An Optical Particle Counter (OPC) has been designed with a single ellipsoid reflector as the main optical element.
Photodiodes with low noise transimpedance are used to detect forward and backscatter responses of particles scattering
laser light (685 nm) at the ellipsoid focus. The Zemax® ray tracing program has been used to estimate the OPC's light
collection efficiency. The design process has included modeling the optical response of various lenses, reflector
coatings, and laser wavelengths. Simulations show that our OPC with a single ellipsoid reflector has 58.2% total
efficiency for collecting forward and backscattered light.
We report on the development of instrument concepts for a European ELT, expanding on studies carried out as part of the ESO OWL concept. A range of instruments were chosen to demonstrate how an ELT could meet or approach the goals generated by the OPTICON science team, and used to push the specifications and requirements of telescope and adaptive optics systems. Preliminary conclusions are presented, along with a plan for further more detailed instrument design and technology developments. This activity is supported by the European Community (Framework Programme 6, ELT Design Study, contract number 011863).
A new use for a 2-dimensional position sensitive diode (PSD) is described. A duolateral PSD was used with a microchannel
plate image intensifier as a proof-of-concept photon counting (event driven) imager for astronomical imaging and photometry.
This produced an imager capable of counting 25-30 kcps over the astronomical bands B, V & R, with an overall
efficiency of ~19%.
A system is described which makes best use of the high quantum efficiency and high count rate capability of avalanche
photodiodes for high time resolution observations of optical pulsars. The use of three APDs allows simultaneous photometry
of the target and a reference star, and the monitoring of the sky background. By minimising the optical components in
the light path the optical efficiency of the system is maximised. The TRIFFID1 and OPTIMA2 have shown that fibre-fed APD arrays can produce excellent results. This, new, system was used on the 6m BTA in November 2003-results on the
Crab pulsar are presented.
A new modular high time resolution imaging camera system with sub-microsecond timing accuracy has been built in the Physics Dept. of NUI, Galway. The system was designed to be mounted on large telescopes for observing the temporal, spectral and polarisation characteristics of faint astronomical objects, such as optical pulsars. The camera system developed allows simultaneous and independent observing of multiple wavebands of emission from the target objects. This is achieved using optics that split images into their different spectral or polarisation components. The system currently incorporates a multi-anode microchannel array (MAMA) photon detecting and imaging camera with a time resolution of up to 100ns. This is combined with three high quantum efficiency avalanche photodiodes (APDs) with count rates of up to 16 million photons per second. The high time resolution recording system can allow for the removal of telescope tracking inaccuracy and wind shear off-line. This yields better PSFs for bright objects such as crowded globular star clusters. This combination of different detectors allows the system to be operated as a multi purpose, high QE, high time resolution system. The modular nature of the design electronics also allows the addition and removal of detectors without limiting the performance of other elements within the system. The data path is also designed so that archiving integrity is maintained while the data path is simultaneously used for real-time analysis and display systems. Future applications in the bio-medical imaging sector are envisaged for high time resolution fluorescence imaging, and astronomical polarisation studies.
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