Dependence of TPB-coated and uncoated polytetrafluoroethylene reflectance on thickness at visible and ultraviolet wavelengths in air

Polytetrafluoroethylene (PTFE) is an excellent diffuse reflector widely used in light collection systems for particle physics experiments. The NEXT experiment uses PTFE inside the detector to provide highly reflective surfaces to increase the light collection. This light collection is further improved using wavelength shifters, specifically TPB. We describe investigations into the reflectance of PTFE based on thickness, in both TPB-coated and uncoated PTFE. These investigations occurred for light of wavelengths 128 nm, 260nm and 450nm using two complementary methods. The 450 and 260 nm light are generated using LEDs, while 128 nm light is generated by argon scintillation in the presence of an alpha source. Finally, we investigate the variations in reflectivity between different PTFE suppliers.