JP2001015837A - Solid state laser oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain such a resonating condition as to make a laser beam output oscillated from a laser resonator always stable by forming convex lens-shaped portions at both axial ends of a laser medium. SOLUTION: Convex lens-shaped portions 5 respectively projecting toward reflecting mirrors 3 are formed at both axial ends of a laser medium 2. The focal distance of the portions 5 and the length L of a solid state laser oscillator 1 are set to such values that, even when a laser beam 4 stays on the side of the concentric point in the vicinity of the confocal point even in a low-output region. The length of the medium 2 is set to such a value that the focal distance of the portions 5 is sufficiently shorter than that of a thermal lens, so that the beam 4 does not enter an unstable region while going over the concentric point even in a high output region. According to this configuration, the resonating condition always stays in a stable region between the confocal point and the concentric point.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state laser oscillator.

[0002]

2. Description of the Related Art Conventionally, laser devices have been used for various purposes such as processing of articles and medical treatment, and one example is shown in FIG.

In FIG. 4, reference numeral 1 denotes a solid-state laser oscillator used in a laser device. The solid-state laser oscillator 1 is a solid rod-shaped laser medium 2 having both ends in the axial direction formed in parallel planes.
And two reflection mirrors 3 arranged at predetermined intervals on both ends of the laser medium 2 in the axial direction.

In the above-described solid-state laser oscillator 1, when light from a laser excitation light source (not shown) is applied to the laser medium 2, a laser beam 4 is generated from the laser medium 2, and the generated laser beam 4 The laser beam 4 is resonated and amplified between the reflection mirrors 3 and becomes a high-intensity laser beam 4 to be extracted from the solid-state laser oscillator 1.

By the way, in the solid-state laser oscillator 1 in which a high-quality laser beam 4 can be obtained, when the amount of excitation input is changed due to the thermal lens effect, the focal length of the thermal lens changes, so that it functions as a resonator. The resonance condition of the reflecting mirror 3 is not constant. For this reason, if the pump input amount is increased in order from the low pump input, the resonance condition changes from a condition equivalent to a parallel plane resonator to confocal and concentric.

This is illustrated as shown by an arrow A in FIG. FIG. 5 is a graph showing the relationship between g1 and g2, where the horizontal axis is g1 and the vertical axis is g2.

G1 = 1− (L / (R1)) where g2 is

G2 = 1- (L / (R2)) In [Equation 1] and [Equation 2], L is the distance between the reflecting mirrors 3 and 3, that is, the length of the oscillator, R1 and R2 are the radii of curvature of the reflecting mirror 3, and as shown in FIG. In the case of a plane mirror, the radii of curvature R1, R2 are infinite.

In FIG. 5, A is a position of a low excitation input without a thermal lens effect, B is a confocal point, C is a concentric center, hatched portions indicated by D and E are stable regions, F, G, H, and The part without hatching indicated by I is an unstable area.

[0008]

However, in the case of the solid-state laser oscillator 1 shown in FIG. 4, the resonance condition of the solid-state laser oscillator 1 is in the vicinity of the unstable region depending on the set value of the excitation input amount. This is near the confocal point B in FIG. That is, since the stable region is narrow near the confocal point B as shown in FIG. 5, the relationship between g1 and g2, that is, the resonance condition enters the unstable regions H and I with a slight mechanical shift. As a result, the resonance of the laser beam 4 becomes unstable, and vibration may be applied to the reflection mirror 3, or the output of the laser beam 4 may fluctuate due to the fluctuation of air in the optical path.

In other words, when a high-quality laser beam 4 is to be obtained from a solid-state laser, the volume of the laser beam 4 passing through the laser medium 2 in the laser medium 2 must be sufficient to effectively use energy. To increase the size, it is necessary to set resonance conditions equivalent to a co-center resonator. However, in the case of the conventional solid-state laser oscillator 1 shown in FIG. 4, if the conditions are set so that a high-power laser beam 4 can be obtained,
In a medium output range, resonance conditions equivalent to confocal are obtained. Thus, under such resonance conditions, the reflection mirrors 3, 3
There is a problem that the resonance of the laser beam 4 in between becomes very unstable, and the quality of the laser beam 4 is poor, so that the solid-state laser oscillator 1 becomes difficult to use.

