Infrared transparent optical element and infrared imaging camera using the same

A method of producing an infrared transparent optical element for use as an optical window for an infrared imaging camera comprising an infrared transparent substrate having first and second major surfaces opposite to each other, wherein infrared rays of light emanating from an object enter the infrared transparent substrate through the first major surface and emerge outwardly from the infrared transparent substrate through the second major surface, an antireflection film formed on each of the first and second major surfaces of the substrate, and a protective film made of a polymer material and formed on an outer surface of the antireflection film on the first major surface of the substrate, said method comprising:

• placing a ultrahigh molecular weight, high density polyethylene film, which is used for the protective film, on the antireflection film of the first major surface so as to form a multi-layer body;
• and
• sandwiching the multi-layer body between a pair of molds by hot pressing, thereby fusion bonding the polyethylene film to the antireflection film of the first major surface side.