DUAL FOCAL PLANE VISIBLE OPTICAL LIMITER

Abstract

Experiments measuring the transmission of 5 nanosecond (FWHM), 532 nm pulses through an optical limiter using two different nonlinear materials at two separate focal planes show by far the highest dynamic-range measured to date. This cascaded focus, f/5 optical limiter combines self focusing and consequent nonlinear scattering in CS 2, with reverse saturable absorption in lead-phthalocyanine (PbPc). Both the AC Kerr effect and electrostriction contribute to the total refractive index change in CS 2. Our beam propagation code is used to model the propagation of light through the 2 cm thick CS 2 cell placed at the first focus, which protects a second 0.1 mm cell containing a solution of PbPc placed at the second focus. An aperture is placed in the focal plane of a final focusing lens to measure the "encircled" energy, defined as the energy passing through a 1.5 mrad diameter focal-plane aperture. Experiments and modeling show that the strong self-focusing in the CS 2 keeps the energy at the second cell below its damage threshold. This combination of nonlinearities clamps the maximum encircled energy below 1 μ J for input energies up to 14.5 mJ at a 10 Hz repetition rate. This corresponds to a dynamic range of at least 7500 while it is possibly much greater since no damage occurred to any device components. Here we present details of the operation of this device.