JPH01258483A - Pulsed laser device - Google Patents

Abstract

PURPOSE:To eliminate the angle deviation of a projecting beam by a method wherein at least two or more mirrors which constitute a laser resonator are periodically slanted so as to enable an optical axis at the misalignment to be parallel with an optical axis at the alignment. CONSTITUTION:A laser beam 8 totally reflected as being magnified by a convex total reflection mirror 2 is amplified through a laser medium 7 and then collimated to be a parallel laser beam 9 with a collimating mirror 6, and the laser beam 9 is amplified again through the medium 7 and its peripheral part is taken out as a ring-shaped laser beam 10 through a window 1 via the circumference of the total reflection mirror 2. When a mis-aligning state that an optical axis does not penetrates through the centers of the mirrors 2 and 6 is made to occur by changing the slant of the mirror 6 and the window 1 held by an elastic piece 3 through the expansion and contraction of a piezoelectric element 4, the laser oscillation stops. When an optical axis at the mis-alignment is made to be parallel with the optical axis at the alignment by slanting the mirror 6 and the window 1 at the same time, the angle of the laser beam 10 is prevented from deviating, so that the positional change of the beam 10 can be decreased even if it is transmitted through a long distance.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a pulse laser device that performs Q-switch pulse oscillation.

[Conventional technology]

Figure 6 shows, for example, the Laser Handbook (Ohmsha).

1975) p. 225 and patent application 1982-31135
This is a cross-sectional configuration diagram showing a conventional pulsed laser device in which a pulsed laser beam is obtained by applying the rotating mirror Q-switch method shown in the γ specification to an unstable resonator. window, (2) is window (
11 is a total reflection mirror provided at the center of the inner surface, (3) is an elastic body, and (4) is an elastic element, such as a piezo element, (
5) is the power supply that drives the telescopic element (4), (6) is the total reflection collimating mirror, and (7) is the laser medium, which is C02.
For example, gas lasers such as lasers and excimer lasers can be used for gas excited by discharge, and solid lasers such as YAG lasers can be used for example, such as flash lamps.
Glass excited (by semiconductor laser), (8),
(9) is a total reflection mirror (2) and a collimating mirror (6)
A laser beam generated in a co-occurrence consisting of 0
1 is a laser beam taken out from around the total reflection mirror (2) in a ring shape. Also, (100) is an outer work.

Next, the operation will be explained.

The convex total reflection mirror (2) and the collimating mirror (6) constitute a so-called unstable resonator. The laser beam (8) that has been totally reflected by the total reflection mirror (2) is amplified in the laser medium (7) and then collimated into a parallel laser beam (9) by the collimating mirror (6). It is amplified by a laser medium (7).

The peripheral part is taken out from around the total reflection mirror (2) as a ring-shaped laser beam α, and the central part is reflected by the total reflection mirror (2) in an enlarged manner and travels back and forth within the resonator. do. As described above, the laser output is obtained from the collimating mirror (6) and the total reflection mirror (2).
This is when the so-called alignment, which is adjusted so that the optical axis connecting the spherical center of the mirror and the mirror passes through the center of each mirror, is good.

On the other hand, the collimating mirror (6) and the total reflection mirror (2)
), etc., if the resonator mirrors are tilted and the optical axis does not pass through the center of each mirror, a so-called misalignment condition occurs, the obtained laser output decreases, and if the mirror is tilted significantly, The oscillation suddenly stops. This is because the resonance index (Q value) of the resonator decreases due to misalignment of the resonator mirror. Therefore, the tilt of the resonator mirror can be changed by providing a piezo element (4) on the back side of one of the resonator mirrors as shown in Figure 6, and expanding and contracting its length according to changes in the voltage of the driving power source. Ba,
A pulsed laser output whose output changes over time can be obtained externally.

