We have observed the phase dependence of microwave above-threshold ionization (ATI) of Rydberg potassium atoms at a microwave intensity of 3\ifmmode\times\else\texttimes\fi{} ${10}^{4}$ W ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$. By using 5-ps pulses derived from a mode-locked tunable dye laser to create the initial Rydberg state, and phase locking the microwave field to a high harmonic of the mode-locking frequency, we are able to excite the atom at a specific phase of the microwave field. Measurement of the ejected electrons' energy as a function of the initial Rydberg state and the phase of the microwave field show that it is the phase of the field at which the electron becomes free of the atom that determines its kinetic energy. The energy dependence is described by a simple, classical theory that reveals the relationship between the so-called ``quiver'' and ``drift'' terms in the electron energy previously observed in ATI experiments at higher frequencies.We have observed the phase dependence of microwave above-threshold ionization (ATI) of Rydberg potassium atoms at a microwave intensity of 3\ifmmode\times\else\texttimes\fi{}${10}^{4}$ W ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$. By using 5-ps pulses derived from a mode-locked tunable dye laser to create the initial Rydberg state, and phase locking the microwave field to a high harmonic of the mode-locking frequency, we are able to excite the atom at a specific phase of the microwave field. Measurement of the ejected electrons' energy as a function of the initial Rydberg state and the phase of the microwave field show that it is the phase of the field at which the electron becomes free of the atom that determines its kinetic energy. The energy dependence is described by a simple, classical theory that reveals the relationship between the so-called ``quiver'' and ``drift'' terms in the electron energy previously observed in ATI experiments at higher frequencies.

Physical Review ANov 1, 199013 citations

Photoexcitation of near-threshold atomic energy

David A. Cardimona

Jan 1, 19830 citations

PHASE DEPENDENCE IN ABOVE THRESHOLD IONIZATION IN THE PRESENCE OF A MICROWAVE FIELD

Vincent Carrat, Tom K. Gallagher, Eric Magnuson

begin{wrapfigure}{l}{0pt} includegraphics[scale=0.38]{Energy_exchange.eps} caption{Electrons gaining or losing energy during the first microwave cycle depending of the initial launching direction. Here the phase of the microwave field is adjusted to provide a maximum energy transfer. The oscillations in energy are synchronized with the 14GHz microwave field.} end{wrapfigure} Exciting an atom with high-frequency radiation in the presence of a low frequency field can result in energy transfer between the photoelectron and the low frequency field, depending on the phase of the low frequency field when the excitation occurs. We excite Li atoms with IR lasers in the presence of a microwave field. In a previous experiment, detection of highly excited states with excitation by a ps laser tuned above the limit clearly showed a phase dependence. The variation of the signal due to a phase change reach 0.1% of the total excitation in that case. We are using a new excitation scheme with a CW amplitude modulated laser, the modulation being phase locked to the microwaves. We now observe a signal variation of 10% of the total excitation. The ps pulses spreads the population over a broad energy spectrum while the modulated excitation keeps it in narrow bands. The modulated laser frequency can be tuned to couple one band to the highly excited states, enhancing the collection efficiency, additionally it is closer to the limit. Furthermore, the modulated laser allows the observation of phase dependent transfer to both higher and lower energies. The observations can be described with relatively simple models.begin{wrapfigure}{l}{0pt} includegraphics[scale=0.38]{Energy_exchange.eps} caption{Electrons gaining or losing energy during the first microwave cycle depending of the initial launching direction. Here the phase of the microwave field is adjusted to provide a maximum energy transfer. The oscillations in energy are synchronized with the 14GHz microwave field.} end{wrapfigure} Exciting an atom with high-frequency radiation in the presence of a low frequency field can result in energy transfer between the photoelectron and the low frequency field, depending on the phase of the low frequency field when the excitation occurs. We excite Li atoms with IR lasers in the presence of a microwave field. In a previous experiment, detection of highly excited states with excitation by a ps laser tuned above the limit clearly showed a phase dependence. The variation of the signal due to a phase change reach 0.1% of the total excitation in that case. We are using a new excitation scheme with a CW amplitude modulated laser, the modulation being phase locked to the microwaves. We now observe a signal variation of 10% of the total excitation. The ps pulses spreads the population over a broad energy spectrum while the modulated excitation keeps it in narrow bands. The modulated laser frequency can be tuned to couple one band to the highly excited states, enhancing the collection efficiency, additionally it is closer to the limit. Furthermore, the modulated laser allows the observation of phase dependent transfer to both higher and lower energies. The observations can be described with relatively simple models.

International Symposium on Molecular Spectroscopy (ISMS)Jun 23, 20150 citations

Electronic excitation by atomic collisions

R. Dueren

Dec 1, 19750 citations

Resonant generation of few-cycle pulses in hydrogenlike atoms

Yevgeny V. Radeonychev, V. A. Polovinkin, Olga A. Kocharovskaya

We show the possibility to produce nearly bandwidth-limited few-cycle pulses based on time-dependent resonant interaction of an incident radiation with the bound states of hydrogenlike atoms. A time-dependence of an atomic resonance is provided by far-off-resonant laser field with intensity much below the atomic ionization threshold via time-dependent tunnel ionization from the excited states and temporal adiabatic Stark splitting of the excited energy levels. Without external synchronization of the spectral components it is possible to produce a train of two-cycle pulses at 121.6 nm with duration 800 as in atomic hydrogen.We show the possibility to produce nearly bandwidth-limited few-cycle pulses based on time-dependent resonant interaction of an incident radiation with the bound states of hydrogenlike atoms. A time-dependence of an atomic resonance is provided by far-off-resonant laser field with intensity much below the atomic ionization threshold via time-dependent tunnel ionization from the excited states and temporal adiabatic Stark splitting of the excited energy levels. Without external synchronization of the spectral components it is possible to produce a train of two-cycle pulses at 121.6 nm with duration 800 as in atomic hydrogen.

Laser PhysicsSep 3, 20127 citations

We have observed the phase dependence of microwave above-threshold ionization (ATI) of Rydberg potassium atoms at a microwave intensity of 3\ifmmode\times\else\texttimes\fi{}

{10}^{4}

W ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$. By using 5-ps pulses derived from a mode-locked tunable dye laser to create the initial Rydberg state, and phase locking the microwave field to a high harmonic of the mode-locking frequency, we are able to excite the atom at a specific phase of the microwave field. Measurement of the ejected electrons' energy as a function of the initial Rydberg state and the phase of the microwave field show that it is the phase of the field at which the electron becomes free of the atom that determines its kinetic energy. The energy dependence is described by a simple, classical theory that reveals the relationship between the so-called ``quiver'' and ``drift'' terms in the electron energy previously observed in ATI experiments at higher frequencies.