Question

1. You are imaging a fibroblast (cell type involved in wound healing) with a microscope. In standard bright-field mode, the image does not exhibit a strong contrast, so you switch to using differential interference contrast (DIC) microscopy. For the purposes of this question, assume you are using a green laser (o 532 nm in vacuum) to illuminate thee sample. a) What is the phase shift (in terms of the number of wave cycles, N) between light travelling along paths a and b in the image shown? Path a passes only through water (n-1.33), while path b passes through a thin section (thickness -1.20 um) of cytoplasm, with n-1.38. b) What is the phase shift (in terms of the number of wave cycles, N) between light travelling along paths c and d in the image shown? Both paths start in water; path d then passes through a thin section of cytoplasm (thickness 1.20 um, n-1.38), while path c then passes through the cell nucleus (thickness-2.10 μm, n-1.48; ignore the very thin sections of cytoplasm in this path c) ANedl cycles c) Which of the previous two interfaces (water/cytoplasm beam paths in part (a) or cytoplasm/nucleus beam paths in part (b)) would result in a darker spot in the DIC image? Briefly explain your answer.

Answer 1

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