Optical amplification in the random gain media

The influence of the excitation spot area and the scatter concentration on the laser threshold were investigated in the TiO2/Rhodamine B gain media. Frequency-doubled output of a mode-locked Nd:YAG laser(20 Hz repetition rate, 6 ns pulse width) was used as the pump laser. Monte Carlo method with ring laser was used to calculate the threshold gain required for modeling the input-output characteristics in scattering gain media. The model is based on the transient two-level laser equations and includes the detailed spectral properties of the dye gain system. Monte Carlo simulation of random walks is performed in the geometry. The calculated results show that the laser threshold is related to the length of photons in gain media and the possibility of photons reflected from boundary. With the i