JPH06138507A - Higher harmonic generator - Google Patents

Abstract

PURPOSE:To efficiently and stably generate higher harmonic wave output by suppressing a higher transverse mode and resonating only the TEM00 basic mode. CONSTITUTION:A light shielding plate 11 having a variable type diaphragm or rotary type conversion diaphragm is disposed into a discrete type resonator constituted of reflection mirrors 5, 6 and an nonlinear optical material 7. The higher transverse mode is attenuated by the light shielding plate 11 when the basic wave 8 emitted from a semiconductor laser 2 is made incident on the resonator.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a harmonic generator for converting a fundamental wave emitted from a laser light source into a harmonic using a resonator having a non-linear optical material.

[0002]

2. Description of the Related Art In recent years, various devices have been proposed for obtaining a wavelength-converted second harmonic or third harmonic by passing a fundamental wave emitted from a semiconductor laser or the like through a nonlinear optical material. In these devices, a nonlinear optical material is arranged in a resonator composed of a plurality of reflecting surfaces, and a fundamental wave is confined in the resonator to be amplified so that harmonics are efficiently generated. As a resonator, a reflection film is provided on the end face of the nonlinear optical material, and a monolithic resonator that resonates inside the resonator and a plurality of mirrors are arranged to form a resonator. Arranged discrete resonators are known.

FIG. 4 shows a harmonic generator using a discrete resonator as an example of a conventional harmonic generator.

This harmonic generation device 1 includes a semiconductor laser (hereinafter referred to as LD) 2, a collimator lens 3, a mode matching lens 4, reflection mirrors 5 and 6, and KNbO _3.
It is composed of a nonlinear optical material 7 such as a crystal. The LD 2 emits the fundamental wave 8 having a wavelength of 860 nm, for example. The LD-side end surface of the reflection mirror 5 is a flat surface, and an antireflection film that totally transmits the fundamental wave 8 is applied to this surface. The end surface of the reflection mirror 5 on the side of the nonlinear optical material forms a concave mirror that partially transmits the fundamental wave 8. In addition, the end surface of the reflection mirror 6 on the LD side has a fundamental wave 8
On the other hand, a concave mirror that is highly reflective and highly transmissive to the second harmonic 10 is formed, and the emission side of the second harmonic 10 is a flat surface. It has an antireflection film that allows total transmission. Furthermore, the nonlinear optical material 7
On both left and right end surfaces in the figure, an antireflection film having high transmission of both the fundamental wave 8 and the second harmonic wave 10 is applied.

In the above structure, the fundamental wave 8 having a wavelength of 860 nm emitted from the LD 2 is collimated by the collimator lens 3, passes through the mode matching lens 4, and is composed of the reflection mirrors 5 and 6 and the nonlinear optical material 7. It is incident on the separated discrete resonator. The incident fundamental wave 8 is amplified by repeating multiple reflections between the reflection mirrors 5 and 6. Then, by making the crystal axis a of the nonlinear optical material 7 placed between the reflection mirrors 5 and 6 coincide with the direction of multiple reflection, part of the amplified fundamental wave 8 has a wavelength of 430 nm.
Is converted into the second harmonic wave 10 and is emitted from the reflection mirror 6. The nonlinear optical material 7 is temperature-controlled by the Peltier element 9 or the like in order to meet the phase matching condition and stabilize the conversion efficiency to the harmonic. By using such a harmonic generator, the fundamental wave can be efficiently converted into a harmonic.

[0006]

However, in the above-mentioned conventional harmonic generator 1, the beam shape of the semiconductor laser is elliptical, and the reflecting mirrors 5 and 6 and the non-linear optical material 7 which form the discrete resonator. Due to the imperfect alignment of, higher-order modes other than the TEM ₀₀ mode occur in the transverse mode pattern of the second harmonic 10.
There were problems such as deterioration of conversion efficiency and stability.

Therefore, it is an object of the present invention to provide a harmonic generator capable of suppressing the high-order transverse mode as described above and efficiently and stably generating a harmonic output.

[0008]

In order to achieve the above object, a harmonic generator of the present invention comprises a light source for generating a fundamental wave, a coupling optical system, and a discrete resonator having a nonlinear optical material. According to another aspect of the present invention, there is provided a higher harmonic wave generating device having a transverse mode control mechanism in the discrete resonator.

In a preferred aspect of the present invention, a light-shielding plate having a variable diaphragm or a light-shielding plate having a rotary conversion diaphragm is used as the transverse mode control mechanism.

[0010]

In the present invention, by adjusting the diaphragm of the light shielding plate inserted in the resonator, the higher-order transverse modes can be attenuated and only the TEM ₀₀ fundamental mode having the smallest transverse mode can resonate. This makes it possible to generate harmonics efficiently and stably.

In particular, when the light shielding plate is arranged between the reflection mirror on the laser light source side and the nonlinear optical material, the light from the laser light source that is not effective for generating harmonics is shielded from entering the nonlinear optical material. By preventing the temperature increase of the nonlinear optical material by using the plate, more stable harmonic output can be obtained.

[0012]

FIG. 1 shows an embodiment in which the present invention is applied to a second harmonic generation device. The present invention is not limited to the second harmonic generation device and can be applied to the third harmonic generation device and the like.

The second harmonic generation device 101 comprises a laser light source LD2, a collimator lens 3, a mode matching lens 4, a reflection mirror 5, a light shielding plate 11, a non-linear optical material 7, and a reflection mirror 6 which are sequentially arranged. Has been done.

