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Spatial Orientation and Disorientation
Published in Anthony N. Nicholson, The Neurosciences and the Practice of Aviation Medicine, 2017
In military operations, there are important tactical advantages to be gained from the use of night vision devices. However, the potential increase in safety that such devices might afford may be outweighed by the increased hazard associated with the night-time operations that they enable. Night vision goggles amplify the residual light to create a monochromatic image of the view ahead. However, they restrict the field of view to about 40 degrees and so deprive the pilot of important peripheral visual orientation cues. The image presented to the pilot is of lower resolution and its single green colour leads to problems with depth perception. In helicopter operations, the spatial disorientation accidents associated with the use of night vision goggles have most frequently involved undetected drift or descent from the hover or controlled flight into terrain or water. Other night vision devices generate a visible image using the thermal radiation from ground features. Contrast within the image is determined by the amount of infrared radiation from different objects in the field of view. This does not remain constant over time since it is dependent on the amount of previously absorbed solar radiation and the rate at which it is re-radiated during the night. More so than with daytime flying, the pilot has to exercise particular care during flight over featureless terrain when using these devices.
The Proposal for an ‘Optical Maser’
Published in Mario Bertolotti, The History of the Laser, 2004
Townes in his research set out to build an ammonia maser at a wavelength of about 0.5 mm and then converted to the much longer wavelength of 1.25 cm for reasons of convenience in construction. All the other masers built afterwards operated in the centimetre range. There was no generator based on stimulated emission able to emit in the millimetre and sub-millimetre region. Although other kinds of traditional generators had been improved, like klystrons, magnetrons and the travelling wave tubes that successfully went down to somewhat more than 1 mm, this wavelength was the shortest thought possible for these devices and their power was very low. Indeed there was no real demand for a coherent emitter in the millimetre and infrared region. One of the most important applications—night vision—employs infrared rays emitted by the thermal scene and needs only a good detector but does not need any emitter. For another important application, spectroscopy, ordinary infrared lamps had sufficient power already. Therefore there was no pressure to develop new sources. However, researchers are curious and like to extend the frontiers of knowledge. So even if without any haste, once the maser was built, one started to think towards the application of its working principle to build a light generator then referred to as an optical maser, and the task was taken up independently both in the United States and in the former Soviet Union.
Tellurium-oxide coated silicon-nitride hybrid waveguide for near-to-mid-IR supercontinuum generation: design and analysis
Published in Journal of Modern Optics, 2021
Than Singh Saini, V. R. Supradeepa
Light sources with the spectral range from ultra-violet to the visible are applicable for environmental monitoring and absorption spectroscopy. Such sources are also required for various clinical investigation techniques, including Raman spectroscopy, optical coherent tomography, etc. Light spectra spanning near-infrared (near-IR) to mid-infrared (mid-IR) are useful for guided missile technology, gas-sensing, free space communication, and mid-IR spectroscopy. Infrared light is applicable in thermal imaging and night vision equipment. In the literature, the broadband supercontinuum light has been reported using various conventional fibre, waveguide, and photonic crystal fibre geometries in different materials including silica, tellurite, and chalcogenide glasses [1–7]. Both the strong modal confinement and desire dispersion characteristic can be achieved in silica based waveguides. However, silica has a weak optical nonlinearity and therefore requires a pump source with very high peak power to generate supercontinuum spectrum. Furthermore, silica material is not transparent over 2.5 µm which restricts the spectral growth in to the mid-IR region. An ultra-broadband mid-IR supercontinuum generation was theoretically reported in a suspended germanium-membrane ridge waveguide pumped with 180 fs laser pulses centred at 4.8 µm [8]. The high power broadband mid-IR supercontinuum light with average power >10 mW can be generated in an air clad silicon-germanium waveguides pumped at 4.0 µm [9]. One of the limitations of these air clad silicon-germanium waveguides is the requirement of an unconventional laser pump source at ≥4.0 µm to generate mid-IR supercontinuum spectrum. The transparency of highly nonlinear tellurite and chalcogenide glasses can have reached upto mid-IR region. However, the dispersion profile of the chalcogenide waveguides also restricts the pumping at higher wavelengths using unconventional laser systems.