Dual-wavelength synchronously mode-locked Cr:LiSAF laser with a tunable beating frequency and a central wavelength

We demonstrate a versatile dual-wavelength synchronous mode-locking of a diode-pumped Cr:LiSAF laser for the first time, to our knowledge. A two-color mode-locked operation is achieved by using intracavity birefringent filters (BRFs) or etalons as frequency-selective elements. Using filters with different thicknesses and hence different free spectral ranges (FSRs), wavelength separation in two-color mode-locking could be selected between 1 and 9 nm, with corresponding beating frequencies in the 0.4-3.5 THz range. Moreover, the central wavelength of the two-color output could be tuned smoothly between 840 and 875 nm, only limited by the bandwidth of the semiconductor saturable absorber mirror (SESAM) used for mode-locking. The method, which enables easy adjustment of the central wavelength and beating frequency of a dual-wavelength operation, is suitable for use in other laser gain media as well.