Methods and laser systems for reduction of undesired speckle
A system and method for using a laser, including using a coherent light source to generate a beam having a dominant wavelength wl; and providing along the beam's light path, at least one optical element having a surface upon which the beam impinges, whose roughness is between D and ½ wl−D where D is double the tolerance of the laser's dominant wavelength.
1. A method for using a laser, the method comprising:
using a coherent light source to generate a beam having a dominant wavelength wl; and
providing along the beam's light path, at least one optical element having a surface upon which the beam impinges, whose roughness is between D and ½ wl−D where D is double the tolerance of the laser's dominant wavelength.
2. A method according to claim 1 wherein the roughness is between ¼ and ⅛ of wl.
3. A method according to claim 1 wherein the roughness is between 75 and 90 nanometers.
4. A method according to claim 1 and also comprising providing a display surface on which an image is generated by said laser beam.
5. A method according to claim 4 wherein said optical element comprises said display surface.
6. A method according to claim 1 wherein said using comprises using plural coherent light sources to generate plural beams having respective dominant wavelengths wl1, wl2, . . . ;
and wherein said optical element has a surface whose roughness is greater than 10 nanometers and less than the shortest of said dominant wavelengths wl1, wl2, . . . .
7. A method according to claim 1 wherein said using comprises using plural coherent light sources to generate plural beams having respective dominant wavelengths wl1, wl2, . . . ;
and wherein said providing comprises providing plural optical elements for positioning along the beams' respective light-paths, having plural surfaces respectively whose respective roughnesses are greater than 10 nanometer and are D less than the dominant wavelengths wl1, wl2, . . . respectively.
8. A method according to claim 1 wherein said optical element comprises at least one of: lens, display screen, mirror, diffuser, image plane, optical cover, optical coating.
9. A method according to claim 1 wherein said laser serves at least one of: laser based display system such as a laser television or laser projector; and a laser sensing system such as a LiDAR.
10. A method according to claim 1 and also comprising providing an optical element having a surface whose roughness exceeds wl and reducing said roughness to between 10 nanometer and wl using a mechanical process.
11. A method according to claim 10 wherein said mechanical process comprises any of: etching, molding, polishing, machining, lapping, electro-polishing, grinding, boring.
12. A method according to claim 11 wherein said mechanical process comprises polishing including using a slurry having a particle size and wherein said particle size is selected to achieve roughness of between 10 nanometers and wl.
13. A method according to claim 1 and also comprising providing an optical element having a surface whose roughness is less than 10 nm and increasing said roughness to between 10 nanometers and wl using a roughening process.
14. A method according to claim 1 wherein said optical element is manufactured by a molding process characterized by a known, controlled relationship (tolerance) between a workpiece's roughness as a function of the mold's roughness and wherein the mold has a roughness which, given said tolerance, results in a workpiece whose roughness is between 10 nanometers and wl.
15. A method according to claim 11 wherein said machining comprises selecting a machining tool which yields roughness between 10 nanometers and wl in a workpiece machined thereby.
16. A method according to claim 9 wherein said laser based display system comprises a laser projector.
17. A method according to claim 1 wherein said roughness is between 10 nanometers and ½ wl−10 nm.
18. A method according to claim 1 wherein said roughness is between 15 nanometers and ½ wl−15 nm.
19. A method according to claim 13 wherein said roughening process comprises etching.
20. A laser system comprising:
a coherent light source operative to generate a beam having a dominant wavelength wl; and
positioned along the beam's light path, at least one optical element having a surface upon which the beam impinges, whose roughness is between D and ½ wl−D where D is double the tolerance of the laser's dominant wavelength.