tbmed524.pdf

January 2006

TB MED 524

TECHNICAL BULLETIN

OCCUPATIONAL AND ENVIRONMENTAL HEALTH

CONTROL OF HAZARDS TO HEALTH FROM LASER

RADIATION

APPROVED FOR PUBLIC RELEASE; DISTRIBUTION IS UNLIMITED.

HEADQUARTERS, DEPARTMENT OF THE ARMY

TB MED 524*

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TECHNICAL BULLETIN HEADQUARTERS

MEDICAL 524 DEPARTMENT OF THE ARMY

Washington, DC, 31 January 2006

CONTROL OF HAZARDS TO HEALTH FROM LASER RADIATION

Paragraph Page

CHAPTER 1 BACKGROUND

Purpose 1–1 1 References 1–2 1 Explanation of abbreviations and terms 1–3 2 Responsibilities 1–4 2

CHAPTER 2 INTRODUCTION TO LASERS

Background 2–1 5 Nature of light 2–2 5 Production of light 2–3 6 Components of a laser 2–4 7 Lasing medium 2–5 8 Pumping system 2–6 8 Optical cavity 2–7 9 Types of lasers 2–8 10 Temporal modes of operation 2–9 14 Spatial transverse electromagnetic modes of operation 2–10 15 Beam diameter 2–11 16

* This bulletin supersedes TB MED 524, 20 June 1985

You can help to improve this bulletin. If you find any mistakes or have a recommendation to improve procedures, please let us know. Mail a memorandum or DA Form 2028 (Recommended Changes to Public and Blank Forms) directly to USACHPPM, ATTN: MCHB-TS-OLO, 5158 Blackhawk Road, Aberdeen Proving Ground, MD 21010-5403.

APPROVED FOR PUBLIC RELEASE; DISTRIBUTION IS UNLIMITED

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Divergence 2–12 17 Hot spots 2–13 18

CHAPTER 3 EFFECTS OF LASER EXPOSURE

Introduction 3–1 19 Skin 3–2 20 Eye 3–3 20 Medical surveillance 3–4 22 Overexposure reporting 3–5 22 Low-level adverse visual effects 3–6 22

CHAPTER 4 LASER HAZARD CLASSIFICATION AND EVALUATION

Introduction 4–1 25 Laser classification 4–2 26 Hazard evaluations 4–3 29 Evaluation of personal injury hazards 4–4 30 Determining ocular maximum permissible exposures 4–5 30 Determining skin maximum permissible exposures 4–6 32 Use of apertures 4–7 33 Nominal ocular hazard distance 4–8 33 Nominal hazard zone 4–9 33 Specular reflection nominal ocular hazard distance 4–10 34 Buffer zones 4–11 34

CHAPTER 5 INDOOR CONTROL MEASURES

Introduction 5–1 35 Types of control measures 5–2 36 Indoor laser installations 5–3 37 Warning signs 5–4 38 Education and training 5–5 43 Authorized personnel 5–6 43 Beam alignment procedures 5–7 43

CHAPTER 6 RANGE CONTROL AND OUTDOOR APPLICATIONS

Force-on-Force exercises 6–1 45 Background 6–2 45 Laser systems 6–3 47 User instructions 6–4 49 Range boundaries 6–5 49 Range control procedures 6–6 54 Image intensifiers 6–7 55 iii

Countdown 6–8 55 Communications 6–9 55 Operation outside of range area 6–10 55 Laser operations from aircraft 6–11 56 Hangar, garage, and maintenance shop procedures 6–12 58 Inclement weather 6–13 58 Visual interference hazards 6–14 58

CHAPTER 7 LASER EYE PROTECTIVE DEVICES

Background 7–1 63 Operational requirements for laser protective eyewear 7–2 64 Other laser protective devices 7–3 65 Laser eye protective device parameters 7-4 66 Selecting appropriate eyewear 7–5 69 Army laser eye protectors 7–6 70 Commercial sources of laser eye protectors 7–7 73 Inspection and testing of laser eye protective devices 7–8 73

