Spatial shaping for generating arbitrary optical dipole traps for ultracold degenerate gases

Abstract

We present two spatial-shaping approaches - phase and amplitude - for creating two-dimensional optical dipole potentials for ultracold neutral atoms. When combined with an attractive or repulsive Gaussian sheet formed by an astigmatically focused beam, atoms are trapped in three dimensions resulting in planar confinement with an arbitrary network of potentials - a free-space atom chip. The first approach utilizes an adaptation of the generalized phase-contrast technique to convert a phase structure embedded in a beam after traversing a phase mask, to an identical intensity profile in the image plane. Phase masks, and a requisite phase-contrast filter, can be chemically etched into optical material (e.g., fused silica) or implemented with spatial light modulators; etching provides the highest quality while spatial light modulators enable prototyping and realtime structure modification. This approach was demonstrated on an ensemble of thermal atoms. Amplitude shaping is possible when the potential structure is made as an opaque mask in the path of a dipole trap beam, followed by imaging the shadow onto the plane of the atoms. While much more lossy, this very simple and inexpensive approach can produce dipole potentials suitable for containing degenerate gases. High-quality amplitude masks can be produced with standard photolithography techniques. Amplitude shaping was demonstrated on a Bose-Einstein condensate.

Minimally destructive, Doppler measurement of a quantized flow in a ring-shaped Bose–Einstein condensate

“…We position the DMD in our imaging system to directly image the surface of the DMD onto the atoms. (This method is similar to the photomask method used in [26], with the DMD replacing the photomask.) The DMD generates a double ring trap.…”

Conical refraction: fundamentals and applications

“…The numerical simulations agree well with the experimental results on the dynamics of a trapped 87 Rb BEC in the PDR of CR. In addition to the advantages commented above in terms of power efficiency and beam quality, the minimum (and practically null) intensity circle offered by the toroidal dark trap avoids photon scattering and presents no corrugation of the potential minimum at the focal plan, at variance with techniques based on LG beams [209] or amplitude masks [210][211][212]. A range of applications of this technique can be envisioned: for optimized beam geometries, i.e., small w 0 , R 0 , and z R , the toroidal dark focus of the PDR generated by CR could be used to built an all-optical trap for BECs using a single beam.…”

“…For ultra-cold atoms, dark ORPs have the advantage of substantially reducing atom heating and decoherence rates [198] because of the low rate of spontaneous photon scattering as well as producing intrinsically flat potential minima. Blue-detuned ORPs have been experimentally reported by means of LG beams generated with spatial light modulators (SLMs) [209] and by amplitude masks [210][211][212]. These two techniques might experience the following limitations: (i) a significant fraction of the input power is lost and, therefore, it does not contribute to create the optical trap, (ii) the smoothness and, therefore, the quality of the trapping potential is limited by the size and number of pixels for the SLMs and the resolution of the printing system for the amplitude masks, and (iii) an accurate control on the position and alignment of the optical elements being used is required.…”

Resonant wavepackets and shock waves in an atomtronic SQUID

“…The BEC is formed in a crossed optical dipole trap with the same procedures as in [12]. The trap is created by two laser beams: a red-detuned laser beam shaped like a sheet for the vertical confinement and a blue-detuned laser beam transmitting through an intensity mask [26]. The intensity mask is imaged onto the atoms, providing inplane confinement.…”