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`

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`Laser Safety
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`Laser Safety
`
`‘Roy Henderson
`
`Bioptica, Cambridge, UK
`
`and
`
`Karl Schulmeister
`
`ARC SeibersdmfResearch, Seibersdorfi Austria
`
`New Yoyk London
`
`‘ Tayior & Francis
`Tayior & Francis Group
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`'
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`_n,,Roy;.Schu1meister,Kari,‘Dec0.1,2003,LaserSafetyPhiladelphia,
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`ISBN:9781420034042
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`Published in 20.04 by
`Taylor & Francis Group
`270 Madison Avenue
`New York, NY 10016
`-
`
`Published in Great Britain by _
`Taylor & Francis Group
`2 Park Square
`Milton Park, Abingdon
`Oxon OXI4 4RN
`
`© 2004 by Taylor -& Francis Group, LLC
`No claim to original U.S. Government works
`Printed in the United States of America on aeid—free paper
`10 9 8 7 6 5 4 3 2
`
`International Standard Book Number-i0: O—7503-0859-l (Hardcover)
`International Standarjd ‘Book Number’-13: 978«0~7503~0859~5 (Hardcover)
`
`The image of the laser eye—proteetion'reproduced on the cover was kindly provided by the Nolli Laser Company
`(www.jnoirl’aser.com) and used with permission.
`
`This book contains information obtained‘ from auJ.he_nti_c and highly regarded sources. Reprinted material is
`quoted with ~p_ern_1issioI1. and sources are indicated. A_wide variety of references are listed. Reasonable efforts
`'have'been made to publish reliable data andinforrnation, -but the author and the "publisher cannotassume
`responsibility for. the validity of all materials or for the consequences of their use.
`'
`No part of this book may be reprinted, reproduced, transmitted. orutilized in any form by any el_e6tronic,
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`recording, or in any information storage or retrieval system. without written permission from the publishers.
`Tradem‘ark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only
`for identification and explanation without intent to infringe.
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`Library of Congress Cataloging¥in.—Pubiication Data
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`Catalog record is available from the Library of Congress
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`is the)‘/xcademic Division Of Informa plc.
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`
`©Henderson,Roy;Schulmeister,Kari,Dec01,2303,LaserSafetyCRCPress,Phiiadelphia,ISBN:9781420034042
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`To Ruth (RH) and Gabi (KS)
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`

`
`Contents
`
`
`Preface
`
`1 Lasers, light and safety
`1.1
`Lasers: stimulating light
`1.1.1 Creating light
`1.1.2 Quantifying light
`The properties of laser radiation
`The safety of laser technology
`Safety standards
`References
`
`1.2
`1.3
`1.4
`
`2.3
`
`2 Quantifying levels of laser radiation
`2.1
`Power and energy
`2.2
`Irradiance and radiant exposure
`2.2.1
`Terminology
`2.2.2 Averaginggover area~«limiting aperture
`Angle and intensity
`2.3.1
`Plane angle
`2.3.2
`Solid angle
`2.3.3 Radiant intensity
`Field—of-—'view——~.angle' of acceptance
`2.4.1
`Terminology and optical set»up
`Radiance-
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`2.4
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`2.5
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`2.5.1 Averaging over the FOV
`2.5.2 Transforming radiance to irradiance
`2.5.3 Actual measurement FOV-simp1ilication for small sources
`Wavelength issues
`2.6.1 Wavelength bands
`2.6.2 Visible radiation
`
`Spectral quantities
`2.6.3
`2.6.4 Action spectra
`2.6.5
`Photometric quantities and units
`Absorption, reflection and scattering
`
`2.6
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`2.7
`
`xiii
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`10
`13
`15
`17
`19
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`21
`21
`27
`29
`30
`32
`3.3.
