By: Michael Woods
SLAC National Accelerator Laboratory
SLAC National Accelerator Laboratory has developed a Laser Alignment Practical Training Course as one of its core laser safety classes. The course is taught to small groups of up to three students and takes 1-3 hours to complete. This practical course is not a substitute for site-specific On-the-Job Training. It does, however, provide a good introduction in core laser safety practices that can be broadly applied. Alignment and diagnostic tasks are performed with low power lasers. Students learn safe alignment and diagnostic techniques and how to avoid common mistakes that might lead to an accident. The class is taught by laser supervisors, enabling them to assess the skill level of new laser personnel and determine the subsequent level of supervision needed. The course has six alignment tasks (beam expander alignment, 2-pinhole alignment, periscope alignment, use of beam-splitting polarizers, co-alignment of two laser beams, and gratings and diffractive optics principals). For each task, discussion points are given for the instructor to review with the students. The optics setup includes different wavelength lasers, a beam expander, mirrors, irises, a periscope, a beam-splitting polarizer and a diffraction grating. Diagnostic tools include viewing cards, an IR viewer and a ccd camera. Laser eyewear is available to block some laser wavelengths in the setup.
As an example, the tasks and discussion points for beam expander alignment are:
- Block or disable green beam
- Remove lenses from the beam path
- Align beam through irises to a beam block and mark the beam spot
- Insert the first lens into the beam path and optimize position & alignment
- Insert the second lens into the beam path and optimize position & alignment
- Check beam collimation
- Does student remove rings, badges, and jewelry before starting alignment?
- How do you tell that the beam is collimated?
- What is the expected beam magnification and lens separation?
- How do you center lenses? Why?
- How do you control back reflections?
- Which back reflections should you be particularly worried about and why?
- Does the student block the laser beam when inserting and removing optics elements?
Four upgrades to the class are currently planned:
- Add a 785nm diode laser, with power of 3 mW (Class 3R).
- Add a 405 nm diode laser with power of 5 mW (Class 3R).
- Replace the 543nm HeNe laser with a 532nm diode laser, with power of 1 mW (Class 2).
- Add additional camera diagnostics to demonstrate different camera options.
The laser upgrades will make the same laser wavelengths available as for Ti:sapphire operation at 785nm with a 532nm pump beam, and for operation with the 2nd harmonic of the Ti:sapphire beam at ~400 nm.