Safe clinical application of laser radiation

explanation and details of calculations go to calculations : website-app back to home screen

PROGRAM OBJECTIVE:

see VIDEO:

instruction video

Safe clinical application of lasers: calculation of

· MPE (Maximum Permissible Exposure MPE in W/m²)

· NOHD (Nominal Ocular Hazard Distance in m)

· Transmission of safety goggles,

for pulsed and continuous lasers,

according to EU-Directive 2005/26..

Safety Condition:

The laser intensity at the target (“exposure”, in W/m²), MUST remain smaller than the MAXIMUM PERMISSIBLE EXPOSURE (MPE).

This MPE is tabulated for different laser light wavelengths, pulse lengths (or continuous), divergence angles (target seen from focus) and subtense angles (focus, seen from target).

From this MPE a NOMINAL OCULAR HAZARD DISTANCE can be calculated, which is the smallest distance from focus where the Safety Condition is fulfilled.

Publications: (in Dutch)

- Veiligheidsaspecten bij klinisch gebruik van lasers

- De keuze van een laserveiligheidsbril

Overview of Maximum Permissible Exposures (MPE; in W/m^2)

MPE depends on the angular subtense (alpha) of the source, as seen from the target. See the publications.

(This figure is made with the stand-alone version of the program, which is incorporated in the HYGIRAD-package).

Input screen of the program .

A laser treatment is considered to consist of a set of (one or more) trains of laser pulses.

Each train may contain one or more pulses.

A treatment with a continuous laser will contain (one or more) trains, each consisting of one single pulse,

with a pulse duration equal to the train duration.

Example of downloaded output screen with calculations.

The output contains MPE- , NOHD- and OD-calculations, together with details of the calculations,

like the applied Directive formulae and data about thermal and other corrections.

.

*** CALCULATION OF LASER HAZARD DISTANCE ***

according to Directive 2006/25/EG

Laser: *** standard laser ***

Laser type : Pulsed

Wavelength [nm] : 532.0

(full) Divergence angle [rad] : 0.0125

Profile Correlation Factor [-] : 2

Focus (waist) diameter [m] : 4.000E-04

Distance laserhousing to focus [m] : 0.3000

Pulse : power [W] : 1000000

... : energy [J] : 5.000E-03

... : duration [s] : 5.000E-09

... : repetition frequency [Hz] : 1000.0

Train : power [W] : 5.0000

... : energy [J] : 50.000

... : duration [s] : 10.000

... : repetition frequency [Hz] : 0.1000

... : # pulses per train [-] : 10000

Total : power [W] : 5.0000

... : energy [J] : 50.000

... : duration [s] : 10.000

... : # trains in total [-] : 1

Safe distance eye from focus [m] : 0.2500

For this wavelength the damage is:

EYE: photochemical + retina (thermal) + thermal

SKIN: thermal

Number of pulses and trains in Tmin (= 1.80E-05 s)

= 1 <= 1,

so no thermal correction needed.

Calculation with: CA = 1.000 | CB = 43.65 | CC = 1.000

T1 = 100.0 s | Tmin= 1.8E-05 s - see Directive EU.

CE and T2: dependent on alpha: see table Results.

RESULTS: (H: energy density in J/m^2 - E=MPE: power density (intensity) in W/m^2)

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WITHOUT THERM. CORR.: formula CE T2 [s] MPE alpha [rad] NOHD [m] Transm. OD

eye: 1 pulse H=5E-3.CE 1.000E+00 1.000E+01 1.000E+06 3.132E-06 127.93 3.837E-06 5.416

..id. with CF1 .. N= 10000, CF= 1.000E-01 1.000E+00 1.000E+01 1.000E+05 9.914E-07 403.96 3.836E-07 6.416

..id. with CF2 .. N= 10000, CF= 1.000E-01 1.000E+00 1.000E+01 1.000E+05 9.914E-07 403.96 3.836E-07 6.416

eye: 1 train H=18.CE.t^0.75 1.000E+00 1.000E+01 1.012E+01 4.463E-06 89.991 7.769E-06 5.110

eye: total H=18.CE.t^0.75 1.000E+00 1.000E+01 1.012E+01 4.463E-06 89.991 7.769E-06 5.110

skin: 1 pulse H=200.CA 1.000E+00 1.000E+01 4.000E+10 6.601E-04 0.9063 1.700E-01 0.769

..id. with CF1 .. N= 10000, CF= 1.000E-01 1.000E+00 1.000E+01 4.000E+09 2.014E-04 2.2865 1.584E-02 1.800

..id. with CF2 .. N= 10000, CF= 1.000E-01 1.000E+00 1.000E+01 4.000E+09 2.014E-04 2.2865 1.584E-02 1.800

skin: 1 train H=1.1E4.CA.t^0.25 1.000E+00 1.000E+01 1.956E+03 6.234E-05 6.7222 1.515E-03 2.819

skin: total H=1.1E4.CA.t^0.25 1.000E+00 1.000E+01 1.956E+03 6.234E-05 6.7222 1.515E-03 2.819

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NOHD includes distance laser housing-focus; transmission is from the focus onward.

CF1,2 : correction factors for number of pulses (N) in train (or Tmin) resp. totaa: CF = N^(-0.25)

(correction only with thermal damage and if number of pulses in Tmin > 1;

the actual number is: 1 => correction not needed.)

Transm. = transmission of safety goggles, while at safety distance (0.2500 m)

OD = Optical density of goggles.

Alpha = angular subtence of the source: waist as seen from target (in rad).

AEL = (Accessible Emission Limit) [W] = MPE x LA; .

LA = Limiting Aperture [m^2] (3.85E-5 m^2; diam.=7 mm for Visible and IR lasers).

If NOHD=999999: iterations not convergent.

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