Optical product and light concentrator

An optical product comprising:

• a base member;
• and
• an optical multilayer film formed directly on or indirectly above a film formation surface of the base member, wherein
• the optical multilayer film reflects light on a short wavelength side and suppresses reflection of a light on longer wavelength side than the light on the short wavelength side,
• the optical multilayer film has a first layer counted from the base member side, the first layer being a metal layer formed of a metal,
• the optical multilayer film further has
• one or more Al layers,
• at least one of a low-refractive-index layer disposed on the base member side relative to each of the Al layers and a high-refractive-index layer disposed on the base member side relative to the Al layer, and
• at least one of a low-refractive-index layer disposed on an air side relative to the Al layer and a high-refractive-index layer disposed on the air side relative to the Al layer,
• wherein the low-refractive-index layer is formed of a low-refractive-index material and the high-refractive-index layer is formed of a high-refractive-index material,
• the metal layer has a physical film thickness of not smaller than 20 nm, and
• the Al layer that is closest to the air side has a physical film thickness of not smaller than 5 nm and not larger than 35 nm.