Section D : How to choose safety goggles ?

The first letter on the protective goggles label is the letter M , because the Ti:Sa laser is a mode-locked pulsed laser emitting pulses shorter than 1 ns.

The next information on the label is the wavelength of the radiation, expressed in nanometers : 800. If a source emits in a wide spectral range, the wavelength can be replaced by the two extremal wavelengths of the spectrum (600-900 for example).

The next information is the “L-number”, as presented in Appendix 4. We need however the energy per surface unit :

In Appendix 4, the relevant information is written in the column “wavelength : from 315 to 1400 nm” and laser type “M”. The relevant line is the one with the nearest value higher than 8.42 102 J/m². Presently, the L7 number corresponds to 1.5 103 J/m².

Warning : the previous calculation does not take into account the repetition rate of the laser. In order to take this parameter into account and to respect the standard (NF)EN 207, one must consider a typical pulse number N = 100. (see the section on individual protection).

The value of H previously considered must thus be corrected by a factor N1/4.

H' = N1/4 x H = 3.103 J/m². Thus, the L-number must finally be L8.

To conclude, the label written on the goggles must be : M 800 L8

One must first evaluate the maximal intensity on the axis of this beam, using its power (10 W) and diameter (2 w = 1.6 mm)

Using Appendix 4 for a continuous (D) laser emitting at 647 nm, one can deduce the appropriate goggles label : D 647 L6.