108c and 110 having different refractive indexes. The first guide layer 108a, the MQW layer 108b, and the second guide layer 108c can constitute the first core layer 108 that propagates light (light pulse) generated in the MQW layer 108b.

  The second cladding layer 110 is provided on the first core layer 108. The second cladding layer 110 is, for example, a second conductivity type (for example, p-type) AlGaAs layer.

  In the illustrated example, the optical waveguide 8 is configured by the first cladding layer 106, the first core layer 108, and the second cladding layer 110. The optical waveguide 8 extends from the end surface 109a of the first core layer 108 to the end surface 109b of the first core layer 108 opposite to the end surface 109a.

  In the pulse source 2, when a forward bias voltage of a pin diode is applied between the first electrode 130 and the second electrode 132, recombination of electrons and holes occurs in the first core layer 108 (MQW layer 108b). . This recombination causes light emission. Starting from the generated light (light pulse), stimulated emission occurs in a chain, and the intensity of light (light pulse) is amplified in the optical waveguide 8.

  The buffer layer 104, the first cladding layer 106, the first core layer 108, and the second cladding layer 110 are provided over the first region 102a, the second region 102b, and the third region 102c of the substrate 102. That is, these layers 104, 106, 108, 110 are layers that are common to the pulse source 2, the frequency chirp unit 4, and the group velocity dispersion unit 6, and are continuous layers. The optical waveguide 8 includes a first cladding layer 106, a first core layer 108, and a second cladding layer 110 that are continuous in the pulse source 2, the frequency chirp unit 4, and the group velocity dispersion unit 6.

  The cap layer 112 is provided on the second cladding layer 110 and above the first region 102 a and the second region 102 b of the substrate 102. The cap layer 112 can be in ohmic contact with the second electrode 132. The cap layer 112 is, for example, a p-type GaAs layer.

  The cap layer 112 and a part of the second cladding layer 110 provided above the first region 102a and the second region 102b constitute a columnar portion 111a. For example, in the pulse source 2, the current path between the electrodes 130 and 132 is determined by the planar shape viewed from the stacking direction of each layer of the columnar portion 111 a.

As shown in FIG. 5, the insulating layer 120 is provided on the second cladding layer 110 and on the side of the columnar portion 111a. Further, the insulating layer 120 is provided on the cap layer 112 above the second region 102b. The insulating layer 120 is, for example, a SiN layer, a SiO ₂ layer, a SiON layer, an Al ₂ O ₃ layer, a polyimide layer, or the like.

  The first electrode 130 is provided on the entire lower surface of the substrate 102. The first electrode 130 is in contact with a layer (the substrate 102 in the illustrated example) that is in ohmic contact with the first electrode 130. The first electrode 130 is electrically connected to the first cladding layer 106 via the substrate 102. The first electrode 130 is one electrode for driving the pulse source 2. As the first electrode 130, for example, a layer in which a Cr layer, an AuGe layer, a Ni layer, and an Au layer are stacked in this order from the substrate 102 side can be used. Note that the first electrode 130 may be provided only below the first region 102 a of the substrate 102.

The second electrode 132 is provided on the upper surface of the cap layer 112 and above the first region 102a. Further, the second electrode 132 may be provided on the insulating layer 120. The second electrode 132 is electrically connected to the second cladding layer 110 through the cap layer 112. The second electrode 132 is the other electrode for driving the pulse source 2. As the second electrode 132, for example, a layer in which a Cr layer, an AuZn layer, and an Au layer are stacked in this order from the cap layer 112 side can be used.

  The second core layer 114 is provided on the second cladding layer 110. More specifically, the second core layer 114 is provided on the second cladding layer 110 and above the third region 102c. The second core layer 114 is, for example, an i-type AlGaAs layer.

  The third cladding layer 116 is provided on the second core layer 114. The third cladding layer 116 is, for example, an n-type AlGaAs layer.

  In the illustrated example, the optical waveguide 9 is constituted by the second cladding layer 110, the second core layer 114, and the third cladding layer 116.

