Bonn 2000 – scientific programme
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Q: Quantenoptik
Q 25: Poster: Anwendungen ultrakurzer Pulse
Q 25.3: Poster
Wednesday, April 5, 2000, 10:30–13:30, Aula
Femtosecond laser preparation of He2* excimers and third harmonic generation in superfluid He — •G. Śliwiński1, M. Sawczak1, and N. Schwentner2 — 1Pol. Acad. Sci., IF-FM, Fiszera 14, PL-80952 Gdańsk — 2Institut für Experimentalphysik FU, Arnimallee 14, D-14195 Berlin
Nonresonant laser excitation of superfluid He by means of sub-femtosecond pulses (λ=766 nm, 160 fs, 1 kHz) at intensities below breakdown results in a strong emission at 255.3 nm corresponding to the third harmonics of the pump beam. Above a threshold this colinear emission shows a nearly linear dependence on the input pulse energy yielding absolute UV energies up to 10 nJ and a conversion eficiency of about 10−4. The effect is ascribed to laser-induced ionisation of 4HeII and the subsequent preparation of He2* triplet excimers. The triplet state population is diffusion-controlled [1]. It is expected that in analogy to the gas phase experiments and to results from rare gas crystals [2] also higher harmonics in 4HeII can be observed.
[1] A.V. Benderski, R. Zadoyan, N. Schwentner, V.A. ApkarianJ. Chem. Phys. 110, 1542 (1999)
[2] G. Schilling, W.E. Ernst, N. SchwentnerIEEE J. Quantum Electronics 29, 2702 (1993)