JP2008134094A - Terahertz electromagnetic wave producing system and terahertz electromagnetic wave detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a terahertz electromagnetic wave producing device capable of producing a terahertz electromagnetic wave variable in frequency by a simple constitution. <P>SOLUTION: In the terahertz electromagnetic wave producing system 1, the laser beam L oscillated by a laser resonator, which is constituted of the second surface 112 of a semiconductive emission element 11 and a mirror 12, is collimated by a lens 14 to be condensed by a lens 15 and the condensed beam is thrown on the gap of a pair of the electrodes of a photoconductive antenna element 16. The terahertz electromagnetic wave is produced from the photoconductive antenna element 16 on which the laser beam L is thrown. The length of the resonator is altered by parallely moving the mirror 12 by a moving stage 13. The frequencny of the terahertz electromagnetic wave produced from the photoconductive antenna element 16 is continuously changed corresponding to the length of the resonator. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a terahertz electromagnetic wave generator and a terahertz electromagnetic wave detector.

  A terahertz electromagnetic wave is an electromagnetic wave having a frequency of about 0.01 THz to 100 THz corresponding to an intermediate region between a light wave and a radio wave, and has an intermediate property between the light wave and the radio wave. As an application of such a terahertz electromagnetic wave, a technique for acquiring information on the measurement object by measuring a time waveform of an electric field amplitude of the terahertz electromagnetic wave transmitted or reflected by the measurement object has been studied. In addition, technologies for generating and detecting terahertz electromagnetic waves have been studied.

  Patent Document 1 and Non-Patent Document 1 disclose a technique for generating terahertz electromagnetic waves by causing laser light output from a semiconductor laser light source to enter a photoconductive antenna element. In the terahertz electromagnetic wave generation techniques disclosed in these documents, the frequency spectrum of the generated terahertz electromagnetic wave is discrete and the peak frequency cannot be controlled.

On the other hand, the terahertz electromagnetic wave generation technology disclosed in Patent Document 2 prepares two resonators composed of an external resonant mirror and a semiconductor laser element, and two laser beams output from these two resonators are nonlinearly optical. A terahertz electromagnetic wave is generated by mixing the difference frequency in the material. The frequency of the terahertz electromagnetic wave can be changed by moving the external resonant mirror.
JP 2001-021503 A JP 2006-227433 A M. Tani, et al., "Multiple-Frequency Generation of Sub-Terahertz Radiation by Multimode LD Excitation of Photoconductive Antenna", IEEE Microwave and Guided Wave Lett., Vol. 7, No. 9, (1997) pp.282-284

  As described above, in the terahertz electromagnetic wave generation technology disclosed in Patent Document 1 and Non-Patent Document 1, the frequency spectrum of the generated terahertz electromagnetic wave is discrete, and the peak frequency cannot be controlled. On the other hand, although the terahertz electromagnetic wave generation technique disclosed in Patent Document 2 can control the frequency of the terahertz electromagnetic wave, there is a problem that the configuration for that is complicated.

  That is, the conventional terahertz electromagnetic wave generator cannot generate a terahertz electromagnetic wave having a variable frequency with a simple configuration. Further, a terahertz electromagnetic wave detection device that performs measurement using terahertz electromagnetic waves generated by such a terahertz electromagnetic wave generation device cannot perform highly accurate measurement with a simple configuration.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide a terahertz electromagnetic wave generator capable of generating a terahertz electromagnetic wave having a variable frequency with a simple configuration. It is another object of the present invention to provide a terahertz electromagnetic wave detection device capable of performing highly accurate measurement with a simple configuration.

  A terahertz electromagnetic wave generator according to the present invention includes: (1) a semiconductor light emitting device having an active layer sandwiched between a first surface and a second surface, and emitting light in the active layer; and (2) a semiconductor light emitting device A mirror provided opposite to the first surface and constituting a resonator with the second surface of the semiconductor light emitting element; (3) a resonator length changing means for changing a resonator length of the resonator; And a photoconductive antenna element for generation that has a pair of electrodes formed on a semiconductor substrate and inputs light output from the resonator between the pair of electrodes to generate a terahertz electromagnetic wave. It is characterized by.

