JP4276323B2 - Terahertz wave generator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a terahertz wave generator that is an electromagnetic wave around a frequency of 1 THz (terahertz).
[0002]
[Prior art]
An electromagnetic wave region around a frequency of 1 THz (terahertz) (terahertz wave region, for example, approximately 100 GHz to 10 THz, or a wide frequency region including the surrounding region) is a frequency region located at the boundary between light waves and radio waves, and is terahertz. Waves are effective for applications such as infrared spectroscopy and imaging. In such a frequency range, development of light sources and detectors is relatively delayed, and there are many undeveloped parts in both technical and application aspects. In particular, in terms of industrial application, a terahertz wave generator, which is a small and simple light source, is indispensable. In recent years, development of such a light source using an optical switch element is being promoted. Although it is difficult to generate electromagnetic waves in the terahertz wave region by a method using an electric circuit oscillator, a light source for generating electromagnetic waves in this region can be realized by modulating current using pulsed light (for example, as a reference, for example, "Laser Research Vol. 26, No. 7, pp.515-521 (1998)").
[0003]
FIG. 5 shows a configuration diagram of an example of an optical switch element 1 conventionally used for generating terahertz waves. In this optical switch element 1, a parallel transmission line 12 comprising transmission lines 12a and 12b is formed on a semiconductor substrate 15 such as GaAs that responds at high speed and a photoconductive thin film 16 such as low-temperature grown GaAs, and a minute dipole antenna is formed at the center thereof. A single optical switch 10 is provided. In the center of the optical switch 10, there is a minute gap 11 of about several μm, for example, and an appropriate voltage is applied to the gap 11 by a DC power source 17.
[0004]
When laser light having an energy higher than the band gap of the semiconductor is incident as an optical pulse between the gaps 11, for example, free carriers are generated in the semiconductor and a pulsed current flows, and the pulsed current causes the terahertz to pulse. A wave is generated. Further, a continuous terahertz wave can be generated by making two-wavelength laser light incident on the optical switch 10 and utilizing the difference frequency.
[0005]
[Problems to be solved by the invention]
As a device for generating a continuous terahertz wave as described above, there is one disclosed in, for example, “Appl. Phys. Lett. 70 (5), pp. 559-561 (1997)” (FIG. 6). In this apparatus, two semiconductor lasers 9a and 9b that supply laser beams having different wavelength components are used as light sources for two-wavelength laser beams. The laser beams from the semiconductor lasers 9a and 9b are incident on the optical fibers 93a and 93b through the optical system including the lens 91 and the isolator 92, and are combined by the coupler 94, and include the optical fiber 95a and the chopper 96. The light enters the optical switch element 1 through the optical system.
[0006]
Here, the optical switch of the optical switch element 1 functions as an optical mixer. At this time, the optical switch responds to the difference frequency of the two wavelength components of the laser light, and a continuous terahertz wave is generated as an electromagnetic wave due to the difference frequency. In the apparatus shown in FIG. 6, the terahertz wave generated by the optical switch element 1 is output through the output lens 1a, and is incident on the bolometer 1d by the two parabolic mirrors 1c, and is detected and measured. The light from the coupler 94 is also incident on the spectrum analyzer 97 via the optical fiber 95b, and its wavelength distribution and the like are measured.
[0007]
When the terahertz wave generator is applied as a light source for spectroscopy, it is necessary to increase the output intensity of the obtained terahertz wave in order to improve the SN ratio and measurement accuracy of the spectroscopic measurement. Here, the semiconductor laser used as the excitation light source in the above-described apparatus has an advantage that the oscillation wavelength can be varied by temperature and driving current, but the output of the obtained terahertz wave cannot be increased. For example, in the above-described apparatus, the wavelength variable range of the semiconductor lasers 9a and 9b is 810 to 830 nm, the maximum total power is 50 mW, and the terahertz wave obtained at this time has an upper limit of about 9 THz for the frequency. The maximum output intensity is about 10 nW.
