DEAP-3600 uses liquid argon contained in a spherical acrylic vessel as a target medium to perform a sensitive spin-independent dark matter search .
Argon scintillates in the vacuum ultraviolet spectrum , which requires wavelength shifting to convert the VUV photons to visible so they can be transmitted through the acrylic light guides and detected by the surrounding photomultiplier tubes .
The wavelength shifter 1,1,4,4-tetraphenyl-1,3-butadiene was evaporatively deposited to the inner surface of the acrylic vessel under vacuum .
Two evaporations were performed on the DEAP-3600 acrylic vessel with an estimated coating thickness of 3.00 \pm 0.02 \upmu m which is successfully wavelength shifting with liquid argon in the detector .
Details on the wavelength shifter coating requirements , deposition source , testing , and final performance are presented .