Double Pass Interferometer Displacement Calculator
Convert signed whole fringes and residual phase to ideal double-pass mirror displacement.
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Result
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Calculation steps
Work through one step at a time or reveal the complete calculation. The steps use your current inputs.
How to calculate
Distinguish optical path change from physical mirror travel in a double-pass geometry.
Mirror displacement=(fringes+phase/360) λvac/(2n)
Worked example
100 fringes at632.8 nm in index1 correspond to31.64 μm mirror displacement.
Assumptions and input details
Ideal collinear double pass, signed phase already unwrapped to the entered whole-fringe count. No cosine/Abbe error, environmental refractive-index estimation, wavelength calibration or absolute measurement certification.
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Using this calculator
Can I enter my own problem?
Yes. Replace the example values with your own inputs. The result, calculation steps, tables and applicable diagrams update from those inputs. Blank or invalid values clear the result; example values are never silently substituted for missing inputs.
Are the results exact?
Results use floating-point arithmetic and displayed rounding. Read the formula, assumptions and any stated data precision before interpreting the result.
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