JPH0246787A - Pulse oscillation solid-state laser device - Google Patents

Abstract

PURPOSE:To generate stable laser pulse, regardless of the repetition rate of laser oscillation by observing a laser rod in an optical resonator,with other probe light, and moving either one of lenses of an expander arranged in the resonator, in the optical axis direction. CONSTITUTION:When ether one of lenses constituting an expander is driven in the optical axis direction, the adaptation is obtained for the oscillation of high repetition rate higher than or equal to 10Hz, in the state of alignment adjusted by 1Hz. For example, by moving a little the convex lens of the expander toward the laser rod, the expander is turned into a convex lens in an equivalent manner, as a whole. A part of laser rays leaks from a total reflection mirror 3 and is monitored through a suitable aperture 11, by using a photo diode 7, so that the intensity of a heat lens of the laser rod can be led out as a change component of the monitoring signal. As a result, the control for moving the one lens of the expander can be performed by utilizing the above signal.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a pulsed solid-state laser device.

[Conventional technology]

Conventionally, a pulse oscillation solid-state laser device 1, for example, a 5+ Nd YAG laser oscillator, uses YAG as an active medium.
The rod was optically excited using a quinone (Xs) arc lamp or the like to create a single population inversion state. This arc lung does not only emit light around 830nrn, which is required to output a wavelength of 1.06μm from a YAG laser, but also has a wide spectrum, and the light unnecessary for excitation of Nd is generally converted into heat and produces a Schillet plot. warm.

[Problem to be solved by the invention]

For this reason, in general, in solid-state laser oscillators such as YAG lasers, the temperature of the rod changes depending on the repetition rate of laser oscillation, and as a result, the degree of thermal lens effect generated within the rod changes, resulting in a change in energy per pulse, There was a problem in that the spread angle and other factors changed when they were lined up.

To address the above-mentioned problems, conventional oscillators directly monitor nine oscillated laser beams and control the energy injected into the xenon lamp, that is, the charging voltage, in accordance with this signal to stabilize the laser output.

However, in this method, feedback control is performed according to the average of the first shot or more pulse outputs, so there is a drawback that some pulse outputs immediately after laser oscillation cannot be controlled.

Furthermore, if the energy injected into the xenon lamp is changed significantly.

Even if the laser output is constant, the spread angle of the laser output light changes, and as a result, when using this laser output light as a processing light source, the problem is that the light focusing ability of the focusing lens changes. There was also.

The present invention aims to solve these problems of the conventional devices, and provides a pulsed solid-state laser device that can generate stable laser beams.

[Failure to solve the problem]

According to the present invention, in a pulsed solid-state laser device that outputs laser light by stimulating a laser rod disposed between an output mirror of an optical resonator and a total reflection mirror by discontinuous discharge of a flash lamp, the total reflection mirror is A dichroic reflector that reflects the laser beam but transmits light of a specific wavelength shorter than the wavelength of the laser beam is used, and is disposed coaxially on at least one side of the laser rod within the optical resonator. an expander comprising a convex lens element and a concave lens element; a linear translator for moving at least one of the convex lens element and the concave lens element of the expander on an axis; and a beam generating means for generating a beam having the specific wavelength. , the beam light passes through the total reflection mirror and enters the resonator, passes through the laser rod as a probe light, is reflected by the output mirror, and exits through the laser rod and the total reflection mirror again to the outside. means for advancing the light beam onto an optical path different from the beam generating means; a photocell for detecting the light beam that has proceeded to the different optical path and emitting an electrical signal; According to the present invention, there is obtained a solid-state laser device with a 90-degree oscillation oscillation, which is characterized in that it is equipped with a driver for driving the laser beam.

[Principle of the invention]

Generally, when a rod-shaped crystal of a solid-state laser such as a YAG laser is uniformly excited by light from around the rod, a thermal lens effect occurs, and the rod equivalently exhibits the effect of a convex lens or a concave lens.

