 |
Laser Safety
In most cases, a laser emits light in the form of a laser beam. This means that the light dominantly propagates in a certain direction, typically with most of the optical power
concentrated to a small area. This characteristic combined
with spatial coherence i.e. a fixed phase relationship
between the electric field values at different locations,
has as result that the power of laser is independent of the
distance to the radiation source.
The most recent classification norms (EN60825-1) have
catalogued lasers into several hazard classes, depending
on the Accessible Emission Limits. AELs are defined as the
exposure levels which are inherently safe for the eye; the
classification scheme is a measure of the laser system to
produce injures to the personnel.
| Class | Concept | Comment |
| 1 | The radiation emitted by this laser is not dangerous | No need for protection equipment |
| 1M | Eye safe when used without optical instruments, may not be safe when optical instruments are used | No need for protection equipment, if used without optical instruments |
| 2 | Eye safe by aversion responses including the blink reflex. | No need for protection equipment |
| 2M | The light that can hit the eye has the values of a class 2 laser, depending on a divergent or widened beam, it may not be safe when optical instruments are used | No need for protection equipment, if used without optical instruments |
| 3R | The radiation from this laser exceeds the MPE values (MPE: maximum permissible exposure). The radiation is max. 5 x AELs of class 1 (invisible) or 5 x of class 2 (visible). The risk is slightly lower than that of class 3B | Dangerous to the eyes, safety glasses are recommended |
| 3B | Old class 3B without 3R.
The view into the laser is dangerous. Diffuse reflections are not considered as dangerous. | Dangerous to the eyes, safety glasses are obligatory |
| 5 | Old class 4
Even scattered radiation can be dangerous, also danger of fire and danger to the skin | Personal safety equipment is necessary (glasses, screens) |
Laser safety regulations have the purpose of defining
the necessary guidelines to every operator working with
lasers. Most of the existing norms are for the major part
intended to deal with eye protection, being this the most
critical organ in relation to laser injury.
The current European norm - EN 60825 - requires that
laser safety eyewear provide sufficient optical density to
reduce the power of a given laser to equal to or less than
the listed Maximum Permissible Exposure levels (MPE).
EN 207 contains the specifications that eye
protection equipment shall have to be safe for
the laser operator: requirements related to optical
density (OD) and to stability to laser radiation.
| Duration of test for filters and eye protectors against laser radiation. |
| Testing conditions for laser type | Typical laser type | Pulse length (s) | Number of pulses |
| D | continuous wave laser | 5 | 1 |
| I | pulsed laser | 10-4 to -1 | 50 |
| R | Q-Switched pulsed laser | 10-9 to 10-7 | 50 |
| M | mode-locked pulsed laser | <10-9 | 50 |
Reference: EN 207
According to this norm, protection due to optical density
alone is not sufficient when the material of the eyewear
cannot withstand a direct hit. Filter and frame must be
able to resist a direct hit from the laser for which they have
been selected for at least 5 seconds (CW) or 50 pulses
(pulsed mode).
| Scale number | Maximum spectral trasmittance for laser wavelength
τ (λ) | Power and energy density (E, H) for testing the protective effort and stability to laser radiation in the wavelength range |
| 180 nm to 315 nm | >315 nm to 1400 nm | >1400 nm to 1000 µm |
| For test condition |
D
>3·104 |
I, R
10-9 to
3·104 |
M
<10-9 |
D
>5·10-4 |
I, R
10-9 to
5·10-4 |
M
<10-9 | D
>0,1 |
I, R
10-9 to 0,1 |
M
<10-9 |
ED
W/m2 | HI/R
J/m2 | EM
W/m2 | ED
W/m2 | HI/R
J/m2 | HM
W/m2 | ED
W/m2 | HI/R
J/m2 | EM
W/m2 |
| LB1 | 10-1 | 0,01 | 3·102 | 3·1011 | 102 | 0,05 | 1,5·10-3 | 104 | 103 | 1012 |
| LB2 | 10-2 | 0,1 | 3·103 | 3·1012 | 103 | 0,5 | 1,5·10-2 | 105 | 104 | 1013 |
| LB3 | 10-3 | 1 | 3·104 | 3·1013 | 104 | 5 | 0,15 | 106 | 105 | 1014 |
| LB4 | 10-4 | 10 | 3·105 | 3·1014 | 105 | 50 | 1,5 | 107 | 106 | 1015 |
| LB5 | 10-5 | 102 | 3·106 | 3·1015 | 106 | 5·102 | 15 | 108 | 107 | 1016 |
| LB6 | 10-6 | 103 | 3·107 | 3·1016 | 107 | 5·103 | 1,5·102 | 109 | 108 | 1017 |
| LB7 | 10-7 | 104 | 3·108 | 3·1017 | 108 | 5·104 | 1,5·103 | 1010 | 109 | 1018 |
| LB8 | 10-8 | 105 | 3·109 | 3·1018 | 109 | 5·105 | 1,5·104 | 1011 | 1010 | 1019 |
| LB9 | 10-9 | 106 | 3·1010 | 3·1019 | 1010 | 5·106 | 1,5·105 | 1012 | 1011 | 1020 |
| LB10 | 10-10 | 107 | 3·1011 | 3·1020 | 1011 | 5·107 | 1,5·106 | 1013 | 1012 | 1021 |
Reference: EN 207
EN 208 refers to glasses for laser alignment: these
glasses allow the user to see the beam spot while
aligning the laser. Alignment glasses must be able to
limit the incident power to the power of a class II laser and
to withstand a direct hit.
| Scale Number | CW lasers and pulsed lasers with pulse length of >2·10-4 s
Max. laser power in W | Pulsed lasers with a pulse length >10-9 to 2·10-4 s
Max. pulse energy in J |
| RB1 | 0.01 W | 2·10-6 |
| RB2 | 0.1 W | 2·10-5 |
| RB3 | 1 W | 2·10-4 |
| RB4 | 10 W | 2·10-3 |
| RB5 | 100 W | 2·10-2 |
Reference: EN 208
|
 |
