EChO Payload electronics architecture and SW design

EChO is a three-modules (VNIR, SWIR, MWIR), highly integrated spectrometer, covering the wavelength range from 0.55 $\mu$m, to 11.0 $\mu$m. The baseline design includes the goal wavelength extension to 0.4 $\mu$m while an optional LWIR module extends the range to the goal wavelength of 16.0 $\mu$m. An Instrument Control Unit (ICU) is foreseen as the main electronic subsystem interfacing the spacecraft and collecting data from all the payload spectrometers modules. ICU is in charge of two main tasks: the overall payload control (Instrument Control Function) and the housekeepings and scientific data digital processing (Data Processing Function), including the lossless compression prior to store the science data to the Solid State Mass Memory of the Spacecraft. These two main tasks are accomplished thanks to the Payload On Board Software (P-OBSW) running on the ICU CPUs.Comment: Experimental Astronomy - EChO Special Issue 201

A light-in-flight single-pixel camera for use in the visible and short-wave infrared

This is the final version. Available on open access from the Optical Society of America via the DOI in this recordSingle-pixel cameras reconstruct images from a stream of spatial projection measurements recorded with a single-element detector, which itself has no spatial resolution. This enables the creation of imaging systems that can take advantage of the ultra-fast response times of single-element detectors. Here we present a single-pixel camera with a temporal resolution of 200 ps in the visible and short-wave infrared wavelengths, used here to study the transit time of distinct spatial modes transmitted through few-mode and orbital angular momentum mode conserving optical fiber. Our technique represents a way to study the spatial and temporal characteristics of light propagation in multimode optical fibers, which may find use in optical fiber design and communications.Engineering and Physical Sciences Research Council (EPSRC)European Union Horizon 2020Office of Naval Research (ONR)National Science Foundation (NSF

Short-Wave Infrared Compressive Imaging of Single Photons

We present a short-wave infrared (SWIR) single photon camera based on a single superconducting nanowire single photon detector (SNSPD) and compressive imaging. We show SWIR single photon imaging at a megapixel resolution with a low signal-to-background ratio around 0.6, show SWIR video acquisition at 20 frames per second and 64x64 pixel video resolution, and demonstrate sub-nanosecond resolution time-of-flight imaging. All scenes were sampled by detecting only a small number of photons for each compressive sampling matrix. In principle, our technique can be used for imaging faint objects in the mid-IR regime

Ultrafast Laser Control of Molecular Quantum Dynamics from a Core-Electron Perspective

This work introduces two experimental approaches to control quantum dynamics in molecules, employing core electrons as messengers. A laser source providing ultrashort pulses has been developed to access the timescale of electronic and structural dynamics inside molecules. Pulses of few-cycle durations in the 1 µm to 2 µm short-wavelength infrared (SWIR) spectral region provide intensities up to 1015 W/cm2 . In combination with a vacuum beamline, this experimental setup allows for ultrafast laser control of molecular dynamics probed by core-electron transitions via x-ray absorption spectroscopy (XAS). The first experiment investigates the manipulation of molecular electronic structure. Here, a soft x-ray (SXR) pulse probes simultaneously to an SWIR pulse of variable intensity. The measured intensityvii dependent absorbance changes in SF6 reveal an increased effective electronic-exchange energy. This demonstrates the alteration of this purely quantum-mechanical component of the electron-electron interaction for the first time. In a second experiment, an SWIR pulse induces coherent molecular vibrations with amplitudes of ten times the diameter of the nucleus. Subsequently, a time-delayed SXR pulse probes the bond-length changes via core-level transitions. This enables an unprecedented 14 femtometer precision which paves the way for site-specific vibrational metrology in gas-phase molecules. Overall, these results enable ultrafast chemical control on a quantum level

Organic Bulk Heterojunction Infrared Photodiodes for Imaging Out to 1300 nm

This work studies organic bulk heterojunction photodiodes with a wide spectral range capable of imaging out to 1.3 μm in the shortwave infrared. Adjustment of the donor-to-acceptor (polymer:fullerene) ratio shows how blend composition affects the density of states (DOS) which connects materials composition and optoelectronic properties and provides insight into features relevant to understanding dispersive transport and recombination in the narrow bandgap devices. Capacitance spectroscopy and transient photocurrent measurements indicate the main recombination mechanisms arise from deep traps and poor extraction from accumulated space charges. The amount of space charge is reduced with a decreasing acceptor concentration; however, this reduction is offset by an increasing trap DOS. A device with 1:3 donor-to-acceptor ratio shows the lowest density of deep traps and the highest external quantum efficiency among the different blend compositions. The organic photodiodes are used to demonstrate a single-pixel imaging system that leverages compressive sensing algorithms to enable image reconstruction