  The optical waveguide 8 and the optical waveguide 9 are arranged at a distance for mode coupling. That is, the optical waveguide 8 and the optical waveguide 9 constitute a coupled waveguide.

  The cap layer 118 is provided on the third cladding layer 116. The cap layer 118 is, for example, an n-type GaAs layer. The cap layer 118 and a part of the third cladding layer 116 form a columnar part 111b.

As shown in FIG. 5, the insulating layer 122 is provided on the third cladding layer 116 and on the side of the columnar portion 111 b. Furthermore, the insulating layer 122 is provided on the cap layer 118. The insulating layer 122 is, for example, a SiN layer, a SiO ₂ layer, a SiON layer, an Al ₂ O ₃ layer, a polyimide layer, or the like.

  Here, the light sources 12-1 to 12-n constituting the multi-wavelength output unit 12 have different wavelengths of laser light output from the pulse source 2 (DFB laser) of the short light pulse generator 1 described above. Yes. That is, the light sources 12-1 to 12-n constituting the multi-wavelength output unit 12 have different periods of the periodic structure constituting the DFB type resonator. Thereby, each light source 12-1 to 12-n of the multi-wavelength output unit 12 can output optical pulses having different wavelengths.

2. Operation of Measuring Device Next, the operation of the measuring device 100 will be described. FIG. 7 is a diagram for explaining a method for acquiring a time waveform of a terahertz wave (signal light) in the measurement apparatus 100.

  In the optical pulse generator 10, first, the controller 18 sends a wavelength control signal to the optical switching unit 16 so that the optical pulse generated by the first light source 12-1 is selected. As a result, the optical pulse generated by the first light source 12-1 is emitted from the optical pulse generator 10. The first light source 12-1 is a light source that generates an optical pulse having the longest wavelength in the multi-wavelength output unit 12.

The light pulse emitted from the light pulse generation unit 10 is divided into the pump light L1 and the probe light L2 by the light pulse branching unit 20. The pump light L <b> 1 irradiates the terahertz wave generation unit 30 through the mirror 60. Thereby, a terahertz wave is generated from the terahertz wave generation unit 30. The terahertz wave generated by the terahertz wave generation unit 30 irradiates the sample S via the mirrors 62 and 64. Then, the terahertz wave transmitted through the sample S irradiates the terahertz wave detection unit 50 through the mirrors 66 and 68.

  On the other hand, the probe light L <b> 2 divided by the optical pulse branching unit 20 enters the delay optical system 40. In the delay optical system 40, the probe light L2 is given an optical path length corresponding to the wavelength, and an optical time delay occurs between the probe light L2 and the pump light L1. The probe light L <b> 2 emitted from the delay optical system 40 irradiates the terahertz wave detection unit 50 through the mirrors 70 and 72. Thereby, the terahertz wave detection unit 50 can detect the terahertz wave with a delay time corresponding to the optical path difference between the pump light L1 and the probe light L2.

  Here, in the optical pulse generation unit 10, the control unit 18 includes an optical switching unit 16 in which the first light source 12-1, the second light source 12-2, the third light source 12-3,. The optical switching unit 16 is controlled so as to select and output the optical pulses of the light sources 12-1 to 12-n in the order of n. That is, since the wavelength of the light pulse emitted from the light pulse generation unit 10 continuously changes (the wavelength continuously decreases), the optical path length of the probe light L2 continuously changes in the delay optical system 40. (Continuously longer optical path length). Therefore, the delay time corresponding to the optical path difference between the pump light L1 and the probe light L2 continuously changes (the delay time continuously increases).

  Since the terahertz wave detection unit 50 detects the terahertz wave with a delay time corresponding to the optical path difference between the pump light L1 and the probe light L2 as described above, as shown in FIG. 7, different positions (phases) of the terahertz wave are detected. ), A signal (current) corresponding to the intensity (vibration electric field) of the terahertz wave can be acquired. By plotting this signal, the time course of the terahertz wave is recorded, and a time waveform of the terahertz wave having the horizontal axis indicating the time of the probe light L2 and the vertical axis indicating the signal intensity (current value) is obtained.

