JPH10260438A - Laser wavelength converting element and converting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve wavelength conversion efficiency by extending the interaction length between a basic wave and a wavelength-converted wave in nonlinear optical crystal by the wavelength converting element which utilizes the crystal. SOLUTION: An incidence end surface 1a and a projection end surface 1b of the nonlinear optical crystal 1 are partially coated with totally reflecting optical thin films 2a and 2b; and the remaining part of the incidence end surface 1a and the remaining part of the projection end surface 1b are coated with reflection preventive films 3a and 3b for the basic wave and the wavelength- converted wave respectively. The wavelength conversion efficiency increases in proportion to the square of the crystal length, so the totally reflecting optical thin films 2a and 2b reflect the light zigzag to extend the effective crystal length, thereby improving the wavelength conversion efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser wavelength conversion device for efficiently converting a laser beam to a desired wavelength and a laser wavelength conversion device using the device. Measuring equipment, optical information processing equipment,
It can be applied to fine processing devices such as semiconductors, spectral devices, and defense equipment.

[0002]

2. Description of the Related Art In a wavelength conversion element utilizing the birefringence of an optical crystal, the wavelength conversion efficiency increases in proportion to the square of the length of the optical crystal. In a conventional wavelength conversion element,
In order to improve the wavelength conversion efficiency, there are (1) an example in which a crystal having a long crystal length is used, and (2) an example in which a plurality of crystals are arranged on an optical axis to be longer. Specifically, as a representative example of (1), Applied Physics B Vol. 48 (1989)
Years) pp. 293-297 (Applied Physics B. V)
ol. 48 (1989) pp. 293-297), and as a representative example of (2), Optics Letters
Volume 19 (1994), pages 713 to 715 (OP
There is a form discussed in TICS LETTERS Vol.19 (1994) pp.713-715).

[0003]

Among the above techniques, the method (1) using an optical crystal having a long crystal length is difficult because it is difficult to grow a single crystal and a large crystal, and the method is expensive. There is a problem of sticking. The method (2) of improving the conversion efficiency by arranging a plurality of crystals on the optical axis and lengthening the crystals is excellent as a wavelength conversion method for a high-power laser. However, in this method, when passing between crystals, the phase velocity of the fundamental wave and the wavelength converted wave differs due to the wavelength dispersion of air,
It is necessary to optimize the distance between crystals for the phase compensation. In addition, the cost is increased by the number of crystals, which is problematic in terms of cost effectiveness.

In order to solve the above-mentioned problems, the laser wavelength conversion element and the conversion device according to the present invention use effectively only one optical crystal to improve the wavelength conversion efficiency of laser light. That is the purpose.

[0005] Other objects and novel features of the present invention will be clarified in embodiments described later.

[0006]

In order to achieve the above object, a laser wavelength conversion element according to the present invention utilizes the birefringence of an optical crystal, and a part of an entrance surface and an exit surface of the optical crystal. Is coated with a total reflection optical thin film to form a waveguide structure in which the laser light is folded in a zigzag manner, and the overall working length in the optical crystal is increased to improve the wavelength conversion efficiency of the laser light.

The first laser wavelength conversion device of the present invention comprises a laser wavelength conversion element utilizing birefringence of an optical crystal, wherein the laser wavelength conversion element has an incident surface and an emission surface of the optical crystal. Is a waveguide structure in which a part of the laser light is coated in a zigzag shape by coating a total reflection optical thin film, and a total reflection mirror is provided for returning the laser light emitted from the laser wavelength conversion element in the original direction. In addition, the wavelength conversion efficiency of laser light is improved by increasing the total operating length in the optical crystal.

A second laser wavelength conversion device according to the present invention includes a laser wavelength conversion element utilizing birefringence of an optical crystal, wherein the laser wavelength conversion element is one of an incident surface and an emission surface of the optical crystal. A waveguide structure in which a portion is coated with a total reflection optical thin film and a laser beam is folded in a zigzag shape, and is characterized in that it is disposed in a resonator.

A third laser wavelength conversion device according to the present invention includes a laser wavelength conversion element utilizing birefringence of an optical crystal, wherein the laser wavelength conversion element is one of an incident surface and an emission surface of the optical crystal. A waveguide structure in which a portion is coated with a total reflection optical thin film and a laser beam is folded in a zigzag shape, and is characterized in that it is disposed in a resonator together with a laser oscillation element.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a laser wavelength conversion device and a conversion device according to the present invention will be described below with reference to the drawings.

