JP2000235203A - Terahertz wave generating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to output a high intensity terahertz wave. SOLUTION: A two-wavelength oscillation laser 2 used for supplying an excitation beam for generating terahertz waves from an optical switch element 1 is constituted of an exciting laser 3, a main resonator 4 and a two-wavelength setting means 5 having a first sub-resonator 6 and a second sub-resonator 7, and two-wavelength oscillation is realized using the prisms 61, 71 of the sub- resonators 6, 7 and total reflection mirrors 62, 72 and selecting respectively different wavelength components. By such a constitution, the two-wavelength oscillation is made to be efficient, and the output of the generated terahertz waves is made be large in intensity. Further, the control and the setting change of the frequency, etc., of the terahertz waves are realized easily by adjusting/ controlling each of the sub-resonators 6, 7 also.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
(Terahertz) The present invention relates to a terahertz wave generator which is an electromagnetic wave in the vicinity.

[0002]

2. Description of the Related Art An electromagnetic wave region around a frequency of 1 THz (terahertz) (terahertz wave region, for example, about 100 GHz)
z to 10 THz, or a wide frequency region including the peripheral region thereof) is a frequency region located at the boundary between light waves and radio waves, and a terahertz wave is effective for application to infrared spectroscopy and imaging, for example. It is. In such a frequency range, the development of light sources and detectors is relatively delayed, and there are many unexplored parts in terms of technology and application. In particular,
In terms of industrial applications, a terahertz wave generator, which is a small and simple light source, is indispensable.
Development of such a light source using an optical switch element is being advanced. Although it is difficult to generate electromagnetic waves in the terahertz wave region by a method using an oscillator in an electric circuit, a light source for generating electromagnetic waves in this region can be realized by modulating current using pulsed light (for example, as a document,
“Laser Research Vol. 26, No. 7, pp. 515-521 (1998)”).

FIG. 5 shows an example of the configuration of an optical switch element 1 conventionally used for generating terahertz waves. In this optical switch element 1, a parallel transmission line 12 composed of transmission lines 12a and 12b is formed on a substrate 15 of a semiconductor which responds at a high speed such as GaAs and a photoconductive thin film 16 such as a low-temperature grown GaAs. A single optical switch 10 is provided. Optical switch 10
A small gap 11 of, for example, about several μm is provided at the center of the gap, and an appropriate voltage is applied to the gap 11 by a DC power supply 17.

When a laser beam having an energy higher than the band gap of the semiconductor is injected into the gap 11 as, for example, an optical pulse, free carriers are generated in the semiconductor and a pulse-like current flows. A terahertz wave is generated in the shape. Further, continuous terahertz waves can be generated by injecting laser light of two wavelengths into the optical switch 10 and utilizing the difference frequency.

[0005]

As an apparatus for generating a continuous terahertz wave as described above, for example, "Appl. Phys.L
ett. 70 (5), pp. 559-561 (1997) "(FIG. 6). In this apparatus, two semiconductor lasers 9a and 9b for supplying laser light of different wavelength components are used as light sources of laser light of two wavelengths. Laser beams from the semiconductor lasers 9a and 9b are incident on optical fibers 93a and 93b via optical systems including a lens 91 and an isolator 92, are combined by a coupler 94, and include an optical fiber 95a and a chopper 96 and the like. The light enters the optical switch element 1 via the optical system.

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 between the two wavelength components of the laser light, and a continuous terahertz wave is generated as an electromagnetic wave based on the difference frequency. In the apparatus shown in FIG. 6, the terahertz wave generated by the optical switch element 1 is output through the exit lens 1a, is incident on the bolometer 1d by two parabolic mirrors 1c, and is detected and measured. The light from the coupler 94 is transmitted to the spectrum analyzer 97 via the optical fiber 95b.
And its wavelength distribution and the like are measured.

When the terahertz wave generator is applied as a light source for spectroscopy or the like, it is necessary to increase the output intensity of the obtained terahertz wave in order to improve the SN ratio and the measurement accuracy of the spectroscopic measurement. Here, the semiconductor laser used as an excitation light source in the above-described device has an advantage that the oscillation wavelength can be varied by temperature or driving current, but cannot increase the output of the obtained terahertz wave. 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 obtained terahertz wave has an upper limit of about 9 THz for its frequency, , The maximum output intensity is about 10 nW.

