Electrical: More people have been killed by electrocution from the laser electronics than blinded from exposure to a laser beam. Lethal voltages are present in the power supplies of all of our lasers, as well as in the lasers themselves. If you are not experienced working with high voltages in general, and laser power supplies in particular, you have no business doing any work inside a power supply except the regular maintenance described in the relevant laser manual (invariably done with the power off and the power supply unplugged from its electrical outlet).
Fire: If a Class IV laser beam hits anything flammable, you are almost guaranteed of ignition. Care must be taken with all the lasers.
Eye and Skin Damage: The greatest daily hazards are in this area. All of the Class IV lasers in our lab can easily cause total blindness or painful sores. The type of damage inflicted depends on the wavelength, pulse energy, pulse width, power, and repetition rate. Damage from ultraviolet radiation tends to reside in the outer layers of the skin for body exposure or in the cornea if the eyes are exposed. Low energy/power beams can cause burns like sunburns. Higher energy/power can ablate skin. In general, long-term exposure to ultraviolet beams or even diffuse scatter may lead to cataracts, glaucoma, and skin cancer.
Optical and infrared radiations penetrate more deeply into the body. Beams entering the eyes are focused by the cornea onto the fovea. The intensity of the beam at the focus can be enormous, even though the total energy present in the beam may be small. Not only can the region of the fovea at the focus be damaged, but the laser can generate a shock wave damaging other parts of the eye. Eye and skin damage may be immediately painful, or not noticed for a time.
It is difficult to place an upper limit on the energy a laser pulse can have and not cause blindness because of the many factors involved. Any beam should be considered hazardous. Even diffuse scatter can be dangerous, especially if the radiation is in the ultra-violet. There will in general be many more beams in the lab than the ones coming directly from the lasers. Every time a laser beam passes through any object, there will be reflections from the input and output surfaces. Suppose a laser passes through a lens. One or both of the surfaces will be curved, hence, the reflections that leave the lens will either converge or diverge. The converging beams can hurt nearby people or damage optics. Diverging beams are also dangerous because they can fill a large area with laser radiation. Unless everyone in the lab is careful, the lab will be filled with dangerous light. We must continually work hard to contain all the beams in the lab.
This is a description of some components that pose special hazards.
Dielectric Mirrors: If a mirror is a dielectric mirror, than it can actually transmit if it is placed at the wrong angle initially. Even if it is at the correct angle, there can be leakage light through it. Usually this can be blocked with black tape.
Glan-Thompson Polarizers: These polarizers work by transmitting light of one polarization and reflecting light of the orthogonal polarization. They are often placed in mounts that allow them to be rotated. As one is rotated, the reflected beam traces out a cone, which can easily intersect your eye or anyone else's in the laboratory. The output port for the reflected light must be blocked unless you intend to use this light. (Note: if the output port is blocked, you can damage the polarizer if you send a high power beam through it.)
Gratings: Here, you just need to be aware that a grating will typically have multiple beams leaving it from the different diffraction orders. Each one must be blocked if it is not used.
Dye lasers: These tend to produce a large number of extra beams as well as copious diffuse scatter. This light should be well contained, but do not assume it is. This is difficult to arrange during alignment.
Infrared Viewing Cards: These cards glow red when exposed to infrared light. They are essential when working with weak infrared beams. The problem is they are often laminated and the lamination acts as a good reflector. You must always hold one of these cards such that a specular reflection would be directed downward. Actually, this is a good idea for anything you place in the beam path. These cards must not be used in high power beams.
Infra-red Viewer: This is a device that converts IR light to electrons which then create an image on a screen. It looks a little like a camera or monocular, however it should not be treated as such. A beam that enters the device can reach your eye. This is for surveying a scene only.
Machined Hardware: You will probably have to machine your own mounting hardware on occasion. Generally, this presents no difficulty. Still, you must avoid creating shiny surfaces. These can cause dangerous reflections. If you use aluminum, the hardware can be anodized after the machining is complete if there is a dangerous surface present. Anodization is a chemical process that gives aluminum a flat black outer layer. Most of our optical hardware is made from anodized aluminum.
Watches and Jewelry: The face of a wristwatch is reflective, as are rings, metal wristbands and jewelry. If you are wearing a wrist watch and, as you reach towards an optical component, the face intersects a laser beam and you will send a dangerous reflection in an uncontrolled direction. All such apparel should be removed before working with laser radiation.