JPH0945984A - Two frequency laser beam oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a small and compact two frequency laser beam oscillator by creating two optical resonator lengths using a birefringence material arranged in a laser resonator and oscillating the laser beam with two frequencies corresponding to the resonator lengths. SOLUTION: A reflector 1 reflects an incident laser beam in a laser resonator. A solid state laser medium 2 is pumped by a pumping means and oscillated. A birefringence material 3 creates two optical resonator lengths in the laser resonator. The light propagates through a crystal while being separated into two intrinsic polarized lights involving characteristic refractive indexes. In the case of a material exhibiting only birefringence, the intrinsic polarized beams are orthogonal polarized beams involving respective refractive indexes. When such a birefringence material is arranged in a laser resonator, laser beam can be oscillated with two frequencies.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-frequency laser light oscillating device suitable for measuring distance or displacement by optical heterodyne method, surface shape measurement and the like.

[0002]

2. Description of the Related Art Generally, a laser light oscillation device is a device for amplifying and oscillating light emitted by stimulated emission from a laser medium in a population inversion state by an optical resonator. 8 and 9 show the configuration of a general laser light oscillation device. As shown in FIG. 8 and FIG. 9, the laser light oscillation device usually includes a laser in an optical resonator formed by two or more reflection mirrors (for example, the reflection mirrors 33 and 34 and the output mirror 35 in FIG. 9). It has a configuration in which a medium is arranged, and is classified into a gas laser, a solid-state laser, a semiconductor laser, etc. depending on the type of the laser medium. In this laser light oscillating device, at least one of the reflection mirrors is used as an output mirror for outputting the laser light by lowering the reflectance than the other reflection mirrors in order to take out the laser light to the outside. The oscillation frequency of the laser light oscillated by the laser light oscillation device is mainly determined by the gain of the laser medium and the resonator length of the optical resonator, and the oscillation frequency can be changed by adjusting the resonator length.

The optical heterodyne method is an optical undulation (beat) in which a signal light having a certain frequency having information is superposed with a reference light whose frequency is slightly different from the frequency of the signal light.
Is generated, and various information that the signal light has is extracted by detecting this. In this optical heterodyne method, it is considered that a dual-frequency orthogonal polarization laser using light of two frequencies distinguished by orthogonality of polarization is an extremely effective light source. 2 currently known
Examples of the frequency orthogonal polarization laser include a Zeeman laser utilizing the Zeeman effect, a synthetic two-frequency laser, and a two-frequency laser utilizing the fact that polarizations between adjacent longitudinal modes are orthogonal to each other.

Japanese Laid-Open Patent Publication No. 54-160196 describes a two-frequency laser oscillation method utilizing the Zeeman effect. In the two-frequency laser oscillation method utilizing the Zeeman effect disclosed in Japanese Patent Laid-Open No. 54-160196, in a gas laser having no deflection selectivity, a DC or AC magnetic field is applied in the axial direction of the laser gain tube to contribute to laser oscillation. The oscillation gain curve is divided by subjecting the spontaneous emission spectrum to Zeeman division, and different longitudinal longitudinal modes of the laser resonator are simultaneously tuned to the respective divided gain curves to oscillate a two-frequency laser. In addition, JP-A-61
JP-A-124490 describes a synthetic two-frequency laser light oscillation device in which a light source such as a He-Ne laser and a semiconductor laser and an optical frequency shifter are combined. JP 6
The combined dual frequency laser light oscillating device of Japanese Patent No. 11-124490 is an optical frequency shifter, which is composed of a laser source, a high frequency generator for providing two frequencies, an electronic amplifier, an acousto-optic Bragg cell, a birefringent prism and an opaque diaphragm. The acousto-optic Bragg cell converts the incident light into two intermediate beams with a frequency difference equal to the driving frequency difference of the acousto-optic Bragg cell. Further, in Japanese Patent Application Laid-Open No. 61-250125, incident light is split into two, and the split two lights are individually operated for polarization, and finally the two lights are combined to form a straight line. A two-frequency laser light oscillator that forms polarized light is described.

[0005]

However, since the conventional two-frequency laser light oscillating device is a gas laser or a laser using an acousto-optical element, the device main body becomes large and it is difficult to miniaturize it. there were. Therefore, it is inconvenient to handle as a light source for measuring instruments and the like. Further, in the optical heterodyne method, it is desirable to set the frequency of the beat signal generated by the interference of the laser light output from the two-frequency laser light oscillator to a value that can be easily handled as an electric signal. It was difficult for the optical oscillator to freely change the frequency of the beat signal.