`34
`35
`36
`37
`40
`43
`44
`45
`46
`46
`46
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`49
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`viii
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`Contents
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`2.8
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`2.7.1 Absorption law
`2.7.2 Volume scattering
`2.7.3 Diffuse reflection-surface scattering
`Measurement instruments and detectors
`A 2.8.1
`
`Parameters and uncertainty
`Types of radiometers
`2.8-.2
`Refer'eno6$
`
`' 3.5
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`3.6
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`Laser radiation hazards
`3.1
`Introduction
`V
`3.2
`The human. skin
`3.3
`The human eye
`3.4
`. The concept of exposure limits (MPE)
`3.4.1
`Exposures above the MPE
`_
`Laser—tissue‘ interaction
`3.5.1 General optical absorption characteristics
`3.5.2
`Types of interaction
`3
`.
`MPE .ev_aluation and measurement concept
`3.6.1
`Limiting aperture and angle of acceptance
`3.6.2 Exposure location and exposure duration
`3.6.3 Representation of MPE values
`3.6.4
`Summaryand overview of dependencies
`3.6.5
`Evaluation and measurement position
`3.6.6
`Backgrounydl to the "concept of dosimetry
`Injury to the skin
`_
`3.7.1
`_AV'ersion response, typical exposure durations
`Skin MPE‘val~ues
`'
`—
`. Injury to the eye
`3.9.1‘
`yUltraviolet*radiation
`3'.9.2" Retinal damage
`--36.9.3
`.CorneaI.damage from infrared radiation
`3.9.4 - Aversion response andtypical exposure durations
`M-PE values for the eye~a:lso relevant to AEL values ’
`MPE values in the ultraviolet
`
`3.7
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`3.8
`3.9
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`3.10
`3.11
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`3.11.1 Multiple pulses
`3.1 1.2 Ultrashort pulses
`Retinal MPE values
`
`3.12
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`3.12.1 Apparent source.
`3.12.2 General evaluation -approach
`3.12.3 Retinal thermalwwavelength dependence
`3.12.4 Retinal thermal»--time dependence
`3.12.5 Retinal thermal-edependence on at
`A 3.12.6 ' Retinal photochemical
`'
`3.12.7 Comparison of thermal and photochemical retinal limits
`
`54
`54
`56
`56
`57
`62
`6'5
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`66
`66
`67
`68
`74
`78
`79
`80
`80
`87
`87
`‘90
`93
`96
`99
`I02
`103
`106
`107
`113
`1 15
`-116
`1'19.
`120
`122
`123
`126
`131
`132
`135
`149
`151
`156
`1161
`186
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`Contents
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`3.12.8
`Multiple pulses in the retinal hazard region
`3.13 MPE values in the far~infra'red
`3.13.1 Multiple Pulse exposures
`3.14 Multiple wavelength exposures
`References
`
`4.1.4
`4.1.5
`
`4.2.5
`4;2.-6
`4.2.7
`
`4.4.2 '
`4.4.3.
`
`' Laser pI*0'du.ct classificafion
`.
`.
`4.1 Overview
`4.1.1
`Diffuse .ve.rsus intrabeam (direct) viewing
`4.1.2
`Viewing duration
`“
`‘
`4.1.3-
`Naked (unaiclcd) eye versus exposure with optical
`viewing instruments
`Tabular overview
`Manufacturing requirements
`4.2 Classification scheme
`4.2.1 ‘
`Derivation of the AEL values
`4:22
`Time base
`A
`_
`492.3
`Measurement requirements
`4.2.4
`Classification -scheme summary
`Embedded laser products
`Old Class 3A and USA Class II-Ia
`.O.ve.r:view.ta_ble
`4.3 M;anufactu1*-er’s ‘classification procedure
`Intreduction A
`4.3.1
`4.3.2:
`General. issue«s
`4.3.3
`Single fault condition
`4.3.4
`;MeasfureIn_ent»requirements
`4.3.5
`M'ea's_‘uremen‘t' requi1'em;ents for extended sources
`_Equiva_1enec.to MPE eyalbuation
`. 4.3.6’
`4.4 Requirements for the manufacturer
`4.4.1 .