[0008]
The present invention has been made in view of the above problems, and an object of the present invention is to provide a terahertz wave generator capable of outputting a high-intensity terahertz wave.
[0009]
[Means for Solving the Problems]
In order to achieve such an object, a terahertz wave generator according to the present invention includes a pumping light source and an optical switch element having at least one optical switch, and pumping light from the pumping light source is incident on the optical switch element. The terahertz wave generating device generates a terahertz wave by an excitation light source including a laser medium excitation unit, a main resonator, and a two-wavelength setting unit, and pumps laser beams having two different wavelength components. The main resonator includes a laser medium pumped by the laser medium pumping means, at least two resonator mirrors, and input / output of light to the two-wavelength setting means. Optical input / output means to perform, Any one of the resonator mirrors is configured to function as an optical input / output unit, The two-wavelength setting means selectively selects the first sub-resonator that selectively returns the light having the first wavelength component to the main resonator and the light having the second wavelength component that is different from the first wavelength component. A second sub-resonator returning to the resonator; an optical input / output means; and an optical branching device disposed between the first sub-resonator and the second sub-resonator. And a second sub-resonator are wavelength selection means for selecting the first wavelength component and the second wavelength component, respectively, of the light from the light input / output means, and the light input / output means for selecting the wavelength-selected light. An optical feedback means for returning to the main resonator via the laser, and outputting laser light as excitation light from the two-wavelength oscillation laser to either the laser medium excitation means, the main resonator, or the two-wavelength setting means Optical output means is provided to reduce the wavelength selection means of the first sub-resonator and the second sub-resonator. One and also is characterized by its selective wavelength is variable wavelength selection unit that is configured to be variable.
[0010]
In the above-described apparatus, in a terahertz wave generating apparatus that makes light of two wavelength components incident on an optical switch and generates a continuous terahertz wave from the difference frequency, light of two wavelength components used as excitation light is supplied by a two-wavelength oscillation laser. is doing. This two-wavelength oscillation laser is configured by arranging two sub-resonators in combination with a main resonator having a laser medium such as a solid-state laser medium, and these two sub-resonators in the two-wavelength setting means are main resonances. A different wavelength component is selected from the light from the resonator and returned to the main resonator. This makes it possible to efficiently generate and supply laser light having two wavelength components that can be used to generate a terahertz wave, and therefore, it is possible to obtain a terahertz wave having a high output intensity.
[0011]
Here, the laser medium of the two-wavelength laser is preferably titanium sapphire. Thereby, the output intensity of the obtained terahertz wave can be particularly increased. For example, in the conventional apparatus using the above-described semiconductor laser, the wavelength variable range (gain bandwidth) of the semiconductor laser is narrow, so that the selection range of the frequency of the terahertz wave obtained by the difference frequency is narrowed. On the other hand, by using a titanium sapphire laser with a wide wavelength variable range, the frequency of the terahertz wave can be set in a wide frequency range.
[0012]
Further, at least one of the wavelength selecting units of the first sub-resonator and the second sub-resonator may be a variable wavelength selecting unit configured such that the selected wavelength is variable.
[0013]
Further, at least one of the first sub-resonator and the second sub-resonator may include a light amount adjusting means for adjusting the light amount of the wavelength-selected light that is returned to the main resonator.
[0014]
In this way, with respect to light of two wavelength components, by setting means for changing the selected wavelength or light quantity in one or both of the corresponding sub-resonators, the difference frequency / light quantity ratio of the two wavelength components can be made variable. The frequency of the obtained terahertz wave, the generation efficiency thereof, and the like can be changed.
[0015]
The two-wavelength laser includes a laser beam measurement unit that measures the wavelength / intensity distribution of the laser beam, a terahertz wave monitor obtained based on the measurement result of the laser beam measurement unit, or a control unit that controls each part of the apparatus. It is characterized by having.