The present invention has been made in view of the above points, and an object thereof is to realize a two-frequency laser light oscillating device which is small in size, easy to handle, and has variable output laser light frequency. .

[0007]

In order to achieve the above-mentioned object, the invention according to claim 1 is a solid-state laser medium that emits light by stimulated emission, and reflects the light emitted from the solid-state laser medium. Of a plurality of reflection mirrors that resonate, an output mirror that outputs at least one part of the resonated light and that is at least one of the plurality of reflection mirrors, and an optical path formed by the plurality of reflection mirrors, The two-frequency laser light oscillation device is provided with the birefringence means arranged in at least one optical path.

The invention described in claim 2 is the same as the invention described in claim 1.
In the frequency laser light oscillation device, a two-frequency laser light oscillation device is provided which includes a reflection mirror position adjusting means for adjusting the position of at least one of the reflection mirrors.

According to a third aspect of the present invention, there is provided the two-frequency laser light oscillating device according to the first aspect, wherein the birefringence means comprises retardation varying means having a variable retardation.

According to a fourth aspect of the present invention, the birefringence means is an electro-optic effect means having an electro-optic effect.
The described two-frequency laser light oscillator was used.

The invention according to claim 5 provides the two-frequency laser light oscillation device according to claim 4, wherein the electro-optic effect means is an electro-optic crystal belonging to the point group 3 m or 32.

[0012]

According to the first aspect of the present invention, two optical resonator lengths are generated by the birefringent material disposed inside the laser resonator, and laser light having two frequencies corresponding to the resonator lengths is oscillated. To do.

According to a second aspect of the present invention, in the first aspect of the invention, an electric signal from the outside is input to the reflecting mirror position adjusting means, and the reflecting mirror position adjusting means is operated to move the position of the reflecting mirror. Control to adjust the laser cavity length.

According to a third aspect of the present invention, in the first aspect of the present invention, the retardation varying means is used as the birefringent means, whereby the optical path difference between the intrinsic polarized lights generated by the birefringent means is variable.

According to a fourth aspect of the present invention, in the first aspect of the present invention, an electro-optical effect means is used as the birefringence means, whereby the optical path difference between the intrinsic polarizations generated by the birefringence means is
It is controlled by an electric signal.

According to a fifth aspect of the present invention, in the invention according to the fourth aspect, two lasers output from the two-frequency laser light oscillating device are used by using the electro-optic crystal of the point group 3m or 32 for the birefringence means. The oscillation frequency of one of the laser beams, which is the reference, is kept constant, and the oscillation frequency of the other laser beam is controlled by an electric signal.

[0017]

Embodiments of the present invention will be described below. In general, light in a crystal is propagated after being separated into two unique polarized lights, and the unique refractive indexes correspond to the unique polarized lights. Birefringence and optical rotation are phenomena that cause a phase difference between intrinsic polarized lights in a crystal, but in the present invention, a material having at least birefringence is used as a material to be inserted into an optical resonator. As a material having birefringence, a material in which birefringence and optical rotation coexist and a material having only birefringence are conceivable. When a material in which birefringence and optical rotation coexist is used as the laser medium, the eigen polarization becomes elliptically polarized light, so that the output light from the laser light oscillator has two different frequencies and the major axes of the ellipses are orthogonal to each other. It becomes elliptically polarized light. Also,
When a material having only birefringence is used as the laser medium, the output light from the laser light oscillation device is two orthogonally polarized lights having different frequencies and orthogonal polarization directions. Hereinafter, an example using a material having only birefringence as a laser medium will be described, but the laser medium of the present invention is not limited to a material having only birefringence,
A material in which birefringence and optical rotation coexist may be used.

The invention according to claim 1 will be described based on the embodiment of FIG. FIG. 1 shows a basic configuration of a two-frequency laser light oscillation device using a birefringent material. In this two-frequency laser light oscillation device, a reflection mirror 1, a laser medium 2, a birefringent material 3, and an output mirror 4 are arranged as shown in FIG. 1, and two optical resonances having different polarization modes are provided inside a laser resonator. By generating the device length, the laser beams of two frequencies are oscillated simultaneously.

