JPH03265179A - Laser resonator - Google Patents

Abstract

PURPOSE:To make it possible to extract the energy of laser beams efficiently by using a total reflection concave mirror as at least one mirror and amplifying and growing the laser beams, which rise from the periphery, by bending back to near the optical axis with the concave mirror. CONSTITUTION:Laser beams are emitted through a front mirror 3 by causing high-voltage discharge between electrodes 1a and 1b arranged oppositely with a laser tube 1 therebetween. The emitted laser beams are reflected by a total reflection concave rear mirror 2 and radiated approximately parallel by a mechanical lens 5 through the opening 4 of the mirror 3. Laser gain rises earlier from the periphery near the wall of the tube 1 than from near the optical axis, therefore, the laser beams rising from the periphery grow by receiving light amplification timely when passing near the optical axis with delay corresponding to the distance between the mirrors of the resonator. Hence optical energy can efficiently be extracted.

Description

[Detailed description of the invention] [Industrial application fields] The present invention relates to an optical resonator for a laser device.

[Conventional technology] The structure of a conventional laser resonator is shown in FIGS. 2 to 5.

The configuration shown in Figure 2 shows the most basic laser resonator, with a laser tube 2 sealed with a predetermined laser medium.
01 is provided with electrodes (not shown) facing each other across the laser optical axis. The laser medium between the electrodes is provided with mirrors facing each other on the optical axis with the electrodes in between (the position of the mirrors does not matter inside or outside the laser tube), and by applying a predetermined voltage to the electrodes, the laser medium between the electrodes is A laser beam is generated from the laser beam, which is amplified and grown by the front and rear mirrors.

By the way, the configuration shown in FIG. 2 is generally called a stable type, in which the laser medium is sandwiched between a total reflection mirror 202 and a partially transmitting mirror 203, and the laser beam is outputted from the partially transmitting fi 203.

Such a stable resonator has the advantage of being able to extract only the amplified and grown laser beam with high energy intensity, but the intensity differs between the center and the periphery near the optical axis of the laser medium, and the intensity varies within the beam cross section. occurs.

In addition to this stable type, there is a laser resonator configuration called an unstable type, and this type is shown in FIGS. 3 and 4.

The mirror of the resonator shown in FIG. 3 consists of a combination of a concave mirror 302 with a large total reflection and a convex mirror 303 with a small one.
Laser light is extracted from the convex mirror 303 side. Furthermore, in the resonator shown in FIG. 4, a total reflection mirror 404 having an opening in the center is provided in front of the small convex mirror 403, and the laser beam reflected by this total reflection 1ii 404 is taken out. The direction of amplification of the laser light within is the same as that shown in FIG.

Such an unstable resonator generally has a large laser gain, and has the advantage of being able to extract laser light with a similar energy intensity in the cross section within the laser tube, especially in the beam cross section perpendicular to the optical axis of the laser medium between the electrodes. It is often used to efficiently extract a high-quality beam from a large pulse laser device.

The configuration shown in FIG. 5 is a modification of the unstable resonator and is called an injection locking system. In this device, an aperture is provided in the center of a concave mirror 502 with large total reflection, and seed laser light is injected from the outside through the aperture.
The beam is magnified and reflected by the concave mirror 502, and a substantially parallel output beam is obtained from the convex mirror 503 side.

This device has the feature of being able to perform remote control of the output laser beam.

[Problems to be Solved by the Invention] In the conventional unstable resonator as described above, the amplification and growth of the laser pulse within the resonator first occurs from the laser medium near the optical axis in the beam cross section within the laser tube. After rising and being reflected by a concave total reflection mirror, it is strongly amplified as it passes through the periphery of the laser medium, and is output as a high-intensity laser beam.

Therefore, it is effective for the rise of laser gain in the laser medium between the electrodes to be delayed in time in the peripheral area far from the optical axis than in the vicinity of the optical axis of the laser medium. Ideally, you should be late.

However, in metal vapor lasers such as copper vapor lasers,
Due to the skin effect of the discharge, the laser gain rises faster at the periphery of the laser medium (closer to the inner wall of the laser tube) than near the optical axis, which causes the problem that the energy of the laser beam cannot be extracted efficiently. there were.

