A simple 2 W continuous-wave laser system for trapping ultracold metastable helium atoms at the 319.8 nm magic wavelength

Abstract

extracted. This method was employed to determine charge radii of the halo nuclei 6 He and 8 He [8] but also to measure the 4 He − 3 He differential nuclear charge radius [9,10]. These measurements are relevant to current investigations into the so-called proton radius puzzle which arose when a similar measurement of the proton radius in µH found a 7σ discrepancy with the 2010 CODATA value [11]. Current efforts investigating the nuclear charge radii of µ 3 He + and µ 4 He + are projected to reach an experimental uncertainty at the sub-attometer (am) level [12]. Determinations of the 4 He − 3 He differential nuclear charge radius with comparable accuracy in electronic systems provide a valuable cross-check for these measurements.Currently, the two most accurate measurements of the 4 He − 3 He differential nuclear charge radius have achieved accuracies of 3 [9] and 11 am 2 [10], roughly an order of magnitude less precise than the projection of the µHe experiment, but disagree by 4σ. The former experiment resolved the 2 3 S → 2 3 P transition to within one thousandth of the 1.6-MHz natural linewidth and is not expected to be improved upon in the near future. The latter experiment was performed on the doubly forbidden 2 3 S → 2 1 S transition whose 8 Hz natural linewidth is not a limiting factor but has a very low excitation rate and thus requires a long interaction time. To achieve this He * atoms were cooled to quantum degeneracy (a BoseEinstein condensate (BEC) of 4 He * , and in a degenerate Fermi gas of 3 He * ) and trapped in an optical dipole trap (ODT). The accuracy of this experiment was limited by experimental effects, mainly the ac-Stark shift induced by the ODT.This problem is also encountered in optical lattice clocks where it is solved by employing so-called magic wavelength traps [13]. In a magic wavelength trap, the wavelength of the trapping laser is chosen such that AbstractHigh-precision spectroscopy on the 2 3 S → 2 1 S transition is possible in ultracold optically trapped helium, but the accuracy is limited by the ac-Stark shift induced by the optical dipole trap. To overcome this problem, we have built a trapping laser system at the predicted magic wavelength of 319.8 nm. Our system is based on frequency conversion using commercially available components and produces over 2 W of power at this wavelength. With this system, we show trapping of ultracold atoms, both thermal (~0.2 μk) and in a Bose-Einstein condensate, with a trap lifetime of several seconds, mainly limited by off-resonant scattering .

Precision spectroscopy of helium in a magic wavelength optical dipole trap

“…1.0(1) × 10 8 Wm −2 using a 1 W ODT beam. This intensity is roughly half of our estimate assuming perfect focusing conditions and beam quality [44]. The constant offset correction to the polarizability is found to be 3.4(5) a 3 0 .…”

“…The optical and electronic setup for generating the probe and ODT laser light are described in refs. [42] and [44].…”

Tunable cw UV laser with <35 kHz absolute frequency instability for precision spectroscopy of Sr Rydberg states

“…Our approach, shown in Fig. 1(b), is based on that described in [32], and is similar to that used in [23,33]. Two infra-red seed lasers are amplified and combined using sum frequency generation (SFG) in a periodically-poled stoichiometric lithium tantalate (PPSLT) crystal to produce red light at ∼ 633 nm -639 nm.…”

“…The conventional approach to generating tunable CW light in the near-UV region of the spectrum has been to frequency-double a dye laser [22,30,31]. Solid-state systems using sumfrequency generation (SFG) have been developed for particular cooling transitions, offering high power and narrow linewidth [23,32,33], but a tuning range of only a few GHz. Recently these techniques have been extended to lasers for Rydberg spectroscopy [23], where the restricted tuning range means that only a narrow range of principal quantum numbers are accessible.…”

Development and characterization of a 22 W narrow-linewidth 3186 nm ultraviolet laser

“…However, such systems are large and expensive, and their operation and maintenance are very complex. Newly-developed fiber lasers and amplifiers are more simple and reliable to operate and maintain [13,14]. For years, a number of nonlinear materials have been used to generate the UV, and among them -BaB2O4 (BBO) and LiB3O5 (LBO) are prime choices.…”