Next, each component will be described. The reflection mirror 1 reflects incident laser light inside the laser resonator. The laser medium 2 using a solid laser medium is excited by a pumping means (not shown) and oscillates. The birefringent material 3 produces two optical cavity lengths inside the laser cavity. In general, light in a crystal is propagated after being separated into two eigenpolarizations, and these eigenpolarizations have their own refractive indices. In the case of a material having only birefringence, the intrinsic polarized light is orthogonal polarized light which is orthogonal to each other, and there exists a corresponding refractive index. Therefore, when the thickness of the material having the birefringence is d, the optical path difference δ between the two intrinsic polarized lights is expressed by Equation 1.

Δ = (n1-n2) d (1)

Here, n1 and n2 are the refractive indices for the respective intrinsic polarized lights. However, here, it is assumed that the oscillation frequencies of the two laser beams are close to each other. Placing such a birefringent material in a laser cavity causes a difference in optical cavity length by δ in equation 1 in the polarization modes of the cavity corresponding to the intrinsic polarization of the birefringent material, resulting in two It is possible to oscillate laser light having a frequency. The two oscillation frequencies f1 and f2 at this time are expressed by Equations 2 and 3, respectively.

F1 = qc / (2L1) (2)

F2 = qc / (2L2) (3)

Here, c is the speed of light and q is a number representing the longitudinal mode. Further, L1 and L2 are optical resonator lengths corresponding to respective frequencies, and have a relationship as shown in Expression 4 with each other.

LI-L2 = δ (4)

In the present invention, if the gain of the laser medium is not taken into consideration as can be seen from the equations 1 to 4, the optical path difference δ between the cavity length L of the laser resonator and the intrinsic polarization generated by the material having birefringence. Two oscillation frequencies are determined by. The output mirror 4 is realized by a semitransparent mirror or the like, and outputs the laser beams of two frequencies having different optical resonance lengths separated by the birefringent material 3 to the outside of the laser resonator.

The invention according to claim 2 will be described based on the embodiment of FIG. In the optical heterodyne method, a beat signal generated by the difference between two oscillation frequencies is detected and electrical processing is performed based on this beat signal. Therefore, the frequency of the beat signal is set to a value suitable for electrical signal processing. It is desirable to keep. Therefore, the resonator length of the laser resonator is controlled to adjust the oscillation frequencies of the two laser beams. 2 of FIG.
The frequency laser light oscillator includes a reflection mirror 5, a laser medium 6, a birefringent material 7, an output mirror 8, and a piezo stage 9 that supports the reflection mirror 5 and adjusts the position of the reflection mirror 5. When an electric signal is given to this piezo stage 9 from an external control means (not shown),
The piezoelectric effect expands and contracts in the optical axis direction to finely adjust the position of the supporting reflection mirror 5. That is, the position of the reflection mirror 5 is finely adjusted by expansion and contraction using the piezoelectric effect of the piezo stage 9 to control the resonator length of the laser resonator.
Here, the beat frequency is controlled as follows. First, a beat signal is generated by causing laser light of two frequencies output from the laser resonator to interfere with each other using an analyzer. Next, the beat signal is converted into an electric signal by the light receiving element, and while monitoring the frequency of the electric signal,
The beat frequency is controlled by finely adjusting the position of the reflecting mirror 5 in the optical axis direction by controlling the piezo stage 9.

The invention according to claim 3 will be described based on the embodiment of FIG. In the invention described in claim 2, the beat frequency is controlled by finely adjusting the reflection mirror 5 supported by the piezo stage 9 in the optical axis direction. However, in the invention described in claim 3, the birefringence having birefringence is controlled. The beat frequency is controlled by adjusting the optical path difference δ between the intrinsic polarized lights generated in the refractive material, that is, by adjusting the retardation. Here, the retardation is a phase difference between two light rays passing through the anisotropic crystal and having different polarization directions. Birefringence can be adjusted by changing the retardation. The two-frequency laser light oscillation device shown in FIG. 3 is an example in which the compensating plate 12 is used as the retardation varying means. The reflecting mirror 10, the laser medium 11, and the output mirror 13 are the same as those described in the first and second aspects, and therefore their individual explanations are omitted. In the dual-frequency laser light oscillation device having the configuration of FIG. 3, a change in the optical path difference δ between the intrinsic polarizations caused by finely adjusting the position of the compensation plate 12 in the direction perpendicular to the optical axis of the laser light inside the laser resonator. By using it, the beat frequency is made variable. here,
Similarly to the embodiment of the invention described in claim 2, the beat frequency is controlled by converting the beat signal obtained by causing the output laser beams of different frequencies to interfere with each other by the light receiving element,
Control is performed by finely adjusting the position of the compensator 12 in the direction perpendicular to the optical axis of the laser light while monitoring the frequency of this electric signal.

