Lossless reshaping of structured light

Structured light concerns the control of light in its spatial degrees of freedom (amplitude, phase and polarization), and has proven instrumental in many applications. The creation of structured light usually involves the conversion of a Gaussian mode to a desired structure in a single step, while the detection is often the reverse process, both fundamentally lossy or imperfect. Here we show how to ideally reshape structured light in a lossless manner in a simple two-step process. We outline the core theoretical arguments, and demonstrate reshaping of arbitrary structured light patterns, in the process highlighting when the technique is applicable and when not, and how best to implement it. This work will be a useful addition to the structured light toolkit, and particularly relevant to those wishing to use the spatial modes of light as a basis in classical and quantum communication

A deterministic detector for vector vortex states

Encoding information in high-dimensional degrees of freedom of photons has led to new avenues in various quantum protocols such as communication and information processing. Yet to fully benefit from the increase in dimension requires a deterministic detection system, e.g., to reduce dimension dependent photon loss in quantum key distribution. Recently, there has been a growing interest in using vector vortex modes, spatial modes of light with entangled degrees of freedom, as a basis for encoding information. However, there is at present no method to detect these non-separable states in a deterministic manner, negating the benefit of the larger state space. Here we present a method to deterministically detect single photon states in a four dimensional space spanned by vector vortex modes with entangled polarisation and orbital angular momentum degrees of freedom. We demonstrate our detection system with vector vortex modes from the |[Formula: see text]| = 1 and |[Formula: see text]| = 10 subspaces using classical and weak coherent states and find excellent detection fidelities for both pure and superposition vector states. This work opens the possibility to increase the dimensionality of the state-space used for encoding information while maintaining deterministic detection and will be invaluable for long distance classical and quantum communication

Genome-Wide Distribution of RNA-DNA Hybrids Identifies RNase H Targets in tRNA Genes, Retrotransposons and Mitochondria

During transcription, the nascent RNA can invade the DNA template, forming extended RNA-DNA duplexes (R-loops). Here we employ ChIP-seq in strains expressing or lacking RNase H to map targets of RNase H activity throughout the budding yeast genome. In wild-type strains, R-loops were readily detected over the 35S rDNA region, transcribed by Pol I, and over the 5S rDNA, transcribed by Pol III. In strains lacking RNase H activity, R-loops were elevated over other Pol III genes, notably tRNAs, SCR1 and U6 snRNA, and were also associated with the cDNAs of endogenous TY1 retrotransposons, which showed increased rates of mobility to the 5'-flanking regions of tRNA genes. Unexpectedly, R-loops were also associated with mitochondrial genes in the absence of RNase H1, but not of RNase H2. Finally, R-loops were detected on actively transcribed protein-coding genes in the wild-type, particularly over the second exon of spliced ribosomal protein genes

Human Pose Inference Using an Elevated mmWave FMCW Radar

Human monitoring using radar systems operating in the GHz regime has generated significant interest as a result of the increasing availability of commercial radar systems. These sensors offer all weather performance, the ability to measure range and velocity, and the protection of anonymity. However, visually inferring activities present in radar data is often challenging without prior knowledge. Here, we address this by implementing a radar-to-pose system that converts the raw radar data into human poses, such that human forms can be identified and activities monitored. In comparison to prior works, we place our radar in an elevated position, more in line with the placement of existing real world monitoring systems e.g. cameras, or emerging systems, e.g. quadcopters. We present an ensemble predictor network and apply it to a number of human poses of increasing complexity, reporting accuracies in excess of 90%, and verify the generalizable nature of our approach with unseen validation data. We perform an in depth explainability analysis, exploiting the unique mappings created by our radar placement and network structure to confirm that the network is making rational predictions based on the true location of limbs

Imaging the temporal profile of structured optical modes

Spatially structured optical modes exhibit a group velocity lower than c, resulting in a measurable temporal delay with respect to plane waves. Here, we develop a technique to image this temporal delay and measure it across a set of optical modes. An inevitable consequence of spatially varying delay is temporal broadening of the mode. As such, for a focused Gaussian, we observe an ≈ 1 % increase in the temporal profile, corresponding to a narrowing of the optical spectrum by ≈ 0.03 nm. This work shows that imaging is essential to fully understanding the changes to the group velocity for structured modes.</p

General design principle for structured light lasers

Using custom laser cavities to produce as the output some desired structured light field has seen tremendous advances lately, but there is no universal approach to designing such cavities for arbitrarily defined field structures within the cavity, e.g., at both the output and gain ends. Here we outline a general design approach for structured light from lasers which allows us to specify the required cavity for any selected structured light fields at both ends. We verify the approach by numerical simulation as well as by an unwrapped cavity experiment. The power of this approach is that the cavity can be designed to maximise the overlap with the available pump for higher powers, minimise thermal effects for higher brightness, and at the same time output a desired structured light field that may differ substantially from the gain-end profile. These benefits make this work appeal to the large laser communities interested in cavities for high brightness and/or customized output beams