[0016]
For terahertz waves that are difficult to measure, such as frequency distribution, instead of directly measuring terahertz waves, two-wavelength components of laser light that is excitation light are measured, and the difference frequency is obtained by the control means. The wavelength etc. can be monitored. It is also possible to control each part of the apparatus based on the measurement result.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of a terahertz wave generator according to the present invention will be described in detail with reference to the drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. Further, the dimensional ratios in the drawings do not necessarily match those described.
[0018]
FIG. 1 is a configuration diagram showing a first embodiment of a terahertz wave generator according to the present invention. In this terahertz wave generator, a two-wavelength laser 2 is used as a pumping light source that outputs pumping light incident on an optical switch element 1 in which an optical switch (not shown) is formed. Laser light having two different wavelength components output from the two-wavelength oscillation laser 2 is incident on the optical switch element 1 as excitation light through the condenser lens 1b. A small gap (for example, 5 μm) is formed in the optical switch composed of a small dipole antenna of the optical switch element 1, and a predetermined voltage is applied to the gap by a bias power source 17.
[0019]
At this time, the optical switch of the optical switch element 1 functions as an optical mixer, but the response of the optical switch to the laser light having the two wavelength components cannot follow the sum frequency of the two wavelength components, and the difference frequency is not reached. In response, an electromagnetic wave with a difference frequency is emitted. This difference frequency corresponds to about 0 to several THz, for example, and a continuous terahertz wave is obtained. The excited photocurrent is proportional to the intensity of the laser beam from the two-wavelength oscillation laser 2 that is the excitation light, and is therefore proportional to the square of the incident electric field.
[0020]
The generated continuous terahertz wave is emitted toward an external measurement system or the like via the emission lens 1a. For the optical switch element 1, not only a configuration having a single optical switch but also various optical switch elements such as a configuration having a one-dimensional or two-dimensional optical switch array composed of a plurality of optical switches are used. Can do. At this time, the incident optical system of the excitation light to the optical switch element is not limited to the single condensing lens 1b shown in FIG. 1, and optical systems having various configurations such as corresponding to each optical switch are used. be able to. Further, for example, an optical fiber may be used for the incident optical system.
[0021]
The two-wavelength laser 2 used in the terahertz wave generator according to the present embodiment includes an excitation laser 3 that is laser medium excitation means, a main resonator 4 that generates laser light, a first sub-resonator 6, and a second resonator. And a two-wavelength setting means 5 having a sub-resonator 7.
[0022]
As the laser medium excitation means, the excitation laser 3 is used here. As the laser medium excitation means, for example, current, discharge, gas laser light such as Ar laser, semiconductor laser, flash lamp light, dye laser or the like can be used. The excitation laser beam output from the excitation laser 3 is input to the main resonator 4.
[0023]
The main resonator 4 includes a laser medium 40, two resonator mirrors 41 and 42, and reflecting mirrors 43 and 44 each including a concave reflecting mirror. The reflecting mirror 43 transmits light having a wavelength component corresponding to the excitation laser beam at a high rate and reflects light having a wavelength component corresponding to the laser beam formed in the main resonator 4 at a high rate. Is used. Similarly, the reflecting mirror 44 is used that reflects light having a wavelength component corresponding to the laser beam formed in the main resonator 4 at a high rate. With such a configuration, the excitation laser light from the excitation laser 3 is efficiently incident on the laser medium 40 and the laser medium 40 is excited.
[0024]
Here, as the laser medium 40, for example, titanium sapphire is preferably used. A titanium sapphire laser, which is one of typical solid-state lasers, has the widest wavelength band of about 680 to 1100 nm, and is widely used as a wavelength tunable laser or a femtosecond laser. Various media can be used as the laser medium 40 depending on conditions such as the wavelength band to be used. For example, Ti ³⁺ Examples of solid-state laser media other than titanium sapphire, which is a doped crystal, include chromium forsterite and Cr: YAG. ⁴⁺ Cr, such as doped crystals, alexandrite and emerald ³⁺ Doped crystal, also V ²⁺ There are doped crystals.
