Resonant ionization of atoms under conditions of adiabatic level inversion

Mikhail Vladimirovich Fedorov

С. А. Бахрамов, Konstantin N. Drabovich, А. М. Коххаров +2 more

Shuichi Hasegawa, Hitoshi Maeda, Takafumi Kakudoh +1 more

Adiabatic inversion in two- and three-level systems excited by stochastic fields is investigated. The stochastic electric fields, which are called the chaotic field and the phase-diffusion field, can invert the population of a two-level atom. In a three-level system, we compare the method of sweeping the laser frequency with that of the resonance excitation by lasers that have bandwidths appropriate to the width of Doppler broadening. When the Doppler shift is taken into account, bandwidths of the electric fields are effective to ionize atoms efficiently. When sweeping the first exciting laser frequency, the delay of the second laser pulse increases the ionization probability. If the half width at half maximum of Doppler broadening is narrow and two lasers irradiate atoms simultaneously, the finite bandwidths of the lasers ionize more atoms than sweeping the laser frequency. On the other hand, if the Doppler broadening is large or the second laser irradiates the atoms properly after the first laser, sweeping the first laser frequency is efficient for ionization. Sweeping the laser frequency is not suitable for the system where the intermediate state's spontaneous-decay constant is short. For that system it is efficient to ionize the atoms by lasers that have the finite bandwidth appropriate for the Doppler broadening.

Alexey E. Kazakov, Vyacheslav P. Makarov, Mikhail Vladimirovich Fedorov

N. A. Hart

The coherent control of atomic energy level population is important for several areas physics and engineering including fluorescent spectroscopy, resonantly enhanced multiphoton ionization, harmonic generation, remote sensing and lasing. At low intensities where the Stark shift can be neglected, coherent control mechanisms usually exploit resonances created from stationary energy states dressed by integer multiples of the photon energy. However, in the strong field limit where large laser pulse intensities lead to significant Stark shifts, the resonant conditions are dynamic both in time and space and will likely not be satisfied for the entire laser pulse or beam.\n\nIn this research, we experimentally and theoretically demonstrate coherent control of atomic energy level population in sodium vapor as well as the selective excitation of sodium Rydberg levels using high intensity laser pulses. We also make a direct measurement of the ponderomotive shift of the continuum. While techniques based on resonance interferences and rapid adiabatic passage have been introduced for selective excitation, the conditions that must be satisfied for these phenomena can be hampered by short femtosecond pulse durations and large Stark shifts. In contrast, a technique referred to here as Resonance Sampling, uses the AC Stark shifts to selectively induce Freeman resonances and is resilient to changes in the spectral phase. Freeman resonances established in this way can result in population inversion of the excited state, and may lead to new lasing mediums and remote sensing applications.\n\n\nIn this research, we experimentally and theoretically demonstrate coherent control of atomic energy level population in sodium vapor as well as the selective excitation of sodium Rydberg levels using high intensity laser pulses. While techniques based on resonance interferences and rapid adiabatic passage have been introduced for selective excitation, the conditions that must be satisfied for these phenomena can be hampered by short femtosecond pulse durations and large Stark shifts. In contrast, a technique referred to here as Resonance Sampling, uses the AC Stark shifts to selectively induce Freeman resonances and is resilient to changes in the spectral phase. Freeman resonances established in this way can result in population inversion of the excited state, and may lead to new lasing mediums and remote sensing applications.

С. А. Бахрамов, А. М. Коххаров, Vladimir Tikhonenko