Optical limiters crystal

Several isovalent ions form solid solutions with KTP (Table II), showing that this structure is relatively tolerant, with respect to isovalent impurities, as are the traditional nonlinear optical oxide crystal structures. But due to the relatively limited range of nonstoichiometry in KTP, aliovalent impurities, such as divalent Ba, Sr and Ca introduced through ion exchange in nitrate melts, which substitute on the K site, are incorporated at concentrations less than one mole percent.(36) Typical impurity concentrations present in flux and hydrothermally grown KTP are shown in Table ID. 

As optic and crystal axes are common in the case of uniaxial crystals, singlecrystal CD experiments are generally limited to these kinds of crystals. For cases where moderate macroscopic anisotropies exist, these can be studied on the UCS J-800-KCM as is described in V.A.3. 

Optical Limiting of a Low Power CO, Laser with a Nematic Liquid-crystal Film," Appl. Phys. Letts., 5i. 2108 (1988). 

Isotropic Liquid Crystal Film and Fiber Structure for Optical Limiting Application," Int. J. Nonlinear Optical Phys. Vol. 2, No. 4 (1993). 

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.

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. 

Khoo, 1. C., H. Li, P. G. LoPresti, and Yu Liang. 1994. Observation of optical limiting and backscattering of nanosecond laser pulses in liquid crystal fibers. Opt. Lett. 19 530. 

Khoo, I. C., M. V. Wood, B. D. Guenther, Min-Yi Shih, P. H. Chen, Zhaogen Chen, and Xumu Zhang. 1998. Liquid crystal film and nonlinear optical liquid cored fiber array for ps-cw frequency agile laser optical limiting application. Opt Express. 2 471-82. 

Khoo, 1. C., J. Ding, A. Diaz, Y. Zhang, andK. Chen. 2002. Recent studies of optical limiting, image processing and near-infrared nortiinear optics with nematic liquid crystals. 

Self-Focusing and Self-Phase Modulation and cw Optical Limiting with Nematic Liquid Crystals... 

Figure 12.3. Experimental set up for optical limiting action using laser induced nematic liquid crystal axis realignment effect. Upper diagram shows the geometry of the twisted nematic cell. The focused spot diameter of the Argon laser on the film is 150 microns. Sample thickness 25 microns. Dye concentration 0.5 %.

NONLINEAR ABSORPTION AND OPTICAL LIMITING OF SHORT LASER PULSES IN ISOTROPIC PHASE LIQUID CRYSTALS AND LIQUIDS... 

Khoo. I. C., 1996. US Patent 5,589,101, Liquid crystal fiber array for optical limiting of laser pulses and for eye/sensor protection. Issued 31 December 1996. 

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