An optical valve in a laser that prevents light from transmitting outside the resonating cavity. The Q switch allows for the build-up of energy before it is switched open to allow light to move out. Specification for LiNbO3 Q-Switch Elements If a LiNbO3 with specifications listed in the following Table is used as Q-switch crystal, i.e., the light propagates in z-axis and electric field applies to x-axis, the refractive retardation will be G=pLnr22V/1d. The electro-optic coefficients of LiNbO3 are:r33=32pm/V,r22=6.8 pm/V at low frequency and r33=31 pm/V, r31=8.6 pm/V,r22=3.4 pm/V at high electric frequency.