DE2105480A1 - Method and arrangement for generating reproducible and steep giant laser pulses - Google Patents

Description

Method and arrangement for the generation of reproducible and provide giant laser pulses

The present invention relates to a method and a Arrangement for generating reproducible and steep laser reams enimpulsen by means of an optical Q-switch and a laser containing a feedback circuit.

The optical Q-switches most widely used to date for giant pulse lasers work with Pockels cells, which require high switching voltages of at least 3 kV. This results in long switching times, which increase the time constant of the rising edge of the giant pulse. The distance between the ignition pulse and the light pulse of the flashlamp is subject to fluctuations, so that the giant laser pulses contain different energies if the changeover time of the Q switch is derived from the ignition pulse time of the flashlamp. Another disadvantage arises from the fact that the light output deteriorates as the lamp ages, which means that the level of the giant pulses decreases. In addition, different properties from lamp to lamp and irregularities in the power supply cause further fluctuations in the pulse height. If there are also thermally induced changes in the existing Fabry-Perot effects, further irregularities arise from them.

The present invention is based on the object of specifying a method and an arrangement for generating giant laser pulses by means of a laser containing an optical Q-switch and a feedback system, which can be used to generate reproducible giant laser pulses with the same energy.

To Iiö,: ii.m £ di · - :;

fgabe it is suggested that at the moment

point of reaching the threshold occupancy of the active material, a signal decoupled from the interior of the optical resonator is fed to the feedback circuit, which the optical. Switch operated and switched to high quality, ι

There is preferably an arrangement for carrying out this method made of an active material in rod shape, in particular a solid material, which is arranged in an optical resonator is, a pump arrangement and an optical Q-switch which blocks the optical resonator in the closed state with a Feedback circuit, the feedback circuit consisting of a photodiode, which is connected to a high-voltage generator via a matching network is connected, steal; and wherein the high voltage generator is connected to the electrodes of the optical Q-switch and is controlled by the photodiode.

The photodiode is advantageously arranged in such a way that it detects the active material after the threshold state has been reached emitted signal through reflection at every Brewster surface contained in the resonator, e.g. at the optical Q-switch receives ».

The optical Q-switch preferably consists of a crystal exhibiting the electro-optical effect.

The electro-optical material is preferably LiNbO. *.

The electro-optical crystal is advantageously included with the Brewster angle to the direction of the light beam provided so that no "polarizer is required in the optical resonator of the laser.

With the method according to the invention, as well as the arrangement for Execution of the process results in steep, giant pulses with reproducible rising edges and pulse peaks. The time constant of the increase in momentum is of the order of magnitude

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1 nsee. Since these impulses are independent of disturbances due to aging, Power supply, as well as replacement of the flash lamp are, the inventive method and the arrangement is suitable for the Use in an optical rangefinder and for pulse holography. !

In the following, the invention will be explained in more detail with reference to the figure will.

1 "denotes the active material, for example a YAG rod, which is arranged together with an optical Q-switch 2, for example a LiKTbO -, - crystal, in the optical resonator, the consists of the two mirrors 3 and 4. The arrangement of a Polarizer in the optical resonator is unnecessary, since the end face of the active material facing the optical Q switch, as well as the two areas of the electro-optical crystal penetrated by the light beam, which is shown here in dashed lines the Brewsterv / angle are arranged to the direction of the light beam. This arrangement of surfaces under the Brewster angle Fabry-Perot effects caused by temperature changes are avoided can cause a different quality of the optical resonator in the open state. 5 represents a photodiode, which is connected via a matching network 6 to a high-voltage generator 7, which in turn is connected to the two electrodes, which serve to change the transmission of the Q-switch 2 is connected.

