Generation of programmable near-Fourier-transform-limited pulses of narrow-band laser radiation from the near infrared to the vacuum ultraviolet

Abstract

Fourier-transform-limited pulses of programmable length and shape have been generated in the range λ=720–825nm from the continuous-wave output of a Ti3+-doped sapphire (Ti:Sa) ring laser using a pulsed acousto-optic modulator (AOM). The minimal rise time of the pulses amounts to 10ns and is limited by the size of the cw laser beam in the active medium of the AOM. Amplification of the radiation pulses in Nd:YAG-pumped Ti:Sa crystals into intense pulses of near-infrared (NIR) radiation with pulse energies of up to 15mJ was demonstrated at a repetition rate of 25Hz. Frequency upconversion into the ultraviolet (UV) by frequency doubling (νUV=2νNIR) or by mixing the fundamental NIR radiation with the doubled radiation (νUV=3νNIR) in nonlinear crystals was achieved under conditions where the pulse shapes could be preserved. The pulse energies amounted to up to 1mJ for the doubled radiation and 100μJ for the tripled radiation for NIR pulses of 30ns duration. Vacuum ultraviolet (VUV) radiation pulses of 108–109photons∕pulse at 120000cm−1 were generated by two-photon resonance-enhanced third-harmonic generation in a pulsed gas beam of xenon. The VUV pulse length could be adjusted between 10 and 20ns, and double pulses of VUV radiation separated by a variable delay of up to 100ns could be generated. Frequency chirps arising in the AOM and the pulsed amplification were found to be negligible, but a frequency shift of −5MHz was determined. The bandwidth of the generated radiation was estimated to be 35MHz in the UV at a wave number of ≈40000cm−1 and 55MHz in the VUV at a wave number of ≈120000cm−1 in a Doppler-free measurement of the (5p)6S01→(5p)56p[1∕2](J=0) two-photon resonance of xenon. The absolute accuracy of the wave-number calibration is limited by uncertainties in the positions of NIR lines of I2 taken as reference standard.