File Name: semiconductor laser construction and working .zip
Technology of Quantum Devices pp Cite as. The first working laser was built by Maiman in , and used a ruby crystal optically pumped by a flash lamp. Unable to display preview. Download preview PDF.
Light is generated by flowing the forward current to a p-n junction. Active region is present in between the n-type and p-type semiconductor layers. Energy Level Diagram of Semiconductor Laser. In a pn junction diode the Fermi energy level remain in equilibrium, uniform in both sides. The Fermi energy concept is useful here to explain about the filled and unfilled energy levels by the electrons. In the absence of external current source battery the Fermi energy level remain just above the valence band in p type semiconductor while in n type of semiconductor it remains below the conduction band. P-type and N-type.
A laser diode , or LD also known as injection laser diode or ILD , is an electrically pumped semiconductor laser in which the active laser medium is formed by a p-n junction of a semiconductor diode similar to that found in a light-emitting diode. The term laser stands for light amplification by stimulated emission of radiation. Laser light is also called coherent light, a single wavelength, as compared to incoherent light, which consists of a wide band of wavelengths. The basic construction of a laser diode is shown in Figure b. The length of the pn junction bears a precise relationship with the wavelength of the light to be emitted. The basic operation is as follows. The laser diode is forward-biased by an external voltage source.
It uses p-n junction to emit coherent light in which all the waves are at the same frequency and phase. And since a p-n junction is used to produce laser light, this device is named as a laser diode. The light from sunlight or from most of the artificial light sources contains waves of multiple wavelengths and they are out of phase with each other. The light waves from monochromatic light sources like incandescent bulb also are not in phase with each other. In contrast to the previous light sources, laser diodes produce a narrow beam of laser light in which all the light waves have similar wavelengths and they travel together with their peaks lined up. This is why laser beams are very bright, and can be focused over a very tiny spot. Of all the devices that produce laser light, laser diodes or semiconductor lasers are the most efficient and they come in smaller packages.
PN-junction Laser: A semiconductor laser is a specially fabricated pn junction device both the p and n regions are highly doped which emits coherent light when it is forward biased. Now the semiconductor lasers are also made to emit light almost in the spectrum from UV to IR using different semiconductor materials. They are of very small size 0. A p type region is formed on the n type by doping zinc atoms. The diode chip is about micrometer long and micrometer wide and thick. When high doped p and n regions are joined at the atomic level to form pn-junction, the equilibrium is attained only when the equalization of fermi level takes place in this case the fermi level is pushed inside the conduction band in n type and the level pushed inside the valence band in the p type Fig 2. When the junction is forward biased, at low voltage the electron and hole recombine and cause spontaneous emission.
The natural white light is made up of all the VIBGYOR colours of the visible light spectrum, which is a broad wide band of many different frequencies. The ordinary LEDs give a light output often consisting of one colour, but even that light contains electromagnetic waves, which cover a quite wide band of frequencies. The lens system focussing the light has a fixed focal length, but the focal length required to focus various wavelengths colours of light is different. The laser diode light contains only a single frequency. Therefore, it can be focused by even a simple lens system to an extremely small point. There is no chromatic aberration since only one wavelength exists, also all of the energy from the light source is concentrated into a very small spot of light. The above figure shows a simplified construction of a laser diode, which is similar to a light emitting diode LED.
The semiconductor laser is very small in size and appearance. It is similar to a transistor and has the operation like LED but the output beam has the characteristics of laser light. The material which often used in semiconductor laser is the gallium Arsenide, therefore semiconductor laser is sometimes known as Gallium Arsenide Laser. It is also called Injection Laser. In reality a semiconductor laser is simply a semiconductor diode, because its active medium is the junction of the forward biased P-N diode, shown as.
A laser diode emits radiation of a single wavelength or sometimes a narrow band of closely spaced wavelength. It emits light due to stimulated emission, in this when an incident photon strike semiconductor atom, the electrons at higher energy level recombine with lower energy level hole. Due to this two photons are emitted one incident photon and other is emitted due to recombination of electrons and hole.
Semiconductor Diode laser:. It is specifically fabricated p-n junction diode. This diode emits laser light when it is forward biased. When a p-n junction diode is forward biased, the electrons from n — region and the holes from the p- region cross the junction and recombine with each other.
Когда серебряный кубок оказался на уровне его глаз, возникло какое-то движение, и в полированной поверхности смутно отразилась приближающаяся фигура. Беккер заметил металлический блеск в тот самый миг, когда убийца поднимал пистолет, и, как спринтер, срывающийся с места при звуке стартового выстрела, рванулся. Насмерть перепуганный священник упал, чаша взлетела вверх, и красное вино разлилось по белому мрамору пола. Монахи и служки у алтаря бросились врассыпную, а Беккер тем временем перемахнул через ограждение.
Глаза Джаббы по-прежнему выражали шок и растерянность, когда сзади раздался душераздирающий крик: - Джабба. Джабба. Это кричала Соши Кута, его технический ассистент, подбегая к платформе с длиннющей распечаткой в руке.
- Теперь, мистер Клушар, позвольте спросить, почему такой человек, как вы, оказался в таком месте. В Севилье есть больницы получше. - Этот полицейский… - Клушар рассердился. - Он уронил меня с мотоцикла, бросил на улице, залитого кровью, как зарезанную свинью. Я еле добрел .
Он знал, что где-то за этой витиеватой резной дверью находится кольцо. Вопрос национальной безопасности. За дверью послышалось движение, раздались голоса. Он постучал.
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