Light-induced Drift Effect Research Articles

Trap for radioactive atoms in the gas phase based on light induced drift

A trap for radioactive atoms in the gas phase based on the light induced drift effect is presented. 24Na atoms have been held in this trap for 30 min. The atom retention half-time is not less than 4 h. Possible applications of the trap in nuclear physics and chemical physics are discussed.

Light-induced drift and abundance anomalies

view Abstract Citations (27) References (25) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Light-induced Drift and Abundance Anomalies LeBlanc, F. ; Michaud, G. Abstract Light-induced drift (LID) has been suggested by Atutov and Shalagin (1988) to be more efficient at causing abundances anomalies than radiation driven diffusion. A formalism is developed to simplify the accurate evaluation of LID in stars. The LID velocity is written in such a way that the effect of LID can easily be compared to the effect of the radiative acceleration of the same transition of an element. We also compare approximations that facilitate the evaluation of this phenomenon. Our calculations show that LID accelerates the separation of He-3 from He-4 in the atmosphere of a main-sequence star with T(eff) = 18,000 K. While He-4 is present, LID increases the upward drift of He-3 thus causing the relative overabundance of He-3 to appear earlier in the evolution. As He-4 settles gravitationally, the anisotropy disappears in the lines of He-3 and it is supported only by radiation pressure so that the same final abundance is maintained in the atmosphere as when LID is neglected. The effect was also calculated for Li III at the base of the convection zone of a star with T(eff) = 6700 K. At this depth, LID is about two orders of magnitude smaller than radiatively driven diffusion, thus playing a negligible role in the transport of this element. Publication: The Astrophysical Journal Pub Date: May 1993 DOI: 10.1086/172584 Bibcode: 1993ApJ...408..251L Keywords: Abundance; Drift Rate; Helium Isotopes; Stellar Atmospheres; Stellar Physics; Main Sequence Stars; Radiative Transfer; Astrophysics; RADIATIVE TRANSFER; DIFFUSION; STARS: ABUNDANCES full text sources ADS |

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.

Radioactive isotope and isomer separation using the light induced drift effect

Isotope separation with using light induced drift (LID) is discussed. Two basic theoretical characteristics of the method are deduced. I, separation simultaneously with an arbitrary high enrichment and without significant losses; 2, high separation productivity up to 100 μg/h. These characteristics are sufficient and very convenient for the separation of expensive radioactive isotopes and isomers for applications in medicine and science. The first experimental separation of the radioactive isotopes ( 22,24Na) using the LID effect is reported.

Light-induced drift of 22,23,24Na in a wide cold tube

This paper presents results of a test experiment for using the light-induced drift (LID) effect for measurements of the optical transition frequencies of short-lived isotopes and isomers. The LID of 23Na atoms was observed in a wide (8 mm) cold glass tube. Isotope enrichments were measured for radioactive sodium isotopes. The 22Na enrichment reaches a value of about 10. The LID velocities of 22Na and 24Na atoms reache values of ≈22 cm/s.

Light-induced drift under conditions of ground state optical hyperfine pumping

Analytical expressions describing the light-induced drift (LID) of alkali metal vapours reasonably well both under conditions of ground state optical hyperfine pumping and in its absence are obtained. It is shown that under the conditions of optical pumping the LID effect of the particles arises under the action of its own fluorescent radiation. The drift velocity for sodium atoms in a argon atmosphere reaches a value of 1 cm s-1 for fluorescent radiation of intensity 20 mW cm-2.

Effect of phase memory under collisions on field work and light-induced drift of gas particles

The influence of phase memory under collisions on the field work and the light induced drift (LID) effect of two-level gas particles is studied. It is shown that the phase memory effects may lead to the case where about half of the particles interacting with radiation amplify the incident radiation. The integral absorption coefficient for this remains positive due to growing radiation absorption by another half of the particles. It has been found that the phase memory strongly affects the LID under v ≫ kv̄ (v is the collision frequency, kv̄ is the Doppler line width): calculation of LID without regard for the phase memory can lead to underestimation of the LID effect value by a factor of (v/kv̄)2 ≫ 1. Interaction of the particles in the hard sphere model is used to illustrate that the phase memory begins to affect the LID when the relative difference of the transport cross-sections of the particles is ground and excited states is small: Δσ/σ ≲ λ̄/R, where λ̄ is the de Broglie wavelength at thermal velocities, R is the sphere radius.

Onsager reciprocity relation for rarefied gas flow in a laser radiation field

The Onsager relations are established in general form on the basis of the fundamental properties of the transport equations describing the motion of a rarefied gas in a laser radiation field. Expressions are obtained for the transport coefficient corresponding to the lightinduced drift effect and for the cross coefficient. The relation between them is found.

Light-induced drift of quantum-confined electrons in semiconductor heterostructures.

The effect of light-induced drift of quantum-confined electrons in semiconductor heterostructures is predicted. The effect manifests itself as the electric current in the heterostructure plane in response to optical excitation with the frequency close, but not exactly equal, to a transition frequency between levels in the heterostructure. The current reverses its direction with a change in the detuning sign, and vanishes if the radiation polarization is normal to the heterostructure plane.

