Moran J M, Kaminow I P
Appl Opt. 1973 Aug 1;12(8):1964-70. doi: 10.1364/AO.12.001964.
Polymethyl methacrylate, PMMA, sensitized for lambda = 0.325 microm, is shown to exhibit a peak refractive index change of 2.3 x 10(-3). The index change has been characterized in relation to its sensitivity, temperature dependence, and development time. The sensitivity of the material is shown to be 1.7 x10(-4) alpha, where alpha is the intensity absorption coefficient. Laser light scattered by an exposed region is found to produce a double ring pattern due to the graininess of the index variation. Three-dimensional holographic diffraction gratings were made in the PMMA, and its diffraction efficiency was measured as a function of thickness, refractive index change, and reconstruction angle. The efficiencies measured agree fairly well with the theoretical sin(2) curve; however, higher peak diffraction efficiencies were obtained further out on this oscillatory curve. A maximum diffraction efficiency of 96% was obtained. Angular sensitivity measurements indicated that the effective thickness of the grating was less than its actual thickness due to the nonuniformity of the index variation with thickness. Potential applications as a dielectric waveguide, diffraction grating, and wavelength selector are discussed. Scattering, the relatively small maximum index change, and poor reproducibility are the chief limiting factors.
对波长λ = 0.325微米敏化的聚甲基丙烯酸甲酯（PMMA），其峰值折射率变化为2.3×10⁻³。已对该折射率变化在灵敏度、温度依赖性和显影时间方面进行了表征。该材料的灵敏度为1.7×10⁻⁴α，其中α是强度吸收系数。由于折射率变化的颗粒性，发现曝光区域散射的激光会产生双环图案。在PMMA中制作了三维全息衍射光栅，并测量了其衍射效率与厚度、折射率变化和重构角度的函数关系。测量得到的效率与理论sin²曲线相当吻合；然而在此振荡曲线上，离峰值更远时获得了更高的衍射效率峰值。获得了96%的最大衍射效率。角度灵敏度测量表明，由于折射率随厚度变化不均匀，光栅的有效厚度小于其实际厚度。讨论了其作为介质波导、衍射光栅和波长选择器的潜在应用。散射、相对较小的最大折射率变化以及较差的再现性是主要限制因素。
