Optically pumped lasing

V.G. Kozlov, V. Bulovic, P.E. Burrows, M. Baldo, V.B. Khalfin, G. Pailhasarathy, S.R. Forrest, Y. You, M. E. Thompson, Study of lasing action based on Forster energy transfer in optically pumped otganic semiconductor thin films, J. Appl. Phys. 1998, 4, 4096. 

We have studied, theoretically and experimentally, the characteristics of a novel class of lasers that are based on radial Bragg reflectors. Lasing action with low threshold levels are demonstrated at room temperature under pulsed optical pumping. The observed Q factors are in the order of several thousands. The unique characteristics on these lasers make them promising candidates for numerous applications in telecommunications, sensing, and basic research. 

All systems presented in this section show lasing only in the optical pumping mode. There is much interest in electrically pumped devices, but for molecular glasses the difficulties in achieving high excitation densities and low absorption due to charge carriers and electrodes have yet to be overcome. This problem and the related semiconducting polymer lasers that are based on the same principles will not be covered here, but are treated in recent reviews [214-216]. 

Films of this material can be optically pumped to induce amplified spontaneous emission at 535 nm, as shown in Figure 14. The lasing threshold (Eth) h the pump energy at which amplified spontaneous emission is observable, and depends strongly, among other factors, upon the lifetime of the polymer excited state. A longer excited state lifetime allows more emissive excitons to build up in... 

To test the suitability of MBE-grown GaN/AlGaN heterostructures for lasing, a few groups have investigated optically pumped stimulated emission [75,76], observing thresholds down to 90 kW/cm2 at 300 K. 

C5.1 InGaN/GaN/AlGaN-based laser diodes C5.2 Optically pumped lasing and current injection lasing in GaN-based laser structures... 

Stimulated emission and lasing in GaN-based structures can be achieved by both optical pumping and current injection. We have presented some of the most recent results of optically pumped SE and laser action studies in GaN and related heterostructures. Current injection LD operation repotted in the literature has been presented in a table in chronological order. 

Optical pumping experiments were first used to achieve lasing m GaN-based structures. Stimulated emission from GaN was observed as early as 1971 [17]. More recently, there have been a large number of reports on stimulated emission [18,19], without an intentionally formed cavity. This may partly be due to the well known difficulty of cleaving mirrors in the wurtzite nitrides grown on sapphire, due to the 30° tilt of the GaN unit cell with respect to the sapphire. 

However, real optically pumped lasing was observed both for GalnN/GaN and for GaN/AlGaN structures. The mirrors were formed either by cleaving or by dry etching. The threshold power densities were of the order of a few hundred kW/cm2 [20-22], In fact, even optically pumped second-... 

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