  In this terahertz electromagnetic wave generator, a resonator is configured between a mirror provided facing the first surface of the semiconductor light emitting element and the second surface of the semiconductor light emitting element. In this resonator, light is stimulated and emitted from the active layer of the semiconductor light emitting device and oscillates to output laser light. The output laser light is incident between a pair of electrodes of the generating photoconductive antenna element. A terahertz electromagnetic wave is generated from the generating photoconductive antenna element on which the laser light is incident. Further, the resonator length of the resonator is changed by the resonator length changing means. The frequency of the terahertz electromagnetic wave generated by the generating photoconductive antenna element changes continuously according to the resonator length.

  In the terahertz electromagnetic wave generator according to the present invention, it is preferable that collimating means for collimating light traveling from the first surface of the semiconductor light emitting element toward the mirror is provided on the first surface. In this case, since the light emitted from the first surface of the semiconductor light emitting device is collimated by the collimating means, the light reflected by the mirror is maintained from the first surface of the semiconductor light emitting device while maintaining the waveguide mode. Re-enters. From this, even if the resonator length of the resonator is changed by the resonator length changing means, a laser resonator is always formed between the second surface of the semiconductor light emitting element and the mirror.

  In the terahertz electromagnetic wave generator according to the present invention, it is preferable that the semiconductor light emitting element is a vertical cavity surface emitting laser element. In this case, since the resonator length of the resonator formed by the second surface of the semiconductor light emitting element and the mirror can be shortened, the variable range of the frequency of the obtained terahertz electromagnetic wave can be expanded.

  A terahertz electromagnetic wave detection device according to the present invention includes (1) the terahertz electromagnetic wave generation device according to the present invention, and (2) light between the resonator included in the terahertz electromagnetic wave generation device and the photoconductive antenna element for generation. A branching section that is provided on the road and branches a part of the light output from the resonator and outputs it as probe light; (3) a terahertz electromagnetic wave output from the photoconductive antenna element for generation and transmitted or reflected by the measurement object And a detection unit that receives the probe light output from the branching unit and detects the correlation between the terahertz electromagnetic wave and the probe light.

  In this terahertz electromagnetic wave detection device, a part of the light output from the resonator is branched by a branch portion provided on the optical path between the resonator included in the terahertz electromagnetic wave generator and the photoconductive antenna element for generation. Is output as probe light. The terahertz electromagnetic wave output from the photoconductive antenna element for generation and transmitted or reflected by the object to be measured and the probe light output from the branching unit are input to the detection unit, and the correlation between the terahertz electromagnetic wave and the probe light is detected. Is done.

  The terahertz electromagnetic wave detection device according to the present invention includes any one of the optical path length of the terahertz electromagnetic wave from the generating photoconductive antenna element to the detection unit and the optical path length of the probe light from the branching unit to the detection unit. It is preferable to further include an optical path length adjusting unit for adjusting the above. In this case, the optical path length of the terahertz electromagnetic wave or the probe light is adjusted by the optical path length adjustment unit, so that the timing difference between the terahertz electromagnetic wave incident on the detection unit and the probe light can be adjusted.

  Moreover, in the terahertz electromagnetic wave detection device according to the present invention, the detection unit has a pair of electrodes formed on the semiconductor substrate, and the detection photoconductive device inputs the terahertz electromagnetic wave and the probe light between the pair of electrodes. It is preferable to include an antenna element. Further, the terahertz electromagnetic wave detection device according to the present invention includes (a) a signal generator that applies a sinusoidally modulated voltage between a pair of electrodes of the photoconductive antenna element for generation, and (b) a signal generator. A synchronization detector that detects a correlation between the terahertz electromagnetic wave and the probe light by synchronously detecting a current generated between the pair of electrodes of the photoconductive antenna element for detection based on the output sine wave modulated voltage; It is preferable to further include In this case, a sinusoidally modulated voltage is applied between the pair of electrodes of the generating photoconductive antenna element by the signal generator. The synchronization detector detects the current generated between the pair of electrodes of the photoconductive antenna element for detection based on the sine wave modulated voltage output from the signal generator, and detects the terahertz electromagnetic wave and the probe. Correlation with light is detected.

  The terahertz electromagnetic wave generator according to the present invention can generate a terahertz electromagnetic wave having a variable frequency with a simple configuration. In addition, the terahertz electromagnetic wave detection device according to the present invention can perform highly accurate measurement with a simple configuration.

