Claims
- 1. A method for measuring retardance in samples, said method comprisingproviding a source of monochromatic, polarized light having a wavelength λ; providing a detector for detecting the intensity of light incident thereon, said detector and said source defining an optical path therebetween; providing in said optical path a sample location for a sample whose retardance is to be measured, said sample having a retardance less than λ/24; providing in said optical path a pair of variable light retarders positioned so that the slow optical axes thereof are at a 45 degree angle to each other; measuring the light intensity at said detector for four different retarder settings with said sample in at said sample location, yielding light intensity values I1, I2, I3, and I4; measuring the light intensity at said detector for said four different retarder settings without said sample at said sample location, yielding light intensity values I1BG, I2BG, I3BG; and I4BG, determining a compensated retardance magnitude value for the sample corrected for background retardance directly from said measured light intensities with and without said sample at said sample location according to the equation magncase1=arctan(tan (swing2)*(term2term1-term2BGterm1BG)2+(term3term1-term3BGterm1BG)2)wherein term1=I3+I4−2I1, term2=I3-I4term3=I3+I4-2I2 term1Bg=I4BG+I4BG−2I1BG term2Bg=I3BG−I4BGterm3Bg=I3BG+I4BG−2I2BG and “swing” represents a selected retardance value which is typically the same magnitude as the retardance expected to be measured in the sample.
- 2. A method as in claim 1 wherein a raw azimuth value azimraw for said sample corrected for background retardance is determined according to the equation azimraw=arctan(&LeftBracketingBar;(term3term1-term3BGterm1BG)(term2term1-term2BGterm1BG)&RightBracketingBar;)2and an actual azimuth value is determined from the raw azimuth value and different sign combinations of expressions (term3/term1−term3BG/term1BG) and (term2/term1−term2BG/term1BG).
- 3. A method as in claim 2 wherein for (term2/term1−term2BG/term1BG)>0 and (term3/term1−term3BG/term1BG)>0, azim=180° −azimraw.
- 4. A method as in claim 2 wherein for (term2/term1−term2BG/term1BG)>0 and (term3/term1−term3BG/term1BG)≦0, azim=azimraw.
- 5. A method as in claim 2 wherein for (term2/term1−term2BG/term1BG)<0 and (term3/term1−term3BG/term1BG)≧0, azim=90° +azimraw.
- 6. A method as in claim 2 wherein for (term2/term1−term2BG/term1BG)<0 and (term3/term1−term3BG/term1BG)<0, azim 90° −azimraw.
- 7. A method as in claim 2 wherein for (term2/term1−term2BG/term1BG0) =0 and (term3/term1−term3BG/term1BG)<0, azim=45°.
- 8. A method as in claim 2 wherein for (term2/term1−term2BG/term1BG)=0 and (term3/term1−term3BG/term1BG)>0, azim=135°.
- 9. A method for measuring retardance in samples, said method comprising providing a source of monochromatic, polarized light having a wavelength λ;providing a detector for detecting the intensity of light incident thereon, said detector and said source defining an optical path therebetween; providing in said optical path a sample location for a sample whose retardance is to be measured, the sample having a retardance greater than λ/24; providing in said optical path a pair of variable light retarders positioned so that the slow optical axes thereof are at a 45 degree angle to each other; measuring the light intensity at said detector for four different retarder settings with said sample in at said sample location, yielding light intensity values I1, I2, I3, and I4; measuring the light intensity at said detector for said four different retarder settings without said sample at said sample location, yielding light intensity values I1BG, I2BG, I3BG; and I4BG, determining a compensated retardance magnitude value for the sample corrected for background retardance from said measured light intensities with and without said sample at said sample location.
- 10. A method as in claim 9 wherein a raw azimuth value for said sample corrected for background retardance is determined according to the equation azimraw=arctan(&LeftBracketingBar;[term3term1-term3BGterm1BG][term2term1-term2BGterm1BG]&RightBracketingBar;)2wherein term1=I3+I4−2I1 term2=I3-I4 term3=I3+I4−2I2term1Bg=I4BG+I4BG−2I1BG term2Bg=I3BG−I4BG term3Bg=I3BG+I4BG−2I2BG and an actual azimuth value azim is determined from the raw azimuth value and different sign combinations of expressions (term3/term1−term3BG/term1BG) and (term2/term1−term2BG/term1BG).
- 11. A method as in claim 10 wherein for (term2/term1−term2BG/term1BG)>0 and (term3/term1−term3BG/term1BG)>0, azim=180°−azimraw.
- 12. A method as in claim 10 wherein for (term2/term1−term2BG/term1BG)>0 and (term3/term1−term3BG/term1BG)≦0, azim=azimraw.
- 13. A method as in claim 10 wherein for (term2/term1−term2BG/term1BG)<0 and (term3/term1−term3BG/term1BG)≧0, azim=azimraw.
- 14. A method as in claim 10 wherein for (term2/term1−term2BG/term1BG)<0 and (term3/term1−term3BG/term1BG)<0, azim=azimraw.
- 15. A method as in claim 10 wherein for (term2/term1−term2BG/term1BG) =0 and (term3/term1−term3BG/term1BG)<0, azim=45°.
- 16. A method as in claim 10 wherein for (term2/term1−term2BG/term1BG)=0 and (term3/term1−term3BG/term1BG)>0, azim 135°.
- 17. A method as in claim 10 wherein said compensated retardance magnitude value is determined according to the equationmagn2=magnstep 1−magnBG·cos(2(azimstep1−azimBG))·[1−cos2(magnstep)] wherein magnstep1=magnstep1=arctan(tan(swing2)·&AutoRightMatch;&AutoLeftMatch;&AutoRightMatch;&AutoLeftMatch;(term2term1-term2BGterm1BG)2+(term3term1-term3BGterm1BG)2) wherein magnBG=magnBG=arctan(tan(swing2)(term2Bgterm1Bg)2+(term3Bgterm1Bg)2) wherein azimBG is determined from azimrawBG and different sign combinations of expressions (term3/term1−term3BG/term1BG) and (term2/term1−term2BG/term1BG), and “swing” represents a selected retardance value which is typically the same magnitude as the retardance expected to be measured in the sample.
Parent Case Info
This application claims the benefit of provisional application No. 60/212,173, filed Jun. 16, 2000.
US Referenced Citations (2)
Number |
Name |
Date |
Kind |
5521705 |
Oldenbourg et al. |
May 1996 |
A |
6320657 |
Aspnes et al. |
Nov 2001 |
B1 |
Provisional Applications (1)
|
Number |
Date |
Country |
|
60/212173 |
Jun 2000 |
US |