F-SIN (.THETA.) LENS SYSTEM AND METHOD OF USE OF SAME

摘要

An optical system for focusing an incidentlight so as to obtain a linear output (as a functionof the wavelength, or of the order of diffraction, orof the grating spacial frequency or of the inverse ofthe index of refraction) comprises a diffractiongrating and a lens, or a group of lenses, having af-Sin(.theta.) characteristic, where f is the effectivefocal length of the lens, or group of lenses, and .theta.is an output angle of the light exiting from thediffraction grating. Therefore, a light incident onthe diffraction grating reaches the lens, or thegroup of lenses, and results in a linear output.Using the present invention in a spectrometer reducesthe time consuming calibration process required andrenders it easier because of the linear outputbetween wavelength and pixels positions. The lens,or.group of lenses, has a diffractive, refractive orreflective property, or any combination thereof. Theincident light can be a collimated, converging ordiverging beam. The diffraction grating can be aplane, concave or convex grating.