  The best mode for carrying out the present invention will be described below in detail with reference to the accompanying drawings. In the description of the drawings, the same or equivalent elements are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a configuration diagram of a terahertz electromagnetic wave generator 1 according to the present embodiment. A terahertz electromagnetic wave generator 1 shown in this figure includes a semiconductor light emitting element 11, a mirror 12, a moving stage 13, a lens 14, a lens 15, and a photoconductive antenna element 16 for generating a terahertz electromagnetic wave.

  The semiconductor light emitting element 11 has an active layer sandwiched between a first surface 111 and a second surface 112, and emits light through the active layer, and is preferably a laser diode. The mirror 12 is provided to face the first surface 111 of the semiconductor light emitting element 11, and constitutes a resonator with the second surface 112 of the semiconductor light emitting element 11. That is, the first surface 111 of the semiconductor light emitting element 11 has a low reflectance, and the second surface 112 of the semiconductor light emitting element 11 has a high reflectance.

  The moving stage 13 translates the mirror 12 along the optical axis direction, and acts as a resonator length changing unit that changes the resonator length of the resonator. The moving stage 13 may be any of a motor driven type, a piezoelectric element type, a MEMS (Micro Electro Mechanical Systems) type, etc., or may be manually operated, or a combination thereof. It may be. The semiconductor light emitting element 11, the mirror 12 and the moving stage 13 constitute an external resonance type laser oscillator 3 capable of continuously changing the resonator length over a certain range.

  The lens 14 collimates the laser light L output from the laser oscillator 3. The lens 15 condenses the laser light L collimated by the lens 14 and irradiates the photoconductive antenna element 16. As shown in FIG. 2, the photoconductive antenna element 16 has a pair of electrodes formed on a semiconductor substrate, and inputs light output from the resonator between the pair of electrodes to generate a terahertz electromagnetic wave. T is generated.

  In the terahertz electromagnetic wave generator 1, in a laser resonator composed of the second surface 112 of the semiconductor light emitting element 11 and the mirror 12, light is stimulated and emitted from the active layer of the semiconductor light emitting element 11 and oscillates to emit laser light. Is output. The output laser light L is collimated by the lens 14, collected by the lens 15, and incident between the pair of electrodes of the photoconductive antenna element 16. Then, a terahertz electromagnetic wave is generated from the photoconductive antenna element 16 on which the laser beam L is incident. Further, the resonator length is changed by the parallel movement of the mirror 12 by the moving stage 13. The frequency of the terahertz electromagnetic wave generated by the photoconductive antenna element 16 continuously changes according to the resonator length.

  FIG. 2 is a perspective view of the photoconductive antenna element 100. The photoconductive antenna element 100 shown in this figure is used as the photoconductive antenna element 16 for generating terahertz electromagnetic waves in FIG. The photoconductive antenna element 100 is also used as a photoconductive antenna element 25 for detecting terahertz electromagnetic waves, which will be described later.

  The photoconductive antenna element 100 includes, for example, a semi-insulating GaAs substrate 101, a GaAs layer 102 formed on the GaAs substrate 101, and a pair of electrodes 103 and 104 formed on the GaAs layer 102. Have. The GaAs layer 102 is epitaxially grown at a low temperature (for example, 200 to 250 ° C.) by MBE, and has a thickness of 1 to 3 μm, for example. The electrode 103 and the electrode 104 are ohmic electrodes such as AuGe / Au, the length of the antenna is, for example, 20 μm to 2 mm, and the distance between them is, for example, 3 to 10 μm.

  The GaAs layer 102 formed by low temperature epitaxial growth has a short carrier lifetime, high carrier mobility, and high impedance. When a voltage is applied between the electrode 103 and the electrode 104 and the region of the GaAs layer 102 between the electrode 103 and the electrode 104 is irradiated with the laser light L, electron holes are generated in the GaAs layer 102. Pairs occur. The electrons move by being accelerated by a voltage applied between the electrode 103 and the electrode 104. Thereby, a current is generated between the electrode 103 and the electrode 104, and a terahertz electromagnetic wave T is generated.

