Measurement of nonlinear refractive-index coefficients using time-resolved interferometry: Application to optical materials for high-power neodymium lasers

An improved time-resolved interferometric method for measuring intensity-dependent changes in the refractive index of optical materials is described. An intense 125-ps pulse from a 1064-nm Nd : YAG laser-glass amplifier system is propagated throguh the sample which is placed in one arm of a modified Michelson interferometer. The nonlinear refractive-index coefficient is measured from the time-dependent fringe formed at the output of the interferometer. Values are reported for several low-index optical glasses (BK-7, FC-5, FK-51), fused silica, a silicate laser glass (ED-2), a Faraday rotator glass (FR-5), and a nonlinear crystal (KH2PO4). Possible sources of error in using this approach are discussed.