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 ${\mathrm{CS}}_2$ 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 ${\mathrm{CS}}_2$ 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 $1 \mathit{\mu }\mathrm{J}$ 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.