Shaped few-cycle pulses in the deep ultraviolet for molecular coherence spectroscopy*

We present a new apparatus for generating, shaping, and measuring few-cycle pulses in the deep ultraviolet.  The fourth harmonic of a pulsed near-infrared laser is sent through a two-stage, stretched hollow-core fiber apparatus.  The set-up generates pulses centered near 260 nm with sufficient spectral bandwidth to support pulses sub-20 fs in duration.  The pulses are sent into an acousto-optic based pulse shaper that allows control over both the phase and amplitude of the light, including pulse compression.  The shaping and compression allow for propagation and delivery without requiring vacuum. The apparatus is designed to produce phase-stable, few-cycle pulse pairs with independent control over their relative amplitude, delay and phase for single-photon excitation in coherence spectroscopy experiments capable of examining coupled electron-nuclear dynamics in molecules.