[0025]
The resonator mirror 41 reflects (for example, 99.2%) most of the laser light formed by the stimulated emission light from the excited laser medium 40 and confines the laser light. The resonator mirror 41 transmits a part of the laser light at a predetermined ratio and outputs the laser light to the two-wavelength setting unit 5, and the light selected by the two-wavelength setting unit 5 as the main resonator 4. It also functions as a light input / output means for inputting to the camera.
[0026]
On the other hand, similarly to the resonator mirror 41, the resonator mirror 42 reflects most of the laser light (for example, 99.2%) to confine the laser light, and transmits a part of the laser light at a predetermined ratio. Therefore, it also functions as a light output means for outputting the light to the outside of the two-wavelength oscillation laser 2, that is, in the direction of the optical switch element 1 in this apparatus. The main resonator 4 is configured to oscillate laser even when the two-wavelength setting means 5 is not installed.
[0027]
The light incident on the two-wavelength setting means 5 via the resonator mirror 41 functioning as an optical input / output means is branched by an optical branching device 51 composed of a half mirror or a beam splitter, and is configured symmetrically. The light enters the first sub resonator 6 and the second sub resonator 7.
[0028]
The first sub-resonator 6 includes a first wavelength component (wavelength λ) of the incident light. ₁ Is selected and returned to the main resonator 4, and includes a prism 61 and a total reflection mirror 62 as optical feedback means. The second sub-resonator 7 includes a second wavelength component (wavelength λ) different from the first wavelength component in the incident light. ₂ Is selected and returned to the main resonator 4 and includes a prism 71 and a total reflection mirror 72 as optical feedback means. Each selected wavelength λ ₁ , Λ ₂ Is determined by the configuration and arrangement of the prisms 61 and 71 and the total reflection mirrors 62 and 72. Therefore, the prism 61 and the total reflection mirror 62 in the first sub-resonator 6 and the prism 71 in the second sub-resonator 7 are used. And the total reflection mirror 72 becomes each wavelength selection means.
[0029]
In the present embodiment, the prism 61 and the total reflection mirror 62 of the first sub-resonator 6 are fixed, and therefore the selected wavelength λ ₁ Is fixed. On the other hand, the second sub-resonator 7 is configured such that the total reflection mirror 72 can be rotated by a rotary stage or the like in the direction indicated by the arrow in the drawing. At this time, the wavelength of the laser beam component returning to the main resonator 4 changes depending on the angle of the total reflection mirror 72, and therefore the selected wavelength λ ₂ Is variable.
[0030]
Further, the second sub-resonator 7 is provided with a variable attenuation filter 73 that is a light amount adjusting means for adjusting the amount of light returned to the main resonator 4. As the variable attenuation filter 73, for example, a rotationally driven variable ND filter that adjusts and changes the attenuation amount by rotating a disk-shaped glass on which a deposition film of chromium or the like whose concentration is gradually changed is formed. Can be used.
[0031]
With the above configuration, the light incident on the two-wavelength setting unit 5 from the main resonator 4 is incident on the first sub-resonator 6 or the second sub-resonator 7, and the wavelength λ ₁ Or λ ₂ These two wavelength components are selected and input to the main resonator 4 again. By such an operation, the wavelength λ finally enters the main resonator 4. ₁ And λ ₂ Are emitted from the resonator mirror 42 functioning as a light output means to the optical switch element 1.
[0032]
In the two-wavelength laser 2 having the above-described configuration, a spectrum analyzer 23 serving as a laser beam measuring unit is installed in order to measure and monitor the wavelength and intensity ratio of each of the two wavelength components in the formed laser beam. . That is, a part of the laser beam is branched by the optical branching device 51 installed in the two-wavelength setting unit 5, enters the optical fiber 22 through the incident lens 21, and is guided to the spectrum analyzer 23.
