Q-switched and gain-switched mid-infrared fluoride glass fiber lasers

Pulsed fiber laser sources operating in the mid-infrared spectral region, a region which contains the characteristic fingerprint spectra of many important molecules and also a number of transparent atmospheric transparency windows, is attracting increased attention motivated by the multitude of practical applications in this region. Over the past decade, significant progress has been made in the development of compact energetic and powerful mid-infrared pulsed fiber lasers at the wavelengths >2.5 μm, wavelengths that are difficult to be addressed with the use of traditional silicate fibers. Achievements made in this area provide new opportunities for a variety of applications, for example, special material processing, diagnostics and treatment in medicine, infrared countermeasures, etc. In this chapter, we will focus on two widely implemented technologies for the generation of optical pulses, that is, Q-switching (using loss modulation) and gain-switching (using gain modulation) and present some of the important representative demonstrations. For each group, different laser platforms based on different transitions and rare-earth-doped fibers will be classified. Finally, the outlook for future development of pulsed mid-infrared laser sources using loss or gain modulation is discussed.