Optical limiters nonlinear photonic crystal

The reflectivity and width of the band gaps increase as the refractive index modulation increases. The basic principle for optical limiting by a ID nonlinear photonic crystal material can be understood from Figure 2. Initially, (A), the refractive indices of the different layers are matched, and the sample... 

Figure 2. The concept of a nonlinear photonic crystal optical limiter.

Ultra-fast optical switches based on one dimensional-polymeric photonic crystals doped with nonlinear-optical dyes have been recently reported by Katouf et al. [150]. They presented optical switches operating at 1,064 nm wavelength, that can be controlled either by an applied electric-field voltage or by a pump light by use of two different optical-configurations. The response time of the electro-optic switch and the all-optical switch are limited by the applied voltage and the laser used. 

Ultrashort fluorescence lifetimes are best determined by photon upconversion. An excellent description of the technique for non-specialists wishing to set up an experiment is in preparation as part of a current IUPAC project on ultrafast intense laser chemistry .181 The time resolution is basically limited by the temporal width of the laser pulses that are being used. An intense gate pulse at frequency vq is mixed with the fluorescence at a frequency vp in a nonlinear optical crystal (Special Topic 3.1), to create a short pulse at the sum frequency i j. The gate pulse thus represents a time window for the fluorescence... 

Since the probability per cycle of detecting a fluorescence photon has to be smaller than unity, the cycle frequency should be large and is only limited by the requirement that the time between successive excitation pulses should be larger than the lifetime of the excited molecules. Therefore, mode-locked synchronously pumped cavity-dumped CW dye lasers are ideal excitation sources. For the excitation of higher electronic states, the visible output pulses can be converted into ultraviolet pulses by optical frequency doubling in optically nonlinear crystals. 

Fabrications of such fibers with isotropic phase hquid crystals are much eas-iej. 27.29 Because of the fluid property and much lower scatteriug loss, liquid ciystal fibers of much longer dimension have been fabricated and shown to exhibit interesting nonlinear optical properties high quality image transmitting fiber arrays - have also been fabricated for passive pulsed laser limiting applications. Other optical devices based on liquid ciystal filled photonic ciystal (holey) fibers have also been reported. ... 

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