Fig. 1. (a) Calculated effective pumping areas versus cavity length for different LG modes with an annular pump. (b) Schematic of the 2 µm wavelength-tunable Tm:YAP vortex laser. LD, laser diode; L, lens; IM, input mirror; BF, birefringent filter; OC, output coupler.

Fig. 2. (a) Laser slope efficiency, (b) wavelength tuning performance, and (c) the polarization measurement of the annular light pumped Tm:YAP laser with E∥b and E∥c polarization. Inset in (a): beam pattern and the corresponding optical spectrum of the Tm:YAP laser without BF.

Fig. 3. Simulated beam radius of laser in the YAP crystal as a function of absorbed pump power by considering the thermal lens effect. Inset: beam profiles of the output laser at different pump powers.

Fig. 4. (a) Laser output performance of the LG_0,+1 modes with and without the BF. (b) Beam profiles and the corresponding interference fringe patterns of LG_0,+1 and LG_0,-1 modes. Insets in (a): optical spectra and polarization measurement of LG_0,+1 and LG_0,-1 modes without the BF in the cavity.

Fig. 5. (a) Measured tuning spectra for LG_0,+1 and LG_0,-1 modes at the fixed absorbed pump power of 4.27 W. (b) and (c) The measured spectral lines at several typical wavelengths for the LG_0,+1 and LG_0,-1 modes.