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Optical Path Difference given Fringe Width Calculator

Formula

The formula to calculate Optical Path Difference is:

$\Delta = (RI - 1) \cdot t \cdot \frac{\beta}{\lambda}$

Where:

$\Delta$ is the Optical Path Difference (m)
$RI$ is the Refractive Index
$t$ is the Thickness (m)
$\beta$ is the Fringe Width (m)
$\lambda$ is the Wavelength (m)

Definition

Optical Path Difference is the difference in distance traveled by two light waves having the same frequency and initial phase but taking different paths to reach the same point.

Example Calculation

Let's assume the following values:

Refractive Index ( $RI$ ) = 1.333
Thickness ( $t$ ) = 1 m
Fringe Width ( $\beta$ ) = 0.5107 m
Wavelength ( $\lambda$ ) = 0.268 m

Using the formula:

$\Delta = (1.333 - 1) \cdot 1 \cdot \frac{0.5107}{0.268}$

Evaluating:

$\Delta = 0.634563805970149 \text{ m}$

The Optical Path Difference is 0.634563805970149 m.

Conversion Chart

Refractive Index (RI)	Thickness (t)	Fringe Width (β)	Wavelength (λ)	Optical Path Difference (Δ, m)
1.3	1	0.5107	0.268	0.571679104478
1.31	1	0.5107	0.268	0.590735074627
1.32	1	0.5107	0.268	0.609791044776
1.33	1	0.5107	0.268	0.628847014925
1.34	1	0.5107	0.268	0.647902985075
1.35	1	0.5107	0.268	0.666958955224
1.36	1	0.5107	0.268	0.686014925373
1.37	1	0.5107	0.268	0.705070895522
1.38	1	0.5107	0.268	0.724126865672
1.39	1	0.5107	0.268	0.743182835821