Nd:YLF laser active elements are made of yttrium lithium fluoride (YLiF4) crystal. YLF stands for Yttrium Lithium Fluoride. Usually neodymium-doped YLF crystal is used for YLF laser equipment; however, it can also be doped with rare earth elements, such as ytterbium (Yb), erbium (Er), thulium (Tm), holmium (Ho) or praseodymium (Pr).
Yttrium ions in YLF crystal may be substituted with laser-active rare earth ions, because of its similar size, without distorting the structure of crystal lattice. In neodymium-doped YLF crystal its (Nd3+) concentration is usually up to 1% of its total weight.
YLF crystal has a natural strong birefringence, which removes thermal polarization losses. Besides the emission wavelength and the gain of the Nd:YLF crystal waves are polarization-dependent, there is a stronger wave of 1047 nm and a weaker one of 1047 nm. It makes Nd:YLF crystal better for a less powerful laser equipment that require extra precision.
1053 nm wavelength matches the maximum for loop gain of phosphate laser glass, that contains neodymium ions, that is why Nd:YLF lasers are often used as a master oscillator and preamplifier for the subsequent stages of the neodymium phosphate glass amplifier.
Diode-pumping and lamp-pumping is possible for Nd:YLF laser. It has lower thermal conductivity in comparison with Nd:YAG laser, but its thermal distortions are weaker, which leads to a better beam quality and worse fracture resistance, hence it limits the output power in the laser equipment.