Sodium Atomic Beam Research Articles

Sodium atom beam collisions with the liquid glycerol surface: Mass effects of deuteration

Gas-phase sodium atom collisions with liquid glycerol were investigated by atomic beam scattering from normal and deuterated surfaces. The scattering signal of the recoiling effusive Na atom beam was monitored by a mass spectrometer. Because all thermally equilibrated Na atoms ionize into the liquid surface, this system was uniquely suited to interrogate the subtle kinematic effect of glycerol deuteration on the collisional energy transfer process within the impulsive scattering regime. An interplay of kinematic and vibrational effects explains the Na scattering behavior from variously deuterated glycerol surfaces, extending our fundamental understanding of collisional energy transfer, and ultimately, chemical reaction dynamics.

Supersonic sodium atomic beam hyperfine structure measurement orthogonally with dye laser R6G

Supersonic sodium atomic beam hyperfine structure measurement orthogonally with dye laser R6G

Effect of finite detection efficiency on the observation of the dipole-dipole interaction of a few Rydberg atoms

We have developed a simple analytical model describing multiatom signals that are measured in experiments on dipole-dipole interaction at resonant collisions of a few Rydberg atoms. It has been shown that finite efficiency of the selective field-ionization detector leads to the mixing up of the spectra of resonant collisions registered for various numbers of Rydberg atoms. The formulas which help to estimate an appropriate mean Rydberg atom number for a given detection efficiency are presented. We have found that a measurement of the relation between the amplitudes of collisional resonances observed in the one- and two-atom signals provides a straightforward determination of the absolute detection efficiency and mean Rydberg atom number. We also performed a testing experiment on resonant collisions in a small excitation volume of a sodium atomic beam. The resonances observed for 1--4 detected Rydberg atoms have been analyzed and compared with theory.

Using atomic diffraction of Na from material gratings to measure atom-surface interactions

In atom optics a material structure is commonly regarded as an amplitude mask for atom waves. However, atomic diffraction patterns formed using material gratings indicate that material structures also operate as phase masks. In this study a well collimated beam of sodium atoms is used to illuminate a silicon nitride grating with a period of 100 nm. During passage through the grating slots atoms acquire a phase shift due to the van der Waals (vdW) interaction with the grating walls. As a result the relative intensities of the matter-wave diffraction peaks deviate from those expected for a purely absorbing grating. Thus a complex transmission function is required to explain the observed diffraction envelopes. An optics perspective to the theory of atomic diffraction from material gratings is put forth in the hopes of providing a more intuitive picture concerning the influence of the vdW potential. The van der Waals coefficient ${C}_{3}=2.7\ifmmode\pm\else\textpm\fi{}0.8\phantom{\rule{0.3em}{0ex}}\mathrm{meV}\phantom{\rule{0.3em}{0ex}}{\mathrm{nm}}^{3}$ is determined by fitting a modified Fresnel optical theory to the experimental data. This value of ${C}_{3}$ is consistent with a van der Waals interaction between atomic sodium and a silicon nitride surface.

Phasor analysis of atom diffraction from a rotated material grating

The strength of an atom-surface interaction is determined by studying atom diffraction from a rotated material grating. A phasor diagram is developed to interpret why diffraction orders are never completely suppressed when a complex transmission function due to the van der Waals interaction is present. We also show that atom-surface interactions can produce asymmetric diffraction patterns. Our conceptual discussion is supported by experimental observations with a sodium atom beam.

Magnetic field tomography

Neutral atoms may be trapped via the interaction of their magnetic dipole moment with magnetic field gradients. One of the possible schemes is the cloverleaf trap. It is often desirable to have at hand a fast and precise technique for measuring the magnetic field distribution. We introduce a novel diagnostic tool for instantaneous imaging the equipotential lines of a magnetic field within a region of space (the vacuum recipient) that is not accessible to massive probes. Our technique is based on spatially resolved observation of the fluorescence emitted by a hot beam of sodium atoms crossing a thin slice of resonant laser light within the magnetic field region to be investigated. The inhomogeneous magnetic field spatially modulates the resonance condition between the Zeeman-shifted hyperfine sublevels and the laser light and therefore the amount of scattered photons. We demonstrate this technique by mapping the field of our cloverleaf trap in three dimensions under various conditions.