  Further, by moving a stage (not shown) that supports the sample S, the irradiation region of the terahertz wave in the sample S is changed, and the time waveform of the terahertz wave is acquired for each region, thereby imaging the sample S It can be performed.

  As described above, since the wavelength of the optical pulse emitted from the optical pulse generator 10 changes, the wavelength of the pump light L1 also changes. That is, the wavelength of the pump light L1 irradiated to the terahertz wave generation unit 30 changes. The following equation is a PCA theoretical equation.

Here, E _THz represents a terahertz electromagnetic wave, and J is a current that flows when a femtosecond laser is irradiated. Also, μ ₀ is the permeability in vacuum, R is the reflectance, q is the elementary charge, μ _e is the magnetic moment of the electron, E _bias is the applied bias, and h is the Planck constant. Ν is the frequency (c / λ), τ _c is the carrier lifetime, τ p is the excitation light pulse width, L _gap is the gap length, and w _gap is the gap width.

  In the above formula, it is the reflectance R and the frequency ν that have wavelength dependency. If it is assumed that the reflectance changes little with the wavelength, the terahertz wave electromagnetic wave intensity generated by the PCA depends on the wavelength.

  Therefore, the measurement apparatus 100 corrects the intensity of the time waveform of the terahertz wave obtained by the above-described method using, for example, the intensity distribution of the terahertz wave generated by the PCA with respect to the wavelength of the pump light L1. Here, the intensity distribution of the terahertz wave generated by the PCA with respect to the wavelength of the pump light L1 can be obtained by measuring the terahertz wave generated by the PCA by changing the wavelength of the pump light L1 without the sample S. it can. In addition, you may correct | amend the intensity | strength of the time waveform of a terahertz wave using said PCA theoretical formula.

  The measuring device 100 has the following features, for example.

  In the measuring apparatus 100, the optical pulse generation unit 10 generates optical pulses having a plurality of different wavelengths, and the delay optical system 40 probe light from the optical pulse branching unit 20 to the terahertz wave detection unit 50 according to the wavelength of the probe light L2. The optical path length of L2 is changed. Therefore, in the measuring apparatus 100, the optical path length of the probe light L2 can be changed electrically. Therefore, in the measurement apparatus 100, for example, the measurement time can be shortened compared to a case where the delay optical system mechanically moves the mirror to change the optical path length of the probe light. Therefore, for example, even when the measurement apparatus 100 performs imaging using THz-TDS, the total measurement time can be shortened.

  In the measurement apparatus 100, the delay optical system 40 includes two prism pairs 42 and 44. Thereby, in the delay optical system 40, the optical path length can be changed according to the wavelength of the probe light L2. In addition, the prism pairs 42 and 44 have a smaller light loss than other optical elements such as a diffraction grating pair. Therefore, the delay optical system 40 can efficiently delay the probe light L2.

3. Next, a modified example of the measuring apparatus according to the present embodiment will be described with reference to the drawings. In the measuring device (measuring device 200, 300, 400, 500) according to the modification of the present embodiment described below, members having the same functions as the constituent members of the measuring device 100 described above are denoted by the same reference numerals. Detailed description thereof will be omitted.

3.1. First Modification First, a measurement apparatus according to a first modification will be described with reference to the drawings. FIG. 8 is a diagram schematically illustrating a measuring apparatus 200 according to the first modification.

  In the measurement apparatus 100 described above, as shown in FIG. 1, the delay optical system 40 includes two prism pairs 42 and 44.

  On the other hand, in the measuring apparatus 200, as shown in FIG. 8, the delay optical system 40 includes one prism pair 42 and a mirror (reflection mirror) 210.

