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Register a new userUltralow-power local laser control of the dimer density in alkali-metal vapors through photodesorption
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Ultralow-power diode-laser radiation is employed to induce photodesorption of cesium from a partially transparent thin-film cesium adsorbate on a solid surface. Using resonant Raman spectroscopy, we demonstrate that this photodesorption process enables an accurate local optical control of the density of dimer molecules in alkali-metal vapors.
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We show how a single linearly polarized control field can produce a sharply tunable group velocity of a weak probe field at resonance in a four-level atomic configuration of alkali vapors. The dispersion can be switched from normal to anomalous along with vanishing absorption, just by changing intensity of the resonant control field. In addition, by allowing different intensities of the different polarization components of the control field, the anomalous dispersion can be switched back to the normal. This thereby creates a valley of anomaly in group index variation and offers two sets of control field intensities, for which the system behaves like a vacuum. The explicit analytical expressions for the probe coherence are provided along with all physical explanations. We demonstrate our results in $J = 1/2 leftrightarrow J = 1/2$ transition for D_1 lines in alkali atoms, in which one can obtain a group index as large as $3.2times10^{8}$ and as negative as $-1.5times10^{5}$ using a control field with power as low as 0.017 mW/cm$^2$ and 9.56 mW/cm$^2$ .
We present a joint experimental and theoretical study of spin coherence properties of 39K, 85Rb, 87Rb, and 133Cs atoms trapped in a solid parahydrogen matrix. We use optical pumping to prepare the spin states of the implanted atoms and circular dichroism to measure their spin states. Optical pumping signals show order-of-magnitude differences depending on both matrix growth conditions and atomic species. We measure the ensemble transverse relaxation times (T2*) of the spin states of the alkali-metal atoms. Different alkali species exhibit dramatically different T2* times, ranging from sub-microsecond coherence times for high mF states of 87Rb, to ~100 microseconds for 39K. These are the longest ensemble T2* times reported for an electron spin system at high densities (n > 10^16 cm^-3). To interpret these observations, we develop a theory of inhomogenous broadening of hyperfine transitions of ^2S atoms in weakly-interacting solid matrices. Our calculated ensemble transverse relaxation times agree well with experiment, and suggest ways to longer coherence times in future work.
We have shown that it is possible to model accurately optical phenomena in intense laser fields by taking into account the intensity distribution over the laser beam. We developed a theoretical model that divided an intense laser beam into concentric regions, each with a Rabi frequency that corresponds to the intensity in that region, and solved a set of coupled optical Bloch equations for the density matrix in each region. Experimentally obtained magneto-optical resonance curves for the $F_g=2longrightarrow F_e=1$ transition of the $D_1$ line of $^{87}$Rb agreed very well with the theoretical model up to a laser intensity of around 200 mW/cm$^2$ for a transition whose saturation intensity is around 4.5 mW/cm$^2$. We have studied the spatial dependence of the fluorescence intensity in an intense laser beam experimentally and theoretically. An experiment was conducted whereby a broad, intense pump laser excited the $F_g=4longrightarrow F_e=3$ transition of the $D_2$ line of cesium while a weak, narrow probe beam scanned the atoms within the pump beam and excited the $D_1$ line of cesium, whose fluorescence was recorded as a function of probe beam position. Experimentally obtained spatial profiles of the fluorescence intensity agreed qualitatively with the predictions of the model.
We present electric dipole polarizabilities ($alpha_d$) of the alkali-metal negative ions, from H$^-$ to Fr$^-$, by employing four-component relativistic many-body methods. Differences in the results are shown by considering Dirac-Coulomb (DC) Hamiltonian, DC Hamiltonian with the Breit interaction, and DC Hamiltonian with the lower-order quantum electrodynamics interactions. At first, these interactions are included self-consistently in the Dirac-Hartree-Fock (DHF) method, and then electron correlation effects are incorporated over the DHF wave functions in the second-order many-body perturbation theory, random phase approximation and coupled-cluster (CC) theory. Roles of electron correlation effects and relativistic corrections are analyzed using the above many-body methods with size of the ions. We finally quote precise values of $alpha_d$ of the above negative ions by estimating uncertainties to the CC results, and compare them with other calculations wherever available.
An electrically-controllable, solid-state, reversible device for sourcing and sinking alkali vapor is presented. When placed inside an alkali vapor cell, both an increase and decrease of the rubidium vapor density by a factor of two are demonstrated through laser absorption spectroscopy on 10 to 15 s time scales. The device requires low voltage (5 V), low power (<3.4 mW peak power), and low energy (<10.7 mJ per 10 s pulse). The absence of oxygen emission during operation is shown through residual gas analysis, indicating Rb is not lost through chemical reaction but rather by ion transport through the designed channel. This device is of interest for atomic physics experiments and, in particular, for portable cold-atom systems where dynamic control of alkali vapor density can enable advances in science and technology.
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