SMELLIE: A Laser Calibration System for SNO+

SNO+ is a general purpose neutrino detector 2km underground in SNOLAB. Its main aim is a neutrinoless double beta decay search in 130 ^{130} Te. It consists of a 6m radius acrylic vessel filled with the detection medium and surrounded by ~9300 PMTs on a support structure (PSUP) at a radius of ~8.9m.

Having a good understanding of detector response is vital for success. One contribution to this is SMELLIE (the Scattering Module for the Embedded LED/Laser Light Injection Entity). SMELLIE is an in-situ optical calibration system designed to measure and characterise scattering properties of the detector. It consists of 15 optical fibres attached to the PSUP, connected to 5 lasers above the detector, with a wavelength range from 375 – 700nm.

SMELLIE has been commissioned during the water phase of SNO+, in which the longer scattering and absorption lengths and lack of re-emission make it possible to extract the beam profiles and understand the response of the internal monitoring system.