A simple, versatile laser system for the creation of ultracold ground state molecules

Abstract

A simple, versatile laser system for the creation of ultracold ground state molecules Here we describe how a relatively simple apparatus consisting of a single fixed-length optical cavity can be used to narrow the linewidth of the two different wavelength lasers required for STIRAP simultaneously. The frequency of each of these lasers is referenced to the cavity and is continuously tunable away from the cavity modes through the use of non-resonant electro-optic modulators. Selfheterodyne measurements suggest the laser linewidths are reduced to several 100 Hz. In the context of 87 Rb 133 Cs molecules produced via magnetoassociation on a Feshbach resonance, we demonstrate the performance of the laser system through one-and two-photon molecular spectroscopy. Finally, we demonstrate transfer of the molecules to the rovibrational ground state using STIRAP.

Production of Ultracold 87Rb133Cs in the Absolute Ground State: Complete Characterisation of the Stimulated Raman Adiabatic Passage Transfer

“…We see this as the long vertical "ridge" of good fits in figure 6(b). However, the noise amplitude √ DG is much more sensitive, and we fit √ DG ∼ 2π × 130 kHz, also consistent with our measurements of the shot-to-shot stability of our laser frequency [32]. In our case, where the correlation time is much longer than the transfer time, the frequency noise is effectively a nearly constant detuning, which matches with slow, shot-to-shot noise variation in the laser frequency.…”

“…In this article, we build a model of the transfer including the effects of finite laser linewidth, based on [31], and find excellent agreement with experimental measurements of the STIRAP transfer and independent measurements of the laser linewidth and shot-to-shot noise [32]. We also completely characterise the transitions used in the transfer with direct measurements of the Rabi frequencies, and we estimate the excited-state lifetime.…”

“…A full description of our laser system for STIRAP has been presented elsewhere [32]. Briefly, a pair of external cavity diode lasers at 1557 nm and 977 nm supply the light for STIRAP.…”

“…We focus up to 16 mW of each wavelength to waists of 37.7(1) µm (pump) and 35.6(6) µm (Stokes) at the molecule sample. In our earlier publication [32], we measured the short-term linewidth of the 1557 nm laser to be 0.52(2) kHz and a frequency drift of ∼ 100 kHz over the few hours it normally takes to map out the transfer as in figure 2. The 977 nm laser system is identical, so it is reasonable to assume it has similar noise characteristics.…”

“…The best fit occurs at a phase correlation time of around 300 µs, which corresponds to a shortterm laser linewidth of G =∼ 2π × 3 kHz. Measurements from delayed self-heterodyne interferometry [32] estimated the laser linewidth as 2π × 0.5 kHz. These are consistent, as we note that the best-fit point is remarkably insensitive to the phase correlation time, with only an order-of-magnitude estimate possible.…”