We present a laser beam shaping method using acousto-optic deflection of light and discuss its application to dipole trapping of ultracold atoms. By driving the acousto-optic deflector with multiple frequencies, we generate an array of overlapping diffraction-limited beams that combine to form an arbitrary-shaped smooth and continuous trapping potential. Confinement of atoms in a flat-bottomed potential formed by a laser beam with uniform intensity over its central region confers numerous advantages over the harmonic confinement intrinsic to Gaussian beam dipole traps and many other trapping schemes. We demonstrate the versatility of this beam shaping method by generating potentials with large flat-topped regions as well as intensity patterns that compensate for residual external potentials to create a uniform background to which the trapping potential of experimental interest can be added.
We present a laser beam shaping method using acousto-optic deflection of light and discuss its application to dipole trapping of ultracold atoms. By driving the acousto-optic deflector with multiple frequencies, we generate an array of overlapping diffraction-limited beams that combine to form an arbitrary-shaped smooth and continuous trapping potential. Confinement of atoms in a flat-bottomed potential formed by a laser beam with uniform intensity over its central region confers numerous advantages over the harmonic confinement intrinsic to Gaussian beam dipole traps and many other trapping schemes. We demonstrate the versatility of this beam shaping method by generating potentials with large flat-topped regions as well as intensity patterns that compensate for residual external potentials to create a uniform background to which the trapping potential of experimental interest can be added.
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.
Ultracold atomic gases with uniform density can be created by flat-bottom optical traps. These gases provide an ideal platform to study many-body physics in a system that allows for simple connections with theoretical models and emulation of numerous effects from a wide range of fields of physics. In Earth-bound laboratories the trap sizes, number of species and states, as well as the range of physical effects are largely restricted by the adopted levitation technique. Homogeneous ultracold gases in microgravity simulators and space however offer an interesting perspective which is actively being pursued. To effectively make use of a gravity-compensated laboratory, realizing box potentials with large spatial extent enables access to previously inaccessible length scales and reduce finite-size and boundary effects. We present an approach based on two identical orthogonally aligned acousto-optic deflector setups to generate large time-averaged optical potentials with trapping volumes up to three orders of magnitude larger than conventional setups. These potentials follow power-law scalings with exponents of up to 152. We characterize the system and validate its performance through simulations of the mean-field ground state of a quantum gas, including dynamical excitations arising from the realistic time-dependent painting potentials. The implementation of this setup may open new directions at the interface with condensed matter, few-body Efimov physics or the exploration of critical, non-equilibrium phenomena.
The loading of ultra-cold atoms into two-dimensional, time-averaged optical potentials was demonstrated. The time-averaging scheme allows us to make arbitrary and two dimensional potentials, where the potential shape and depth can be dynamically controlled. Traps are produced by rapidly scanning a red-detuned laser focus in any desired pattern using a two-dimensional acousto-optical modulator (AOM). Smooth optical potentials are created when the scanning speed is much higher than any trapping frequency in system, resulting in a time-averaged dipole potential for the atoms. The depth of the potential can be controlled at any time and place by modulating the amplitude of the applied radio frequency to the AOM.
Acousto-optic deflectors (AOD) enable spatiotemporal control of laser beams through diffraction at an ultrasonic grating that is controllable by radio-frequency (rf) waveforms. These devices are a widely used tool for high-bandwidth random-access scanning applications, such as optical tweezers in quantum technology. A single AOD can generate multiple optical tweezers by multitone rf input in one dimension. Two-dimensional (2D) patterns can be realized with two perpendicularly oriented AODs. As the acousto-optical response depends nonlinearly on the applied frequency components, phases, and amplitudes, and in addition experiences dimensional coupling in 2D setups, intensity regulation becomes a unique challenge. Guided by coupled-wave theory and experimental observations, we derive a compute-efficient model which we implement on a graphics processing unit. Only one-time sampling of single-tone laser-power calibration is needed for model parameter determination, allowing for straight-forward integration into optical instruments. We implement and experimentally validate an open-loop diffraction efficiency control system that enables programmable 2D multibeam trajectories with intensity control applied at every time step during digital signal generation, overcoming the limited flexibility, pattern-size constraints, and bandwidth limitations of methods using precalculation and precalibration of a predefined pattern set or closed-loop feedback. The system is capable of stable real-time waveform streaming of arrays with up to 50 x 50 tweezers with minimal time resolution of 1.4 ns (700 MS/s) and a peak latency below 257 microseconds for execution of newly requested patterns. Reactive, real-time 2D multibeam laser patterning and scanning with strict intensity matching will substantially benefit parallelization and increasing data rates in materials processing, microscopy, and optical tweezers.
Ultracold atomic gases with uniform density can be created by flat-bottom optical traps. These gases provide an ideal platform to study many-body physics in a system that allows for simple connections with theoretical models and emulation of numerous effects from a wide range of fields of physics. In Earth-bound laboratories the trap sizes, number of species and states, as well as the range of physical effects are largely restricted by the adopted levitation technique. Homogeneous ultracold gases in microgravity simulators and space however offer an interesting perspective which is actively being pursued. To exploit the full potential of any gravity-compensated laboratory the box potentials created need to be as large as possible. By using two orthogonally aligned acousto-optic deflectors, we create large time-averaged optical potentials with trapping volumes a thousandfold larger than conventional setups, described by power-law scalings with exponents of up to 152. We verify the performance of our setup by simulating the mean-field behaviour of a quantum gas ground state in conjunction with dynamical excitations due to the realistic time-dependent painting potentials. The implementation of this setup may open new directions at the interface with condensed matter, few-body Efimov physics or the exploration of critical, non-equilibrium phenomena.
Time-varying fields are widely used to extend the accessible range of trapping potentials for ultracold atoms. This work explores two very different examples of such fields, in the radiofrequency and optical regimes, whose interactions with trapped atoms can both be described in terms of the dressed atom picture. Forming the basis of this work are radiofrequency dressed adiabatic potentials based on macroscopic trapping coils. Atoms are confined at the south pole of the resultant oblate spheroidal trapping surfaces. This work describes the extension of these potentials by two different methods: the application of multiple dressing radiofrequencies, and addition of a rapidly-scanned optical dipole trap. This is the first experimental demonstration of a multiple-radiofrequency dressed adiabatic potential, explored using ultracold 87Rb atoms confined in a highly configurable double well. Due to the independent generation of each constituent dressing frequency, the depth of each trapping well and the height of the barrier are easily manipulated, enabling precise and reliable transfer of atoms between the available trapping geometries. Experimental work includes an exploration of the potential-shaping capabilities of the three-radiofrequency system, and characterisation of the potential landscape using radiofrequency spectroscopy with good agreement to the eigenvalues numerically calculated using Floquet theory. This initial exploration of multiple-radiofrequency techniques lays the groundwork for applications in studying double well physics in a two-dimensional system, and independent state or species selective manipulation of trapped atoms. The potential shaping capabilities of this method can also be extended by applying additional trapping frequencies. In a supplementary line of experimental work, an optical dipole trapping system has been constructed, and the trapping beam aligned to the lower surface of the radiofrequency dressed trapping shell in order to sculpt the radial confinement. Beam shaping is achieved using an acousto-optic deflector, which can be used to produce either a composite array of static deflected beams, a rapidly-scanned painted potential, or some combination of the two approaches. The development and extension of the experimental apparatus required to implement these enhanced dressed state potentials is explored, and the challenges of their experimental implementation considered.