[0033]
The spectrum analyzer 23 is further connected to a control device 24. The operation of the spectrum analyzer 23 is controlled by the control device 24, and a measurement result by the spectrum analyzer 23 is sent to the control device 24. Based on this measurement result, the control device 24 drives and controls the total reflection mirror 72 and the variable attenuation filter 73 of the second sub-resonator 7 in the present embodiment, whereby the wavelength, intensity ratio, etc. of the laser beam are controlled. The control of the laser beam obtained from the two-wavelength oscillation laser 2 based on the measurement result and the control / adjustment of the laser beam are realized.
[0034]
Note that the wavelength selection means in the first sub-resonator 6 and the second sub-resonator 7 is not limited to the method using the prism, and various methods can be used. FIG. 2 shows a modification of the first sub-resonator 6 for the embodiment shown in FIG. The first sub-resonator 6 includes an AOTF (acousto-optical tunable filter) 64.
[0035]
The AOTF 64 has a predetermined frequency f from the RF driver 64a. ₁ The drive signal is supplied to the wavelength λ by the acoustic wave generated in the AOTF 64. ₁ Only the laser beam component is deflected. The wavelength component is changed in angle when passing through the compensation prism 65 and is incident on the total reflection mirror 62 perpendicularly to select the wavelength λ. ₁ Are selected. Similarly, the second sub-resonator 7 may be configured to use AOTF. At this time, the selection wavelength can be made variable by changing the frequency supplied from the RF driver. In this case, the control device 24 is configured to control the RF driver and the like.
[0036]
Below, the effect of the terahertz wave generator by this embodiment is demonstrated.
[0037]
In the above-described terahertz wave generator, the two-wavelength oscillation laser 2 that selects the two-wavelength components by the two sub-resonators 6 and 7 is used as the excitation light source. For a laser device including a main resonator and a sub-resonator, the wavelength selective self-injection locking method disclosed in Japanese Patent Application Laid-Open No. 5-226749 and “Optical Vol. 25, No. 9, pp.505-511 (1996)” is used. There is a tunable laser used. In this wavelength tunable laser, a large output is obtained for a wide wavelength range of 822 to 922 nm, for example.
[0038]
However, this laser device makes the wavelength of laser light variable by a single sub-resonator. On the other hand, the two-wavelength laser 2 used in the terahertz wave generator according to the present embodiment is not variable in the selection wavelength, but coexistence and simultaneous supply of the two selection wavelengths and the terahertz wave at the difference frequency due thereto. This is realized by providing two sub-resonators together.
[0039]
As a conventional two-wavelength oscillation laser, there is an electronically controlled two-wavelength oscillation laser using AOTF, which is described in “The 59th JSAP Scientific Lecture (Autumn 1998), 17p-P2-19”. In the above apparatus, no sub-resonator is provided, and two different frequencies f are supplied from the RF driver to the AOTF installed in the main resonator. ₁ , F ₂ A drive signal consisting of two different wavelengths λ ₁ , Λ ₂ Are selected. Note that wavelength selection by a laser using AOTF is described in, for example, “Optics Lett., Vol. 21, No. 10, pp. 731-733 (1996)”.
[0040]
In such an apparatus, in order to install an AOTF which is a means for selecting two wavelengths in the main resonator, signals of two frequencies are simultaneously supplied to the AOTF. In this case, the operation becomes unstable, for example, an abnormal resonance beat occurs in the AOTF when the two selected wavelengths are close. On the other hand, the two-wavelength laser 2 in the present embodiment is provided with two-wavelength setting means 5 separately from the main resonator 4, and two sub-resonators 6 and 7 are installed in the two-wavelength setting means 5. Wavelength selection is performed. Accordingly, it is possible to stably oscillate at two wavelengths, and various means can be applied to the wavelength selection means.
[0041]
Two selected wavelengths λ ₁ , Λ ₂ Since the sub-resonators 6 and 7 are separately provided, the wavelength and the intensity ratio can be set separately and independently. This is particularly important for efficiently generating and controlling terahertz waves. Further, for example, by installing a movable total reflection mirror or a variable ND filter in one or both of the sub-resonators, it is possible to variably control the correlation between the difference frequency of two wavelength components, the intensity ratio, and the like.
