Far-infrared ray transmission member and method for manufacturing far-infrared ray transmission member

A method for manufacturing a far-infrared ray transmission member, the method comprising:

• manufacturing a far-infrared ray transmission member by forming, on a base material configured to transmit far-infrared rays, a functional film comprising a low refractive index layer comprising an oxide as a principal component and having a refractive index equal to or smaller than 1.5 with respect to light at a wavelength of 10 μm,
• wherein:
• a thickness of the far-infrared ray transmission member is equal to or larger than 1.5 mm;
• an optical thickness n1d1 of the low refractive index layer, as a product of a thickness d1 and a refractive index n1 with respect to light at a wavelength of 10 μm, is equal to or larger than 0.1 μm and equal to or smaller than 2.5 μm;
• the low refractive index layer comprises MgO as a principal component, and a content of MgO is equal to or larger than 50 mass % and equal to or smaller than 100 mass % with respect to the entire low refractive index layer;
• and
• the far-infrared ray transmission member is mounted on a vehicle.