White-light-induced drift in a gas with one optically active species.

A new light-induced drift effect is discussed in which a white-light source separates a gas mixture containing a single optically active (absorbing) species and a buffer gas which does not interact with the light. A three-level model with one upper level and two closely spaced lower levels is used for the active atoms, and strong collisions with the more abundant surrounding buffer gas atoms are assumed. The intensity spectrum in the vapor (including the effects of hyperfine pumping), and the resulting drift velocity are calculated as a function of optical depth into the vapor.

General diffusion equation for light-induced drift

We derive a general diffusion equation for the density of an atomic vapor immersed in a buffer gas and irradiated by nearly resonant light. The combination of velocity-selective excitation with state-dependent rates of velocity-changing collisions then gives rise to a drift term, and at the same time the diffusion tensor becomes anisotropic and intensity dependent. Both the effect of light-induced drift and diffusive pulling of atoms by the light are described by this diffusion equation in a consistent and correlated fashion.

Modelling gas-kinetic effects of light on gases with Keilson-Storer collision kernels

The authors consider a system of optically active two-state atoms immersed in a buffer gas and irradiated by a light beam. The corresponding Bloch equations are augmented by Keilson-Storer (KS) collision kernels (1952) which account for velocity-changing collisions. Expansion of the density operator elements in the eigenfunctions of KS kernels allows one to obtain exact solutions for the Laplace transforms of the density operator elements which may be expressed as rational approximants with any prescribed degree of accuracy. As an example they apply this method to discussion of the light-induced drift effect. In particular they give analytic expressions for the drift velocity, which are illustrated by numerical results. Finally, they briefly discuss possible generalisations and applications of the presented method.

Optical piston in rubidium

We report observation of an optical piston due to the effect of light induced drift in a rubidium-argon mixture. A tunable semiconductor diode laser is used for diagnostics of rubidium density and isotropic ratio. Sign and magnitude of the light induced drift effect depend directly on fine and hyperfine structure of rubidium.

Adsorption effects in light-induced drift

We describe the effect of light-induced drift, while allowing for adsorption of the active atoms on the wall of the cell. Assuming a rapid rate of adsorption and desorption, we express this effect by a modification of the diffusion equation for the volume density in the boundary layer near the wall. Explicit solutions are discussed in opposite special cases, corresponding to a large or a small mean free path of the active atoms.

Light-induced drift of Na vapor without physical adsorption on the inner surface of the cell

The experimental results are presented, which are obtained by the light-induced drift (LID) of Na vapor in helium without physical adsorption on the cell surface. This condition can be obtained by treatment of the cell surface with vacuum pump oil, which was extracted out of vaseline. By elimination of the physical adsorption the time for establishing the stationary distribution of the vapor density can be reduced (by a factor of ≈ 10 5). The attainable maximum of the drift velocity of Na vapor in helium was 580 cm/s. The relative variation of Na diffusion coefficient was experimentally estimated by optical excitation. The variation is ≈ 0.1. With the help of the LID effect, Na vapor can be localized in a region smaller tha 1 mm.

Effect of hyperfine splitting on light-induced drift

The influence of the hyperfine structure (hfs) of the levels upon the light-induced drift (LID) effect is investigated. It is shown that hfs considerably affects the dependence of the LID velocity upon the radiation frequency. It is concluded that for decreasing separation between the hfs components the LID effect can both increase and decrease depending upon the relationship of the system parameters (collision frequencies in different levels, the pressure of a buffer gas, etc.). A considerable decrease of the effect however is highly unlikely. It is shown that a change in the buffer gas pressure can lead to reversal of the LID velocity direction.

Studies on separation and conversation of spin modification of CH3F molecules

The spatial separation of nuclear spin modifications of CH 3 F by the light-induced drift (LID) effect has been investigated. The separations occurs

Radiative-collisional source of sound

The transport equations for a gas interacting with light are obtained in the framework of the 13-moment Grad approximation. It is shown that under transient conditions the light-induced drift effect generates acoustic vibrations. The proposed mechanism of the generation of sound is characterized by a dependence of the vibration amplitude on the sign of detuning relative to an optical resonance, which makes it possible to avoid the masking effect of thermal excitation of sound.

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.

Light-induced drift of CH 3F molecules

The light-induced drift (LID) of CH 3F molecules under vibrational excitation by a cw CO 2 laser has been investigated experimentally. The frequency dependence of the LID effect has been studied. The characteristic feature of this dependence (the effect is zero at the absorption line center) proves that the phenomenon observed is associated solely with the LID. The effect has been detected in 13CH 3F + 12CH 3F mixture with the fractionation coefficient of the gas mixture components equal to 1.7. The LID effect has been studied in CH 3F + H 2, CH 3F + He mixtures. A relative variation in the transport cross-section at vibrational excitation of CH 3F has been determined.