`General hardware
`‘Labels;
`.
`Informational requirements
`4.5 US requirements
`4.5 .1
`Regi-stering laser products in the US
`4.5.2
`Changes to CDRH requirements
`4.6: Enclosure and classification
`Embedded Class‘ -1' laser pr_oiducts~—.nice but not necessary!
`4.5.1
`4.6.2
`Requirements for laser guards IEC 60825-4
`4.7 A'pp1ic-ation specific. requirements
`4.7.1
`Laser processingjmachines (ISO 11553 and EN 12626)
`4.7.2
`Medical laser pr_oduc'ts, IEC 60601 ~2;22
`4.7.3
`Optical telecommunications
`4.7.4
`Laser light shows
`
`ix
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`200
`214
`21 7
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`21 8
`220'
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`222
`225
`227-
`228
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`229
`229
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`.230
`23 1
`234
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`236
`2359‘
`247‘
`247
`249
`250
`7 254
`- 254
`2.54
`259
`261
`267
`27 1
`272
`272
`2'79.
`283‘
`283
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`283
`286
`287
`287
`289
`291
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`296
`298
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`Con ten ts
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`4.8
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`Case studies
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`I-'IeNe alignment laser
`4.8.1
`Low—1eVel therapy laser
`4.8.2
`4.8.3 Line laser
`4.8.4
`Scanner
`
`-Ne_ar—I-R and visible beam
`4.8.5
`References
`
`Beam propagation and exposure assessment
`Measurement versus calculation
`5.1
`5.2
`Classification apertures
`5.3
`Beam profiles
`5.3.1
`’Gaus'sia‘n beams
`
`5.3.2 Beam divergence
`5.3.-3
`Fractional power through apertures
`5.3.4
`Emission from optical fibres
`5.3.5
`N011-Ciauss_ian‘be‘a_ms
`I‘-I-azard-distance
`
`Beam reflections
`Optical viewing instruments
`5.6.1 Aided viewing
`5.6.2, Binocular viewing
`5.6.3 Closeup viewing
`5.6.4 Magniiifedwviewing of extended sources
`Assessment accuracy
`References
`
`5.4
`5.5
`5.6
`
`5.7
`
`_
`. Additional laserjnazargis
`6.1
`"Other hazards. of laser operation
`6.2
`Ad§1i_ti0jna;l.Abearn' hazards} '
`6.2.1’ "1_3)azzle '.
`6.2-.2
`9Bea'mj—ini’tia‘ted fire and explosion
`6.2.3 Other thermal hazards
`» 6.2.4
`Fume
`
`6.2.5 Additional. laser emission
`Non—bea_m ‘hazards
`6.3.1
`Electricity
`6.3.2 No'n—beam fire and explosion hazards
`6.3.3 Collateral radiation '
`6.3.4 Hazardous substances
`
`‘Laser-generated noise
`6.3.5
`6.3.6 Mechanical hazards
`6.3-.7 Temperature and humidity
`6.3.8 ' External shock and vibration
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`6.3.9 Computer malfunction
`
`300
`300
`300
`302
`307
`312
`313
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`314
`314
`318
`321
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`321
`323
`327
`329
`331
`334
`339
`342
`342
`343
`347
`351
`35.1
`352
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`353
`353
`.354
`354
`355
`355
`356
`358
`358
`358
`359
`359
`359
`360
`36]
`361
`362
`362
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`Contents
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`6.3.10 Ambient noise
`
`6.3.11 Compressed gases
`References
`
`Assessment of laser risk
`
`7.1 Workplace evaluation
`7.1.1
`The laser class
`
`7.1.2 Does ‘safe’ mean Class 1'? Does Class 1 mean ‘safe’?