Structure in the angular dependence of optical suppression of photoassociative ionization collisions within an optically cooled and collimated sodium atom beam

We report measurements of the angular distribution of optical suppression in photoassociative ionization collisions taking place within a bright, slow Na atom beam. At a collision “temperature” (T=Ekin/kB) of about 5 mK we observe rich structure in the suppression measure as a function of the angle between the atom-beam axis and the polarization axis of the suppressor light beam. This structure cannot be explained by the superposition of individual partial-wave contributions to the suppression measure, and we propose a partial-wave interference phenomenon to account for it.

Continuous, dense, highly collimated sodium beam

We have developed a slow, highly collimated, and bright sodium atom beam suitable for orientation and alignment studies in cold collisions. A combination of transverse-optical collimation, longitudinal cooling, rapid decoupling from the longitudinal cooling cycle, and a final “optical-force extrusion” stage produces an atom density of 1×1010 cm−3 within a beam-divergence solid angle of 2×10−6 sr. Rapid Zeeman-cooler decoupling results in a narrow laboratory velocity distribution of 5 m/s full width at half maximum and a cold binary intrabeam collision temperature of 4 mK.

Mechanical Hanle effect on the sodium D1line

We present an experimental and theoretical analysis of the mechanical Hanle effect, i.e., the modification of the atomic trajectories following the interaction with laser fields in the Hanle configuration. The case of open transitions is examined. In our experiment a thermal sodium atomic beam is crossed perpendicularly by a single-mode linearly polarized laser beam. The laser field is tuned to resonance with an Fg Fe transition of the sodium D1 line. A static magnetic field B is applied collinear to the laser light propagation direction. The atomic beam flux at the position corresponding to its maximum in the absence of laser light is studied as a function of the applied magnetic field. For the Fg = F Fe = F,F-1 transitions the atomic flux shows a sharp increase at B = 0, as a result of the coherent trapping of the population into the ground state. For the Fg = 1 Fe = 2 transition this effect is absent and no significant variation of the atomic flux with the magnetic field is observed. A theoretical description of the mechanical Hanle effect in open transitions is given and it is clarified why in our experiment the mechanical Hanle/CPT-resonances associated to different hyperfine transitions have different contrasts.

Measurement of the Density Matrix of a Longitudinally Modulated Atomic Beam

We present the first measurement of the longitudinal density matrix of a matter-wave beam. Using a unique interferometric scheme, both the amplitude and phase of off-diagonal density matrix elements were determined directly, without the use of traditional tomographic techniques. The measured density matrix of a doubly amplitude modulated atomic sodium beam compares well with theoretical predictions.

Mechanical detection of coherent population trapping on the sodium D 1 line

We consider the coherent population trapping phenomenon in a transversally excited thermal sodium atomic beam. Two different atom-light interaction schemes are investigated. In the first the ground states forming the nonabsorbing coherent superposition belong to different hyperfine levels and in the second they belong to the same level. The preparation of the system into the dark state is studied by simultaneously detecting the atomic fluorescence intensity and the atomic density at the position of the beam corresponding to its maximum when the laser is turned off.

Observation of V-Type Electromagnetically Induced Transparency in a Sodium Atomic Beam

We have conducted an experimental study of V-type electromagnetically induced transparency in sodium. Its principles are elucidated by a simple model. Measurements show decreased fluorescence and absorption depending on the detuning of the driving and probe fields, which is in agreement with the results of numerical simulation.

Dynamics of coherent optical pumping in a sodium atomic beam

This work is concerned with the temporal evolution of the coherent population trapping (CPT) process in the case of additional optical pumping to states not contributing to the CPT superposition states. Special attention is paid to the influence of weak external magnetic fields that can change the laser-atom interaction considerably. The theoretical analysis is completed by experimental observations on a sodium atomic beam, which show good agreement with our theory. The results obtained are of importance for a realistic picture of CPT schemes in practical applications.