The present invention has been made in view of the above problems, and has as its object to provide a terahertz wave generator capable of outputting a high-intensity terahertz wave.

[0009]

In order to achieve the above object, a terahertz wave generator according to the present invention comprises an excitation light source and an optical switch element having at least one optical switch. A terahertz wave generation device that generates a terahertz wave by making excitation light incident on an optical switch element, wherein the excitation light source includes a laser medium excitation unit, a main resonator, and a two-wavelength setting unit. A two-wavelength oscillation laser for supplying laser light having two wavelength components as excitation light, the main resonator comprising: a laser medium excited by laser medium excitation means; at least two resonator mirrors; Light input / output means for inputting / outputting light to / from the setting means, the two-wavelength setting means comprising: a first sub-resonator for selectively returning light of the first wavelength component to the main resonator; 1 A second sub-resonator returns light of a different second wavelength component selectively to the main resonator to the wavelength components,
An optical branching device is provided between the optical input / output means and the first sub-resonator and the second sub-resonator. Wavelength selecting means for selecting a first wavelength component and a second wavelength component of the light from the output means, and optical feedback for returning the wavelength-selected light to the main resonator via the optical input / output means. And a laser output means for outputting a laser beam serving as excitation light from a two-wavelength oscillation laser to any one of the laser medium pumping means, the main resonator, and the two-wavelength setting means. And

In the above-described device, in a terahertz wave generating device in which light of two wavelength components is incident on an optical switch and a continuous terahertz wave is generated from the difference frequency, light of two wavelength components used as excitation light is oscillated by two wavelengths. Powered by laser. This two-wavelength oscillation laser is configured by adding two sub-resonators to a main resonator having a laser medium such as a solid-state laser medium. The different wavelength components of the light from the device are selected and returned into the main resonator. This makes it possible to efficiently generate and supply laser light of two wavelength components that can be used for generation of a terahertz wave, and thus to obtain a terahertz wave having a large output intensity.

Here, the laser medium of the two-wavelength oscillation laser is preferably titanium sapphire. Thereby, the output intensity of the obtained terahertz wave can be particularly increased. Further, for example, in a conventional device 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 becomes narrow.
On the other hand, by using a titanium sapphire laser having a wide wavelength variable range, it is possible to set the frequency of the terahertz wave in a wide frequency range.

Further, at least one of the wavelength selecting means of the first sub-resonator and the second sub-resonator is a variable wavelength selecting means configured so that the selected wavelength is variable. good.

Further, 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. good.

As described above, by installing means for changing the selected wavelength or the light amount in one or both of the corresponding sub-resonators for the light of the two wavelength components, the difference frequency / light amount ratio of the two wavelength components, etc. Can be varied to change the frequency of the obtained terahertz wave, its generation efficiency, and the like.

The two-wavelength oscillation laser performs a laser beam measuring means for measuring the wavelength and intensity distribution of the laser beam, and monitors a terahertz wave obtained based on the measurement result by the laser beam measuring device or controls each unit of the apparatus. And control means.

For a terahertz wave for which it is difficult to measure a frequency distribution or the like, two wavelength components of laser light as excitation light are measured instead of directly measuring the terahertz wave, and the difference frequency is obtained by control means. It is possible to monitor the wavelength of the terahertz wave and the like. In addition, it becomes possible to control each unit of the device based on the measurement result.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a terahertz wave generator according to the present invention will be described below in detail with reference to the drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description. Also, the dimensional ratios in the drawings do not always match those described.

FIG. 1 is a configuration diagram showing a first embodiment of a terahertz wave generator according to the present invention. In this terahertz wave generation device, a two-wavelength oscillation laser 2 is used as an excitation light source that outputs excitation light incident on an optical switch element 1 in which an optical switch (not shown) is formed. The laser light having two different wavelength components output from the two-wavelength oscillation laser 2 is collected by the condenser lens 1b.
Through the optical switch element 1 as excitation light.
A small gap (for example, 5 μm) is formed in the optical switch composed of the small dipole antenna of the optical switch element 1, and a predetermined voltage is applied to this gap by the bias power supply 17.

