Two-color excitation by spatially coherent and incoherent laser beams has been used to study three-photon-resonant excitation and subsequent ionization of xenon in conditions, when internally generated sum-frequency field plays an important role in excitation of atomic resonances through interfering one-photon excitation pathway. We show that the incoherence in one of the pumping fields reduces the efficiency of generated sum-frequency field, and thus suppresses the interference between the three- and the one-photon excitation channels. The degree of suppression is controlled by varying the crossing angle between coherent and incoherent laser beams. We show that ionization profiles can be analyzed on the basis of the well-studied interference of one- and three-photon transition amplitudes, but with pumping field decomposed into multiple small-scale uncorrelated domains where coherent process of four-wave mixing occurs. The gain length for a coherent process in these domains depends on the coherence degree and excitation geometry. It gives a possibility of controlling the contribution of coherent processes to the excitation of multiphoton resonances.Two-color excitation by spatially coherent and incoherent laser beams has been used to study three-photon-resonant excitation and subsequent ionization of xenon in conditions, when internally generated sum-frequency field plays an important role in excitation of atomic resonances through interfering one-photon excitation pathway. We show that the incoherence in one of the pumping fields reduces the efficiency of generated sum-frequency field, and thus suppresses the interference between the three- and the one-photon excitation channels. The degree of suppression is controlled by varying the crossing angle between coherent and incoherent laser beams. We show that ionization profiles can be analyzed on the basis of the well-studied interference of one- and three-photon transition amplitudes, but with pumping field decomposed into multiple small-scale uncorrelated domains where coherent process of four-wave mixing occurs. The gain length for a coherent process in these domains depends on the coherence degree and excitation geometry. It gives a possibility of controlling the contribution of coherent processes to the excitation of multiphoton resonances.

Physical Review AOct 22, 20034 citations

Resonance, antiresonance, and decoherence in the excitation of channeled ions in crystals

A. Salin, A. Arnau, Pedro Miguel Echenique

We discuss general criteria differentiating incoherent excitation processes from coherent processes allowing the production of resonant coherent excitation (RCE) of channeled ions in crystals. We give special consideration to the ionization of C ${}^{5+}$ ions traveling with energies between 15 and 25 MeV along the $〈100〉$ direction of a gold crystal. We show that incoherent ionization of the $n=2$ state by the valence electrons partially destroys the coherence producing resonant coherent excitation of the $n=\stackrel{\ensuremath{\rightarrow}}{1}n=2$ transition by the target static potential. It thus causes a considerable broadening of the resonance signal, as observed in the experiments. Finally we show that far from resonance, coherence quenches projectile excitation by the target static potential (anti-Okorokov effect).We discuss general criteria differentiating incoherent excitation processes from coherent processes allowing the production of resonant coherent excitation (RCE) of channeled ions in crystals. We give special consideration to the ionization of C${}^{5+}$ ions traveling with energies between 15 and 25 MeV along the $〈100〉$ direction of a gold crystal. We show that incoherent ionization of the $n=2$ state by the valence electrons partially destroys the coherence producing resonant coherent excitation of the $n=\stackrel{\ensuremath{\rightarrow}}{1}n=2$ transition by the target static potential. It thus causes a considerable broadening of the resonance signal, as observed in the experiments. Finally we show that far from resonance, coherence quenches projectile excitation by the target static potential (anti-Okorokov effect).

Physical Review AApr 1, 199815 citations

Photoemission by Large Electron Wave Packets

Michael J. Ware, Justin B. Peatross, Eric Flint Cunningham

Bulletin of the American Physical SocietyJun 15, 20110 citations

Laser Spectroscopy Of Electronic Resonances: An Electro-Optic Technique For Probing Coherent And Incoherent Decay Processes

Ahmed H. Zewail

A new technique is presented for measuring the incoherent resonance decay (IRD) and the coherent optical ringing of selectively (5 MHz) prepared electronic states. The method utilizes electro-optic switching of a single laser mode that is on or off resonance with respect to the homogeneous molecular packets in the excited ensemble. The technique was applied to a variety of systems (gases at low pressures, gases at relatively high pressures, and solids at low temperatures) to give information about their phase memory (optical T2 processes), radiative and radiationless decay (optical T1 processes), and to measure directly their optical transition moment between the ground state and the prepared electronic state. The theory of coherent and incoherent states is also given.A new technique is presented for measuring the incoherent resonance decay (IRD) and the coherent optical ringing of selectively (5 MHz) prepared electronic states. The method utilizes electro-optic switching of a single laser mode that is on or off resonance with respect to the homogeneous molecular packets in the excited ensemble. The technique was applied to a variety of systems (gases at low pressures, gases at relatively high pressures, and solids at low temperatures) to give information about their phase memory (optical T2 processes), radiative and radiationless decay (optical T1 processes), and to measure directly their optical transition moment between the ground state and the prepared electronic state. The theory of coherent and incoherent states is also given.

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIEDec 30, 19764 citations

{}^{5+}

ions traveling with energies between 15 and 25 MeV along the

〈100〉

direction of a gold crystal. We show that incoherent ionization of the

n=2

state by the valence electrons partially destroys the coherence producing resonant coherent excitation of the $n=\stackrel{\ensuremath{\rightarrow}}{1}n=2$ transition by the target static potential. It thus causes a considerable broadening of the resonance signal, as observed in the experiments. Finally we show that far from resonance, coherence quenches projectile excitation by the target static potential (anti-Okorokov effect).