Question

Design a portable electro-optic instrument that can measure the color of the sky. Be specific. Describe the optical elements, field-of-view, detectors and sensors, and readout method.

Answer 1

PORTABLE ELECRO-OPTIC INSTRUMENT:-

The atmosphere cause a wide range of spectacular optical phenomena. The blue colour of the sky is a direct result of Rayleigh scattering which redirects higher frequency (blue) sunlight back into the field of view of the observer. Because blue light is scattered more easily than red light, the sun takes on a reddish hue when it is observed through a thick atmosphere, as during a sunrise or sunset. Additional particulate matter in the sky can scatter different colours at different angles creating colourful glowing skies at dusk and dawn. Scattering off of ice crystals and other particles in the atmosphere are responsible for halos, afterglows, coronas, rays of sunlight, and sun dogs. The variation in these kinds of phenomena is due to different particle sizes and geometries.

Mirages are optical phenomena in which light rays are bent due to thermal variations in the refraction index of air, producing displaced or heavily distorted images of distant objects. Other dramatic optical phenomena associated with this include the Novaya Zemlya effect where the sun appears to rise earlier than predicted with a distorted shape. A spectacular form of refraction occurs with a temperature inversion called the Fata Morgana where objects on the horizon or even beyond the horizon, such as islands, cliffs, ships or icebergs, appear elongated and elevated, like "fairy tale castles".

Rainbows are the result of a combination of internal reflection and dispersive refraction of light in raindrops. A single reflection off the backs of an array of raindrops produces a rainbow with an angular size on the sky that ranges from 40° to 42° with red on the outside. Double rainbows are produced by two internal reflections with angular size of 50.5° to 54° with violet on the outside. Because rainbows are seen with the sun 180° away from the centre of the rainbow, rainbows are more prominent the closer the sun is to the horizon.

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OPTICAL ELEMENTS :-

Many laser applications require optical elements to focus or shape the beam. Chapter 2 described the focusing properties of laser light, including the minimum diffraction-limited focal spot size and the effect of spherical aberration. The discussion in that chapter was limited to single-element lenses (singlets) with spherical surfaces. Here, we will describe some of the choices available for optical elements for use with lasers, and discuss how they may improve the focusing for laser applications.

As we saw, in many cases singlet lenses yield focal spots with diameter dominated by spherical aberration, rather than by diffraction. In such cases, the focal diameter may be reduced by use of multielement lenses or lenses with specially formed surfaces that are not spherical (aspheric lenses). The simplest case is that of a two-element spherical lens (doublet). A properly designed doublet lens can reduce the distortion of the wavefront as it passes through the lens, and it can also substantially reduce the effect of aberrations that increase the focal diameter above the diffraction limit. The cost of doublet lenses is higher than that of singlets, but the performance advantages may often be worth the added cost. Doublet lenses used with lasers should generally be air-spaced, rather than cemented lenses. The high laser irradiance can easily damage the cement. Another option is the use of aspheric lenses, which can give excellent performance and which theoretically may be designed to eliminate spherical aberration completely. But aspherics are difficult to polish accurately, and their cost becomes very high. Aspheric optics may now be fabricated by a computer-controlled diamond turning process, and they are becoming more readily available than in the past. Still, aspheric lenses are usually employed only in specialized cases where a high degree of control of wavefront errors is needed.

FIELD OF VIEW :-

The field of view is the extent of the observable world that is seen at any given moment. In the case of optical instruments or sensors it is a solid angle through which a detector is sensitive to electromagnetic radiation. the term "field of view" is typically only used in the sense of a restriction to what is visible by external apparatus, like when wearing spectacles or virtual reality goggles. Note that eye movements are allowed in the definition but do not change the field of view. The range of visual abilities is not uniform across the visual field, and varies from animal to animal binocular vision, which is the basis for stereopsis and is important for depth perception, covers 114 degrees horizontally of the visual field in humans the remaining peripheral 40 degrees on each side have no binocular vision because only one eye can see those parts of the visual field. Some birds have a scant 10 to 20 degrees of binocular vision.

DETECTORS AND SENSORS :-

A sensor or a detector is a device that responds to a stimulus, such as heat, light, or pressure. It then generates a signal that can be measured or interpreted.

Humans, animals and even plants have sensors that can detect the world around them. Detectors are used in physical science to respond to energy signals and forces.

They are necessary for measurements and experiments. Signals can be manipulated to make their information more usable.

We also use detectors to study energy forms that we are not able to sense, such as magnetic fields. Detectors and sensors make up the starting point for most scientific studies.

Scientists have invented various types of sensors to detect energy forms. For example, a smoke detector in you home will set off an alarm when the energy from smoke or heat reaches its detection device. The microphone on you tape recorder detects the energy from sound waves and creates an electric signal that records the sound.

A sensor or a detector is a device that responds to a stimulus or form of energy. It then generates a signal that can be measured or interpreted. Humans, animals and even plants have sensors that can detect the world around them. Detectors are used in physical science to respond to energy signals and forces. They are necessary for measurements and experiments. Signals can be manipulated to make their information more usable.

READOUT METHOD :-

Electro-optical sensors are electronic detectors that convert light, or a change in light, into an electronic signal. These sensors are able to detect electromagnetic radiation from the infrared up to the ultraviolet wavelengths.They are used in many industrial and consumer applications.

Electro-optical sensors are used whenever light needs to be converted to energy. Because of this, electro-optical sensors can be seen almost anywhere. Common applications are smartphones where sensors are used to adjust screen brightness, and smartwatches in which sensors are used to measure the wearer's heartbeat.

Optical sensors can be found in the energy field to monitor structures that generate, produce, distribute, and convert electrical power. The distributed and nonconductive nature of optical fibres makes optical sensors perfect for oil and gas applications, including pipeline monitoring. They can also be found in wind turbine blade monitoring, offshore platform monitoring, power line monitoring and downhole monitoring. Other applications include the civil and transportation fields such as bridge, airport landing strip, dam, railway, airplane, wing, fuel tank and ship hull monitoring.