FIG. 1 shows a first embodiment of the present invention, which is suitable for generating higher-order harmonics of laser light utilizing the birefringence of an optical crystal or for mixing sum / difference frequency light. 3 shows a direction-passing laser wavelength conversion element. In this figure, reference numeral 1 denotes a rectangular parallelepiped nonlinear optical crystal having birefringence cut to a phase matching angle, and the cut angle θ of the crystal with respect to the crystal axis direction is set to be equal to the phase matching angle.
One of the input end face 1a and the output end face 1b of the nonlinear optical crystal 1
The portions are coated with total reflection optical thin films 2a and 2b, respectively, and the remaining portions of the incident end face 1a and the output end face 1b are coated with antireflection films 3a and 3b, respectively. Here, the total reflection optical thin films 2a and 2b have a waveguide structure in which a laser beam incident from a portion of the incident end face 1a coated with the anti-reflection film 3a is folded in a zigzag manner. In this case, when the laser light is turned back in a zigzag manner, the parallelism between the incident end face 1a and the outgoing end face 1b of the crystal must be obtained when polishing the flat surface so that the phase matching angle does not change. The anti-reflection film 3a is made of an anti-reflection dielectric film for a fundamental wave, and the anti-reflection film 3b is made of an anti-reflection dielectric film for a wavelength-converted wave (wavelength-converted light).

In the first embodiment shown in FIG. 1, excitation light (laser light) enters the crystal 1 from the portion of the incident end face 1a coated with the antireflection film 3a, and the fundamental wave and the wavelength-converted wave are converted. The light is reflected in a zigzag manner at the portions of the total reflection optical thin films 2a and 2b, and is emitted from the portion of the emission end face 1b coated with the antireflection film 3b.

According to this embodiment, in a laser wavelength conversion element for generating harmonics of laser light or for mixing sum / difference frequency light utilizing the birefringence of the nonlinear optical crystal 1, A part of the incident end face 1a and a part of the exit end face 1b are coated with the total reflection optical thin films 2a and 2b to form a waveguide structure in which the laser light is folded in a zigzag shape. The wavelength conversion efficiency of laser light can be improved. That is, the laser light that has entered the crystal is folded back in a zigzag manner in the crystal, and the energy of the fundamental wave is converted into the energy of the wavelength-converted wave. In this process, if the absorption coefficient in the crystal is negligibly small and it can be assumed that there is no attenuation of the pump light, the conversion efficiency of the wavelength conversion increases by the square of the number of times of folding. If the optical path is long enough, it will approach 100% conversion efficiency with respect to the optical path length according to the hyperpolaric tangent function.

FIG. 2 shows a second embodiment of the present invention, in which laser wavelength conversion for generating higher-order harmonics of laser light or mixing for sum / difference frequency light utilizing the birefringence of an optical crystal. The device is shown. The laser wavelength conversion device shown in FIG. 2 includes, in addition to the laser wavelength conversion device 10 shown in the first embodiment in FIG.
A dichroic mirror 4 for extracting a wavelength-converted wave is provided on the incident side of the laser light, and a concave total reflection mirror 5 for totally reflecting the laser light emitted from the laser wavelength conversion element 10 is provided. The configuration is such that the emission end face of the crystal 1 is arranged at a location. Further, the total reflection optical thin film 2a,
Antireflection films 3a, 3b for the excitation light and the converted wavelength wave on both the remaining incident end face 1a and the exit end face 1b provided with
Is coated.

In this case, the excitation light is transmitted through the dichroic mirror 4 and is incident on the portion of the incident end face 1a of the laser wavelength conversion element 10 where the antireflection film 3a is provided. The light exits from the portion where the antireflection film 3b is provided on the exit end face 1b, is further folded back in the original direction by the concave total reflection mirror 5, and is again folded in a zigzag shape in the crystal 1 and enters. The light exits from the end face 1a where the antireflection film 3a is provided and reaches the dichroic mirror 4. The fundamental wave passes through the dichroic mirror 4 without being reflected, and only the wavelength-converted wave is reflected by the dichroic mirror 4 and extracted.

In the case of the laser wavelength converter according to the second embodiment shown in FIG. 2, a concave total reflection mirror 5 which folds outgoing light in the original direction is provided so that the overall working length in the crystal can be made longer. There is an advantage that the effective crystal length is twice that of FIG.

FIG. 3 shows a third embodiment of the present invention, which is a laser wavelength converter for an optical parametric oscillator or an external resonance type second harmonic generator utilizing the birefringence of an optical crystal. The device is shown. The device shown in FIG. 3 has a laser wavelength conversion element 10 having a non-linear optical crystal 1 disposed in an external resonator including a dichroic mirror 4 and an output coupling mirror 6, and is particularly suitable for an optical parametric oscillator or a continuous oscillation type. Is used when a laser having a low peak value is used as an excitation light source. The output coupling mirror 6 has an appropriate reflectance (for example, 40 to 90%) of 100% for the fundamental wave and less than 100% for the converted wavelength wave.

