21. The transmission gratings, which swing into the optical path behind the mirrors, provide Chandra with high resolution spectroscopy. 22. In this manner, gravity ( fail safe ) returns the red roundel into the lamp's optical path . 23. Also the difference in optical path length through each of the two objective lenses is carefully aligned to be minimal. 24. Since the beam is no longer traveling the full optical path length to the floor, its reflected angle changes. 25. The Gladstone Dale term ( n " 1 ) is the non-linear optical path length or time delay. 26. The optical path difference between the paths taken by two identical waves can then be used to find the phase change. 27. In the simplest case, a single gel is inserted into the optical path to produce light of the same color. 28. The intensity data as a function of the optical path difference are processed and converted to height information of the sample. 29. Also, the difference in optical path length through each of the two objective lenses is carefully aligned to be minimal. 30. In this mode no dispersive element is placed in the optical path and any objects are directly imaged on the detector.
