Features of Free Polarization Decay in Ultrathin Gas Cells
- PDF / 354,953 Bytes
- 4 Pages / 612 x 792 pts (letter) Page_size
- 23 Downloads / 173 Views
TROSCOPY AND PHYSICS OF ATOMS AND MOLECULES
Features of Free Polarization Decay in Ultrathin Gas Cells A. Ch. Izmailov* Institute of Physics, Azerbaijan National Academy of Sciences, Baku, AZ-1143 Azerbaijan *e-mail: [email protected] Received February 6, 2020; revised February 6, 2020; accepted April 2, 2020
Abstract—The optical effect of free polarization decay in an ultrathin gas cell the inner thickness of which is less than or of the order of the wavelength of the exciting monochromatic laser pulse transmitted orthogonally to plane-parallel walls of this cell is studied theoretically. A new mechanism of the studied effect is established; it is caused by the specificity of phase mismatch of light-induced atomic dipole moments due to transit-time relaxation of atoms in such a cell. As a result, the dynamics of free polarization decay in the considered situation radically differs from the known case in a usual (macroscopic) gas cell. Nontrivial oscillatory dependences of free polarization decay signals on the ratio of the thickness of such ultrathin cell to the radiation wavelength of the exciting pulse are revealed and analyzed. Keywords: free polarization decay, ultrathin gas cell, coherent radiation, dipole moment phases DOI: 10.1134/S0030400X20080159
INTRODUCTION The signal of free polarization decay (FPD) is caused by the coherent radiation emitted by atoms (molecules) of the medium after they are excited by a laser radiation pulse [1, 2]. Indeed, such a pulse, which is resonant to a certain atomic transition a ↔ b , creates superposition of the quantum levels a and b. As a result, a collection of dipole moments oscillating in time is formed in the medium. After the termination of the initial laser pulse, such atomic dipoles continue to oscillate for some time and to emit the recorded FPD signal. This coherent signal propagates in the direction of the exciting pulse because radiation of these dipoles turns out to be phased only in this direction. Due to the translational motion of atoms (molecules) of the gas medium, their dipole moments become phasemismatched, which just causes the observed FPD signal. In a usual macroscopic cell with a gas medium, the characteristic time of the FPD induced by a laser pulse is very short because it is determined by a quantity reciprocal to Doppler broadening of the spectral line of the resonant optical transition [1, 2]. At the same time, by present, ultrathin gas cells with a characteristic inner thickness l up to tens nanometers are manufactured and used in spectroscopy [3]. In particular, in the process of laser sounding of atoms in such cells, sub-Doppler absorption resonances the structure of which significantly depends on the ratio of the thickness l to the wavelength λ ~ 1 μm of the irradiated light are recorded [4]. This is caused by the specificity of induction and destruction of optical coherence of atoms during their flight between plane-parallel walls
of the cells. In this work, it is shown that when atoms (molecules) of a gas medium in an ultrathin cell are
Data Loading...