In this case, the excitation light passes through the dichroic mirror 4 and is incident on the portion of the incident end face 1a of the laser wavelength conversion element 10 where the antireflection film 3a is provided, and the fundamental wave and the wavelength-converted wave are converted into the crystal 1 The light exits from the portion provided with the antireflection film 3b on the emission end face 1b, is further folded back in the original direction by the output coupling mirror 6, and is again folded in the zigzag shape within the crystal 1 and enters. The light exits from the end face 1a where the antireflection film 3a is provided and reaches the dichroic mirror 4. The fundamental wave passes through the dichroic mirror 4 without being reflected, but the wavelength-converted wave is reflected by the dichroic mirror 4 and repeats the above operation, amplified, and extracted from the output coupling mirror 6.

FIG. 4 shows a fourth embodiment of the present invention, which is a laser wavelength converter for an internal resonance type high-order harmonic generator of laser light utilizing the birefringence of an optical crystal.
The apparatus shown in FIG. 4 has a laser wavelength conversion element 10 having a nonlinear optical crystal 1 in an internal resonator in which a laser oscillation element 7 is arranged between a total reflection mirror 5 and an output coupling mirror 6.

In this case, the laser light excited by the laser oscillation element 7 is incident on the portion of the incident end face 1a of the laser wavelength conversion element 10 where the antireflection film 3a is provided, and the fundamental wave and the converted wavelength wave are formed in the crystal 1. Output end face 1b folded in a zigzag shape
Out of the portion provided with the anti-reflection film 3b, is further turned back by the output coupling mirror 6 in the original direction, is turned back again in a zigzag manner in the crystal 1, and the anti-reflection film 3a on the incident end face 1a is formed.
The light exits from the portion where is provided and reaches the total reflection mirror 5. The wavelength converted wave amplified by the repetition of such an operation is taken out of the output coupling mirror 6.

Although the embodiments of the present invention have been described above, it is obvious to those skilled in the art that the present invention is not limited to the embodiments and various modifications and changes can be made within the scope of the claims. There will be.

[0022]

As described above, according to the present invention, it is possible to improve the wavelength conversion efficiency of a nonlinear optical crystal with a single crystal. Further, since the wavelength conversion is performed by a waveguide structure in which the laser light is folded in a zigzag shape in the crystal, compared with a structure in which a plurality of crystals are arranged on the optical axis to extend the optical path length, the air and the ferroelectric film are used. Since no refractive index dispersion occurs between the fundamental wave and the wavelength-converted wave, there is no need for phase difference compensation.

Further, in the case of a crystal having a small nonlinear optical constant, it is strongly focused (increased laser beam size) and made incident in order to increase the power density of the excitation light, so that the size of the incident surface of the crystal cannot be utilized. There is. By using the configuration of the present invention, high conversion efficiency can be obtained with only one nonlinear optical crystal without wasting the size of the nonlinear optical crystal.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a front surface and a bottom surface of a one-way-pass laser wavelength conversion element according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram showing a laser wavelength converter according to a second embodiment of the present invention.

FIG. 3 is a configuration diagram illustrating a laser wavelength conversion device including an external resonator according to a third embodiment of the present invention.

FIG. 4 is a configuration diagram illustrating a laser wavelength conversion device including an internal resonator according to a fourth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Nonlinear optical crystal 2a, 2b Total reflection optical thin film 3a, 3b Antireflection film 4 Dichroic mirror 5 Total reflection mirror 6 Output coupling mirror 7 Laser oscillation element

Claims (4)

[Claims] 1. A laser wavelength conversion element utilizing the birefringence of an optical crystal, wherein a part of an incident surface and an outgoing surface of the optical crystal is coated with a total reflection optical thin film to guide a laser beam in a zigzag manner. A laser wavelength conversion element having a structure and a wavelength conversion efficiency of laser light improved by increasing a total action length in the optical crystal. 2. A laser wavelength conversion device comprising a laser wavelength conversion element utilizing birefringence of an optical crystal, wherein the laser wavelength conversion element has a total reflection optical thin film on a part of an entrance surface and an exit surface of the optical crystal. A waveguide structure that coats and folds the laser light in a zigzag shape, and is provided with a total reflection mirror that folds the laser light emitted from the laser wavelength conversion element in the original direction. A laser wavelength conversion device characterized by improving the wavelength conversion efficiency of laser light by increasing the length. 3. A laser wavelength conversion device including a laser wavelength conversion element utilizing birefringence of an optical crystal, wherein the laser wavelength conversion element has a total reflection optical thin film on a part of an entrance surface and an exit surface of the optical crystal. A laser wavelength conversion device having a waveguide structure which is coated and folds a laser beam in a zigzag shape, and which is disposed in a resonator. 4. A laser wavelength conversion device provided with a laser wavelength conversion element utilizing birefringence of an optical crystal, wherein the laser wavelength conversion element has a total reflection optical thin film on a part of an entrance surface and an exit surface of the optical crystal. A laser wavelength conversion device having a waveguide structure which is coated and folds a laser beam in a zigzag shape, and which is disposed in a resonator together with a laser oscillation element.