JP2001007421A - Solid-state laser light propagation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a solid-state laser light propagation device by which a beam diameter and diverging angle that is all the same as those at the output point can be precisely transferred to the incident point even if the thermal lens effect varies with oscillation output of the laser light. SOLUTION: Regarding the solid-state laser light propagation device in which the laser light outputted from the output point returns in a U-shape through a pair of returning mirrors is inputted to an incident point, each of the returning mirrors is composed of a first concave mirror 7 and a second concave mirror 8 respectively having the same focal length (f), the first concave mirror 7 is placed in a position separated from the output point by a distance equal to the focal length (f) and the second concave mirror 8 is placed in a position separated from the incident point by a distance equal to the focal length (f) in such a way that the space between the first and second concave mirrors 7 and 8 is set twice as long as the focal length (f).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a solid-state laser light propagation device.

[0002]

2. Description of the Related Art FIG. 2 shows an example of a general laser oscillation device. Solid laser media 4 and 4 (which form a laser resonator between a transmission mirror 2 and a reflection mirror 3 forming an optical resonator 1) are shown. For example, Nd: YAG laser rod) are arranged in series,
The solid-state laser media 4 and 4 are excited by an excitation source (not shown) such as a krypton lamp to emit light, and the light is reciprocated between the transmission mirror 2 and the reflection mirror 3 to be transmitted to the solid-state laser media 4 and 4. By repeating input and output, optical resonance is caused to amplify light energy, and laser light can be oscillated through the transmission mirror 2.

Further, the solid-state laser mediums 5, 5 forming a laser amplifying section are compared with the solid-state laser mediums 4, 4 forming a laser resonator.
Are arranged in series on the same optical axis, and the laser light oscillated from the laser resonator side via the transmission mirror 2 is further amplified by passing through the respective solid-state laser media 5 and 5 which are excited by an excitation source (not shown). Thus, a high output laser beam can be obtained.

Then, the laser beam oscillating while expanding the diameter at a required beam divergence angle toward the laser amplifying section with the laser beam condensing position of the laser output of the laser resonating section (the surface on the opposite side of the transmission mirror 2) as the emission point. In order to transfer the same beam diameter as the emission point to the incidence point set on the entrance side of the laser amplifying section and to make the same incident, the convex lens 6 having the focal length f forming the laser beam propagation device is connected to the geometrical optics. It is arranged at an intermediate position at a distance of twice the focal length f from both the exit point and the entrance point based on the image formula.

[0005]

However, in the solid-state laser, the solid-state laser mediums 4, 4 and 5, 5 are heated by the excitation light from the excitation source and cooled by the cooling water.
Of the solid-state laser medium 4, 4, 5, 5 have the same effect as the convex lens, and this thermal lens effect changes according to the oscillation output of the laser light. Therefore, in the propagation optical system that simply transfers the beam diameter from the emission point to the incidence point as described above, the beam diameter is transferred when the thermal lens effect changes and the transverse mode of the laser beam changes. However, there is a problem that the beam divergence angle cannot be transferred.

That is, as shown in FIG. 2, when the thermal lens effect appears strongly, a laser beam having a small beam diameter and a large beam divergence angle at the emission point is oscillated, and is based on the imaging formula of geometrical optics. Even if one-to-one image transfer is performed, as shown in FIG. 3, when the oscillation output of the laser beam is low and the thermal lens effect is weak, a laser having a large beam diameter at the emission point and a small beam divergence angle is used. As a result of the light being oscillated, the condensing position after the lens is in front (convex lens 6 side)
, So even if the beam diameter is kept the same,
The beam divergence angles will be significantly different.

On the laser resonator side, since light passes through all the cross sections of the solid-state laser media 4 and 4, only the beam diameter is transferred from the emission point to the incidence point, and the beam divergence angle is not transferred. In such a case, the laser light incident on the side of the laser amplifying section having the same thermal lens effect always impinges on the side surfaces of the solid-state laser media 5 and 5, causing a decrease in beam quality. It has to be made smaller and the outside of the beam must be cut, causing waste.

The present invention has been made in view of the above-described circumstances, and even if the thermal lens effect changes according to the oscillation output of laser light, the same beam diameter and beam divergence angle as the exit point are set with respect to the incident point. It is an object of the present invention to provide a solid-state laser light propagation device capable of accurately transferring.

[0009]

SUMMARY OF THE INVENTION The present invention relates to a solid-state laser light propagation device wherein a laser beam emitted from an emission point is folded in a U-shape through a pair of folding mirrors and is incident on the incidence point. Each of the folding mirrors is composed of a first concave mirror and a second concave mirror having the same focal length from each other, and the first concave mirror is located at a position away from the exit point by the focal length, and the focal length is equal to the focal length from the entrance point. The second concave mirrors are respectively arranged at positions apart from each other, and the distance between the first concave mirror and the second concave mirror is set to be twice the focal length of each other.

Therefore, in the present invention, by making the focal length equal to the distance from the emission point to the first concave mirror, the beam divergence angle is infinite at a position equidistant from the focal length after reflection of the first concave mirror. Moreover, since the same optical system composed of the second concave mirror is constructed behind the first concave mirror so as to be symmetrical with respect to this position as a base point, it is completely symmetrical from the exit point to the incident point. A beam trajectory is formed, and the same beam diameter and beam divergence angle as the exit point are transferred at the entrance point where the distance from the exit point is four times the focal length.

