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 μm 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 μm resonators to 385 nm for the 600 μm resonators is observed due to absorption of the higher energy photons and re-emission at longer wavelengths in the un-pumped sections.