JPH07170003A - Laser oscillation equipment capable of changing wavelength - Google Patents

Abstract

PURPOSE:To obtain a laser oscillation equipment which can stably continuously change output wavelength. CONSTITUTION:The equipment is provided width the following; an end mirror(EM)31 which reflects only the light in a specific frequency range, a nonlinear optical crystal 27 which is arranged on the input reflection optical axis of the EM31 and generates parametric light from supplied pumping light (LP), a grating (G)29 which can adjust the angle to the optical axis of output light to spectrally analyze the light outputted from the nonlinear optical crystal, and a total reflecting mirror 30 which totally reflects the specific light spectrally analyzed by the G29 toward the G29. Further the following are installed; a polarization prism 26 which is arranged between the EM31 and the nonlinear optical crystal, reflects the circularly poralized LP and makes it enter the nonlinear optical crystal, a conversion member 28 which is arranged between the G29 and the nonlinear optical crystal, turns the linearly polarized light into a circularly polarized light and turns the circularly polarized light into a linearly polarized light, and pumping wave supply means 21, 23, 24 capable of order selection which generates harmonics of desired order from the fundamental light from a laser oscillating means generating the fundamental light, and supplies the harmonics to a prism, as the LP of polarization characteristics which the polarization prism reflects.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength tunable laser device using the principle of optical parametric oscillation.

[0002]

2. Description of the Related Art In a parametric oscillation laser device, laser oscillation is performed by injecting light for exciting laser oscillation into an optical resonator. The light for exciting this laser oscillation is used as a pump wave. Call.

Then, when a nonlinear optical crystal is placed in an optical resonator in which a signal wave or an idler wave resonates and a strong pump wave is made incident, one or both of the signal wave and the idler wave oscillate. The parametric oscillation is called the single resonance type and the latter is the multiple resonance type. If the angular frequency of the pump wave P is ω _p , the angular frequency of the signal wave S is ω _s , and the angular frequency of the idler wave I is ω _i , then these three angular frequencies ω _p , ω _s , and ω _i are , Ω _p = ω _s + ω _i .

However, the incident light wave to the nonlinear optical crystal is only the pump wave P. Further, particularly when ω _s = ω _i is called degenerate parametric oscillation. In a nonlinear optical crystal,
The second-order non-linear polarization causes power transfer from the pump wave P to the signal wave S and the idler wave I, and the latter two waves can be amplified. If the intensity of the pump wave is large enough to overcome the loss of the resonator by this parametric amplification gain, the signal wave S
And the self-oscillation of the idler wave I occurs.

Since the ω _s and ω _i can be continuously changed by adjusting the phase by a method such as temperature tuning or angle tuning, the optical parametric oscillation is one of important means for obtaining wavelength tunable coherent light. Used.

In the conventional solid-state laser device using such an optical parametric oscillation principle, a single wavelength (for example, as a pump wave P having an angular frequency ω _p in the resonator) (for example,
Since the configuration uses only light of 355 nm),
The optical system structure as shown in is used.

For example, when the third harmonic wave 355 nm of the YAG laser (having a frequency of ω _p ) is used as the pump wave P, the input pump wave P is incident from the end mirror 2 as shown in the figure.

In this case, the end mirror 2 employs a dichroic mirror which transmits light having a wavelength component of 355 nm or less and reflects light having a wavelength component longer than that, for example, 400 nm or more. A wavelength component of 355 nm is obtained by passing through the end mirror 2. The situation is shown in FIG.

In FIG. 8, the vertical axis represents reflectance and the horizontal axis represents wavelength (nm). The pump wave P having the angular frequency ω _p that has passed through the end mirror 2 enters the nonlinear optical crystal 3. In the nonlinear optical crystal 3, the pump wave P having the angular frequency ω _p is divided into a signal wave S having the angular frequency ω _s and an idler wave I component having the angular frequency ω _i by the optical parametric effect, and the signal wave S and the idler wave I grow in the nonlinear optical crystal 3 as it progresses.

That is, the pump wave P having the angular frequency ω _p becomes ω _p = ω _s + ω _i due to the optical parametric effect in the nonlinear optical crystal 3, and each point in the nonlinear optical crystal 3 through which the incident laser beam passes. At this point, a signal wave S having an angular frequency ω _s and an idler wave I having an angular frequency ω _i are generated, and the signal wave S and the idler wave I generated at each point travel in the traveling direction of the laser light. Generated signal wave S
And the idler wave I are integrated and grow (intensity increases).

After these lights P, S, and I are emitted from the crystal, they are incident on the grating (diffraction grating) 4 provided on the emission optical path, and part of them are emitted as specular reflection light 5 from the cavity.

Here, the above-mentioned cavity in the laser device means a resonator, and is usually a portion sandwiched between two mirrors (the laser light resonates at this portion to cause laser oscillation).
Refers to.

