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Introduction
LIGO Laser Safety Program LIGO-M960001-v1
Based on ANSI Z136.1
American National Standard for Safe Use of Lasers
Introduction (cont)
Topics covered: Why bother with laser
safety? What is light? What is a laser? Point and extended
sources Vision and skin
» The eye » The retina » The skin
Injuries
Laser classifications Laser eye protection
(LEP) Laser warning signs Terminology Responsibilities What to do in case of
an incident?
Why bother with laser safety?
Compared to natural light, laser light or laser radiation has some very special properties. These properties cover the nature of laser light and its biological risk factors. Most importantly …
What is light?
Light (noun) The form of energy that makes it possible to
see things: the brightness produced by the Sun, by fire, a lamp … etc.
(Merriam-Webster online dictionary)
What is light?
Biblically … (Genesis 1:3) And God said and there was light.
�𝑬.𝑑𝑑 = 𝑞𝜀0
�𝑩. 𝑑𝑑 = 0
�𝑬. 𝑑𝑑 = − 𝑑Φ𝐵𝑑𝑑 �𝑩.𝑑𝑑 = 𝜇0𝜀0
𝑑Φ𝐸𝑑𝑑 + 𝜇0𝑖
The electromagnetic spectrum
What is a laser?
Laser is an acronym for Light Amplification by Stimulated Emission of Radiation
Properties of laser light
Monochromatic Low beam divergence Waves are in phase
Polychromatic Highly divergent Waves have random phase
Biological effects of laser radiation
The nature and site of the injury depend on the following: Wavelength
» Determines what part is exposed Output power Exposure duration
» Calculations done at 0.25 s for visible light, 10 s for infrared wavelengths, or the appropriate exposure duration (eg. 8 hours)
The eye
How do I see?
Retina has two types of photoreceptors Rods Cones
Rods are more sensitive Cones provide colour sensitivity Concentrated in the
macula
Image formation by the eye
Light is focussed by both the lens and cornea Focal length, feye ~ 17 mm Pupil diameter, d ~ 7 mm
Point and extended sources
Point and extended sources (cont)
Pretty much all lasers can be treated as point sources Irradiated spot on the retina can be as small as 7 – 20 µm in diameter 5 mW (legal laser pointer) → 13 kW.cm-2
Optical gain of 100000
Wavelengths between 400 – 1400 nm focus onto the retina The retinal hazard region
The smallest pupil diameter is 2.2 mm The smallest resolvable spot on the retina is
7 µm in diameter The ratio of the two is approximately 100000
Absorption of radiation by the eye
Wavelengths in LIGO
Spectral response of the eye
Peaks in green Just because you don’t see it, doesn’t mean it’s not hazardous
What is wrong with this picture?
Visual acuity
Visual acuity is the ratio of the distance at which the letter is read to the distance at which it is normally read Dutch opthalmologist Herman Snellen (1834 – 1908)
An optical illusion
An optical illusion
An optical illusion
An optical illusion
An optical illusion
Aversion response
When exposed to bright, or intense, light a person’s natural reaction is to blink and move their head out of the way Aversion response 0.25 seconds
The skin
UVC – dangerous rays UVB – burning rays UVA – tanning rays Strong absorption in the infrared
INJURIES A small compendium of laser related injuries
Retinal injury example #1
Laser light show at a dance club 510 nm, 2 mW laser
Corrected visual acuity was 20/800 Patient recovered
after surgery Remember 2 mW is generally considered safe! Image credit: Clin Ophthalmol 2014: 8: 2467 - 2470
Retinal injury example #2
510 nm, 2 mW laser Corrected visual acuity was 20/800 Received medical treatment to remove hæmorrhage Remember 2 mW is generally considered safe!
Image credit: Clin Ophthalmol 2014; 8: 2467 - 2470
Retinal injury example #3
Repetitively pulsed IR laser Reported seeing 2 or 3 yellowish flashes at
time of exposure Visual acuity decreased to 20/50 after a few hours
Retinal injury example #4
Viewed output of a laser range finder despite reading the warning labels and receiving laser safety training. Immediate loss of vision, some improvement after 5 minutes.
