Tunable superradiant emission from a planar dye laser

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Abstract
A new, simple scheme to tune a double-pass, superradiant dye laser is reported. A planar cell with a thickness below 100 μm filled with a highly concentrated (4–5 × 10−3-M/liter) solution of Rhodamine 6G in ethanol is used. An unsaturated gain value of 1.7 cm−1 has been measured with flashlamp pumping, and the amplifier has been found to operate at a well saturated regime. Smooth laser linewidths ranging from broadband, gain narrowed values of 10 nm to narrowband values of 8 GHz have been achieved by using appropriate frequency dispersive feedback elements and suitable cell thickness. A 5-GHz output has been observed with a 25-μm gap cell. The absence of a resonant cavity avoids modal structure and ensures improved frequency and intensity stability. The reported configuration should be scalable up as far as output energy is concerned. Simultaneous two-wavelength operation is possible. Pumping with a frequency-doubled Nd-laser should allow a further reduction of the usable cell thickness with narrower output bandwidths.