Laser Alignment Safety
AHD Guidlines for LASER Alignment
The following are requirements and suggestions for the laser alignment section of a laser AHD at LBNL (note that the alignment procedures are only one part of the laser AHD).
Laser Alignment Guidelines to Help Prevent Accidents
- No unauthorized personnel will be in the room or area.
- Laser protective eyewear must be worn.
- All laser users must attend the LBNL laser safety class, EHS0280.
- The individual who moves or places an optical component on an optical table is responsible for identifying and terminating every stray beam coming from that component.
- To reduce accidental reflections, watches and reflective jewelry should be taken off before any alignment.
- Beam blocks must be secured.
- When the beam is directed out of the horizontal plane, it must be clearly marked.
- A solid stray beam shield must be securely mounted above the area to prevent accidental exposure to the laser beam.
- All laser users must receive an orientation to the laser use area by an authorized laser user of that area.
- Laser users must have had their baseline eye examination prior to performing any alignment procedures.
- The lowest possible/practical power will be used during alignments.
- When possible, a course alignment should be performed with a HeNe alignment laser.
- Have beam paths at a safe height, below eye level when standing or sitting, not at a level that tempts one to bend down and look at the beam. If necessary, place a platform around the optical table to raise one’s height.
The techniques for laser alignment listed below will be used to help prevent accidents during alignment of the lasers covered by this AHD.
Access to the room/area is limited to authorized personnel only.
Persons conducting the alignment have been authorized by the PI and are listed in this AHD.
A NOTICE sign must be posted at entrances when temporary laser control areas are used or when unusual conditions exist that warrant additional hazard information be available to personnel wishing to enter the area.
If the laser is a Class IIIb or IV open-beam system, make sure exterior warning signs/indicators are functioning.
Use beam blocking barrier or laser curtain to contain beam - Use "Notice" and "Danger" signs per ANSI standards.
Consider having someone present to help with the alignment.
Remove watches, rings, dangling badges, necklaces, reflective jewelry, etc. before any alignment begins. The use non-reflective tools should be considered.
Remove all unnecessary equipment, tools, combustible material (if fire is a possibility) to minimize the possibility of stray reflections and non-beam accidents.
Skin protection should be worn on the face, hands and arms when aligning UV systems.
Identify equipment and materials necessary to perform alignment.
Have all equipment and materials needed before beginning the alignment. This system requires the following items: tools, targets, beam stops/blocks, power meter/detector, beam profiling system, curtain, signage, caution tape, personal protective equipment (PPE): alignment eyewear, face shields for scattered UV.
Pay attention to housekeeping; make sure the immediate work area/benchtop/optical table is free from opportunistic specular reflectors not need for alignment (e.g., glass bottles, razor blades, forceps, screw drivers, optical posts, photographic paper, plastic, dye cells, etc.)
Cover windows or viewing ports within the controlled area.
Prepare the beam delivery system: remove beam tubes or other parts of the protective housing as necessary, including extended sections that may be covered by beam tubes or bellows; check all optics (mirrors, lenses, filters, polarizers, expanders, etc.) and optomechanical components (base plates, post holders and fasteners, mirror mounts, etc.) ensuring they are currently aligned (for changes/ additions to an existing alignment) and securely mounted.
Isolate and demarcate the area to avoid distractions and minimize the hazard to others.
If the high-power laser is embedded in other equipment, establish temporary laser controlled area.
Appropriate laser protective eyewear MUST be worn by all persons within the Nominal Hazard Zone (NHZ) whenever there is an open Class 3B or Class 4 beam. The NHZ is considered to be the entire room or lab in which the laser is located unless otherwise specified in the AHD. Violation of this policy is cause for a STOP WORK action.
ANYONE witnessing a violation of this policy has the right and the obligation to initiate a STOP WORK action and report it to the LSO and division management.
You must have the correct eyewear for your wavelength(s) and power.
The LSO has authorized reduced optical density eyewear to allow the beam spot to be seen. Measures shall be taken and documented to ensure that no stray hazardous specular reflections are present before the lower OD eyewear is worn. A return to the Maximum OD eyewear as listed in the laser table will be made when the alignment is complete. The eyewear is labeled as alignment eyewear and is stored in a different location than the standard laser eyewear for this operation.
No direct (intrabeam) viewing by eye is allowed unless specifically evaluated and approved by the LSO. Intrabeam viewing is to be avoided by using cameras or fluorescent devices.
When using viewing aids to visualize the beam, reach into the beam path slowly and deliberately with the card slightly angled so you can see the diffuse reflection. Adjust the optic so that the beam strikes the card just in front of the surface of the component.
Invisible beams are viewed with IR/UV cards, business cards or card stock, craft paper, viewers, 3x5 cards, thermal fax paper, Polaroid film or similar technique. Operators are aware that specular reflections off some of these devices is possible, and that they may smoke or burn.
Label all areas where the beam leaves the horizontal plane. If the beam path changes elevation (+Z), be aware of the increased potential for vertical reflections.
Terminate all stray or unused beams.
Confine the beam to the optical table or benchtop. Be aware of the potential for errant reflections (stray beams) from components such as polarizers and dielectric mirrors. Check for stray beams at each step and again after completing all alignment steps. As you progress down the optical path, place beam blocks behind optics to be adjusted to stop errant (stray) beams.
Close the shutter or insert the beam block during adjustments; resecure optics making sure components are properly located/adjusted.
Make sure that the beam shutter is closed or a beam block is in front of the end window. Make sure beam block is securely mounted.
If the beam path to be aligned is located in different rooms, locate a beam block in the beam path between the rooms, and align one room, then the other. If line of sight with personnel in other rooms is blocked, use two-way, real-time communications. Be patient at each step.
Restore the system to normal operational mode (pay attention to the protective housing, interlock switches, and shutters) and verify normal operation.
Light power reduction
Perform the "rough" or coarse" alignment with the beam blocked.
Reduce the beam power through the use of ND filters, beam splitters and dumps, or reducing power at the power supply. Avoid the use of high-power settings during alignment as much as is practical. If the alignment has been performed at lower power or with a low-power collinear beam but final steps will be performed at operational power levels, be sure and change to the appropriate eyewear for the high-power beam.
Pulsed lasers are aligned by firing single pulses when practical. For pulsed lasers, use single pulses and/or reduce pump power.
For Q-switched lasers, turn off the Q-switch and use in the low-power, CW mode
For CW lasers with adjustable power, adjust the power to a minimum stable level.
Co-axial low power lasers should be used when practical for alignment of the primary beam.
Enclose the beam as much as practical, close the shutter as much as practical during course adjustments, secure optics/optics mounts to the table as much as practical, secure beam stops to the table or optics mounts.
If the primary laser is optically pumped by another laser and alignment of the pump beam is necessary, block the primary beam to limit potential multi-wavelength exposure/eyewear concerns, align the pump beam, and then replace beam enclosure in the pump-to-laser beam path.