Laser Linewidth Calculator
Calculate laser linewidth from coherence length or derive coherence length and wavelength shift from linewidth.
Laser Linewidth and Coherence
Laser linewidth describes the spectral width of the emitted light. It is inversely related to coherence length — narrower linewidths correspond to longer coherence lengths and are important for interferometry, spectroscopy, and precision measurements.
Formulas
$$\Delta\nu = \frac{c}{2 L_c}$$ $$\Delta\lambda = \frac{\lambda^2 \cdot \Delta\nu}{c}$$\(L_c\) is coherence length, \(\Delta\nu\) is linewidth in hertz, \(\lambda\) is the center wavelength, and \(c\) is the speed of light.
Practical Notes
Single-frequency lasers can have linewidths from kilohertz to megahertz. Multimode lasers have much broader spectra. This calculator uses the standard Fourier-transform relationship between coherence length and linewidth.
Frequently Asked Questions
What is coherence length?
Coherence length is the maximum path difference over which a laser maintains a predictable phase relationship, typically \(L_c = c / (2\Delta\nu)\).
How is linewidth related to wavelength spread?
Spectral width in wavelength follows \(\Delta\lambda = \lambda^2 \Delta\nu / c\), linking frequency and wavelength uncertainties.
Why is linewidth given in MHz?
Many lasers are characterized in megahertz because their linewidths fall in the kHz to MHz range, which is convenient for engineering use.
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