`
`7.2
`
`Supplier and purchaser responsibilities
`7.1.3
`Risk assessment
`7.2.1 - Hazards and risks
`
`7.2.2 The risk assessment process
`7.2.3 Risk factors
`
`7.2.4 Determining the level of risk
`References
`
`8.1
`
`Protective measures and safety controls
`Introduction to protective control measures
`8.1.1
`The -use-of safety control measures
`8.1.2 Control rneasures as a function of the laser class.
`
`4
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`8.2
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`8.3
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`8.4
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`8.5
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`8.6
`
`8.7
`8.8
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`,
`Laser controlled areas
`8.2.1
`Types of laser controlled areas
`8.2.2 Controlling access
`8.2.3 Use of warningusigns for laser controlled areas
`
`Engineering control measures
`.8;.3_.1_ . Cl:as_s~depjendent safety features
`8.3.2 Additional engineering control measures
`Administrative control measures .
`8.4.1
`The .use_ of product safety features
`8.4.2 Other procedural control measures
`Personal protection
`
`Personal protective equipment
`8.5 .1
`8.5.2 Types of protection
`
`p
`_
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`Eye protection
`8.6.1
`The use of protective eyewear
`8.6.2
`Specifying eye protection
`
`European standards for laser protective eyewear
`8.6.3
`Working in laser -controlled areas
`Laser servicing
`References
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`362
`362
`363
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`364
`364
`364
`370
`371
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`374
`374
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`375
`377
`379
`381
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`382
`382
`382
`383
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`386
`386
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`389
`389
`390
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`390
`392
`398
`399
`400
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`401 ‘
`40 I
`402
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`403
`403
`406
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`. 415
`420
`421
`423
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`xii
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`Con tents
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`9 The management of laser safety
`9.1V
`Health and safety responsibilities
`9.2
`The framework policy
`9.3
`The role of the laser safety officer
`9.4
`Safety training
`Human factors
`95
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`Appendix A
`
`Glosséiry
`
`Appendix B
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`Special parameters
`
`Appendix C
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`Appendix D
`Index
`
`Common misunderstandings
`
`Some M1->12 and AEL values
`
`424
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`424
`425
`427
`430
`43 3'
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`435
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`444
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`A 447
`452
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`453
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`Appendix A
`
`
`Glossary
`
`accessible emission level—-«the quantity of laser radiation emitted by a laser when
`measured in accordance: with the classification conditions specified in the
`safety standard and intended to be compared with the AEL.
`
`administrative contr_o‘ls—~protecti-ve measures based on rules and procedures.
`
`AEL——~accessible-emission limit, the maximum allowable emission for a given
`class of laser product, where laser emission is measured in accordance with
`specifed conditions.
`
`angle of acceptance (also .c_one angle or fieldof view)~«the limiting angle used
`in safety asselssmentis to restrict a radiation measurement to that radiation
`emitted by only part of the source.
`angular subtense (of apparent source)~——-the planeangle (usually specified in
`milleiradian) subtended by the apparent source at a defined distance from the
`source. (symbol 0:). '
`
`ANSi~«A=merican- National Standards Institute,
`
`limit the
`aperture (also aperture stop)~a circular hole used to restrict (i.e..
`cross—sec'tional’ area of) a beam» of optical radiation, often for measurement
`purposes.
`
`apparent source——the source from which emitted optical radiation appears to
`orginate (which may or may not be the actual physical source of radiation).
`For laser beams it is more appropriate to consider the apparent source as
`being that which gives rise to the smallest retinal image.
`'
`
`astigmatic beam-~a beam having an asymetric (i.e. nomcircular) cross-section.
`
`average powerwpower (emitted or received) averaged over time (for pulsed
`lasers, both average power and peak power can be of relevance in safety
`evaluations).
`
`435
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`436
`
`Glossary
`
`averaging aperture~—see limiting aperture.
`
`aversion resp‘onse~—-—the reflex avoidance action (closing the eyes and turning
`away) when a person is suddenly exposed to a bright source of light.
`
`beam———see laser beam.
