Cr-doped yttrium aluminum garnet (Cr:YAG) crystal

opticallaser

Passive Q-switches or saturable absorbers provide high power laser pulses without electro-optic Q-switches, thereby reducing the package size and eliminating a high voltage power supply. Cr4+:YAG is more robust than dyes or color centers and is the material of choice for 1 micron Nd lasers. A small fraction of the chromium ions in YAG can be induced to change valence from the normal Cr3+ to Cr4+ with the addition of charge compensating impurities such as Mg2+ or Ca2+. The convenient measure of the Cr4+ concentration is the low power absorption coefficient at 1064 nm. Typical values vary from about 1.5 cm-1 for tunable laser crystals to 3 - 6 cm-1 for passive Qswitches. The actual Cr4+ ion density N in the crystal can be calculated from N = / A where A is the absorption cross-section with a value1 of 5 x 10-18 cm2 . Passive Q-switches are typically specified by the low power Optical Density (or %T) at the laser wavelength. Synoptics measures the value in the Cr4+:YAG boule and adjusts the part thickness to the Optical Density specified. Thickness is a free parameter, but typically 1 - 5 mm.