This situation is the same with the injection locking method, and the off-axis injection method [Oxford Lasers, published August 1988, Technical Note No. 1 (catalog)] has been adopted as a solution.

In this method, the position of the small convex mirror that makes up the resonator is shifted from near the optical axis in the beam cross section to a peripheral position, but since the area that the convex mirror itself can cover is part of the peripheral area, the overall The disadvantage is that it is inefficient.

The present invention has been made in view of these conventional problems, and an object of the present invention is to provide an unstable resonator that can efficiently extract the energy of laser light.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention includes electrodes facing each other with the optical axis interposed therebetween, and a mirror facing the optical axis with the electrodes sandwiched therebetween. A laser resonator that applies a predetermined voltage to electrodes and generates laser light from a laser medium located between the electrodes, wherein at least one of the mirrors is a total reflection concave mirror, and a laser beam that rises from the periphery of the laser medium between the electrodes is provided. The concave mirror returns the laser beam to the vicinity of the optical axis of the laser medium to amplify and grow the laser beam, and the amplified and grown laser beam is taken out as an output.

That is, the resonator structure is such that the direction in which the laser light is amplified in the normal unstable resonator is reversed, and it also has the advantages of a stable resonator.

[Function] Since the present invention is configured as described above, the flow of laser energy in the unstable resonator is in the opposite direction to that in the conventional unstable resonator.

For this reason, when used in a laser device, such as a copper vapor laser, where the laser gain rises faster at the periphery of the laser medium than near the optical axis, the laser light that rises from the periphery first is reflected by the concave mirror. , passes near the optical axis with a time delay, so the energy of the laser light can be extracted efficiently by utilizing the delay in amplification timing.

[Example code] Embodiments of the present invention will be described with reference to the drawings.

FIG. 1(a) is a schematic diagram showing the configuration of a resonator according to a first embodiment of the present invention, in which copper vapor is used as the laser medium.

As shown in FIG. 1(a), the resonator consists of a laser tube (gas chamber) 1 in which an active medium such as copper vapor is sealed at a predetermined pressure and gas mixture ratio, and a laser tube 1 on the optical path of the laser beam. It has a front mirror 3 and a rear mirror 2 that are arranged in front and behind with the laser tube 1 in between, and two electrodes 1a and 1 that are arranged to face each other with the laser tube 1 in between.
It is configured to oscillate a laser beam via the front mirror 3 by causing a high voltage discharge between the front mirror 3 and the front mirror 3. In this embodiment, the beam mirror 2 is a total reflection concave mirror, and after the laser beam emitted by the discharge is reflected by the beam mirror 2, the front mirror 3 (reflectance 1
00%) is oscillated through the opening 4 formed substantially at the center. Further, a negative meniscus lens 5 is installed in front of the front mirror 3 (aperture 4), and the output beam is emitted from the lens 5 substantially in parallel.

Here, the interval between the mirrors 2 and 3 constituting the resonator is 3 m, and the hole diameter at the center (opening 4) of the mirror 3 is 3 mm in diameter. The values of the resonator length (mirror spacing) and mirror center hole diameter are both examples, and are not limited thereto.

The operation of the copper vapor laser device having the resonator configured as described above will be described below.

Generally, when a laser is excited by generating a high-speed pulse discharge in a rare gas containing copper vapor, the laser gain rises due to the skin effect of the discharge. It is known that this time difference is about 10 nanoseconds.

In the laser device according to this example, the mirror-to-mirror length of the resonator is 3 m.
When the laser light that rises at the periphery of the laser tube is reflected by the rear mirror (concave surface 2) and passes near the optical axis, the excitation in this area is delayed and rises, so optical amplification is performed at the right time. It grows in response to light, making it possible to efficiently extract light energy.

Here, the meniscus lens 5 is provided to make the laser beam parallel.

In this embodiment, both sides of the lens 5 are coated with an AR coating, but if one or both sides are coated with a partial reflection coat and used as a semi-transmitting mirror, or if the aperture 4 is made into a semi-transmitting mirror, it is possible to use a laser beam. A part of the light is fed back to the laser tube 1 side, and it becomes possible to configure a resonator that can be called a quasi-stable type with the rear mirror 2. Furthermore, by selecting the curvature of the meniscus lens 5, the laser mode can be controlled to some extent.