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. An electromagnetic wave is emitted in response to the difference frequency in response to the difference frequency. This difference frequency is, for example, 0 to
This corresponds to about several THz, whereby a continuous terahertz wave can be obtained. The excited photocurrent is excitation light 2
It is proportional to the intensity of the laser beam from the wavelength oscillating laser 2, and is therefore proportional to the square of the incident electric field.

The generated continuous terahertz wave is emitted toward an external measurement system or the like via the emission lens 1a. In addition, as 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 including a plurality of optical switches can be used. Can be. At this time, the optical system for inputting the excitation light to the optical switch element is not limited to the single condenser lens 1b shown in FIG.
Optical systems having various configurations can be used, for example, corresponding to each optical switch. Further, for example, an optical fiber may be used for the incident optical system.

The two-wavelength oscillation laser 2 used in the terahertz wave generator according to the present embodiment includes an excitation laser 3 as a laser medium excitation means, a main resonator 4 for generating laser light, and a first sub-resonator 6. And the second sub-resonator 7
And a wavelength setting means 5.

As the laser medium exciting means, an exciting laser 3 is used here. As the laser medium exciting 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 light output from the excitation laser 3 is input to the main resonator 4.

The main resonator 4 includes a laser medium 40, two resonator mirrors 41 and 42, and a reflecting mirror 4 comprising a concave reflecting mirror.
3 and 44. The reflecting mirror 43 transmits the light of the wavelength component corresponding to the excitation laser light at a high rate and reflects the light of the wavelength component corresponding to the laser light formed in the main resonator 4 at a high rate. Is used. As the reflecting mirror 44, a mirror that reflects light of a wavelength component corresponding to the laser light formed in the main resonator 4 at a high rate is used. 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.

Here, for example, titanium sapphire is preferably used as the laser medium 40. Titanium sapphire laser, which is one of the typical solid-state lasers, has the widest wavelength band of about 680 to 1100 nm, and is widely used as a tunable laser and a femtosecond laser. Note that various media can be used as the laser medium 40 depending on conditions such as a wavelength band to be used. For example, solid laser media other than titanium sapphire, which is a Ti ³⁺ doped crystal, include chromium forsterite and C
r: Cr ⁴⁺ doped crystal such as YAG, Cr ³⁺ doped crystal such as alexandrite and emerald, and V ²⁺ doped crystal.

The resonator mirror 41 includes the excited laser medium 4.
Most of the laser light formed by the stimulated emission light from 0 is reflected (for example, 99.2%) to confine 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 means 5.
It also functions as an optical input / output unit for inputting the light whose wavelength has been selected by the two-wavelength setting unit 5 to the main resonator 4.

On the other hand, the resonator mirror 42 reflects most of the laser light (for example, 99.2%) to confine the laser light as in the case of the resonator mirror 41, and also a part of the laser light to a predetermined ratio. The device also functions as an optical output means for transmitting the light to the outside of the two-wavelength oscillation laser 2, in this device, in the direction of the optical switch element 1. The main resonator 4 is configured to oscillate laser even when the two-wavelength setting means 5 is not provided.

Resonator mirror 41 functioning as light input / output means
Incident on the two-wavelength setting means 5 via the optical splitter 5 is a light splitter 5 such as a half mirror or a beam splitter.
1 and each symmetrically configured first
The light is incident on the sub-resonator 6 and the second sub-resonator 7.

The first sub-resonator 6 is the first sub-resonator
Wavelength component (wavelength λ₁To the main resonator 4
And the prism 61 and the optical feed
It has a total reflection mirror 62 which is a locking means.
The second sub-resonator 7 has a first wavelength of the incident light.
A second wavelength component (wavelength λ_TwoSelect)
To return to the main resonator 4, the prism 71,
And a total reflection mirror 72 as an optical feedback means.
It is configured. Note that each selected wavelength λ ₁, Λ
_TwoOf the prisms 61 and 71 and the total reflection mirrors 62 and 72
Since it is determined by the configuration and arrangement, the first sub-resonator 6
The prism 61, the total reflection mirror 62, the second sub-resonator
7, a prism 71 and a total reflection mirror 72 are respectively provided.
Wavelength selection means.

