Cavity Ring-Down Spectroscopy
Model CRDS ring-down time, sensitivity, and finesse. Visualize exponential decay with and without sample absorption.
Empty-Cavity Ring-Down τ₀
33.35 µs
effective path cτ₀ = 9.999 km
Ring-Down with Sample τ
1.388 µs
round-trip loss Λ = 0.004805
Sample Absorption α
0.00002303 cm⁻¹
(1/c)(1/τ − 1/τ₀) = A ln 10/L
Minimum Detectable α
1.00e-8 cm⁻¹
(Δτ/τ)/(cτ₀); 3.16e-9 cm⁻¹ Hz⁻¹ᐟ² averaged
Finesse ℱ
1308
π√ρ/(1 − ρ), ρ = e^(−Λ/2) ≈ 2π/Λ
Mode Spacing c/2L
149.9 MHz
mode FWHM 1/(2πτ) = 114.6 kHz
Model and references
Exact. The equations are exact within the stated assumptions, or are a standard's tabulated values. The results are as good as the inputs. About the tiers
Exact decay envelope of a two-mirror cavity filled with the sample (single-mode excitation); the detection limit assumes the stated ring-down-time noise per decay and white-noise averaging.
- O'Keefe A., Deacon D. A. G. (1988). Cavity ring-down optical spectrometer for absorption measurements using pulsed laser sources. Rev. Sci. Instrum. 59, 2544–2551. doi:10.1063/1.1139895
- Berden G., Peeters R., Meijer G. (2000). Cavity ring-down spectroscopy: experimental schemes and applications. Int. Rev. Phys. Chem. 19, 565–607. doi:10.1080/014423500750040627
- Siegman A. E. (1986). Lasers, ch. 11. University Science Books.