FIG. 3 is a perspective view of the laser oscillator 3 including the semiconductor light emitting element 11 and the mirror 12 and having a variable resonator length. In addition, illustration of the movement stage 13 is abbreviate | omitted in this figure. The laser medium 101 of the semiconductor light emitting device 11 has an active layer formed by stacking hetero multilayer films made of, for example, a plurality of types of Al _x Ga _1-x As (0 ≦ x ≦ 1). The first surface 111 of the semiconductor light emitting element 11 facing the mirror 12 is coated with an antireflection film 113 made of Al ₃ O ₄ , SiO ₂ or the like or a multilayer film thereof. The second surface 112 of the semiconductor light emitting element 11 is coated with a highly reflective film 114 made of Al ₃ O ₄ , SiO ₂ or the like. The second surface 112 may be a mirror surface that has been cleaved.

  The antireflection film 113 on the first surface 111 is formed with a diffraction grating pattern 115 having a lens function as collimating means for collimating light traveling from the first surface 111 of the semiconductor light emitting element 11 toward the mirror 12. . Such a diffraction grating pattern 115 is generally put into practical use as a diffractive optical element (DOE). As a result, the reflectance on the first surface 111 is reduced, and collimated light is emitted from the first surface 111 toward the space.

  Since the light emitted from the first surface 111 of the semiconductor light emitting element 11 is collimated by the diffraction grating pattern 115, the light reflected by the mirror 12 is transmitted from the first surface 111 of the semiconductor light emitting element 11 while maintaining the waveguide mode. Re-enters the active layer. Therefore, even when the mirror 12 is translated by the moving stage 13, a laser resonator is always formed between the second surface 112 of the semiconductor light emitting element 11 and the mirror 12. Laser oscillation occurs when a forward current equal to or greater than a threshold value is applied to the semiconductor light emitting element 11, and the laser light L is emitted through the mirror 12.

  As the laser oscillator having a variable resonator length included in the terahertz electromagnetic wave generation device 1 according to the present embodiment, the configurations shown in FIGS. 4 to 7 are also preferable.

  FIG. 4 is a plan view showing another configuration example of the semiconductor light emitting element 11 included in the laser oscillator 3. Compared to the configuration shown in FIG. 3, the semiconductor light emitting device 11 shown in FIG. 4 does not have the diffraction grating pattern 115 provided on the antireflection film 113 formed on the first surface 111. The antireflection film 113 is different in that it also acts as a collimating means. That is, the antireflection film 113 has a convex lens shape, collimates light by the action of the convex lens, and emits the light to the outside. Such shape processing is performed by a highly controlled ion beam or the like.

  FIG. 5 is a plan view showing still another configuration example of the semiconductor light emitting element 11 included in the laser oscillator 3. Compared with the configuration shown in FIG. 3, the semiconductor light emitting device 11 shown in FIG. 5 does not have the diffraction grating pattern 115 provided on the antireflection film 113 formed on the first surface 111. The difference is that a convex lens-shaped resin 116 is formed on the antireflection film 113. This convex lens shaped resin 116 acts as collimating means, collimates the light and emits it to the outside. In general, when the resin is solidified, it automatically becomes convex due to surface tension. Therefore, in order to produce the resin 116 having such a shape that collimated light can be obtained, it is necessary to accurately control the viscosity and drying conditions of the resin 116.

  FIG. 6 is a perspective view showing another configuration example of the laser oscillator 3. Compared with the configuration shown in FIG. 3, the laser oscillator 3 shown in FIG. 6 is different in the light emission direction. That is, in the laser oscillator 3 shown in FIG. 6, the mirror 12 is a total reflection mirror, and the laser light L is emitted from the second surface 112 of the semiconductor light emitting element 11. In this configuration, since the shape and divergence angle of the laser light L emitted from the second surface 112 are constant, optical coupling with the optical components in the subsequent stage is facilitated, and a lens or the like provided on the light emission side is facilitated. The mirror 12 can be moved so as not to interfere with the optical components.

