TUTORIAL TEXTS SERIES

Chapter 5Fluoride Laser Crystals:YLiF (YLF)4Fluoride crystals are among the most important hosts for laser materials because oftheir special optical properties. Of these, LiYF (YLF) is one of the most common4rare-earth-doped laser materials, with a variety of efficient mid-IR laser lines from3+ 1the UV (Ce :YLF) to mid–IR range. Generally, YLF has good optical proper-ties with high transparency throughout the emission spectrum of the conventionalsources used for pumping solid state lasers. YLF does not show UV damage, andit has lower nonradiative decay rates for processes occurring between electroniclevels participating in the pumping and lasing process. YLF also has a low, two-photon absorption coefficient. Because of its low nonradiative rates, the material2can be used for cascade emission between intermediate levels as well as an up-converter, as will be discussed later.YLF is also a good medium for mode locking at 1047 or 1053 nm and 1.313 µmas a result of its natural birefringence and low thermal lensing. Mode-locked pulsesfrom YLF are shorter thanks to its broader linewidth, both for the 1047/1053-nmand 1.313-µm emission peaks. The crystallographic structure of LiYF (or YLF) is43the same as CaWO , which was developed years ago as a potential laser material.42+However, when a trivalent rare-earth material substitutes for the Ca ion, chargecompensation is necessary. However, the process of charge compensation may re-sult in inhomogeneities in the ...