`
`beam proflle——-the cross-section of a laser beam, in a plane that is perpendicular
`to the beam propagation direction.
`'
`
`beam stop——a device that intentionally prevents ‘a laser beam from propagating
`‘
`further. With high~power beams, a beam stop may need to be cooled in order
`to prevent it suffering thermal damage.
`
`beam waist-—the position along the beam having the smallest cross—sectional
`area.
`"
`~
`
`biologically effective exposurewan exposure level assessed in. _accordance with
`the measurement conditions (including averaging or weighting criteria)
`specified in the safety standard and "intended to be compared with the MPE.
`It will often be different to the actual physical level of exposure.
`
`blink reflex»-~sudden closing of the eyes in response to a bright source of light.
`blue~light hazardfithe cumulative photochemical effect of short—wavelength
`visible radiation on the retina.
`
`brightnessmsee radiance.
`CI)RI¥-—‘-‘Center for Devices and Radiologicallrlealth (‘a division of the US Food
`‘ and Drug Administration responsible for radiation safety).
`
`C‘fE———Comymission Internationale de l’Eclairage (International Commission on
`Illumination)
`
`class-—see laser product class.
`
`collimated'beam-a laser beam ‘that has a very lowdivergence and so "is
`effectively parallel;
`its diameter" therefore increases only slowly with
`distance.
`
`continuous wave laser-—a laser whose output is at a steady continuous level
`(abreviated cw laser).
`
`control measuresmprotective precautions adopted by a user organization and
`intended to ensure the safe use of laser equipment.
`
`cornea~_~—the transparent ‘bulge’ at the front the eye through .which light enters.
`
`cw——-con.tinuous_ wave.
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`Glossary
`
`437
`
`L153--the diameter of the central portion of a Gaussian laser beam that contains
`63 per cent of the total beam power or energy. This definition of beam
`diameter is used because the maximum (on—axis)
`irradiance or radiant
`exposure in a Gaussian beam is equal to the total beam power or beam energy
`divided by the area of the beam defined by the dog diameter.
`
`diffuse refl'ection———a reflection in which the reflected radiation is scattered in all
`
`directions away from the reflecting suri'ace‘(as with visible ‘light incident
`onto a sheet of paper). (Compare with specular reflection.)
`
`direct viewing (of a so.urce)——.d‘irect (i.e. not diffused or scattered) exposure of
`the eye to optical radiation, includingexposure to a specular reflection. (It is
`not necessary that the eye be looking directly at the source.)
`
`divergence-——the angular spread of a laser beam.
`
`dose~'-«an exposure of the eyes or skin to optical radiation specified in terms of
`the radiant exposure.
`'
`
`effective exposure—.—see biologically effective exposure.
`
`electromagnetic radiation-~’see radiation.
`
`embedded laserma laser inside an enclosed laser product, such that its full
`emission is not accessible under normal conditions of operation of the laser
`pr.od’uct.
`'
`
`-embedded laser productwan enclosed laser product that is classified on the
`basis of the lower level of radiation accessible under normal conditions of
`operation than the level of the internal (inaccessible) radiation.
`emission .aperture:—;«the opening in. a laser housing "through which laser radiation
`(i.e. the laser; beam) emerges.
`..
`-
`
`energywa‘ quantity of radiation, expressed in units of ' joules. For constant,
`uniform emission it is the product of the radiant power and the emission
`duration.
`
`engineering c0nt1'0ls———protective measures based on the use of physical design
`features, such as enclosures and interlocks;
`’
`
`ENQHD+——extended nominal ocular hazard distance, the distance from a laser
`over which the MPE for the eye may b.e exceeded, taking into account the
`possible use of .magnifying1 instruments (telescopes and binoculars).
`
`exitances-«the emitted power per unit area.
`
`exposuremoptical radiation incident on the surface of the eyes or skin, or the .
`quantity (specified inappropriate units) of such incident radiation.
