Partially coherent interaction of the feedback light with the field in the laser cavity is affirmed with the fiber Bragg grating (FBG) stabilized 980-nm pump lasers, on the contrast of normally accepted totally incoherent state of operation in the “coherence collapse” regime. Coherence parameter y was defined in this paper to identify the fraction of feedback light working coherently. It is shown that y can be determined by fitting the measured power-difference versus pumping-rate curve to the simulation results. Experiments confirm that coherence parameter y decreases while the distance between the FBG and the laser facet increases, and vice versa. While, if the device is kept operating in the “coherence-collapse” regime, y would not change with the amount of feedback. This work will be help to improve the performance of the high power FBG stabilized 980-nm pump laser. / Thesis / Master of Applied Science (MASc)

The applications of low-light imaging are widespread in areas such as biomedical imaging, remote sensing, ratiometric imaging, lithography, etc. The goal of this work is to develop a radiometrically scaled hybrid RCWT calculator to count the photons detected for such applications. The rigorous computation of different imaging models are discussed. An approach to calibrate the radiometry of the hybrid RCWT model for partially coherent illumination is presented. The diffraction from the object is evaluated rigorously using the hybrid RCWT model. A test bench is set up to validate the radiometrically scaled simulations. In all the cases considered, simulation and experiment agree within a 40% difference.

In this thesis, I have developed a range of theoretical and numerical techniques for modelling the behaviour of partially coherent optical systems and multi-mode detectors. The numerical simulations were carried out for the ultra-low-noise Transition Edge Sensors (TESs) being proposed for use on the SAFARI instrument on the cooled aperture infrared space telescope SPICA (34 - 210 μm). The optical behaviour of the SAFARI system is described in terms of the optical modes of the telescope, as distinct from the optical modes of the detector. The performance of the TESs were assessed in terms of signal power, background power and photon noise. To establish a method for precisely characterising and calibrating ultra-low-noise TESs, a cryogenic test system was designed and engineered to measure the optical efficiencies of the SAFARI TESs. The multi-mode, partially coherent illumination conditions of the measurement system were engineered to be precisely the same as those of the telescope. A major difference between the test system and the telescope’s optics is that the telescope will have focusing elements, but the test system was designed to avoid focusing elements in order to keep the optical path as clean as possible. The theoretical formalism and numerical models were adapted accordingly to address this difference. The numerical simulations show that the test system could provide near identical optical performance as that of the telescope system even though the focusing elements were absent. I also performed experimental measurements to investigate the optical efficiencies of the multi-mode TESs. The detectors worked exceedingly well in all respects with satisfactory optical efficiencies. In addition, it has been shown that the optical model provides a good description of the optical behaviour of the test system and detectors. Further modal analysis was developed to study losses in the multi-mode horns. The optical behaviour of the waveguide-mounted thin absorbing films in the far-infrared was modelled using a mode-matching method.

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