Light filtering apparatus
A light filtering apparatus includes a first dispersion device, a spatial filter and a second dispersion device. The first dispersion device is arranged to cause spatial dispersion of an incident light beam as a function of its frequency. The spatial filter is arranged to filter the dispersed light beam so as to produce a spatially filtered resultant beam. The second dispersion device is arranged to recombine the dispersed and filtered light beam so as to produce an output light beam having a substantially similar spectrum at any position within the output beam cross-section.
1. Light filtering apparatus comprising:
a first dispersion device arranged to cause spatial dispersion of an incident light beam as a function of its frequency;
a spatial filter arranged to filter the dispersed light beam so as to produce a spatially filtered resultant beam; and
a second dispersion device arranged to recombine the dispersed and filtered light beam so as to produce an output light beam having a substantially similar spectrum at any position spatially and angularly within the output beam cross-section.
2. Light filtering apparatus according to claim 1 , wherein the second dispersion device operates in the opposite sense to the first dispersion device with respect to the respective beam direction.
3. Light filtering apparatus according to claim 1 , wherein the spatially dispersed beam is angularly dispersed by the first dispersion device.
4. Light filtering apparatus according to claim 1 , wherein the spatial filter is a transmissive filter.
5. Light filtering apparatus according to claim 1 , wherein the spatial filter comprises a replaceable filter.
6. Light filtering apparatus according to claim 1 , wherein the light filtering properties of the spatial filter are controllable.
7. Light filtering apparatus according to claim 6 , wherein the spatial filter is controllable or programmable.
8. Light filtering apparatus according to claim 7 , wherein the light filtering properties are controllable as a function of the position of incidence of the dispersed beam upon the filter.
9. Light filtering apparatus according to claim 8 , wherein the filter is a spatial light modulator.
10. Light filtering apparatus according to claim 1 , further comprising at least one mirror arranged to focus the light upon the second dispersion device.
11. Light filtering apparatus according to claim 1 , further comprising at least one lens arranged to focus the light upon the second dispersion device.
12. Light filtering apparatus according to claim 1 , wherein the first dispersion device functions by a refractive mechanism.
13. Light filtering apparatus according to claim 12 , wherein the first dispersion device is a prism.
14. Light filtering apparatus according to claim 12 , wherein the first dispersion device comprises two prisms.
15. Light filtering apparatus according to claim 1 , wherein the first dispersion device functions by a diffractive mechanism.
16. Light filtering apparatus according to claim 15 , wherein the first dispersion device is a diffraction grating.
17. Light filtering apparatus according to claim 15 , wherein the first dispersion device comprises two diffraction gratings.
18. Light filtering apparatus according to claim 12 , wherein the first dispersion device is a reflective device.
19. Light filtering apparatus according to claim 12 , wherein the first dispersion device is a transmissive device.
20. Light filtering apparatus according to claim 1 , wherein the second dispersion device functions by a refractive mechanism.
21. Light filtering apparatus according to claim 20 , wherein the second dispersion device is a prism.
22. Light filtering apparatus according to claim 20 , wherein the second dispersion device comprises two prisms.
23. Light filtering apparatus according to claim 1 , wherein the second dispersion device functions by a diffractive mechanism.
24. Light filtering apparatus according to claim 23 , wherein the second dispersion device is a diffraction grating.
25. Light filtering apparatus according to claim 23 , wherein the second dispersion device comprises two diffraction gratings.
26. Light filtering apparatus according to claim 20 , wherein the second dispersion device is a reflective device.
27. Light filtering apparatus according to claim 20 , wherein the second dispersion device is a transmissive device.
28. Light filtering apparatus according to claim 1 , wherein the first and second dispersion devices are a common dispersion device.
29. Light filtering apparatus according to claim 1 , wherein a mirror is provided to direct the filtered beam back along the path of the spatially dispersed beam.
30. Light filtering apparatus according to claim 1 , further comprising a light source for generating the incident beam.
31. Light filtering apparatus according to claim 30 , further comprising a collimator, for receiving light from the source and producing a collimated incident beam.
32. Light filtering apparatus according to claim 30 , wherein the light source and first dispersion device are an integral device.
33. Light filtering apparatus according to claim 1 , wherein the light beam has frequencies in at least one of the visible, ultra-violet or infra-red parts of the electromagnetic spectrum.
34. Light filtering apparatus according to claim 33 , wherein the light beam is a white light beam.
35. Light filtering apparatus according to claim 6 , further comprising a control system for controlling the filtering properties of the spatial filter.
36. Light filtering apparatus according to claim 1 , wherein the output beam is substantially uniform spatially and angularly as a function of position within the output beam cross section.
37. Light filtering apparatus according to claim 1 , wherein the spatial filter is a reflective filter.