`
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`438
`
`Glossary
`
`extended source—~an apparent source that has an angular subtense greater than
`1.5 milliradians (mrad).
`
`eye loupewan optical magnifying aid to allow Close~up viewing.
`
`fail safeman attribute of a component or engineering feature in which failure
`does not increase the hazard of the system of which it forms a part.
`
`far-field-~that portion of an emitted laser beam (furthest from the laser) in which
`the beam diameter increases linearly with distance.
`
`field of View (of a detect0r)——see angle of acceptance.
`
`fumewthe material generated by the vaporizing of target material using the beam
`of a high~power laser. The fume may contain both gaseous and particulate
`matter, including (in the case of medical applications) viable biomatter.
`
`Gaussian b‘eam~——a laser beam whose e_ross—seetional distributionof power or
`energy follows a.Gaussian equation; the simplest form of laser beam.
`
`ha'zard——an entity (such as a laser beam, or the fume generated by a laser process)
`having the potential for causing harm or injury.
`
`human accesswthe capability for anylpart of the human body to encounter a
`laser hazard. (Specific definitions of human access are given in laser safety
`standards.) '
`
`ICNIRP-International Commission on Non~Ionizing Radiation Protection.
`
`IEC~—~International Electrotech.nic'al Commission
`
`infrared. radiation»-invisible optical radiation having wavelengths longer than
`in the visible band.
`‘
`
`integrated radia,neew~the energy emitted periunit area per unit solid angle (the
`energy—equ_ivalent quantity to radiance).
`
`intermediate sourcewan apparent source having an angular subtense between
`1.5 and 100 milliradians (m-rad).
`’
`
`intrabearn evi'ewing—-«the direct viewing of a laser beam; the exposure condition
`arising when a laser beam is incident on the eye.
`
`irradiance»-«the incid‘ent.power1per..unit area.
`
`4;
`
`ISO~—-——International Standardization .Organization..
`
`3-oul'e——the unit of energy. "An energy rate of one joule per second is equivalent to
`a power of one watt.
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`Glossary
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`439
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`laser~—a device that generates directional, coherent, optical radiation through a
`process of stimulated emission. (It is an acronym for light amplification by _
`the stimulated emission of radiation.)
`
`laser beamwthe path through space occupied by the radiation emitted by a laser.
`
`laser controlled area—-—'au area within which laser hazards may exist and
`protective. measures are adopted.
`
`laser equ’i'pm‘ent»-—a general term used in this book to mean any hardware item,
`assembly of components, or system that is, or incorporates, a laser.
`
`laser prod'uct—-—-any laser device or equipment that is subject to classification
`under a laser safety standard.
`
`laser product classmathe hazard category assigned to a laser product on the basis
`of the maximum level of its accessible laser emission.
`
`laser radiation--optical radiation emitted by .a laser.
`
`Laser Safety Offlcer—a person given some level of responsibility on behalf of
`his/her employer for overseeing laser safety._
`
`large sourcewan apparent source having an angular subtense greater than
`‘100-_milliradi_an‘s (mrad).
`LE-l).~.+l»ight emit-ti'ng diode, a semiconductor‘: device.-thatfletnits incoherent light
`over a m_oderate- range of wavelengths (typically 20 to 50 nm).
`_l'esion~—~an' observable injury (often used with regard to laser injury of the retin-a),
`'light~—-see visible radiation. The term ‘light’ is also sometimes used more loosely
`to mean optical radiation generally (thatis ultraviolet and infrared radiation
`in addition to visible:~Iight)‘.
`
`limiting; aperture (also. called averaging aperture)—.—-the aperture within which
`measurements of irradiance or radiant exposure are averaged.
`
`loupe~—~see eye loupe.
`
`LSO»—wLaser Safety Ofiicel‘.
`
`maintenancem routine adjustments and other basic procedures (other than
`operation) intended by the manufacturer of a laser product to be carried out
`by the user of the product. (Compare with operation and service.)