In the present invention, in view of such circumstances, the output of a laser beam oscillated from a laser resonator is always in a stable region for effective use of energy regardless of the set value of the excitation input amount. It is an object of the present invention to provide a solid-state laser oscillator capable of obtaining such resonance conditions and outputting a high-quality laser beam.

[0011]

According to the present invention, there is provided a solid-state laser oscillator in which a reflecting mirror having a flat reflecting surface for a laser beam is provided at both ends in the axial direction of the laser medium at predetermined intervals. A convex lens-shaped portion is formed at both ends in the axial direction.

The present invention also provides a solid-state laser oscillator in which a reflecting mirror having a flat reflecting surface for a laser beam is provided at both ends in the axial direction of a laser medium at predetermined intervals. A convex lens is provided between the light source and the reflection mirror.

In the solid-state laser oscillator of the present invention, when light from a laser excitation light source irradiates a laser medium, a laser beam is generated from the laser medium, and the generated laser beam resonates and amplifies between the reflection mirrors. Then, a high-quality laser beam is extracted from the solid-state laser oscillator.

In the present invention, since a convex lens-shaped portion is formed in the laser medium or a convex lens is provided between both ends in the axial direction of the laser medium and the reflection mirror, the focal length of the convex lens-shaped portion or the convex lens and the laser medium are determined. Is shorter than the focal length due to only the thermal lens effect of the laser medium. For this reason, the length of the solid-state laser oscillator can be made shorter and smaller than the conventional one.

Further, since the resonance condition can be set in a stable region between the confocal point and the concentric point, a high-quality laser beam can be obtained with a small solid-state laser oscillator.

[0016]

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

FIGS. 1, 2 and 3 show an embodiment for carrying out the present invention, in which the same components as those shown in FIGS. 4 and 5 are denoted by the same reference numerals. Thus, in this embodiment, the basic configuration of the solid-state laser oscillator 1 is the same as that of the conventional one shown in FIGS. 4 and 5, but the feature of this illustrated example is that, as shown in FIG. At both ends in the axial direction of the medium 2, a convex lens-shaped portion 5 protruding toward the reflection mirror 3 is provided, or as shown in FIG. 2, between the both ends of a parallel plane in the axial direction of the laser medium 2 and the reflection mirror 3. Is provided with a convex lens 6.

The focal lengths of the convex lens portions 5 and the convex lens 6 and the length L of the solid-state laser oscillator 1 are such that the laser beam 4 is near the confocal point B in FIG. And the laser medium 2 so that the focal lengths of the convex lens-like portion 5 and the convex lens 6 can be sufficiently shorter than the focal length of the thermal lens so as not to enter the unstable region G beyond the concentric center C even in the case of the high power region. Determine the length of

That is, for example, in FIG. 2, if the focal length of the convex lens 6 is f1 and the focal length due to the thermal lens effect of the laser medium 2 is f2, the composite focal position of the convex lens 6 is the length L of the solid-state laser oscillator 1. 1 in the center
/ 2 × f1. Thus, when the thermal lens effect is zero,
In order to set the resonance condition to be closer to the concentric center C than the confocal B in FIG. 3, the relationship between the length L of the solid-state laser oscillator 1 and the focal length f1 of one convex lens 6 is expressed by

## EQU3 ## It is determined that L ≧ f1.

In order to set the resonance condition to a position closer to the concentric center C than the confocal point B in FIG. 3 when the thermal lens effect is the maximum,

Since the relationship of L = 4 × (2 / (f1) · 1 / (f2)) ⁻¹ must be established,

L × (2 / (f1) + 1 / (f2)) = 4

[Mathematical formula-see original document] When L = f1 is calculated,

[Mathematical formula-see original document] L / (f2) = 2.

## EQU8 ## The relationship L = 2f2 is obtained. To make the resonance condition closer to the concentric center C, it is expressed by [Equation 3].

