Resonator-Length Dependence of Electron-Beam-Pumped UV-A GaN-Based Lasers

The dependence of resonator length on the threshold power and emission wavelength of electron-beam-pumped UV-A edge-type emitting lasers is demonstrated. The lowest pump power thresholds are achieved for 100-200 mu m long resonators, where there is good overlap of the focused e-beam spot with the resonator cavity. For longer resonator lengths the focused circular e-beam spot excites only a segment of the resonator cavity, yet lasing is observed. Absorption of the e-beam generated photons in the un-pumped sections of the resonator results in increased absorption losses and, consequently, higher laser thresholds. In addition, a significant wavelength shift from 375 nm for the 50 mu m resonators to 385 nm for the 600 mu m resonators is observed due to absorption of the higher energy photons and re-emission at longer wavelengths in the un-pumped sections.