Abstract

Frequency down-conversion of established highperformance ultrafast sources in the near-infrared represents an attractive method to access the important applications-related blue and UV spectral regions. The high peak powers of ultrafast pulses allow for better utilisation of the available nonlinearity, and the short duration of the resulting down-converted pulses gives increased functionality in such areas as time-resolved spectroscopy. Normally, relatively complex and inefficient ultrafast Ti:sapphire lasers are used as the pump sources, but their typical electrical-to-optical efficiencies are less than 0.05% for the generation of near-infrared pulses. We report here a compact, directly diode-pumped Cr:LiSAF laser as an alternative pump source. This laser has an electrical-to-optical efficiency in excess of 1% and produces transform-limited pulses of ~ 150 fs in duration at ~865 nm. The average power is 35 mW and the repetition rate is ~250 MHz, which implies modest peak powers of less than 1 kW. At these low power levels, efficient frequency doubling usually requires complex arrangements, especially if the pulse duration is to be preserved. In this paper we describe the use of a relatively thick doubling crystal in a single-pass, extra-cavity arrangement.¹ Although the second harmonic pulses suffer temporal broadening, this represents an effective way to achieve efficient frequency conversion in a simplified configuration.

© 2002 Optical Society of America