Browsing by Subject "absorption measurement"

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    Spectrally Dependent Radiation Noise In Thermal Emission And Long-Wave Infrared High-Q Diamond Microdisks
    (2020-03) Lee, Yu-Jen
    Spectrally Dependent Radiation Noise in Thermal Emission The theory has predicted that Bose-Einstein statistics are a fundamental feature of thermal emission into one or a few optical modes; however, the resulting Bose-Einstein-like photon noise has never been experimentally observed. There are at least two reasons for this: 1) relationships to describe the thermal radiation noise for an arbitrary mode structure have yet to be set forth, and 2) the mode and detector constraints necessary for the detection of such light is extremely hard to fulfill. Herein, photon statistics and radiation noise relationships are developed for systems with any number of modes and couplings to an observing space. The results are shown to reproduce existing special cases of thermal emission and are then applied to resonator systems to discuss physically realizable conditions under which Bose-Einstein-like thermal statistics might be observed. Examples include a single isolated cavity and an emitter cavity coupled to a small detector space. Low mode-number noise theory shows major deviations from solely Bose-Einstein or Poisson treatments and has particular significance because of recent advances in perfect absorption and subwavelength structures both in the long-wave infrared and terahertz regimes. These microresonator devices tend to utilize a small volume with few modes, a regime where the current theory of thermal emission fluctuations and background noise, which was developed decades ago for free space or single-mode cavities, has no derived solutions. Long-Wave Infrared High-Q Diamond Microdisks High-quality factor (Q) photonic devices in the room temperature thermal infrared region, corresponding to deeper long-wave infrared with wavelengths beyond 9 microns, have been demonstrated for the first time. Whispering gallery mode diamond microresonators were fabricated using single crystal diamond substrates and oxygen-based inductively coupled plasma (ICP) reactive ion etching (RIE) at high angles. The spectral characteristics of the devices were probed at room temperature using a tunable quantum cascade laser that was free-space coupled into the resonators. The light was extracted via 1) an arsenic selenide (As2Se3) chalcogenide infrared fiber and directed to a cryogenically cooled Mercury Cadmium Telluride (HgCdTe) detector or 2) directly an HgCdTe detector. The quality factors were tested in multiple microresonators across a wide spectral range from 9 to 9.7 microns with similar performance. The highest Q among these measurements was found to reach 3648 at 9.601 μm. Fourier analysis of the many resonances of each device showed free spectral ranges slightly greater than 40 GHz, matching theoretical expectations for the microresonator diameter and the overlap of the whispering gallery mode with the diamond. Long-Wave Infrared Absorption Measurement Germanium is one of the most common materials in the semiconductor industry and infrared optics. However, almost all of the whole experimental absorption spectrum for germanium between 9 and 11 μm is missing. The main reason might be that the absorption of germanium is low in this range so the most common measurement techniques such as Fourier-transform infrared spectroscopy (FTIR) or grating spectroscopy reach their detection limits. Photothermal common-path interferometry (PCI) is one of the techniques that has been developed recently and can overcome this limitation. In this experiment, a measurement using the PCI method with a quantum cascade laser (QCL) was demonstrated. Moreover, the gap of the absorption spectrum for germanium between 9 and 11 μm was filled. Furthermore, the absorption spectrum even shows a near-perfect fit to the presently calculated absorption curve between 10 and 11 μm.