The invention according to claim 4 will be described with reference to the embodiment shown in FIG. According to the invention described in claim 4, an electro-optic crystal is used as the birefringent material having birefringence, and an electric signal is applied to the electro-optic crystal to adjust the optical path difference δ. FIG.
As shown in FIG. 11, the reflection mirror 14, the laser medium 15, and the output mirror 17 are the same as those in the above-mentioned embodiment, and therefore their explanations are omitted. The electro-optic crystal 16 is a material in which the refractive index of intrinsically polarized light changes by applying an electric field. The electro-optic crystal 16 has electrodes mounted on two opposite surfaces, and a voltage power supply 18 is connected to the electrodes. The optical path difference δ between the intrinsic polarizations of the electro-optic crystal 16 is adjusted by controlling the voltage applied to the electro-optic crystal 16 by the voltage power supply 18. A specific example of this electro-optic crystal 16 is KD
P, DKDP, ADP, BSO, BGO, SiO2 (crystal) and the like can be mentioned. For example, K as an electro-optic crystal
The optical path difference δ in the case of using the DP for the lateral modulation arrangement as shown in FIG.

[0030]

[Equation 1]

Here, V is the applied voltage, d is the length of the electro-optic crystal, D is the distance between the electrodes, and r63 is the electro-optic constant. The oscillation frequencies f1 and f2 can be obtained by substituting the equation 5 into the equations 2, 3, and 4. Furthermore, it is assumed that the two oscillation frequencies are close to each other.

The invention according to claim 5 will be described with reference to the embodiments shown in FIGS. In the inventions of claim 2, claim 3, and claim 4, when the beat frequency is changed, both of the two oscillation frequencies change, which is inconvenient in precision measurement by the optical heterodyne method. Therefore,
An electro-optic crystal belonging to the point group 3m or 32 is used.
The electro-optic crystal of the point group 3m or 32 can change the refractive index of only one of the two intrinsic polarized lights. For example, FIG. 5 and FIG. 6 show quartz 27 (Si
In this example, O2) and lithium niobate 29 (LiNbO3) were used for the electro-optic crystal. As shown in FIG. 5, in the case of quartz, the crystal axis and the electrode 26 are arranged, and the laser light is made incident from the Y-axis direction. At this time, the refractive indices nx and nz for the intrinsic polarization in the X-axis direction and the Z-axis direction are expressed by Equations 6 and 7
become that way.

[0033]

[Equation 2]

[0034]

(Equation 3)

Here, n0 and ne are the refractive indices for the intrinsic polarized light in the X-axis and Z-axis directions when no voltage is applied to the electrode 26, r11 is the electro-optical constant, V is the voltage applied to the electrode, and D is the voltage. Represents the distance between the electrodes. As can be seen from Expression 6, the change in the refractive index with respect to the voltage V applied to the electrode 26 occurs only in the intrinsic polarization in the X-axis direction. Therefore, the change in the optical path length of the intrinsic polarization due to the voltage V occurs only in the intrinsic polarization in the X-axis direction, and as a result, the oscillation of the polarization mode in the X-axis direction is maintained with the oscillation frequency for the polarization mode in the Z-axis direction kept constant. The frequency can be controlled, that is, the beat frequency can be controlled.

Next, as shown in FIG. 6, when lithium niobate 29 is used, the crystal axis and the transparent electrode 28 are arranged, and laser light is made incident from the y-axis direction in parallel with the electric field direction. At this time, the refractive indices n0 and nz for the intrinsic polarized light in the X-axis direction and the Z-axis direction are as shown in Expressions 8 and 9.

[0037]

(Equation 4)

[0038]

(Equation 5)

Therefore, similarly to the crystal 27, the oscillation frequency of the polarization mode in the X-axis direction can be adjusted while keeping the oscillation frequency for the polarization mode in the Z-axis direction constant. Similar to Equations 6 and 7, in Equations 8 and 9, n0 and ne are the refractive indexes for the intrinsic polarization in the X-axis and Z-axis directions when no voltage is applied to the transparent electrode 28, and r22 is electro-optic. A constant, V represents the applied voltage, and D represents the distance between the electrodes.

