Sensor protection

Materials are also classified according to a particular phenomenon being considered. AppHcations exploiting off-resonance optical nonlinearities include electrooptic modulation, frequency generation, optical parametric oscillation, and optical self-focusing. AppHcations exploiting resonant optical nonlinearities include sensor protection and optical limiting, optical memory appHcations, etc. Because different appHcations have different transparency requirements, distinction between resonant and off-resonance phenomena are thus appHcation specific and somewhat arbitrary. 

Reverse saturable absorption is an increase in the absorption coefficient of a material that is proportional to pump intensity. This phenomenon typically involves the population of a strongly absorbing excited state and is the basis of optical limiters or sensor protection elements. A variety of electronic and molecular reorientation processes can give rise to reverse saturable absorption many materials exhibit this phenomenon, including fuUerenes, phthalocyanine compounds (qv), and organometaUic complexes. 

Two contact wires Heating Supporting Zr02 sensor Protective... 

Detect remotely activated no apparent hazard or threat, need more effective biomimetic sensors, protective suit that will block or inactivate a threat challenge Detect self-repUcating biothreats that deliver toxins... 

Energy Production Signal transduction/actuation Sensor Protection Conductive Plastics/Stealth Bio-molecular electronics... 

It is important to note that since the thermal/density and order parameter changes could be induced in microseconds or tens of nanoseconds (cf preceding chapters), these director-axis-reorientation or order-parameter-change mediated limiting actions will work well for sensor protection in these time scales. For shorter laser pulses, for example, nanosecond and picosecond or subpicosecond laser pulses, the response will not be able to build up sufficiently in time to provide the necessary attenuation effect. In those time regimes, electronic optical nonlinear mechanisms, in particular, nonlinear photonic absorptions, have to be employed. This is discussed in... 

Section 12.6, where other nonlinear device/concepts that are effective for the short time scale will be introduced. It is interesting to note that if one combines the nematic films with the nonlinear (image transmitting) fiber array for nanosecond/picosecond limiting apphcation (cf. Sec. 12.6), it is possible to fashion optical sensor protection devices capable of covering an extremely wide temporal range (from ps laser pulses to cw hght sources). 

Khoo, I. C., M. V. Wood, M. Y. Shih, and P. H. Chen. 1990. Extremely nonhnear photosensitive hquid crystals for image sensing and sensor protection. Opt. Express. 4(11) 431 2. 

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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