Before You Start
- Inform lab users of the types of activities you will be engaged in and any precautions that need to be taken, for example, removal of barriers, need for protective eyewear, venting a chamber, using cryogens, etc.
- Remove all watches, rings, bracelets, earrings, and ID badges. These items can reflect light, which can be hazardous. If these items cannot be removed (i.e. a ring), cover it with tape, which will produce a diffuse reflection.
- There should be no line of sight between the room entrance and optics on the optical table(s). In addition to actual safety precautions, it is also important to reduce the perception that passers-by are at risk. Perimeter guards, enclosures around the table, and a curtain at the door also reduce the perception of risk to uninformed visitors.
- Glass in the lab and even laminated posters are possible reflection hazards. They can send reflections to totally unexpected areas. Contain the beam to the optical table to avoid this hazard.
- Enclosure of the laser equipment or beam path is the preferred method of control, since the enclosure will isolate or minimize the hazard. When engineering controls do not provide adequate means to prevent access to direct or reflected beams at levels above the Maximum Permissible Exposure (MPE), it may be necessary to use personal protective equipment (please see Appendix 14.2.). Note that use of personal protective equipment may have serious limitations when used as the only control measure with higher power Class 4 lasers or laser systems. The protective equipment may not adequately reduce or eliminate the hazard and may be damaged by the incident laser radiation.
| Table 14.4 Eyewear selection chart | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Simplified Method for Selecting Laser Eye Protection for Intrabeam Viewing for Wavelengths between 400 and 1400 nm | |||||||||
Q-Switched Lasers (1 ns to 0.1 ms) | Non-Q-Switched Lasers (0.4 ms to 10 ns) | Continuous Lasers Momentary (0.25 to 10 s) | Continuous Lasers Long-Term Staring Greater than 3 hours | Attenuation | |||||
| Maximum Output Energy(J) | Maximum Beam (J-cm-2) | Maximum Energy(J) | Maximum Beam (J-cm-2) | Maximum Power Output Energy(W) | Maximum (W-cm-2) | Maximum Power Output Energy(W) | Maximum (W-cm-2) | Attenuation Factor | OD |
| 10 | 20 | 100 | 200 | NR | NR | NR | NR | 1 x 108 | 8 |
| 1.0 | 2.0 | 10 | 20 | NR | NR | NR | NR | 1 x 107 | 7 |
| 10-1 | 2 x 10-1 | 1.0 | 2 | NR | NR | 1.0 | 2 | 1 x 106 | 6 |
| 10-2 | 2 x 10-2 | 10-1 | 2 x 10-1 | NR | NR | 10-1 | 2 x 10-1 | 1 x 105 | 5 |
| 10-3 | 2 x 10-3 | 10-2 | 2 x 10-2 | 10 | 20 | 10-2 | 2 x 10-2 | 1 x 104 | 4 |
| 10-4 | 2 x 10-4 | 10-3 | 2 x 10-3 | 1.0 | 2 | 10-3 | 2 x 10-3 | 1 x 103 | 3 |
| 10-5 | 2 x 10-5 | 10-4 | 2 x 10-4 | 10-1 | 2 x 10-1 | 10-4 | 2 x 10-4 | 1 x 102 | 2 |
| 10-6 | 2 x 10-6 | 10-5 | 2 x 10-5 | 10-2 | 2 x 10-2 | 10-5 | 2 x 10-5 | 10 | 1 |
| NR= Not Recommended | |||||||||
Protective eyewear is necessary for Class 3 and 4 laser use where irradiation of the eye is possible. Such eye protection should be used only at the wavelength and energy/power for which it is intended (Table 14.4). Eye protection may include goggles, face shields, spectacles or prescription eyewear using special filter materials or reflective coatings (or a combination of both) to reduce exposure below the MPE. The following information is needed to select the appropriate laser safety eyewear:
- Wavelength(s)
- Mode of operation (continuous wave or pulsed)
- Maximum exposure duration (assume worst case scenario)
- Maximum irradiance (W/cm2) or radiant exposure (J/cm2)
- Maximum permissible exposure (MPE)
Optical density (OD) could be calculated easily (https://www.lia.org/evaluator/od.php)