Retinal injury example #5
Accidental exposure to a Q-switched Nd:YAG laser without laser eye protection Experienced a bright flash, followed by sudden loss of vision No recovery of visual acuity after 6 years
Image credit: Korean J Ophthalmol 2009 Sep; 23(3) 207 - 209
Retinal injury example #6
532 nm, 150 mW laser pointer Immediate blurred vision Waited two weeks before seeking medical attention Visual acuity was
20/32 in right eye, 20/25 in left eye after treatment Image credit: N Engl J Med 2010; 363; 1089 - 1091
Retinal injury example #7
Exposure to 200 ps stretched pulses Peak intensity > 1012
W.cm-2, average power a few watts
Laser eye protection was worn Intense blue light, loud sounds of pops and a crackling noise, dark cloud in vision
Retinal injury example #8
Laser exposure 4 hours after
exposure, hæmorrhaging
3 days 10 days, hole in
macula appears 6 months,
permanent scarring Image credit: Health Physics, vol. 56, no. 5, pp 705 – 710 (1989)
Retinal injury example #9
Both eyes exposed Top: left eye Bottom: right eye
Visual acuity in right eye decreased to 20/28 Permanently scarred
Image credit: Health Physics, vol. 56, no. 5, pp 705 – 710 (1989)
Retinal injury example #10
Direct hit whilst aligning a Pockels cell Visual acuity reduced to 20/200 Hole developed in the macula
Image credit: Health Physics, vol. 56, no. 5, pp 705 – 710 (1989)
Corneal injury example #1
Injury suffered whilst having CO2 laser skin resurfacing Pain in both eyes, decreased visual acuity and distorted vision Visual acuity was
20/100 20/50 after 2 months
of treatment Image credit: Korean J Ophthalmol 2014 Sep; 55(9) 1376 - 1379
Sclera injury example #1
Combined CO2/Nd:YAG laser 20 – 25 W CO2 laser 7 – 8 W Nd:YAG laser
Visual acuity was 20/125, 5 days after treatment Recovered after 7
months
Image credit: Arch Ophthalmol 2000; 118(6) 848 - 850
Skin injury example #1
CO2 laser burn study conducted over 20 years 5 W.cm-2, 1 s pulse
Other than scarring, no detrimental effects
Possible eye injury symptoms
Headache after exposure Excessive watering of the eyes Sudden appearance of floaters An audible pop at time of exposure Difficulty detecting the colours blue or green Vision going cloudy at time of exposure or shortly thereafter Burning pain
Possible skin injury symptoms
A sensation of warmth resulting from the skin’s absorption of laser energy 0.1 W.cm-2 produced a sensation of warmth
UVA (315 – 400 nm) Skin discolouration or darkening Reddening of the skin (erythema)
UVB (280 – 315 nm) and UVC (200 – 280 nm) Blistering Reddening of the skin
LASER CLASSIFICATIONS AND LASER EYE PROTECTION
Laser classifications
The higher the class, the greater the potential hazard Class 1, Class 1M Class 2, Class 2M
» Visible light only, output less than 1 mW Class 3R All classes listed above present little or no eye
hazard Within LIGO we are mainly concerned with Class 3B and Class 4 lasers
Class 3B, Class 4 comparison Class 3B Class 4
Can be visible or invisible
Can be visible of invisible
Output between 5 – 500 mW
Output greater than 500 mW
Hazard from Direct or intra beam
exposure Direct or intra beam
exposure Specular reflection Specular reflection Eye hazard Diffuse reflection
Eye hazard Skin hazard Combustion hazard
Terminology
Maximum Permissible Exposure (MPE) The level of laser radiation to which an
unprotected person may be exposed to without adverse biological effects to the eye or skin.
Nominal Hazard Zone (NHZ) The space within which the level of direct,
reflected or scattered radiation may exceed the MPE. At the observatories, the entire LVEA is an NHZ.
Terminology (cont)
Standard Operating Procedure (SOP) Formal written description of the safety and
administrative procedures to be followed in performing a specific task.
Laser Safety Officer (LSO) One who has responsibility and authority to
monitor and enforce the control of laser hazards
» At LHO, Peter King » At LLO, Danny Sellers » At Caltech, Eric Gustafson » At MIT, Peter Fritschel
How do we protect ourselves? Awareness through training Control measures Engineering
» Laser enclosures » Beam enclosures » Access control
Administrative » Following procedures (SOPs) » Warning signs » Communication to and with others
Personal protective equipment Laser eye protection
Optical density
What is optical density? OD = − log10 transmittance
Alternatively
OD = log101
transmittance
Optical density (cont)
Optical density
Transmission
0 100%
+1 10%
+2 1%
+3 0.1 %
Laser eye protection
The purpose of laser eye protection (LEP) is to attenuate any laser radiation that might strike it to a safe level Types of LEP Absorptive Reflective Combination of absorptive and reflective
LEP should (preferably) conform with ANSI Z87.1 Should be marked with Z87+ somewhere
Examples of LEP
Absorptive polycarbonate
Typically green or orange coloured Relatively light
Examples of LEP (cont)
Absorptive glass
Typically have a grey/bluish tinge Heavy
Examples of LEP (cont)
Absorption coated glass
Grey/bluish tinge with a coating
Examples of LEP (cont)
Reflection coated polycarbonate
Examples of LEP (cont)
Combination absorptive glass and reflection coating
Prescription LEP
Prescription LEP is available Unfortunately not many frame styles to
choose from Use an prescription insert
LEP accessories
Anti-fog insert
Identification of LEP
What to look for? Structural integrity of the frames Scratches, cracks and pits in the lenses OD and wavelength region markings
EN 207 LEP
Markings are somewhat more complicated Rated by: Working mode Wavelength range Scale numbers (similar to OD) Pulse length
A precautionary tale
Always check the condition of the LEP 300 mW
through a good region 4.3 W through
damaged region
Trade-offs in selecting LEP
Visible light transmission Ideally as high as possible
Comfort Weight Fit
Prescription eyewear Coated LEP is only good for a small range of acceptance angles (~ 30�)
What is wrong with this picture?
Laser warning signs
Old signs
Laser warning signs
New signs
Signal words
Danger Imminently hazardous situation which, if not
avoided will result in death or injury Warning Potentially hazardous situation which, if not
avoided, could result in death or serious injury Caution Potentially hazardous situation which, if not
avoided, may result in minor or moderate injury
Matching eyewear to the laser use area
This set of eyewear is marked: OD7+@532, 755-810
1064 nm OD5+ 10600 nm
Responsibilities
As a person with basic laser safety training you are allowed to … Do what you are told to do …
As a person with basic laser safety training you are NOT allowed to: Operate a laser by yourself Make unsupervised changes to the beam
path by yourself
What to do in case of an incident?
What do I do if I think I was hit by a laser? Notify those in the immediate area and
switch off the laser Remove yourself from the hazard zone Seek medical attention as necessary Notify your supervisor or the LSO as soon
as possible
Other hazards
Remember that more can hurt you than just the laser … Electricity Pressure Chemicals Mechanical hazards Confined space Cryogenics Laser generated airborne contaminants Housekeeping Fatigue
Summary
Working safely around lasers is possible Respect all warning signs Always wear your laser eye protection If you have questions, please ask the LSO
What is wrong with this picture?
