Optical partial wave plate and method of fabricating and using same

Claim 2

In an optical partial wave plate formed from a birefringent crystalline material having a known optic axis direction and known indices of refraction in a manner such that said plate may be used for introducing a predetermined phase retardation, Delta lambda o, between two components of a beam of polarized light of wavelength lambda o by passing said beam through said plate in a direction orthogonal to the surfaces of the entrance and exit windows thereof, the improvement comprising: a. a slab of said birefringent material, said slab having two plane parallel opposed major surfaces the normal to each of which is directed at an acute angle of inclination theta to said direction of said optic axis in said material; b. said slab also having a thickness T, measured perpendicularly between said two major surfaces which form said entrance and exit windows for said beam of light, which thickness T has a predetermined relationship to said angle of inclination, theta ; and, c. said predetermined relationship between said thickness, T, and said angle of inclination, theta , being given by the expression, Delta lambda o ( Eta o - Eta e) sin2 theta T, where Delta lambda o is said predetermined phase retardation, Eta o is the index of refraction for the ordinary ray in said material, Eta e is the index of refraction for the extraordinary ray in said material for a direction of propagation perpendicular to said optic axis of said material, sin2 theta is the square of the sine of said angle theta between said optic axis and said normal to said major plane surfaces, and T is said thickness, the value of sin2 theta being such as to reduce the produce ( Eta o - Eta e) sin2 theta to permit the thickness T for a given desired value of Delta lambda o to have a value which not only produces the desired phase retardation but also is large enough to increase the strength of the plate.

Claim 3

A partial waveplate as in claim 1, wherein the value of said phase retardation is less than 1 wavelength, lambda o, of the light with which said plate is intended to be used so that said plate is of zero order to reduce the temperature dependence of said phase retardation produced by said plate.

Claim 4

A partial waveplate as in claim 1, wherein said wavelength, lambda o, of the light with which said plate is intended to be used lies in the infrared region of the spectrum.

Claim 5

A partial waveplate as in claim 1, wherein the value of said phase retardation is less than 1 wavelength, lambda o, and wherein said wavelength, lambda o, lies in the infrared region of the spectrum.

Claim 6

A partial waveplate as in claim 1, in which said birefringent material is quartz.

Claim 7

A partial waveplate as in claim 1, in which said birefringent material is sapphire.

Claim 8

A partial waveplate as in claim 1, wherein said angle theta has a value lying in the range between 3* and 60*.

Claim 9

In the process of introducing a predetermined phase retardation, Delta lambda o, between two orthogonal components of a beam of polarized light of wavelength lambda o by passing said beam through an optical partial wave plate cut from a birefringent crystalline material having a known optic axis direction and known indices of refraction, said plate being cut to have two plane parallel opposed major surfaces which are positioned in use to be perpendicular to the transmission path of said beam of light to form entrance and exit windows therefor, the improvement comprising: a. dimensioning said plate during fabrication thereof to have a predetermined thickness, T, where T is the perpendicular distance between said two plane parallel opposed surfaces of said plate; and b. fabricating said plate to incline said optic axis of said birefringent material at an acute angle, theta , to the normal to said major plane surfaces of said plate, the properties of said partial wave plate thereby being predetermined to have a relationship such that said phase retardation, Delta lambda 0, of light of said wavelength, lambda 0, produced in passing through said plate in said transmission path direction normal to said surfaces forming said exit and entrance windows is equal to the value of said thickness T of the plate times the product of the square of the sine of said angle theta between said optic axis and said normal to said major plane surface of said plate times the difference between the index of refraction, eta 0, for the ordinary ray in said material and the index of refration, eta e, for the extraordinary ray In said material for a direction of propagation perpendicular to said optic axis of said birefringent material, wherein the value of theta has been determined in accordance with said relationship, Delta lambda o ( eta 0- eta e) sin2 theta T, by the known values of said indices of refraction of said birefringent material and by the preselected desired values of Delta lambda o and T, to permit the thickness, T, for a given desired value of Delta lambda o to have a value which produces the desired phase retardation and also produces desirable structural properties of the plate.

Claim 10

In the process of introducing a predetermined phase retardation, Delta lambda o, between two orthogonal components of a beam of polarized light of wavelength lambda o by passing said beam through an optical partial wave plate cut from a birefringent crystalline material having a known optic axis direction and known indices of refraction, said plate being cut to have two plane parallel opposed major surfaces which are positioned in use to be perpendicular to the transmission path of said beam of light to form entrance and exit windows therefor, the improvement comprising: a. dimensioning said plate during fabrication thereof to have a predetermined thickness, T, where T is the perpendicular distance between said two plane parallel opposed surfaces of said plate; and b. fabricating said plate to incline said optic axis of said birefringent material at an acute angle, theta , to the normal to said major plane surfaces of said plate, the properties of said partial wave plate thereby being predetermined to have a relationship such that said phase retardation, Delta lambda 0, of light of said wavelength, lambda 0, produced in passing through said plate in said transmission path direction normal to said surfaces forming said exit and entrance windows is equal to the value of said thickness T of the plate times the product of the square of the sine of said angle theta between said optic axis and said normal to said major plane surface of said plate times the difference between the index of refraction, eta 0, for the ordinary ray in said material and the index of refration, eta e, for the extraordinary ray In said material for a direction of propagation perpendicular to said optic axis of said birefringent material, wherein the value of theta has been determined in accordance with said relationship, Delta lambda o ( eta 0- eta e) sin2 theta T, by the known values of said indices of refraction of said birefringent material and by the preselected desired values of Delta lambda o and T, to permit the thickness, T, for a given desired value of Delta lambda o to have a value which produces the desired phase retardation and also produces desirable structural properties of the plate.

Claim 11

A process as in claim 8, wherein the value of said phase retardation is less than one wavelength lambda 0 of the light with which the plate is intended to be used and wherein a single plate of zero order is used to reduce the temperature dependence of said phase retardation, Delta lambda o, produced by said plate.

Claim 12

A process as in claim 8, wherein said beam of polarized light is the output of a laser.

Claim 13

A process as in claim 10, wherein said design wavelength, lambda o, of the light with which said plate is intended to be used lies in the infrared region of the spectrum.

Claim 14

A process as in claim 10, wherein the value of said phase retardation is less than one wavelength, lambda o, and wherein said wavelength lambda o lies in the infrared region of the spectrum.

Claim 15

A process as in claim 8, in which said birefringent material is quartz (SiO2).

Claim 16

A process as in claim 8, in which said birefringent material is sapphire (Al2O3).

Claim 17

A process as in claim 8, wherein said angle theta has a value lying in the range between 3* and 60*.

Claim 18

A process as in claim 8 wherein said beam of light is the plane polarized output of a laser and has a wavelength, lambda o, in the infrared region of the spectrum.