Nonlinear Fiber Core Liquid and Nematic Liquid Crystal Film for Wide Temporal Bandwidth Optical Limiting Application
- PDF / 1,540,802 Bytes
- 12 Pages / 417.6 x 639 pts Page_size
- 96 Downloads / 239 Views
ABSTRACT Nonlinear absorption processes in an extremely nonlinear optical fiber core liquid, and recently observed supra-optical-nonlinearity in dopant modified nematic liquid crystals, are discussed in the context of optical limiting and anti-laser dazzling application. INTRODUCTION Various nonlinear optical materials are currently being investigated for the purpose of optical limiting and laser hardening application. These include organic and inorganic materials exhibiting nonlinear absorption and refraction effects, materials capable of plasma generation, composite materials exhibiting nonlinear scattering effects, photorefractive materials, liquids and liquid crystals. With the advent of lasers and optical systems employing lasers of wide-ranging temporal characteristics and spectral bandwidth, the problem of protecting the eye and sensor from over-exposure to these laser radiation becomes increasing difficult. At the very least, the materials should respond throughout the visible spectrum [400 -700 nm], and be able to control the transmission to below the sensor/eye damage level [the so-called Maximum Permissible Exposure (MPE) level as defined by the American National Standards Institute]. In the case of nanosecond laser pulses, this translates to the requirement that the energy density entering the eye be clamped to a value below I iW1/ cm2 . Equivalently, in an optical system with gain of 105 such as the eye, a fluence of 0.1 -0.2 J/ cm2 at the focal plane (the retina). Moreover, the material should have a very large dynamic range and the device should have a wide field of view. We have previously reported[1,2] that a patented opaque-cladding nonlinear fiber array, with the fiber core liquid L34, possess optical limiting characteristics that meet these requirements for nanosecond laser pulses. We have also shown [3] that it is possible to employ the supra-optical-nonlinearity (SON) of specially doped nematic liquid crystalline film[ 4 ' 5 for long-pulse or CW laser limiting application. In this paper, we report the results of recent studies of the nonlinear molecular photonics of these fiber core liquids and the liquid crystalline films. MOLECULAR PHOTONICS OF NONLINEAR FIBER CORE LIQUID L34 Among various candidate liquids for use as the nonlinear fiber core in our fiber array limiter, L34[1,2] was found to give the best optical limiting performance, owing to its high linear transmission as well as intensity dependent nonlinear absorption characteristics. Fig. 1 shows the output vs. input plot of nanosecond laser pulses through 281 Mat. Res. Soc. Symp. Proc. Vol. 597 © 2000 Materials Research Society
single free-standing fibers and the constituent fibers of an opaque-cladding fiber array. In general, because of spurious scattering from the single fiber's cladding into downstream detection optics, the clamped levels in the transparent-cladding single fiber are higher than in the constituent fibers of the opaque-cladding fiber array. Notice that for the 5mm single-fiber and the fiber array, the transmission
Data Loading...
