JPH09237931A - Tunable laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tunable laser the structure of which allows increase in product yield. SOLUTION: A tunable laser is provided with a non-linear optical material 4 as a wavelength changing element in a laser resonator 5, and uses one of the light transmitting faces 4b of the non-linear optical material 4 as an output mirror for the laser resonator 5. The face 4b of the non-linear optical material 4 to be the output mirror is positioned outside the laser resonator 4 to form a convex spherical surface. The radius of curvature of the convex spherical surface is set in a predetermined range so that there is always such an adjustment range where both the phase matching conditions and the resonating conditions of the laser resonator 5 will be simultaneously met.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a wavelength conversion laser.

[0002]

2. Description of the Related Art In a solid-state laser using a semiconductor laser or the like as a light source for excitation, there is an intracavity SHG (second harmonic generation) system in which a nonlinear optical material is arranged in a laser resonator as a wavelength conversion element. This type of laser is a very useful laser in that it can obtain an output beam having a half wavelength with respect to the fundamental wave of laser oscillation and can be applied to the visible region and a wide wavelength range.

In such an intracavity SHG type laser, since the wavelength conversion efficiency is proportional to the square of the fundamental wave output, it is possible to reduce the loss inside the resonator and improve the fundamental wave output. This is an important point for increasing the conversion efficiency, and as a means for achieving this, there have been conventionally proposed some techniques in which one transmission surface of a nonlinear optical material is used as an output mirror.

[0004]

By the way, in the technique of using one transmission surface of the nonlinear optical material as the output mirror, conventionally, the processing accuracy of the nonlinear optical material has not been considered at all, and the setting accuracy of the crystal axis is the maximum. Therefore, when the nonlinear optical material is tilted so as to satisfy the phase matching condition for wavelength conversion, depending on the shape of the surface serving as the output mirror, the nonlinear optical material may be a resonant mirror. The resonance conditions cannot be satisfied at the same time, which has been a factor that significantly reduces the yield of products.

The present invention has been made in view of such circumstances, and a nonlinear optical material used as a wavelength conversion element is
It is an object of the present invention to provide a wavelength conversion laser which has a shape capable of simultaneously satisfying a phase matching condition and a resonance condition regardless of whether or not the setting accuracy of a crystal axis is good, and which can enhance the yield of products.

[0006]

In order to achieve the above-mentioned object, the present invention is directed to a fundamental wave of laser oscillation on one light transmitting surface of a nonlinear optical material arranged as a wavelength conversion element in a laser resonator. With a high reflectance, a film having a high transmittance for the second harmonic generated by wavelength conversion is coated, and the coated surface is used as an output mirror of the second harmonic in a wavelength conversion laser, It is characterized in that the coating surface of the nonlinear optical material is a spherical surface convex to the outside of the laser resonator, and the radius of curvature R thereof is set in the range defined by the following equation.

R ≦ (d−r) / 2 tan (Δρ) where Δρ is the finished tolerance angle of the crystal axis set and processed to satisfy the phase matching condition in the nonlinear optical material. Further, d is the minimum dimension of the portion of the light transmitting surface of the nonlinear optical material that effectively acts (see FIG. 1), and is the diameter when the longitudinal sectional shape of the nonlinear optical material is circular, and the square when the sectional shape is quadrangular. Is not a diagonal line but the length of one side (short side). Furthermore, r is the maximum value of the diameter of the laser beam,
If the beam is circular, it is the diameter, and if it is not circular, it is the longest diameter.

As described above, the light transmission surface (output mirror) of the nonlinear optical material is a spherical surface, and the radius of curvature thereof is defined in the above range, so that the fundamental wave beam in the laser resonator has a phase matching condition. Even when the non-linear optical material is tilted so as to satisfy the condition, there always exists a range in which the fundamental wave beam is reflected vertically by the output mirror, and a standing wave can be generated. The reason will be described below.

First, by making the light-transmitting surface forming the output mirror in the non-linear optical material a spherical surface, the light-transmitting surface can satisfy the condition as the resonator mirror even if the non-linear optical material is tilted within a certain range. it can.

On the other hand, when the nonlinear optical material differs from the designed value of the phase matching angle for wavelength conversion by Δρ, assuming that the nonlinear optical material is tilted with respect to the laser optical axis by the angle Δρ, FIG. As shown, the light transmitting surface 4b
If the range of the portion effectively operating as an output mirror is [ε + (r / 2)] at the minimum, the fundamental wave beam is incident on the light transmitting surface 4b.

Here, when the light transmitting surface 4b is a spherical surface,
ε≈Rtan (Δρ), and [ε + (r / 2)] = d
Since it is / 2, [Rtan (Δρ) + (r / 2)] = d / 2 → R = (d
-R) / 2tan (Δρ) Therefore, if the light transmission surface 4b of the nonlinear optical material is a spherical surface and its radius of curvature R satisfies the condition of R ≦ (d−r) / 2tan (Δρ), No matter how the optical material is tilted in the range of an angle of 0 ° to Δρ with respect to the laser optical axis, the fundamental wave beam is always incident perpendicularly to the light transmitting surface 4b, that is, the output mirror. A standing wave is generated reliably.

[0012]

FIG. 1 is a block diagram of an embodiment of the present invention. The pumping light source 1 is, for example, a semiconductor laser (LD), and the pumping light E from this pumping light source 1 is a lens system 2.
It is condensed by the laser beam and is irradiated onto the end face of the laser medium 3.

