We report the slowing of a supersonic beam by elastic reflection from a receding atomic mirror. We use a pulsed supersonic nozzle to generate a $511\pm 9\mathrm{m}/\mathrm{s}$ beam of helium that we slow by reflection from a $\mathrm{Si}(111)\mathrm{\text{−}}\mathrm{H}(1\times 1)$ crystal placed on the tip of a spinning rotor. We were able to reduce the velocity of helium by $246\mathrm{m}/\mathrm{s}$ and show that the temperature of the slowed beam is lower than 250 mK in the comoving frame.

We have demonstrated Zeeman slowing and capture of neutral ${}^{225}\mathrm{Ra}$ and ${}^{226}\mathrm{Ra}$ atoms in a magneto-optical trap. The intercombination transition ${}^{1}S_0\to {}^{3}P_1$ is the only quasicycling transition in radium and was used for laser-cooling and trapping. Repumping along the ${}^{3}D_1\to {}^{1}P_1$ transition extended the lifetime of the trap from milliseconds to seconds. Room-temperature blackbody radiation was demonstrated to provide repumping from the metastable ${}^{3}P_0$ level. We measured the isotope shift and hyperfine splittings on the ${}^{3}D_1\to {}^{1}P_1$ transition with the laser-cooled atoms, and set a limit on the lifetime of the ${}^{3}D_1$ level based on the measured blackbody repumping rate. Laser-cooled and trapped radium is an attractive system for studying fundamental symmetries.

We report on the first measurement of a temperature dependence of the Casimir-Polder force. This measurement was obtained by positioning a nearly pure ${}^{87}\mathrm{Rb}$ Bose-Einstein condensate a few microns from a dielectric substrate and exciting its dipole oscillation. Changes in the collective oscillation frequency of the magnetically trapped atoms result from spatial variations in the surface-atom force. In our experiment, the dielectric substrate is heated up to 605 K, while the surrounding environment is kept near room temperature (310 K). The effect of the Casimir-Polder force is measured to be nearly 3 times larger for a 605 K substrate than for a room-temperature substrate, showing a clear temperature dependence in agreement with theory.

Vacuum-stimulated Raman transitions are driven between two magnetic substates of a ${}^{87}\mathrm{Rb}$ atom strongly coupled to an optical cavity. A magnetic field lifts the degeneracy of these states, and the atom is alternately exposed to laser pulses of two different frequencies. This produces a stream of single photons with alternating circular polarization in a predetermined spatiotemporal mode. MHz repetition rates are possible as no recycling of the atom between photon generations is required. Photon indistinguishability is tested by time-resolved two-photon interference.

We present a theoretical study of fast-electron emission produced in ${\mathrm{H}}_2$ and ${\mathrm{H}}_2^{+}$ photoionization. We show that, when the electron wave length is comparable to the molecular size, the electron angular distributions arising from fixed-in-space molecules exhibit pronounced interference effects that critically depend on orientation and energy sharing between electrons and nuclei. In particular, for molecules oriented parallel to the polarization direction, the angular patterns reveal a complex nodal structure, while for molecules oriented perpendicularly, typical Young’s double-slit interferences are observed. These patterns change dramatically as the molecule vibrates.

We present an experiment where a single molecule strongly affects the amplitude and phase of a laser field emerging from a subwavelength aperture. We achieve a visibility of $-6\%$ in direct and $+10\%$ in cross-polarized detection schemes. Our analysis shows that a close to full extinction should be possible using near-field excitation.

Gas-phase singly protonated organic molecules of mass 410 Da (Alexa Fluor 350) have been cooled from ambient temperature to the hundred millikelvin range by Coulomb interaction with laser-cooled barium ions. The molecules were generated by an electrospray ionization source, transferred to and stored in a radio-frequency trap together with the atomic ions. Observations are well described by molecular dynamics simulations, which are used to determine the spatial distribution and thermal energy of the molecules. In one example, an ensemble of 830 laser-cooled ${}^{138}\mathrm{Ba}^{+}$ ions cooled 200 molecular ions to less than 115 mK. The demonstrated technique should allow a large variety of protonated molecules to be sympathetically cooled, including molecules of much higher mass, such as proteins.