In this embodiment, the prism 61 and the total reflection mirror 62 of the first sub-resonator 6 are fixed, so that the selected wavelength λ ₁ is fixed. On the other hand, in the second sub-resonator 7, the total reflection mirror 72 is configured to be rotatable by a rotary stage or the like in a direction indicated by an arrow in the drawing. At this time, since the wavelength of the laser beam component returning to the main resonator 4 changes depending on the angle of the total reflection mirror 72, the selected wavelength λ ₂ is therefore variable.

Further, the second sub-resonator 7 is provided with a variable attenuation filter 73 which 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 rotary drive type variable ND filter or the like that adjusts and changes the amount of attenuation by rotating a disk-shaped glass on which a deposited film of chromium or the like whose concentration is gradually changed is formed. Can be used.

With the above configuration, the light that has entered the two-wavelength setting means 5 from the main resonator 4 enters the first sub-resonator 6 or the second sub-resonator 7 and has a wavelength of λ ₁ or λ ₂ . The wavelength component is selected and input to the main resonator 4 again. By such an operation, finally, the wavelength λ in the main resonator 4 is obtained.
A laser beam having two wavelength components of ₁ and λ ₂ is formed,
The light is emitted from the resonator mirror 42 functioning as light output means to the optical switch element 1.

In the two-wavelength oscillation laser 2 having the above-described configuration, a spectrum analyzer 23 as a laser light measuring means is installed in order to measure and monitor the respective wavelengths and intensity ratios of the two wavelength components in the formed laser light. Have been. That is, a part of the laser light is 2
The light is split by an optical splitter 51 provided in the wavelength setting means 5, enters the optical fiber 22 via the incident lens 21, and is guided to the spectrum analyzer 23.

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 the measurement result by the spectrum analyzer 23 is sent to the control device 24. The control device 24 controls the second sub-resonator 7 in the present embodiment based on the measurement result.
Drive of the total reflection mirror 72 and the variable attenuation filter 73 to monitor characteristics such as the wavelength and intensity ratio of the laser light, and to control the laser light obtained from the two-wavelength oscillation laser 2 based on the measurement result. Control and adjustment are realized.

The first sub-resonator 6 and the second sub-resonator 7
Is not limited to the above-described method using the prism, and various methods can be used. FIG. 2 shows a modification of the first sub-resonator 6 in the embodiment shown in FIG. The first sub-resonator 6 is an AOTF
(Acousto-optical tunable filter).

The AOTF 64 includes an RF driver 64
a is supplied with a drive signal of a predetermined frequency f ₁ ,
As a result, only the laser beam component of the wavelength λ ₁ is deflected by the acoustic wave generated in the AOTF 64. The wavelength components in the angle is changed during the passage of the compensating prism 65, and perpendicularly incident on the total reflection mirror 62, the light components of selected wavelengths lambda ₁ is selected. Similarly, the second sub-resonator 7 may be configured to use AOTF. At this time, the selected 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 an RF driver and the like.

Hereinafter, effects of the terahertz wave generator according to the present embodiment will be described.

In the above-described terahertz wave generator, a two-wavelength oscillation laser 2 that selects two wavelength components by two sub-resonators 6 and 7 is used as an excitation light source. A laser device having a main resonator and a sub-resonator is disclosed in
No. 226,749 and "Optics, Vol. 25, No. 9, pp. 505-5
11 (1996) ", there is a wavelength tunable laser using the wavelength selective self-injection locking method. In this wavelength tunable laser, a large output is obtained in a wide wavelength range of, for example, 822 to 922 nm.

However, in this laser device, the wavelength of the laser light is tunable by a single sub-resonator. On the other hand, the two-wavelength oscillation laser 2 used in the terahertz wave generator according to the present embodiment is not a tunable selected wavelength but a coexistence and simultaneous supply of two selected wavelengths and a terahertz wave at a difference frequency due to the simultaneous supply. This is realized by providing two sub-resonators side by side.

As a conventional two-wavelength oscillation laser,
"The 59th Annual Meeting of the Japan Society of Applied Physics (Autumn 1998), 17p-P
There is an electronically controlled two-wavelength oscillation laser using the AOTF shown in 2-19. In the above device, the sub resonator is not provided, and the AOTF installed in the main resonator has R
A driving signal having _two different frequencies f ₁ and f ₂ is supplied from the F driver, whereby two different wavelengths λ and f ₂ are provided.
₁ and λ ₂ are selected. The wavelength selection by the laser using the AOTF is described in, for example, “Optics Let
t., Vol. 21, No. 10, pp. 731-733 (1996) ".