With this configuration, even when the amount of excitation input to the laser medium 2 without the thermal lens effect is low (low current), the resonance condition is set to the confocal B as shown in FIG.
Therefore, the resonance condition is a condition on the side of the concentric center C, so that the resonance condition can be obtained without obtaining the laser beam 4 of high quality without passing through the confocal point B near the unstable regions I and H. Can be reached. This is for the following reason.

That is, as in this embodiment, convex lens-shaped portions 5 are formed at both ends in the axial direction of the laser medium 2, or convex lenses 6 are provided between both ends in the axial direction of the laser medium 2 and the reflection mirror 3. This is considered to be equivalent to providing a concave mirror as a reflection mirror of the solid-state laser oscillator 1 from the viewpoint of Gaussian beam propagation. Then, even when the laser medium 2 has a low current without a thermal lens effect, the resonance condition moves from the low excitation input position A in FIG. 3 to the confocal point B or the concentric point C by an amount corresponding to the focal length of the lens. Will be located at that point. Further, the focal length of the lens can be directly replaced with the radius of curvature R of the concave mirror. Accordingly, if the focal length f1 of the convex lens-shaped portion 5 or the convex lens 6 is set as in [Equation 3], the resonance condition is always in the stable region E between the confocal point B and the concentric point C.

As described above, in the present embodiment, the convex lens-shaped portion 5 is formed on the laser medium 2 or the convex lens 6 is provided between both end portions of the laser medium 2 in the axial direction and the reflection mirror 3. Therefore, the composite focal length of the focal length of the convex lens-shaped portion 5 or the convex lens 6 and the focal length of the laser medium 2 due to the thermal lens effect is shorter than the focal length of the laser medium 2 due to the thermal lens effect alone. For this reason,
The length L of the solid-state laser oscillator 1 can be made shorter and smaller than the conventional one.

Since the resonance condition is in the stable region E between the confocal point B and the concentric point C in FIG. 3, a high-quality laser beam 4 can be obtained with the small solid-state laser oscillator 1.

It should be noted that the solid-state laser oscillator of the present invention is not limited to the illustrated example described above, and it goes without saying that various changes can be made without departing from the spirit of the present invention.

[0026]

As described above, the first aspect of the present invention is as described above.
According to the solid-state laser oscillator described in (2) and (3), the length can be made shorter and smaller than that of the conventional one, and the resonance condition is in the stable region between the confocal point and the concentric point. It is possible to obtain an excellent effect that it can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of an embodiment of a solid-state laser oscillator of the present invention.

FIG. 2 is a schematic diagram showing another example of the embodiment of the solid-state laser oscillator of the present invention.

FIG. 3 is a graph for explaining a resonance condition in the present invention.

FIG. 4 is a schematic diagram showing an example of a conventional solid-state laser oscillator.

FIG. 5 is a graph for explaining a resonance condition of a conventional oscillator.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Solid-state laser oscillator 2 Laser medium 3 Reflection mirror 4 Laser beam 5 Convex lens-like part 6 Convex lens

Continuation of the front page (72) Inventor Yoshihisa Yamauchi 3-1-1, Toyosu, Koto-ku, Tokyo Ishikawajima Harima Heavy Industries, Ltd. Tokyo Engineering Center F term (reference) 5F072 AK01 JJ01 JJ05 KK18 YY01 YY06

Claims (2)

[Claims] 1. A solid-state laser oscillator in which a reflecting mirror having a flat reflecting surface of a laser beam is provided at both ends in the axial direction of a laser medium at predetermined intervals, and a convex lens shape is provided at both ends in the axial direction of the laser medium. A solid-state laser oscillator characterized in that a part is formed. 2. A solid-state laser oscillator in which a reflecting mirror having a flat reflecting surface for a laser beam is provided at both ends in the axial direction of a laser medium at predetermined intervals, and both ends in the axial direction of the laser medium, a reflecting mirror and A solid-state laser oscillator comprising a convex lens provided therebetween.