The development of optical projection tomography instrumentation and its application to in vivo three dimensional imaging of zebrafish

OPT is a three dimensional (3D) imaging technique that can produce 3D reconstructions of transparent samples, requiring only a widefield imaging system and sample rotation. OPT can be readily applied to chemically cleared samples, or to live transparent organisms such as nematodes or zebrafish. For preclinical imaging, there is a trade-off between optical accessibility and biological relevance to humans. Adult Danio rerio (zebrafish) represent a promising compromise, with greater homology to humans than smaller animals, and superior optical accessibility than mice. However, their size and physiology present a number of imaging challenges including non-negligible absorption and optical scattering, and limited time for image data acquisition if the fish are to be recovered for longitudinal studies. A key goal of this PhD thesis research was to develop OPT to address these challenges and improve in vivo imaging capabilities for this model organism. This thesis builds on previous work at Imperial where angularly multiplexed OPT using compressed sensing was developed and applied to in vivo imaging of a cancer-burdened adult zebrafish, with a sufficiently short OPT data acquisition time to allow recovery of the fish after anaesthesia. The previous cross-sectional study of this work was extended to a longitudinal study of cancer progression that I undertook. The volume and quality of data acquired in the longitudinal study presented a number of data processing challenges, which I addressed with improved automation of the data processing pipeline and with the demonstration that convolutional neural networks (CNN) could replace the iterative compressed sensing algorithm previously used to suppress artifacts when reconstructing undersampled OPT data sets. To address the issue of high attenuation through the centre of an adult zebrafish, I developed conformal-high-dynamic-range (C-HDR) OPT and demonstrated that it could provide sufficient dynamic range for brightfield imaging of such optically thick samples, noting that transmitted light images can provide anatomical context for fluorescence image data. To reduce the impact of optical scattering in OPT, I developed a parallelised quasi-confocal version of OPT called slice-illuminated OPT (slice-OPT) to reject scattered photons and demonstrated this with live zebrafish. To enable 3D imaging with short wave infrared (SWIR) light, without the requirement of an expensive Ge or InGaAs camera, I implemented a single pixel camera and demonstrated single-pixel OPT (SP-OPT) for the first time.Open Acces

Fast and Accurate Retrieval of Methane Concentration from Imaging Spectrometer Data Using Sparsity Prior

The strong radiative forcing by atmospheric methane has stimulated interest in identifying natural and anthropogenic sources of this potent greenhouse gas. Point sources are important targets for quantification, and anthropogenic targets have potential for emissions reduction. Methane point source plume detection and concentration retrieval have been previously demonstrated using data from the Airborne Visible InfraRed Imaging Spectrometer Next Generation (AVIRIS-NG). Current quantitative methods have tradeoffs between computational requirements and retrieval accuracy, creating obstacles for processing real-time data or large datasets from flight campaigns. We present a new computationally efficient algorithm that applies sparsity and an albedo correction to matched filter retrieval of trace gas concentration-pathlength. The new algorithm was tested using AVIRIS-NG data acquired over several point source plumes in Ahmedabad, India. The algorithm was validated using simulated AVIRIS-NG data including synthetic plumes of known methane concentration. Sparsity and albedo correction together reduced the root mean squared error of retrieved methane concentration-pathlength enhancement by 60.7% compared with a previous robust matched filter method. Background noise was reduced by a factor of 2.64. The new algorithm was able to process the entire 300 flightline 2016 AVIRIS-NG India campaign in just over 8 hours on a desktop computer with GPU acceleration.Comment: 13 pages, 11 figure

Generation of 1.5-octave intense infrared pulses by nonlinear interactions in DAST crystal

Infrared pulses with large spectral width extending from 1.2 to 3.4 μ m are generated in the organic crystal DAST (4-N, N-dimethylamino-4′-N′-methylstilbazolium tosylate). The input pulse has a central wavelength of 1.5 μ m and 65 fs duration. With 2.8 mJ input energy we obtained up to 700 μ J in the broadened spectrum. The output can be easily scaled up in energy by increasing the crystal size together with the energy and the beam size of the pump. The ultra-broad spectrum is ascribed to cascaded second order processes mediated by the exceptionally large effective χ 2 nonlinearity of DAST, but the shape of the spectrum indicates that a delayed χ 3 process may also be involved. Numerical simulations reproduce the experimental results qualitatively and provide an insight in the mechanisms underlying the asymmetric spectral broadening