[0042]
Note that when a two-wavelength laser is used in a terahertz wave generator, only the difference frequency between the two wavelength components is important. Therefore, by installing variable wavelength selection means or the like in one sub-resonator, Control is possible.
[0043]
In the above-described embodiment, the second sub-resonator has the selected wavelength λ by the total reflection mirror 72 being rotatably installed. ₂ The wavelength selection means is configured to be variable. As a result, the selected wavelength λ ₁ Light frequency and selected wavelength λ ₂ The frequency of the terahertz wave generated by the difference frequency from the light frequency of can be made variable. If the wavelength of the obtained terahertz wave is λ, 1 / λ = | 1 / λ ₁ -1 / λ ₂ | Holds. For example, λ ₁ = 800 nm, λ ₂ = 810 nm, the obtained terahertz wave is λ = 65 μm (frequency 4.6 THz), and λ ₁ = 800 nm, λ ₂ When t = 880 nm, the terahertz wave obtained is λ = 8.8 μm (frequency 34 THz).
[0044]
Here, the titanium sapphire laser has an extremely large output power as compared with, for example, a semiconductor laser, and therefore, it is possible to obtain a terahertz wave having a high output intensity. Further, the titanium sapphire laser has a wide wavelength band, and therefore a wide range of difference frequencies between two wavelength components that can be taken. In other words, it is possible to realize a device configuration that generates terahertz waves of various wavelengths (frequencies). In particular, the difference frequency is made larger than that of conventional devices to obtain terahertz waves of short wavelengths (high frequencies). It is possible.
[0045]
For example, if the wavelength bandwidth is 200 nm, which is 750 to 950 nm, it is possible to generate a terahertz wave up to about λ = 3.6 μm (frequency: 83 THz). However, the upper limit of the frequency of the obtained terahertz wave is generally limited to about several tens of THz due to the response speed of the optical switch formed in the optical switch element 1. Even when a medium other than titanium sapphire is used, it is possible to increase the output intensity and widen the wavelength band.
[0046]
Furthermore, by changing one of the two wavelength component laser lights as excitation light as described above as described above, characteristics such as frequency distribution can be varied over a wide wavelength (frequency) range. It can be set as a terahertz wave generator. When there is no need to change the frequency distribution of the obtained terahertz wave, the wavelength selection means of the first sub-resonator 6 and the second sub-resonator 7 may be fixed together. The variable attenuation filter 73 may be an attenuation filter such as an ND filter having a fixed attenuation rate when it is not necessary to change the light quantity ratio of the two wavelength components. It is also possible to employ a configuration in which no attenuation filter is provided.
[0047]
In addition, regarding the characteristics such as the frequency of the obtained terahertz wave and the control thereof, in this embodiment, the laser light obtained from the two-wavelength laser 2 is measured using the spectrum analyzer 23, and the control device 24 determines the difference from the measurement result. The frequency is calculated, and the wavelength of the terahertz wave that is the generated infrared light is determined. In the infrared wavelength region, there is no efficient spectroscope or photodetector, and therefore it is difficult to monitor the wavelength of the terahertz wave. In contrast, by using a method of determining the wavelength of the terahertz wave by measuring laser light having a wavelength of about 800 nm, detection with high sensitivity becomes possible. Further, since the two-wavelength oscillation laser 2 is controlled based on the result of the monitor, the wavelength of the terahertz wave can be kept stable even when the external environment or the like changes.
[0048]
FIG. 3 is a configuration diagram showing a second embodiment of the terahertz wave generation device according to the present invention.
[0049]
The main resonator 4 in the present embodiment includes a laser medium 40, a resonator mirror surface 41a formed by coating on one end surface of the laser medium 40, and a resonator mirror 42 that is a concave reflecting mirror. . The resonator mirror surface 41a is formed so as to transmit the excitation laser beam from the excitation laser 3 and totally reflect the formed laser beam. The resonator mirror 42 also functions as a light input / output unit that transmits part of the laser light to the two-wavelength setting unit 5 at a predetermined ratio. In this case, the configuration of the main resonator 4 is simplified as compared with the first embodiment.
