Book contents
- Frontmatter
- Contents
- Preface
- Properties of common semiconductors
- 1 Quantum mechanics of the electron
- 2 Quantum mechanics of the photon
- 3 Quantum mechanics of electron–photon interaction
- 4 Laser oscillations
- 5 Semiconductor band structure
- 6 Electronic properties of semiconductors
- 7 Optical properties of semiconductors
- 8 Semiconductor heterostructures and quantum wells
- 9 Waveguides
- 10 Elements of device physics
- 11 Semiconductor photodetectors
- 12 Optical frequency conversion
- 13 Light emitting diodes and laser diodes
- Index
4 - Laser oscillations
Published online by Cambridge University Press: 04 August 2010
- Frontmatter
- Contents
- Preface
- Properties of common semiconductors
- 1 Quantum mechanics of the electron
- 2 Quantum mechanics of the photon
- 3 Quantum mechanics of electron–photon interaction
- 4 Laser oscillations
- 5 Semiconductor band structure
- 6 Electronic properties of semiconductors
- 7 Optical properties of semiconductors
- 8 Semiconductor heterostructures and quantum wells
- 9 Waveguides
- 10 Elements of device physics
- 11 Semiconductor photodetectors
- 12 Optical frequency conversion
- 13 Light emitting diodes and laser diodes
- Index
Summary
Introduction
We were able to show in Chapter 3 that a medium in which we can obtain a population inversion (i.e. a situation in which the population density in the excited state is greater than that in the fundamental level) allows for optical gain of an electromagnetic wave having a frequency near to the resonant frequency of the system. By introducing feedback of the amplified signal into the medium, the system can be made to oscillate naturally, resulting in laser oscillations. To obtain this population inversion, we must introduce at least a third (and perhaps even a fourth) energy level into the system. (We saw how a two-level system under the influence of an intense pump beam will saturate with no resulting population inversion.) The aim then of this chapter is to introduce the concepts necessary to extend our two-level system into a working model capable of illustrating the phenomenon of laser oscillation. We will not spend too much time discussing atomic transition lasers as they do not figure readily in our treatment of quantum electronic properties of semiconductors. An exception will be made, however; we brush upon the particular topics of a diode pumped laser in Complement 4.E and a quantum cascade laser in Complement 13.H.
Population inversion and optical amplification
Population inversion
We will show how population inversion can be achieved by carrier transfer from higher lying levels to the upper level of a two-level subsystem of interest.
- Type
- Chapter
- Information
- Optoelectronics , pp. 139 - 166Publisher: Cambridge University PressPrint publication year: 2002