JPH06186605A - Optical parametric oscillator - Google Patents

Abstract

(57) [Summary] [Structure] The first nonlinear optical crystal 11 is arranged between the input side mirror 9 and the output side mirror 10 which form the resonator 8, and the same material as the first nonlinear optical crystal 11 is used. The output side mirror 10 and the first non-linear optical crystal 11 are arranged so that the signal light 6 having the same cutting angle and generated from the first non-linear optical crystal 11 is made to enter the output side mirror 10 at a substantially right angle. And a second non-linear optical crystal 12 is arranged between and. Effect Since the signal light 6 is incident on the output side mirror 10 by the second nonlinear optical crystal 12 at a substantially right angle, when the signal light 6 resonates by the resonator 8, part of the signal light 6 is input side. The signal light 6 can be efficiently amplified without being reflected to the outside without entering the mirror 9 or the output side mirror 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical parametric oscillator.

[0002]

2. Description of the Related Art FIG. 5 shows an example of a conventional general optical parametric oscillator, wherein 1 is a resonator and 2 is a nonlinear optical crystal arranged inside the resonator 1. Reference numeral 1 is composed of an input side mirror (dichroic mirror) 3 and an output side mirror (dichroic mirror) 4 which are arranged substantially parallel to each other.

In the optical parametric oscillator composed of the above-mentioned members, when the excitation light (laser light) 5 is incident on the input side mirror 3 at a substantially right angle, the excitation light 5 passes through the input side mirror 3. Upon entering the nonlinear optical crystal 2, a signal light 6 and an idler light 7 having a wavelength different from that of the excitation light 5 are generated inside the nonlinear optical crystal 2 based on the following formula (1). 1 / λ _p = 1 / λ _s + 1 / λ _i (1) (λ _p : pumping light wavelength, λ _s : signal light wavelength, λ _i :
Idler light wavelength)

The output side mirror 4 has a high reflectance for the wavelength of the signal light 6 and a low reflectance for the wavelengths of the pumping light 5 and the idler light 7, The mirror 4 outputs the signal light 6 amplified by the resonator 1, the idler light 7 generated by the nonlinear optical element 2, and the signal light 6 and the remaining pumping light 5 that did not generate the idler light 7. It has become so.

[0005]

In the above-mentioned optical parametric oscillator, the signal light 6 and the remaining pumping light 5 that did not generate the idler light 7 are transmitted straight through the nonlinear optical crystal 2 and the output side mirror 4 is provided. On the other hand, since the optical axes of the signal light 6 and the idler light 7 generated inside the nonlinear optical crystal 2 travel in a direction separating from the optical axis of the excitation light 5, The idler light 7 obliquely enters the output side mirror 4.

Therefore, when the signal light 6 resonates by the resonator 1, a part of the signal light 6 does not enter the input-side mirror 3 or the output-side mirror 4 and is reflected toward the outside. The light 6 could not be amplified efficiently.

The present invention has been made in view of the above situation, and an object thereof is to provide an optical parametric oscillator capable of efficiently amplifying signal light.

[0008]

In order to achieve the above object, in an optical parametric oscillator according to the present invention, an input side mirror and an output side mirror forming a resonator, and an input side mirror arranged between the two mirrors are provided. A first nonlinear optical crystal that generates signal light and idler light from transmitted excitation light, and a signal that is made of the same material as the first nonlinear optical crystal and that has the same cutting angle and that is generated from the first nonlinear optical crystal A second non-linear optical crystal is provided between the output-side mirror and the first non-linear optical crystal so that light is incident on the output-side mirror substantially at right angles.

[0009]

In the optical parametric oscillator of the present invention, the signal light generated by the excitation light incident on the first nonlinear optical crystal is made incident on the output side mirror substantially at right angles by the second nonlinear optical crystal, The signal light output from the first nonlinear optical crystal is efficiently amplified by the resonator including the input side mirror and the output side mirror.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the optical parametric oscillator according to the present invention. Reference numeral 8 is a resonator, and the resonator 8 and an input-side mirror (dichroic mirror) 9 are arranged in parallel and face each other. And an output side mirror (dichroic mirror) 10.

Reference numeral 11 denotes a first non-linear optical crystal having a predetermined cutting angle, and the first non-linear optical crystal 11 is provided in the input mirror 9 slightly in the intermediate portion between the input side mirror 9 and the output side mirror 10. It is located close to each other.

When the excitation light 5 transmitted through the input side mirror 9 at a substantially right angle is incident on the first nonlinear optical crystal 11, the inside of the first nonlinear optical crystal 11 is
Based on the above formula (1), the signal light 6 and the idler light 7 having a wavelength different from the excitation light 5 are generated.

The output side mirror 10 has a high reflectance for the wavelength of the signal light 6 and a low reflectance for the wavelengths of the excitation light 5 and the idler light 7.

