Introduction to Laser Safety Goggles
Warning
Laser safety goggles are the last step of laser safety and are not a substitute for learning and applying laser safety rules.
Safety Standards
In Europe, the norm that specifies requirements for laser safety goggles is EN 207. Certified goggles are marked with the CE logo. Certified goggles can sustain their advertised optical depth for 5 seconds of direct exposure to a CW laser or 50 pulses of a pulsed laser.
This norm uses a simplified model to determine the required optical density for a given wavelength and intensity based the IEC 60825-14 norm. The latter defines the Maximum Permissible Exposure (MPE) and explains how to calculate it for your own lasers.
This simplified model used by EN 207 imposes stricter requirements on the attenuation needed compared to the more complicated model used by the IEC and is the only norm that should be used to find the correct laser safety goggles.
Beam Diameter
The EN 207 certifies goggles for a certain power density (or energy density for pulsed lasers). Since the power (or energy) of the laser is usually known, you must find the relevant beam diameter. The diameter d that should be used is the 1/e diameter: at least 63% of the laser power must fit in a circle of diameter d. The diameter used should be the minimum laser beam diameter that could hit the goggles under reasonably foreseeable circumstances.
If you are not wearing glasses and are exposed to visible light, collimated beams (up to a diameter of 7 mm) are more dangerous than focused beams because your eye will focus the light down to a 0.1 mm spot on your retina. However, when wearing goggles, focused beams are always more dangerous since they heat up the goggles to higher temperatures. Thus, you should use the minimum laser beam diameter that could hit the goggles under reasonably foreseeable circumstances when you are looking for safety goggles.
EN 207
To calculate the correct EN 207 rating for your laser safety goggles, you must refer to the following tables:
| Scale number | OD | Maximum power (E) and energy (H) density | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| 180 nm to 315 nm | 315 nm to 1400 nm | 1400 nm to 1000 μm | ||||||||
| Laser type | ||||||||||
| D | I, R | M | D | I, R | M | D | I, R | M | ||
| E (W/m2) | H (J/m2) | E (W/m2) | E (W/m2) | H (J/m2) | E (W/m2) | E (W/m2) | H (J/m2) | E (W/m2) | ||
| LB1 | 1 | 0.01 | 3×102 | 3×1011 | 102 | 0.05 | 1.5×107 | 104 | 103 | 1012 |
| LB2 | 2 | 0.1 | 3×103 | 3×1012 | 103 | 0.5 | 1.5×108 | 105 | 104 | 1013 |
| LB3 | 3 | 1 | 3×104 | 3×1013 | 104 | 5 | 1.5×109 | 106 | 105 | 1014 |
| LB4 | 4 | 10 | 3×105 | 3×1014 | 105 | 50 | 1.5×1010 | 107 | 106 | 1015 |
| LB5 | 5 | 102 | 3×106 | 3×1015 | 106 | 5×102 | 1.5×1010 | 108 | 107 | 1016 |
| LB6 | 6 | 103 | 3×107 | 3×1016 | 107 | 5×103 | 1.5×1011 | 109 | 108 | 1017 |
| LB7 | 7 | 104 | 3×108 | 3×1017 | 108 | 5×104 | 1.5×1012 | 1010 | 109 | 1018 |
| LB8 | 8 | 105 | 3×109 | 3×1018 | 109 | 5×105 | 1.5×1013 | 1011 | 1010 | 1019 |
| LB9 | 9 | 106 | 3×1010 | 3×1019 | 1010 | 5×106 | 1.5×1014 | 1012 | 1011 | 1020 |
| LB10 | 10 | 107 | 3×1011 | 3×1020 | 1011 | 5×107 | 1.5×1015 | 1013 | 1012 | 1021 |
| Symbol | Laser Designation | Typical pulse duration (in seconds) |
|---|---|---|
| D | Continuous wave (CW) laser | > 0.2 |
| I | Pulsed laser | 10-6 to 0.2 |
| R | Giant-pulsed laser | 10-9 to 10-6 |
| M | Mode-coupled laser | < 10-9 |
To use these tables, find the correct laser designation (D, I, R or M) for your laser by using Table 2. Then, divide the power (or energy) by the beam area and use Table 1 to find the correct scale number.
For example, if you have a 10 mW 632 nm CW laser with a 5 mm beam diameter, according to Table 2, the laser type is D. The power density is 10×10-3/(π×(2.5×10-3)2) = 5.1 × 102 W/m2. Thus, according to Table 1, you need D LB2 goggles.
How to Choose the Right Goggles
The safety glasses you must wear must have the correct EN 207 rating (both scale number and laser type) in order to give you enough time to move your head out of the beam's path. If you are working with multiple lasers at the same time, it is not enough to buy goggles with the correct EN 207 rating for each wavelength independently and you should seek advice from a laser safety officer.
Uncomfortable goggles might discourage you from wearing them so you don't hesitate to try a few different goggles. Moreover, good goggles should not prevent you from seeing so you should check the VLT of the goggles before buying them.