  FIG. 7 is a perspective view showing still another configuration example of the laser oscillator 3. The semiconductor light emitting devices shown in FIGS. 3 to 6 have been of the edge-emitting type, but the semiconductor light emitting device 11 included in the laser oscillator 3 shown in FIG. It is different in that it is a light emitting laser element (VCSEL: Vertical Cavity-Surface Emitting Laser). In the semiconductor light emitting element 11, the light reflectance of the first surface 111 facing the mirror 12 is formed to be small, and the surface of the first surface 111 is not given a special lens effect. . It is preferable that the light emitting unit 117 which is a light emitting region on the first surface 111 is larger than a normal VCSEL. As a result, a relatively large amount of light emitted from the light emitting unit 117 of the semiconductor light emitting element 117 and reflected by the mirror 12 can be incident again on the light emitting unit 117 of the semiconductor light emitting element 11 without passing through a lens. In addition, since the distance between the first surface 111 and the second surface 112 of the semiconductor light emitting element 11 is as short as several μm, the laser resonator constituted by the second surface 112 of the semiconductor light emitting element 11 and the mirror 12. Can be changed over a wide range from about 10 μm to several mm. As a result, the frequency of the terahertz electromagnetic wave generated by the photoconductive antenna element 16 can be changed in a very wide band. In addition, even when using a VCSEL having a large light emitting portion diameter as in the present embodiment, a lens may be provided between the light emitting element and the mirror in order to make the laser light re-enter the light emitting portion efficiently.

  Next, the relationship between the resonator length and the frequency of the terahertz electromagnetic wave in the terahertz electromagnetic wave generator 1 according to the present embodiment will be described. FIG. 8 is a diagram illustrating a spectrum of the terahertz electromagnetic wave generated in the terahertz electromagnetic wave generating device 1 according to the present embodiment. (A) shows the spectrum when the resonator length is 0.6 mm, (b) shows the spectrum when the resonator length is 0.75 mm, and (c) shows the spectrum. The spectrum when the resonator length is 1.0 mm is shown.

The resonator length is an effective optical path length considering the refractive index distribution on the optical path in the laser resonator constituted by the second surface 112 of the semiconductor light emitting element 11 and the mirror 12. That is, the distance between the first surface 111 of the semiconductor light emitting element 11 and the second surface 112 and _{L C,} the group refractive index of the semiconductor light emitting element 11 and _{n CG,} the first surface 111 of the semiconductor light emitting element 11 mirror When the distance from 12 is L _A , the resonator length L _cavity is expressed by the expression “L _cavity = n _CG · L _C + L _A ”.

  As shown in FIGS. 8A to 8C, regardless of the value of the resonator length, the spectrum of the generated terahertz electromagnetic wave includes the component of the fundamental frequency that is the lowest frequency, and its fundamental It has a component that is an integral multiple of the frequency. However, as can be seen by comparing FIGS. 8A to 8C, the longer the resonator length, the narrower the frequency interval.

  FIG. 9 is a graph showing the relationship between the resonator length and the fundamental frequency of the terahertz electromagnetic wave in the terahertz electromagnetic wave generator 1 according to the present embodiment. The vertical axis in the figure is the reciprocal of the fundamental frequency f of the terahertz electromagnetic wave. This figure shows the relationship of the fundamental frequency of the terahertz electromagnetic wave with respect to each value of the resonator length shown in FIGS. As shown in this figure, the reciprocal of the fundamental frequency f of the terahertz electromagnetic wave is proportional to the resonator length.

As described above, the terahertz electromagnetic wave generated by the terahertz electromagnetic wave generation device 1 according to the present embodiment has a discrete spectrum composed of a fundamental frequency component and an integral multiple frequency component, and the resonator length changes. The fundamental frequency component and the integral frequency component also change. Assuming that the speed of light in vacuum is c, the spectrum of the obtained terahertz electromagnetic wave is “f _N = N · f” in addition to the component of the fundamental frequency f represented by the formula “f = c / (2L _cavity )”. having a component of the frequency f _N of the formula. Here, N is a positive integer.

According to the results and analysis of the experiment by the inventors, the distance between the second end 112 of the semiconductor light emitting element 11 and the mirror 12 (L _C + L _A ) is in the range of about 0.5 mm to 2 mm. By translating, gaps between discrete spectra of the obtained terahertz electromagnetic waves can be filled. Thereby, a continuous terahertz spectrum can be obtained. In order to use the component of the fundamental frequency f having the strongest radiation intensity, the mirror 12 may be translated beyond the above range.

When the semiconductor light emitting device 11 is a vertical cavity surface emitting laser device (VCSEL) as shown in FIG. 7, the distance between the first surface 111 and the second surface 112 of the semiconductor light emitting device 11. since L _C is small, it is possible to further shorten the resonator length L _cavity. Therefore, in this case, the spectrum of the terahertz electromagnetic wave can have a higher fundamental frequency f.