  The mirror 210 is an optical element for returning the probe light L <b> 2 that has passed through the prism pair 42 to the prism pair 42. The mirror 210 reflects the probe light L2 so as to return to the optical path from when the probe light L2 is incident on the first prism 42a until it reaches the mirror 210 through the second prism 42b. Therefore, in the delay optical system 40, the probe light L2 enters the first prism 42a, passes through the first prism 42a and the second prism 42b, is reflected by the mirror 210, and returns to the original path again. That is, the probe light L2 reflected by the mirror 210 passes through the second prism 42b and the first prism 42a and is emitted from the first prism 42a. Thereby, similarly to the optical system using the two prism pairs 42 and 44 shown in FIG. 1, the optical path length can be changed according to the wavelength of the probe light L2.

  In the measuring apparatus 200, the mirror 210 is tilted by a minute angle from a position perpendicular to the incident direction of the probe light L2, so that the optical path of the probe light L2 incident on the first prism 42a and the first prism 42a are emitted. The optical path of the probe light L2 can be shifted. Thereby, the delayed probe light L2 can be extracted from the delay optical system 40.

  The measuring device 200 further includes a mirror 220 for guiding the probe light L2 emitted from the first prism 42a to the mirror 70.

  Since the operation of the measuring device 200 is the same as the operation of the measuring device 100, description thereof is omitted.

  In the measuring apparatus 200, the delay optical system 40 includes a prism pair 42 and a mirror 210 that returns the probe light L2 that has passed through the prism pair 42 to the prism pair 42. Thereby, in the delay optical system 40, as described above, the optical path length can be changed according to the wavelength of the probe light L2. Further, in the measuring apparatus 200, for example, the number of prisms can be reduced as compared with a case where two prism pairs are used (see, for example, FIG. 1).

3.2. Second Modification Example Next, a measurement apparatus according to a second modification example will be described with reference to the drawings. FIG. 9 is a diagram schematically illustrating a measurement apparatus 300 according to the second modification.

  In the measurement apparatus 100 described above, as shown in FIG. 1, the delay optical system 40 includes two prism pairs 42 and 44.

  On the other hand, in the measuring apparatus 300, the delay optical system 40 includes diffraction grating pairs 310 and 312 as shown in FIG.

  The delay optical system 40 is an optical system including two diffraction grating pairs 310 and 312 in the illustrated example. The two diffraction grating pairs 310 and 312 are arranged symmetrically (plane symmetry).

  The first diffraction grating pair 310 includes a first diffraction grating 310a and a second diffraction grating 310b. The second diffraction grating pair 312 includes a third diffraction grating 312a and a fourth diffraction grating 312b.

The first to fourth diffraction gratings 310a, 310b, 312a, and 312b have a property of diffracting more as the wavelength of incident light is longer. The optical properties (the shape, the period of the grating, the magnitude of the diffraction angle with respect to the wavelength, etc.) of the first to fourth diffraction gratings 310a, 310b, 312a, 312b are equal, for example. The diffraction surface of the first diffraction grating 310a and the diffraction surface of the second diffraction grating 310b are, for example, parallel. Similarly, the diffraction surface of the third diffraction grating 312a and the diffraction surface of the fourth diffraction grating 312b are parallel, for example.

In the delay optical system 40, the probe light L2 is diffracted (reflected) in this order by the first diffraction grating 310a, the second diffraction grating 310b, the third diffraction grating 312a, and the fourth diffraction grating 312b. The optical path length of the probe light L2 changes according to the wavelength of. For example, in the delay optical system 40, the optical path length when the wavelength of the probe light L2 is λ1 (the optical path length from the incidence on the first diffraction grating 310a to the emission from the fourth diffraction grating 312b) is L _λ1 . when the wavelength of the probe light L2 is an optical path length when the λ2 (λ1 <λ2) and L _.lambda.2, holds the relationship of _L λ1 <L λ2. The delay optical system 40 uses the wavelength dependence of the diffraction angle (angle formed between the diffracted light and the diffraction grating normal) by the two diffraction grating pairs 310 and 312 to change the optical path difference with respect to the probe light L2 having different wavelengths. I'm wearing it.