[Problem to be solved by the invention]

A conventional pulse laser device is configured as described above, and the angle of only one laser resonator mirror is changed. Therefore, there is a problem in that the optical axis of the laser beam, that is, the direction in which the laser beam is emitted, angularly shifts due to changes in the angle of the mirror, and that the position of the laser beam shifts significantly, especially when the laser beam is transmitted over a long distance. For example, the curvature R4 of the collimating mirror (6) is 10 m, the curvature of the total reflection mirror (2) is 4u2--5 m, and the distance between both mirrors is 2.
．． Taking as an example a laser resonator with a magnification of 2 and a magnification of 5 m, it is necessary to change the angle of the collimating mirror (6) by about 100 μrad in order to pulse the laser output. At the point where the laser beam was separated, the position of the laser beam would shift by about 9 degrees, causing problems such as hitting the transmission duct in the middle and heating it, or not being able to enter the condensing lens. .

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a pulsed laser device that can obtain pulsed laser output without causing angular deviation of the emitted beam.

[Means to solve the problem]

The pulse laser device according to the present invention periodically tilts at least two of the plurality of mirrors constituting the laser beam [6 to misalign the center of each of the mirrors and the optical axis, and generates a pulse. The optical axis at the time of misalignment is parallel to the optical axis at the time of alignment.

Further, the laser resonator is composed of an enlarged exit mirror having nine partial reflection parts, and a collimating mirror arranged opposite to the enlarged exit mirror and which reflects the laser beam reflected by the partial reflection parts to the enlarged exit mirror. It is more effective to use an unstable resonator.

[Effect]

The laser resonator in this invention alternates between a misaligned state and an aligned state.

Moreover, a pulsed laser output is always obtained from the laser resonator without any change in the emission direction angle.

〔Example〕

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

FIG. 1 is a cross-sectional configuration diagram showing a pulse laser device according to an embodiment of the present invention, and FIGS. 2(a) and 2(b) are explanatory diagrams illustrating the operation of the conventional pulse laser device and the pulse laser device according to an embodiment of the present invention, respectively. In Figure 9, the same reference numerals as in Figure 6 indicate the same or equivalent parts.

Next, the operation will be explained.

As in the conventional case, the convex total reflection mirror (2) and the collimating mirror (6) constitute a so-called unstable resonator. The laser beam (8) that has been totally reflected by the total reflection mirror (2) is amplified within the laser medium (7).

Collimated laser beam (9) by collimating mirror (6)
In the process of being collimated, it is amplified again by the laser medium (7), and its peripheral portion is taken out from the total reflection mirror (2) as a ring-shaped laser beam α1, while its central portion is amplified by the laser medium (7). The light is magnified and reflected by the reflecting mirror (2) and travels back and forth within the resonator. As described above, the laser output is obtained from the spherical center 01 of the collimating mirror (6).
and the spherical center 02 of the total reflection mirror (2).
This is when so-called alignment, which is adjusted so that the mirror passes through the center of each mirror, is good.

On the other hand, the co-acquisitor mirror is tilted (each sphere center changes from 01 to 0
When the optical axis does not pass through the center of each mirror, a so-called misalignment condition occurs (optical axis L1 → L2), the obtained laser output decreases, and the mirror If it is tilted, the laser will stop detecting the laser beam. This is because the resonance index (Q value) of the resonator decreases due to misalignment of the resonator mirror. Therefore, if a piezo element (4) is provided on the back of the resonator mirror as shown in Figure 1, and the length of the piezo element (4) is expanded or contracted by changing the voltage of the driving power source to change the inclination of the resonator mirror, the external A pulsed laser output whose output changes over time can be obtained.

In this invention, this mirror inclination change is performed for a plurality of mirrors so that the changes in the optical axes Lj and L2 become parallel to each other (FIG. 2(b)).

This means that if the curvature of the collimating mirror is R1t and the curvature of the total reflection mirror is -R2, this means that the collimating mirror (6) is tilted downward within the 01 resonator.

It can be performed by tilting only.

For example, in order to pulse in the same resonator as explained in the conventional example with R1-10m, R2-5m, distance d2.5yx between both mirrors, and magnification rate 2, θ1-10.
It is calculated as 0/jrad, θ2-2004rad.

At this time, the laser optical axis L2 is deviated from the original optical axis L1 in parallel with the original optical axis L1. This value is sufficiently small considering that the diameter of the laser beam is usually 20 WM or more, and
Since the shift is parallel to the original optical axis L1, the position of the laser beam will not shift significantly even during long-distance transmission.

