Broad band pass filter including metal layers and dielectric layers of alternating refractive index

An optical interference filter for a substrate, comprising:

• twelve layers, said layers designated the first through the twelfth in consecutive numerical order beginning with the layer furthest from the substrate;
• said first layer of a material having a low refractive index and having an optical thickness of about one-eighth wavelength at a first wavelength in the near-infrared spectral region;
• said second and twelfth layers of a material having a high refractive index and having an optical thickness of about one-quarter wavelength at said first wavelength;
• said third and eleventh layers of a material having a low refractive index and having an optical thickness between one-quarter and one-eighth wavelength at said first wavelength;
• said fourth and tenth layers of a material having a high refractive index and having an optical thickness of less than one-quarter wavelength at a second wavelength in the visible spectrum;
• said fifth, seventh and ninth layers being metal layers and having a thickness between about 12.5 and 30.0 nanometers;
• said sixth and eighth layers of a material having a high refractive index and having an optical thickness less than one-half wavelength at said second wavelength;
• said first wavelength being between about 800 and 1250 nanometers and said second wavelength being between about 480 and 560 nanometers;
• and
• said high refractive index being between about 1.65 and 2.65 at a wavelength of about 520 nm and said low refractive index being between about 1.35 and 1.65 at a wavelength of about 520 nm.