A light beam changes direction as it enters a liquid at an angle from another medium, such as air. Should the liquid contain molecules that lack mirror symmetry, then it has been predicted by Fresnel that the light beam will not only change direction, but will actually split into two separate beams with a small difference in the respective angles of refraction. Here we report the observation of this phenomenon. We also demonstrate that the angle of reflection does not equal the angle of incidence in a chiral medium. Unlike conventional optical rotation, which depends on the path-length through the sample, the reported reflection and refraction phenomena arise within a few wavelengths at the interface and thereby suggest a new approach to polarimetry that can be used in microfluidic volumes.

We report the first observation of the laser-assisted photoelectric effect from a solid surface. By illuminating a Pt(111) sample simultaneously with ultrashort 1.6 eV and 42 eV pulses, we observe sidebands in the extreme ultraviolet photoemission spectrum. The magnitude of these sidebands as a function of time delay between the laser and extreme ultraviolet pulses represents a cross-correlation measurement of the extreme ultraviolet pulse. This effect promises to be useful to extend extreme ultraviolet pulse duration measurements to higher photon energies, as well as opening up femtosecond-to-attosecond time-scale electron dynamics in solid and surface-adsorbate systems.

When an atom absorbs a photon from a laser beam that is not an infinite plane wave, the atom’s recoil is less than $\hslash k$ in the propagation direction. We show that the recoils in the transverse directions produce a lensing of the atomic wave functions, which leads to a frequency shift that is not discrete but varies linearly with the field amplitude and strongly depends on the atomic state detection. The same lensing effect is also important for microwave atomic clocks. The frequency shifts are of the order of the naive recoil shift for the transverse wave vector of the photons.

A Rydberg atom mirror has been designed and its operational principle tested experimentally. A supersonic expansion containing H atoms moving with a velocity of $720\mathrm{m}/\mathrm{s}$ initially propagates toward a quadrupolar electrostatic mirror. The H atoms are then photoexcited to $n=27\mathrm{Rydberg}$ states with a positive Stark shift and move in a rapidly increasing electric field. The H atom beam is stopped in $4.8\mu \mathrm{s}$, only 1.9 mm away from the photoexcitation spot, and is then reflected back. The reflection process is monitored by pulsed field ionization and imaging.

We report the first observation of anti-Stokes laser-induced cooling in the ${\mathrm{Er}}^{3+}:{\mathrm{KPb}}_2{\mathrm{Cl}}_5$ crystal and in the ${\mathrm{Er}}^{3+}:\mathrm{CNBZn}$ (${\mathrm{CdF}}_2\mathrm{\text{−}}{\mathrm{CdCl}}_2\mathrm{\text{−}}\mathrm{NaF}\mathrm{\text{−}}{\mathrm{BaF}}_2\mathrm{\text{−}}{\mathrm{BaCl}}_2\mathrm{\text{−}}{\mathrm{ZnF}}_2$) glass. The internal cooling efficiencies have been calculated by using photothermal deflection spectroscopy. Thermal scans acquired with an infrared thermal camera proved the bulk cooling capability of the studied samples. The implications of these results are discussed.

We observe that the group velocity of light is reduced to an extremely low value of $0.091\mathrm{mm}/\mathrm{s}$ in a biological thin film of bacteriorhodopsin at room temperature. By exploiting unique features of a flexible photoisomerization process for coherent population oscillation, the velocity is all-optically controlled over an enormous span, from snail-paced to normal light speed, with no need of modifying the characteristics of the incident pulse. Because of the large quantum yield for the photoreaction in this biochemical system, the ultraslow light is observed even at low light levels of microwatts, indicating high energy efficiency.

