Calculate coherence length, center wavelength, or wavelength bandwidth from two values using Lc ≈ λ0²/Δλ with metric or imperial units.

Coherence Length Calculator

Enter any 2 values to calculate the missing variable (uses Lc ≈ λ0²/Δλ for a narrowband source).

Coherence Length Formula

The following two example problems outline the steps and information needed to calculate the coherence length using the common narrowband approximation (results depend on how bandwidth is defined, e.g., full-width at half-maximum).

L_c \approx \lambda_0^2 / \Delta\lambda
  • Where Lc is the coherence length (units of length, e.g., m)
  • λ0 is the center wavelength of the source
  • Δλ is the wavelength bandwidth (wavelength spread), in the same units as λ0

To calculate the coherence length, square the center wavelength, then divide by the wavelength bandwidth.

How to Calculate Coherence Length?

The following example problems outline how to calculate coherence length.

Example Problem #1:

  1. First, determine the center wavelength.
    • The center wavelength is given as: 3.
  2. Next, determine the wavelength bandwidth.
    • The wavelength bandwidth is provided as: 4.
  3. Finally, calculate the coherence length using the equation above: 

Lc = λ02 / Δλ

The values provided above are inserted into the equation below and computed.

Lc = 32 / 4 = 2.25

Example Problem #2: 

For this problem, the variables required are provided below:

center wavelength = 10

wavelength bandwidth = 20

Test your knowledge using the equation and check your answer with the calculator.

Lc = λ02 / Δλ = ?