The effect of circularly polarized light on NMR spectra

Atoms and molecules subjected to a constant circularly polarized light beam carry a timeindependent current density proportional to the intensity. The direction of the current is opposite for right and left polarization. As a result there is an induced magnetic moment, which is the inverse Faraday effect, and a magnetic field at a nucleus. Formulae are derived for the current density and the induced magnetic field at a nucleus; an equivalence is established between this field and the antisymmetric polarizability resulting from the nuclear magnetic moment. The shifts in the NMR frequencies of 1H, 13C, 19F and 205Tl due to a continuous-wave 10 W cm-2 beam are estimated to be 0·2 to 50 μHz for right circular polarization at transparent wavelengths, with larger shifts for near-resonance conditions. If the full width at half maximum height of an electric-dipole allowed transition were 10 cm-1, the circularly polarized radiation at resonance would cause shifts of the order of a few hundred hertz for 19F. Shifts are expected for all magnetic nuclei. In a beam of sodium atoms the 10 W cm-2 circularly polarized light, whose frequency is 6 GHz from resonance with a yellow D line, is predicted to induce an NMR shift of the order of 1 MHz.

Associative ionization in collisions between excited Na atoms in the and the states

For the first time, associative ionization has been observed in an atomic beam of excited sodium atoms in both the and the state. Relative values for the partial cross sections were obtained specified according to the different magnetic substate combinations of the two fine-structure states. These were found to be comparable to those for associative ionization between two atoms. However, the effect of the excitation on the ion production rate was found to be considerable and to depend strongly on the relative polarizations of the laser beams producing the two populations due to the redistribution of the involved magnetic sublevels. The results indicate that the initial orientation of the electron spin S does not significantly influence the associative ionization reaction at the mean collision energy of 25 meV.

Coherent population trapping with losses observed on the Hanle effect of theD1sodium line

We consider the coherent-population-trapping phenomenon in a thermal sodium atomic beam. We compare the different coherent-population-trapping schemes that can be established on the ${\mathrm{D}}_{1}$ line using the Zeeman sublevels of a given ground hyperfine state. The coherent-population-trapping preparation is examined by means of a Hanle-effect configuration. The efficiency of the coherent-population-trapping phenomenon has been examined in presence of optical pumping into hyperfine levels external to those of the excited transition. We show that both the contrast and the width of the coherent population trapping resonance strongly decrease when the optical pumping rate is increased. In the experiment, the loss rate due to optical pumping has been controlled by means of a laser repump of variable intensity.

Reflection cooling of sodium atoms in an evanescent light wave

Studied in this work is the cooling of a beam of sodium atoms upon its reflection from an evanescent light wave. The cooling mechanism is associated with the spontaneous transitions of the atoms between the hyperfine-structure sublevels of the ground state. Subject to studies is the relationship between the reflection angle of the atoms and the frequency detuning and intensity of the light wave. It is demonstrated experimentally that the transverse atomic momentum component can be reduced by more than one half ( Δp⊥ p⊥ ≅ 0.5 ) in a single reflection event, the number of cooled atoms in the reflected beam exceeding 50%. It should be noted that the loss of atoms in reflection can be made as small as desired, and so the reflection cooling cycle can be repeated many times over.

Limit of resolution of a standing wave atom optical lens

Using a Gaussian standing wave at λ=589 nm as an atom optical lens, we have focused a thermal atomic sodium beam. We have examined the limits of the resolution of this focusing technique, and have made structures with linewidths of 13 nm and contrast of 6:1 with a short focal length atom optical lens. While numerical simulations predict that smaller structures should be attainable with shorter focal lengths, we find that the resolution deteriorates for focal length shorter than f≊16 μm.

Optical collimation and compression of a thermal atomic beam

We have performed an experiment to optically cool and compress a thermal beam of sodium atoms by employing a two-dimensional version of a magneto-optical trap. The beam compressor employs a tapered transverse magnetic field gradient formed by four pairs of permanent magnets. We measure the efficiency of collimation and compression as function of longitudinal velocity group.

Transverse laser cooling of a velocity-selected sodium atomic beam

The transverse velocity distribution of a sodium atomic beam, laser cooled in one dimension, has been measured with sub-recoil resolution. A velocity-selective detection system was employed to separate the longitudinal and transverse velocity components to provide a direct measure of the transverse velocity distribution. The effects of varying the cooling laser intensity and detuning on the derived transverse temperature are presented, and show a remarkable insensitivity to the laser intensity. Atomic velocities within a factor of two of the recoil velocity are