Analysis of impact factors of output characteristics for optically pumped THz lasers

• The analytical formulas for calculating the THz laser output power and output frequency drift have been derived.
• Some major factors contributing to the THz output have been analyzed quantitatively.
• The pump conditions have further been optimized and the optimal working gas pressure range is 15–20 Pa.

Optically pumped terahertz (THz) lasers as a reliable THz radiation sources have been widely used in THz application area. Considering the Doppler-broadened effects and the two-photon light shift effects, the physical model for the THz output power and the THz output frequency drift of optically pumped THz lasers has been established based on the rate equations. The main factors affecting THz laser output have been analyzed quantitatively. The results indicate that the THz output power increases with the increasing of the pump power, while decreases with the increasing of the pump frequency offset from the operating gas absorption centre. The THz output frequency drift is mainly caused by two-photon light shift when the pump offset is small, whereas Doppler-broadened becomes main factor if the pump frequency offset is relatively larger. Furthermore, the THz output frequency drift increases in proportion to the pump power. The stability of the THz output frequency can be enhanced and the THz output power can be improved by choosing pressure in the cavity reasonably, and the optimal working gas pressure range is 15–20 Pa. Stabilizing the pump laser frequency in the range of gas absorption centre, choosing reasonable working gas pressure in the THz cavity and the pump power can efficiently improve the performance of the THz laser output.