In such an apparatus, signals of two frequencies are simultaneously supplied to the AOTF in order to install the AOTF as means for selecting two wavelengths in the main resonator. In this case, especially when the two selected wavelengths are close, AOT
The operation becomes unstable, for example, an abnormal resonance beat occurs in F. On the other hand, in the two-wavelength oscillation laser 2 according to the present embodiment, the two-wavelength setting means 5 is provided separately from the main resonator 4.
Two sub-resonators 6 and 7 are installed in the two-wavelength setting means 5 to perform wavelength selection. Thereby, oscillation at two wavelengths can be performed stably, and various means can be applied to the wavelength selecting means.

Further, since the sub-resonators 6 and 7 are provided separately for the two selected wavelengths λ ₁ and λ ₂ , the respective wavelengths and intensity ratios can be set separately and independently. This is particularly important for efficient generation and control of terahertz waves. Further, for example, by installing a movable total reflection mirror, a variable ND filter, or the like in one or both of the sub-resonators, it is possible to variably control the correlation between the difference frequency and the intensity ratio of the two wavelength components.

When a two-wavelength oscillation laser is used in a terahertz wave generator, only the difference frequency between the two wavelength components is important. Therefore, by installing a variable wavelength selection means or the like in one of the sub-resonators, Terahertz wave control is possible.

In the above embodiment, the second sub-resonator is
By total reflection mirror 72 is rotatably mounted, the selected wavelength lambda ₂ is the configuration of the wavelength selection means is variable. This can be the frequency of the selected wavelength lambda ₁ of the light, the frequency of the terahertz wave generated by the difference frequency between the frequency of the selected wavelength lambda ₂ of the optical variable. Here, assuming that the wavelength of the obtained terahertz wave is λ, 1 / λ
= | 1 / λ ₁ −1 / λ ₂ |. For example, λ ₁ = 8
When the wavelength is 00 nm and λ ₂ = 810 nm, the terahertz wave obtained is λ = 65 μm (frequency 4.6 THz).
_{If 1} = 800 nm and λ ₂ = 880 nm, the terahertz wave obtained is λ = 8.8 μm (frequency: 34 THz).

Here, the output power of a titanium sapphire laser is much higher than that of a semiconductor laser, for example.
Therefore, it is possible to obtain a terahertz wave having a large output intensity. Further, the titanium sapphire laser has a wide wavelength band, and thus has a wide range of possible difference frequencies of two wavelength components. That is, it is possible to realize a device configuration for generating terahertz waves of various wavelengths (frequency), and obtain a terahertz wave of a short wavelength (high frequency) by increasing the difference frequency as compared with a conventional device. It is possible.

For example, if the wavelength bandwidth is 750 to 950 nm and 200 nm, λ = 3.6 μm (frequency 8
It is possible to generate a terahertz wave up to about 3 THz). However, the upper limit of the frequency of the obtained terahertz wave is generally limited to about several tens THz depending on the response speed of the optical switch formed in the optical switch element 1. Even when a medium other than titanium sapphire is used, the output can be similarly increased in intensity and the wavelength band can be widened.

Furthermore, by making one of the selected wavelengths variable among the two-wavelength component laser light as the excitation light as described above, the characteristics such as the frequency distribution over a wide wavelength (frequency) range are obtained. Can be varied. When it is not necessary to change the frequency distribution of the obtained terahertz wave, a configuration may be adopted in which the wavelength selecting means of the first sub-resonator 6 and the second sub-resonator 7 are both fixed. Also, the variable attenuation filter 73
When it is not necessary to change the light amount ratio of the two wavelength components, an attenuation filter such as an ND filter having a fixed attenuation rate may be used. It is also possible to adopt a configuration in which no attenuation filter is provided.