The mode of operation of the arrangement is as follows: In the locked state of the optical goods holder 2, the active material 1 is pumped by an optical pump arrangement (not shown here). The material then reaches the Scii ^ ellv / ertbesetsung after some time and it builds a laser oscillation aiii, the oscillation of the laser in the blocked state of the optical Q-switch is registered by the photodiode, because the photodiode is arranged in such a way that it builds that up one of the Brewster _{surfaces, S 4} B. of the Q-switch, falling and from this by reflection

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receives coupled light. The resulting signal becomes a high-voltage generator via a matching network 6

7 supplied, which actuates the optical Q-switch and switches the optical resonator to high quality. After switching the photodiode can no longer receive light, because im ge! In the open state, no reflection occurs on the Brewster surfaces.

An estimate for the power gain gives a net gain per cycle of 6.5. The total power gain per cycle results from a decoupling of $ 20 from this to about 8. With this value, the time constant for a 50 cm long laser with a YAG rod of 5 cm length and 6 mm diameter is the rising edge of the giant pulse is about 1.8 nsec. The pulse itself is about 15 nsec long and reaches the Peak about the power of 200 kW. A fast switching time of the optical Q-switch results from the low half-wave voltage, for a LiNbO., crystal of 30 mm length, square cross-section and 20 pF capacitance is about 500 Y.

The time constant of 1.8 nsec resulting from the power gain per cycle of 8 can be shortened if at Use of powerful flashlights to introduce further refractive surfaces into the resonator at the Brewster angle "or but materials with a higher refractive index are used for the elements in the resonator (laser rod, switch). This causes a higher blocking effect and, as a result, greater overstaffing at the time of the switchover, resulting in a "shortening of the time constants of the impulse rise.

For flash lamps that have a power gain per cycle of

8 do not reach, the blocking effect of the Q-switch must be reduced will. The reduction in the barrier effect of the Schelters is generally achieved by reducing the number of refractive surfaces under the Brewster angle. For example, the side of the LiNbO, crystal facing away from the active material can be used Cut perpendicular to the rod axis and directly add a dielectric!

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vaporize laser mirror. Another way to reduce the blocking effect, "is _s, the LiNbO - switch with only part of the full circuit voltage." Operate.

It is also possible to combine the proposed arrangement to operate with a continuous wave laser. As a result of the feedback The Q-switch via the photodiode then creates a pulse chain in the emission, which is used in the PuIs-Code-Modnlation application Can be found.

6 claims
1 figure

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Claims (6)

Claims 1.! Process ssur generation of reproducible and steep Giant laser pulses by means of an optical Q-switch and a feedback circuit containing Laser, characterized in that at the time the threshold value is reached of the active material, a signal coupled out from the interior of the optical resonator is fed to the feedback circuit which actuates the optical switch and switches to high quality. 2. Arrangement for generating reproducible and steep giant laser pulses according to the method according to claim 1, consisting of an active material in the form of a rod, in particular plague material, which is contained in an optical resonator is arranged, a pump arrangement and a blocking the optical resonator in the closed state optical Q-switch with a feedback circuit, characterized in that the feedback circuit made up of a photodiode connected to a high-voltage generator via a matching network is, the high voltage generator is connected to the electrodes of the optical Q-switch and controlled by the soda diode. 3. Arrangement for generating reproducible and steep giant laser pulses according to claim 2, characterized in that the photodiode is arranged so that they that of the active material after reaching the threshold occupancy emitted signal by reflection on one of the Brewster surfaces, preferably on the optical quality switch, eepccepts. TPA 1/71 S / 1039 -7- 209834/0956 4. Arrangement for generating reproducible and steep giant laser pulses according to claim 2, characterized shows that the optical Q-switch consists of a crystal "showing the electro-optical effect. 5. An arrangement for generating reproducible and steep giant laser pulses according to claim 4, characterized thereby draws that the electro-optic crystal consists of. 6. An arrangement for generating reproducible and steep giant laser pulses according to claims 4 and 5, characterized in that both the electro-optical ^ Crystal as well as the active material with under the Brewster angle to the light beam direction arranged surfaces are provided, so that no polarizer in the optical resonator of the laser is required. 209834/0956 YPA 9/712/1039 Blank page