Hands-On Laser Beam Path Alignment Practical Environment, Safety, Health & Quality Office SERF E141 Last updated: 12/28/2017
Hands-On Laser Beam Path Alignment Practical 1-3 hour course Required for new Class 3B and Class 4 laser operators. Optional for existing operators. Taught as needed by a Laser System Supervisor (LSS) with the assistance of the Laser Safety Officer (LSO) LSS receives practical training from the LSO 3 students maximum NREL 2
Technical Objectives Teach laser beam path alignment best practices to new laser operators. Interactive practical for LSS to assess skill level and technique of new laser operators. NREL 3
Exercise Outline Students must complete the 2 required exercises and 1 additional exercise at minimum, to be selected by the LSS based on the operator s scope of work. Exercise 1: Laser Hazards & Controls* Exercise 2: 2-Iris Alignment* Exercise 3: Power Attenuation Exercise 4: Co-Alignment of Two Beams Exercise 5: Retroreflector Safety & Lessons Learned Exercise 6: Periscope Safety & Use Exercise 7: Alignment Through a Monochromator Exercise 8: Aligning IR Beams Exercise 9: Motorized Remote Alignment *Required, at minimum NREL 4
Practical Objectives Student Objectives Demonstrate safe alignment practices to be used with Class 3B and Class 4 lasers Learn techniques for assisted viewing with invisible beams and while wearing laser protective eyewear Recognize hazards of Class 3B and Class 4 lasers Identify appropriate controls to mitigate laser beam hazards Recognize how to avoid common mistakes that may lead to an accident LSS Objectives Assess skill level of new laser operators or operators who are learning new alignment techniques Assess subsequent level of mentorship and supervision that may be needed NREL 5
Optical Beam Path Diagram Beam splitter Iris Objective Iris Iris Polarizer Motorized mirror Flipup mirror ND Filters Pinhole Collimating Lens λ/2 waveplate 405 nm 850 nm Target Polarizer 635 nm Periscope (Insertable) Monochromator Focusing Lens Flipup mirror Retroreflectors (Shrouded & Unshrouded) Iris Motorized mirror NREL 6
Exercise 1: Laser Hazards & Controls Discuss common hazards involved with Class 3B and 4 laser work and the need for appropriate controls. Talk about the culture that the new worker is coming from and understand how hazards and controls may differ at NREL. Demonstrate the controls available in the training lab, including: Proper eyewear selection Viewing cards and IR viewers Fully-enclosed Class 1 systems Enclosure interlocks Temporary enclosures and beam blocks Techniques for tracking stray beams Window coverings Warning signage and enclosure labeling NREL 7
Exercise 2: 2-Iris Alignment 635 nm Beam splitter Iris Iris Tools Laser safety eyewear Beam blocks IR viewing cards IR viewer Power meter The purpose of this exercise is to align the beam through two adjustable irises by adjusting the mirrors and checking for stray reflections. Tasks 1. Initial setup: Start with all laser beams blocked or disabled Remove the neutral density filters, objective, pinhole, and collimating lens if present Open the two irises fully 2. Don laser safety eyewear 3. Enable the red 635 nm laser. 4. Optimize alignment through the two irises by hand adjusting the mirrors, checking for alignment with the IR viewing card. 5. Place the power meter in line with the beam and demonstrate it s use. 6. Close down the two irises and adjust their alignment if needed to center on the beam. 7. Discuss how clipping of the expanded beam through the irises affects the alignment quality. 8. Verify all stray beams are contained by performing an area survey with the IR viewer. NREL 8
2-Iris Alignment Discussion Points Does the student remove rings, badges, and jewelry before starting? How to chase the beam through the beam path. How to use an IR card or IR viewer to verify and set alignment while wearing laser eyewear. How to properly hold an IR card, such that a reflected beam from it would go down rather than up at the worker. Note the reflected beams from the card and the potential hazard. Why does the mirrored surface of the flipup mirror point down when the mirror is down? Which back reflections should be particularly worried about? Why? What are the potential points of stray reflections? Check for and block any stray beams. NREL 9
Exercise 3: Power Attenuation Polarizer 635 nm Beam splitter Iris ND Filters Iris λ/2 waveplate Polarizer Tools Laser safety eyewear Beam blocks Power meter Power attenuation is an important way to reduce the hazard level for open-beam alignment. Using the power meter, show how neutral density filters and polarization can be effective attenuators. Tasks 1. Initial setup: o o o Start with all laser beams blocked or disabled Remove the neutral density filters, objective, pinhole, and collimating lens if present Open the two irises fully 2. Don laser safety eyewear 3. Enable the red 635 nm laser. 4. Place the power meter in line with the beam and measure the beam. 5. Install various neutral density (ND) filters in the filter wheel and demonstrate power measurement changes. 6. Remove the ND filter and install the λ/2 waveplate and second polarizer, adjusting the two to demonstrate power measurement changes. NREL 10
Power Attenuation Discussion Points Discuss how to select an appropriate ND filter and how to verify the right filter is installed. Explain the benefits of installing ND filters as far upstream in the beam path as possible to reduce power throughout the optical setup. Before polarizer is inserted into the beam path, discuss how polarizers are mounted and adjusted. Share lessons learned about how pulsed lasers can damage optic coatings like polarizers Discuss how λ/2 waveplate is used to rotate linear polarization and can be used (together with polarizers) for intensity control. How to inspect for stray beams with fluorescent cards and IR viewer. NREL 11
