Cr4+:YAG(Chromium-doped Yttrium Aluminum Garnet ) is a passive Q-switch crystal which is widely used on Nd:YAG, Nd:Ce:YAG, Nd: YLF, Nd:YVO4, Yb:YAG lasers at wavelength of 800nm~1200nm. The Passive Q-switches or saturable absorbers can provide high power laser pulses without EO Q-switches
Cr4+:YAG crystals as a relatively new laser material and their spectroscopic properties are presented. The possibilities of using these crystals for manufacturing of passive Q-switch modulators are pointed.
Compact efficient laser systems of short pulse duration and stable single-frequency operation are required for various applications. Passive Q-switching of continuously pumped solid-state lasers is a simple, cost-effective means to obtain high-peak-power pulses in the nanosecond and sub-nanosecond regimes. Diode-pumped microchip lasers passively Q-switched with Cr4+:YAG saturable absorbers offer such a simple compact design. The concept of microchip lasers was proposed in 1989 independently by Dixon  and by Zayhowski and Mooradian . Most of the experimental work was performed using neodymium-doped crystals as the gain medium, and Cr4+:YAG as the saturable absorber .
Investigations of non-linear absorption of q-switching absorbers were carried out. Three types of saturable absorbers were examined (Cr4+:YAG at the wavelength of 1064 nm, V3+:YAG and Co2+:YAG at the wavelength of 1332 nm) and their principal parameters were estimated. To appropriately determine these parameters 48 samples of Cr4+:YAG, 42 samples of V3+:YAG and 26 samples of Co2+:YAG were investigated making the results more reliable. Three different models of analysis of saturation effect were described and the best one chosen. Using the best model for the analysis the main parameters of the saturable absorbers were determined. On the basis of so many samples the standard deviation of the ground state absorption cross section, the excited state absorption cross section and the unsaturable losses were calculated showing how the value of these parameters may differ even for the same type of crystal.