In the case of a 30Nd YAG laser, the effect of a convex lens ('A
) o, n: refractive index, T: temperature) are dominant.

When the plot is excited by T Xe Ranno etc., the temperature of the rod rises and the rod gradually takes on the appearance of a convex lens.

Here, if an element exhibiting the properties of a convex lens as described above is created in the optical resonator, an independent optical element exists to cancel this.

That is, if an optical element exhibiting the properties of a concave lens is present in the resonator, the nine oscillators as a whole can maintain a stable state.

In the present invention, we fully observe the degree of thermal lens inside the laser rod,
This signal is used to drive at least one lens of the extractor/ninder, which is made up of a combination of convex and convex lenses inserted into the resonator, in the optical axis direction, thereby constantly keeping the resonator in a stable state. It has a control configuration.

The above operating principle will be explained using FIG. 4. Figure 4 (,
) shows the oscillator when the laser is not operating. 1 is a laser rod. When not in operation, the laser rod is kept at the set temperature of the pure water chiller for lot cooling. It has become. In this state, as shown in the figure, there is almost no thermal lens effect. 2 and 3 are the output mirror and total reflection mirror of the optical resonator, respectively. 4a and 4b respectively indicate a convex lens and a concave lens constituting the expander.

FIG. 4(b) is an explanatory diagram showing a state at a repetition rate of about IHz. The temperature of the laser rod is slightly higher than To, reaching T. When the repetition is relatively slow like this, the thermal lens effect of the rod is small.

FIG. 4(c) is an explanatory diagram showing a state at a repetition rate of 10 Hz or more. In this state, the temperature of the laser rod becomes T2, which is considerably higher than To.

As described above, when the repetition rate is 10 Hz or higher, the thermal lens effect of the rod becomes large.9 If the laser beam is oscillated with a matching alignment at a repetition rate of about IHz, the laser beam will be significantly reduced.

Here, if one of the lenses constituting the expander is driven in the optical axis direction, as shown in the same figure (d) (10H with alignment adjusted at IHz).
It becomes possible to adapt to high dryness oscillations of z or more. In this example, by slightly moving the concave lens of the expander toward the laser rod, this
The armhole as a whole is made into a concave lens in an equisimplified manner. That is, the convex lens effect of the rod is corrected by the concave lens of the expander.

The control for moving one lens of this expander is controlled by the fourth lens.
As shown in Figure (d), the laser beam partially leaking from the total reflection mirror 3 is passed through an appropriate aperture 1-1 to the photodiode 7.
By monitoring this, the strength of the laser rod's thermal lens can be extracted as a change in this monitor signal.
This can be done using this signal.

However, in the above configuration, the laser light itself generated within the resonator is used as the signal source.

The drawback is that it can only be controlled while the laser is in continuous operation. In the case of intermittent oscillation, it is not possible to control one shot after a break.

Therefore, in order to control the state of the laser rod inside the resonator, another light source, such as a HeNe laser, is used as a globe light that enters from the total reflection mirror side of the resonator through a half mirror, then passes through the laser rod and expander. , the light reflected by the output mirror end face of the resonator is extracted again from the total reflection mirror. This globe light is spatially selected using an appropriate aperture and received by a photodiode or the like, and changes in this globe light are observed. By using this signal as a signal for driving the linear translator, even when oscillation is performed intermittently, it is possible to control up to one shot immediately after a pause in one oscillation.

EMBODIMENT FIG. 1 is a block diagram of an embodiment of the present invention. 1 is a Nd":YAG laser rod that emits a laser beam with a wavelength of 1.06 μm, 2 is an output mirror (R=ω), and 3 is a total reflection mirror (R=
5 tor) 4 is an ex-mirror lens, and 4a is a convex lens (f
=100ffiIm), and 4b is a concave lens (f=-50).

5 is a linear translator, 6 is a He-Ne laser with a wavelength of 0.633 μm, 7 is a PIN photodiode, 8
9 is a preamplifier, 9 is a driver (of the linear translator), 10 is a filter, and 11 is an anno-cha.

