Method for manufacturing a Fresnel phase reversal plate lens

Claim 2

Fresnel phase plate lens, characterized in that the lens body consists of a plate that is selected according to the desired range of optical transmission from the group of materials silicon, germanium, glass, high silica glass and fused quartz glass.l

Claim 3

Fresnel lens according to claim 1, characterized in that the lens is a phase reversal plate with the thickness of the plate changing by one-half wavelength in a step-like manner from zone to zone and having an overall lens thickness of between about 1 to 4 millimeters.

Claim 4

Fresnel lens according to claim 1, characterized in that the lens is a sinusoidal phase reversal plate with the thickness of the plate changing by one-half wavelength in a sinusoidal manner from zone to zone and having an overall lens thickness of between about 1 to 4 millimeters.

Claim 5

Method for making a high quality Fresnel phase reversal plate lens having light transmission of substantially all incident light, in particular according to any one of claims 1 - 3 characterized by the steps of: providing a polished lens blank (10, 20) composed of a material suited for the wavelength of light for which it will ultimately be used; depositing upon the polished side of the lens blank a photosensitive layer (12, 22) capable of having photochemical changes by exposure to light; exposing the photosensitive layer with light to form therein a pattern of the Fresnel phase reversal plate; developing the exposed photosensitive layer to leave therein a physical Fresnel phase reversal plate; anisotropically etching the lens blank in a suitable reactive ambient until the phase plate pattern in the photosensitive layer is replicated in the lens blank and a depth of one-half of the desired wavelength is reached in the lens blank to form the Fresnel lens; and removing any remaining photosensitive layer from the Fresnel phase reversal plate lens.

Claim 6

Method according to claim 4, in particular for making lenses according to claim 2, characterized in that exposing with light is through a master mask to form a Fresnel phase reversal plate type pattern in the photosensitive layer and which produces in the lens blank after the completion of etching a Fresnel phase reversal plate lens.

Claim 7

Method according to claim 4, in particular for making lenses according to claim 3, characterized in that exposing with light is by a pattern of interferences fringes from two mutually coherent monochromatic point light sources to form a Fresnel sinusoidal phase reversal plate type pattern in the photosensitive layer and which produces in the lens blank after the completion of the etching a Fresnel sinusoidal phase plate lens.

Claim 8

Method according to any of the claims 4 - 6, characterized in that the lens blank consists of silicon and that the anisotropically etching is done in a reactive ion etching process in an ambient of 96 to 95 % by volume CCl 2 F 2 and 1 to 5% by volume oxygen, and at a pressure of less than about 60 millitorr.

Claim 9

Method according to any of the claims 4 - 6, characterized in that the lens blank consists of glass, fused quartz glass or high silica glass, and that the anisotropically etching is done in a reactive ion etching process in an ambient of 99 to 95% by volume CF 4 and 1 to 5% by volume oxygen, and at a pressure of less than about 60 millitorr.

Claim 10

Method according to any of the claims 4 - 8, characterized in that etching is continued until the photosensitive layer is completely removed.

Claim 11

Method according to any of the claims 4 - 9, char-It acterized in that the photosensitive layer is a photoresist.