Monochromators

Claim 1

The method of making a monochromator using a concave, reflecting holographically formed diffraction grating, which comprises the steps of: (a) determining the physical parameters of the monochromator by using a concave classical reflective diffraction grating having straight, parallel lines which are equidistantly spaced to provide a line density n, a height L 0 and a width W 0 , the monochromator having fixed entrance and exit slits spaced from the grating to provide a predetermined magnification and a predetermined angle 2θ between the incident and diffracted beams, whereby the odd terms of the aberration wavefront is minimized, the grating being mounted for rotation only with respect to said slits whereby to scan a spectral range of interest, said physical parameters being the distances of said entrance and exit slits with respect to the intersection of their optical axes at the center of the reflective surface of said grating, and said physical parameters being selected to provide a defect of focus which balances second order aberration terms excepting astigmatism whereby the partial derivative ∂F 1 /∂w is equal to zero, F 1 being the optical path associated with said classical grating and w and l being Cartesian coordinates with respect to the center of said grating extending respectively perpendicular and parallel to said grating lines; (b) holographically forming a grating by locating two point sources of monochromatic light of wavelength λ 0 in a plane containing the axis of the coordinate w and passing through the center of and normal to a holographic blank having the concavity of said classical grating, such that said point sources are located by four position parameters which are the respective distances r C and r D of said point sources from said center of the holographic blank and the angle η and δ which lines from such point sources to said center respectively make with a line passing through such center and normal to said holographic blank; said four position parameters being established by four simultaneous equations the first of which defines the number n of grating lines holographically formed, the second of which defines astigmatic correction effected by the hologram provided by said point sources, the third of which defines coma correction effected by the hologram provided by said point sources, and the fourth of which defines the focussing condition in said plane effected by the hologram provided by said point sources; and (c) substituting the holographically formed grating for said classical grating.

Claim 2

The method of making a monochromator using a concave, reflecting holographically formed diffraction grating, which comprises the steps of: (a) determining the physical parameters of the monochromator by using a concave classical reflective diffraction grating having straight, parallel lines which are equidistantly spaced to provide a line density n, a height L 0 and a width W 0 , the monochromator having fixed entrance and exit slits spaced from the grating to provide a predetermined magnification and a predetermined angle 2θ between the incident and diffracted beams, whereby the odd terms of the aberration wavefront is minimized, the grating being mounted for rotation only with respect to said slits whereby to scan a spectral range of interest, said physical parameters being the distances of said entrance and exit slits with respect to the intersection of their optical axes at the center of the reflective surface of said grating, and said physical parameters being selected to provide a defect of focus which balances second order aberration terms excepting astigmatism whereby the partial derivative ∂F 1 /∂w is equal to zero, F 1 being the optical path associated with said classical grating and w and l being Cartesian coordinates with respect to the center of said grating extending respectively perpendicular and parallel to said grating lines; (b) holographically forming a grating by locating two point sources of monochromatic light of wavelength λ 0 in a plane containing the axis of the coordinate w and passing through the center of and normal to a holographic blank having the concavity of said classical grating, such that said point sources are located by four position parameters which are the respective distances r C and r D of said point sources from said center of the holographic blank and the angle η and δ which lines from such point sources to said center respectively make with a line passing through such center and normal to said holographic blank; said four position parameters being established by four simultaneous equations the first of which defines the number n of grating lines holographically formed, the second of which defines astigmatic correction effected by the hologram provided by said point sources, the third of which defines coma correction effected by the hologram provided by said point sources, and the fourth of which defines the focussing condition in said plane effected by the hologram provided by said point sources; and (c) substituting the holographically formed grating for said classical grating.