The implementation of spatial light modulators (SLMs) in quantum gas experiments has allowed the realization of ever more complex trapping geometries. As ultracold atoms may be sensitive to perturbations of the trapping potential at the 1% level, the high contrast ratios of digital micromirror devices are proving advantageous for use in optical trapping. Our laboratory pursues configurable traps based on the direct (nearly diffraction limited) imaging of a digital micromirror device (DMD). We achieve highly flexible potentials using commercially available microscope objectives external to our vacuum chamber that directly project the DMD to the atom plane, producing optical traps over an area of 130 μm × 200 μm, with a resolution of 630(10) nm full width at half maximum (FWHM) at 532 nm illumination. We combine these potentials with a horizontally propagating TEM00 or TEM01 Hermite-Gaussian optical sheet that provides vertical confinement. With the dynamic control enabled by the maximum full-frame rate of 20 KHz and on-board storage of <13,000 frames of the DMD, we study the transport of atoms and superfluid dynamics in configurable trapping geometries. Using the fast frame rate of the DMD we also produce intermediate grey levels that complement half-toning techniques for producing optimized grayscale patterns.
The implementation of spatial light modulators (SLMs) in quantum gas experiments has allowed the realization of ever more complex trapping geometries. As ultracold atoms may be sensitive to perturbations of the trapping potential at the 1% level, the high contrast ratios of digital micromirror devices are proving advantageous for use in optical trapping. Our laboratory pursues configurable traps based on the direct (nearly diffraction limited) imaging of a digital micromirror device (DMD). We achieve highly flexible potentials using commercially available microscope objectives external to our vacuum chamber that directly project the DMD to the atom plane, producing optical traps over an area of 130 μm × 200 μm, with a resolution of 630(10) nm full width at half maximum (FWHM) at 532 nm illumination. We combine these potentials with a horizontally propagating TEM00 or TEM01 Hermite-Gaussian optical sheet that provides vertical confinement. With the dynamic control enabled by the maximum full-frame rate of 20 KHz and on-board storage of <13,000 frames of the DMD, we study the transport of atoms and superfluid dynamics in configurable trapping geometries. Using the fast frame rate of the DMD we also produce intermediate grey levels that complement half-toning techniques for producing optimized grayscale patterns.
The development of novel trapping potentials for degenerate quantum gases has been an important factor driving experimental progress in the field. The introduction of spatial light modulators (SLMs) into quantum gas laboratories means that a range of configurable geometries are now possible. Here we demonstrate the production of arbitrary and dynamic high-resolution traps for Bose-Einstein condensates (BECs) using a (1200 x 1920) pixel digital-micromirror device (DMD) and commercially available microscope objectives. Direct imaging of the DMD provides significant advantages over phase-based SLMs, while still providing high resolution projected patterns. We find that atoms confined in a hybrid optical/magnetic or all-optical potential can be patterned using repulsive blue- detuned (532 nm) light with 630(10) nm full-width at half-maximum (FWHM) resolution, while imaging at 780 nm similarly achieves 960(80) nm resolution FWHM, within 5% and 8% of the diffraction limit respectively. This performance is > 7 times improved over previously reported DMD trapping. The result is near arbitrary control of the atomic distribution over the spatial extent of the BEC trapping volume. Furthermore, we produce time-averaged potentials with the DMD, demonstrating the ability to produce multiple grayscale levels with minimal heating of the atomic cloud. These techniques, along with the high level of dynamic control afforded by DMDs, will enable the realization and control of diverse optical potentials for superfluid dynamics and atomtronics applications with quantum gases.
Programable spatial light modulators (SLMs) have significantly advanced the configurable optical trapping of particles. Typically, these devices are utilized in the Fourier plane of an optical system, but direct imaging of an amplitude pattern can potentially result in increased simplicity and computational speed. Here we demonstrate high-resolution direct imaging of a digital micromirror device (DMD) at high numerical apertures (NA), which we apply to the optical trapping of a Bose-Einstein condensate (BEC). We utilise a (1200 x 1920) pixel DMD and commercially available 0.45 NA microscope objectives, finding that atoms confined in a hybrid optical/magnetic or all-optical potential can be patterned using repulsive blue-detuned (532 nm) light with 630(10) nm full-width at half-maximum (FWHM) resolution, within 5% of the diffraction limit. The result is near arbitrary control of the density the BEC without the need for expensive custom optics. We also introduce the technique of time-averaged DMD potentials, demonstrating the ability to produce multiple grayscale levels with minimal heating of the atomic cloud, by utilising the high switching speed (20 kHz maximum) of the DMD. These techniques will enable the realization and control of diverse optical potentials for superfluid dynamics and atomtronics applications with quantum gases. The performance of this system in a direct imaging configuration has wider application for optical trapping at non-trivial NAs.
