Second-harmonic generation

Abstract: A theoretical study is presented on the optimization of second harmonic generation (SHG) and parametric generation (PG) by a laser beam in a uniaxial nonlinear crystal. Numerically computed curves show the dependence of the SHG power, and the reciprocal of the PG threshold power, on the parameter l/b, where l is the optical path length in the crystal and b is the confocal parameter (determined by the focal length of the focusing lens and the minimum radius of the laser beam, assumed to be in the TEM00 mode of an optical resonator). The calculations take full account of diffraction and double refraction. In the absence of double refraction, the optimum focusing condition is found to be l/b=2.84. For PG the optimization of the crystal length l is also discussed, and curves are given showing the dependence of the threshold on l for the case in which signal and idler have the same losses. It is shown that the computed functions are also relevant to the mixing of two Gaussian beams and to parametric amplificat...

Abstract: Bulk transparent organic nonlinear optical (NLO) single-crystals of imidazolium L-tartrate (IMLT), with a low near-UV cutoff wavelength at 235 nm and a large powder second harmonic generation (SHG) efficiency, being 4.5 times larger than that of KH2PO4 (KDP), have been successfully grown by the slow cooling method. Kurtz and Perry powder test reveals that IMLT is a phase-matchable NLO material with good optical transmittance in the entire visible region. The laser-induced damage threshold experiments show that the grown IMLT bulk crystals possess an excellent resistance to laser radiation with a high threshold up to 7.45 GW cm−2, much larger than those of several known inorganic and organic NLO materials. Furthermore, the thermal properties associated with its high laser-induced damage threshold, including the specific heat and thermal expansion coefficients, have been investigated thoroughly as a function of temperature. The intrinsic origin of the laser-induced damage was also analyzed based on studying the surface morphologies triggered with the laser-induced damage using an optical microscope. All the findings in the present work indicate that IMLT has a potential application as a useful NLO candidate.

Abstract: A high power and efficient 588 nm yellow light is demonstrated through intracavity frequency doubling of an acousto-optic Q-switched self-frequency Raman laser. A 30-mm-length double-end diffusion-bonded Nd:YVO4 crystal was utilized for efficient self-Raman laser operation by reducing the thermal effects and increasing the interaction length for the stimulated Raman scattering. A 15-mm-length LBO with non-critical phase matching (θ = 90°, ϕ = 0°) cut was adopted for efficient second-harmonic generation. The focus position of incident pump light and both the repetition rate and the duty cycle of the Q-switch have been optimized. At a repetition rate of 110 kHz and a duty cycle of 5%, the average power of 588 nm light is up to 7.93 W while the incident pump power is 26.5 W, corresponding to an overall diode-yellow conversion efficiency of 30% and a slope efficiency of 43%.