  Specifically, in the first diffraction grating 310a, the long wavelength probe light L2 (λ2) has a larger diffraction angle than the short wavelength probe light L2 (λ1). Therefore, in the space between the first diffraction grating 310a and the second diffraction grating 310b, the long wavelength probe light L2 (λ2) propagates an optical distance longer than the short wavelength probe light L2 (λ1). Thereby, in the first diffraction grating pair 310, the optical path length of the long wavelength probe light L2 (λ2) is longer than the optical path length of the short wavelength probe light L2 (λ1). In the second diffraction grating 310b, similarly to the first diffraction grating 310a, the long-wavelength probe light L2 (λ2) has a larger diffraction angle than the short-wavelength probe light L2 (λ1). Thus, the traveling direction of the short wavelength probe light L2 (λ1) and the traveling direction of the long wavelength probe light L2 (λ2) are the same direction.

  Similarly, in the second diffraction grating pair 312, in the third diffraction grating 312a, the long-wavelength probe light L2 (λ2) has a larger diffraction angle than the short-wavelength probe light L2 (λ1). Therefore, in the space between the third diffraction grating 312a and the fourth diffraction grating 312b, the long wavelength probe light L2 (λ2) propagates a longer optical distance than the short wavelength probe light L2 (λ1). Thereby, in the second diffraction grating pair 312, the optical path length of the long wavelength probe light L2 (λ2) is longer than the optical path length of the short wavelength probe light L2 (λ1). In the fourth diffraction grating 312b, similarly to the third diffraction grating 312a, the long wavelength probe light L2 (λ2) has a larger diffraction angle than the short wavelength probe light L2 (λ1). As a result, the traveling direction of the short wavelength probe light L2 (λ1) and the traveling direction of the long wavelength probe light L2 (λ2) are the same direction, and the short wavelength probe light emitted from the fourth diffraction grating 312b. L2 (λ1) and the long-wavelength probe light L2 (λ2) take the same optical path.

  Thus, in the delay optical system 40, the optical path length is changed according to the wavelength of the probe light L2 by using the two diffraction grating pairs 310 and 312. For example, in order to increase the optical path difference according to the wavelength, the optical distance between the first diffraction grating 310a and the second diffraction grating 310b (the optical distance between the third diffraction grating 312a and the fourth diffraction grating 312b). Target distance) should be increased.

  Since the operation of the measuring device 300 is the same as that of the measuring device 100, the description thereof is omitted.

In the measuring apparatus 300, the delay optical system 40 includes two diffraction grating pairs 310 and 312. Thereby, in the delay optical system 40, as described above, the optical path length can be changed according to the wavelength of the probe light L2. Further, the diffraction grating pair 310, 312 is easier to align than, for example, a prism pair. Further, the optical properties of the diffraction gratings 310a, 310b, 312a, and 312b can be easily changed by changing the periodic structure of the diffraction grating. Therefore, in the measuring apparatus 300, the degree of freedom in design can be increased by using the diffraction grating pair 310 and 312 as the delay optical system 40.

3.3. Third Modification Next, a measurement apparatus according to a third modification will be described with reference to the drawings. FIG. 10 is a diagram schematically illustrating a measurement apparatus 400 according to the third modification.

  In the measurement apparatus 300 described above, as shown in FIG. 9, the delay optical system 40 includes two diffraction grating pairs 310 and 312.

  On the other hand, in the measuring apparatus 200, as shown in FIG. 10, the delay optical system 40 includes one diffraction grating pair 310 and a mirror (reflection mirror) 410.

  The mirror 410 is an optical element for returning the probe light L <b> 2 that has passed through the diffraction grating pair 310 to the diffraction grating pair 310. The mirror 410 reflects the probe light L2 so that the probe light L2 returns to the optical path from the time when the probe light L2 enters the first diffraction grating 310a until it is diffracted by the second diffraction grating 310b and reaches the mirror 410. Therefore, in the delay optical system 40, the probe light L2 enters the first diffraction grating 310a, is diffracted by the first diffraction grating 310a and the second diffraction grating 310b, is reflected by the mirror 410, and again returns to the original path. Return to. That is, the probe light L2 reflected by the mirror 410 is diffracted by the second diffraction grating 310b and the first diffraction grating 310a, and is emitted from the first diffraction grating 310a. Thereby, the optical path length can be changed according to the wavelength of the probe light L2, similarly to the optical system using the two diffraction grating pairs 310 and 312 shown in FIG.