The remaining light not emitted from the cavity has respective frequencies ω _p , ω _s , and ω _i , and the wavelengths are different from each other. Therefore, the light is dispersed by the grating 4 at an angle corresponding to the wavelength. Then, when the angle of the grating 4 is set so that only the signal wave S of the angular frequency ω _s thereof is vertically incident on the total reflection mirror 7 as indicated by reference numeral 6, the total reflection mirror 7 The totally reflected signal wave S is incident on the grating 4 again, is diffracted in the original direction by the grating 4, passes through the nonlinear optical crystal 3, and returns to the end mirror 2.

The end mirror 2 is 400 nm as described above.
Since the above light is reflected, the wavelength of the signal wave S is 400 nm.
If it is above, it is reflected. Here, when the expression of ω _p = ω _s + ω _i showing the relationship among the pump wave P, the signal wave S, and the idler wave I is expressed by wavelength, 1 / λ _p = (1 / λ _s ) + (1 / λ _i ) , Λ _p is the wavelength of the pump wave having the angular frequency ω _p , λ _s is the wavelength of the signal wave S having the angular frequency ω _s , and λ _i is the angular frequency ω _i
Shows the wavelength of the idler wave. And λ _p = 355
In the case of nm, since λ _s and λ _i > 0, λ _s and λ
_i > 355 nm, which is usually λ _s , λ _i > 400 nm due to the wavelength transparency of the crystal and the reflected light characteristics of the end mirror 2.
Becomes

Angular frequency ω _s reflected by the end mirror 2
The signal wave S is incident on the nonlinear optical crystal 3 again, but at this time, it grows together with the signal wave S newly generated by another pump wave P that is present at the same time, and is amplified.

Therefore, for the wavelength of the signal wave S, laser oscillation can be performed in the cavity formed by the end mirror 2, the nonlinear optical crystal 3, the grating 4 and the total reflection mirror 7.

According to such a configuration, the end mirror 2
Also, by changing the angle of the grating 4 with respect to the optical axis of the nonlinear optical crystal 3, the wavelength of the light that is vertically incident on the total reflection mirror 7 is different. Therefore, by adjusting this angle, laser oscillation is performed at various wavelengths. be able to.

However, in the case of ω _s to ω _i , that is, when approaching ω _s to ω _p / 2, this system has a drawback that it becomes unstable in principle and laser oscillation does not occur. For example, when the pump wave has a wavelength of 355 nm, the wavelength of 4
Oscillation of 10 nm to 2000 nm is possible, but wavelength 7
Normal oscillation does not occur in a region of about ± 25 nm near 10 nm.

[0019]

In the conventional solid-state laser device using the optical parametric oscillation principle, as described above, the parametric oscillation (ω _p = ω _s + ω _i ) causes ω _s
In the case of ω _i , the signal wave S (angular frequency ω _s ) and the idler wave I (angular frequency ω _i ) interfere with each other in the crystal, and the signal wave S
Alternatively, the amplifying action of the idler wave I is distorted, the oscillation becomes unstable, and finally it does not oscillate.

Normally, when the pump wave has a wavelength of 355 nm,
Oscillation is possible in the wavelength range of 410 nm to 2000 nm, but ± 25 near the wavelength of 710 nm where ω _s to ω _i.
It does not oscillate normally in the nm range. FIG. 9 shows the oscillation output.

In the spectroscopic measurement using the laser beam, the continuity of the wavelength is very important.
If there is a region where oscillation is possible, even in a small region of about 25 nm, it becomes a serious defect.

Of course, if the wavelength of the pump wave can be switched, the ± 25 nm region near the wavelength of 710 nm can be eliminated by using the pump wave of another wavelength.
However, in the case of the conventional method in which the pump wave is made incident from the end mirror, for example, when the wavelength of the pump wave is 355 nm, the end mirror of the cavity reflects light of 400 nm or more. For example, light having a wavelength of 532 nm cannot be made incident. In this case, since the laser oscillation frequency can be varied only by the spectrum of the grating using the pump wave of 355 nm, it is inevitable that the region where the laser oscillation does not occur normally occurs though it is a slight wavelength range.

That is, in the optical parametric oscillation, the laser oscillation does not normally occur although it is a slight wavelength range in the wavelength range half the wavelength of the pump wave. Since this is the method in which the pump wave is incident from the end mirror in the conventional system, it cannot be configured to switch to the pump wave of another wavelength due to the reflection characteristic of the end mirror that removes unnecessary wavelengths. Due to.

Therefore, the object of the present invention is to
It is an object of the present invention to provide a wavelength tunable laser oscillating device capable of allowing a pump wave having a desired wavelength to be incident, and thus capable of stably continuously varying the output wavelength.

[0025]

In order to achieve the above object, the present invention is configured as follows. That is, an end mirror that reflects only light in a predetermined frequency range, a non-linear optical crystal that is arranged on the incident / reflected optical axis of this end mirror and that generates parametric light from a supplied pump wave, and that exits from this non-linear optical crystal. An angle-adjustable grating with respect to the optical axis of the emitted light for separating the separated light, a total reflection mirror arranged at an angle for totally reflecting the specific light separated by the grating toward the grating, and the end mirror Is arranged between the grating and the nonlinear optical crystal, and is disposed between the grating and the nonlinear optical crystal, and is disposed between the grating and the nonlinear optical crystal. And the fundamental light from the laser oscillation means that generates the fundamental light and the conversion member that converts the circularly polarized light into the linearly polarized light. Harmonics generated more configuration and orders selectable pumping wave supplying means for supplying a polarizing prism as the pump wave of the polarization characteristic of reflecting the polarizing prism.

