Abstract: A method to examine laser induced plasma or bubble formations in nonlinear limiter cells includes splitting a laser pulse into an initiation pulse, a first probe pulse and a second probe pulse. The initiation pulse is focussed at a site in the cell, so that a formation of interest occurs there. The probe pulses are converted to frequencies different from each other and different from the initiation pulse frequency. Then the probe pulses are sent through single mode fibers of different measured lengths, so that the probe pulses are retarded relative to the initiation pulse by different, controlled intervals. The probe pulses exit the fibers in coherent collimated condition and travel along a common path crossing the site. The initiation pulse will have arrived at the site and created the formation before the first probe pulse arrives, and the second probe pulse arrives at the site after the first probe pulse. Shadowgraphs resulting from passage of the probe pulses past the formation are then imaged.

Abstract: Disclosed herein is an optical system which allows light below a given flce to pass but which blocks light above the given fluence so that a human viewer using the system is not harmed by high energy lasers directed at the system. The optical system concentrates incoming light at a first focal zone in a NLASM, or nonlinear absorbing or scattering material. During a time delay, the system reconcentrates the light at a second focal zone to which the plasma zone has had time to expand. The character and number of light concentrations in the NLASM can be varied to protect the human viewer from a wider range of harmful light fluences.