Dual-wavelength Nd:CALGO laser based on differential loss of birefringent filter

Continuous-wave dual-wavelength (DW) operation of an a-cut Nd:CALGO (Nd:CaGdAlO₄) laser around ∼1.08 μm was demonstrated using a single plate quartz birefringent filter (BRF) with an on-surface optical axis. A wide range of wavelength separations between the two laser lines ranging from sub-nm up to 10 nm was observed with controllable intensity ratios. A new regime of operation of DW laser was also identified where one of the oscillating spectral lines was in the rejection band of the filter. This is in sharp contrast with typical operation of DW lasers with BRF where wavelength separation was limited either to the free spectral range or to the linewidth of a single transmission peak of the used filter. This was enabled by differential loss introduced by a single transmission peak of the BRF. Using this mechanism, generation of a large number of laser wavelength pairs became possible.