Sum and difference frequency generation by femtosecond laser pulses in a nonlinear crystal

We solve using the finite-difference time domain method the Maxwell's equations describing the sum and difference frequency generation by a femtosecond laser pulse in a nonlinear crystal. We model the propagation of an ordinary polarized signal pulse of a few optical cycles duration in the presence of extraordinary polarized femtosecond pump pulse in a negative uniaxial crystal in the direction normal to the optical axis. As an example, we apply our model to study the propagation of a signal pulse of τs = 10 fs duration at λs = 800 nm central wavelength in the presence of pump pulse of τp = 100 fs duration at λp = 532 nm central wavelength in a LiNbO3 crystal of 60-μm thickness at a temperature of 230 °C. We focus on the conversion efficiency as a function of temperature and pump intensity, and find that the temperature tuning bandwidth for the conversion efficiency in the near infrared spectral range is about 70 °C.