Abstract

Tunable subpicosecond pulses in the spectral range -145-200 nm have been generated with four-wave difference-frequency mixing in Xe.¹ There were then used as seed pulses at 157 nm and amplified in an F₂ discharge. However, a substantial amount of amplified spontaneous emission generated from the F₂ laser amplifier decreases the contrast ratio of the amplified short pulses. Alternatively, subpicosecond vacuum UV (VUV) pulses can be generated by a direct pulse compression method using the effect of induced-phase modulation (IPM) of a visible pump pulse upon a relatively weak signal pulse. A VUV signal pulse experiences a substantial phase modulation during propagating through a rare gas-filled capillary waveguide where the sum of the pump and signal frequency is near a two-photon resonance.² A gratingpair compresses this chirped VUV pulse by subtracting from the phase a term quadratic in the frequency deviation. Essentially, the broader the bandwidth obtained by IPM, the shorter the pulse can be compressed.

© 1995 IEEE