Book contents
- Frontmatter
- Contents
- Preface
- 1 Introduction
- 2 Light propagation through dispersive dielectric slabs
- 3 Interaction of light with generic active media
- 4 Optical Bloch equations
- 5 Fiber amplifiers
- 6 Semiconductor optical amplifiers
- 7 Raman amplifiers
- 8 Optical parametric amplifiers
- 9 Gain in optical metamaterials
- Index
- References
7 - Raman amplifiers
Published online by Cambridge University Press: 03 May 2011
- Frontmatter
- Contents
- Preface
- 1 Introduction
- 2 Light propagation through dispersive dielectric slabs
- 3 Interaction of light with generic active media
- 4 Optical Bloch equations
- 5 Fiber amplifiers
- 6 Semiconductor optical amplifiers
- 7 Raman amplifiers
- 8 Optical parametric amplifiers
- 9 Gain in optical metamaterials
- Index
- References
Summary
Light gets scattered when it encounters an obstacle or inhomogeneity even on a microscopic scale. A well-known example is the blue color of the sky, resulting from Rayleigh scattering of light by molecules in the air. Such redirection of energy can be used to amplify signals by taking power from a “pump” wave co-propagating with the signal in an appropriate optical medium. An example of this is provided by Raman scattering. Having said that, it is important to realize that scattering does not always occur when light interacts with a material [1]. In some cases, photons get absorbed in the medium, and their energy is eventually dissipated as heat. In other cases, the absorbed light may be re-emitted after a relatively short time delay in the form of a less energetic photon [2], a process known as fluorescence. If fluorescence takes place after a considerable delay, the same process is called phosphorescence [3].
For a photon to get absorbed by a material, its energy must correspond to the energy required by the atoms or molecules of that material to make a transition from one energy level to a higher energy level. In contrast, the scattering of photons from a material can take place without such a requirement. However, if the energy of the incident photon is close to an allowed energy transition, significant enhancement of scattering can occur.
- Type
- Chapter
- Information
- Light Propagation in Gain MediaOptical Amplifiers, pp. 173 - 207Publisher: Cambridge University PressPrint publication year: 2011