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  • 1
    Electronic Resource
    Electronic Resource
    Coherent population transfer and dark resonances in SO2 (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 7068-7072 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Highly efficient population transfer between the (0,0,0) and the (9,1,0) vibrational levels of the electronic ground state X˜ 1A1 of SO2 is demonstrated. The process relies on stimulated Raman scattering with adiabatic passage induced by two suitably delayed ultraviolet laser pulses with nearly transform-limited bandwidth. A transfer efficiency of 100% is achieved. The associated dark resonance is observed. Properties of the latter are compared for delayed and fully overlapping pulses. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471424
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  • 2
    Electronic Resource
    Electronic Resource
    Efficient adiabatic population transfer by two-photon excitation assisted by a laser-induced Stark shift (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 534-546 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We demonstrate and analyze a novel scheme for complete transfer of atomic or molecular population between two bound states, by means of Stark-chirped rapid adiabatic passage (SCRAP). In this two-laser technique a delayed-pulse laser-induced Stark shift sweeps the transition frequency between two coupled states twice through resonance with the frequency of the population-transferring coupling laser. The delay of the Stark-shifting pulse with respect to the pulse of the coupling-laser Rabi frequency guarantees adiabatic passage of population at one of the two resonances while the evolution is diabatic at the other. The SCRAP method can give a population-transfer efficiency approaching unity. We discuss the general requirements on the intensity and timing of the pulses that produce the Rabi frequency and, independently, the Stark shift. We particularly stress extension to a double-SCRAP technique, a coherent variant of stimulated emission pumping in the limit of strong saturation. We demonstrate the success of the SCRAP method with experiments in metastable helium, where a two-photon transition provides the Rabi frequency. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481829
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  • 3
    Electronic Resource
    Electronic Resource
    Analytical study of four-wave mixing with large atomic coherence (2003)
    Springer
    The European physical journal 23 (2003), S. 167-180 
    Details
    ISSN: 1434-6079
    Keywords: PACS. 42.50.Gy Effects of atomic coherence on propagation, absorption, and amplification of light – 42.65.Ky Harmonic generation, frequency conversion – 32.80.Qk Coherent control of atomic interactions with photons
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: Four-wave mixing in resonant atomic vapors based on maximum coherence induced by Stark-chirped rapid adiabatic passage (SCRAP) is investigated theoretically. We show the advantages of a coupling scheme involving maximum coherence and demonstrate how a large atomic coherence between a ground and an highly excited state can be prepared by SCRAP. Full analytic solutions of the field propagation problem taking into account pump field depletion are derived. The solutions are obtained with the help of an Hamiltonian approach which in the adiabatic limit permits to reduce the full set of Maxwell-Bloch equations to simple canonical equations of Hamiltonian mechanics for the field variables. It is found that the conversion efficiency reached is largely enhanced if the phase mismatch induced by linear refraction is compensated. A detailed analysis of the phase matching conditions shows, however, that the phase mismatch contribution from the Kerr effect cannot be compensated simultaneously with linear refraction contribution. Therefore, the conversion efficiency in a coupling scheme involving maximum coherence prepared by SCRAP is high, but not equal to unity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1140/epjd/e2003-00029-5
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  • 4
    Electronic Resource
    Electronic Resource
    Investigation of auto-ionizing states in xenon by resonantly enhanced multi-photon ionization (2003)
    Springer
    The European physical journal 23 (2003), S. 35-42 
    Details
    ISSN: 1434-6079
    Keywords: PACS. 32.80.Dz Autoionization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: We have examined the autoionization spectrum of xenon by resonantly enhanced three-photon ionization (2 + 1 REMPI) involving intermediate states 5p 56p[J = 0, 2]. The properties of the observed autoionization resonances change significantly with the choice of the intermediate state. For ionization via an intermediate state with predominantly 5p 5(2P3/2) core character, a strong continuum with embedded window-type 5p 5(2P 1/2)nd'-autoionization resonances is observed. For intermediate states, predominantly with 5p 5(2P1/2) core character, both 5p 5(2P 1/2)nd'- as well as 5p 5(2P 1/2)ns'-resonances are present in the spectrum as overlapping, nearly symmetric peaks on a rather weak continuum. Calculations confirm the significant dependence of the spectral lineshapes upon the excitation pathway to the autoionizing state. The ionization data are compared with spectra obtained by monitoring third-harmonic generation via autoionizing states without resonant excitation of intermediate states. These spectra also exhibit the signature of both the nd'- and ns'-resonances.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1140/epjd/e2003-00021-1
