Nd:YAG Laser: Bohren und Gravieren - Fakultät 06 - Hochschule ...

Nd:YAG Laser: Bohren und Gravieren
Version 3.1
and frequency quadrupling, respectively. Other emission lines are at 946, 1123, 1319, 1338
and 1444 nm. When used at the 946-nm transition, Nd:YAG is a quasi-three-level gain
medium, requiring significantly higher pump intensities.
Nd:YAG is usually used in monocrystalline form, fabricated with the Czochralski growth
method, but there is also ceramic (polycrystalline) Nd:YAG available in high quality and in
large sizes. For both monocrystalline and ceramic Nd:YAG, absorption and scattering losses
within the length of a laser crystal are normally negligible, even for relatively long crystals.
Typical neodymium doping concentrations are of the order of 1 at. %. High doping
concentrations can be advantageous e.g. because they reduce the pump absorption length, but
too high concentrations lead to quenching of the upper-state lifetime e.g. via upconversion
processes. Also, the density of dissipated power can become too high in high-power lasers.
Note that the neodymium doping density does not necessarily have to be the same in all parts;
there are composite laser crystals with doped and undoped parts, or with parts having different
doping densities.
Property Value
chemical formula Nd 3+ :Y3Al5O12
crystal structure cubic
mass density 4.56 g/cm 3
Moh hardness 8–8.5
Young's modulus 280 GPa
tensile strength 200 MPa
melting point 1970 °C
thermal conductivity 10–14 W / (m K)
thermal expansion coefficient 7–8 × 10 −6 /K
thermal shock resistance parameter 790 W/m
birefringence none (only thermally induced)
refractive index at 1064 nm 1.82
temperature dependence of refractive index 7–10 × 10 −6 /K
Nd density for 1 at. % doping 1.36 × 10 20 cm −3
fluorescence lifetime 230 μs
absorption cross section at 808 nm 7.7 × 10 −20 cm 2
emission cross section at 1064 nm 28 × 10 −20 cm 2
gain bandwidth 0.6 nm
Table 1: Some properties of Nd:YAG = neodymium-doped yttrium aluminum garnet.
Other Laser-active Dopants in YAG
In addition to Nd:YAG, there are several YAG gain media with other laser-active dopants:
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