Engineering physics phy1 common for all branches unit. This book has been written to serve as a text for revised syllabus of laser system and applications of dr. Semiconductor lasers or laser diodes play an important part in our everyday lives by providing cheap and compactsize lasers. In 1962, nick holonyak has come up with an idea of light emitting diode, and he was working for the general electric company. In lasers, photons are interacted in three ways with the atoms. The first is a pulsed laser with pulse duration of 2 to 10 ms versapulse, coherent medical lasers, palo alto, ca. Mechanical devices shutters, chopper wheel or spinning mirror. Maimans laser, however, was only capable of pulsed operation due to its threelevel pumping scheme. There is a great variety of different semiconductor lasers, spanning wide parameter regions and many different application areas.
Nov 24, 2015 semiconductor laser full topic engineering physics, b. It progresses from basic diodes through bipolar and field effect transistors. The requirements of the students have been fulfilled by explaining the basic principles of laser action, components of laser, various systems involved in. Law of mass action the np product is constant in te n o p o n i 2 t. Lasers are devices that produce or amplify a beam of narrow, convergent light with a welldefined wavelength within the electromagnetic spectrum. Semiconductor devices mohawk valley community college. A remarkable illustration of this concept is the qc terahertz laser, in which by judiciously introducing less than 2% of al atoms into a gaas crystal we transform a piece of bulk semiconductor into. The term laser is an abbreviation which stands for light amplification by stimulated emission of radiation. Tech first year page 1 of 10 question bank in physics lasers 1. Principle of a laser excerpt from field guide to lasers in order to understand the basic principle of a laser, it is instructive to first consider a passive resonator cavity, such as an arrangement of mirrors that creates a closed path for a light beam. The basic principle of an oscillator is a feedback circuit that is unstable. Crosssection and circuit symbol of an ntype metaloxidesemiconductorfieldeffecttransistor. In practise laser action cannot be achieved for only two levels, as described above. The acronym laser stands for light amplification by stimulated emission of radiation.
Their theoretical description is important not only from a fundamental point of view, but also in order to generate new and improved designs. The concept of the semiconductor laser diode was proposed by basov and javan. The figure is calculated for a 10 nm wide well containing an electron with mass m0. To explain the process of light amplification in a laser requires an understanding of the energy transition phenomena in the atoms of its active medium. Semiconductor laser diodes are no different in this respect. The basic principle of an oscillator is a feedback circuit that is. Laser, a device that stimulates atoms or molecules to emit light at particular wavelengths and amplifies that light, typically producing a very narrow beam of radiation. They consist of complex multilayer structures requiring nanometer scale accuracy and an elaborate design. Engineering physics pdf notes enginering physics notes. In order to make effective use of this text, students should have already taken coursework. Laser diode construction, working and its applications. The emission generally covers an extremely limited range of visible, infrared, or ultraviolet wavelengths. The lights can be produced through a process of optical amplification based on the stimulated emission of electromagnetic radiati. The led is a special type of diode and they have similar electrical characteristics of a pn junction diode.
It may be a bulk semiconductor, but more often a quantum heterostructure. For understanding, it is worthwhile to look closer at. The manual is intended for listeners of preparatory courses. Introduction of lasers, types of laser systems and their operating principles, methods of generating extreme ultravioletvacuum ultraviolet euvvuv laser lights, properties of laser radiation, and modi. Principles of semiconductor devices l length m ln electron diffusion length m lp hole diffusion length m m mass kg m0 free electron mass kg me effective mass of electrons kg mh effective mass of holes kg n electron density m3 ni intrinsic carrier density m3 ne electron density per unit energy and per unit volume m3 n0 electron density in thermal equilibrium m3. Whenever a photon is incident on an atom, that atom is excited from a lower energy state to a higher energy state and two photons are released in this process. Spontaneous and stimulated emissions, laser action, characteristics of laser beamconcepts of coherence, hene and semiconductor lasers simple ideas, applications. Semiconductor lasers are said to be the laser of the future. Principle of laser action and methods of pumping action brainkart. College on micro and nano photonics for life sciences 8 basic principles of light emission and absorption 1 absorption. The light emitting diode is a twolead semiconductor light source. For us, today, this statement sounds totally strange and we may question how this point of view came up. Lasers are devices that produce or amplify a beam of narrow, convergent light with a welldefined wavelength within.
Fundamentals, types, and operations n n e 0 e e 1 e 3 e 0 e e 1 2 fast decay fast decay fast decay pumping pumping lasing lasing a b figure 1. Apj abdul kalam technical university aktu, lucknow and other universities where such types of courses are running. Definition, symbol, and types of diodes electrical4u. The mode of operation is somewhat di erent than that of the laser described in the previous chapter. To help avoid confusion in terminology with the semiconductor laser, solid state lasers are sometimes now referred to as doped insulator lasers. Calculate the number of photons emitted per second. Rp photonics encyclopedia semiconductor lasers, laser diodes. The wavefunctions and the probability density functions are not normalized and shifted by the corresponding electron energy. Semiconductors, diodes, transistors horst wahl, quarknet presentation, june 2001 electrical conductivity. Light is emitted at a junction between two regions of opposite doping as shown in gure 4. The lasing action is controlled by the incident current so modulation by the current is. The material which often used in semiconductor laser is the gallium arsenide, therefore semiconductor laser is sometimes known as gallium arsenide laser.