In the present embodiment, the characteristics of the obtained terahertz wave, such as the frequency and the control thereof, are described below.
Is measured, and the control device 24 calculates the difference frequency from the measurement result to determine the wavelength of the generated terahertz wave as the infrared light. In the infrared wavelength region, there is no efficient spectrometer or photodetector,
It is difficult to monitor the wavelength of the terahertz wave. On the other hand, by using a method of determining the wavelength of the terahertz wave by measuring a laser beam 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 this monitor, the wavelength of the terahertz wave can be stably maintained even if the external environment or the like fluctuates.

FIG. 3 is a block diagram showing a second embodiment of the terahertz wave generator according to the present invention.

The main resonator 4 in this embodiment has a laser medium 40, a resonator mirror surface 41a formed by coating one end face of the laser medium 40, and a resonator mirror 42 which is a concave reflecting mirror. Have been. The resonator mirror surface 41a is formed so as to transmit the excitation laser light from the excitation laser 3 and totally reflect the formed laser light. The resonator mirror 42 also functions as an optical input / output unit that transmits a part of the laser beam to the two-wavelength setting unit 5 at a predetermined ratio. In this case, the configuration of the main resonator 4 is the first
Is simplified as compared with the embodiment.

The light incident on the two-wavelength setting means 5 passes through the collimator lens 52 and is split by the optical splitter 51. The first sub-resonator 6 and the second sub-resonator 7 have the same configuration, and include prisms 61 and 71, respectively.
Total reflection mirrors 62 and 72 and variable attenuation filters 63 and 7
3. Further, the total reflection mirrors 62 and 72
Are rotatable, and therefore, in the present embodiment, the two selected wavelengths λ ₁ and λ ₂ and the light quantity thereof are both variable. This enables more detailed condition adjustment. In particular, when the two selected wavelengths are significantly different from each other, a terahertz wave with a large output is always obtained by setting two selected wavelengths around the wavelength at which the highest laser output intensity is obtained. It becomes possible.

The optical splitter 51 functions as an optical output means for outputting laser light in the direction of the optical switch element 1. As described above, the laser power is output from the two-wavelength setting unit 5, so that the laser power in the main resonator 4 can be kept higher.

At this time, a part of the output light is split by an optical splitter 25 such as a half mirror and the like.
3 and the laser beam is measured. The control device 24 includes a total reflection mirror 62 and a variable attenuation filter 63 installed in the first sub-resonator 6, and a total reflection mirror 72 and variable attenuation filter 7 installed in the second sub-resonator 7.
3 to control the wavelength and intensity ratio of the two wavelength components of the laser light.

FIG. 4 is a configuration diagram showing a third embodiment of the terahertz wave generator according to the present invention.

In the present embodiment, the main resonator 4 has the same configuration as that of the second embodiment. on the other hand,
Regarding the two-wavelength setting means 5, the first sub-resonator 6 and the second
The sub-resonator 7 is not provided with an attenuation filter, and the total reflection mirrors 62 and 72 are rotatable, and are movably installed in the optical axis direction by being installed on a moving stage.

At this time, when the total reflection mirrors 62 and 72 are moved so as to increase the distance from the prisms 61 and 71,
The light in a narrower wavelength range returns to the main resonator 4 when the light is separated by the prism, and the light amount is reduced. As a result, the light can be made to function as a light amount adjusting unit similarly to the attenuation filter. In this case, the configurations of the sub resonators 6 and 7 are further simplified. Further, the control device 24 controls the total reflection mirrors 62 and 72 to control the wavelength and the intensity ratio of the two wavelength components of the laser light.

The collimating lens 52 and the optical splitter 5
1, an optical splitter 53 is provided as an optical output unit to the optical switch element 1. The light emitted in the direction opposite to the optical switch element 1 is reflected by the reflecting mirror 54.
, And is returned to the inside of the resonator or output to the optical switch element 1.

The terahertz wave generator according to the present invention is not limited to the above-described embodiment, but may have various configurations. The two-wavelength oscillation laser 2 can be variously deformed by using other optical elements such as an etalon, a grating, a birefringent filter, and an interference filter for both the main resonator 4 and the sub resonators 6 and 7. it can.

The light output means may have various structures other than those shown in the above embodiment. For example, it is also possible to adopt a configuration in which a part of the formed laser light is output to the excitation laser 3 side, and is output to the outside from there. Further, a half mirror can be provided in the main resonator 4.

