A multi-referenced optical attenuator using a reflective interface and smart lighting in an open lab

Abstract

In this study we present a referenced optical attenuator for measuring changes in the refractive of index of liquids. The technique uses a modified version of a standard photo lithographic optical set-up. The set-up is easy to construct, and compatible with a host of label free systems. The measurement system was based on reflective intensity attenuation. Reflectivity was controlled by altering the refractive index of the fluid at the liquid/glass interface. Measurements were conducted using both commercial and smart lighting. In regards to the latter, a minimum of 3 peak wavelengths 405, 436 and 611 nm were identified as replacements for conventional laser diodes, exhibiting bandwidths ranging from 1 to 2 nm. For the first week of operation (99 h) the mean reflectivity signal fluctuated by an average of 3.1%. The best time to conduct an experiment with a free energy source occurred on a Thursday morning from 7.30 to 11.30a. m. when the reflected signal fluctuated by an average of < 0.5%. In the absence of a suitable gradient index lens (GRIN) a thin film Fresnel stack was fabricated in house. The optical technique exhibited a bulk sensitivity of 0.31% glycerol solution and a resolution of 1 x 10(-4) refractive index units RIU. (c) 2014 Elsevier B.V. All rights reserved.