Reference numeral 12 denotes a second nonlinear optical crystal made of the same material as the first nonlinear optical crystal 11 and having the same cutting angle. The second nonlinear optical crystal 12 has an input side mirror 9 and an output side. The first non-linear optical crystal 11 is provided at a position slightly near the output side mirror 10 in the middle of the mirror 10.
It is arranged so as to confront.

When the pumping light 5, the signal light 6, and the idler light 7 are incident on the second nonlinear optical crystal 12 from the first nonlinear optical crystal 11, these are converged on the same optical axis and output. The light is incident on the side mirror 10 at a substantially right angle.

In this embodiment having the above-mentioned structure,
When the excitation light 5 is incident on the input side mirror 9 at a substantially right angle, the excitation light 5 passes through the input side mirror 9 and is incident on the first nonlinear optical crystal 11, and the inside of the first nonlinear optical crystal 11 is excited. In, the signal light 6 and the idler light 7 having a wavelength different from that of the excitation light 5 are generated based on the above equation (1).

The signal light 6 and the idler light 7 generated from the first nonlinear optical crystal 11 and the remaining excitation light 5 that did not generate the signal light 6 and the idler light 7 are
It is incident on the second nonlinear optical crystal 12, and the excitation light 5, the signal light 6, and the idler light 7 are converged on the same optical axis by the second nonlinear optical crystal 12 and are incident on the output side mirror 10 at a substantially right angle. To do.

Further, the signal light 6 resonates by a resonator 8 composed of an input side mirror 9 and an output side mirror 10, and the amplified signal light 6 is output from the output side mirror 10 to the outside of the resonator 8. At the same time, the excitation light 5 and the idler light 7 pass through the output side mirror 10.

As described above, in this embodiment, the signal light 6 output from the first nonlinear optical crystal 11 is incident on the output side mirror 12 at a substantially right angle by the second nonlinear optical crystal 12. When the signal light 6 resonates with the resonator 8, a part of the signal light 6 is input to the input side mirror 9
Alternatively, the signal light 6 output from the first nonlinear optical crystal 11 can be efficiently amplified without being reflected to the outside without entering the output side mirror 10.

FIG. 2 shows an example of a laser generator having the above-mentioned optical parametric oscillator. In the figure, the same reference numerals as those in FIG. 1 represent the same parts.

Reference numeral 13 is a YAG laser oscillator that outputs a YAG laser fundamental wave having a wavelength of 1064 nm, and 14 is a YAG laser fundamental wave that is output from the YAG laser oscillator 13, and 1 / λ ₂ = 1 / λ ₁ + 1 / λ ₁ ( 2) A YAG laser second harmonic generator that generates a YAG laser second harmonic having a wavelength of 532 nm by the relationship (second harmonic generation) of (λ ₁ : fundamental wave, λ ₂ : second harmonic).

Reference numeral 15 denotes a YAG laser second harmonic generator 14
1 / λ ₃ = 1 / λ ₁ +1 from the YAG laser second harmonic generated by the YAG laser second harmonic and the YAG laser second harmonic that remains in the YAG laser second harmonic generator 14 without being converted into the YAG laser second harmonic. / Λ ₂ (3) (λ ₁ : fundamental wave, λ ₂ : second harmonic, λ ₃ : third harmonic)
Of YAG with wavelength of 355 nm
A YAG laser third harmonic generator that generates a laser third harmonic, 16 reflects the YAG laser third harmonic generated by the YAG laser third harmonic generator 15, and the YAG laser third harmonic YAG in the generator 15
It is a dichroic mirror that transmits the YAG laser fundamental wave remaining without being converted into the laser third harmonic and the YAG laser second harmonic, and the YAG laser third harmonic having a wavelength of 355 nm reflected by the dichroic mirror 16 is the excitation light. 5 is incident on the input side mirror 9 of the optical parametric oscillator.

Reference numeral 17 is a prism for separating the signal light 6 amplified by the resonator 8 from the excitation light 5 and idler light 7 which are transmitted through the output side mirror 10.

In the optical parametric oscillator used in the laser generator shown in FIG. 2, the cutting angle conditions for the first nonlinear optical crystal 11 and the second nonlinear optical crystal 12 are angle φ = 0 ° and phase matching angle, respectively. β-BaB with θ = 32 °
₂ O ₄ crystal is used.

The angle φ and the phase matching angle θ are the angles described below.

That is, as shown in FIG. 3, when the main refractive indices of light of the crystal are nx, ny, and nz, nx≤n
Assuming the x-axis, y-axis, and z-axis with y <nz, the angle formed by the projection of a vector extending in an arbitrary direction through the origin on the xy plane with the x-axis is angle φ, and z of the vector is z. The angle formed with the axis is the phase matching angle θ.

In the laser generator having the above structure, when the YAG laser oscillator 13 is operated, the YAG laser second harmonic is generated from the YAG laser fundamental wave output from the YAG laser oscillator 13 in the YAG laser second harmonic generator 14. Waves are generated.

