Optical characterization of RTV615 silicone rubber compound

TL;DR

This study measures the ultraviolet light transmission of RTV615 silicone rubber, demonstrating its suitability for optical coupling in detectors and analyzing how curing methods affect its transmission properties.

Contribution

It provides detailed transmission data for RTV615 silicone rubber across UV wavelengths and compares curing methods, informing its use in optical applications.

Findings

RTV615 transmits ~93% of UV light between 360-400 nm.

High-temperature curing improves transmission by 5-10%.

Transmission drops sharply below 230 nm, with absorption coefficients varying with wavelength.

Abstract

Room Temperature Vulcanized (RTV) silicone compounds are commonly used to bond optical components. For our application, we needed to identify an adhesive with good ultraviolet transmission characteristics, to couple photomultipliers to quartz windows in a Heavy Gas Cerenkov detector that is being constructed for Experimental Hall C of Jefferson Lab to provide pi/K separation up to 11 GeV/c. To this end, we present the light transmission results for Momentive RTV615 silicone rubber compound for wavelengths between 195-400 nm, obtained with an adapted reflectivity apparatus at Jefferson Lab. All samples cured at room temperature have transmissions ~93% for wavelengths between 360-400 nm and fall sharply below 230 nm. Wavelength dependent absorption coefficients were extracted with four samples of different thicknesses cured at normal temperature (25oC for 7 days). The absorption coefficient drops approximately two orders in magnitude from 220-400 nm, exhibiting distinct regions of flattening near 250 nm and 330 nm. We also investigated the effect of a high temperature curing method (100oC for 1 hour) and found 5-10% better transmission than with the normal method. The effect was more significant with larger sample thickness (3.35 mm) over the wavelength range of 220-280 nm.