[0026]

In such a structure, the end mirror, the nonlinear optical crystal for generating parametric light from the supplied pump wave, and the angle of the emitted light for separating the light emitted from the nonlinear optical crystal with respect to the optical axis can be adjusted. A polarizing prism is provided in the cavity of the laser oscillation by the grating and the total reflection mirror that totally reflects the specific light dispersed by this grating toward the grating, and the harmonics of the desired order are generated from the pump wave supply means. And guides it to the cavity through the polarizing prism.

Then, parametric light is generated in the cavity and resonated between the end mirror and the total reflection mirror to obtain output laser light. By adjusting the angle of the grating, output laser light of a desired wavelength is obtained, but since the pump wave is guided into the cavity through the polarization prism, the wavelength is not affected by the characteristics of the end mirror.

Therefore, it is possible to use pump waves of a plurality of types of wavelengths, so that the wavelength of the output laser light can be varied like a laser oscillator using the parametric effect of a pump wave having only a single specific wavelength. When
The fact that oscillation becomes unstable in the specific wavelength range
This can be avoided by switching to a pump wave of another wavelength. Therefore, according to the present invention, it is possible to provide a solid-state laser oscillator capable of continuously varying the output wavelength.

[0029]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) When a pump wave is incident from the end mirror as in the conventional case, the end mirror normally reflects light of 400 nm or more if the wavelength of the pump wave is 355 nm. In order to improve the drawback that the light of wavelength 532 nm cannot enter the cavity, the device of the present invention uses a polarization prism, which is arranged in the cavity, and the polarization of the pump wave is reflected by the polarization prism. After making it (for example, P-polarized), it is made incident on a polarizing prism from a certain direction, and its reflected light is made incident on a cavity so that pump waves of a plurality of wavelengths (two wavelengths in the embodiment) can be used.

In the apparatus of the present invention, the λ / 4 plate is provided between the nonlinear optical crystal in the cavity and the grating so that the signal wave S can resonate through the polarizing prism. In order to introduce the pump wave into the cavity, the polarization prism must have a polarization characteristic that reflects the polarization mode of the pump wave that is introduced,
By this reflection, it becomes possible to introduce a pump wave into the cavity, but with this state as it is, the signal wave S (the angular frequency is ω from the nonlinear optical crystal obtained by this pump wave).
_{Since s} ) is reflected by the polarizing prism, a λ / 4 plate is provided so as not to be reflected by the polarizing prism.
Then, when the signal wave S from the nonlinear optical crystal is emitted, λ
When passing back through the / 4 plate and being reflected by the reflection mirror of the cavity, the λ / 4 plate is passed again, and as a result, the λ / 4 plate is passed twice, resulting in a λ / 2 phase shift. Since the polarization prism is S-polarized, it can pass through the polarization prism this time, which enables laser oscillation.

The third harmonic of the YAG laser can be generated by mixing the second harmonic and the fundamental wave with a mixing crystal. Therefore, when oscillating a wavelength near 710 nm, the mixing crystal is removed and the wavelength of 532 nm is generated. The second harmonic is directly incident on the nonlinear optical crystal. For a pump wave of 532 nm, the unstable region is 106
Since it is 4 nm, it becomes possible to oscillate stably in the vicinity of 710 nm.

As described above, by using the polarization prism, two kinds of wavelengths of 355 nm and 532 nm can be used as the pump wave.
When nm is used, it is impossible to oscillate in the vicinity of 710 nm. When oscillates in the vicinity of 710 nm, the wavelength is 532.
It can be switched to nm and used as a pump wave, which allows stable oscillation. Also,
A polarization prism is used, and two types of wavelengths are used as pump lasers (pump waves) (for example, the third harmonic wave 35 of the YAG laser 35).
5 nm and the second harmonic wave 532 nm), so that while monitoring the wavelength of the output laser light or signal wave from the cavity with a wavelength measuring device,
When it approaches 710 nm, it is possible to stably oscillate near 710 nm by switching the pump wave from 355 nm to 532 nm automatically or manually.

FIG. 1 shows the main structure of the first embodiment of the device of the present invention. In the figure, 21 is a laser light source, for example YAG
A laser oscillator, 22 is a laser beam, 23 is a second harmonic generator, 24 is an optical mixing device, 25 is a mirror, 2
6 is a polarizing prism, 27 is a nonlinear optical crystal similar to that described in the conventional example, 28 is a λ / 4 plate, 29 is a grating, and 30 is a mirror.

The YAG laser oscillator 21 is a laser light source that oscillates a laser beam 22 of a fundamental wave that is a source of a pump wave, and the second harmonic wave is in the optical path of the laser beam 22 emitted from the YAG laser oscillator 21. A generator 23, a light mixing device 24, and a mirror 25 are provided.

