Generation of high-power, wavelength-tunable UV picosecond laser pulses is commonly believed to require the use of pulse compression and cavity dumping or the use of second harmonic generation in either an intracavity geometry or an external-ring resonator. These approaches use either high peak power or high circulating power to increase the generated UV. However, the addition of a pulse compressor increases the laser linewidth, while the use of a cavity dumper reduces the repetition rate of the laser. Both increase the cost and complexity of the laser system. Intracavity frequency doubling requires modification of the dye laser optics, which slaves the dye laser to UV operation and makes scanning the wavelength difficult. Moreover, the majority of such intracavity designs utilize ring dye lasers, which are more difficult to maintain in proper alignment than are standing-wave dye lasers. External ring resonators require additional optical components and critical matching of the two cavity frequencies. In comparison, we have found that normal, angle-tuned, extra-cavity frequency doubling can produce conversion efficiencies from 1 to 7% by careful adjustment of the dye laser cavity length.
G. J. Fiechtner, G. B. King, N. M. Laurendeau, R. J. Kneisler, and F. E. Lytle, "Efficient Frequency Doubling for Synchronously Mode-Locked Dye Lasers," Appl. Spectrosc. 43, 1286-1287 (1989)