Frequency comb referenced spectroscopy of A-X 0-0 transitions in SH.

We report absolute transition frequencies for the allowed transitions from the X2Π3/2, v″ = 0, J″ = 3/2 rovibronic ground state of 32S1H to the A2Σ+, v' = 0 vibronic state. The frequencies have been determined with an uncertainty of less than 1 MHz, representing a more than 1000-fold improvement over previous measurements. Spectral traces are measured by scanning a frequency comb stabilized continuous-wave spectroscopy laser over the molecular transitions and detecting laser-induced fluorescence from SH molecules in a highly collimated molecular beam. To determine the absolute transition frequencies, the traces are fit with a quantum-mechanical model that accounts for saturation effects and shifts due to quantum interference. The model also provides estimates of the predissociation rate of the excited-state levels. Weighted averages of the hyperfine-resolved transition frequencies are computed in order to enable comparisons to measurements where the hyperfine structure is not resolved. These hyperfine-averaged frequencies indicate that the absolute transition frequencies determined in previous measurements were about ∼2.1 GHz (0.07 cm-1) too high. Finally, the measured transition frequencies are fit using an effective Hamiltonian model, resulting in more precise estimates of the spectroscopic constants.

Sub-ppb Measurement of a Fundamental Band Rovibrational Transition in HD.

We report a direct measurement of the 1-0 R(0) vibrational transition frequency in ground-state hydrogen deuteride (HD) using infrared-ultraviolet double resonance spectroscopy in a molecular beam. Ground-state molecules are vibrationally excited using a frequency comb referenced continuous-wave infrared laser, and the excited molecules are detected via state-selective ionization with a pulsed ultraviolet laser. We determine an absolute transition frequency of 111 448 815 477(13) kHz. The 0.12 parts-per-billion (ppb) uncertainty is limited primarily by the residual first-order Doppler shift.

Doppler-free Fourier transform spectroscopy.

Sub-Doppler broadband multi-heterodyne spectroscopy is proposed and experimentally demonstrated. Using two laser frequency combs of slightly different repetition frequencies, we have recorded Doppler-free two-photon dual-comb spectra of atomic rubidium resonances of a width of 6 MHz, while simultaneously interrogating a spectral span of 10 THz. The atomic transitions are uniquely identified via the intensity modulation of the observed fluorescence radiation. To the best of our knowledge, these results represent the first demonstration of Doppler-free Fourier transform spectroscopy and extend the range of applications of broadband spectroscopy towards precision nonlinear spectroscopy.

A traveling wave decelerator for neutral polar molecules.

Recently, a decelerator for neutral polar molecules has been presented that operates on the basis of macroscopic, three-dimensional, traveling electrostatic traps [A. Osterwalder, S. A. Meek, G. Hammer, H. Haak, and G. Meijer, Phys. Rev. A 81, 051401 (2010)]. In the present paper, a complete description of this decelerator is given, with emphasis on the electronics and the mechanical design. Experimental results showing the transverse velocity distributions of guided molecules are shown and compared to trajectory simulations. An assessment of non-adiabatic losses is made by comparing the deceleration signals from (13)CO with those from (12)CO and with simulated signals.

An electrostatic elliptical mirror for neutral polar molecules.

Focusing optics for neutral molecules finds application in shaping and steering molecular beams. Here we present an electrostatic elliptical mirror for polar molecules consisting of an array of microstructured gold electrodes deposited on a glass substrate. Alternating positive and negative voltages applied to the electrodes create a repulsive potential for molecules in low-field-seeking states. The equipotential lines are parallel to the substrate surface, which is bent in an elliptical shape. The mirror is characterized by focusing a beam of metastable CO molecules and the results are compared to the outcome of trajectory simulations.

Driving rotational transitions in molecules on a chip.

Polar molecules in selected quantum states can be guided, decelerated, and trapped using electric fields created by microstructured electrodes on a chip. Herein we explore how transitions between two of these quantum states can be induced while the molecules are on the chip. We use CO (a(3) Π(1) , v=0) molecules, prepared in the J=1 rotational level, and induce the J=2←J=1 rotational transition with narrow-band sub-THz (mm-wave) radiation. First, the mm-wave source is characterized using CO molecules in a freely propagating molecular beam, and both Rabi cycling and rapid adiabatic passage are examined. Then we demonstrate that the mm-wave radiation can be coupled to CO molecules that are less than 50 µm above the chip. Finally, CO molecules are guided in the J=1 level to the center of the chip where they are pumped to the J=2 level, recaptured, and guided off the chip.

Trapping molecules on a chip.

Magnetic trapping of atoms on chips has recently become straightforward, but analogous trapping of molecules has proved to be challenging. We demonstrated trapping of carbon monoxide molecules above a chip using direct loading from a supersonic beam. Upon arrival above the chip, the molecules are confined in tubular electric field traps approximately 20 micrometers in diameter, centered 25 micrometers above the chip, that move with the molecular beam at a velocity of several hundred meters per second. An array of these miniaturized moving traps is brought to a standstill over a distance of only a few centimeters. After a certain holding time, the molecules are accelerated off the chip again for detection. This loading and detection methodology is applicable to a wide variety of polar molecules, enabling the creation of a gas-phase molecular laboratory on a chip.

Trapping molecules on a chip in traveling potential wells.

A microstructured array of over 1200 electrodes on a substrate has been configured to generate an array of local minima of electric field strength with a periodicity of 120 microm about 25 microm above the substrate. By applying sinusoidally varying potentials to the electrodes, these minima can be made to move smoothly along the array. Polar molecules in low field seeking quantum states can be trapped in these traveling potential wells. This is experimentally demonstrated by transporting metastable CO molecules in 30 mK deep wells that move at constant velocities above the substrate.

The radiative lifetime of metastable CO (a 3Pi, v=0).

We present a combined experimental and theoretical study on the radiative lifetime of CO in the a (3)Pi(1,2), v=0 state. CO molecules in a beam are prepared in selected rotational levels of this metastable state, Stark-decelerated, and electrostatically trapped. From the phosphorescence decay in the trap, the radiative lifetime is measured to be 2.63+/-0.03 ms for the a (3)Pi(1), v=0, J=1 level. From the spin-orbit coupling between the a (3)Pi and the A (1)Pi states a 20% longer radiative lifetime of 3.16 ms is calculated for this level. It is concluded that coupling to other (1)Pi states contributes to the observed phosphorescence rate of metastable CO.