Abstract:
A spectral scan by using a rotating spiralling toroidal mirror. The scan is made of a light beam from a source. A beamsplitter divides the beam into two components. One component is reflected off of a fixed mirror back to the beamsplitter. The second component is reflected off of the spiralling toroidal mirror back to the beamsplitter. As the mirror rotates, the pathlength constantly changes producing an interference pattern for all wavelengths within the range of the instrument.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to spectral scanning interferometers and more particularly to interferometers made with spiralling toroidal mirrors. 
     2. Description of the Prior Art 
     Previous interferometers have been made using a reciprocating mirror to obtain repetitive interferograms. Interferograms, representing an arrangement of various wavelengths of radiation incidented upon the beamsplitter, may be transformed into spectra. Computers have been used to make this transformation and plot radiant intensities versus frequency or wavelengths. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is the basic concept of the present invention, 
     FIG. 2 is the preferred embodiment of the present invention, and 
     FIGS. 3, 4, 5 and 6 are alternative construction designs of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Throughout the following description, like numbers refer to like elements. 
     FIG. 1 shows the basic schematic of a revolving mirror interferometer. Incoming radiation 10 is focused by a lens 12 to a point before a beamsplitter 14. Beamsplitter 14 is located within optical beam 10 and a spiralling toroidal mirror 16 which rotates in the direction shown by arrow 18. The distance between beamsplitter 14 and the focused point of radiation 10 depends on how much area of beamsplitter 14 is to be illuminated. Radiation 10 is divided into two components by beamsplitter 14. The component shown by arrow 20 is transmitted through beamsplitter 14 to a fixed mirror 22. Component 20 is reflected back to beamsplitter 14 from fixed mirror 22. The component shown by arrow 24 is reflected off of beamsplitter 14 to the interior surface of spiralling toroidal mirror 16. Component 24 is also reflected back to beamsplitter 14. The recombination of components 20 and 24 will produce a fringe pattern for various wavelengths corresponding to the path difference travelled by components 20 and 24. This fringe pattern is recorded by detector 26. 
     FIG. 1 shows spiralling toroidal mirror 16 mounted so it rotates in an X-Y plane. The X-Y plane is the plane of symmetry of spiralling toroidal mirror 16. In this plane, the radius R(θ) of the spiral gradually increases as the angle of rotation, θ, increases. Planes perpendicular to the X-Y plane and perpendicular to the center of the spiral intersect the spiralling toroidal mirror surface. Each intersection is an arc of circle radius R(θ). The mirror surface is spiral shaped in the X-Y plane and spherical shaped in the perpendicular plane. 
     Rays of component 24 that are in the perpendicular plane are reflected from a spherical arc and have identical optical path lengths. By making the spiral gradual, rays of component 24 in the X-Y plane will have small variations in optical path length. This geometric design results in a large number of rays used in the fringe image. In a Michelson interferometer, only the principle ray is perpendicular to the mirror surface and remains perpendicular as the mirror moves. This difference provides a high throughput advantage for the current invention. Throughput is defined as the amount of flux per unit sterance when all rays in a beam have equal steronoid. 
     As spiralling toroidal mirror 16 rotates, the path length travelled by component 24 changes. Thus, the rotation of spiralling toroidal mirror 16 produces components of the interferogram for each wavelength as a function of the rotational angle, θ. The spectral components of radiation 10 are obtained from the interferogram. This provides a complete spectral scan within the range of the optical components of the interferometer. 
     FIG. 2 shows a schematic of the preferred embodiment. Source 30 emits radiation 10. Radiation 10 is collected by lens 12 and focused to a point before beamsplitter 14 which is located within the radiation beam. Converging rays are desirable and a lens 32 may be added to improved the performance, by decreasing the variation of the optical path differences within the field of view. Lens 32 is not normally present in the preferred embodiment. Spriralling toroidal mirror 16 is rotated by a drive means 38. Drive means 38 can be any of several well known devices. Examples include belt drive, gear drive and friction wheel among others. Detector 26 views the fringe patterns reflected from output mirror 34 after they are focused by lens 36. Detector 26 can be either a photographic or electronic detection system. At the user&#39;s option, detector 26 can include means for comparing observed spectral with known patterns. 
     FIGS. 3, 4, 5 and 6 show alternative embodiments of the present invention. 
     FIG. 3 shows use of a folding mirror 40. Folding mirror 40 permits other elements to be located outside of the cavity of the spiralling toroidal mirror 16. 
     FIG. 4 uses two spiralling toridal mirrors 16 rotating counter to one another. This arrangement permits increased spectral range since both components have varying pathlengths from the beamsplitter. 
     FIG. 5 uses a convex spiralling toroidal mirror 16. The convex reflecting surface is the exterior surface. This arrangement permits several units to be placed around the convex mirror. 
     FIG. 6 has a canted spiralling toroidal mirror 16. The principle ray of the incoming radiation 10 is at an angle of 45° with the rotational axis of the mirror. This permits the space in front of the mirror to be completely open, providing easy access for cutting tools. An optical frame 40 is supported by an air bearing 42. They support an optical cylinder 44 which is adjusted by aligning and clamping screws 46. 
     FIG. 6 also shows means for comparing known spectra with observed spectra Detector 26 sends a signal of the information it is receiving to a correlator 50. Correlator 50 compares this information to known spectral information recorded on magnetic coating 52 which is on the base of spiralling toridal mirror 16. Magnetic coating 52 can be either a magnetic drum, magnetic tape or any similar device. Read and write heads 54 are used to record the spectra desired and to read the spectra back to correlator 50 which can make the comparison with observed spectra from detector 26. 
     It is obvious that other modifications and variations can be made on what has been disclosed.