Infrared diffractive lens
This invention provides an infrared diffractive lens capable of focusing infrared rays within a wide range of wavelength band effectively. According to the present invention, there is provided an infrared diffractive lens including a concave-convex shape with predetermined depth defined based on a predetermined standard wavelength in a wavelength band of incident infrared rays, wherein: the incident infrared rays are within the wavelength band of 1.1-16 μm; a depth h of the concave-convex shape is defined by mλ/(n−1) with regard to a refractive index n of material of lens, the standard wavelength λ and a harmonic order m; and the harmonic order m is an integer between 2 and 10. Using the infrared diffractive lens with such a configuration makes it possible to focus infrared rays within a wide range of wavelength band effectively.
1 . An infrared diffractive lens including a concave-convex shape with predetermined depth defined based on a predetermined standard wavelength in a wavelength band of incident infrared rays, wherein:
the incident infrared rays are within the wavelength band of 1.1-16 μm;
a depth h of the concave-convex shape is defined by formula 1 with regard to a refractive index n of material of lens, the standard wavelength λ and a harmonic order m,
h
=
m
λ
n
-
1
;
(
formula
1
)
and
the harmonic order m is an integer between 2 and 10.
2 . The infrared diffractive lens according to claim 1 , wherein the concave-convex shape is formed by etching.
3 . The infrared diffractive lens according to claim 1 , wherein the concave-convex shape is formed by reactive ion etching.
4 . The infrared diffractive lens according to claim 1 , wherein the concave-convex shape is formed by transfer molding based on a matrix formed by etching.
5 . The infrared diffractive lens according to claim 1 , wherein the concave-convex shape is formed by transfer molding based on a matrix formed by cutting work.
6 . The infrared diffractive lens according to claim 1 , wherein the incident infrared rays are within the wavelength band of 6-10 μm.
7 . The infrared diffractive lens according to claim 1 , wherein a cross-section surface cut at a plane surface including an optical axis has a saw-like shape in at least a part of the concave-convex shape.
8 . The infrared diffractive lens according to claim 1 , wherein:
a cross-section surface cut at a plane surface including an optical axis has a stepwise shape of N steps (N is an integer of 3 or more) in at least a part of the concave-convex shape; and
the depth h of the concave-convex shape is approximated by a depth h′ defined by formula 2.
h
′
=
m
λ
n
-
1
×
N
-
1
N
(
formula
2
)
9 . The infrared diffractive lens according to claim 1 , wherein the material of lens with refractive index of 2 or more is used.
10 . The infrared diffractive lens according to claim 1 , wherein the material of lens is selected from a group including Si, Ge, GaAs, InP and GaP.
11 . The infrared diffractive lens according to claim 1 , wherein non-reflecting coating is performed on the surface of the infrared diffractive lens.
12 . The infrared diffractive lens according to claim 1 , wherein non-reflecting coating is performed on the rear surface of the infrared diffractive lens.
13 . The infrared diffractive lens according to claim 1 , wherein non-reflecting coating is performed on the surface and the rear surface of the infrared diffractive lens.