FIG. 1(b) shows a second embodiment of the present invention, in which the direction of extraction of the laser beam is opposite to that of the first embodiment shown in FIG. 1(a).

In the resonator according to this embodiment, the laser tube 101 (
Front mirror 10 across electrodes 101a, 101b)
2 rear mirror 103 is arranged, rear mirror】03
(100% reflectance), for example, a diameter of 3InI
A convex mirror 104 with total reflection of n is formed. moreover,
In this embodiment, the front mirror 102 is a total reflection concave mirror, and an opening 105 having a diameter of 3+nm, for example, is formed at the center of the concave mirror 102, and the laser beam is extracted from the opening 105.

Even in a device with such a configuration, the laser beam rising from the peripheral part near the tube wall of the laser tube 1 passes through the vicinity of the optical axis with a time delay after being reflected by the concave mirror. As in the example, by utilizing the delay in the rise of the laser beam near the optical axis, it becomes possible to efficiently extract the laser beam.

In this embodiment as well, the opening 105 may be a semi-transmissive mirror to constitute a resonator having an intermediate function between a stable type and an unstable type. Furthermore, if a negative meniscus lens is placed in front of the front mirror 102, the N1
It is clear that the same effect as in the embodiment can be obtained.

In the first and second embodiments of the present invention, copper vapor laser devices have been described, but for example, metals other than copper (Ar, Nd
The present invention can be similarly applied to a vapor laser (YAG, etc.).

In other words, the gist of the present invention is to perform optical amplification in accordance with the transition of the portion of high laser gain inside the laser tube, so that the portion of high laser gain is transferred from the peripheral portion of the laser tube with a time delay. Similar effects can be obtained by applying the present invention to any laser device that moves near the axis.

Further, according to the present invention, since the laser beam is output in a converged form, there is no need for an external condensing element, and there is an advantage that a laser beam with high energy density can be obtained.

Furthermore, nonlinear optical crystals (ADP, KDP).

The present invention is particularly effective when generating harmonics using a nonlinear optical crystal (β-B, B204, etc.), since it is necessary to make a focused laser beam with high energy intensity enter the nonlinear optical crystal.

[Effects of the Invention] As explained above, according to the laser resonator of the present invention, when excitation rises faster in the periphery of the laser medium than in the vicinity of the optical axis due to the skin effect, etc. Since the optical amplification system is arranged in such a way that the growth of the laser light proceeds from the periphery to the vicinity of the optical axis, there is an effect that the extraction efficiency of the laser light energy can be increased.

Furthermore, in the present invention, the beam diameter of the laser output is very small compared to the diameter of the laser medium. This has the advantage that the optical system of the entire apparatus can be simplified because it can be omitted.

[Brief explanation of drawings]

FIG. 1(a) is an explanatory diagram showing a laser resonator according to a first embodiment of the present invention, FIG. 1(b) is an explanatory diagram showing a laser resonator according to a second embodiment of the present invention, and FIG. The figure is an explanatory diagram showing the configuration of a conventional stable resonator, Figures 3 and 4 are explanatory diagrams showing the configuration of a conventional unstable resonator, and Figure 5 is an explanatory diagram showing the configuration of a conventional unstable resonator. It is an explanatory view showing the composition of a container. [Explanation of symbols of main parts 1.101...Laser tube, 2,102...Concave mirror, 3,103...Total reflection mirror, 4.105...Aperture, 104...Convex mirror, 5... Negative meniscus lens, Fig. 1 (a) Fig. 1 (b) ○

Claims (1)

[Scope of Claims] Comprising electrodes facing each other with an optical axis in between, and a pair of mirrors facing each other along the optical axis with the electrodes in between, a predetermined voltage is applied to the electrodes to reduce the gap between the electrodes. A laser resonator that generates a laser beam from a laser medium, wherein at least one of the mirrors is a total reflection concave mirror, and the laser beam rising from the periphery of the laser medium between the electrodes is directed to the optical axis of the laser medium by the concave mirror. A laser resonator is characterized in that the laser beam is amplified and grown by returning it to the vicinity, and the amplified and grown laser beam is taken out as an output.