Waveguide and Luminescent Properties of Thin-Film Pb-Salt Injection Lasers
Quarterly rept. no. 1, 1 Mar-30 Jun 1973
FORD MOTOR CO DEARBORN MI RESEARCH STAFF
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The authors describe the waveguide properties of the asymmetric dielectric slab formed by a very high index film on a low index substrate. The analysis is appropriate for Pb-salt films grown on fluorite structure substrates. The mode reflectivities, surface scattering losses, and gain enhancements for the low order TE and TM modes are considered. The stronger confinement of the TM modes leads to larger gain enhancements and larger scattering losses than for the TE modes of the same order. For the film thicknesses of interest, 2-4 micrometers, the TE and TM mode reflectivities are comparable. Experimental results are presented for thin-film diode lasers made with Pb Schottky barriers on p-type PbTe index 6.4 grown epitaxially on BaF2 substrates index 1.42. Laser emission at 6.5 micrometers, both pulsed and cw, is observed at 10-15K. The optical gain is estimated from the measured current and quantum efficiency, while the free carrier and reflection losses are calculated from the device parameters. The remaining losses, attributed to surface scattering, can then be estimated from the threshold condition.
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