ABSTRACT
We present the results of time-dependent x-ray and visible light (VIS) scattering measurements during formation of surface relief grating (SRG). These gratings are formed on polymer films containing azobenzene side groups during pulselike exposure with a holographic pattern of circularly polarized light at 488 nm. The SRG formation is accompanied by a density grating just below the film surface. Assuming viscoelastic flow, a change in polymer's elastic properties upon light exposure can explain the massive material transport. Finite element calculations reveal a dynamic model of grating formation characterized by different relaxation times. The simultaneous formation of a surface relief grating and of a density grating explains quantitatively the findings of the VIS experiment, but only qualitatively the findings of the x-ray measurements.
ABSTRACT
Resonant grating waveguide structures were used to fabricate narrow-bandwidth optical filters. Azopolymer films were deposited on top of slab waveguides, and surface relief gratings were optically inscribed on them to be used as couplers. This technique is a simple one-step process and produces efficient gratings with high accuracy. Sharp resonant peaks are observed in the transmission and the reflection spectra of these structures. The thickness and the index of refraction of the waveguide can be accurately determined from these resonances by use of modal theory. These parameters are then used in the design of an optical filter. Bandwidths of less than 1 nm and a decrease in transmitted signal of 60% are reported. Measurement of these values was limited by the divergence of the probe beam.
