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Probing Power-Absorbing Structures at Near-Infrared Wavelengths using Energy Absorption Interferometry



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Moinard, Dan 


Energy Absorption Interferometry was recently proposed as an interferometric technique capable of fully characterizing the optical response of single-mode, few-mode and multi- mode power-absorbing structures, such as near-infrared detectors. A detector’s output can be written as the full spatial contraction of the external field correlation tensor and detector response correlation tensor representing their respective spatial coherence states; EAI recovers the latter, solely using power measurements. EAI is essentially a generalization of holography, and allows the reconstruction of the individual degrees of freedom through which the device under test can absorb energy, including their relative sensitivities and spatial forms. The natural modes of the detector response are intimately related to its optical coupling mechanisms and the underlying solid-state phenomena responsible for power absorption: their study therefore has direct applications in improving current infrared detector technology. In particular, device properties dependent on its geometry and material are directly obtained, such as the absorber’s spatial coherence length. EAI yields an experimental procedure where the system under test is excited with two external coherent sources, and the fringe in the total power dissipated is measured as the relative phase between the sources is varied. Iterating for multiple source positions, the fringes’ complex amplitudes allow the two-point detector response function to be retrieved: this correlation function can then be decomposed into a set of natural modes. In this thesis, we demonstrate the application of EAI at near-infrared wavelengths. We describe the theoretical basis of EAI and numerically investigate its feasibility at infrared wavelengths. We present for the first time the design of a room-temperature, fiber-based, 1550 nm-wavelength experiment and its performance. We report the first measurement of the complex-valued DRF of fiber-coupled photodetectors, with single-mode, few-mode and multi-mode behaviors; this includes extending the experimental system to suppress environmental phase drift in optical fibers. We recover the natural modes of the devices under test, and compare their spatial forms to numerical simulations. Finally, we discuss the application of EAI to many-body structures as varied as spin systems and energy-harvesting absorbers, and its extension to measure quantum correlation functions using a pair of probes creating generalized forces.





Withington, Stafford


Optics, Energy-absorption interferometry, Detectors, Modes, Optical measurements, Optical fibers, Near-infrared, Detector characterization


Doctor of Philosophy (PhD)

Awarding Institution

University of Cambridge
Science and Technology Facilities Council (1641674)
STFC (1641674)