  In the measuring apparatus 400, the mirror 410 is tilted by a minute angle from a position perpendicular to the incident direction of the probe light L2, thereby causing the optical path of the probe light L2 incident on the first diffraction grating 310a and the first diffraction grating 310a. The optical path of the emitted probe light L2 can be shifted. Thereby, the delayed probe light L2 can be extracted from the delay optical system 40.

  The measuring apparatus 400 further includes a mirror 420 for guiding the probe light L2 emitted from the first diffraction grating 310a to the mirror 70.

  Since the operation of the measuring device 400 is the same as the operation of the measuring device 300, the description thereof is omitted.

  In the measuring apparatus 400, the delay optical system 40 includes a diffraction grating pair 310 and a mirror 410 that returns the probe light L2 that has passed through the diffraction grating pair 310 to the diffraction grating pair 310. Thereby, in the delay optical system 40, as described above, the optical path length can be changed according to the wavelength of the probe light L2. Further, in the measuring apparatus 400, for example, the number of diffraction gratings can be reduced as compared with a case where two diffraction grating pairs are used (see, for example, FIG. 9).

3.4. Fourth Modification Example Next, a measurement apparatus according to a fourth modification example will be described with reference to the drawings. FIG. 11 is a diagram schematically illustrating a measurement apparatus 500 according to the fourth modification.

  In the measurement apparatus 100 described above, as shown in FIG. 1, the delay optical system 40 includes two prism pairs 42 and 44.

On the other hand, in the measuring apparatus 500, the delay optical system 40 includes chirp mirrors 510 and 512 as shown in FIG. The delay optical system 40 further includes mirrors 520 and 522.

  In the delay optical system 40, as shown in FIG. 11, the pair of the first chirp mirror 510 and the first mirror 520 and the pair of the second chirp mirror 512 and the second mirror 522 are symmetrical (plane symmetry). Has been placed. The reflective surface of the first chirp mirror 510 and the reflective surface of the first mirror 520 are, for example, parallel. Further, the reflection surface of the second chirp mirror 512 and the reflection surface of the second mirror 522 are parallel, for example.

  FIG. 12 is a cross-sectional view schematically showing the first chirp mirror 510. As shown in FIG. 12, the first chirp mirror 510 has a substrate 5000, a high refractive index layer 5010, and a low refractive index layer 5012. In the first chirp mirror 510, high refractive index layers 5010 and low refractive index layers 5012 are alternately stacked on the substrate 5000. The first chirp mirror 510 is a kind of dielectric multilayer mirror.

  In the first chirp mirror 510, the film to be reflected (depth from the mirror surface) differs according to the wavelength, and an optical path length according to the wavelength of the incident light can be given. In the example shown in the drawing, the film thicknesses of the stacked high refractive index layer 5010 and low refractive index layer 5012 are adjusted so that light having a longer wavelength is reflected by a deeper film (depth from the mirror surface). Therefore, in the first chirp mirror 510, the optical path length of the long-wavelength probe light L2 (λ2) is longer than the optical path length of the short-wavelength probe light L2 (λ1).

  The second chirp mirror 512 has the same configuration as the first chirp mirror 510 shown in FIG. That is, in the second chirp mirror 512, similarly to the first chirp mirror 510, the film to be reflected (depth from the mirror surface) differs according to the wavelength, and the optical path length according to the wavelength of the incident light is given. Can do. Note that both the first chirp mirror 510 and the second chirp mirror 512 may be designed such that light having a short wavelength is reflected by a deeper film, contrary to the example shown in FIG.

  The first mirror 520 and the second mirror 522 are mirrors for guiding the probe light L <b> 2 reflected by the first chirp mirror 510 to the second chirp mirror 512.

  In the delay optical system 40, the optical path difference is given to the probe light L2 having different wavelengths by using the two chirp mirrors 510 and 512.