The laser medium used in the present invention preferably has no gain anisotropy. For example, Nd: YA
G crystals and the like are preferable. FIG. 7 shows a two-frequency laser light oscillation device in which a laser medium is Nd: YAG crystal and a semiconductor laser is used as a light source for excitation. FIG. 7 shows an end face excitation type embodiment, and by adopting such a configuration, it becomes possible to realize a more compact two-frequency laser light oscillation device.

[0041]

As described above, according to the invention described in claim 1, it is possible to realize a two-frequency laser light oscillation device which is smaller than the conventional one.

According to the invention described in claim 2, in addition to the effect of the invention described in claim 1, the beat generated by the interference of the laser light output from the two-frequency laser light oscillation device by expanding and contracting the piezo stage 9 The frequency of the signal can be controlled to a value that is easy to handle as an electric signal.

According to the third aspect of the invention, in addition to the effect of the first aspect of the invention, the beat generated by the interference of the laser light output from the two-frequency laser light oscillator by operating the compensator 12 The frequency of the signal can be controlled to a value that is easy to handle as an electric signal.

According to the invention described in claim 4, in addition to the effect of the invention described in claim 1, by adjusting the voltage applied to the electro-optic crystal 16, the laser light output from the dual frequency laser light oscillation device is obtained. It is possible to control the frequency of the beat signal generated by the interference of 1 to a value that is easy to handle as an electric signal.

According to the invention of claim 5, in addition to the effects of the inventions of claims 1 and 4, the two of the two laser lights having different frequencies output from the two-frequency laser light oscillator are used as a reference. It becomes possible to adjust the frequency of the beat signal while keeping the oscillation frequency of one of the laser beams constant.

[Brief description of drawings]

FIG. 1 is a diagram showing a basic configuration of a two-frequency laser light oscillation device of the present invention.

FIG. 2 is a diagram showing a configuration of a two-frequency laser light oscillation device according to a second aspect.

FIG. 3 is a diagram showing a configuration of a two-frequency laser light oscillation device according to a third aspect.

FIG. 4 is a diagram showing a configuration of a two-frequency laser light oscillation device according to a fourth aspect.

FIG. 5 is a diagram showing an example in which quartz is used for the electro-optic crystal having the structure according to the fourth aspect of the present invention.

FIG. 6 is a diagram showing an example in which a lithium niobate crystal is used as the electro-optic crystal having the structure according to the fourth aspect of the present invention.

FIG. 7 is a diagram showing an example in which an Nd: YAG laser crystal is used as a laser medium in the two-frequency laser light oscillation device of the present invention.

FIG. 8 is a diagram showing a configuration of a general laser light oscillator.

FIG. 9 is a diagram showing a configuration of a general laser light oscillator.

[Explanation of symbols]

1, 5, 10, 14, 22, 30, 33, 34 Reflecting mirror 2, 6, 11, 15, 31, 36 Laser medium 3, 7, 24 Birefringent material 4, 8, 13, 17, 25, 32, 35 Output Mirror 9 Piezo Stage 12 Compensation Plate 16 Electro-Optical Crystal 18 High Voltage Power Supply 19 Semiconductor Laser Driving Circuit 20 Semiconductor Laser 21 Lens 23 Nd: YAG Crystal 26 Electrode 27 Crystal 28 Transparent Electrode 29 Lithium Niobate.

Claims (5)

[Claims] 1. A solid-state laser medium that emits light by stimulated emission, a plurality of reflecting mirrors that reflect and resonate the light emitted from the solid-state laser medium, and output a part of the resonated light. An output mirror, which is at least one of the plurality of reflection mirrors, and a birefringence unit arranged in at least one optical path of the optical paths formed by the plurality of reflection mirrors. Two-frequency laser light oscillator. 2. The two-frequency laser light oscillating device according to claim 1, further comprising a reflecting mirror position adjusting means for adjusting the position of at least one of the reflecting mirrors. Optical oscillator. 3. The dual-frequency laser light oscillating device according to claim 1, wherein the birefringence means comprises retardation varying means having a variable retardation. 4. The dual-frequency laser light oscillation device according to claim 1, wherein the birefringence means is an electro-optic effect means having an electro-optic effect. 5. The two-frequency laser light oscillating device according to claim 4, wherein the electro-optic effect means is an electro-optic crystal belonging to the point group 3m or 32.