K. A. H. van Leeuwen

Bright thermal atomic beams by laser cooling::a 1400-fold gain in beam flux

Using a three-step transverse laser cooling scheme, a strongly diverging flow of metastable Ne(3s3P2] atoms is compressed into a well-collimated, small diameter atomic beam (e.g., 1.4 mrad HWHM divergence at 3.6 mm beam diameter) with an unmodified axial velocity distribution centered at 580 m/s. The maximum increase in beam flux 1.04 m downstream of the source is a factor 1400; the maximum increase in phase space density, i.e., brightness, is a factor 160. The laser power used is only 140 mW. The scheme is extendable to a large variety of atomic species and enables the application of bright atomic beams in many areas of physics.

Intermolecular potentials for the metastable Ne*-rare gas and Ne*-molecule systems

Abstract The absolute value and the velocity dependence of the total cross section Q ( g ) has been measured in a crossed beam machine for the Ne*-Ar, Kr, Xe and Ne*-O 2 , N 2 , CH 2 and CO 2 systems, using a mixed beam containing Ne*( 3 P( 0 ) and Ne * ( 3 P 2 ) fine structure states in a 1:5 ratio. The range of velocities is typically 1000 ⩽ g ⩽ 8000 m s −1 , always including the interesting N = 1 glory oscillation. The results for the Ne* -rare gas systems are in excellent agreement with the predictions of the ion-atom Morse-Morse-spline-van der Waals potentials of Gregor and Siska, both with regard to the absolute value (1.5%), position of the N = 1 glory maximum (2.7%) and the amplitude of the N = 1 glory maximum (4.3%). The predictions of the potentials proposed by Hausamann are less satisfactory, most likely due to the specific switchover function used to connect the well area at R/R M ≈ 1.1 to the van der Waals long-range attractive branch at R/R M ≈ 2 ( R M is the well position). By using a semiclassical scaling method the potential parameters ϵ (well depth), R M (well position) and C 6 (van der Waals constant) have been determined for the Ne*-molecule systems, using the Gregor and Siska IAMMSV potential for the Ne*-Xe system as a reference. The well parameters are (ϵ (meV), R M (A)) = (3.21, 5.43), (4.24, 5.17), (13.55, 4.74) and (7.08, 5.44) for the Ne*-N 2 , O 2 , CO 2 and CH 4 , systems, respectively. For the C 6 values we observe a fair scaling with the polarisibility α of the molecule. For the Ne*-CO 2 system we observe a damping of the amplitude of the glory oscillations, which increases rapidly with decreasing velocity. This damping is interpreted in terms of the probability for ionisation along the glory trajectory, providing useful information for determining a complex potential for this system.

Grating feedback in a 810 nm broad-area diode laser

Narrow linewidth, single spectral mode operation has been obtained in a high power, 810 nm broad-area diode laser in an extended cavity configuration with a grating as external reflector (grating feedback). For stable operation it was necessary to misalign the feedback slightly in the plane of the laser junction. Characteristics of the thus obtained laser system are a linewidth below 5 MHz, an output intensity of about 50% of the free running power, a large-scale tuning range of 15 nm and continuous scanning over 4 GHz. In the spatial domain, the laser remains multimode and astigmatic. To show the practical applicability of this system, saturated absorption of a krypton line is demonstrated.

Magic wavelengths for the 2 3 S → 2 1 S transition in helium

We have calculated ac polarizabilities of the 2 3 S and 2 1 S states of both He 4 and He 3 in the range 318 nm to 2.5 µm and determined the magic wavelengths at which these polarizabilities are equal for either isotope. The calculations, only based on available ab initio tables of level energies and Einstein A coefficients, do not require advanced theoretical techniques. The polarizability contribution of the continuum is calculated using a simple extrapolation beyond the ionization limit, yet the results agree to better than 1% with such advanced techniques. Several promising magic wavelengths are identified around 320 nm with sufficient accuracy to design an appropriate laser system. The extension of the calculations to He 3 is complicated due to the additional hyperfine structure, but we show that the magic wavelength candidates around 320 nm are predominantly shifted by the isotope shift.

Magnetically Induced Laser Cooling for Ne*: Approaching the Recoil Limit

Magnetically induced laser cooling to temperatures close to the recoil limit is investigated in one dimension. For a metastable neon beam, we present high-precision measurements investigating the actual temperature limit in this cooling process. Using time-of-flight techniques to reduce the effect of the longitudinal velocity spread, we observe cooling at small magnetic field toward ν = 0 with an r.m.s. width of the distribution of 5.4 cm/s, well below the Doppler limit. At a larger magnetic field (0.4 Gauss) the velocity-selective resonances are extremely sharp. Here we find the r.m.s. width of the distribution to be 3.4 cm/s, only 1.1 times the recoil speed k/M, corresponding to a temperature T = 2.7 μK.

Ionization and excitation of hydrogen and helium Rydberg atoms by microwaves

We have used the interaction of hydrogen Rydberg atoms with microwave fields to study multiphoton ionization. The minimum number of photons absorbed in the experiments ranges from about 300 to only 15. A brief overview is given of the extensive theoretical work that is under development to explain experimental data, including various observed structures. Similarly we report on ionization of helium Rydberg atoms, qualitatively explained in terms of a static picture. Finally we show selective excitation of He triplet s‐state to higher angular momentum states, via absorption of several photons from the field. Using the Floquet method a close analogy between the microwave problem and slow atomic collisions can be made. Sharp resonant structures in the spectra can be linked to individual avoided crossings of calculated Floquet quasi‐energy curves. Our theory that exploits a separation of timescales explains very well the positions, depths, and shapes of the observed structures, but a discrepancy still remains ...

A factor 1600 increase in neutral atomic beam intensity using laser cooling

Using a three-step transverse cooling scheme, a strongly diverging flow of metastable Ne*(/sup 3/P/sub 2/) atoms is compressed into a small diameter (3 mm), well-collimated (1 mrad) atomic beam, using only 200 mW total laser power. This extremely valuable technique for frequency standard applications is applicable to many different atomic systems.<<ETX>>

Production of bright, cold beams for atomic collision experiments

Laser manipulation techniques for neutral atoms can be used to produce atomic beams which are more intense, brighter and colder than can be achieved by any other means. These beams will have a tremendous impact on the experimental study of low‐energy atomic collisions. We first describe the design and operation of an intensifier for a thermal (axial velocity 600 m/s) beam of metastable neon atoms. The intensifier produces a gain in beam brightness of a factor 160 and a typical gain in usable flux of a factor 1400. Next, we discuss the design, construction and preliminary tests of a setup to produce an atomic beam which is slow and cold as well as bright and intense. The setup is expected to produce a beam of metastable atoms with an axial velocity of 100 m/s, a spread therein of 1.5 m/s, a diameter of 1 mm, a residual divergence of 1 mrad and a flux of 1012 atoms/s.