Laser Safety Video 2

Описание: Laser safety video
P1. Laser radiation and the body
Laser radiation is monochromatic, coherent, plane polarized and has very small divergence.
100um diameter at retina is the spot from sun light if you stare at it.
Unfortunately, eye can focus the laser beam into a small size of 20um increasing the power density at that spot. That can damage the retina.
Blinking happens in 0.1s. Laser can damage retina much before that, 1e-6s
Eyes need to move while reading.
Fovea is a cover in retina 200um thick that holds the photoreceptors.
If Fovea is damaged, you’re only left with peripheral vision. That does not recover and you will be registered as blind.
The radiation absorved is the one damaged.
Cornea absoves in the far UV and can get damaged. You don’t see that radiation.
Near UV is absoved in the lens. That happens too.
Near IR goes focused in the retina where it will damaged without you blinking or looking away.
Far IR is absoved in the cornea.

Laser classes
Class I. Inherently safe. Low output or lowest ALS levels can’t be exceeded, for example if they are inside enclosures.
Class II. Safe for accidental viewing.
Class IIIa. They can cause damage if you stare into the beam or with optical instruments.
Class IIIb. Not only staring but other exposure is damaging. Protection of eyes is needed. HeNe lasers
Class IV. They can even cause fire, not only damage your eyes. Even diffuse reflections can be damaging to the eyes. Eye protection is needed. Skin protection may be needed too.
IIIb and IV should be enclosed as much as possible.

Lines of defense
Engineering controls: Full enclosures. Covers must be interlocked with beam power. Warning lights and labels of laser hazard if parts of beam can’t be enclosed.
Safety screens are a way to constraint beam into an area.
Spectral reflections are caused when beam hits polished surfaces.
Filters can be used to reduce power of beam and simplify alignment.
For alignment use powermeters, not trust your eye.
Beamstops must produce minimum scattered radiation.
Beam should not point to doors, neither their reflections.
Administrative controls
When not used, class 3b or 4 keys must be removed and brought to key holders.
Goggles must have an optical density enough for the specific wavelength you are working at.
For tunable lasers, there are broadband goggles.
Semiconductor lasers emit between red and infrared and are portable, so are harder to regulate and people may not treat them as dangerous
Several lasers will be used only in the same room if they are under the control of the same person.
Other problems like metallic parts heaten, or sparks from high power lasers, or gasses from toxic surfaces generated by heating.
UV lasers generate Ozone from air (what can be formed from HV discharge from electronic components and electrostatic from dust distractors too). Therefore adequate ventilation is important.
The same applies to solvants such as methanol in chemicals for die solutions. A lot of the solvants are flammable and often the dies themselves are carcinogenic.
Do preparations in a fume cover
The same applies to burning cryocoolants N2 or He. Watch for possible cryogenic burns
The coolant gases can displace oxygen and you end up suffocated.
Liquid nitrogen condenses easily oxygen from the air. Overpressure of oxygen in a recipient that was previously filled with air. Boiling point of N2 is 30 degC lower than of O2. Therefore, once N2 is removed, O2 may come back to gas and generate an overpressure if it has been sealed into some recipient. That’s because the expansion ratio of liquified oxygen is 1 to 860 (that happens with a lot of gases).
Decoration of the lab: lab well lighted and use light coloured walls to reduce the pupil size of people working there. Mate black surfaces to avoid reflections. Don’t have desk space for reading. Use of fire resistant blinds to avoid laser striking passers by
Invisible UV radiation can damage eyes and skin from plasma tubes from lasers, can damage eyes and skin. PS operating more 5kv may generate xrays.
The worst is HV electricity. Capacitors charged must be well earthed before working.
Solid state lasers have choke inductances for generating hv pulses up to 30kV.
Cooling water at high pressure with hoses can have leaks near HV may cause accidents.
The main sockets (multiple)/distribution boards should not be put in the ground since often there’s no light in the room and you may fall and electrocute.
Everybody working should not be fatigued and psychologically ok.
Pulses from lasers may cause epileptics.
If you are working with lasers you must look after your safety and that of others.
Eye injuries must be rushed to the next hospital. You better know where it is beforehand.
Safety laser safety officers should be informed of any event.