Optical limiters are nonlinear materials that exhibit a drop in transmittance as the energy of incident laser pulses increases, usually above a certain threshold. They have potential for protecting optical sensors, and possibly even human eyes, from laser-pulse damage. Some of the best-performing optical limiters are materials containing carbon nanotubes (CNTs); however, such materials are difficult to prepare and have problems with stability. Scientists at the National University of Singapore have created an optical limiter based on silver nanoprisms that bests the performance of CNT-based optical limiters, and is simpler to prepare and more stable.
Prepared by a photochemical method, silver prisms averaging 100 nm in size suspended in water (to a concentration at which optical transmission was 70%) were subjected to 7 ns, 532 nm pulses at 10 Hz from a frequency-doubled Nd:YAG laser. At an input fluence of 0.12 J/cm2 the transmittance began to drop; the limiting threshold, or the point where transmission dropped by a factor of 2, was 1.2 J/cm2, which compares favorably to the CNT version’s 1.6 J/cm2. A similar form of nanoprism that had a gold core and a silver shell was also tested, and showed a limiting threshold of 1.3 J/cm2. Contact Qing-Hua Xu at [email protected].