MULTIPASS DEGENERATE 4-WAVE-MIXING IN A DIODE-PUMPED ND-YVO4 SATURABLE AMPLIFIER

The process of saturable-gain four-wave mixing (DFWM) in a diode-pumped Nd:YVO4 amplifier with interacting beams provided by a Nd:YAG oscillator is investigated. Multipass geometries are employed that arrange for the signal beam to experience an increased interaction length relative to that of the pump beams. DFWM reflectivities up to R = 170% and a diffraction efficiency eta = 6% of the volume population hologram written in the Nd:YVO4 amplifier are obtained experimentally. A theoretical analysis of multipass DFWM is presented in the transient (pulsed) regime, including the laser amplification and the mutual interaction of all the interacting beams as well as the spectral mismatch between the beam frequency and the gain line-center frequency of the Nd:YVO4 amplifier. It is shown that because of the close spectral matchup of the Nd:YAG oscillator and the Nd:YVO4 amplifier, the amplitude (gain) grating contribution is predominant compared with that of the phase grating.