Search

A technique for accurate measurement of the principle refractive indices and birefringence for silklike samples is presented. It is based on rotating the linear polarization of the illuminating light on a silk immersed in reference liquid to achieve index matching at the silk/liquid interface. The technique was used to measure the principal refractive indices of a P. eburnus radial silk at different strains. This in turn allows the calculation of strain-optic coefficients. The first measurement of the strain-optic coefficients of spider silk is presented. The technique is more generally applicable to strain-optic study of birefringent micro-optic samples., Pub. in Optics Letters, v36 n20, p4098-4100, 15 Oct 2011. Sponsored in part by Defense Advanced Research Projects Agency.

Spider orb webs are known to produce colour displays in nature, both in reflection and transmission of sunlight, under certain illumination conditions. The cause of these colours has been the subject of speculation since the time of Newton. It has also been the topic of observational interpretation and some experiment which has proposed diffraction by the fine silks, scattering from rough/structured surfaces and thin film effects as the primary causes. We report systematic studies carried out using the silks of Australian orb web weaving spiders. Studies of both white light and laser light scattering/propagation by natural spider silks have definitively determined the primary cause of the colour displays is rainbows that can be understood by the application of geometric optics combined with new knowledge of the optical properties of the spider web strands, silks, and proteins as optical materials. Additionally, a range of microscopies (optical, AFM, optical surface profiling) show the silks to be optically flat. Overall, spider silks emerge as fascinating optical materials with high dispersion, high birefringence and the potential for future research to show they have high nonlinear optical coefficients. Their importance as a bioinspiration in optics is only just beginning to be realised. Their special optical properties have been achieved by 136 million years of evolution driven by the need for the web to evade detection by insect prey., The original document contains color images. Sponsored in part by Defense Advanced Research Projects Agency. Published in Bioinspiration, Biomimetics, and Bioreplication, the Proceedings of SPIE, v7975, p79750G-1, 2011.

A technique for measuring the refractive index of micron sized fibers using a series of immersion index matching oils, and image contrast measurements is proposed and demonstrated. It has been applied to radial silks of the orb web weaving spider Plebs eburnus. These have widths of 1-2 microns. Values about 1.5500 are obtained, with birefringence values between 0.0000 and 0.0133 for individual silks. An uncertainty in the range +/- 5 x 10(exp -4) to +/- 2 x 10(exp -3) is achieved for these challenging samples. This accuracy is about a twenty times improvement on previously reported measurements for spider silks using other techniques. The technique is used to obtain measurements of the refractive index of spider silks as a function of wavelength, for the first time. An Abbe number for the radial silks of Plebs eburnus of 32 is found., Pub. in Optics Express, v19 n20, 26 Sep 2011.