FIG. 3('b) shows an example of the laser output pulsed in this manner in comparison with that which is not pulsed (FIG. 3(a)).

In the above embodiment, an example is shown in which the present invention is applied to an unstable resonator, but the same effect can be obtained even if the present invention is applied to a stable resonator shown in FIG. Note that (1υ is a partially reflecting mirror.

FIG. 5 shows an example of application to an improved unstable resonator. In the figure, I:XJ is a partially reflecting mirror. In this embodiment, the laser beam is outputted from the partially reflecting mirror (1) and its surroundings in a converging manner, so that the condensing characteristics are good. That is, in the case shown in FIG. 1, it is necessary to increase the ratio of the inner diameter to the outer diameter of the laser beam α1 in order to improve the focusing characteristics.

This leads to an increase in the magnification of the resonator and thus a decrease in the curvature of the resonator mirror. This is, for example, the magnification rate M,
Assuming that the curvatures of the occultary mirrors are R+ and R2, and the octopus length L.

This is because there is a relationship of 1R11-□・2L. However, the reduction in the curvature of the mirror causes the problem that when changing the optical axis by changing the inclination of the mirror as in this invention, the mirror must be tilted more in order to change the optical axis by the same amount. occurs. On the other hand, in the embodiment shown in FIG. 5, the output beam has a condensed shape, so that the light focusing property is good. Therefore, the optical axis can be changed significantly with a small change in the angle of the mirror without increasing the magnification factor that much. For example, the collimating mirror (6), which should bring about one optical axis change, and the total reflection mirror (2) (
or the inclination θ1 of the partial reflection mirror (■). Comparing θ2, in the one shown in Figure 1, θ, -100μrad,
θ2-200 μrad, but if M -1,5 in the configuration of Fig. 5, R1 = 15 m, R2--
Since it is 10m, θ1 depth 6γμrad, θ2 = 1
It can be significantly reduced to 0.00 μraa. Of course, if the thickness of the 9-partial reflection mirror is controlled to match the phase between the partial reflection mirror and the laser beam passing around it, the focusing ability can be improved and a laser beam of even better quality can be obtained.

〔Effect of the invention〕

As described above, according to the present invention, at least two of the a number of mirrors constituting the laser resonator are periodically tilted to misalign the centers of the respective mirrors and the optical axis, thereby causing pulse oscillation. Since the optical axis at the time of misalignment is made parallel to the optical axis at the time of alignment, it is possible to obtain a pulsed laser beam with little change in beam position even when transmitted over long distances.

Furthermore, if the laser resonator is constituted by an enlarged exit mirror having a partial reflection part, and a collimating mirror arranged opposite to the enlarged exit mirror and which reflects the laser beam reflected by the partial reflection part to the enlarged exit mirror, , even if the mirror tilt is small, a pulsed laser beam with good focusing ability can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional configuration diagram showing a pulse laser device according to an embodiment of the present invention, and FIGS. 2(a) and 2(b) are explanatory diagrams illustrating the operation of the conventional pulse laser device and the pulse laser device according to an embodiment of the present invention, respectively. , 3(a) and 3(t)) respectively show a pulse laser device according to an embodiment of the present invention. FIGS. 4 and 5 are waveform diagrams showing the laser output when not pulsed and when pulsed, respectively. FIGS.
The figure is a cross-sectional configuration diagram showing a conventional pulse laser device. (2)... Total reflection mirror, (4)... Telescopic element, (
6)...Collimating mirror, +81+9)ill・
...Laser beam, αυ■...S portion reflecting mirror. In addition, in FIG. 9, the same reference numerals indicate the same or corresponding parts.

Claims (2)

[Claims] (1) At least two of the multiple mirrors constituting the laser resonator are periodically tilted to misalign the centers of each of the mirrors and the optical axis, causing pulse oscillation, and the optical axis at the time of misalignment , a pulsed laser device that is parallel to the optical axis during alignment. (2) The laser resonator is composed of a magnifying exit mirror having a partial reflection section, and a collimating mirror placed opposite to the magnifying exit mirror and reflecting the laser beam reflected by the partial reflecting section to the magnifying exit mirror. 2. The pulsed laser device according to claim 1, which is an unstable resonator.