On the end face 3a of the laser medium 3, the excitation light source 1
Is coated with a film having a high transmittance for the wavelength of the output excitation light and a high reflectance for the wavelength of the fundamental wave of the laser oscillation, and the other end face 3b of the laser medium 3 is coated. Is coated with a film showing a high transmittance for the wavelength of the fundamental wave of the laser.

A nonlinear optical material 4 used as a wavelength conversion element is arranged facing the end surface 3b of the laser medium 3. Of the light transmitting surface of the nonlinear optical material 4, the surface 4a facing the end surface 3b of the laser medium has a high transmittance for each wavelength of the fundamental wave of the laser and the second harmonic generated by this wavelength conversion element. Is coated.

The other light transmitting surface 4b of the nonlinear optical material 4 has a high reflectance for the wavelength of the fundamental wave of the laser and a high transmittance for the wavelength of the second harmonic. A film is coated, and between the light transmitting surface 4b of the nonlinear optical material 4 and the end surface 3a of the laser medium 3 described above,
A laser resonator 5 having the light transmitting surface 4b as an output mirror is configured, and the second harmonic is extracted from the output mirror.

What is noteworthy in this embodiment is that the light transmitting surface 4b of the nonlinear optical material 4 is processed into a spherical surface, and the radius of curvature R thereof is defined in the range of the following equation. R ≦ (d−r) / 2 tan (Δρ) d; the minimum dimension of the effective portion of the light transmitting surface of the nonlinear optical material Δρ; the finished tolerance angle r of the crystal axis of the nonlinear optical material r; the maximum diameter of the laser beam As described above, by setting the light transmitting surface 4b of the nonlinear optical material 4 to be a spherical surface and defining the radius of curvature R thereof, as described in the section of means for solving the above-mentioned problem, Even if the phase matching angle differs from the design by Δρ, it becomes possible to adjust so that the fundamental wave beam B is always incident perpendicularly to the output mirror (light transmitting surface 4b) of the laser resonator 5 ( 2), a standing wave can be established in the laser resonator 5.

Further, in this embodiment, the radius of curvature R of the light transmitting surface 4b is [(d-r) /
2tan (Δρ)], it is possible to widen the allowable range of Δρ within a certain range. Therefore, depending on the setting method of the radius of curvature R, the processing accuracy of the nonlinear optical material 4 is loosened. It becomes possible to do it.

In the above embodiment, the end surface 3a of the laser medium 3 is a flat surface, but the end surface 3a may be a spherical surface having a convex curvature on the pump light source 1 side and an appropriate radius of curvature.
In this case, the cross-sectional area of the laser fundamental wave in the nonlinear optical material 4 is reduced and the energy density thereof is increased, so that the conversion efficiency can be improved.

If a material having a high reflectance with respect to the pumping light wavelength is used for the film coating the end face 3b of the laser medium 3, the pumping efficiency of the laser medium 3 is improved, and the second harmonic is further improved. The second harmonic can be more effectively taken out by using a material having a high reflectance with respect to waves.

In the above embodiment, an example in which the present invention is applied to a laser having a structure in which one end face of a laser medium is used as a resonator mirror by the end face excitation method has been shown, but the present invention is not limited to this. According to the present invention, a side-pumping type in which pumping light is incident from the side of a laser medium or one mirror of a laser resonator is separately arranged between a lens system 2 and a laser medium 3 in FIG. The present invention can be applied to a laser having the configuration described above, and in any case, the same effect as that of the above-described embodiment can be achieved.

[0021]

As described above, according to the wavelength conversion laser of the present invention, the surface serving as the output mirror of the non-linear optical material arranged in the laser resonator has a spherical shape convex to the outside of the laser resonator. By defining the radius of curvature within a predetermined range, there is always an adjustment range that can satisfy the phase matching condition and the resonance condition in the laser resonator at the same time even if the crystal axis of the nonlinear optical material is not accurate. As a result, the product yield is significantly improved compared to the conventional product yield.

Further, according to the present invention, it is possible to loosen the processing accuracy of the nonlinear optical material depending on the setting method of the radius of curvature of the portion to be the output mirror, so that the wavelength conversion laser can be manufactured at low cost. Can also be achieved.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is an explanatory view of the operation of the present invention.

[Explanation of symbols]

 1 Excitation Light Source 2 Lens System 3 Laser Medium 4 Nonlinear Optical Material 4b Light Transmission Surface 5 Laser Resonator B Fundamental Wave Beam E Excitation Light

Claims (1)

[Claims] 1. A laser of a system in which a nonlinear optical material is arranged as a wavelength conversion element in a laser resonator, wherein one light transmitting surface of the nonlinear optical material has a high reflectance with respect to a fundamental wave of laser oscillation, A film having a high transmittance with respect to the second harmonic generated by the wavelength conversion is coated, and the coated surface is used as an output mirror of the laser resonator.
In a laser configured to extract harmonics to the outside, the coating surface of the nonlinear optical material is a spherical surface convex to the outside of the laser resonator, and its radius of curvature R is R ≦ (d−r) / 2tan ( Δρ) d; the minimum dimension of the effective portion of the light transmitting surface of the nonlinear optical material Δρ; the finished tolerance angle r of the crystal axis of the nonlinear optical material r; the maximum value of the laser beam diameter. Wavelength conversion laser.