Theory Of Light-induced Drift Research Articles

Theory of light-induced drift. VI. Roles of accommodation of normal and tangential momenta in surface light-induced drift with positive spontaneous relaxation parameter

Surface light-induced drift of a rarefied gas in cells with flat-plate and circular-cylindrical geometries is studied, and exact analytical solutions to the model rate equations are obtained in the limit of large Knudsen number. The work is a continuation of part V of this series of papers, in which the model rate equations were tailored specifically in order to study the roles played by both the tangential and normal momentum molecule-surface accommodation coefficients. In part V, the ``spontaneous decay'' parameter, $\ensuremath{\gamma}$, was set equal to zero, and the case of general ``laser excitation'' parameter, $q$, was studied. In the present paper, we get exact analytical results for the case of arbitrary $\ensuremath{\gamma}$ in the limit of small $q$; we also get accurate numerical results for arbitrary $\ensuremath{\gamma}$ and $q$. In passing, one serious, and other less serious, typographical errors in part V are corrected.

Theory of light-induced drift. V. Roles of accommodation of normal and tangential momenta in surface light-induced drift

Surface light-induced drift (SLID) of a rarefied gas in cells with flat-plate and circular-cylindrical geometries is studied, and exact analytical solutions to the model rate equations are obtained in the limit of large Knudsen number. The model rate equations, which have not appeared before, have been tailored specifically in order to study the roles played in SLID, in a physically realistic setting, by both the tangential momentum and the normal momentum molecule-surface accommodation coefficients. Because the model equations are new (to the best of our knowledge), the results are generally different from those of previous work, although emphasis is placed on obtaining relations between the present and previous results; applications to experiments may be made by means of those relations.

Theory of light-induced drift. III. Models of surface and bulk light-induced drift in one dimension

Light-induced drift (LID) of a rarefied gas in a cell is studied, and exact analytical closed-form solutions to the model rate equations, which model the gas motion in one dimension, are obtained for cases of both surface LID (SLID) and bulk LID (BLID); the special case of the limit of low radiation absorption by the gas is given particular attention. Similarities and differences among the results for SLID and BLID are discussed. This is part III of a series of papers, parts I and II having studied LID, but concentrating on SLID, with flat-plate and circular-cylindrical cell geometries, respectively [F. O. Goodman, Phys. Rev. A 65, 064309 (2002); 65, 064310 (2002)].

Theory of light-induced drift. IV. Models of bulk light-induced drift in three dimensions

Light-induced drift (LID) of a rarefied gas in a cell is studied, and exact analytical closed-form solutions to the model rate equations are obtained for bulk LID (BLID) in three dimensions, emphasis being placed on the limit of low radiation absorption by the gas. Comparisons are made with an existing model of BLID in one dimension [F. O. Goodman, preceding paper, Phys. Rev. A 67, 013410 (2003)], and we examine whether there are any conditions under which that model is satisfactory. Comparisons are also made with the author's models of surface LID in one dimension (above reference) and in three dimensions [F. O. Goodman, Phys. Rev. A 65, 063409 (2002); 65, 063410 (2002)].

Theory of light-induced drift. II. Circular-cylindrical geometry

Light-induced drift (LID) of a rarefied gas in a cell with circular-cylindrical geometry is studied, and exact solutions to the model rate equations are obtained, with exact analytical solutions for the case of surface LID (SLID); the special case of the limit of low radiation absorption by the gas in SLID is given particular attention. Many results are different from those of previous work. Emphasis is placed on considerations of comparison with experiment. This is part II of a series of papers, part I having studied LID with flat-plate geometry [F. O. Goodman, preceding paper, Phys. Rev. A 65, 063409 (2002)].

Theory of light-induced drift. I. Flat-plate geometry

Light-induced drift (LID) of a rarefied gas in a cell with flat-plate geometry is studied in the limits of large length and width of the cell, and exact solutions to the model rate equations are obtained, with exact analytical solutions for the case of surface LID (SLID); the special case of the limit of low radiation absorption by the gas in SLID is given particular attention. Many results are different from those of previous work. Emphasis is placed on considerations of comparison with experiment.

Theory of light-induced drift of a binary gas mixture in a capillary

The drift of a binary gas mixture in capillaries induced by resonant light is studied theoretically. The surface and bulk mechanisms of flow of the mixture components are analyzed for arbitrary values of the Knudsen number and the rate parameter (the ratio of the radiative decay rate of an excited molecular level to the intermolecular collision rate). Finally, the theoretical results are compared with the experimental data.

Theory of light-induced drift of electrons in coupled quantum wells.

A theory of the new effect of light-induced drift (LID) in coupled potential wells is developed on the basis of the density-matrix method. The effect appears when light excites intersubband electronic transitions. LID manifests itself as the photocurrent of the two-dimensional electron gas in the well plane, which depends on coherent electron tunneling between the coupled wells. The theory shows the effect to possess distinctive features such as a characteristic antisymmetric spectral contour consisting of four alternating positive and negative peaks and the change of sign of the LID current with the sign change of the bias normal to the quantum-well plane. The quantitative estimates for GaAs wells show the LID current to be readily detectable.

Kinetic theory of light-induced drift of particles with degenerate energy levels

The theory of light-induced drift of particles with degenerate levels is proposed. Kinetic equations which are semiclassical with respect to rotational degrees of freedom and with a phase memory accounting are obtained. The drift velocity dependence on radiation polarisation is predicted. Numerical calculation, which has been made in a strong collision model, shows that the accounting of level degeneracy leads to a velocity change of up to 10-20% under some conditions.

Theory of light-induced drift and the optical piston.

Light-induced drift arises when optically excited atoms with a Doppler-selected velocity suffer a diffusive friction that is different from that of ground-state atoms. When the atoms form an optically dense system, this drift can cause a piston effect, which sweeps the atoms in the propagation direction of the field. We derive coupled differential equations for the density of atoms and the light intensity, with an explicit expression for the drift velocity in terms of easily accessible parameters. Solutions of these equations are obtained for the stationary state in a closed cell. The density at the dark end of the cell, considered as the response to the incident-light intensity as its driving force, exhibits a discontinuity resembling a second-order phase transition for an optically dense system. We also obtain solutions with a soliton character, describing a localized density packet moving at uniform speed.

Combination rules in the theory of light-induced drift

Simple combination rules are derived for the parameter ΔD/D which is important in the light-induced drift effect. Calculations are carried out in the first approximation in respect of variations of the parameters of the particle interaction potential.