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Laser safety

Laser safety. Paul van Kampen 02/02/11. Almost all you need to know about laser safety. Beware of electrical safety Don’t expose your eyes or skin Minimise the number of shiny surfaces Wear goggles Beware of water leaks Use warning signs Use interlocks. Types of laser.

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Laser safety

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  1. Laser safety Paul van Kampen 02/02/11

  2. Almost all you need to know about laser safety • Beware of electrical safety • Don’t expose your eyes or skin • Minimise the number of shiny surfaces • Wear goggles • Beware of water leaks • Use warning signs • Use interlocks

  3. Types of laser • Continuous wave (cw) or pulsed • Power • Wavelength • Visible/invisible • Effect on skin, cornea, retina

  4. Laser classification • What is it based on? • Maximum Permissible Exposure (MPE) • 10% of dose that has 50% chance of doing damage • Depends on wavelength, body part, cw or pulsed • Visible-IR range, cornea, cw: 1 mW/cm2 • Example: class 1 or class I laser limit • Fully dilated pupil: diameter 7 mm, area 0.39 cm2 • Maximum permissible power: 0.39 mW

  5. Laser classification (old) • Class I: safe (UNFOCUSSED!) • Class II: safe - your aversion to bright light will protect you • Class IIIA: cw: 1-5 mW, safe unless you look at it, or its reflection, directly • Class IIIB: cw 5-500 mW, pulsed <10 J/cm2, sometimes diffuse reflection hazard • Class IV: cw >500 mW, pulsed >10 J/cm2, diffuse reflection, fire, skin hazard

  6. More data become available

  7. More data become available

  8. Laser classification (new) • Class 1(M): safe (UNFOCUSSED!) <0.4 mW • Class 2(M): safe - your aversion to bright light will protect you. <1 mW • Class 3R: cw: 1-5 mW, safe unless you look at it, or its reflection, directly. Low risk • Class 3B: cw 5-500 mW, (<300 mW visible), pulsed <10 J/cm2, diffuse reflection OK • Class 4: cw >500 mW, pulsed >10 J/cm2, diffuse reflection, fire, skin hazard, interlock required

  9. UV lasers • Excimer lasers:gas premix typically contains 0.1 percent of fluorine/chlorine • ArF, KrCl, KrF: UV-C radiation • Eye: snowblindness • Skin: sunburn, skin cancer • XeCl: UV-B radiation • Eye: snowblindness • Skin: skin aging, increased pigmentation • XeF, Nd:YAG tripled: UV-A radiation • Eye: cataracts • Skin: skin burn, pigment darkening

  10. Germicidal lamps • 15 W UV-C lamp 254 nm, cylindrical, 30 cm tall • 40% efficient in UV-C so 6 W of UV-C light • Model: every ring 1 cm high centred on lamptransmits a total of 200 mW outward • Irradiance of 30/r mW/cm2 at r cm from lamp • Skin/eye MPE = 3 mJ/cm2, cumulative so MPE = 3/t mW/cm2 for exposure of t seconds • For every second of exposure, you must be about 10 cm from the lamp • Place lamp in enclosed reflective chamber • WEAR GOGGLES & DON’T EXPOSE SKIN

  11. What about cooling tube made of Pyrex? Transmits ~80% in UV-C range (Some sources give cut-off as 300 nm) Almost no protection Perhaps not surprising – the lamp kills bacteria in 5 seconds! Germicidal lamps (2)

  12. Visible/IR lasers • CW/pulsed: • protect your eyes • blue-green worse than red-infrared • don’t shoot at your skin • Dye lasers: dyes are carcinogens • CO2 lasers: fire hazard

  13. Good lab design • Often a competition between hazards: • Water • Electrical • Trip • Laser radiation • Scatter • Direct exposure • Good management is mostly common sense • e.g., don’t forget to remove your watch!

  14. A laser lab (1) • Data: • Vacuum chamber • Pulsed IR class IV laser • Target 10 cm behind glass • Target 1.5 m above floor • Lens: F.L. 20 cm • Lens holder: aluminium • Can you do better?

  15. A laser lab (2) • Beam height: • Unsafe for people >5 ft • If you can’t adjust target, move beam out of the way • Door: • Don’t shoot laser in that direction! • Make sure the system is interlocked – door open, laser off

  16. A laser lab (3) • Lens: • Beware of scatter • Each surface reflects 4% as a mirror (back into laser!) • AR coating • Turn lens around • You may hit lens holder • Spray paint black • Window: • 4% reflection focused on lens

  17. A laser lab (4) • Adaptability • Can’t easily adjust beam • Tripping: • Water/electrical leads all over the floor • Invisibility • Can you mount a collinear visible alignment laser?

  18. A laser lab (5) • Possible solution: • Collinear weak visible laser • Shorter FL lens • Turn lens or beam dump • Piped beam • Mirrors allow manipulation • Laser against wall • Beware of pushing against piping • Curtain/screen near door curtain/ screen

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