Configurable trapping potentials are of great interest in cold atom physics, as they enable production of dynamical highly flexible fields that exhibit unprecedented stability and diverse geometries. Direct imaging can be used to create large area trapping potentials but is often overlooked due to its inability to correct for wavefront aberrations of the optical system [1]. This need not be a major disadvantage for a well-corrected optical system and brings advantages including the simplicity and speed of direct imaging. This is in contrast to the Fourier plane method which requires complex calculations to generate proper holograms and suffers from phase defects and speckle. For applications in cold atom trapping, these effects are especially detrimental as the atoms are sensitive to perturbations at the ~1% level of the optical potential. Our approach uses off-the-shelf lenses and microscope objectives and is able to achieve 630(10) nm full width half maximum (FWHM) patterning resolution using a 0.45 NA objective, within 5% of the diffraction limit of the system, while imaging through 1.25 mm of glass. The light field patterning is done using a digital micromirror device (DMD) which allows for dynamic trapping potentials due to its ability to store 13,889 frames and its 22 kHz full frame refresh rate. We use this method to pattern planar potentials for the purpose of cold atom experiments and have found that for atoms, which tend to respond relatively slowly to perturbations, it is possible to combine half-toning and time averaging to produce grey scale patterns, additionally allowing for pattern correction [2]. [1] P. C. Mogensen and J. Glückstad, Optics Communications 175, 75–81 (2000). [2] G. Gauthier, I. Lenton, N. McKay Parry, M. Baker, M. J. Davis, H. Rubinsztein-Dunlop, and T. W. Neely, arXiv preprint arXiv:1605.04928 (2016).
This thesis focusses on the use of a Digital Micromirror Device (DMD) to produce spatially and temporally varying optical potentials for the manipulation of ultracold atoms. I discuss the apparatus used to generate ultracold atomic samples as well as that used to manipulate them, including a comparison of the various light sources used with the DMD. Here I demonstrate the advantages in image quality that can be achieved using a superluminescent diode. I also report on work which uses the capability to produce spatially and temporally controlled potentials to engineer a synthetic dimension of harmonic oscillator sites, forming a lattice consisting of 10s of lattice sites on which Bloch Oscillations are demonstrated. Finally I describe simulations which demonstrate the clustering behaviour of quantised vortices in a Bose-Einstein condensate when arranged in linear structures, as could be done by the method of phase imprinting using a DMD. I demonstrate the use of a cluster detection algorithm which is novel in the field of quantised vortices, and show that in many cases, vortex clusters can be modelled by methods similar to those used for single vortices.
Digital micromirror devices (DMDs) have seen recent popularity as spatial light modulators (SLMs) for arbitrary and dynamic potential generation in the manipulation of neutral atom systems for quantum simulation and quantum computing platforms. In enabling the use of a DMD for this purpose, its latency, frame rate, and micromirror movement dynamics must be well characterized for various settings. In this paper, we present our FPGA-based system to control the DMD and the optical setup developed for its verification. Image information and control parameters are generated and configured using a Python user interface and sent to the FPGA using a C++ wrapper and the Cypress FX2 USB protocol. The FPGA design enables the leveraging of the high frame rate capabilities of the DMD as well as ensuring deterministic operation by first storing this USB data on an external DDR memory and updating the micromirror states upon receiving an external trigger pulse. The DMD is imaged onto a scientific camera and two photodiodes as a means of verifying the system behavior and investigating the metrics of interest. Using this framework, the DLP7000 consisting of 768x1024 micromirrors has been shown to refresh at 22 kHz with 45.4 μs latency. Furthermore, a single block consisting of 48x1024 micromirrors is able to refresh at 140 kHz with 7.1 μs latency. The loading and clearing behavior of micromirrors has also been characterized for varying refresh rates.
This thesis describes the progress achieved towards two goals. One is the construction of a compact magneto-optical trap (MOT) apparatus, used both as a standalone undergraduate laboratory experiment and as part of a public engagement demonstration of cold atom physics. The setup, which utilises a dichroic atomic vapour laser lock (DAVLL) system plus homemade sideband generation electronics, is capable of trapping and cooling up to 8x10⁷ ⁸⁵Rb atoms in a standard six-beam laser cooling scheme. The second goal is the loading of an ultracold ensemble of ⁸⁷Rb atoms into novel optical trap geometries using a phase-only liquid crystal spatial light modulator (LC SLM) for applications to atomtronics and quantum simulation. Details of a double vacuum chamber apparatus, designed to produce the first Bose-Einstein condensates (BECs) at St Andrews, are provided. The setup incorporates a hybrid trap evaporative cooling scheme towards quantum degeneracy and reliably produces BECs of 1.9 10⁵ ⁸⁷Rb atoms. Two computational techniques, developed during the course of this project, are presented with the aim of creating flexible, smooth holographic optical traps. The first method illuminates a single SLM with overlapped, co-propagating light beams of different wavelengths to create a composite optical pattern for atom manipulation. The second uses conjugate gradient minimisation to create exceptionally high fidelity light patterns in both amplitude and phase for light in the output plane. These techniques, combined with the implementation of a light sheet into the experimental setup, are used to trap atoms in both a ring profile and in a set of narrow waveguides connected with a tunnelling barrier.