Optical parametric generation in biaxial KTA crystal under pumping by YAG:Nd laser in arbitrary directions

Herein, on the basis of expressions for the refractive indices of isonormal waves, the possibility of performing collinear phase matching for optical parametric generation in arbitrary directions of a biaxial KTA crystal under pumping by radiation of a YAG:Nd laser is analyzed. The tuning curves that determine the tuning range of the signal and idler for type-I and II-type phase-matching and arbitrary angles θ and φ in cases where the tuning is carried out along the angle θ at a fixed angle φ and vice versa are calculated. The effective nonlinear coefficient is determined. It is shown that their maximum value is achieved аt a polar angle θ = 90° and type-II phase-matching. For the case of generation of eye-safe radiation the spectral and angular phase matching widths were estimated, as well as gain widths of KTA-OPO under monochromatic pumping.

Efficient carrier-envelope phase tunable mid-infrared frequency combs based on CW-seeded optical parametric generation

We present an efficient method for generating frequency combs in the mid-infrared (MIR) spectral range in bulk lithium niobate crystals as well as in waveguides. Our approach is simple and robust, since it is based on single-pass configuration of femtosecond Optical Parametric Generation (OPG) seeded by a telecom continuous-wave laser. Precise and fast tuning of the seed laser allows to rapidly change the offset frequency of the generated MIR comb independent of its repetition rate. The MIR comb offset frequency is inherently known, so its direct detection is not required. An additional degree of freedom that further complements the versatility of our light source is a unique way of repetition rate or mode spacing adjustments. This is achieved by our new concept of coherent multi-seeding that depending on the configuration allows for pulse train modulation and mode spacing, or repetition rate division by an integer number.