Novel elastomeric spiropyran‑doped poly(dimethylsiloxane)optical waveguide for UV sensing

Novel poly(dimethylsiloxane)(PDMS)doped with two diferent spiropyran derivatives(SP)were investigated as potential candidates for the preparation of elastomeric waveguides with UV-dependent optical properties.First,free-standing flms were prepared and evaluated with respect to their photochromic response to UV irradiation.Kinetics,reversibility as well as photofatigue and refractive index of the SP-doped PDMS samples were assessed.Second,SP-doped PDMS waveguides were fabricated and tested as UV sensors by monitoring changes in the transmitted optical power of a visible laser(633 nm).UV sensing was successfully demonstrated by doping PDMS using one spiropyran derivative whose propagation loss was measured as 1.04 dB/cm at 633 nm,and sensitivity estimated at 115%change in transmitted optical power per unit change in UV dose.The decay and recovery time constants were measured at 42 and 107 s,respectively,with an average UV saturation dose of 0.4 J/cm2.The prepared waveguides exhibited a reversible and consistent response even under bending.The sensor parameters can be tailored by varying the waveguide length up to 21 cm,and are afected by white light and temperatures up to 70℃.This work is relevant to elastomeric optics,smart optical materials,and polymer optical waveguide sensors.

Emission spectroscopy of NaYF_(4):Eu nanorods optically trapped by Fresnel lens fibers

NaYF_(4):Eu nanorods with high aspect ratios are elaborated and optically trapped using dual fiber optical tweezers in a counterpropagating geometry. High trapping efficiency is observed using converging beams, emitted from diffractive Fresnel lenses directly 3D printed onto cleaved fiber facets. Stable nanorod trapping and alignment are reported for a fiber-to-fiber distance of 200 μm and light powers down to 10 m W. Trapping of nanorod clusters containing one to three nanorods and the coupling of nanorod motion in both axial and transverse directions are considered and discussed. The europium emission is studied by polarization-resolved spectroscopy with particular emphasis on the magnetic and electric dipole transitions. The respective σ and π orientations of the different emission lines are determined. The angles with respect to the nanorod axes of the corresponding magnetic and electric dipoles are calculated. Mono-exponential emission decay with decay time of 4–5 ms is reported. It is shown that the nanorod orientation can be determined by purely spectroscopic means.