Abstract
We report the use of a second beam to vary the phase-matching condition of high harmonic generation in a semi- infinitive gas cell. The phase-matching can be improved or destroyed by the second beam. The enhancement of the phase-matching at high ionization rate with a second beam can be used to extend the cut-off photon energy in an atomic or molecular gas. The second beam with different carrier frequency can be used for the generation of continuous XUV spectra. In a molecular gas the second beam creates a vibrational and rotational wave packet which leads to a modulation of the HHG intensity and can be used to study the molecular structure
Highlights
Ultra short extreme ultraviolet (XUV) pulses produced by highorder harmonic generation (HHG) from atoms or molecules opens up a new era for time-resolved studies of ultrafast dynamics in atomic [1,2] and molecular systems [3,4,5], and in solid state [6,7,8] and plasma physics [9,10]
In this paper we report the use of a second beam to vary the phasematching condition and driving field in the HHG process in a semi
In a molecular gas the second beam creates a rotational wave packet which leads to a modulation of the HHG intensity at the rotational period
Summary
Ultra short extreme ultraviolet (XUV) pulses produced by highorder harmonic generation (HHG) from atoms or molecules opens up a new era for time-resolved studies of ultrafast dynamics in atomic [1,2] and molecular systems [3,4,5], and in solid state [6,7,8] and plasma physics [9,10]. The degree of phase-matching depends on the harmonic order and a number of experimental parameters including the atomic and molecular dispersion, the absorption coefficient of the target gas at the harmonic frequencies, the ionization fraction, and the gradient of the driving laser field. Phase-matching high harmonic generation at very high photon energy is difficult because a strong driving field is required that creates a large free-electron dispersion through strong ionization of the gas. The cut-off rule for the generated harmonic photon energy is hvmax=Ip+3.2Up, where Ip is the ionization potential of the gas and
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