Mirror

摘要

According to one embodiment, a mirror includes a plurality of dielectric layers stacked in a first direction. A thickness along the first direction of each of the dielectric layers is half a design wavelength. The dielectric layers include a first dielectric layer. The first dielectric layer includes a first portion with a thickness being ⅛ of the design wavelength, a second portion stacked with the first portion with a thickness being ⅛ of the design wavelength, and a third portion provided between the first and second portions with a thickness being ¼ of the design wavelength. The second portion has a refractive index lower than that of the first portion. The third portion has a refractive index gradually decreasing from a side of the first portion toward a side of the second portion.

主权项

1. A mirror, comprising:
a plurality of dielectric layers stacked in a first direction, a thickness along the first direction of each of the dielectric layers being a length of half a design wavelength, the dielectric layers including: a first dielectric layer, the first dielectric layer including:
a first portion having a first portion refractive index, a thickness of the first portion along the first direction being ⅛ of the design wavelength;a second portion stacked with the first portion in the first direction, the second portion having a second portion refractive index lower than the first portion refractive index, a thickness of the second portion along the first direction being ⅛ of the design wavelength; anda third portion provided between the first portion and the second portion, the third portion having a third portion refractive index gradually decreasing from a side of the first portion toward a side of the second portion, a thickness of the third portion along the first direction being ¼ of the design wavelength, and a variance of the third portion refractive index with respect to the first direction being larger than a variance of the first portion refractive index with respect to the first direction and being larger than a variance of the second portion refractive index with respect to the first direction, wherein the first dielectric layer includes a first triple-layer structural body, and the first triple-layer structural body includes:
a first film of dielectric having a first thickness larger than ⅛ of the design wavelength and smaller than ¼ of the design wavelength, and having a first refractive index;a second film of dielectric stacked with the first film in the first direction, having a second thickness larger than ⅛ of the design wavelength and smaller than ¼ of the design wavelength, and having a second refractive index lower than the first refractive index; anda third film of dielectric provided between the first film and the second film, the third film having a third thickness which is obtained by subtracting sum of the first thickness and the second thickness from a value of half the design wavelength, and the third film having a third refractive index gradually decreasing from a side of the first film toward a side of the second film.