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  • 5
    Electronic Resource
    Electronic Resource
    High-order harmonic generation from organic molecules in ultra-short pulses (2001)
    Springer
    The European physical journal 14 (2001), S. 231-240 
    Details
    ISSN: 1434-6079
    Keywords: PACS. 42.65.Ky Harmonic generation, frequency conversion – 42.50.Hz Strong-field excitation of optical transitions in quantum systems; multi-photon processes; dynamic Stark shift
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: We have studied high-order harmonic generation (HHG) from organic molecules irradiated with near-infrared high intensity laser pulses of 70 fs and 240 fs duration. The molecular systems studied were the aromatics benzene and naphthalene and the alkanes cyclopropane and cyclohexane (cyclic) and n-hexane (linear). Harmonic intensities were measured both as a function of laser intensity (in the range 5×1013-5×1015 W cm-2) and as a function of ellipticity of the laser field polarisation. The results were compared with those from the xenon atom. For 70 fs pulses, harmonic generation from the organic systems was similar to that of xenon, revealing an atom-like behaviour for molecules when the laser pulse duration is shorter than the fragmentation timescale of the molecule. We note significant differences between molecules with respect to HHG efficiencies and the suppression of HHG in larger species. We discuss these differences in the context of the molecular properties, electronic structure and behaviour of ionisation and fragmentation that result in enhancement of field ionisation in larger systems. Study of the polarisation ellipticity dependence of HHG shows that the harmonic yield in molecules is less sensitive to the polarisation than for atoms (xenon). This is consistent with the expected behaviour given the larger recollision cross-section presented by the core in the molecular system compared to the atom. Our results suggest that study of HHG from molecules exposed to ultra-short pulses is potentially a powerful tool for understanding the electron dynamics of molecules exposed to an intense field.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100530170221
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  • 6
    Electronic Resource
    Electronic Resource
    Coherent population trapping involving Rydberg states in xenon probed by ionization suppression (2001)
    Springer
    The European physical journal 17 (2001), S. 113-123 
    Details
    ISSN: 1434-6079
    Keywords: PACS. 42.50.Hz Strong-field excitation of optical transitions in quantum systems; multi-photon processes; dynamic Stark shift – 32.80.Rm Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states) – 32.10.Fn Fine and hyperfine structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: We report the observation of pronounced coherent population trapping and dark resonances in Rydberg states of xenon. A weak two-photon coupling with radiation of = 250 nm is induced between the 5p6 1 S 0 ground state of xenon and state 5p 56p[1/2]0, leading to (2+1) resonantly enhanced three-photon ionization. The state 5p 56p[1/2]0 is strongly coupled by radiation with ≃ 600 nm to 5p 5 ns[J C]1 or 5p 5 nd[J C]1 Rydberg states with principal quantum numbers n in the range 18 ?n? 23 and with the rotational quantum number of the ionic core J C = 1/2 or J C = 3/2. The ionization is monitored through observation of the photoelectrons with an energy resolution ΔE = 150 meV which is sufficient to distinguish the ionization processes into the two ionization continua. Pronounced and robust dark resonances are observed in the ionization rate whenever is tuned to resonance with one of the ns- or nd-Rydberg states. The dark resonances are due to efficient population trapping in the atomic ground state 5p6 1 S 0 through the suppression of excitation of the intermediate state 5p 56p[1/2]0. The resolution is sufficient to resolve the hyperfine structure of the ns-Rydberg levels for odd xenon isotopes. The hyperfine splitting does not vary significantly with n in the given range. Results from model calculations taking the natural isotope abundance into account are in good agreement with the observed spectral structures. Pronounced dark resonances are also observed when the dressing radiation field with is generated from a laser with poor coherence properties. The maximum reduction of the ionization signal clearly exceeds 50%, a value which is expected to be the maximum, when the dip is caused by saturation of the transition rate between the intermediate and the Rydberg state due to incoherent radiation. This work demonstrates the potential of dark resonance spectroscopy of high lying electronic states of rare gas atoms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100530170044
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