Alkali Vapor Cells Research Articles

Glass-blown spherical microcells for chip-scale atomic devices

This paper demonstrates spherical vapor cells intended to be used in chip-scale atomic devices. A micro glass blowing process is introduced, in which multiple glass spheres are simultaneously shaped on the top of a silicon wafer and subsequently filled with rubidium. In the presented fabrication process, an array of cylindrical cavities is first etched in silicon. Next, a thin glass wafer is anodically bonded to the silicon wafer. The bonded wafers are then placed inside a furnace set to 850 ° C. At this elevated temperature, the viscosity of the glass is decreased and the heated trapped gas in the cavities expands, thus causing the glass to be blown into spherical cells. Microscopic alkali vapor cells are achieved by evaporation of Rb 87 through a small glass nozzle into the cell cavities. The cells are then sealed by anodic bonding. The fabricated cells are characterized and the presence of rubidium vapor inside the cells is verified by observing an absorption spectrum.

Intrinsic Impurities in Glass Alkali-Vapor Cells

We report NMR measurements of metallic (133)Cs in glass cells. The solid-liquid phase transition was studied by observing the NMR peaks arising from these two phases; surprisingly, many cells yielded two additional NMR peaks below the melting point. We attribute these signals to two distinct impurities which can dissolve in the liquid alkali metal and affect its chemical shift. Intentional contamination of cesium cells with O(2) confirms this hypothesis for one peak. The other contaminant remains unknown but can appear in evacuated cells. Similar effects have been seen in (87)Rb cells.

Differential atomic magnetometry based on a diverging laser beam

The authors demonstrate a novel atomic magnetometer that uses differential detection of the spatially diverging components of a light field to monitor the Larmor precession frequency of atoms in a thermal vapor. The design is implemented in compact form with a micromachined alkali vapor cell and a naturally divergent light field emitted by a vertical-cavity surface-emitting laser. Operating the magnetometer in differential mode cancels common-mode noise and improves the sensitivity by a factor of 26 over single-channel operation. They also suggest ways in which the current sensitivity of 28pT∕√Hz may be improved further without sacrificing size or simplicity.

Classification of Light-Induced Desorption of Alkali Atoms in Glass Cells Used in Atomic Physics Experiments

We attempt to provide physical interpretations of light-induced desorption phenomena that have recently been observed for alkali atoms on glass surfaces of alkali vapor cells used in atomic physics experiments. We find that the observed desorption phenomena are closely related to recent studies in surface science, and can probably be understood in the context of these results. If classified in terms of the photon-energy dependence, the coverage and the bonding state of the alkali adsorbates, the phenomena fall into two categories: It appears very likely that the neutralization of isolated ionic adsorbates by photo-excited electron transfer from the substrate is the origin of the desorption induced by ultraviolet light in ultrahigh vacuum cells. The desorption observed in low temperature cells, on the other hand, which is resonantly dependent on photon energy in the visible light range, is quite similar to light-induced desorption stimulated by localized electronic excitation on metallic aggregates. More detailed studies of light-induced desorption events from surfaces well characterized with respect to alkali coverage-dependent ionicity and aggregate morphology appear highly desirable for the development of more efficient alkali atom sources suitable to improve a variety of atomic physics experiments.

Alkali-vapor cell with metal coated windows for efficient application of an electric field

We describe the implementation of a cylindrical T-shaped alkali-vapor cell for laser spectroscopy in the presence of a longitudinal electric field. The two windows are used as two electrodes of the high-voltage assembly, which is made possible by a metallic coating which entirely covers the inner and outer sides of the windows except for a central area to let the laser beams in and out of the cell. This allows very efficient application of the electric field, up to 2kV∕cm in a rather dense superheated vapor, even when significant photoemission takes place at the windows during pulsed laser irradiation. The body of the cell is made of sapphire or alumina ceramic to prevent large currents resulting from surface conduction observed in cesiated glass cells. The technique used to attach the monocrystalline sapphire windows to the cell body causes minimal stress birefringence in the windows. In addition, reflection losses at the windows can be made very small. The vapor cell operates with no buffer gas and has no magnetic part. The use of this kind of cell has resulted in an improvement of the signal-to-noise ratio in the measurement of parity violation in cesium vapor underway at ENS, Paris. The technique can be applied to other situations where a brazed assembly would give rise to unacceptably large birefringence in the windows.

Detection of nonresonant impurity gases in alkali vapor cells

We show that even small amounts of impurity gases significantly change the properties of the nonlinear Faraday effect in alkali vapor cells. These changes result from velocity-changing collisions. We propose a simple method of detection and measurement of the impurities based on this effect.

Booster for ultra-fast loading of atom traps

We propose a 2D magneto-optical compressor with a very large 40 mm diameter acceptance area to funnel the low velocity tail of the Maxwell–Boltzmann distribution (v≤100 m/s) in a low pressure discharge (Ne*) or alkali vapor cell (Na) into a well-collimated (10 mrad) bright beam of 107 to 108 atoms/s for Ne* or 2×1011 atoms/s for Na, leaving the cell through a 1 mm orifice. After axial cooling in an isotropic light field, resulting in an axial velocity distribution with 〈v〉=8 m/s with a FWHM Δv=3 m/s, this beam can be efficiently loaded into an atom trap. For rubidium, the predicted flux is 8×1011 atoms/s. Compared to all other alkali vapor-cell schemes, the gain in loading rate is a factor of 20 to 100, a major boost for achieving Bose–Einstein condensation. For the metastable rare gas atoms, it is the first table-top scheme for experiments with atom traps.

Optical magnetic resonance imaging of Rb vapor in low magnetic fields

By applying magnetic field gradients to alkali vapor cells, images of the spatial distribution of spin-polarized Rb atoms were obtained. Optical pumping is used to produce precessing spin-polarization in the ground state. Detection of the coherent spin transients is performed in the time-domain by a single optical probe beam covering the whole sample cell. Spatial resolution of better than 1 mm has been achieved by a projection-reconstruction method.

A superheated Na cell for X-ray photoionization experiments

The performance of a superheated alkali vapor cell, with a geometry suitable for x-ray photoionization experiments, is described. An internal heater was used to superheat sodium vapor in a split-wick heat pipe. At a Na pressure of 20 Torr, the transmission through the cell in the region of theC−X molecular band of Na2 increased to 50% from the 5% observed when the cell was operated in a conventional heat-pipe mode. In the presence of a Na atom density of 2×1017 cm−3, the average molecule density over the length of the cell was measured to be 2.5×1015 cm−3. In the hot central region of the superheated cell, the molecule density was predicted to have been reduced by a factor of 50 to 3×1014 cm−3.