The second harmonic generator 23 outputs a wavelength 532 from the laser light 22 (fundamental wave) from the YAG laser oscillator 21.
The second mixing unit 24 generates a second harmonic wave of nm and outputs it together with the fundamental wave. The optical mixing device 24 generates a third harmonic wave of a wavelength of 355 nm from the fundamental wave and the second harmonic wave by optical mixing. is there.

The optical mixing device 24 is constructed so that it can enter and leave the optical path. In addition, the optical mixing device 24
The light emitted after mixing is adjusted so as to be a polarized light of a type reflected by the polarizing prism 26 (for example, P-polarized light).

The mirror 25 is divided into a second harmonic component reflection region 25a and a third harmonic component reflection region 25b, and the mirror 25 has the above-mentioned two components with respect to the laser light emission optical path from the laser oscillator 21. The slide operation is possible so that one of the areas comes. In the second harmonic component reflection area 25a of the mirror 25, the second harmonic component 2ω
_The optical filtering material is coated so as to reflect only ₀ (for example, in the case of a YAG laser, the second harmonic having a wavelength of 532 nm), and in the third harmonic component reflection area 25b, the second harmonic is reflected. Of the output light from the generator 23, an optical filtering material is coated so as to reflect only the third harmonic component 3ω ₀ (for example, in the case of a YAG laser, the third harmonic having a wavelength of 355 nm).

The polarization prism 26 has an entrance / exit surface 26.
a and 26b are arranged so as to pass through the incident / reflected optical axis of the end mirror 30, and in order to receive light from the reflected optical path of the mirror 25, the incident surface 26c for the reflected optical path is provided. The surface 26c is arranged so as to face the reflection optical path of the mirror 25.

When the reflected light from the mirror 25 is incident on the polarization prism 26, the polarization prism 26 emits light having a specific polarization state (for example, P
It is a prism that reflects polarized light and transmits the other light (for example, S-polarized light).

A nonlinear optical crystal 27 and λ /
Four plates 28 and a grating 29 are arranged. The grating 29 is arranged at an angle with respect to the incident / reflected optical axis of the end mirror 30. Also, the grating 29
Is for diffracting incident light, and is for performing spectral analysis according to the incident angle and wavelength. Further, in order to enable laser oscillation at various wavelengths, the grating 29 can adjust the angle with respect to the incident / reflecting optical axis of the end mirror 30, and although not shown, an adjusting mechanism therefor is provided. Is equipped with.

The end mirror 30 has a specific wavelength, for example,
It is coated with a material that reflects all light above 400 nm. Further, the mirror 30 is provided so as to face the grating 29, and reflects the vertically incident light of the light split by the grating 29 back to the grating 29.

Here, the λ / 4 plate 28, P-polarized light, S-polarized light, and the polarization prism 26 will be described. Consider two layers of media n1 and n2 having different refractive indexes as shown in FIG. Now, it is assumed that the laser beam Lb enters from the medium n1 to the medium n2 at an angle. This incident laser beam B
The plane defined by L and the normal L is called the incident plane, and the polarization direction parallel to the plane of incidence (arrows A1 and A2 in the figure) is called P-polarized light, and the polarization direction perpendicular to the plane of incidence (the figure is shown in the figure). Is the direction of the direction symbol indicated by reference sign B and is the direction perpendicular to the paper surface) is called S-polarized light.

The polarizing prism 26 has different transmission and reflection characteristics depending on the polarization direction of the light, and is a prism having different reflection and transmission characteristics depending on the polarization direction of the incident light. Assuming that the polarization prism 26 is a P-polarization reflection type polarization prism, for example, if the incident light BL is P-polarized light, it is reflected in the direction of the reflection path R1 and the incident light BL is S-polarized light. For example, it has a characteristic of being refracted and transmitted through the path R0.

In principle, the polarization prism is basically composed of two triangular prisms p1 and p2 as shown in FIG.
If the incident light BL is a P-polarized light, it is reflected at the boundary surface of the prisms p1 and p2 and is reflected by the reflection path R1. If the incident light BL is an S-polarized light, it has a characteristic of being transmitted through the transmission path R0.

If the transmitted light is linearly polarized light, the quarter-wave plate (λ / 4 plate) 28 converts it to circularly polarized light and outputs the circularly polarized light, and the transmitted light is circularly polarized light. For example, it is an optical element that converts the light into linearly polarized light and outputs it. Where x of polarization
A light having a constant ratio of the component to the y component is called linearly polarized light, and light whose polarization direction spirally rotates with the traveling direction is called circularly polarized light. That is, the linearly polarized light is light polarized only in one direction, for example, the z-axis or the y-axis direction, and the circularly polarized light is shown in FIG.
As shown in FIG. 4, the polarized light rotates in the x and y planes with the z axis as an axis. Therefore, when the state of change with time is shown, the polarization direction is spiral with the traveling direction as shown in FIG. 4B. It is the light that rotates.

That is, when linearly polarized light is passed through the 1/4 λ plate 28, circularly polarized light as shown in FIG. 5A is obtained, and when circularly polarized light is passed through the 1/4 λ plate 28, it is shown in FIG. 5B. Such linearly polarized light is obtained. However, the 1/4 λ plate 28 needs to be installed at a specific angle with respect to the polarization direction. The one having such a property is called a λ / 4 plate.