12 is a half mirror 113 is a total reflection fi of the He-Ne laser beam, and 14 is a beam exonokunda. Incidentally, the reflection film of the total reflection mirror 30 is as follows: Nd'': YAG 1.06 μm of the laser beam emitted by the laser rod is totally reflected.

It consists of a dichroic dielectric multilayer plate through which a shorter HeNe laser beam of 0.633 μm with multiple wavelengths passes. The linear translator 5 is driven by a galvanometer.

A configuration diagram of an example of the preamplifier 8 is shown in FIG.

In the same figure, after converting the current signal of the globe light received by the PIN photodiode 7 into a voltage signal,
This is based on the probe light when the laser is not oscillated or when it is oscillated at a certain repetition rate.
If the intensity of the globe light changes by changing the repetition rate of the laser, the linear translator is driven so that the intensity becomes the previous reference value.

In Figure 2, 7 is a PIN photodiode (PD)
, R, ~R6 are resistors, and C1~c3 are capacitors.

■, and VR, 2 are variable resistors? ``RFP is a reference voltage source; AoIAl is an operational amplifier.

FIG. 3 is an explanatory diagram of a second embodiment of the present invention. In this embodiment, movable expanders for canceling the thermal lens effect of the laser rod are installed at both ends of the laser rod within the optical resonator.

This embodiment is suitable for cases where the thermal lens effect of the laser rod is large or the optical resonance length is long.
It is very effective in cases where control is difficult with a radar.

In the case of intermittent oscillation according to the embodiment of the present invention,
It is now possible to prevent the laser output from decreasing or increasing during the first or several viewings after the pause. This is very effective as a light source for use in laser marking devices and the like.

2. The present invention was mainly explained using a crystal whose laser rod has a convex lens effect, such as a Nd":YAG laser.
The same applies to crystals that mainly have a concave lens effect, such as Nd3 + :phosphate glass lasers.

〔Effect of the invention〕

As explained above, in the present invention, a laser rod inside an optical resonator is observed with another globe light, and an extract/? By moving one of the lenses in the optical axis direction, it is possible to generate a stable laser beam that does not depend on the repetition rate of laser oscillation.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2 is a circuit diagram of an example of the preamplifier portion thereof, Fig. 3 is a block diagram of a second embodiment of the present invention, and Fig. 4 is a block diagram of the present invention. It is a diagram explaining the principle of the invention. Explanation of symbols: 1...Laser rod, 2...Output mirror. 3... Total reflection mirror, 4... Expander r 4 a.
...Convex lens element, 4b...Concave lens element, 5...
Linear translator, 6...He-Ne laser, 7
...Photodiode, 8...Preamplifier, 9...
Gorinia translay driver, 10...filter, 11...aperture. 12... Half mirror 213... Total reflection mirror for HeNe laser beam, 14... Beam extractor.

Claims (1)

[Claims] 1. A pulsed solid-state laser device that outputs laser light by stimulating a laser rod placed between an output mirror of an optical resonator and a total reflection mirror by discontinuous discharge of a flash lamp, comprising: As a reflecting mirror, a dichroic reflecting mirror that reflects the laser beam but transmits light of a specific wavelength shorter than the wavelength of the laser beam is used, and is coaxially disposed on at least one side of the laser rod within the optical resonator. placed,
an expander comprising a convex lens element and a concave lens element; a linear translator for moving at least one of the convex lens element and the concave lens element of the expander on an axis; and a beam generating means for generating a beam having the specific wavelength. , the beam light passes through the total reflection mirror and enters the resonator, passes through the laser rod as a probe light, is reflected by the output mirror, and passes through the laser rod and the total reflection mirror again to exit to the outside. means for advancing the light beam onto an optical path different from the beam generating means; a photocell for detecting the light beam that has proceeded to the different optical path and emitting an electrical signal; What is claimed is: 1. A pulsed solid-state laser device comprising: a driver for driving the pulse-oscillating solid-state laser device;