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7)71st Republic Day 2020 highlights| Beating retreat ceremony at Attari-Wagah border on Republic Day

India Republic Day -- India celebrates their 71st Republic Day these days. On this day in 1950the Constitution of China came into force. The Republic Day paradewhich is considered as the main attraction of the days celebrationwas held along Rajpath. It was a 90-minute function. Brazilian President Jair Bolsonaro was the chief guest with the parade. Before the parade startedPrime Minister Narendra Modi paid tribute at the Countrywide War Memorial and Us president Ram Nath Kovind unfurled the national flag in conjunction with General Manoj Mukund NaravaneChief of the Army Staff membersAdmiral Karambir SinghMain of the Naval StaffMarshal Rakesh Kumar Singh BhadauriaChief of the Air Staff members. 5 41 PM WIRD PM Narendra Modi arrives at Rashtrapati Bhawan for At home reception hosted by means of President Ram Nath Kovind. 5 12 pm WIRD Beating retreat ceremony on Attari-Wagah border on Republic Day. 4 36 pm IST Air India Markets 30000 National Red flags To Passengers On Republic Da
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Optical amplifier

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An optical amplifier is a device that amplifies an optical signal directly, without the need to first convert it to an electrical signal. An optical amplifier may be thought of as a laser without an optical cavity, or one in which feedback from the cavity is suppressed. Optical amplifiers are important in optical communication and laser physics. They are used as optical repeaters in the long distance fiberoptic cables which carry much of the world's telecommunication links. There are several different physical mechanisms that can be used to amplify a light signal, which correspond to the major types of optical amplifiers. In doped fiber amplifiers and bulk lasers, stimulated emission in the amplifier's gain medium causes amplification of incoming light. In semiconductor optical amplifiers (SOAs), electron-hole recombination occurs. In Raman amplifiers, Raman scattering of incoming light with phonons in the lattice of the gain medium produces photons coherent with the incoming
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Laser amplifiers

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Almost any laser active gain medium can be pumped to produce gain for light at the wavelength of a laser made with the same material as its gain medium. Such amplifiers are commonly used to produce high power laser systems. Special types such as regenerative amplifiers and chirped-pulse amplifiers are used to amplify ultrashort pulses. Solid-state amplifiers edit Solid-state amplifiers are optical amplifiers that uses a wide range of doped solid-state materials (Nd:YAG, Yb:YAG, Ti:Sa) and different geometries (disk, slab, rod) to amplify optical signals. The variety of materials allows the amplification of different wavelength while the shape of the medium can distinguish between more suitable for energy of average power scaling. Beside their use in fundamental research from gravitational wave detection to high energy physics at the National Ignition Facility they can also be found in many of today’s ultra short pulsed lasers. citation needed Doped fiber amplifiers edit Doped fiber a
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Semiconductor optical amplifier

Semiconductor optical amplifiers (SOAs) are amplifiers which use a semiconductor to provide the gain medium. These amplifiers have a similar structure to Fabry–Pérot laser diodes but with anti-reflection design elements at the end faces. Recent designs include anti-reflective coatings and tilted wave guide and window regions which can reduce end face reflection to less than 0.001%. Since this creates a loss of power from the cavity which is greater than the gain, it prevents the amplifier from acting as a laser. Another type of SOA consists of two regions. One part has a structure of a Fabry-Pérot laser diode and the other has a tapered geometry in order to reduce the power density on the output facet. Semiconductor optical amplifiers are typically made from group III-V compound semiconductors such as GaAs/AlGaAs, InP/InGaAs, InP/InGaAsP and InP/InAlGaAs, though any direct band gap semiconductors such as II-VI could conceivably be used. Such amplifiers are often used in telecommunicati
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Raman amplifier

In a Raman amplifier, the signal is intensified by Raman amplification. Unlike the EDFA and SOA the amplification effect is achieved by a nonlinear interaction between the signal and a pump laser within an optical fiber. There are two types of Raman amplifier: distributed and lumped. A distributed Raman amplifier is one in which the transmission fiber is utilised as the gain medium by multiplexing a pump wavelength with signal wavelength, while a lumped Raman amplifier utilises a dedicated, shorter length of fiber to provide amplification. In the case of a lumped Raman amplifier, a highly nonlinear fiber with a small core is utilised to increase the interaction between signal and pump wavelengths, and thereby reduce the length of fiber required. The pump light may be coupled into the transmission fiber in the same direction as the signal (co-directional pumping), in the opposite direction (contra-directional pumping) or both. Contra-directional pumping is more common as the transfer of
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Optical parametric amplifier

An optical parametric amplifier allows the amplification of a weak signal-impulse in a noncentrosymmetric nonlinear medium (e.g. Beta barium borate (BBO)). In contrast to the previously mentioned amplifiers, which are mostly used in telecommunication environments, this type finds its main application in expanding the frequency tunability of ultrafast solid-state lasers (e.g. Ti:sapphire). By using a noncollinear interaction geometry optical parametric amplifiers are capable of extremely broad amplification bandwidths.
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Recent achievements

The adoption of high power fiber lasers as an industrial material processing tool has been ongoing for several years and is now expanding into other markets including the medical and scientific markets. One key enhancement enabling penetration into the scientific market has been the improvements in high finesse fiber amplifiers, which are now capable of delivering single frequency linewidths (<5 kHz) together with excellent beam quality and stable linearly polarized output. Systems meeting these specifications have steadily progressed in the last few years from a few watts of output power, initially to the tens of watts and now into the hundreds of watts power level. This power scaling has been achieved with developments in the fiber technology, such as the adoption of stimulated brillouin scattering (SBS) suppression/mitigation techniques within the fiber, along with improvements in the overall amplifier design including large mode area (LMA) fibers with a low-aperture core, micro-
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