`
`maximum anticipated exposure duratio'n——the maximum period for which
`a person may be exposed to laser-radiation under
`the foreseeable
`circumstances of use.
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`Glossary
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`measurement requirementsmdetailed criteria specifed in laser safety standards
`for undertaking measurements of laser emission or exposure (mainly related
`to the measu1'en-ientdi-stance, aperture diameter and angle of acceptance).
`
`milliradianma measure of plane angle, used for specifying angnlar subtense and
`beam divergence. One radian (1000 millitfadian) is equal to the fraction 1 /27r
`of a circle, and so one milliradian is approximately 0.06 degrees.
`
`MPE~—~ma-ximum permissible exposure, the highest level of laser .exposure at the
`eyes or skin that is generally considered safe, where the exposure is measured
`in accordance with specified conditions.
`‘
`
`near-field—-~that portion of an emitted laser beam (closest to the laser) in which
`the b.eam diameter does not increase linearly with distance.
`
`NOHD—-—-nominal.ocu‘l’ar hazard distance, the distance from a laser over which
`the MPE for the eye may be exceeded, provided that no magnifying viewing
`in.str’um.ents are used.
`'
`
`ocular-'pert-aining to the eye.
`
`operationwthe normal use of a laser productf'or the purpose intended by the
`m_anufacturer. (Compare with maintenance and service.)
`optical-pdensity~l—_a measure of) the attenuation (reduction in transmission) of an
`opti'cfa1fi1ter. It is equal to the logarithm of the inverse of the transmittance.
`
`optically aided viewing;-—the use of magnifying viewing instruments, such as
`eye loupes, microscopes, binoculars or telescopes.
`
`optical.r7adiatio'nw—V.that portion of the electromagnetic spectrum comprising
`u~ltravi_olet, visible and infrared radiation, and covering a wavelength range
`from 180 nm to 1 mm.
`-
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`optical viewinginstruments——optieal magnifying devices such as eye loupes,
`microscopes, binoculars and-telescopes.
`peak povt'er———the.powe‘r.'of a laser pulse. (For pulsed lasers, both average power
`andpeakepower can be of relevance in ’safety'evaluations‘.)
`’
`~
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`personal" protect-ion-———items of protection (sucha-s lasersafety eyewear) worn by
`an in’di_v-idual to protect themselves from a specified hazard.
`
`power (radiometric)—.~a quantity of radiation, expressed in watts. For constant,
`uniform emission the power is equal to the energy that is emitted divided by
`the duration of emission. (See also peak power, average power.)
`
`power (refractive)——a measure -of the focusing ability of a lens. It is specified
`in units of dioptre, where one dioptre is equal to the reciprocal of the focal
`length measured in metres.
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`Glossary
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`protective densitya-—a parameter used in the specification of European laser eye
`protection that takes into account both the optical density of the protection
`and its ability to withstand the incident laser radiation.
`
`pulsed laser~———a laser whose output is intermittent, usually taken to apply to
`lasers whose periods of emission (i.e. individualpulses) do not exceed
`0.25 seconds. A pulsed laser may emit single pulses on demand, or
`repetitively at regular intervals, when it may be specified by its pulse
`-repetition rate, inphertz (ie. the number of pulses per second). Lasers that
`emit pulses longer than 0.25 seconds are often referredto as being ‘pseudo-
`cw’, meaning that they are considered to be more like continuous wave lasers
`that are switched on and off rapidly.
`
`radiance (also called brightness)~—-the power emitted by a source per unit area
`per unit solid angle (or the radiant intensity per unit area). Often used
`to characterize the emission of extended sources when evaluating retinal
`hazards, since the retinal ii-radiance is directly proportional to the source
`radiance (ignoring variations in the spectral transmission of the eye).
`
`radiant ititensitymthe power emitted by a source per unit solid angle. Often
`used» to characterize the emission of small (‘point’) sources.