  Specifically, in the first chirp mirror 510, since the longer wavelength light is reflected by the deeper film, the optical path length of the long wavelength probe light L2 (λ2) is the optical path length of the short wavelength probe light L2 (λ1). Longer than. The probe light L 2 reflected by the first chirp mirror 510 is incident on the second chirp mirror 512 via the mirrors 520 and 522. In the second chirp mirror 512, as the first chirp mirror 510 is reflected, the longer wavelength light is reflected by the deeper film. Therefore, the optical path length of the long wavelength probe light L2 (λ2) is the short wavelength probe light L2 ( It becomes longer than the optical path length of λ1).

  In this way, in the delay optical system 40, the optical path length is changed by the two chirp mirrors 510 and 512 in accordance with the wavelength of the probe light L2.

  Here, the chirp mirrors 510 and 512 reflect the longer wavelength light with a deeper film so that the optical path length of the long wavelength probe light L2 (λ2) is longer than the optical path length of the short wavelength probe light L2 (λ1). Although the case where the length is increased is described, the chirp mirrors 510 and 512 are reflected by a deeper film as the light has a shorter wavelength, and the optical path length of the long wavelength probe light L2 (λ2) is changed to the optical path length of the short wavelength probe light L2 (λ1). It may be shorter.

  Although the example in which the delay optical system 40 includes the two chirp mirrors 510 and 512 has been described here, the number of chirp mirrors constituting the delay optical system 40 is not particularly limited. For example, a chirp mirror may be arranged instead of the mirrors 520 and 522. That is, in this case, the delay optical system 40 has four chirp mirrors.

  In the measurement apparatus 500, the delay optical system 40 includes chirp mirrors 510 and 512. Thereby, in the delay optical system 40, as described above, the optical path length can be changed according to the wavelength of the probe light L2. In addition, the optical properties of the chirp mirrors 510 and 512 can be easily changed by adjusting the film thicknesses of the high refractive index layer 5010 and the low refractive index layer 5012. Therefore, in the measuring apparatus 500, the use of the chirp mirrors 510 and 512 as the delay optical system 40 can increase the degree of design freedom.

3.5. Fifth Modification In the example of the measurement apparatus 100 described above, the optical pulse generator 10 selects, with the optical switching unit 16, a plurality of optical pulses with different wavelengths output from the multi-wavelength output unit 12, as shown in FIG. In this modification, the optical pulse generator 10 has various configurations as long as it can generate a plurality of light pulses with different wavelengths. Can do.

  For example, in this modification, the wavelength may be changed by controlling the temperature of the short optical pulse generator 1 shown in FIGS. 5 and 6 to generate a plurality of optical pulses having different wavelengths.

  Specifically, in this modification, for example, a heating element (heater) for heating the short light pulse generator 1 and a cooling element (such as a Peltier element) for cooling the short light pulse generator 1 are provided. The wavelength of the light pulse is changed by controlling the heating element and the cooling element to change the amount of heat applied to the short light pulse generator 1. As a result, the optical pulse generator 10 can generate optical pulses having a plurality of different wavelengths.

  Further, for example, in this modification, a plurality of femtosecond fiber lasers or a plurality of titanium sapphire lasers that generate optical pulses having different wavelengths can be used instead of the light sources 12-1 to 12-n shown in FIG. Good. That is, the optical pulse generation unit 10 generates a plurality of optical pulses with different wavelengths by switching a plurality of femtosecond fiber lasers (or titanium sapphire lasers) that generate optical pulses with different wavelengths by the optical switching unit 16. Also good.

3.6. In the example of the measurement apparatus 100 described above, the terahertz wave generated by the terahertz wave generation unit 30 is irradiated to the sample S, and the terahertz wave transmitted through the sample S is detected by the terahertz wave detection unit 50. In the example, the terahertz wave generated by the terahertz wave generation unit 30 may be irradiated to the sample S, and the terahertz wave reflected from the sample S may be detected by the terahertz wave detection unit 50.

  The above-described embodiments and modifications are merely examples, and the present invention is not limited to these. For example, it is possible to appropriately combine the modified examples.

