As part of investigating the human perception of polarized light, Haidinger’s brushes (HB) is well-known optical phenomena. Although differences in the human polarization perception were well known there was a limited quantifying to them. This paper presents a 3D Stokes model of the human polarized light perception, views the human perception of polarized light as a multivariable applied optics problem to simulation and explored the optical phenomena of Haidinger’s brushes. The images comparison verifies that the simulation patterns and detected images are consistent which proves the model is appropriate for simulating polarization perception of the human eye. Then this paper explored the optical limitations of perception and macula density. The combination of the 3D Stokes model and experimental verification opens up new possibilities to become an early diagnostic method for eye polarization sensitivity and macular degeneration. The objective is to give purpose and new mathematics understanding to the biomedical optical phenomenon.
This paper discusses the resolution required to provide a ‘new affordable generation’ of ophthalmic instrumentation for imaging the retina. The paper describes the evolution of the direct ophthalmoscope as a device that can capture digital images of sufficient detail and contrast such that they both medically useful and can form a wide-field composite image of the human retina comparable to that of a fundus camera.
During the early stages of diagnosis, medical practitioners often rely on an ophthalmoscope for making a first inspection of the retina. It is an instrument which has taken considerable time to change from human observation to a digitally processed image. There is a good reason for this, the instrument relies on the near to diffraction limited imaging ability of the human eye and the ability of the user to scan the instrument over the retina to create a high resolution contiguous mental image. Whereas the more sophisticated instruments such as the fundus camera relies on conventional imaging technology to make a digital imaging record of the retina. The digital ophthalmoscope described creates an image with 5μm resolution over the whole retina.
This paper discusses the comparison of the of resolution quality which can be achieved using digital storage of retinal imaging. Two devices will be considered the direct ophthalmoscope, which is essentially a hand-held portable device for direct inspection and the fundus camera. The analysis argues that currently the resolution of digital camera technology used in the fundus camera, particularly those used for mobile scanning, limits its optical diagnostic power. Whereas, a digital ophthalmoscope using well tried imaging stitching software and digital processing provides an alternative higher imaging resolution, hand-held portable alterative.
In the last two decades digital holography emerged as one of the most promising techniques for obtaining the complex
object-wave (amplitude and phase). However, due to the coherent nature of the light source used in digital holography,
the reconstructed hologram is subjected to speckle noise. Moreover, the resolution and size of the sensor employed in
digital holography are smaller compared to the formerly used holographic plates in optical holography. This results in a
reduced resolution for the reconstructed hologram. This paper discusses two resolution improvement methods, which are
both based on the same recording process. However, the recorded data is processed differently to obtain a resolution
improved reconstruction. The two methods are compared in terms of corresponding optical resolution, phase accuracy
and processing time.
A low-cost, robust, versatile digital shadowgraph visualization system is presented that provides a fast nonintrusive diagnostic for unsteady high-speed flows. The technique is particularly designed for real-time automated tracking of shock positions, enabling high-speed active shock control. The visualization system is based on a high-intensity white LED light source combined with a CMOS-imaging sensor, providing the system with three modes of operation: (1) high-resolution overall instantaneous visualization; (2) high-resolution visualization showing spatial-temporal variations in the flow field, allowing direct identification of areas where changes occur; (3) adjustable windowed visualization at reduced resolution at high frame rate (currently up to 980 Hz). Experimental results are presented together with numerical simulations based on the high-accuracy NTS Navier-Stokes solver and Roe's flux difference splitting method. The flow studied is an adjustable underexpanded jet flow coming from a nozzle that is placed in a counterflowing Mach-2 flow. The interaction of the two flows results in a complex shock and expansion pattern, providing a challenging configuration for the numerical flow solver. By modulating the jet, high-frequency changes are induced in the interaction pattern, allowing simulation of shock movement in a supersonic inlet. Good correspondence between measured and numerical shock position and angle is found.
Two passive optical techniques are described to investigate combustion. Optical Emission Tomography (OET) is used for non-intrusive study of heat release through the detection of chemiluminescence by the hydroxyl radical that is generated in the burning process. The OET technique described here is based on a passive fibre-optic detection system, which allows spatially resolved high-frequency detection of the flame front in a combustion flame, where all fibres detect the emission signals simultaneously. The system withstands the high pressures and temperatures typically encountered in the harsh environments of gas turbine combustors and IC engines. The sensor-array is non-intrusive, low-cost, compact, simple to configure and can be quickly set up around a combustion field. The maximum acquisition rate is 2 kHz. This allows spatially resolved study of the fast phenomena in combustion. Furthermore, the production of NOx is investigated through the emission of green light as a result of adding tri-methyl-borate to a flame. In combustion, the tri-methyl-borate produces green luminescence in locations where NOx would be produced. Combining the green luminescence visualisation with OET detection of the hydroxyl radical allows monitoring of heat release and of NOx production areas, thus giving a means of studying both the burning process and the resulting NOx pollution.