`
`radiant exposur-e~—the incident energy per unit area.
`
`-
`
`-
`
`rad_ia_tion~+—a form of energy that can p_rop.agate”(‘radiate’) through space,
`-and co'l3lectiV.C1y known as electromagnetic radiation (because it comprises
`osciil-ating electric and «magnetic fields).
`It can be characterized by
`wavelength, and extends from x-rays at very short wavelengths to radio
`waves at very long wavelengths. Optical radiation iselectrornagnetic
`radiation having intermediate wavelengths.
`
`Rayleigh rangewthe distance from a laser to the position along the laser beam‘
`where the beam diameter has increased by the square root of two (i.e._ by
`1.414).
`'
`’
`
`reasonably .forese‘eable-that which cannot be disregarded as being very
`unlikely.
`
`fretina-—the light-sensitive layer (analogous to the lilm in a camera) lining the
`inside of the back of the eye on which an image is formed and in which the
`process of vision occurs.
`‘
`
`retinal hazard region (or retinal hazard area)«-the optical waveband from
`400 nm to 1400 nm which can be transmitted through the-eye to reach the
`-retina.
`'
`'
`-
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`the likelihood that a given event or entity will cause
`riskéa combination
`harm-or injury with tlie3severity’"of‘s'uch harm or injury.
`It is often used
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`442
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`Glossary
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`in laser safety in the more restricted sense of a deterministic risk, to mean
`the likelihood that an exposure exceeding the relevant MPE could occur.
`
`risk assessment»-an evaluation -of the risks associated with a_ particular set
`of circumstances, with. the aim of determining the appropriate protective
`measures;
`'
`
`scale number "(of eye protection)-~—the level of protective dens-ity provided by
`an eye protector under European specifications.
`
`second moment—~a weighted measure of the diameter and divergence of a laser
`beam that is used in beam—propagation modelling.
`It is more generally
`applicable than other measures used-, such as those based on 1/e or l/e2,
`which only work well for beams having a Gaussian profile.
`
`service»-~spe‘ciajli.zed attention to a laser product normally carried out by a service
`engineer-and not int_e‘nded'Aby the manufacturer of_ the product to be carried
`out by the laser user, (Compare with operation and ma—in‘tenan'ce.),
`
`than
`small s0urce——~a_n apparent source having an angular subtense less
`1.5 milliradians (mrad). It is often referred to as a ‘point’ source, although a
`point source is physically unrealizable.
`
`specular re-flection-~—a ‘mirronlike’ reflection, in which the reflected radiation is
`-
`' highly directional. (Compale with diffuse reflectiom)
`"
`
`spontaneous ernis'sio[n'.————the' process Abyfiwhich opt—i.c—al- radiation-is generated in
`conventional (-i.e. thermal) lig'htsou1'ce's.
`
`standard»-——_a document ‘issued by -_a‘_nati_onal or international body ‘intended to
`.establish -common criteria in the form of definitions, requirements and
`, specifications, _etc. A -s_tand_ard may or may not have legal_l’o1'<;e. g
`
`_
`
`g
`
`stimulated emissionwthe process by which optical radiation is generated in a
`laser.
`-
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`suprathresholdaan exposure level that is above the threshold for causing injury.
`
`time bas.e——the period of time over which emission of or exposure to laser
`radiation is assessed.
`
`. thresholdwan exposure level that represents the boundary between exposure
`levels causing no injury and those levels that do result in injury.
`
`ultraviolet ratliation———invisible optical radiation having wavelengths shorter
`than in the visible band.
`»
`
`visible radiation——~that portion of the optical spectrum, nominally from 380 nm
`to 780 rim, that is visible to the human eye. In laser safety, becau-se use is
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`Glossary
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`443
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`made of the concept of an aversion response, the visible band is defined more
`narrowly as being between 400 um and 700 nm.
`
`wattwthe unit of power. A power of one watt for one second represents an energy
`of one joule-
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