Characterization of photo-isomerization-induced refractive index response for azobenzene solution based on capillary-assisted Mach-Zehnder interferometer under 473 nm laser excitation

Abstract

We propose a compact silica-capillary-assisted Mach-Zehnder interferometer (SCAMZI) to investigate the light power and polarization dependences of refractive indices in the near-infrared region for ethyl orange (EO) solution, which is one type of azo-based photo-sensitive functional material. Owing to photo-induced trans-to-cis isomerization of azo material, interference dips of the proposed MZI are highly sensitive to applied excitation laser power density, showing a maximum wavelength sensitivity of 0.1959 nm/(mW⋅cm−2) for the silica capillary of 325 μm in length and EO percentage weight of 0.08 wt%. The experimentally observed spectral responses to applied laser power density show good light-controlled spectral reversibility and repeatability. And by adjusting the polarization angle of 473 nm excitation laser, polarization-dependent refractive index of EO solution have been characterized and thus optical birefringence responses can be acquired as well, which provides an important reference for understanding the mechanism of photo-isomerization-induced optical response and the development of related light-controlled photonic devices.