Next, the operation of the present apparatus having the above configuration will be described. In such a configuration, the YAG laser oscillator 21
The laser light 22 having the angular frequency ω ₀ emitted from is incident on the second harmonic generator 23. Then the second harmonic generator 2
3 produces a second harmonic component 2ω ₀ of angular frequency ω ₀ ,
The second harmonic component of 2ω ₀ is output together with the fundamental wave of angular frequency ω ₀ .

The generated second harmonic wave 2ω ₀ emitted from the second harmonic wave generator 23 together with the fundamental wave ω ₀ is incident on the optical mixing device 24 in the outgoing optical path and passes through the optical mixing device 24. The third harmonic component 3ω ₀ is generated by mixing. Then, the third harmonic component 3ω ₀ generated by the optical mixing device 24 is emitted together with the second harmonic 2ω ₀ and the fundamental wave ω ₀ , and is reflected by the mirror 25.
Sent to.

As a result, the output light from the optical mixing device 24 has a fundamental wave with an angular frequency of ω ₀ and an angular frequency of 2ω _0.
The laser light of the three components of the second harmonic of the above and the third harmonic of the angular frequency of 3ω ₀ are mixed, and these are incident on the mirror 25.

The mirror 25 reflects the second harmonic component 2ω ₀ only, that is, the second harmonic component reflection region 25a, which is the first region, and the third harmonic component 3ω ₀ , which reflects only the second component. It is divided into a third harmonic component reflection area 25b, which is a region, and the third harmonic component reflection area 2 is initially provided in the optical path.
It is set so that only 5b is located.

Therefore, the output light from the optical mixing device 24 is a third harmonic component reflection region 2 which is a region coated with a material that reflects only 3ω ₀ in the mirror 25.
5b, and only the light of the component of angular frequency 3ω ₀ is reflected by this mirror 25 and is incident on the polarization prism 26.

At this time, the parametric oscillation is the pump wave P.
In order to oscillate using the component of which the angular frequency is ω _p = 3ω ₀ , the pump wave having the angular frequency ω _p is mixed by light so that the polarization wave of the polarization prism 26 reflects (for example, P polarization). It is adjusted by the device 24.

As a result, as the pump wave (angular frequency ω _p ) P for parametric oscillation, the component of the third harmonic wave 3ω ₀ generated in the optical mixing device 24 of FIG. The optical axis from the mirror 31 to the grating 29 is reflected to the side of the nonlinear optical crystal 27 and made incident on the nonlinear optical crystal 27 as a pump wave P.

The pump wave P causes parametric oscillation. As described above, the input light for causing parametric oscillation is called a pump wave (light for excitation) in optical parametric oscillation, and the angular frequency of the pump wave P is represented by ω _p . Then, the nonlinear optical crystal 27
The pump wave P incident on is generated by the optical mixing device 24.

That is, the pump wave P having the angular frequency ω _p
Is adjusted by the optical mixing device 24 so that the polarized light is polarized by the polarizing prism 26 (for example, P-polarized light), so that the angular frequency ω _p (= third harmonic component 3ω)
_The component ( ₀ ) is reflected by the polarization prism 26 and is incident on the nonlinear optical crystal 27.
7, the signal wave S and the idler wave I are generated for the same reason as in the conventional method described above, and the optical axis from the end mirror 31 to the grating 29 is emitted to the λ / 4 plate 28 side.

The light generated from the nonlinear optical crystal 27 becomes circularly polarized by passing through the λ / 4 plate 28, and only the signal wave S is generated by the grating 2 as in the conventional method described above.
The light is reflected by the mirror 9 and the mirror 30 in the direction opposite to the incident direction, travels again along the optical axis from the end mirror 31 to the grating 29 to the λ / 4 plate 28, and passes through the λ / 4 plate 28.

The signal wave S that has passed through the λ / 4 plate 28 becomes linearly polarized light this time, but the pump wave P (each frequency ω _p = 3ω)
₍₀ ) has a polarization (for example, S-polarized light) perpendicular to the polarization direction of ( ₀ ), this time, it passes through the polarizing prism 26, reaches the end mirror 31, and is regularly reflected by the end mirror 31. In this case, the end mirror 31 is coated with a material that reflects all light having a wavelength of 400 nm or more.

Therefore, the signal wave S having a component component having a wavelength of 400 nm or more is reflected by the end mirror 31 in the incident / reflecting optical axis direction, and the reflected signal wave S having a component component having a wavelength of 400 nm or more passes through the polarization prism 26 again. After passing through, it enters the nonlinear optical crystal 27, is amplified as in the conventional method, and oscillates.

That is, in the nonlinear optical crystal 27, the pump wave P having the angular frequency ω _p is partly converted into the signal wave S having the angular frequency ω _s and the idler wave I component having the angular frequency ω _i by the optical parametric effect. Then, the signal wave S and the idler wave I grow in the nonlinear optical crystal 3 as they progress. That is, the pump wave P having the angular frequency ω _p becomes ω _p = ω _s + ω _i due to the optical parametric effect in the nonlinear optical crystal 27, and the angular frequency at each point in the nonlinear optical crystal 27 through which the incident laser beam passes. A signal wave S of ω _s and an idler wave I of angular frequency ω _i are generated,
Since the signal wave S and the idler wave I generated at each point travel in the traveling direction of the laser light, the signal wave S and the idler wave I generated at each point are integrated and grow (intensity increases). go.

