Diffraction-grating photopolarimeters and spectrophotopolarimeters

An instrument for measuring the state of polarization of light as determined by the four Stokes parameters, comprising:

• a diffraction grating having a surface including a plurality of parallel grating grooves thereon, said grating having a spatial frequency selected to produce at least four diffracted orders;
• a source of an incident light beam whose state of polarization is to be measured, said source oriented such that said incident light beam is directed at said grating so as to form an oblique incidence angle with said surface and such that said grating grooves are perpendicular to a plane of incidence defined by said light beam and a line normal to said surface at the point of incidence of said light beam on said surface;
• at least four photodetectors, each of said photodetectors positioned so as to intercept a different diffracted order from said incident light beam;
• linear polarizing means disposed between said diffraction grating and said photodetectors in the paths of at least two of said diffracted orders;
• and
• calculating means responsive to said photodetectors for determining the four Stokes parameters descriptive of the polarization state of said light beam.

A conical-grating-diffraction division-of-amplitude spectrophotopolarimeter, comprising:

• a diffraction grating having a surface including a plurality of parallel grating grooves thereon, said grating having a spatial frequency selected to produce at least four diffracted orders;
• a source of an incident light beam of unknown polarization having wavelengths within a range of interest, said source oriented such that said incident light beam is directed at said grating so as to form an oblique incidence angle with said surface and such that said grating grooves are inclined at an inclination angle greater than 0.degree. and less than 90.degree. with respect to a plane of incidence defined by said light beam and a line normal to said surface at the point of incidence of said light beam on said surface;
• at least four area photodetector arrays, each of said arrays having individual detector elements and positioned so as to intersect the paths of a different diffracted order from incident light beams having wavelengths within said range;
• and
• calculating means responsive to said photodetector arrays for determining the four Stokes parameters descriptive of the polarization state of said light beam.

A planar-grating-diffraction division-of-amplitude spectrophotopolarimeter, comprising:

• a diffraction grating having a surface including a plurality of parallel grating grooves thereon, said grating having a spatial frequency selected to produce at least four diffracted orders;
• a source of an incident light beam of unknown polarization having wavelengths within a range of interest, said source oriented such that said incident light beam is directed at said grating so as to form an oblique incidence angle with said surface and such that said grating grooves are perpendicular to a plane of incidence defined by said light beam and a line normal to said surface at the point of incidence of said light beam on said surface;
• at least four linear photodetector arrays, each of said arrays having a plurality of detector elements disposed on a linear axis, the linear axis of each of said arrays positioned such that individual ones of said detector elements intercept the path of a different diffracted order from incident light beams having wavelengths within said range;
• linear polarizing means disposed between said diffraction grating and said arrays in the paths of at least two of said diffracted orders;
• and
• calculating means responsive to said photodetector arrays for determining the four Stokes parameters descriptive of the polarization state of said light beam.

A method for simultaneously producing a plurality of electrical signals, each of which is a linear combination of all four Stokes parameters of a light beam, including the steps of:

• directing the light beam onto a diffraction grating to obtain at least four diffracted orders, said incident beam oriented such that the grating grooves are oriented at an angle greater than 0.degree. but less than 90.degree. to the plane of incidence of said incident beam of light;
• simultaneously detecting the intensity of each said at least four diffracted orders and generating output electrical signals related thereto;
• and
• processing said output electrical signals to determine the four Stokes parameters of the light beam.

A method for simultaneously producing a plurality of electrical signals, each of which is a linear combination of all four Stokes parameters of a light beam, including the steps of:

• directing the light beam onto a diffraction grating to obtain at least four diffracted orders, said incident beam oriented such that the grating grooves are perpendicular to the plane of incidence of said incident beam of light;
• simultaneously detecting the intensity of each said at least four diffracted orders in the presence of a linear polarizing element in at least two of said orders and generating output electrical signals related thereto;
• and;
• and
• processing said output electrical signals to determine the four Stokes parameters of the light beam.

An instrument for measuring the state of polarization of an input light beam comprising:

• a diffraction grating having a surface including a plurality of parallel grooves thereon, said grating having a spatial frequency selected to produce at least four diffracted orders;
• means for directing the input light beam to said surface so as to form an oblique incidence angle between the input light beam and said surface so that said grooves are inclined at an inclination angle greater than 0.degree. and less than 90.degree. with respect to a plane of incidence defined by the input light beam and a line normal to said surface at the point of incidence of the input light beam on said surface;
• at least four photodetectors for producing output signals, each of said photodetectors positioned on the surface of an imaginary cone defining conical diffraction of said incident light beam from said grating cone so as to intercept a different diffracted order from said incident light beam;
• linear polarizing means disposed between said grating and said photodetectors in the paths of at least one of said diffracted orders;
• calculating means responsive to said output signals for solving simultaneous linear algebraic equations determined from said output signals;
• and
• output means responsive to said calculating means for outputting the four Stokes parameters descriptive of the polarization state of the input light beam.