Collimated blue and infrared beams generated by two-photon excitation in Rb vapor.

Utilizing two-photon excitation in hot Rb vapor we demonstrate the generation of collimated optical fields at 420 and 1324 nm. Input laser beams at 780 and 776 nm enter a heated Rb vapor cell collinear and circularly polarized, driving Rb atoms to the 5D(5/2) state. Under phase-matching conditions coherence among the 5S(1/2)→5P(3/2)→5D(5/2)→6P(3/2) transitions produces a blue (420 nm) beam by four-wave mixing. We also observe a forward and backward propagating IR (1324 nm) beam, due to cascading decays through the 6S(1/2)→5(1/2) states. Power saturation of the generated beams is investigated by scaling the input powers to greater than 200 mW, resulting in a coherent blue beam of 9.1 mW power, almost an order of magnitude larger than previously achieved. We measure the dependences of both beams in relation to the Rb density, the frequency detuning between Rb ground-state hyperfine levels, and the input laser intensities.

Coherent population trapping with controlled interparticle interactions.

We investigate coherent population trapping in a strongly interacting ultracold Rydberg gas. Despite the strong van der Waals interactions and interparticle correlations, we observe the persistence of a resonance with subnatural linewidth at the single-particle resonance frequency as we tune the interaction strength. This narrow resonance cannot be understood within a mean-field description of the strong Rydberg-Rydberg interactions. Instead, a many-body density matrix approach, accounting for the dynamics of interparticle correlations, is shown to reproduce the observed spectral features.

An auto-incrementing nanosecond delay circuit.

We describe a circuit that acts as an auto-incrementing delay. The circuit allows the user to adjust the total number of delays in a cycle, the incremental delay value, and the amount of time that is spent at each delay step. The circuit is stand-alone, yet is readily interfaced to data acquisition systems. Depending on the delay chip used and the number of steps required, the delay step can be as short as 250 ps or as long as 640 ns. The circuit has been used to control the temporal separation between pulses from independent lasers. This was instrumental in our measurement of population dynamics in an optically excited three-level ladder system.

Photoassociation in cold atoms via ladder excitation.

We explore 2-color photoassociative ionization in cold Rb vapor and present experimental evidence that the molecular ions are produced from the stepwise excitation of a ladder of molecular states. We also explore a new process, dubbed photoassociative-dissociative ionization, by which atomic ions are created by excitation through a ladder of molecular states, finally autoionizing to a dissociative potential curve of Rb2+. We submit that these experiments could be the starting point for the same sort of high resolution spectroscopy that has already been done for lower electronic states of cold Rb2 at large internuclear separation.

Reducing the uncertainty in laser beam size measurement with a scanning edge method.

A modification in the analysis of a conventional laser beam spot size measurement method has been developed. The new analysis significantly decreases the uncertainty in the estimation of the beam-spot size. A conventional beam scanning approach was used in the measurement, but instead of differentiating the data and fitting the result to a Gaussian function, the data were fit to an analytical approximation to the complementary error function. As a result, fitted parameters were obtained that were consistent with the standard differentiation approach, but with considerably smaller uncertainty.

State selective charge transfer cross sections for Na+ with excited rubidium: a unique diagnostic of the population dynamics of a magneto-optical trap.

It is shown how the newly developed technique of magneto-optical-trap recoil-ion momentum spectroscopy can be used to measure the temporal evolution of excited state fraction in such a trap. In this case, the fraction of atoms in a 5p state is measured. The technique can be generalized to allow the measurement of more complicated systems, e.g., a Rb sample having a mixture of 5s, 5p, 4d, and Rydberg states.

Kinematically complete charge exchange experiment in the Cs(+)+Rb collision system using a MOT target.

Charge exchange is examined with unprecedented precision using the newly developed magneto-optical trap-target recoil ion momentum spectroscopy (MOTRIMS) technique. Initial and final state selective, charge exchange cross sections are obtained for 6 keV Cs+ colliding with rubidium in 5s and 5p states. For each charge transfer channel, cross sections differential in scattering angle are measured. These data are used to overturn previous long-standing conjecture as to the origin of oscillations seen in total charge exchange cross section measurements, and compare well with an enhanced Demkov model calculation.

Observation of coherent multiphoton processes in nuclear states.

We have used states of nuclear excitation to demonstrate coherent multiphoton processes that were the analogs of well-known effects occurring at optical frequencies. Success in exciting radio-frequency sidebands on hyperfine components of the 14.4-keV Mössbauer transition of (57)Fe is described. A distinctive feature of this experiment was that the absorbing foil was rigidly bound in a graphite sandwich intended to eliminate detrimental vibrations. A model is proposed that quantitatively explains these results in terms of coherently excited nuclear states and evidentially confirms the multiphoton nature of the sidebands observed in this experiment.