CIVIL APPLICATION OF LASER RANGE FINDER
[laser is a device that emits light (electromagnetic radiation) through a process of optical amplification based on the stimulated emission of photons . Many scientific, military, medical and commercial laser applications have been developed since the invention of the laser , one of these application is laser rangefinder , which is a device that uses a laser beam to determine the distance to an object. The most common form of laser rangefinder operates on the time of flight principle by sending a laser pulse in a narrow beam towards the object and measuring the time taken by the pulse to be reflected off the target and returned to the sender. Due to the high speed of light, this technique is not appropriate for high precision sub-millimeter measurements, where Multiple frequency phase-shift and Interferometry techniques are used for higher precision . laser rangefinder have several applications special in military which it have been invented for that propos , and it have applications in civil such as Construction Rangefinder , and several application that is used in our daily life .] Introduction:
In 1916, Albert Einstein discussed the possibility of stimulating radiant energy based on Niels Bohr’s theory that atoms emitted energy in quanta when transitioning from excited states back to resting states . The first experimental proof of his theory was published by the German physicists Rudolf Ladenburg and Hans Kopfermann in 1928 . However, stimulated emission received little attention from experimentalists during the 1920s and 1930s when atomic and molecular spectroscopy were of central interest to many physicists . In 1939, Valentin A. Fabrikant defended his doctoral thesis, ‘The emission mechanism of a gas discharge’, at the P.N. Lebedev Physical Institute in Moscow. It discussed experimental evidence for the existence of negative absorption (what was later called stimulated emission) and suggested experiments on light amplification. Although the essential ideas for constructing a laser were known around 1930, it was not before the early 1950s that physicists and electrical engineers began to collaborate with the research on monochromatic radiation of constant amplitude at very small wavelengths studying the microwave and radio frequency spectra of molecules. In this context, in 1953 and 1954, several physicists independently suggested the use of stimulated emission for microwave amplification, creating the acronym MASER to stand for ‘microwave amplification by stimulated emission of radiation’ . In 1953, the American physicist Joseph Weber at the University of Maryland published a proposal for a microwave amplifier that was based on stimulated emission in a paramagnetic solid . In 1954, Nikola G. Basov and Alexander M. Prokhorov of the Lebedev Institute in Moscow and J.P. Gordon, H.J. Zeiger, and Charles H. Townes of Columbia University in New York reported on two molecular devices for generating microwave radiation, both using the ammonia molecule as the active species . Charles H. Townes, Nikolay G. Basov, and Alexander M. Prokhorov received the Nobel Prize in Physics 1964 for their ‘fundamental work in the field of quantum electronics which has led to the construction of oscillators and amplifiers based on the maser- laser principle’ . The ammonia beam maser itself was not particularly useful as its operation was limited to the resonant frequency of the ammonia molecule and could only be used at barely detectable power levels . In 1958, C.H. Townes and his brother- in- law Arthur Leonard Schawlow, professor at Stanford University, showed that masers could theoretically be made to operate in the optical and infrared regions . The same year, G. Makov, C. Kikuchi, J. Lambe and R.W. Terhune at the University of Michigan developed and built a solid- state maser . They used crystalline corundum (ruby) in a large magnetic field and a strategy similar to that known as...
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