View source for EN 207

[[image:laser goggles en207.jpg|thumb|300px|EN207-compliant laser goggles. The user has added yellow stickers summarizing the complicated EN207 specifications shown in the inset.]]
'''EN 207''' is the European norm for [[laser safety]] eyewear. Any laser eye protection sold within the European Community must be certified and labeled with the [[CE mark]]. According to this standard, laser safety glasses should not only absorb laser light of a given wavelength, but they should also be able to withstand a direct hit from the laser without breaking or melting. In this respect, the European norm is more strict than the American norm (ANSI Z 136) that only regulates the required [[optical density]]. More precisely, the safety glasses should be able to withstand a [[continuous-wave|continuous wave]] laser for 10 seconds, or 100 pulses for a pulsed laser.

An EN 207 specification might read ''IR 315--532 L6''. Here, the letters ''IR'' indicate the laser working mode, in this case a ''pulsed'' mode. The range ''315--532'' indicates the wavelength range in nanometers. Finally, the scale number ''L6'' indicates a lower limit for the optical density, i.e. the transmittance within this wavelength range is less than 10<sup>-6</sup>.<ref>Laser Vision catalog 2005, printed version. The [http://www.lvg.com/uvex/laservision/intl/en/home.nsf/?Open&DirectURL=7DEA869E7F02D923C12571F4006D3932 online version] is less extensive.</ref>


==Laser working modes==

EN 207 specifies four laser working modes:
{|class="wikitable"
!Working mode
!Letter
!Pulse length
|-
| [[Continuous wave]]
| D
| &gt; 0.25 s
|-
| Pulsed mode
| I
| >1 &mu;s&ndash;0.25 s
|-
| Giant pulsed mode
| R
| 1 ns&ndash;&mu;s
|-
| Modelocked
| M
| &lt; 1 ns
|}

==Scale numbers==

The scale numbers range from L1 to L10, where the number is a lower
limit for the optical density, i.e. L''n'' means that OD&gt;''n'', or
<math>T < 10^{-n}</math>, where ''T'' is the transmittance. The
minimum scale number for a given laser depends on the working mode and
the wavelength as follows:

{|class="wikitable"
! align="top" | Working mode
!align="top" |Wavelength range
!align="top" |Maximum laser<br>power density
!align="top" |Minimum protection level<br>for given power*
|-
|D (continuous)
|180--315 nm
|1&times;10<sup>n-3</sup> W/m<sup>2</sup>
|log(''P'') + 3
|-
|
|315--1400 nm
|1&times;10<sup>n+1</sup> W/m<sup>2</sup>
|log(''P'') - 1
|-
|
|1400 nm--1000 &mu;m
|1&times;10<sup>n+3</sup> W/m<sup>2</sup>
|log(''P'') - 3
|-
|I,R (pulsed)
|180--315 nm
|3&times;10<sup>n+1</sup> J/m<sup>2</sup>
|log(''E''/3) - 1
|-
|
|315--1400 nm
|5&times;10<sup>n-3</sup> J/m<sup>2</sup>
|log(''E''/5) + 3
|-
|
|1400 nm--1000 &mu;m
|1&times;10<sup>n+2</sup> J/m<sup>2</sup>
|log(''E'') - 2
|-
|M (ultrashort pulses)
|180--315 nm
|1&times;10<sup>n+10</sup> W/m<sup>2</sup>
|log(''P'') - 10
|-
|
|315--1400 nm
|1.5&times;10<sup>n-4</sup> J/m<sup>2</sup>
|log(''E''/1.5) + 4
|-
|
|1400 nm--1000 &mu;m
|1&times;10<sup>n+11</sup> W/m<sup>2</sup>
|log(''P'') - 11
|-
| colspan="4" style="background: transparent; text-align:right;" | *''P'' in W/m<sup>2</sup>, ''E'' in J/m<sup>2</sup>.<br>Level numbers should be rounded upwards.
|}

;Examples
# the laser operates at 1064 nm and has a pulse duration of 10 ns, 100 mJ/cm<sup>2</sup> (or 10<sup>3</sup> J/m<sup>2</sup>). You have goggles that are specified as ''DIR 1064 L5''. The pulse duration indicates that we should look at the ''R'' specification, with scale number ''n''=5, which gives an upper limit of 5&times;10<sup>2</sup> J/m<sup>2</sup>, which means that these goggles do not offer suitable protection for this particular laser.
# the laser operates at 780 nm, is continuous wave with a power of 50 mW/cm<sup>2</sup> (''P'' = 500 W/m<sup>2</sup>). This means you need a ''D'' protection level of <math>log(500)-1=1.69</math>, which is rounded up to 2. In other words, the safety goggles should be at least ''D 780 L2''.

From the scale it can be inferred that the power densities that correspond to <math>n=0</math> are considered safe without protective eyewear.

==References==
{{reflist|2}}

[[Category:Lasers]]
[[Category:Occupational safety]]
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