After these lights P, S, I are emitted from the crystal, they are incident on the grating (diffraction grating) 4 provided on the emission optical path, and part of them are emitted as specular reflection light 5 from the cavity. Here, the cavity means a resonator, and usually indicates a portion sandwiched between two mirrors (laser light resonates at this portion to cause laser oscillation).

Therefore, in the laser device of FIG.
It refers to the part sandwiched between the mirror 30 and the end mirror 31.
Further, in the present laser device, the oscillation wavelength can be changed by changing the angle of the grating 29, as in the conventional method.

When the signal wave S approaches 710 nm, stable oscillation cannot be performed. Therefore, if the signal wave S has a wavelength near 680 nm, the pump wave P is changed to the third harmonic component (ω _p =
3ω ₀ ) to the second harmonic component (ω _p = 2ω ₀ ).

As a method of changing the pump wave P from 3ω ₀ to 2ω ₀ , in this apparatus, first, the optical mixing device 24 is shifted to the retracted position 24 'out of the laser emission optical path. Then, since the optical mixing device 24 does not exist on the optical path, the laser light 22 from 21 enters the mirror 25 only via the second harmonic generator 23, and the third
The higher harmonic wave 3ω ₀ is not generated. Therefore, only the output light from the second harmonic generator 23 containing only the second harmonic component 2ω ₀ and the fundamental wave ω ₀ is incident on the mirror 25.

In accordance with the withdrawal of the optical mixing device 24 from the optical path, the mirror 25 is shifted so that the second harmonic component reflection area 25a thereof is located at the position on the laser optical path. Then, the portion of the second harmonic component reflection region 25a coated with a material that reflects only the second harmonic component 2ω ₀ comes on the optical path, and therefore, of the output light from the second harmonic generator 23, , The second harmonic component 2ω ₀ is reflected and is incident on the polarization prism 26.

Also in this case, the polarization direction of the light of the second harmonic wave 2ω ₀ used as ω _p is set to the second type in advance so that the polarization direction of the type reflected by the polarization prism 26 (for example, P polarization).
It is adjusted by the harmonic generator 23.

Therefore, when the light of the second harmonic wave 2ω ₀ is incident on the polarization prism 26, the optical axis from the end mirror 31 to the grating 29 is reflected by the polarization prism 26 and reflected to the nonlinear optical crystal 27 side. Then, the light is incident on the nonlinear optical crystal 27 as the pump wave P.

As a result, the pump wave P changes from 3ω ₀ to 2ω.
_It is changed to ₀ . The operation after the second harmonic wave 2ω ₀ (= ω _p ) is incident on the nonlinear optical crystal 27 as the pump wave P is the same as that of the third harmonic wave 3ω ₀ (= ω _p ). However, when the second harmonic wave 2ω ₀ is the pump wave P, the unstable region has a wavelength of 1,064 nm, so that it is possible to oscillate sufficiently stably in the vicinity of the wavelength of 710 nm. Signal wave S
If the wavelength is around 740 nm or more, the pump wave P
To the third harmonic 3ω ₀ .

As described above, in the present invention, the polarization prism is provided in the cavity, and as the pump wave generator,
A device for generating the second harmonic and the third harmonic of the frequency of the fundamental wave is provided, and any one of the harmonics is made incident on the cavity through the polarization prism and resonated to obtain a laser beam of a desired wavelength. Therefore, it is possible to provide a solid-state laser oscillator capable of continuously varying the output wavelength.

In the case of the conventional method in which the pump wave is incident from the end mirror, for example, the wavelength of the pump wave is 355 nm.
Then, 400n as the end mirror of the cavity
Since it is designed to reflect light of m or more, for example,
Light with a wavelength of 532 nm cannot enter. In this case, since the laser oscillation frequency can be varied only by the spectrum using the grating using the pump wave of 355 nm, it is inevitable that a region in which the laser oscillation does not normally occur occurs in a small wavelength range. That is, in the optical parametric oscillation, the laser oscillation does not normally occur although it is a slight wavelength range in the wavelength region half the wavelength of the pump wave. And this is because the conventional system was a method of injecting the pump wave from the end mirror,
This was due to the fact that it was not possible to configure to switch to pump waves of other wavelengths due to the end mirror reflection characteristics designed to remove unnecessary wavelengths.

Therefore, in the device of the present invention, the pump wave is not made incident from the end mirror, but a polarizing prism is used and installed in the optical path of the cavity so that the pump wave is introduced into the cavity through this polarizing prism. I chose By using this polarizing prism to introduce the pump wave, it becomes possible to introduce the pump wave of the desired wavelength into the optical path of the cavity without being affected by the characteristics of the end mirror. As 355
At least two wavelengths, nm and 532 nm, are now available.