Exercise 4: Co-Align Two Beams Beam splitter Iris Objective Iris 405 nm 635 nm Flipup mirror Pinhole Collimating Lens Tools Laser safety eyewear Beam blocks Fluorescent cards Co-aligning two beams practices precision alignment. Tasks 1. Block or disable the 405 nm beam. 2. Don laser safety eyewear, then verify 635 nm beam alignment through the 2 irises. 3. Block or disable the 635 nm beam. 405 nm beam block and verify beam alignment to the beam splitter. 4. Optimize alignment of both beams through the two irises by adjusting the mirrors. 5. Install the objective, pinhole and collimating lens and demonstrate how to use these to clean up the beam. Demonstrate expanding the 635 nm beam. Diffraction rings can be adjusted and will be different from the 405 nm diffraction rings. NREL 12
Co-Align Two Beams Discussion Points What are some other ways to combine beams on a sample, particularly beams of different colors? Discuss the drawbacks, difficulties and benefits of co-aligning multiple beams in an experiment. NREL 13
Exercise 5: Retroreflector Safety & Lessons Learned Beam splitter Iris Iris Iris Mirror 635 nm Retroreflectors (Shrouded & Unshrouded) Alignment into a retroreflector to achieve beam separation. Limitations of beam separation at the outer edges of the optic, and the mirror hazard that exists at the edges. Demonstrate how shows block this hazard. Iris Tools Mirror Laser safety eyewear Beam blocks Fluorescent cards Tasks 1. Block or disable all beams. Insert the unshrouded retroreflector into the beam path. 2. Don laser eyewear. 3. Unblock the 635 nm beam and verify its alignment entering the retroreflector. 4. Adjust alignment of the retroreflector to optimize beam separation. 5. Demonstrate how beams at the edges reflect out of the optic and can be shrouded. NREL 14
Retroreflector Discussion Points Share lessons learned from the 2015 laser eye incident at NREL. The hazards of the mirror edge reflection and how shrouded optics block stray beams. Beams may be focused through parts of the beam path alignment, and expanded later. Explain how expanding the beam into the mirror edge region can result in unintentional reflections. Use of temporary enclosures and beam blocks as portions of the beam path alignment are finished. NREL 15
Exercise 6: Periscope Safety & Alignment Beam splitter Iris Iris Iris Mirror Target 635 nm Periscope (Insertable) Iris Periscope alignment and hazards of bringing the beam off the table. Tasks 1. Block or disable all beams. Insert the training periscope into the beam path. 2. Don laser eyewear. 3. Unblock the 635 nm beam and verify its alignment entering the periscope. 4. Adjust periscope alignment mirrors as needed to optimize beam against the target. Tools Mirror Laser safety eyewear Beam blocks Fluorescent cards NREL 16
Periscope Alignment Discussion Points Discuss the hazards of bringing the beam up off the table. Advantages of enclosed vs. open periscopes Does the student block beams before removing/inserting optical elements? How do you perform surveys with IR viewers and cards to check for stray beams? NREL 17
Exercise 7: Alignment Through a Monochromator Beam splitter Iris Iris Iris Mirror 635 nm Align through a slit in the monochromator. Explain the use of diffraction gratings. Tasks 1. Block or disable all beams. Flip up mirror to direct beam into monochromator. 2. Don laser eyewear. Monochromator 3. Unblock the 635 nm beam and verify its alignment entering the focusing lens. Focusing Lens 4. Adjust alignment as needed to optimize beam through the slit into the monochromator. 5. Remove the monochromator housing cover, and discuss the use of diffraction gratings. Flipup mirror Tools Laser safety eyewear Beam blocks Fluorescent cards NREL 18
Monochromator & Diffraction Grating Discussion Points Functions of a monochromator. Alignment to a slit. Splitting of the beam using a diffraction grating. Hazards of stray reflections from a diffraction grating. NREL 19
Exercise 8: Aligning IR Beams Repeat any previous exercise using the invisible 850 nm IR beam and the IR viewer. Discuss the difficulties and hazards that arise during alignment of invisible beams. NREL 20
Exercise 9: Motorized Remote Alignment Repeat any previous exercise with the enclosure covers in place, using the motorized mirror mount controls to align the beam path. Observe alignment with the remote camera. Discuss the advantages and disadvantages to remote alignment equipment. NREL 21
Course Summary This course instructs laser safety principles and best practices to new laser operators. The hands-on exercises serve as a skills assessment for Laser System Supervisors to observe new users. The discussion points encourage new laser operators to recognize risky behaviors and situations. The Laser Safety Officer will train LSSs for training uniformity and continuous improvement.
Thank You Please contact the Laser Safety Officer with questions www.nrel.gov or concerns. Alex Lindquist, LSO 303-384-6778 SERF E200-06 NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency NREL and is Renewable a national Energy, laboratory operated of the by U.S. the Department Alliance for of Sustainable Energy, Office Energy, of Energy LLC. Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC. NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.