The LD 2 in this embodiment has a wavelength of 860.
A device that emits a fundamental wave 8 with a small astigmatism in a nm, single longitudinal, and single transverse mode is used. As the light source, light emitted from a solid-state laser medium such as YAG or YLF excited by the LD 2 can also be used. The collimating lens 3 collimates the fundamental wave 8 emitted from the LD 2 into a parallel beam, and the mode matching lens 4 narrows the beam to form a discrete resonance composed of the two reflecting mirrors 5 and 6 and the nonlinear optical material 7. Plays a role of matching the resonance mode of the vessel with the incident beam (mode matching).

A KNbO ₃ crystal is used as the nonlinear optical material 7, and forms a block shape having a length of 5.0 mm in the crystal axis a direction. An antireflection film having high transmission of both the fundamental wave 8 and the second harmonic wave 10 is provided on both left and right end surfaces of the nonlinear optical material 7 in the figure.

Optical quartz glass is used for the reflection mirrors 5 and 6. In the reflection mirror 5 located on the incident side of the fundamental wave 8, the end surface on the side of the nonlinear optical material is R = 25 mm.
It is formed in a concave shape, and the fundamental wave is 93% on this surface.
A reflective film that reflects is vapor-deposited to form a concave mirror. Further, in the reflection mirror 6 located on the emission side of the second harmonic wave 10, the end surface on the side of the nonlinear optical material is the reflection mirror 5.
Similarly, R = 25 mm is formed in a concave shape, and 99.9% of the fundamental wave 8 is reflected on this surface and the second harmonic wave 10 is
A reflective film that transmits 0% is vapor-deposited to form a concave mirror.

The light-shielding plate 11 inserted in the discrete resonator is arranged between the reflection mirror 5 and the nonlinear optical material 7. The light shielding plate 11 may be placed between the nonlinear optical material 7 and the reflection mirror 6.

Light-shielding plate 11 used in this embodiment
Has a pinhole 12 which can be adjusted to an arbitrary diameter by a variable diaphragm 15, as shown in FIG.
Such a variable diaphragm is used, for example, as a lens diaphragm for a camera, and is a known one.

In the above structure, the fundamental wave 8 having a wavelength of 860 nm emitted from the LD 2 is collimated by the collimator lens 3, passes through the mode matching lens 5, and is composed of the reflection mirrors 5 and 6 and the nonlinear optical material 7. It is incident on the separated discrete resonator. The incident fundamental wave 8 is multiply reflected between the reflection mirrors 5 and 6 and amplified.
Then, the crystal axis a of the nonlinear optical material 7 placed between the reflection mirrors 5 and 6 is made to coincide with the direction of multiple reflection, so that part of the amplified fundamental wave 8 has a wavelength of 430 nm.
It is converted into a harmonic wave 10 and emitted from the reflection mirror 6.

Then, the reflecting mirror 5 and the non-linear optical material 7
If the diameter of the pinhole 12 in the light-shielding plate 11 arranged between the two is adjusted by the variable diaphragm 13 so that only the TEM ₀₀ fundamental mode having the smallest transverse mode is passed and the higher order mode is shielded, Higher-order mode resonance in the chamber is suppressed, and a resonance state based only on the TEM ₀₀ fundamental mode can be obtained. As a result, it is possible to efficiently and stably perform harmonic output.

In another embodiment of the present invention, the shading plate 11
As shown in FIG. 3, it may be constituted by a rotary conversion diaphragm having several pinholes 12 having different diameters and capable of changing the diaphragm diameter by rotating.

Also in this embodiment, if the diameter of the pinhole 12 is selected so as to pass only the TEM ₀₀ fundamental mode having the smallest transverse mode and shield the higher-order transverse mode,
Higher-order mode resonance in the resonator is suppressed and TEM ₀₀
It is possible to obtain a resonance state based only on the fundamental mode. This enables efficient and stable harmonic output.

[0023]

As described above, according to the present invention,
By inserting a light shielding plate for controlling the transverse mode in the discrete resonator, it is possible to obtain a stable harmonic wave output only in the TEM ₀₀ fundamental mode. In addition, the light from the laser light source, which is not effective for generating harmonics, is prevented from entering the nonlinear optical material by the light shielding plate, and the temperature rise of the nonlinear optical material is suppressed, so that a more stable harmonic output can be generated. .

[Brief description of drawings]

FIG. 1 is a side view showing an embodiment of a harmonic generator of the present invention.

FIG. 2 is a front view of a light shielding plate used in an embodiment of the present invention.

FIG. 3 is a front view of a light shielding plate used in another embodiment of the present invention.

FIG. 4 is a side view showing an example of a conventional harmonic generator.

[Explanation of symbols]

 1: Harmonic generator 2: Semiconductor laser 3: Collimating lens 4: Mode matching lens 5: Reflecting mirror 6: Reflecting mirror 7: Non-linear optical material 8: Fundamental wave 9: Peltier element 10: Second harmonic wave 11: Shading plate 12: Pinhole 13: Variable diaphragm 101: Harmonic generator

Claims (3)

[Claims] 1. A harmonic generator comprising a light source for generating a fundamental wave, a coupling optical system, and a discrete resonator having a non-linear optical material, wherein a transverse mode control mechanism is provided in the discrete resonator. A harmonic generation device characterized by being provided. 2. The harmonic generator according to claim 1, wherein the transverse mode control mechanism comprises a light shielding plate having a variable diaphragm. 3. The harmonic generator according to claim 1, wherein the transverse mode control mechanism comprises a light shielding plate having a rotary conversion diaphragm.