Self-phase-locked degenerate femtosecond optical parametric oscillator based on BiB3O6

A self-phase-locked degenerate femtosecond optical parametric oscillator (OPO) based on the birefringent nonlinear material, bismuth triborate, BiB3O6, synchronously-pumped by a Kerr-lens-mode-locked Ti: sapphire laser at 800 nm is described. By exploiting versatile phase-matching properties of BiB3O6, including large spectral and angular acceptance for parametric generation and low group velocity dispersion in the optical xz plane, stable self-phase-locked degenerate OPO operation centered at 1600 nm is demonstrated using collinear type I (e -> oo) interaction in a 1.5-mm crystal at room temperature. The degenerate OPO output spectrum extends over 46 nm (similar to 5.4 THz) with 190 fs pulse duration for input pump pulses of 155 fs with a bandwidth of 7 nm. Phase coherence between the pump and degenerate output is verified using f-2f interferometry, and discrete frequency beats caused by different carrier-envelope-offset frequencies are measured using radio frequency measurements.