Absorption is the process by which the energy of the photon is taken up by another entity, e. Introduction to laser technology e1 e4 e3 e2 level populations quantum energy levels population inversion laser action ground energy level pumping process figure 36. In other words, we can say that the concentration of free electrons is high and that of holes is very low in an ntype semiconductor. Formulas and figures in the book are numerated individually for each chapter that makes easy its use by readers. N 1 to achieve the condition of population inversion between e 2 and e 1 at moderate pumping. Designed for graduate students in physics, electrical engineering, and materials science, the text covers many recent developments, including diode lasers using quantum wells. The simplest configuration is made with only two mirrors, one being flat and one being curved. Laser introduction principles of working of a laser population inversion characteristics of laser laser construction methods of achieving population inversion types of lasers ruby laser nd. The basic operating principles of the laser were put forth by charles. Actually, an atom can generally stay at this excited state for 108 secs of time. An ntype semiconductor has plenty of free electrons and a very few numbers of holes. A remarkable illustration of this concept is the qc terahertz laser, in which by judiciously introducing less than 2% of al atoms into a gaas crystal we transform a piece of bulk semiconductor into a performing farinfrared laser. Laser diodes can directly convert electrical energy into light.
The text is intended for use in a first or second year course on semiconductors at the associate or baccalaureate level. Small edgeemitting laser diodes generate a few milliwatts or up to 0. In semiconductor laser theory, the optical gain is produced in a semiconductor material. The choice of material depends on the desired wavelength and properties such as modulation speed. Indirect gap recent challenges use of heterostructure for direct bandgap type i structure ge laser at 1550 nm midinfrared laser based on gesn incorporation of c. Laser diode working principle instrumentation tools. Basic principles of lasers to explain how laser light is generated, we need first to investigate the energy transition phenomena in atoms or molecules. The word laser is an acronym of light amplification by stimulated emission of radiation and aptly describes the theory behind the mechanics of laser generation. It is similar to a transistor and has the operation like led but the output beam has the characteristics of laser light. Semiconductors of p and n type with high carrier density are brought together. Laser light source basic principles of laser action in semi. Name some properties, which make laser light different from ordinary light.
Laser diode working principle 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 pn junction of a semiconductor diode similar to that found in a lightemitting diode. Later in 1960 the iranian physicist ali javan made the first gas laser using helium and neon. It assumes a basic knowledge of stimulated emission, laser action and semiconductor physics and begins with a short historical survey. So, the above process sets the principle for laser diode. Pdf conference lecturer in laser introduction and the the principles of laser systems and the application of laser technology in chemical analysis and. Metal contact ptype material active region ntype material ntype material metal contact from the picture one can see, that in principle you have the same structure like a diode where you. Dec 06, 2015 in this video lecture we will start learning about laser. The purpose of this chapter is to provide an overview of the principles of quantum confined semiconductor lasers relevant to most devices utilising conduction to valence band transitions. Describe how a semiconductor laser diode works a semiconductor laser diode consists of several parts.
Laser light source basic principles of laser action in. The principle of detailed balance tells us that each gr path is in balance. We consider in particular the case when this corresponds to the fundamental transverse mode of the laser cavity, which has a gaussian intensity. An important class of solidstate lasers are semiconductor lasers. In order to understand the basic principle of a laser, it is instructive to first consider a passive resonator cavity, such as an arrangement of mirrors that creates a closed path for a light beam. The semiconductor laser is very small in size and appearance. Department of ophthalmology and hansen experimental physics laboratory, stanford university, stanford, ca. A laser diode, ld, injection laser diode ild, or diode laser is a semiconductor device similar to a lightemitting diode in which a diode pumped directly with electrical current can create lasing conditions at the diodes junction 3 laser diodes can directly convert electrical energy into light. Semiconductor lasers types, applications, construction. The second is pumped by a diode laser and produces a pulse duration of 1 to 100 ms by conjoining a train of qswitched.
It is essential requirement for producing a laser beam. Semiconductor laser theory 1st edition prasanta kumar. Transistor lasers introduction structure and basic working principle principle of operation. Although they probably provide the cheapest form of lasers, they vary greatly in price from cheap to expensive. Driven by voltage, the doped pntransition allows for recombination of an electron with a hole. Doped semiconductors ntype materials ptype materials diodes and transistors. Developed from the authors classroomtested material, semiconductor laser theory takes a semiclassical approach to teaching the principles, structure, and applications of semiconductor lasers. The basic structure of an ntype mosfet and the corresponding circuit symbol are shown in figure 7.
A diodes working principle depends on the interaction of ntype and ptype semico nductors. In case the atom, still in an excited state, is struck by an outside photon having precisely the energy necessary for spontaneous emission, the outside photon is increased by the one given up by the excited atom, moreover, both the photons are released from the same excited state in the same phase, this process, called stimulated emission, is fundamental for laser. The output power of a given laser is 1mw and the emitted wavelength is 630nm. Basic principles of laser action in semi conductors, optical gain, lasing threshold, laser structures and characteristics, laser to fiber coupling, comparison with led source. Pdf on jun 17, 2015, prasanta kumar basu published semiconductor laser theory find, read and cite all the. It is a gas laser built by ali javan at mit, with a wavelength of 632. A laser diode, ld, injection laser diode ild, or diode laser is a semiconductor device similar to a lightemitting diode in which a diode pumped directly with electrical current can create lasing conditions at the diodes junction. There are many ways to qswitch a laser active qswitching 1. Lightemitting diodes circuit, working principle and application.
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