The present invention includes configurations that are substantially the same as the configurations described in the embodiments (for example, configurations that have the same functions, methods, and results, or configurations that have the same objects and effects). In addition, the invention includes a configuration in which a non-essential part of the configuration described in the embodiment is replaced. In addition, the present invention includes a configuration that exhibits the same operational effects as the configuration described in the embodiment or a configuration that can achieve the same object. Further, the invention includes a configuration in which a known technique is added to the configuration described in the embodiment.

DESCRIPTION OF SYMBOLS 1 ... Short light pulse generator, 2 ... Pulse source, 4 ... Frequency chirp part, 6 ... Group velocity dispersion | distribution part, 8, 9 ... Optical waveguide, 10 ... Optical pulse generation part, 12 ... Multi-wavelength output part, 16 ... Light Switching unit 18 ... Control unit 20 ... Optical pulse branching unit 30 ... Terahertz wave generating unit 32 ... Substrate 34 ... Gap 36,38 ... Electrode 40 ... Delay optical system 42 ... First prism pair 42a ... 1st prism, 42b ... 2nd prism, 44 ... 2nd prism pair, 44a ... 3rd prism, 44b ... 4th prism, 50 ... terahertz wave detection part, 52 ... board | substrate, 54 ... gap, 56, 58 ... electrode , 60, 62, 64, 66, 68, 70, 72 ... mirror, 100 ... measuring device, 102 ... substrate, 102 a ... first area, 102 b ... second area, 102 c ... third area, 104 ... buffer layer, 106 1st cladding layer, 108 ... 1st core layer, 108a ... 1st guide layer, 108b ... MQW layer, 108c ... 2nd guide layer, 109a, 109b ... end face, 110 ... 2nd cladding layer, 111a, 111b ... columnar part , 112 ... cap layer, 114 ... second core layer, 116 ... third cladding layer, 118 ... cap layer, 120, 122 ... insulating layer, 130 ... first electrode, 132 ... second electrode, 200 ... measuring device, 210 220 ... Mirror, 300 ... Measuring device, 310 ... First diffraction grating pair, 310a ... First diffraction grating, 310b ... Second diffraction grating, 312 ... Second diffraction grating pair, 312a ... Third diffraction grating, 312b ... First 4 diffraction gratings, 400 ... measuring device, 410, 420 ... mirror, 500 ... measuring device, 510 ... first chirp mirror, 512 ... second chirp mirror, 520 ... first mirror 522 ... second mirror, 5000 ... substrate, 5010 ... high refractive index layer, 5012 ... low-refractive index layer

Claims (8)

An optical pulse generator capable of generating a plurality of optical pulses of different wavelengths;
An optical pulse branching unit that branches the optical pulse generated by the optical pulse generation unit into a first optical pulse and a second optical pulse;
A terahertz wave generator that generates a terahertz wave by being irradiated with the first light pulse;
A terahertz wave detection unit that is irradiated with the second light pulse and the terahertz wave that is irradiated to the sample to be measured and transmitted or reflected;
The optical path length of the second optical pulse from the optical pulse branching unit to the terahertz wave detecting unit is obtained using the optical property that changes according to the wavelength without mechanical movement . A delay optical system configured to change according to the wavelength of the light pulse ;
A measuring device comprising:   The measuring apparatus according to claim 1, wherein the delay optical system includes a prism pair.   The measuring apparatus according to claim 2, wherein the delay optical system includes a reflection mirror that returns the second light pulse that has passed through the prism pair to the prism pair.   The measuring apparatus according to claim 2, wherein the delay optical system includes two prism pairs.   The measuring apparatus according to claim 1, wherein the delay optical system includes a diffraction grating pair.   The measurement apparatus according to claim 5, wherein the delay optical system includes a reflection mirror that returns the second optical pulse that has passed through the diffraction grating pair to the diffraction grating pair.   The measurement apparatus according to claim 5, wherein the delay optical system includes two diffraction grating pairs.   The measuring apparatus according to claim 1, wherein the delay optical system includes a chirp mirror.

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