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Fabry-Perot Cavity Finesse & FSR Calculator engineering
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Fabry-Perot Cavity Finesse & FSR Calculator

Laser optics & optical resonators: Calculate cavity Free Spectral Range (FSR), finesse (ℱ), resonance transmission linewidth (FWHM), and photon lifetime (τ_c).

Cavity Geometry & Mirror Optics

Mirror separation distance
Center optical wavelength
Input coupler power reflectivity
Back mirror power reflectivity
Vacuum = 1.0, Air ~1.0003, Crystal
Scatter, absorption, diffraction losses

Resonance Spectral Properties

Free Spectral Range (FSR)
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Cavity Optical Finesse (ℱ)
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ℱ = π · √R / (1 - R)
Resonance Linewidth (Δν_FWHM)
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Photon Cavity Lifetime (τ_c)
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1 / (2 · π · Δν)
Quality Factor (Q)
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Optical Q = ν / Δν
Intracavity Power Buildup
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Resonant field magnification

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Frequently Asked Questions

What is the physical meaning of optical cavity finesse (ℱ)?

Finesse is the ratio of the spacing between adjacent longitudinal resonance peaks (Free Spectral Range, FSR) to the full-width at half-maximum (FWHM) of an individual transmission peak: ℱ = FSR / Δν. It characterizes the frequency resolving sharpness of the resonator independent of cavity physical length.

How does cavity length affect Free Spectral Range (FSR)?

Free Spectral Range scales inversely with optical path length: FSR = c / (2·n·L). A short micro-cavity (L = 1 mm) has a very wide FSR (150 GHz), ensuring only a single laser mode fits within the gain spectrum, whereas a long cavity (L = 1 meter) has closely spaced modes (FSR = 150 MHz).

What is intracavity circulating power buildup?

At exact optical resonance, constructive interference of stored photons creates an intracavity circulating intensity that is significantly higher than the incident laser beam: I_intra ≈ (2·ℱ / π) · I_incident. In ultra-high finesse cavities (ℱ > 100,000), a 1-Watt laser creates over 60 kW of circulating optical power.