As the pump wave, a harmonic wave is generated based on the laser light emitted from the laser light source, and a harmonic wave of a desired order is selected to be a pump wave, which is introduced into the polarizing prism.
In addition, the polarization of the pump wave is set to a direction in which the polarizing prism reflects (for example, P-polarized light), the light is incident on the return prism from a certain direction, and the reflected light is incident on the nonlinear optical crystal of the cavity to generate two wavelengths, Alternatively, the pump wave having the number of wavelengths larger than that can be selectively used.
This makes it possible to eliminate a region in the specific range where laser oscillation does not normally occur due to the wavelength of the pump wave, by selecting the pump wave.

Further, the structure in which the pump wave is introduced into the cavity by efficiently reflecting the pump wave by using the polarizing prism which reflects only the light of the specific polarization, enables the efficient laser oscillation. The pump wave introduced into the cavity from the polarizing prism cannot pass through the polarizing prism, and cannot resonate with the end mirror of the cavity.

Therefore, in order to solve this, a λ / 4 plate is provided between the nonlinear optical crystal and the grating. Thereby, the signal wave S exiting the nonlinear optical crystal
When the (angular frequency ω _s ) is reflected back by the mirror, it will pass twice through the λ / 4 plate, and therefore λ
Since the phase is shifted by / 2 and becomes S-polarized with respect to the polarizing prism, it can pass through the polarizing prism this time, and laser oscillation becomes possible.

Further, a YAG laser oscillator is used as a laser oscillator which is a pump wave source, and its harmonic, for example, the second harmonic is generated by the second harmonic generator, and the third harmonic is basically the second harmonic. Waves can be generated by mixing with a mixing crystal. Therefore, when oscillating a variable frequency with a pump wave (wavelength 355 nm) by the third harmonic and oscillating a wavelength near 710 nm (this pump of 355 nm is used). In a wave, the oscillation becomes unstable at a wavelength near 710 nm.) In order to switch the third harmonic having a wavelength of 355 nm to the second harmonic having a wavelength of 532 nm, the mixing crystal is removed and the second harmonic is directly incident on the crystal. I did it.

When oscillating a wavelength near 710 nm, by removing the mixing crystal and directly injecting the second harmonic into the crystal, the second harmonic with a long wavelength of 532 nm is pumped to the cavity. It becomes possible to switch and inject, and by introducing this wavelength switching, it is possible to stably oscillate at a wavelength near 710 nm (in the case of a pump wave of 532 nm, the unstable region becomes 1064 nm, According to this, 710n
It is possible to oscillate stably near m).

(Second Embodiment) In the first embodiment, in order to switch the wavelength of the pump wave, an optical mixing device 24 capable of advancing and retreating with respect to the optical path is provided, and the fundamental wave from the light source is changed to the second harmonic. By passing it through the wave generator 23,
A second harmonic is generated from the fundamental wave to obtain a fundamental wave and a second harmonic, and the fundamental wave and the second harmonic are mixed by the optical mixing device 24.
The third harmonic is further generated in the optical mixing device 24 by passing the light through the optical mixing device 24, and in order to switch the wavelength of the pump wave, the optical mixing device 24 is moved forward and backward with respect to the optical path, whereby the second harmonic is generated as the pump wave. The use of either the wave or the third harmonic can be switched and used. However, even if the device for generating the second harmonic or the third harmonic is not used, the configuration as shown in FIG. By doing so, the wavelength of the pump wave can be switched.

That is, FIG. 6 shows a second embodiment of the present invention, in which the components from the mirror 25 to the polarization prism 26 in the configuration of FIG. 1 are changed.
In FIG. 6, laser oscillators 21a and 21b having different oscillation frequencies are prepared as laser light sources, and the oscillated laser light from each of the laser oscillators 21a and 21b is reflected by the mirror 30.
First and second polarization prisms 26a and 26b are provided on the incident / reflecting optical axis of the end mirror 31 so that the light enters the cavity (resonator) portion sandwiched by the end mirror 31.

Then, a λ / 4 plate 28a is provided in the outgoing laser optical path of the laser oscillator 21a, and the outgoing laser light is made incident on the first polarizing prism 26a via the λ / 4 plate 28a and introduced into the cavity. It is a composition. Further, another λ / 4 plate 2 is also provided in the optical path of the laser beam emitted from the laser oscillator 21b.
8b is provided, and the emitted laser light is made incident on the second polarizing prism 26b through the λ / 4 plate 28b and introduced into the cavity.

In such a structure, the optical parametric oscillation action in the cavity portion is basically the same as that of the first embodiment described with reference to FIG. The differences are the supply system of the pump wave to the cavity and the wavelength switching of the pump wave.

In this embodiment, the laser oscillator is provided with 21a and 21b, which have different wavelengths. Therefore,
The laser oscillator required as a pump wave is oscillated and made incident on the polarization prism, and is supplied to the cavity portion as a pump wave. Assuming that linearly polarized light is generated from the laser oscillator 21a (or 21b), the λ / 4 plate 28a corresponding to the laser oscillator 21a (or 21b) is used.
The light is circularly polarized by (or 28b) and then enters the corresponding polarization prism 26a (or 26b). Then, the light is reflected by the polarization prism 26a (or 26b) and is supplied to the cavity portion as a pump wave.