The mechanisms involved in infrared laser tissue ablation are studied using a free electron laser (FELIX) in order to clarify whether the increased ablation efficiency reported in literature for certain infrared wavelengths is due to a wavelength effect or to the specific pulse structure of the lasers that are generally used in these studies. Investigations are presented of ablation of vitreous from pigs’ eyes using several techniques including protein gel electrophoresis and ablation plume visualization. The ablation effects of three different infrared wavelengths are compared: 3 mm, which is currently in clinical surgical use, and the wavelengths associated with the amide I and amide II bands, i.e. 6.2 mm and 6.45mm, respectively. The results suggest a different ablation mechanism to be in operation for each studied wavelength, thus indicating that the generally reported increased ablation efficiency in the 6-6.5 micron range is due to the wavelength rather than the typical free electron laser pulse structure.
A low-cost and low-maintenance digital focused shadowgraph flow visualization system has been developed to provide fast diagnostics of rapidly changing phenomena in supersonic flows. The system is particularly designed for tracking shock positions in a supersonic inlet, enabling high-speed active shock control. It is based on a low-cost, high-intensity white LED light source, which can be flashed with microsecond pulses enabling freeze-frame imaging of constant illumination quality. The system features three modes of operation: (1) High-resolution digital still frames and sequences (1280 x 1024, 2fps), (2) High-resolution digital frames and sequences showing spatial-temporal variation in flow field (1280 x 1024, 12 fps), (3) Adjustable windowed digital frames at reduced resolution, but at high frame rates (980 fps at 1280 x 8 pixel viewing area). The three modes of operation allow high-speed tracking of flow features such as moving of shock waves (up to 980 Hz) as well as overall instantaneous views of the flow. Furthermore, it allows direct identification of areas where high-speed changes occur. The positional shock data can be transmitted directly to a shock-stabilizing control system. Results are presented of the unsteady flow generated by an aspirated cone-shaped nozzle in a supersonic flow in the supersonic wind tunnel of the MIT Gas Turbine Laboratory.
A sensitive CO2 laser-based photoacoustic (PA) detector has been used to perform non-invasive and on-line measurements of ethene (C2H4) production from exhaled air and directly emitted from the skin. Ethene was used as indicator for free- radicals induced lipid peroxidation in the skin of human subjects exposed to ultraviolet (UV) radiation from a solarium. Ethene from the exhaled air was analyzed for a group of 21 male subjects at rest. During 15 minutes of UV exposure, the average ethene emission was 17.2 pmol/kg/min (SD 7.3), while the pre-UV exposure levels were 1.4 pmol/kg/min (SD 0.38). Different types of sun protection creams were tested by means of ethene release in exhaled air. The influence of UV radiation intensity and of exposure time (10 and 15 minutes, respectively) on the ethene emission from the skin has been studied for a second group of 12 subjects. Comparison between measurements of exhaled air and directly on the skin is presented.
A rugged optical method has been designed for making measurements in a hostile industrial environments such as the combustion exit flow ofa gas turbine engine. Typically the gas temperature in such a combustor is 1000 K and the speed of the flow 700m/s. A transient shock tube has been constructed at MET (Massachusetts Institute of Technology ). The objective being to simulate the mixing rate for different types of exit combustor exit nozzles. A direct particle visualisation approach has been developed combining a c/w Argon/ion laser and an electronically shuttered image intensifier. The combination has been used measure the density distribution average over the complete 3ms run time ofthe transient shock tube facility. The system also has the potential to measure the entrainment of the surrounding ambient air and make velocity measurements.
The study of a self-excited compressible jet using single and double-pulsed, phase-shifted interferometry in conjunction with a 9 beam tomographic illumination system is described. A plane wave holographic interferometer using a pulsed ruby laser has been adapted to provide multiple illumination directions of a volume that is approximately 4 centimeters on a side. This set-up is being used to study the transient behavior of compressible jets and may be operated using double-exposure holographic interferometry to study the instantaneous behavior of the flow; alternatively, the system may ge operated in a double-pulse mode to study the fluctuations in the flow. The tomographic reconstructions are made using a Fourier-Bessel expansion. To illustrate the performance of the system, an oscillating pipe-collar nozzle flow producing a wavy flow pattern was studied. The instantaneous measurements show the flow to be oscillating in one plane, whereas from the differential results it is found that this plane is rotating during the oscillation period.
The study of an underexpanded compressible jet using pulsed, phase- shifted interferometry in conjunction with a 9 beam tomographic illumination system is described. A plane wave holographic interferometer using a pulsed ruby laser has been adapted to provide multiple illumination directions of a volume that is approximately 4 centimeters on a side. This set-up is being used to study the transient behavior of compressible jets and may be operated using double-exposure holographic interferometry to study the instantaneous behavior of the flow; alternatively, the system may be operated in a double-pulse mode to study the fluctuations in the flow. The tomographic reconstructions are made using a Fourier-Bassel expansion. To illustrate the performance of the system, an underexpanded nozzle flow producing a series of compression-rarefaction 'diamonds' was studied. The images show sharp reconstructions of the compression-rarefaction diamond pattern as well as some interesting secondary flow structures.
The flow field around an axi-symmetric blunt nose cylinder-flare model has been studied experimentally using a holographic interferometry system with digital image post-processing. The model was placed in a supersonic flow field at a Mach number of 2.95 and at angles of incidence between 0 degree(s) and 20 degree(s). The results have been compared to inviscid flow calculations with a 3D Euler code.
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