Sensitivity of nEXO VUV Silicon Photomultipliers at 410-2400 nm

nEXO is a 5-ton liquid Xenon time projection chamber (TPC) operating at cryogenic temperatures and is one of the most sensitive detectors being proposed to search for neutrinoless double beta-decay, which if discovered would fundamentally change our understanding of the nature of neutrinos. Brookhaven National Laboratory is developing the readout electronics and photon detectors in nEXO, which will detect the scintillation flash at 175 nm produced when a double beta decay event occurs. nEXO scientists are concerned that there is the possibility of a background to the VUV photon measurement due to potential crosstalk from Infrared (IR) photon emissions caused by the electron avalanche in the Silicon PhotoMultipliers (SiPMs). We measured the Photon Detection Efficiency (PDE) of the SiPMs at high wavelengths to help understand this effect. To achieve this, an OPOTEK 355 LD tunable laser was set up and calibrated, then used to determine the PDE of the SiPMs from 410-2400 nm. These measurements, when combined with future measurements of the IR emission from SiPM avalanches, will allow nEXO to estimate the effect of this possible crosstalk on the energy resolution.