Abstract

In this paper we describe a laser system for generating picosecond pulses with wavelengths <250nm at a 5kHz repetition rate. Short pulses from a synchronously-pumped dye laser are amplified to a peak power >5MW in a dye medium pumped by a copper vapor laser. Nonlinear optical techniques can then be used to shift the wavelength well into the UV. The high repetition rate of the pulses is important for pump-probe picosecond spectroscopy. Other laser systems have generally fallen into one of two groups: one with large pulse energies at low repetition rates (>1MW at <100Hz) and one using very small pulses at high repetition rates ( < 3kW at >50MHz). The large pulse experiments can create a transient population large enough to change the sample absorbance considerably, but often unwanted nonlinear effects accompany the extremely high intensities created by squeezing a large number of photons into a pulse of few picoseconds duration. Lower intensities necessitate sensitive probing of the transient population with careful signal averaging. This need has led several research groups to develop the high repetition rate systems using lock-in amplifiers and/or extremely high frequency modulation with AM radio detection [1-6]. The low powers of the high repetition rate systems severely limits the use of nonlinear optical techniques needed to obtain picosecond pulses with UV and VUV wavelengths. Tunable pulses with peak powers of greater than 1MW have been available for several years using Nd:YAG laser pumped amplifiers at 10 Hz repetition [7–10] and more recently at 100Hz using excimer laser pumped amplifiers [11]. In the system to be described here the amplified pulses provide the fundamental wavelength for second harmonic generation and for sum-frequency mixing to generate the third harmonic. Stimulated Raman shifting in liquids is also posible for the generation of probe wavelengths.

© 1984 Optical Society of America