We report a new technique for measuring the stimulated emission spectrum and optical gain of semiconductor materials. Amplified spontaneous emission is used to determine the gain factor by relating the measured variation in light output to variation in the length of the excitation beam. Results for CdS crystals at 2°K are presented that indicate net gains as high as 160 cm−1 at λ = 4907 Å are possible with ∼ 12-MW/cm2 optical pump power density from a nitrogen laser.

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Stimulated emission and laser action have been observed near 3.45 eV in single-crystal needles of GaN. These observations support the earlier suggestion that GaN is a direct band-gap semiconductor with Eg∼3.50 eV at 2°K. Furthermore, the occurrence of very high gain (g∼105 cm−1) in the stimulated emission emphasizes the possible device potential of this material.

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