Thulium laser pumped mid-ir source with broadbanded output

A Thulium laser ( 15 ) is used to directly drive a ZnGeP2 optical parametric oscillator ( 30 ) with a nominal 2 mum output to generate the 3-5 micron wavelengths. In one embodiment, the ZGP OPO is configured as a linear resonator and in another embodiment the ZGP OPO is configured as a ring resonator. The ring resonator prevents optical feedback to the Thulium laser ( 15 ) and eliminates the need for an optical isolator ( 24 ). Moreover, the Thulium laser pump ( 15 ) is implemented as a Tm:YAlO3 laser in which YAlO is the host for the Thulium YAlO is particularly beneficial as it is a mechanically hard optical material allowing high thermal loading without fracture as well as natural birefringence that can minimize thermal birefringence losses. A longer wavelength transition at 1.99 microns is selected to minimize nonlinear crystal loss. More particularly, a high power, high efficiency Tm:YAlO3 laser repetitively Q-switched at 10 kHz is used to drive a ZnGeP2 OPO. The system is run with room temperature components and achieves over 3 W at 3-5 microns with an efficiency of 5% starting from the pump diode. A two crystal resonator ( 40, 42 ) design allows tuning over multiple spectral peaks or alternately as an ultra broad spectral source.