Instrumentation for laser physics and spectroscopy using 32-bit microcontrollers with an Android tablet interface.

Several high-performance lab instruments suitable for manual assembly have been developed using low-pin-count 32-bit microcontrollers that communicate with an Android tablet via a USB interface. A single Android tablet app accommodates multiple interface needs by uploading parameter lists and graphical data from the microcontrollers, which are themselves programmed with easily modified C code. The hardware design of the instruments emphasizes low chip counts and is highly modular, relying on small "daughter boards" for special functions such as USB power management, waveform generation, and phase-sensitive signal detection. In one example, a daughter board provides a complete waveform generator and direct digital synthesizer that fits on a 1.5 in. × 0.8 in. circuit card.

Excitation of weakly bound molecules to trilobitelike Rydberg states.

We observe "trilobitelike" states of ultracold (85)Rb(2) molecules, in which a ground-state atom is bound by the electronic wave function of its Rydberg-atom partner. We populate these states through the ultraviolet excitation of weakly bound molecules, and access a regime of trilobitelike states at low principal quantum numbers and with vibrational turning points around 35 Bohr radii. This demonstrates that, unlike previous studies that used free-to-bound transitions, trilobitelike states can also be excited through bound-to-bound transitions. This approach provides high excitation probabilities without requiring high-density samples, and affords the ability to control the excitation radius by selection of the initial-state vibrational level.

Formation of ultracold Rb2 molecules in the v'' = 0 level of the a(3)Σ+(u) state via blue-detuned photoassociation to the 1(3)Π(g) state.

We report on the observation of blue-detuned photoassociation in Rb(2), in which vibrational levels are energetically above the corresponding excited atomic asymptote. (85)Rb atoms in a MOT were photoassociated at short internuclear distance to levels of the 1(3)Π(g) state at a rate of approximately 5 × 10(4) molecules s(-1). We have observed most of the predicted vibrational levels for all four spin-orbit components; 0(+)(g), 0(-)(g), 1(g), and 2(g), including levels of the 0(+)(g) outer well. These molecules decay to the metastable a(3)Σ(+)(u) state, some preferentially to the v'' = 0 level, as we have observed for photoassociation to the v' = 8 level of the 1(g) component.

A single-chip event sequencer and related microcontroller instrumentation for atomic physics research.

A 16-bit digital event sequencer with 50 ns resolution and 50 ns trigger jitter is implemented by using an internal 32-bit timer on a dsPIC30F4013 microcontroller, controlled by an easily modified program written in standard C. It can accommodate hundreds of output events, and adjacent events can be spaced as closely as 1.5 µs. The microcontroller has robust 5 V inputs and outputs, allowing a direct interface to common laboratory equipment and other electronics. A USB computer interface and a pair of analog ramp outputs can be added with just two additional chips. An optional display/keypad unit allows direct interaction with the sequencer without requiring an external computer. Minor additions also allow simple realizations of other complex instruments, including a precision high-voltage ramp generator for driving spectrum analyzers or piezoelectric positioners, and a low-cost proportional integral differential controller and lock-in amplifier for laser frequency stabilization with about 100 kHz bandwidth.

Local blockade of Rydberg excitation in an ultracold gas.

In the laser excitation of ultracold atoms to Rydberg states, we observe a dramatic suppression caused by van der Waals interactions. This behavior is interpreted as a local excitation blockade: Rydberg atoms strongly inhibit excitation of their neighbors. We measure suppression, relative to isolated atom excitation, by up to a factor of 6.4. The dependences of this suppression on both laser irradiance and atomic density are in good agreement with a mean-field model. These results are an important step towards using ultracold Rydberg atoms in quantum information processing.

Dissociation energies of molecular hydrogen and the hydrogen molecular ion.

We have obtained improved values for the dissociation energies of molecular hydrogen and its ion by using a high-resolution pulse-amplified laser to probe the second dissociation limit. The onset of the vibrational continuum is observed by state-selective detection of the atomic products of dissociation, and several auxiliary measurements link the results to the ground state. The dissociation energies are accurate to 0.010-0.026 cm(-1), improving previous measurements by a factor of 3-7. Agreement with ab initio calculations is good for H2, D2, and their ions, but not for HD and HD+.

Photoassociative production and trapping of ultracold KRb molecules.

We have produced ultracold heteronuclear KRb molecules by the process of photoassociation in a two-species magneto-optical trap. Following decay of the photoassociated KRb*, the molecules are detected using two-photon ionization and time-of-flight mass spectroscopy of KRb+. A portion of the metastable triplet molecules thus formed are magnetically trapped. Photoassociative spectra down to 91 cm(-1) below the K(4s)+Rb(5p(1/2)) asymptote have been obtained. We have made assignments to all eight of the attractive Hund's case (c) KRb* potential curves in this spectral region.

Long-range molecular resonances in a cold Rydberg gas.

We present evidence for molecular resonances in a cold dense gas of rubidium Rydberg atoms. Single UV photon excitation from the 5s ground state to np Rydberg states (n=50-90) reveals resonances at energies corresponding to excited atom pairs (n-1)d+ns. We attribute these normally forbidden transitions to avoided crossings between the long-range molecular potentials of two Rydberg atoms. These strong van der Waals interactions result in avoided crossings at extremely long range, e.g., approximately 58 000 times the Bohr radius (a(0)) for n=70.

Chirp-free nanosecond laser amplifier for precision spectroscopy.

We describe a simple method for greatly reducing optical phase perturbations in a nanosecond pulsed dye amplifier. The laser dye mix is tailored to produce a susceptibility near zero at the operating wavelength. Frequency shifts are reduced to less than 3 MHz, and frequency chirping to less than 10 MHz, without significant loss of amplified power. This technique has been used to improve the accuracy of precision far-UV wavelength measurements in H(2) to ~7 parts in 10(9).

Generation of vacuum ultraviolet radiation for precision laser spectroscopy.

We report on the generation of tunable nanosecond pulsed VUV radiation near 120 nm using difference-frequency mixing in H(2). Our scheme uses two dye lasers, one fixed at 606 nm and the other tunable in the red. These convenient wavelengths simplify the metrology needed for accurate VUV laser spectroscopy. Efficient VUV generation is attained with modest Nd:YAG pump laser energies (approximately 160 mJ at 532 nm), making the scheme attractive even when narrow bandwidths are not essential.

Frequency-modulation spectroscopy with transform-limited nanosecond laser pulses.

We demonstrate high-quality FM spectra with nanosecond laser pulses. Transform-limited pulses with FM sidebands are produced by pulsed amplification of a phase-modulated cw laser. The pulses can be shifted to the UV by nonlinear mixing. We report both initial experiments on I(2) and what is to our knowledge the first observation of a far-UV transition by FM spectroscopy, at 214.5 nm. Major advantages of this method include (1) spectral resolution of the order of 0.001 cm(-1), (2) better-defined optical phase, and (3) a much smaller and more easily detected modulation frequency, ~500 MHz. The absorption sensitivity is ~10(-4), and considerable further improvement is expected.