  Next, a terahertz electromagnetic wave detection device 2 using the terahertz electromagnetic wave generation device 1 according to this embodiment will be described. FIG. 10 is a configuration diagram of the terahertz electromagnetic wave detection device 2 according to the present embodiment. In addition to the terahertz electromagnetic wave generator 1, the terahertz electromagnetic wave detector 2 shown in this figure includes a branching unit 21, a mirror 22, a moving mirror 23, a lens 24, a photoconductive antenna element 25 for detecting terahertz electromagnetic waves, a silicon lens 31, 32, parabolic mirrors 41 and 42, a signal generation unit 51, a synchronization detection unit 52, and an analysis unit 53.

  The terahertz electromagnetic wave generated by the photoconductive antenna element 16 for generating the terahertz electromagnetic wave is incident on the photoconductive antenna element 25 through the silicon lens 31, the parabolic mirror 41, the parabolic mirror 42, and the silicon lens 32 in this order. A measurement object is placed on the optical path of the terahertz electromagnetic wave (for example, on the optical path between the parabolic mirror 41 and the parabolic mirror 42), and the terahertz electromagnetic wave transmitted through the measurement object is transmitted to the photoconductive antenna. Incident on the element 25. The terahertz electromagnetic wave may be transmitted through the measurement object or reflected by the measurement object.

  The branching unit 21 is provided on the optical path between the laser oscillator 3 and the photoconductive antenna element 16 included in the terahertz electromagnetic wave generator 1 (more specifically, on the optical path between the lens 14 and the lens 15). Then, a part of the laser light outputted from the laser oscillator 3 is branched and outputted as probe light. The probe light output from the branching portion 21 passes through the mirror 22 and the moving mirror 23, is collected by the lens 24, and enters the photoconductive antenna element 25.

  The moving mirror 23 functions as an optical path length adjusting unit that changes the optical path length of the probe light from the branching unit 21 to the photoconductive antenna element 25, and is preferably a retro-reflector that can move in the optical axis direction. . An optical path length adjusting unit that adjusts the optical path length of the terahertz electromagnetic wave from the photoconductive antenna element 16 to the photoconductive antenna element 25 may be provided. By this optical path length adjustment unit, the timing difference between the terahertz electromagnetic wave incident on the photoconductive antenna element 25 and the probe light can be adjusted.

  The photoconductive antenna element 25 for detecting terahertz electromagnetic waves has a configuration similar to the configuration shown in FIG. 2 and has a pair of electrodes formed on a semiconductor substrate, and transmits terahertz electromagnetic waves and probe light. Input between a pair of electrodes. In the photoconductive antenna element 25, in response to the incidence of the terahertz electromagnetic wave and the probe light, a current representing the correlation between the two is generated between the pair of electrodes. Based on this correlation, the spectrum of the terahertz electromagnetic wave can be obtained, and further information on the measurement object can be obtained. The photoconductive antenna element 25 functions as a detection unit that detects the correlation between the terahertz electromagnetic wave and the probe light.

  The signal generator 51 applies a sine wave modulated voltage between a pair of electrodes of the photoconductive antenna element 16 for generating a terahertz electromagnetic wave. The synchronization detection unit 52 includes a lock-in amplifier, and a current generated between a pair of electrodes of the photoconductive antenna element 25 for detecting terahertz electromagnetic waves based on a sine wave modulated voltage output from the signal generation unit 51. Are detected synchronously, and the correlation between the terahertz electromagnetic wave and the probe light is detected. Then, the analyzing unit 53 obtains a time correlation waveform between the terahertz electromagnetic wave and the probe light by translating the moving mirror 23, and can obtain a spectrum of the terahertz electromagnetic wave by performing Fourier transform on the correlation waveform. .

  As described above, the terahertz electromagnetic wave generation device 1 according to the present embodiment can generate a terahertz electromagnetic wave having a variable frequency with a simple configuration, and substantially has a continuous spectrum by scanning the frequency. Terahertz electromagnetic waves can be obtained. Further, the terahertz electromagnetic wave detection device 2 according to the present embodiment includes such a terahertz electromagnetic wave generation device 1, and by using a substantially continuous spectrum terahertz electromagnetic wave, highly accurate measurement can be performed with a simple configuration. It can be carried out.