Further, the control means 24 is connected to a display device and an input device, for example, so that the operator can designate various control conditions via the input device based on the displayed measurement results. Configuration is possible.

[0060]

The terahertz wave generator according to the present invention has the following features.
As described in detail above, the following effects are obtained. In other words, a two-wavelength laser having two sub-cavities is used as the laser light having two wavelength components for generating continuous terahertz waves, instead of using two semiconductor lasers or the like. The output of the terahertz wave obtained by increasing the efficiency of light generation can be increased.

In particular, the two-wavelength oscillation laser is configured not to select two wavelength components in the main resonator, but to provide a separate sub-resonator for each wavelength component to perform wavelength selection. Terahertz waves can be generated under favorable conditions by stably generating each wavelength component.

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating a first embodiment of a terahertz wave generator 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 showing a second embodiment of the terahertz wave generator according to the present invention.

FIG. 4 is a configuration diagram showing a third embodiment of the terahertz wave generator 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 generation device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Optical switch element, 1a ... Outgoing lens, 1b ... Condensing lens, 2 ... 2-wavelength oscillation laser, 21 ... Incident lens, 22
... optical fiber, 23 ... spectrum analyzer, 24
... Control device, 25 ... Optical splitter, 3 ... Excitation laser, 4 ...
Main resonator, 40: laser medium, 41, 42: resonator mirror,
41a: Resonator mirror surface, 43, 44: Reflecting mirror, 5: Two wavelength setting means, 51: Optical splitter, 52: Collimating lens,
53: optical splitter, 54: reflecting mirror, 6: first sub-resonator, 6
DESCRIPTION OF SYMBOLS 1 ... Prism, 62 ... Total reflection mirror, 63 ... Variable attenuation filter, 64 ... AOTF, 64a ... RF driver, 65
... compensating prism, 7 ... second sub-resonator, 71 ... prism,
72: total reflection mirror; 73: variable attenuation filter.

Claims (5)

[Claims] 1. A terahertz wave generator comprising: an excitation light source; and an optical switch element having at least one optical switch, wherein the excitation light from the excitation light source is incident on the optical switch element to generate a terahertz wave. Wherein the excitation light source is a laser medium excitation means, a main resonator,
A two-wavelength setting laser, comprising: a two-wavelength oscillation laser that supplies laser light having two different wavelength components as the pumping light, wherein the main resonator is a laser pumped by the laser medium pumping means. A medium, at least two resonator mirrors, and light input / output means for inputting / outputting light to / from the two-wavelength setting means, wherein the two-wavelength setting means selectively outputs light of the first wavelength component A first sub-resonator that returns to the main resonator, a second sub-resonator that selectively returns light of a second wavelength component different from the first wavelength component to the main resonator, An optical input / output means, and an optical branch provided between the first sub-resonator and the second sub-resonator; and the first sub-resonator and the second sub-resonator Is the first wavelength component and the light of the light from the light input / output unit, respectively. And the wavelength selection means for selecting the serial second wavelength component,
An optical feedback unit for returning the wavelength-selected light to the main resonator via the optical input / output unit; and the laser medium pumping unit, the main resonator, or the optical resonator.
A terahertz wave generator, wherein one of the wavelength setting means is provided with an optical output means for outputting the laser light serving as the excitation light from the two-wavelength oscillation laser. 2. The terahertz wave generator according to claim 1, wherein the laser medium is titanium sapphire. 3. The method according to claim 1, wherein at least one of the wavelength selecting means of the first sub-resonator and the second sub-resonator is a variable wavelength selecting means configured to change the selected wavelength. The terahertz wave generator according to claim 1 or 2, wherein: 4. The apparatus according to claim 1, wherein at least one of said first sub-resonator and said second sub-resonator has a light amount adjusting means for adjusting the light amount of the wavelength-selected light to be returned to said main resonator. The terahertz wave generator according to any one of claims 1 to 3, wherein: 5. The laser device according to claim 2, wherein the two-wavelength oscillation laser includes a laser light measuring unit that measures a wavelength and an intensity distribution of the laser light, and a terahertz wave monitor or a component of an apparatus that is obtained based on a measurement result by the laser light measuring unit. The terahertz wave generator according to any one of claims 1 to 4, further comprising control means for performing control.