Efficient photoemission and ionization of He{sup +} by a combined fundamental laser and high-order harmonic pulse

Journal Article · Thu Jul 01 04:00:00 EDT 2004 · Physical Review. A

DOI:https://doi.org/10.1103/PhysRevA.70.013412· OSTI ID:20645777

Ishikawa, Kenichi L ^[1]

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1. Department of Quantum Engineering and Systems Science, Graduate School of Engineering, University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-8656 (Japan)

We theoretically study the behavior of He{sup +} exposed simultaneously to an ultrashort intense Ti:sapphire laser and its 27th or 13th harmonic pulses, by solving the time-dependent Schroedinger equation using the alternating direction implicit method. This system is chosen as an interesting application of state-of-the-art high-order harmonic sources. Our results show that the simple hydrogenlike system exhibits surprising responses. The addition of the 27th harmonic enhances high-order harmonic photoemission from He{sup +} even by 17 orders of magnitude compared with the case of the fundamental pulse alone, i.e., usual high-order harmonic generation, and the H13 addition also increases photoemission efficiency by more than ten orders of magnitude. Moreover, while an individual 10 fs laser (wavelength {lambda}{sub F}=800 nm) or its 27th harmonic pulse with a peak intensity of 3x10{sup 14} and 10{sup 13} W/cm{sup 2}, respectively, ionizes no more than 5x10{sup -6} of He{sup +}, their combined pulse leads to a much higher He{sup 2+} yield of 17%. The photoemission efficiency only weakly depends on the fundamental wavelength, and the main plateau efficiency scales as the intensity of the 27th harmonic pulse. The He{sup 2+} yield is linear in the intensity of the 27th harmonic and quadratic in that of the 13th harmonic pulse. Its dependence on fundamental intensity is much more complex, even containing a range where the yield decreases with increasing laser intensity, due to the dynamic Stark effect. Detailed analyses reveal that the mechanism of the enhancement of harmonic photoemission as well as ionization is a combination of harmonic generation from a coherent superposition of states and two-color frequency mixing enhanced by the presence of a near-resonant intermediate level, and that their relative importance depends on fundamental wavelength.

• OSTI ID: 20645777
• Journal Information: Physical Review. A, Journal Name: Physical Review. A Journal Issue: 1 Vol. 70; ISSN 1050-2947; ISSN PLRAAN
• Country of Publication: United States
• Language: English

Related Subjects

74 ATOMIC AND MOLECULAR PHYSICS
EFFICIENCY
HARMONIC GENERATION
HELIUM
HELIUM IONS
HYDROGEN
IONIZATION
MULTI-PHOTON PROCESSES
PHOTOEMISSION
PHOTON-ATOM COLLISIONS
PULSES
SCHROEDINGER EQUATION
STARK EFFECT
TIME DEPENDENCE
WAVELENGTHS