Comparison of beam generation techniques using a phase only spatial light modulator

Whether in art or for QR codes, images have proven to be both powerful and efficient carriers of information. Spatial light modulators allow an unprecedented level of control over the generation of optical fields by using digital holograms. There is no unique way of obtaining a desired light pattern however, leaving many competing methods for hologram generation. In this paper, we test six hologram generation techniques in the creation of a variety of modes as well as a photographic image: rating the methods according to obtained mode quality and power. All techniques compensate for a non-uniform mode profile of the input laser and incorporate amplitude scaling. We find that all methods perform well and stress the importance of appropriate spatial filtering. We expect these results to be of interest to those working in the contexts of microscopy, optical trapping or quantum image creation

Comparison of beam generation techniques using a phase only spatial light modulator

Whether in art or for QR codes, images have proven to be both powerful and efficient carriers of information. Spatial light modulators allow an unprecedented level of control over the generation of optical fields by using digital holograms. There is no unique way of obtaining a desired light pattern however, leaving many competing methods for hologram generation. In this paper, we test six hologram generation techniques in the creation of a variety of modes as well as a photographic image: rating the methods according to obtained mode quality and power. All techniques compensate for a non-uniform mode profile of the input laser and incorporate amplitude scaling. We find that all methods perform well and stress the importance of appropriate spatial filtering. We expect these results to be of interest to those working in the contexts of microscopy, optical trapping or quantum image creation

Cavity-enhanced frequency up-conversion in rubidium vapour

We report the first use of a ring cavity to both enhance the output power and dramatically narrow the linewidth (<1MHz) of blue light generated by four wave mixing in a rubidium vapour cell. We find that the high output power available in our cavity-free system leads to power broadening of the generated blue light linewidth. Our ring cavity removes this limitation, allowing high output power and narrow linewidth to be achieved concurrently. As the cavity blue light is widely tunable over the 85Rb 5S1/2F=3 → 6P3/2 transition, this narrow linewidth light would be suitable for second-stage laser cooling, which could be valuable for efficient 85Rb BEC production

Optimisation of arbitrary light beam generation with spatial light modulators

Phase only spatial light modulators (SLMs) have become the tool of choice for shaped light generation, allowing the creation of arbitrary amplitude and phase patterns. These patterns are generated using digital holograms and are useful for a wide range of applications as well as for fundamental research. There have been many proposed methods for optimal generation of the digital holograms, all of which perform well under ideal conditions. Here we test a range of these methods under specific experimental constraints, by varying grating period, filter size, hologram resolution, number of phase levels, phase throw and phase nonlinearity. We model beam generation accuracy and efficiency and show that our results are not limited to the specific beam shapes, but should hold for general beam shaping. Our aim is to demonstrate how to optimise and improve the performance of phase-only SLMs for experimentally relevant implementations

Gouy phase-matched angular and radial mode conversion in four-wave mixing

Studying the conversion between transverse light modes via four-wave mixing in a heated rubidium vapor, we demonstrate and explain a transfer between azimuthal and radial mode numbers. They relate to orthogonal modal dimensions, which one would not normally expect to interact. While angular momentum conservation in this nonlinear process dictates the selection rules for the angular mode number, the role of the radial mode number is more esoteric. We demonstrate systematically that the Gouy phase is the key to understanding this conversion, leading to strikingly different conversion behavior in the thick- and thin-medium regimes. Our experimental investigation of the transition between these regimes bridges the gap between previous experiments in atomic thick media and work in nonlinear crystals. Our work sets a clear starting point to explore the thick-medium regime, allowing efficient radial-to-azimuthal and radial-to-radial mode conversion

Increasing frailty is associated with higher prevalence and reduced recognition of delirium in older hospitalised inpatients: results of a multi-centre study

Purpose: Delirium is a neuropsychiatric disorder delineated by an acute change in cognition, attention, and consciousness. It is common, particularly in older adults, but poorly recognised. Frailty is the accumulation of deficits conferring an increased risk of adverse outcomes. We set out to determine how severity of frailty, as measured using the CFS, affected delirium rates, and recognition in hospitalised older people in the United Kingdom. Methods: Adults over 65 years were included in an observational multi-centre audit across UK hospitals, two prospective rounds, and one retrospective note review. Clinical Frailty Scale (CFS), delirium status, and 30-day outcomes were recorded. Results: The overall prevalence of delirium was 16.3% (483). Patients with delirium were more frail than patients without delirium (median CFS 6 vs 4). The risk of delirium was greater with increasing frailty [OR 2.9 (1.8–4.6) in CFS 4 vs 1–3; OR 12.4 (6.2–24.5) in CFS 8 vs 1–3]. Higher CFS was associated with reduced recognition of delirium (OR of 0.7 (0.3–1.9) in CFS 4 compared to 0.2 (0.1–0.7) in CFS 8). These risks were both independent of age and dementia. Conclusion: We have demonstrated an incremental increase in risk of delirium with increasing frailty. This has important clinical implications, suggesting that frailty may provide a more nuanced measure of vulnerability to delirium and poor outcomes. However, the most frail patients are least likely to have their delirium diagnosed and there is a significant lack of research into the underlying pathophysiology of both of these common geriatric syndromes

A simple, powerful diode laser system for atomic physics

External-cavity diode lasers are ubiquitous in atomic physics and a wide variety of other scientific disciplines, due to their excellent affordability, coherence length, and versatility. However, for higher-power applications, the combination of seed lasers, injection-locking and amplifiers can rapidly become expensive and complex. Here we present a high-power, single-diode laser design with specifications: >210 mW, 100 ms-linewidth .427-7/ kHz, >99% mode purity, 10 GHz mode-hop-free tuning range, and 12 nm coarse tuning. Simple methods are outlined to determine the spectral purity and linewidth with minimal additional infrastructure. The laser has sufficient power to collect 1010 87Rb atoms in a single-chamber vapor-loaded magneto-optical trap.With appropriate diodes and feedback, the system could be easily adapted to other atomic species and diode laser architectures