METHOD AND APPARATUS FOR MONITORING AND CONTROL OF LASER EMISSION WAVELENGTH

An apparatus for monitoring and controlling the wavelength of laser radiatio n includes at least one optical filter for receiving laser radiation and for transmitting and reflecting first and second filtered beams, respectively. Alternatively, the first and second beams may be transmitted by separate filters (32, 34). The beams are filtered according to respective first and second spectral filter functions that cross at least one crossing wavelength . A beam comparison element (20) compares the first and second filtered beams (36,38) and produces an error signal (22) representative of the deviation of the wavelength of the laser radiation from a set-point wavelength. The beam comparison element (20) can include first and second optical detectors (40, 42) and error signal (22) by taking a ratio or the difference of the signals detected by the detectors. Varying the angle of incidence of the laser radiation upon at least one optical filter varies the spectral filter functi on of that filter for selecting or varying the operating wavelength of the lase r (12). A laser wavelength controller (24) can receive the error signal (22) f or stabilizing or tuning the wavelength of the laser radiation. Several embodiments of the invention are disclosed.