SINGLE PASS GAIN OF EXCIPLEX 4-MU AND RHODAMINE 6G DYE LASER AMPLIFIERS

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Abstract
Single pass gain has been measured in N2 laser pumped exciplex 4‐Methylumbelliferone (4‐MU) and rhodamine 6G dye lasers using a technique developed by Silfvast and Deech for high‐gain pulsed metal vapor lasers. The gain is measured by comparing the intensities of amplified spontaneous emission in single and double cell lengths with the maximum unsaturated single‐pass gain being limited by the saturation of the spontaneous emission. Maximum unsaturated gains on the order of 20 dB/cm were measured for both dyes. The gain was found to vary linearly with pump power. The technique was also used to measure the variation of gain with wavelength for a given pump power. The maximum gain for exciplex 4‐MU occurred at the fluorescence peak, whereas for rhodamine 6G it was shifted to a longer wavelength due to ground‐state reabsorption. By fitting the measured gain versus wavelength to the theory, it was possible to deduce the fractional excited singlet population in the rhodamine 6G solution.