High-dynamic-range cascaded-focus optical limiter.

We report experimental results of using an f/5 , cascaded-focus optical geometry for a high-dynamic-range optical limiter. The device consists of a 2-cm-thick CS(2) cell at the first focus and a reverse saturable-absorber dye in a thin cell (0.1 mm) at the second focus. The strong self-focusing in the CS(2) that is due to the ac Kerr effect and electrostriction keeps the energy at the second cell below its damage threshold. Using lead phthalocyanine in chloroform as the reverse saturable-absorption material, we clamped the maximum output energy below 1muJ for input energies up to 14.5 mJ without damage. We used a frequency-doubled, Q -switched 5-ns (FWHM) Nd:YAG laser operating at a 10-Hz repetition rate. The measured dynamic range of the device is at least 7500.