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

摘要

Fourier-transform-limited pulses of programmable length and shape have been generated in the range lambda=720-825 nm 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 10 ns 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 15 mJ was demonstrated at a repetition rate of 25 Hz. Frequency upconversion into the ultraviolet (UV) by frequency doubling (nu(UV)=2 nu(NIR)) or by mixing the fundamental NIR radiation with the doubled radiation (nu(UV)=3 nu(NIR)) in nonlinear crystals was achieved under conditions where the pulse shapes could be preserved. The pulse energies amounted to up to 1 mJ for the doubled radiation and 100 mu J for the tripled radiation for NIR pulses of 30 ns duration. Vacuum ultraviolet (VUV) radiation pulses of 10(8)-10(9) photons/pulse at 120 000 cm(-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 20 ns, and double pulses of VUV radiation separated by a variable delay of up to 100 ns could be generated. Frequency chirps arising in the AOM and the pulsed amplification were found to be negligible, but a frequency shift of -5 MHz was determined. The bandwidth of the generated radiation was estimated to be 35 MHz in the UV at a wave number of approximate to 40 000 cm(-1) and 55 MHz in the VUV at a wave number of approximate to 120 000 cm(-1) in a Doppler-free measurement of the (5p)(6) S-1(0)->(5p)(5)6p1/2(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 I-2 taken as reference standard. (c) 2005 American Institute of Physics.