Fig. 1. Schematic of the Tm:CYA laser. L1 and L2 are the pump collimating and focusing lens (f=100  mm), M1 and M2 are the highly reflective concave mirrors with the radius of curvature (ROC) of 100 mm, and the M2 is also the output coupler (OC) with output ratio of 10%, M3 is the highly reflective concave mirror, with the ROC of 200 mm, DM is the dichroic mirror (HR 2000 nm/AR 790 nm). L3 is a quartz-crystal-plate filter. α is the tilted angle, which equals the incidence angle of the ray between the plate surface and laser propagation direction. The effective output is the total of the three output ports (Output1, Output2, and Output3).

Fig. 2. Measured emission spectrums of Tm:CYA crystal and the calculated corresponding water absorption lines [24].

Fig. 3. Output power of tunable mode-locked Tm:CYA lasers with the quartz plate filter in the cavity at different OC mirrors of 10%, 2%, and 0.4%.

Fig. 4. Typical wavelength-tunable mode-locked optical spectrums at (a) 1874, (b) 1890, (c) 1949, and (d) 1973 nm.

Fig. 5. Typical mode-locked pulses at 1890 nm. (a) Intensity trace of a real-time measurement showing 39 pulses with RMS noise below 0.3%; (b) measured single pulse; (c) RF spectrum with large span of 3 GHz; (d) RF spectrum with short span of 30 kHz.

Fig. 6. Autocorrelation traces of ML at (a) typical 1890 and (b) 1950 nm.

Fig. 7. Wavelength shift of ML with the tilted angle of the quartz plate at the typical 10% output ratio.