| 20100128282 | PHASE DIFFERENCE COMPARISON TO MEASURE VERY SMALL SPACING BETWEEN BODIES - An apparatus and a method for measuring very small separations between a transparent or semi-transparent first body and a second body is disclosed. A light source produces light that is split into two distinct paths. One path is directed through the first body at two locations, one where it reflects from the interface at the separation to be measured, and another where the second body does not affect the reflection. The second path is directed at a frequency shifter. The two paths are recombined and interferometric variations of intensity are detected. The difference in phase between the measurement and reference areas with the second body not present, is subtracted from the difference in phase between the measurement and reference areas with the second body present. The difference in differences yields the phase change that occurs when the second body is introduced. The separation is calculated based on this phase change. | 05-27-2010 |
