DE3143056C2 - Waveguide laser with intensity modulation - Google Patents

Abstract

A control loop for stabilizing the frequency and / or amplitude of the laser radiation is assigned to a laser with intensity modulation due to spontaneous coupling of transverse modes. This control loop comprises a highly stabilized oscillator and a comparison circuit for comparing the laser radiation with the oscillator output signal in order to generate a control signal. The control signal acts on the laser resonator in order to influence one or more of its parameters in the sense of adapting the laser radiation to the oscillator output signal.

Description

25th

30th

The invention relates to a waveguide laser with intensity modulation by spontaneous coupling of transversal ones Modes and with devices for the targeted change of the optical and geometrical parameters of the system resonator and active., medium for the purpose of controlling the frequency differences of the transversal Fashion".

From the publications "Proceedings of the IEEE" Vol. 53 (1965), No. 6, page 638 and Vol. 56 (1968), No. 3, Pages 333-335, on the one hand, are lasers with coupling of longitudinal modes and with a control loop for Stabilization of the frequency of laser radiation became known and on the other hand laser with spontaneous Coupling of transversal modes and the corresponding intensiiiäTnodüiation known a technological Use of this spontaneous coupling of the transversal modes is not suggested, however, since this is the case theoretically could not explain. Only in the DE-OS belonging to the earlier application P 3125 544.2-33 31 25 544 a possibility of this technological use is shown by adding a more stable optical Resonator with at least one mirror which is transparent for coupling out the laser beam is designed in such a way that this mirror is only permeable in certain places and small areas and is therefore an essential one

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Laser radiation is achieved.

The present invention is based on these last-mentioned measures. Here is the intensity of the & o Laser radiation is locally modulated when at least two transverse modes occur. This modulation can have a sinusoidal shape or with interaction very many modes be pulse-shaped. The pulse modulation can be used as a superposition of sinusoidal oscillations different frequency, amplitude and phase (Fourier series) viewed and experimentally be detected. Through targeted selection and frequency comparison of the laser radiation to be stabilized with the frequency of a highly stabilized laser oscillator.

Use of high-resolution etalons with time-variable transmission,

3. Absorption behavior of narrow-band absorbent Media.

The method results in a control signal with which, mostly by means of piezo elements, the parameters of the Laser resonators such. B. resonator length, grid position or etalon setting can be optimized.

The amplitude stabilization related to long-term fluctuations and short-term fluctuations. Long-term instabilities were compensated by control loops that influence the pumping mechanism of the laser medium depending on the radiation intensity. The response time of this method is approximately ΙΟ ^"4 s.Zur compensation of short-term fluctuations (response time is about 10" ⁶ s) a resonatorexu rne Pockelszel-Ie was used which, however, caused, depending on the intrinsic stability of the laser intensity losses of about 30%.

The invention is based on the object of the initially described relationships between the spontaneous Coupling of transversal modes and their ability to be influenced to generate stabilized, intensity-modulated To use laser radiation in such a way that the stability of the modulation frequency and amplitude is further improved in the case of the generic laser.

An Ausführungsbeispiei of the invention Waveguide laser with a control loop to stabilize the frequency and / or amplitude of the laser radiation is explained in more detail below with reference to the attached schematic drawing due to the interaction of transverse modes is the intensity distribution

individual area has a characteristic intensity modulation (sinusoidal in the simplest case) of a certain frequency Vm ¹ - (localization and modulation of the optical carrier leads to the designation Va / or Avt / -) with the bandwidth Av ^ . The partially transparent mirror 1 directs a fraction of this radiation onto the detector 2, the electrical signal of which is amplified by the amplifier 3. A control unit 4 (the control can for example take place by means of phase comparison, ie by a phase lock loop circuit, PLL) compares the detector signal

with the signal of a highly stabilized oscillator 5 (center frequency of the oscillator vou & ul · - Avi, {-> vou <nf + Avnf-, bandwidth <dN _ns , < 10 Hz). The oscillator 5 can be a quartz oscillator, but other "frequency landards" are also suitable. A deviation of Vm ¹ - from the setpoint vou leads to a control signal that is amplified by 6 and changes one or more parameters of the laser resonator 7. This change. can for example, without limitation to ditses special procedure, be a variation of the resonator length and / or the mirror settings or the mirror surfaces, the z. B. is carried out by a piezo element 8. As a result, eüie: frequency constancy ^{of vm 1} - of a few Hz is possible.

The advantages of the invention over the previous methods reside in the fact that with a A fraction of the previously necessary technical effort is equally good or considerably better Stabilization of the laser radiation in terms of frequency and amplitude is achieved.

1 sheet of drawings

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Claims (3)

"'_'., ',' '.' ■" '^ Claims: Λ. WeTIenieiterIaser order with intensity modulation by spontaneous coupling of transversal modes and \ 'τηίί Einnphiunjonr change for the targeted the' \ '■, optical and geometrical parameters of the system resonator and' active medium. '' Control of the frequency differences of the transversal modes, characterized by a control circuit for stabilizing the frequency and / or amplitude of the laser radiation, which control circuit has a highly stabilized oscillator (5) and a comparison circuit (4) for comparing the laser radiation with the oscillator output signal in order to generate a control signal and by means (8) acted upon by the control signal for acting on one or more of the parameters of the laser resonator (7) for the purpose of adapting the laser radiation to the oscillator output signal 2. Laser according to claim 1, characterized in that it is a TEA laser 3. Laser according to claim 1 or Z, characterized by one acted upon by the control signal, the Piezo elements influencing resonator geometry (8) Setting the parameters of the laser resonator (tube diameter, tilted mirror, changing the resonator length, Deformation of the resonator, choice of mirrors with different local reflections etc.) Modulation type, frequency and amplitude can be determined within wide limits. 'Besides, is it has been experimentally proven that the intensity modulation with respect to the above. Properties extremely sensitive to the slightest changes in the resonator ίο For a variety of science-technical Applications is a high frequency and amplitude stability of the laser radiation used indispensable. Since the processes of the spontaneous coupling of transversal modes and their technical use for the purpose of generating intensitrtsmoiulated Laser radiation were not known, one had to previously additive measures (inside the resonator and resonator-external) to modulate the intensity of the laser radiation. The frequency stabilization In most cases, the aim was to use the following three methods: