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Abstract

A semiconductor laser HL has an external resonator including a reflector R which reflects the emitted laser beam back into the front facet of the laser. The light emitted from the rear facet of the laser falls on a photodiode PD which generates a signal s which is evaluated by an evaluation unit AE. By differentiation or other processing of the shapes of pulses in the signal s, it is possible to determine the direction of change of any of several operating parameters of the laser system, such as the length L between laser HL and reflector R, the tilt angle of reflector R with respect to the optical axis of the laser or the refractive index n of the medium in the space N defined between the laser and the reflector. For example, one can detect when gas G is fed into space N to change the medium from ordinary air to carbon dioxide, or the reverse. Further, by modulation of one of the operating parameters, such as the pumping current I of the laser, one can measure the time- or phase-shift of the pulses in signal s with respect to the modulation. Further, the pumping current can be corrected to minimize temperature sensitivity of any of the components of the system.

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First Claim