It is a lineblock diagram of terahertz electromagnetic wave generator 1 concerning this embodiment. 1 is a perspective view of a photoconductive antenna element 100. FIG. 2 is a perspective view of a laser oscillator 3 including a semiconductor light emitting element 11 and a mirror 12 and having a variable resonator length. FIG. 6 is a plan view showing another configuration example of the semiconductor light emitting element 11 included in the laser oscillator 3. FIG. 12 is a plan view showing still another configuration example of the semiconductor light emitting element 11 included in the laser oscillator 3. FIG. 6 is a perspective view showing another configuration example of the laser oscillator 3. FIG. 6 is a perspective view showing still another configuration example of the laser oscillator 3. FIG. It is a figure which shows the spectrum of the terahertz electromagnetic wave which generate | occur | produces in the terahertz electromagnetic wave generator 1 which concerns on this embodiment. It is a graph which shows the relationship between the resonator length in the terahertz electromagnetic wave generator 1 which concerns on this embodiment, and the fundamental frequency of terahertz electromagnetic waves. It is a block diagram of the terahertz electromagnetic wave detection apparatus 2 which concerns on this embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Terahertz electromagnetic wave generator, 2 ... Terahertz electromagnetic wave detector, 3 ... Laser oscillator, 11 ... Semiconductor light emitting element, 12 ... Mirror, 13 ... Moving stage, 14, 15 ... Lens, 16 ... Photoconductive antenna element for generation, 21 ... branching part, 22 ... mirror, 23 ... moving mirror, 24 ... lens, 25 ... photoconductive antenna element for detection, 31 and 32 ... silicon lens, 41 and 42 ... parabolic mirror, 51 ... signal generation part, 52 ... Synchronization detection unit, 53... Analysis unit.

Claims (6)

A semiconductor light emitting device having an active layer sandwiched between a first surface and a second surface and emitting light in the active layer;
A mirror that is provided opposite to the first surface of the semiconductor light emitting device and forms a resonator with the second surface of the semiconductor light emitting device;
Resonator length changing means for changing the resonator length of the resonator;
A photoconductive antenna element for generation which has a pair of electrodes formed on a semiconductor substrate and generates terahertz electromagnetic waves by inputting light output from the resonator between the pair of electrodes;
A terahertz electromagnetic wave generator characterized by comprising:   2. The terahertz electromagnetic wave generation device according to claim 1, wherein collimating means for collimating light traveling from the first surface of the semiconductor light emitting element toward the mirror is provided on the first surface.   2. The terahertz electromagnetic wave generator according to claim 1, wherein the semiconductor light emitting element is a surface emitting laser element having a vertical cavity structure. The terahertz electromagnetic wave generator according to any one of claims 1 to 3,
A branch that is provided on an optical path between the resonator and the generating photoconductive antenna element included in the terahertz electromagnetic wave generating device, branches a part of the light output from the resonator, and outputs it as probe light And
The terahertz electromagnetic wave output from the generating photoconductive antenna element and transmitted or reflected by the measurement object is input, and the probe light output from the branching unit is input, and the correlation between the terahertz electromagnetic wave and the probe light is detected. A detector to perform,
A terahertz electromagnetic wave detection device comprising:   An optical path length for adjusting either the optical path length of the terahertz electromagnetic wave from the generating photoconductive antenna element to the detection unit or the optical path length of the probe light from the branching unit to the detection unit The terahertz electromagnetic wave detection device according to claim 4, further comprising an adjustment unit. The detection unit includes a pair of electrodes formed on a semiconductor substrate, and includes a detection photoconductive antenna element that inputs the terahertz electromagnetic wave and the probe light between the pair of electrodes,
A signal generator for applying a sinusoidally modulated voltage between a pair of electrodes of the generating photoconductive antenna element;
Based on the sinusoidally modulated voltage output from the signal generator, the current generated between the pair of electrodes of the photoconductive antenna element for detection is synchronously detected, and the correlation between the terahertz electromagnetic wave and the probe light is detected. A synchronization detection unit to detect;
The terahertz electromagnetic wave detection device according to claim 4, further comprising:

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