We have used a radio frequency quadrupole decelerator to decelerate antiprotons emerging from the CERN Antiproton Decelerator from MeV- to keV-scale energy, and collected five decelerated pulses in a multiring trap. Some $5\times {10}^6$ antiprotons were stacked in this way. Cooling of the trapped antiprotons by a simultaneously trapped electron plasma was studied nondestructively via shifts in plasma mode frequencies. We have also demonstrated the first step in extracting a 10–500 eV antiproton beam from the trap.

We demonstrate that the structure of the outermost orbitals of oxygen and nitrogen can be observed in the angular distribution of coincident ion pairs generated by the double ionization of these molecules by 8 fs laser pulses. We do this by establishing that these ions emerge from well defined excited electronic states of ${\mathrm{O}}_{\mathrm{2}}^{\mathrm{2}\mathrm{+}}$ and ${\mathrm{N}}_{\mathrm{2}}^{\mathrm{2}\mathrm{+}}$ respectively and that they are produced dominantly through a process which involves electron rescattering. The angular distributions of the ions from the two targets are very different, reflecting the different structures of the outermost orbitals of the two molecules.

We have formed nondispersing wave packets from atomic Li Rydberg eigenstates by adding a small microwave field approximately resonant with the $\Delta n=1$ transition. The orbital motion of the Rydberg electron in states of $70\le n\le 78$ becomes phase locked to a 17.5 GHz microwave field and remains so for 900 ns, roughly 15 000 orbits of the Rydberg electron. A Floquet approach provides a reasonable quantum-mechanical description.

We demonstrate that emission-induced self-organization of two-level atoms can effect strong damping of the sample’s center-of-mass motion. When illuminated by far-detuned light, cold cesium atoms assemble into a density grating that efficiently diffracts the incident light into an optical resonator. We observe random phase jumps of $\pi$ in the emitted light, confirming spontaneous symmetry breaking in the atomic self-organization. The Bragg diffraction results in a collective friction force with center-of-mass deceleration up to $1000\mathrm{m}/{\mathrm{s}}^2$ that is effective even for an open atomic transition.

High resolution microwave and infrared spectra of ${\mathrm{H}\mathrm{e}}_N\mathrm{\text{−}}{\mathrm{N}}_2\mathrm{O}$ clusters were studied in the range $N=3$ to 12. The apparent cluster moments of inertia increase from $N=3$ to 6, but then decrease, showing oscillatory behavior for $N=7$ to 12. This provides direct experimental evidence for the decoupling of helium atoms from the rotation of the dopant molecule in this size regime, signaling the transition from a molecular complex to a quantum solvated system and directly exploring the microscopic evolution of “molecular superfluidity.”

We show how a carefully chosen combination of strong linearly and circularly polarized laser fields can bind two same-sign charges, not only suppressing their Coulomb repulsion in all three spatial dimensions, but also creating an effective attraction. As an example, we show how a molecule ${\mathrm{H}\mathrm{D}}^{2+}$ stripped of both electrons can be kept bound by the laser fields.

The atomic level structure of the element fermium was investigated for the first time using a sample of $2.7\times {10}^{10}$ atoms of the isotope ${}^{255}\mathrm{F}\mathrm{m}$ with a half-life of 20.1 h. The atoms were evaporated from a filament and stored in the argon buffer gas of an optical cell. Atomic levels were sought by the method of resonance ionization spectroscopy using an excimer-dye-laser combination. Two atomic levels were found at wave numbers $(25099.8\pm 0.2)$ and $(25111.8\pm 0.2){\mathrm{c}\mathrm{m}}^{-1}$. Partial transition rates to the $5f^{12}7s^2$ ${}^{3}H_6^e$ ground state have been determined from their saturation characteristics. Multiconfiguration Dirac-Fock calculations suggest that the leading orders of these levels could be the $5f^{12}7s7p$ ${}^{5}I_6^o$ and $5f^{12}7s7p$ ${}^{5}G_5^o$ terms.