Search

We theoretically analyze type-I broadband second-harmonic generation (SHG) of femtosecond laser pulses based on a quasi-phase-matching configuration in periodically poled congruent LiNb[O.sub.3] (LN) and periodically poled MgO:LiNb[O.sub.3] (PPMgLN) (5% and 7%). Group-velocity matching (GVM) can be achieved at the fundamental waves of 1.59, 1.56, and 1.55 [micro]m for SHG when the three types of crystals have grating periods of 22.31, 20.07, and 23.45 [micro]m, respectively. It is found that the central wavelength of the fundamental wave for GVM will increase with the decrease of MgO doping in LN. It is concluded that the shift of the GVM central wavelength is due to the difference of MgO doping, which changes the dispersion of the crystal. Therefore, tunable and high efficiency broadband SHG of femtosecond laser pulses in a long crystal can be realized by selecting different doping rates of PPMgLN. OCIS codes: 190.2620, 190.4400.

We report a new algorithm, called the self-adjusting algorithm, to construct an aperiodic optical superlattice in which multiple nonlinear optical parametric processes can be realized simultaneously with high conversion efficiency. The numerical simulations show that a self-adjusting algorithm has obvious advantages that are due to its own physical process and feedback function. Especially in comparison with other existing algorithms, a self-adjusting algorithm can eliminate the need to search blindly and is independent of the initial conditions. OCIS codes: 220.0220, 190.2620.

We have theoretically demonstrated type II broadband second-harmonic generation (SHG) based on a quasi-phase-matching (QPM) configuration in periodically poled KTP (PPKTP). The wavelength dependence of QPM grating periods at different temperatures of 5 [degrees]C, 25 [degrees]C, and 45 [degrees]C is calculated with the crystal length of 1 cm. We find a very wide bandwidth, as large as 42.6 nm, of fundamental wavelength of 1.58 [micro]m at the telecommunication band with the QPM period of 48.9 [micro]m at 25 [degrees]C. The corresponding bandwidths of incident angle and temperature are found to be 4.24[degrees] and 14.8 [degrees]C, respectively. The comparison among PPKTP, periodically poled lithium niobate (PPLN), and MgO:PPLN reveals the unique performance of PPKTP in the broadband SHG. OCIS codes: 190.2620, 190.4400.

We have theoretically demonstrated direct fourth-harmonic generation (FHG) based on a quasi-phase-matching (QPM) configuration in periodically poled lithium niobate. The wavelength dependence of period of FHG QPM gratings is calculated. Bandwidths of fundamental wavelength, temperature, and incident angle are also studied. We find a very wide bandwidth, as large as 115 nm, of fundamental wavelength near the wavelength of 3797 nm with the QPM period of 9.73 [micro]m. The numerical calculation shows that the conversion efficiency for QPM FHG and cascading QPM by two-step second-harmonic generation is almost identical. OCIS codes: 190.2620. 160.4330.