[0011]

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

FIG. 1 shows an example of an embodiment of the present invention, and the portions denoted by the same reference numerals as those in FIG. 2 represent the same components.

In this embodiment, the solid-state laser media 4, 4 forming the laser resonator and the solid-state laser media 5, 5 forming the laser amplifier are arranged in parallel, and the laser output focusing position ( The laser light emitted from the transmission mirror 2 at the output side (the surface opposite to the output side) is turned into a U-shape via a pair of turning mirrors, and is incident on the incident point set on the input side of the laser amplification unit. And each of the folding mirrors is provided with a first concave mirror 7 having the same focal length f.
And the second concave mirror 8.

The relative positions of the first concave mirror 7 and the second concave mirror 8 are determined with respect to the focal length f from the emission point.
A first concave mirror 7 at a position separated by a distance, and a second concave mirror 8 at a position separated by a focal length f from an incident point, and a distance between the first concave mirror 7 and the second concave mirror 8. Is set to be twice the mutual focal length f.

Here, as to the first concave mirror 7 and the second concave mirror 8, it is possible to use, for example, a spherical mirror or a parabolic mirror as the concave mirrors 7, 8, but a parabolic mirror is used. Adopting this method has the advantage that spherical aberration can be reduced.

Thus, by making the distance from the emission point to the first concave mirror 7 equal to the focal length f, the focal length f after reflection of the first concave mirror 7 is equal to the focal length f. Since the beam divergence angle becomes infinite at the position, and the same optical system composed of the second concave mirror 8 is constructed behind the first concave mirror 7 so as to be symmetrical with respect to this position, the emission point A completely symmetrical beam trajectory is formed between the point of incidence and the point of incidence, and at the point of incidence where the distance from the point of emission is four times the focal length f, the same beam diameter and beam divergence angle as the point of emission. Is transferred.

That is, in the case of a Gaussian beam such as a laser beam (a light beam whose amplitude distribution of a wave in a cross section perpendicular to the propagation direction is represented by a Gaussian function), when the beam is reflected by a concave mirror, the beam is reflected at a focal length after reflection. There is a characteristic that the radius of curvature of the wavefront is uniquely determined, and this radius of curvature changes depending on the position of the converging position before reflection, and the distance between the converging position before reflection and the concave mirror is particularly the focal length. Since it is known that infinity (parallel light) is obtained when the distance is equal to the distance, the distance from the emission point to the first concave mirror 7 and the focal length f are
Is equal to the focal length f of the first concave mirror 7, the beam divergence angle becomes infinite at a position equidistant from the focal length f.

Therefore, according to the above embodiment, even if the thermal lens effect changes according to the oscillation output of the laser beam, the exact same beam diameter and beam divergence angle as the emission point can be accurately transferred to the incidence point. Therefore, the laser beam incident on the laser amplifying unit side, which has the same thermal lens effect as the laser resonator unit side, is transmitted through the solid-state laser media 5, 5 without any trouble, and the oscillation output of the laser beam Irrespective of this, the beam quality can be maintained satisfactorily and stably.

Further, since the solid-state laser media 4, 4 forming the laser resonator and the solid-state laser media 5, 5 forming the laser amplifying unit can be arranged in parallel, the arrangement of the entire laser equipment can be made much more compact. can do.

Further, when the laser light is propagated from the emission point to the incidence point, only the reflection by the pair of concave mirrors 7 and 8 is used without using a lens system having a large loss due to transmission. The propagation loss of laser light can be significantly reduced as compared with the used optical system.

It should be noted that the solid-state laser light propagation device of the present invention is not limited to the above-described embodiment, and may be used for other than propagation of laser light from the laser resonance section to the laser amplification section. In addition, it goes without saying that various changes can be made without departing from the spirit of the present invention.

[0022]

According to the solid-state laser light propagation apparatus of the present invention described above, even if the thermal lens effect changes in accordance with the oscillation output of the laser light, the same beam diameter and beam divergence angle as the emission point are obtained. Can be accurately transferred to
By arranging the emission point and the incidence point in parallel, the arrangement of the entire laser equipment can be significantly reduced in size, and further, when transmitting the laser light from the emission point to the incidence point, a lens having a large loss due to transmission. Since only the reflection by a pair of concave mirrors is used without using a system,
An excellent effect that the propagation loss of laser light can be greatly reduced as compared with an optical system using a lens can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of an embodiment for implementing the present invention.

FIG. 2 is a schematic diagram showing a conventional example.

3 is a schematic diagram showing a case where the thermal lens effect of each solid-state laser medium of FIG. 2 is weak.

[Explanation of symbols]

 7 First concave mirror 8 Second concave mirror f Focal length

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshihisa Yamauchi 3-1-1, Toyosu, Koto-ku, Tokyo

Claims (1)

[Claims] 1. A solid-state laser light propagation device in which laser light emitted from an emission point is folded in a U-shape through a pair of folding mirrors to be incident on an incident point, wherein each of said folding mirrors is A first concave mirror and a second concave mirror having the same focal length from each other, the first concave mirror at a position away from the exit point by the focal length, the second concave mirror at a position away from the entrance point by the focal length. A solid-state laser light propagation device, wherein concave mirrors are arranged, and an interval between the first concave mirror and the second concave mirror is set to twice the mutual focal length.