Narrow-Linewidth Tunable Tm:LuYAG Laser Controlled By Volume-Bragg Grating

Tunable thulium (Tm) doped solid-state lasers, of which emission spectrum range iscapable of covering some of atmospheric windows, eye-safe wavelength range andpump band of mid-infrared (3~5μm) OPOs, have attracted a considerable interest.Conventional tuning elements were employed including a single-plate filter andbirefringent filter. These inserted components introduce extra losses inevitably andcomplicate optical alignment of cavity. More importantly, these techniques are unableto narrow the spectral linewidth enough. Whereas in many applications in eye-safespectral region narrow linewidth are highly desired, such as laser radar, beamcombining, or pumping mid-infrared OPOs. In order to realize narrow linewidthoperation with single frequency, the unidirectional ring cavity and microchip lasers iscommonly used. This approach, however, has some shortcomings (e.g. intricateresonator design, critical optical alignment).Volume Bragg gratings (VBGs) are newly developed spectral control opticalelements with extremely high diffraction efficiency exceeding99%, widetransparency ranges from350to2700nm and high damage threshold. Its outstandingcapabilities of spectrum narrowing and wavelength tuning have been demonstrated invarious rare earth ions, transition metal ions doped solid-state lasers andsemiconductor lasers. In particular, a reflecting volume Bragg grating (RBG) could besimply used as one cavity mirror without extra inserted losses.In last two decades, the mixed crystals have been highly regarded because of itscombined advantages of glass (the broader fluorescence line width) and single crystals(the better mechanical and thermal properties). The mixed crystal Tm:LuYAG as anew gain material candidate in2μm spectral range is, therefore, expected to achieveda wider wavelength tuning range. Although the CW lasing of Tm:LuYAG, as well asthe thermal and optical properties relating to the LuYAG solid solution crystal, hasbeen investigated in detail, wavelength tuning and linewidth narrowing performance of Tm:LuYAG has still not been reported.In this paper, we report on a narrow linewidth tunable Tm:LuYAG laser with aRBG, which is capable of tuning in the spectral range of1935~1995nm. The outputspectral linewidth is measured to be independent of pump level and the incident angleof RBG. Additionally, single-frequency oscillation is observed within certain range ofpump power. From the measure of FP interferometer, we can ensure whether theoutput laser is single frequency laser.