Abstract: A Saturable Reflector apparatus comprises a substrate having a first and second surfaces, and a reflector having a saturable absorber layer, attached to the first surface. At least one of the first and second surfaces has been modified to enhance an etalon effect of the substrate due to interference of light reflecting from the first and second surfaces. Either or both of the surfaces may be modified, for example, by polishing or coating. The apparatus may also include means for adjusting an optical thickness of the substrate to tune the etalon effect. Such means may comprise a temperature control element, such as a heater, coupled to a temperature controller. The inventive apparatus may be incorporated into a mode-locked laser. The etalon tuning optimizes a relation between temporal and frequency domains of radiation incident on the saturable reflector.

Abstract: A non-linear optical device in which quasi-phase matching between different optical waves of differing polarizations and refractive indices increases the interaction length between the waves. The quasi-phase matching structure includes a periodic structure over which the non-linear coefficient varies with a given period, preferably the sign of the non-linear coefficient being inverted between two alternating regions. In LiNbO.sub.3, the periodic structure can be achieved by electrical poling. The required period length is increased by selecting light waves of different polarizations for the non-linear interaction such that a large portion of the dispersion between the waves of different wavelength is compensated by the birefringence of the waves of different polarization. In particular, periodic poling can quasi-phase match radiation in the range of 0.80 .mu.m to 1.2 .mu.m to generate second harmonic generation radiation in the blue and green visible spectrum.

Abstract: A laser system in which an intense laser beam of a predefined pumping wavelength traverses a non-linear material, such as crystalline lithium niobate, that has been impressed with one or more quasi phase matching (QPM) gratings is disclosed. Quasi phase matching compensates for the dispersion or birefringence in a non-linear material by modulating the non-linearity with the proper period such that the different wavelengths involved in the non-linear process stay in phase over a long interaction length. The first QPM grating promotes the parametric generation of a resonant signal whose wavelength is determined by the grating period. According to the invention, either a second QPM grating impressed in the same medium or a different order of the first QPM grating promotes the non-linear interaction between the resonant signal and another optical signal traversing the non-linear material.

Abstract: A laser system in which an intense laser beam of a predefined pumping wavelength traverses a non-linear material, such as crystalline lithium niobate, that has been impressed with one or more quasi phase matching (QPM) gratings is disclosed. Quasi phase matching compensates for the dispersion or birefringence in a non-linear material by modulating the non-linearity with the proper period such that the different wavelengths involved in the non-linear process stay in phase over a long interaction length. The first QPM grating promotes the parametric generation of a resonant signal whose wavelength is determined by the grating period. According to the invention, either a second QPM grating impressed in the same medium or a different order of the first QPM grating promotes the non-linear interaction between the resonant signal and another optical signal traversing the non-linear material.