[0050]
The light incident on the two-wavelength setting unit 5 passes through the collimator lens 52 and is branched by the light splitter 51. The first sub-resonator 6 and the second sub-resonator 7 have the same configuration, and include prisms 61 and 71, total reflection mirrors 62 and 72, and variable attenuation filters 63 and 73, respectively. . Further, the total reflection mirrors 62 and 72 are both rotatable, and therefore, in the present embodiment, the two selected wavelengths λ. ₁ And λ ₂ , And their light amounts are variable. Thereby, finer condition adjustment is possible. In particular, when two selected wavelengths are greatly different from each other, a terahertz wave with a large output is always obtained by setting two selected wavelengths on both sides centered on a wavelength at which the highest laser output intensity can be obtained. It becomes possible.
[0051]
Further, the optical branching unit 51 functions as an optical output unit that outputs laser light in the direction of the optical switch element 1. As described above, the laser power in the main resonator 4 can be kept higher by adopting a configuration in which laser light is output from the two-wavelength setting unit 5.
[0052]
At this time, a part of the output light is branched by an optical branching device 25 such as a half mirror, and is input to the spectrum analyzer 23 via the incident lens 21 and the optical fiber 22 to measure the laser light. The control device 24 controls the total reflection mirror 62 and the variable attenuation filter 63 installed in the first sub-resonator 6, and the total reflection mirror 72 and the variable attenuation filter 73 installed in the second sub-resonator 7. Thus, the wavelength and intensity ratio control of the two wavelength components of the laser light is performed.
[0053]
FIG. 4 is a configuration diagram showing a third embodiment of the terahertz wave generation device according to the present invention.
[0054]
In the present embodiment, the main resonator 4 has the same configuration as that of the second embodiment. On the other hand, with respect to the two-wavelength setting means 5, the first sub-resonator 6 and the second sub-resonator 7 are not provided with attenuation filters, the total reflection mirrors 62 and 72 are rotatable, and on the moving stage. It is installed so as to be movable in the optical path axis direction.
[0055]
At this time, if the total reflection mirrors 62 and 72 are moved so that the distance from the prisms 61 and 71 is increased, light in a narrower wavelength range is returned to the main resonator 4 at the time of spectroscopy by the prism, As a result, it is possible to function as a light amount adjusting means in the same manner as the attenuation filter. In this case, the configuration of the sub-resonators 6 and 7 is further simplified. The control device 24 controls the total reflection mirrors 62 and 72 to control the wavelength and intensity ratio of the two wavelength components of the laser light.
[0056]
Further, an optical branching device 53 is installed between the collimating lens 52 and the optical branching device 51 as light output means to the optical switch element 1. The light emitted in the direction opposite to that of the optical switch element 1 is totally reflected by the reflecting mirror 54 and returns to the resonator or is output to the optical switch element 1.
[0057]
The terahertz wave generator according to the present invention is not limited to the above-described embodiment, and can have various configurations. The two-wavelength laser 2 can be variously modified by using other optical elements such as an etalon, a grating, a birefringence filter, and an interference filter for both the main resonator 4 and the sub resonators 6 and 7. it can.
[0058]
Further, the light output means can have various configurations other than those shown in the above embodiment. For example, a part of the formed laser light can be output to the excitation laser 3 side and output from there to the outside. A half mirror can also be installed in the main resonator 4.
[0059]
In addition, the control means 24 can be configured in various ways, for example, by connecting to a display device and an input device and allowing the operator to specify control conditions via the input device based on the displayed measurement results. It is.
[0060]
【The invention's effect】
As described in detail above, the terahertz wave generator according to the present invention obtains the following effects. That is, by using a laser beam having two wavelength components used for generating a continuous terahertz wave as a two-wavelength oscillation laser having two sub-resonators instead of using two semiconductor lasers or the like, a two-wavelength laser is obtained. The output of the terahertz wave obtained by increasing the efficiency of light generation can be increased.