Further, the YAG laser third harmonic generator 15
At the YAG laser second harmonic generated by the YAG laser second harmonic generator 14 and the YAG laser fundamental wave remaining without being converted to the YAG laser second harmonic at the YAG laser second harmonic generator 14. As a result, a YAG laser third harmonic is generated, and only this YAG laser third harmonic is reflected by the dichroic mirror 16 and is incident on the input side mirror 9 of the optical parametric oscillator as the excitation light 5.

In the optical parametric oscillator, the wavelength 35
Signal light 6 and idler light 7 are generated from the excitation light 5 of 5 nm based on the above formula (1), and the excitation light 5, signal light 6 and idler light 7 output from the output side mirror 10 are prisms. They are separated by 17, respectively.

Further, the conversion efficiency of the signal light 6 with respect to the excitation light intensity of the optical parametric oscillator (see FIG. 1) having the first nonlinear optical crystal 11 and the second nonlinear optical crystal 12 and the nonlinear optical crystal 2 are When the conversion efficiency of the signal light 6 with respect to the pumping light intensity of the conventional optical parametric oscillator having only one (see FIG. 5) is compared, as shown in FIG. 4, as compared with the optical parametric oscillator of FIG. The optical parametric oscillator can generate the signal light 6 even if the intensity of the excitation light is low (the signal light 6 can be output if the intensity of the excitation light 5 is about 30 MW / cm ² or more). That is, the one shown in FIG. 1 has a lower threshold of optical parametric oscillation than the one shown in FIG. 5), and the intensity of the excitation light is about 70 MW /
It can be seen that at cm ² , the conversion efficiency is almost double that shown in FIG.

Therefore, when the excitation light 5 having the same light intensity is made incident, the one shown in FIG. 1 can output the signal light 6 more stably than the one shown in FIG. Since the threshold value of parametric oscillation is low, it is possible to reduce damage that occurs in the input side mirror 9 and the output side mirror 10.

The optical parametric oscillator of the present invention is not limited to the above-mentioned embodiments, but the first nonlinear optical crystal and the second nonlinear optical crystal are applied so as to be applied to the excitation light or the signal light to be generated. B for nonlinear optical crystals
Using a non-linear optical crystal other than aB ₂ O ₄ crystal, appropriately changing the cutting angle condition of each non-linear optical crystal, using a laser beam other than the YAG laser fundamental wave as the excitation light, Of course, various changes can be made without departing from the scope of the present invention.

[0034]

As described above, according to the optical parametric oscillator of the present invention, various excellent effects as described below can be obtained.

(1) Since the signal light output from the first nonlinear optical crystal is incident on the output side mirror by the second nonlinear optical crystal at a substantially right angle, when the signal light resonates by the resonator, A part of the signal light is not reflected to the outside without entering the input side mirror or the output side mirror, and thus the signal light output from the first nonlinear optical crystal is efficiently amplified. You can

(2) Since the signal light is efficiently amplified, the threshold value of the optical parametric oscillation becomes lower than that in the conventional case, and when pumping light having the same light intensity is made incident, the signal light is stably output. Can be made.

(3) Since the threshold value of the optical parametric oscillation is low, it is possible to reduce the damage caused to the input side mirror and the output side mirror.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing an embodiment of an optical parametric oscillator of the present invention.

FIG. 2 is a conceptual diagram showing an example of a laser generator to which an embodiment of the optical parametric oscillator of the present invention is applied.

FIG. 3 is a conceptual diagram illustrating a phase matching angle of a nonlinear optical crystal.

FIG. 4 is a graph comparing the conversion efficiency of signal light with respect to the excitation light intensity of the optical parametric oscillator of the present invention and the conversion efficiency of signal light with respect to the excitation light intensity of the conventional optical parametric oscillation device.

FIG. 5 is a conceptual diagram showing an example of a conventional optical parametric oscillator.

[Explanation of symbols]

 5 Excitation Light 6 Signal Light 7 Idler Light 8 Resonator 9 Input Mirror 10 Output Mirror 11 First Nonlinear Optical Crystal 12 Second Nonlinear Optical Crystal

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Daiji Nishizawa 3-15-15 Toyosu, Koto-ku, Tokyo Ishikawajima Harima Heavy Industries Co., Ltd. Toni Technical Center

Claims (1)

[Claims] 1. An input-side mirror and an output-side mirror that form a resonator, and a first nonlinear optical crystal that is arranged between the two mirrors and that generates signal light and idler light from excitation light that passes through the input-side mirror. The output side mirror having the same material as that of the first nonlinear optical crystal and having the same cutting angle and allowing the signal light generated from the first nonlinear optical crystal to enter the output side mirror substantially at right angles; An optical parametric oscillator comprising: a second nonlinear optical crystal disposed between the first nonlinear optical crystal and the first nonlinear optical crystal.