Imaging through obscurants using time-correlated single-photon counting in the short-wave infrared

Single-photon time-of-flight (ToF) light detection and ranging (LiDAR) systems have emerged in recent years as a candidate technology for high-resolution depth imaging in challenging environments, such as long-range imaging and imaging in scattering media. This Thesis investigates the potential of two ToF single-photon depth imaging systems based on the time-correlated single-photon (TCSPC) technique for imaging targets in highly scattering environments. The high sensitivity and picosecond timing resolution afforded by the TCSPC technique offers high-resolution depth profiling of remote targets while maintaining low optical power levels. Both systems comprised a pulsed picosecond laser source with an operating wavelength of 1550 nm, and employed InGaAs/InP SPAD detectors. The main benefits of operating in the shortwave infrared (SWIR) band include improved atmospheric transmission, reduced solar background, as well as increased laser eye-safety thresholds over visible band sensors. Firstly, a monostatic scanning transceiver unit was used in conjunction with a single-element Peltier-cooled InGaAs/InP SPAD detector to attain sub-centimetre resolution three-dimensional images of long-range targets obscured by camouflage netting or in high levels of scattering media. Secondly, a bistatic system, which employed a 32 × 32 pixel format InGaAs/InP SPAD array was used to obtain rapid depth profiles of targets which were flood-illuminated by a higher power pulsed laser source. The performance of this system was assessed in indoor and outdoor scenarios in the presence of obscurants and high ambient background levels. Bespoke image processing algorithms were developed to reconstruct both the depth and intensity images for data with very low signal returns and short data acquisition times, illustrating the practicality of TCSPC-based LiDAR systems for real-time image acquisition in the SWIR wavelength region - even in the photon-starved regime.The Defence Science and Technology Laboratory ( Dstl) National PhD Schem

Optical Methods in Sensing and Imaging for Medical and Biological Applications

The recent advances in optical sources and detectors have opened up new opportunities for sensing and imaging techniques which can be successfully used in biomedical and healthcare applications. This book, entitled ‘Optical Methods in Sensing and Imaging for Medical and Biological Applications’, focuses on various aspects of the research and development related to these areas. The book will be a valuable source of information presenting the recent advances in optical methods and novel techniques, as well as their applications in the fields of biomedicine and healthcare, to anyone interested in this subject

Photonic Crystal Hydrogels: Simulation, Fabrication & Biomedical Application

Photonic crystal (PhC) hydrogels are a unique class of material that has tremendous promise as biomedical sensors. The underlying crystal structure allows for simple analysis of microstructural properties by assessing the diffraction pattern generated following laser illumination. The hydrogel medium provides elasticity, regenerability, and potential functionalization. Combining these two properties, photonic crystal hydrogels have the potential for sensing physical forces and chemical reagents using a low-cost, reusable platform. The development of biomedical sensors using this material is limited due to the lack of a method to accurately predict the diffraction pattern generated. To overcome this, a computational model was developed specifically for PhCs and validated against existing analytical models and an existing electromagnetic scattering model in the literature. Assessment of its accuracy in comparison to existing analytical equations and a more generalized multiparticle scattering model in the literature, CELES, found clear alignment. Another challenge is the lack of a technique to assess the specific positions of each particle in the crystal structure non-destructively. To overcome this, a novel fabrication approach was created using fluorescent particles, allowing subsequent confocal fluorescence microscopy and analyses to extract per-particle position information. This technique was used to directly compare experimental, computational, and analytical results within a single sample. To demonstrate a novel biomedical application of this material, ultrasound detection was chosen since it would be able to leverage the elastomeric structure of the PhC hydrogel as well as the ability to optically measure small changes in crystal microstructure. The sensitivity, frequency bandwidth, and limit of detection of fabricated PhC hydrogels were assessed using three ultrasound transducers. All transducers created a measurable optical response, with the limit of detection growing steadily with transducer frequency. These results provide evidence that the platform can be utilized across a variety of biomedical disciplines. For biomedical imaging, this platform can be used for all-optical non-contact ultrasound sensing. For cell and tissue engineering, this platform can provide a novel approach for characterizing and monitoring contractile cells, such as cardiomyocytes. Finally, for environmental engineering, this platform can be used as a continuous monitoring solution for dangerous toxins in environmental waterways

Novel Atmospheric Monitoring for the H.E.S.S. site and its Industrial Applications

This thesis concerns the atmospheric monitoring instrumentation for the H.E.S.S. (High Energy Stereoscopic System) gamma-ray telescope site and the adaptation of such instruments for commercial use. The effect of the atmosphere on the H.E.S.S. telescopes' response has been demonstrated and the technicalities associated with the atmospheric monitoring instruments have been studied in depth. The responses of a LIDAR (Light Detection And Ranging) and a transmissometer have been checked by customised MODTRAN (MODerate resolution atmospheric TRANsmission) routines. This process revealed a malfunction of the LIDAR, whose raw data was independently treated to yield meaningful results. More importantly, the `Durham-designed' transmissometer, manufactured to operate during the night in parallel with the H.E.S.S. telescopes, was successfully adapted for day-light operation. As a result Durham prototype gained strong interest from Aeronautical & General Instruments Limited (AGI) in Dorset, who are particularly interested in the airport applications, and see the Durham instrument as a potential replacement for the transmissometer which they manufacture currently and is coming to the end of its useful design life. Durham University and AGI drew up a license agreement to pursue further development of the instrument. The resulting Durham aviation transmissometer meets the accuracy requirements for the Runway Visual Range (RVR) assessment imposed by both the World Meteorological Organisation (WMO) and the International Civil Aviation Organisation (ICAO). Moreover, the Durham instrument is easy to align, uses very little power, and is lightweight and portable, enabling its use not only in civil airports, at altitudes exceeding all prior-art aviation transmissometers, but also in tactical military applications, such as remote landing strips

Optical techniques for 3D surface reconstruction in computer-assisted laparoscopic surgery

One of the main challenges for computer-assisted surgery (CAS) is to determine the intra-opera- tive morphology and motion of soft-tissues. This information is prerequisite to the registration of multi-modal patient-specific data for enhancing the surgeon’s navigation capabilites by observ- ing beyond exposed tissue surfaces and for providing intelligent control of robotic-assisted in- struments. In minimally invasive surgery (MIS), optical techniques are an increasingly attractive approach for in vivo 3D reconstruction of the soft-tissue surface geometry. This paper reviews the state-of-the-art methods for optical intra-operative 3D reconstruction in laparoscopic surgery and discusses the technical challenges and future perspectives towards clinical translation. With the recent paradigm shift of surgical practice towards MIS and new developments in 3D opti- cal imaging, this is a timely discussion about technologies that could facilitate complex CAS procedures in dynamic and deformable anatomical regions