Effects of four-wave mixing on four-photon resonance excitation and ionization in the presence of a three-photon intermediate state resonance enhancement

Journal Article · Sun Dec 01 00:00:00 EST 1991 · Physical Review A. General Physics; (United States)

DOI:https://doi.org/10.1103/PhysRevA.44.7684· OSTI ID:5394845

Payne, M G; Miller, J C; Hart, R C; Garrett, W R ^[1]

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1. Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)

We consider effects which occur when four-wave sum frequency generation and multiphoton ionization are induced by lasers tuned near a three-photon resonance and simultaneously near or at a dipole allowed four-photon resonance. In studies with unfocused laser beams, if the phase mismatch of the generated four-wave-mixing field is large and the related two-photon resonance for the absorption of a four-wave-mixing photon and a laser photon results in strong absorption of the four-wave-mixing field, a coherent cancellation occurs between the pumping of the resonance by two- and four-photon processes. This interference effect occurs when the first laser is tuned on either side of the three-photon resonance and {vert bar}{Delta}{ital k}{sub {ital r}L}{vert bar}{much gt}1, where {Delta}{ital k}{sub {ital r}} is the mismatch and {ital L} is the length of the path of the laser beams in the gas. With focused laser beams large differences occur between ionization with unidirectional beams and with counterpropagating laser beams when {vert bar}{Delta}{ital k}{sub {ital r}b}{vert bar}{much gt}1, where {ital b} is the confocal parameter of the focused laser beams. Strong absorption of the four-wave-mixing field is shown not to be necessary for strong destructive interference with focused laser beams when the phase mismatch is large. This work also suggests an explanation for earlier experiments where the presence of a four-photon resonance enabled the generation of third-harmonic light in a positively dispersive wavelength region. We argue that this process can occur when the laser used to achieve the four-photon resonance is focused on the small {ital z} ({ital z} is the coordinate in the direction of propagation) side of the focal point of the laser responsible for the third-harmonic generation.

• DOE Contract Number: AC05-84OR21400
• OSTI ID: 5394845
• Journal Information: Physical Review A. General Physics; (United States), Vol. 44:11; ISSN 1050-2947
• Country of Publication: United States
• Language: English

Related Subjects

74 ATOMIC AND MOLECULAR PHYSICS
42 ENGINEERING
MULTI-PHOTON PROCESSES
FREQUENCY MIXING
CORRELATIONS
E1-TRANSITIONS
EXCITATION
GAIN
GASES
IONIZATION
RESONANCE
AMPLIFICATION
ENERGY-LEVEL TRANSITIONS
FLUIDS
MULTIPOLE TRANSITIONS
664300* - Atomic & Molecular Physics- Collision Phenomena- (1992-)
426002 - Engineering- Lasers & Masers- (1990-)