[0061]
In particular, in the two-wavelength laser, by selecting a wavelength by providing a sub-resonator separately for each wavelength component instead of selecting two wavelength components in the main resonator, It is possible to stably generate components and generate terahertz waves under favorable conditions.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing a first embodiment of a terahertz wave generation device according to the present invention.
FIG. 2 is a configuration diagram showing a modification of the first sub-resonator.
FIG. 3 is a configuration diagram illustrating a second embodiment of the terahertz wave generation device according to the present invention.
FIG. 4 is a configuration diagram showing a third embodiment of a terahertz wave generation device according to the present invention.
FIG. 5 is a diagram illustrating a method for generating a terahertz wave using an optical switch.
FIG. 6 is a configuration diagram illustrating an example of a conventional terahertz wave generator.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Optical switch element, 1a ... Outgoing lens, 1b ... Condensing lens,
DESCRIPTION OF SYMBOLS 2 ... 2 wavelength oscillation laser, 21 ... Incident lens, 22 ... Optical fiber, 23 ... Spectrum analyzer, 24 ... Control apparatus, 25 ... Optical branching device,
DESCRIPTION OF SYMBOLS 3 ... Laser for excitation, 4 ... Main resonator, 40 ... Laser medium, 41, 42 ... Resonator mirror, 41a ... Resonator mirror surface, 43, 44 ... Reflector mirror,
5 ... 2 wavelength setting means, 51 ... optical splitter, 52 ... collimator lens, 53 ... optical splitter, 54 ... reflecting mirror, 6 ... first sub-resonator, 61 ... prism, 62 ... total reflecting mirror, 63 ... variable Attenuation filter, 64 ... AOTF, 64a ... RF driver, 65 ... compensation prism, 7 ... second subresonator, 71 ... prism, 72 ... total reflection mirror, 73 ... variable attenuation filter.

Claims (4)

A terahertz wave generator comprising a pumping light source and an optical switch element having at least one optical switch, and generating a terahertz wave when pumping light from the pumping light source is incident on the optical switch element,
The excitation light source includes a two-wavelength oscillation laser that includes laser medium excitation means, a main resonator, and two wavelength setting means, and supplies laser light having two different wavelength components as the excitation light.
It said main resonator includes a laser medium excited by the laser medium excitation means, and at least two resonators mirrors and an optical output means for inputting and outputting light to the second wavelength setting means, any One of the resonator mirrors is configured to function as the light input / output means;
The two-wavelength setting means selects a first sub-resonator that selectively returns light having a first wavelength component to the main resonator, and light having a second wavelength component that is different from the first wavelength component. A second sub-resonator to be returned to the main resonator, and an optical branching device installed between the optical input / output means, the first sub-resonator and the second sub-resonator. With
The first sub-resonator and the second sub-resonator are wavelength selection means for selecting the first wavelength component and the second wavelength component, respectively, of the light from the light input / output means; Optical feedback means for returning wavelength selected light to the main resonator via the optical input / output means;
The laser medium excitation means, the main resonator, or the two-wavelength setting means is provided with a light output means for outputting the laser light serving as the excitation light from the two-wavelength laser,
At least one of the wavelength selecting units of the first sub-resonator and the second sub-resonator is a variable wavelength selecting unit configured such that the selected wavelength is variable, the terahertz wave Generator.   The terahertz wave generation device according to claim 1, wherein the laser medium is titanium sapphire.   The at least one of the first sub-resonator and the second sub-resonator has a light amount adjusting means for adjusting the light amount of the wavelength-selected light to be returned to the main resonator. The terahertz wave generator according to 1 or 2.   The two-wavelength laser includes a laser beam measuring unit that measures a wavelength / intensity distribution of the laser beam, and a terahertz wave monitor or each part of the device that is obtained in the optical switch element based on a measurement result by the laser beam measuring unit. The terahertz wave generator according to any one of claims 1 to 3, further comprising: a control unit that performs the above control.

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