Characterization of Black-Plastic THz-Low-Pass, IR-Blocking Filter: Observation of a Minimum THz Absorption

1.0-mm-thick black-polyethylene and-polypropylene plates are characterized as THz low-pass, near-IR blocking filters. The blocking at 1550 nm is found to be at least 75 dB, and the THz attenuation is very low, especially around an absorption minimum frequency of ~300 GHz.