Medical Laser Safety Calculator
Surgical laser with a focusing handpiece: NOHD beyond the focus and eyewear OD on the ICNIRP 2013 eye limits, with the spot's power density, fluence and the target's thermal relaxation time.
Educational only — not compliance-grade
These pages implement the published exposure limits for the cases each one states, but they are educational tools: no laser safety officer has signed them off.
- Do not use these results alone for PPE selection, NHZ / NOHD approval, controlled-area sign-off, enclosure/interlock approval, or formal classification.
- Always verify against ANSI Z136.1, IEC 60825-1, your local procedures, and the responsible laser safety officer / CLSO.
Laser and handpiece
Tissue
Power density at the spot, P/(πd²/4)
31831 W/cm²
Fluence per pulse or dwell
3183 J/cm²
Thermal relaxation time of the target
4.81 ms
Pulse longer: heat spreads beyond the target
Eyes of the staff
0.25 s for an unintended view of a visible beam and 10 s in the near infrared, 700–1400 nm; outside 400–1400 nm ICNIRP 2013 (p. 285) uses the longest exposure expected.
NOHD beyond the focus
2.00 m
Beam spreads at 80.0 mrad (b₀/f)
Governing limit
Cornea (IR)
Eyewear optical density
OD 4.71
For the beam at its focus (all of it inside the aperture; its peak below 1 mm and 0.35 s, ICNIRP note c); OD 2.52 for the 8.00 mm beam at the lens
Exposure over each eye limit against distance beyond the focus (log scales); above 1 the limit is exceeded.
Tissue: the power density is the clinical P/A over the 1/e² spot (the peak of a Gaussian spot is twice it). The thermal relaxation time is the time for the centre of a Gaussian temperature profile of 1/e diameter d to cool to half: d²/(16κ) for a cylinder (a vessel; selective photothermolysis, Anderson & Parrish 1983), and by the same rule d²/(27κ) for a sphere and 3d²/(16κ) for a layer, with κ = 0.130 mm²/s for soft tissue. A uniformly heated target instead gives times about 1.45× longer: take τ as an order of magnitude.
Eyes: beyond the focus the beam spreads at b₀/f, so the hazard distance is the standards' lens-on-laser value (f/b₀)√(4P/(πE)) with b₀ the 1/e diameter (the 1/e² input over √2), here on the ICNIRP 2013 limits for an exposure of up to t, averaged over each limit's aperture. For the focus itself a beam under 1 mm viewed for less than 0.35 s counts by its peak radiant exposure (ICNIRP Table 5 note c). The optical density brings the whole beam within every limit; the filter must also survive the beam (EN 207). Not modelled: bare fibres (use the fiber laser page), specular reflections from instruments, pulses, the skin.
Model and references
Textbook approximation. A standard approximation from the literature (for example paraxial, plane-wave or Gaussian-beam), valid within the range the page states. About the tiers
Lens-on-laser beam spreading at b₀/f from the focus; ICNIRP 2013 point-source eye limits over each aperture, exposures up to t; focus under 1 mm and 0.35 s by its peak (Table 5 note c); TRT: a Gaussian centre temperature (1/e diameter d) halves, A&P d²/(16κ) for a vessel, sphere and layer by the same rule. Not modelled: bare fibres, pulses, skin.
- ICNIRP (2013). Guidelines on limits of exposure to laser radiation of wavelengths between 180 nm and 1,000 µm. Health Phys. 105(3), 271–295. Tables 5 and 8. doi:10.1097/HP.0b013e3182983fd4
- ANSI Z136.1-2014, American National Standard for Safe Use of Lasers, Appendix B (lens-on-laser hazard zone); ANSI Z136.3-2018, Safe Use of Lasers in Health Care.
- Anderson, R. R. & Parrish, J. A. (1983). Selective photothermolysis: precise microsurgery by selective absorption of pulsed radiation. Science 220, 524–527. doi:10.1126/science.6836297