High-Order Harmonic Generation by Atoms
in a Two-Color Laser Field:
Phase Control of Recombination Radiation Spectrum
and Duration

V. D. Taranukhin

Faculty of Physics, Moscow State University, Vorob’evy gory, Moscow, 119992 Russia

e-mail: tvd@ssf.phys.msu.su

Received April 21, 2003

Abstract—The feasibility of phase control over above-threshold tunnel ionization and subsequent recombina-
tion emission in two-frequency laser fields is studied. It is shown that, in such fields, we can control the instants
of ionization t₀ (within optical cycle T) and recombination t_k . The conditions that minimize the characteristic
times t₀ T and t_k T, within which effective ionization and recombination occur, were found. Phase control
allows recombination radiation to be generated with the selection of a narrow spectral range, while additional
high-frequency “background illumination” sets up high harmonic “amplification” conditions. It was shown that
special two-frequency pumping with elliptically polarized radiation can generate coherent electromagnetic
pulses of attosecond width. The width of the pulses decreases as the intensity of pumping increases and can
reach subattosecond values. Experimental generation of such pulses may lead to a breakthrough in the devel-
opment of new methods for femto- and attosecond diagnostics of fast processes. © 2004 MAIK “Nauka/Inter-
periodica”.

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