Fibre amplifiers

This course begins with a general introduction to laser amplifiers, explaining the basic physical principles and properties of amplifiers, including e.g. four-level vs. quasi-three-level gain media, gain saturation in steady state and in pulse amplification, and amplified spontaneous emission (ASE). It then continues with more specific details for fibre amplifiers, including an overview on different amplifying ions and host media, double-clad fibres, mode areas, effective transition cross sections, influence of the pump wavelength, and ASE limitations. After a discussion of continuous-wave amplification, specific issues of pulse amplification will be discussed for the pulse duration regimes of nanoseconds, picosecond and femtoseconds. Finally, a brief overview on the physical modelling of amplifiers will be given.