With such a configuration, the wavelength of the pump wave can be switched without providing the second harmonic generator 23, the optical mixing device 24, and the mirror 25. In addition,
The present invention is not limited to the above-described embodiments, and can be appropriately modified and carried out within the scope not changing the gist thereof. For example, in the above-described embodiments, a YAG laser oscillator is used.
An example using a laser oscillator is shown, but this may be another laser oscillator. Further, in the above-mentioned embodiment, the wavelength of the pump wave is two waves, but it can be set to more wavelengths if necessary.

[0082]

As described in detail above, according to the present invention,
Two wavelengths, eg the second harmonic of a YAG laser (355n
By using m) and the third harmonic as a pump wave, it becomes possible to oscillate in the entire range of 410 nm to 2,000 nm, and component analysis can be performed without exception in spectroscopic measurement and the like. Since wavelength continuity is important in spectroscopic measurement, if there is a region where oscillation is not possible even in a small region of about ± 25 nm in the vicinity of 710 nm, it is a serious defect. Provided,
Further, as a pump wave generator, a configuration for generating a plurality of pump waves having different wavelengths is used, and by selecting the pump wave and making it enter the polarizing prism, a pump wave having a desired wavelength is transmitted through this polarizing prism. It becomes possible to enter into the cavity, and it is possible to obtain a laser beam of a desired wavelength by parametric resonance with this pump wave,
It is possible to provide a solid-state laser oscillator capable of continuously varying the output wavelength.

[Brief description of drawings]

FIG. 1 is a diagram for explaining an embodiment of the present invention,
The figure which shows the schematic structure of the apparatus which concerns on 1st Example of this invention.

FIG. 2 is a diagram for explaining the present invention.

FIG. 3 is a diagram for explaining the present invention.

FIG. 4 is a diagram for explaining the present invention.

FIG. 5 is a diagram for explaining the present invention.

FIG. 6 is a diagram for explaining an embodiment of the present invention,
The figure which shows the schematic structure of the principal part of the apparatus which concerns on 2nd Example of this invention.

FIG. 7 is a diagram showing a schematic configuration for explaining a configuration example of a conventional device.

FIG. 8 is a diagram showing reflectance characteristics of an end mirror.

FIG. 9 is a diagram showing wavelength dependence of optical parametric oscillation output by a conventional method.

[Explanation of symbols]

 21 ... YAG laser oscillator 21a, 21b ... Laser oscillator 23 ... Second harmonic generator 24 ... Optical mixing device 25 ... Mirror 26, 26a, 26b ... Polarizing prism 27 ... Nonlinear optical crystal 28, 28a, 28b ... λ / 4 plate 29 ... Grating 30 ... Mirror 31 ... End mirror.

Claims (3)

[Claims] 1. An end mirror for reflecting only light in a predetermined frequency range, a non-linear optical crystal arranged on the incident / reflecting optical axis of the end mirror to generate parametric light from supplied pump light, and this non-linear optical An angle-adjustable grating with respect to the optical axis of the emitted light that disperses the light emitted from the crystal, and a total reflection mirror that is arranged at an angle that totally reflects the specific light dispersed by the grating toward the grating, A polarizing prism disposed between the end mirror and the nonlinear optical crystal, which reflects a circularly polarized pump wave to enter the nonlinear optical crystal, and is disposed between the grating and the nonlinear optical crystal,
Polarization characteristics that generate a harmonic of a desired order from the conversion member that converts linearly polarized light into circularly polarized light and that converts circularly polarized light into linearly polarized light and the fundamental light from the laser oscillating unit that generates the fundamental light, and that is reflected by the polarizing prism. A tunable laser oscillation device comprising: a pump wave supply unit capable of selecting an order for supplying the pump wave as a pump wave to the polarization prism. 2. The pump wave supply means includes a first harmonic generation means for receiving the fundamental light oscillated by the laser oscillation means and generating and outputting a second harmonic, and the first harmonic generation means. Second harmonic generation means for receiving an output and generating a third harmonic is used, and the output of the first or second harmonic generation means is selected and output as a pump wave. The tunable laser oscillation device according to claim 1. 3. An end mirror that reflects only light in a predetermined frequency range, a non-linear optical crystal that is arranged on the incident / reflected optical axis of the end mirror, and that generates parametric light from a pump wave supplied, and the non-linear optics. An angle-adjustable grating with respect to the optical axis of the emitted light that disperses the light emitted from the crystal, and a total reflection mirror that is arranged at an angle that totally reflects the specific light dispersed by the grating toward the grating, A polarizing prism that is arranged between the end mirror and the nonlinear optical crystal, reflects the circularly polarized pump wave, and makes it enter the nonlinear optical crystal, and excitation drive control can be selectively performed on each of them. A plurality of laser oscillating means for generating the basic light of the A wavelength tunable laser oscillating device comprising: a polarizing means for converting into a pump wave having a polarization characteristic reflected by a polarizing prism and giving it to the polarizing prism.