CHAPTER 8 NONBEAM HAZARDS

Introduction 8–1 75 Electrical hazards 8–2 75 Prevention of electrical shock 8–3 75 First-aid procedures for electrical shock victims 8–4 77 Laser-generated air contaminants 8–5 77 Collateral and plasma radiation 8–6 77 Fire hazards 8–7 78 Explosion hazards 8–8 78 Compressed gases 8–9 78 Laser dyes 8–10 79 Cryogenics 8–11 79 Noise 8–12 79 Confining space 8–13 79 Ergonomics 8–14 80

CHAPTER 9 SAFETY DESIGN REQUIREMENTS FOR MILITARY LASERS

Overview 9–1 81 Applicability 9–2 81 Basic policy 9–3 82 Tailoring 9–4 82 Design requirements for exempted lasers 9–5 82 iv

Design requirements for Class 3B and Class 4 exempted lasers 9–6 90 Laser test sets 9–7 92

CHAPTER 10 DESIGN REQUIREMENTS FOR ASSOCIATED

SUPPORT EQUIPMENT

Introduction 10–1 93 General requirements 10–2 93 Requirements for Class 1, Class 2, and Class 3a laser support equipment 10–3 93 Requirements for Class 3b and Class 4 laser support equipment 10–4 93

CHAPTER 11 LASER SAFETY IN HEALTHCARE FACILITIES

Introduction 11–1 95 Healthcare laser system–laser hazard classification 11–2 95 Effects of medical lasers on the biological system 11–3 96 Healthcare laser system–non–Surgical lasers 11–4 98 Medical lasers–control and operation of healthcare laser systems 11–5 98 Healthcare laser system–multi-wavelength laser protective 11–6 99 eyewear hazards

CHAPTER 12 LASER SAFETY PROGRAM–RPO/LSO RESPONSIBILITIES

Introduction 12–1 101 General requirements 12–2 101 Operational procedures 12–3 103

Appendix A REFERENCES 105

Appendix B CALCULATIONS FOR HAZARD EVALUATION

AND CLASSIFICATION

Introduction B–1 111 Definitions B–2 111 Viewing the primary beam (direct intrabeam viewing) B–3 114 Viewing the reflected beam B–4 114 Other factors B–5 117 Calculations for hazard evaluation and classification B–6 118 Maximum permissible exposure determination B–7 121 Laser classification B–8 135 v

Central beam irradiance or radiant exposure for circular beams B–9 138 Beam diameter and beam divergence for circular beams B–10 140 Beam irradiance or radiant exposure for rectangular and elliptical beams B–11 143 Beam diameter versus range B–12 144 Atmospheric attenuation B–13 145 Laser range equation B–14 145 Nominal ocular hazard distance B–15 149 Viewing aided by an optical system B–16 150 Hazards from specular reflections B–17 153 Hazards from diffuse reflections B–18 154 Scanning lasers B–19 158 Laser protective eyewear B–20 160

Appendix C MEDICAL SURVEILLANCE Introduction C–1 165 Employment status and vision screening C–2 165 Classification of laser workers C–3 166 Laser medical surveillance/assessment C–4 166 Protective measures required C–5 166 Emergency care for laser injury C–6 167 Reporting C–7 167

Appendix D SAMPLE SAFETY GUIDELINES Introduction D–1 171 Scope D–2 171 Safety guidelines for ocular safety in healthcare facilities D–3 173 Safety guidelines for multiple integrated laser engagement system and related optical equipment for maintenance workers D–4 175 Safety guidelines for training with portable fire control lasers D–5 177 Safety guidelines for training with tactical laser pointers D–6 179 Safety guidelines for maintenance shop operation of fire control lasers D–7 181 Safety guidelines for laser operations D–8 183 Safety guidelines for laser ranges D–9 187 Safety guidelines for Force-on-Force training with tactical and training lasers D–10 189 Safety guidelines for controlled access to the laser room D–11 193 vi

Safety guidelines for laser operation and safety procedures during preoperative and operating room services D–12 195 Safety guidelines for handling of medical laser fiber delivery systems D–13 199 Safety guidelines for nonbeam hazards associated with medical lasers D–14 201 Safety guidelines for carbon dioxide surgical laser operation D–15 203 Safety guidelines for photocoagulators D–16 205

Appendix E MAXIMUM PERMISSIBLE EXPOSURES Introduction E–1 207 Scope E-2 207

Appendix F CONTROL MEASURES Introduction F–1 227 Scope F–2 227

Appendix G EYE PROTECTION Control measures G–1 231 Optical density requirements for laser systems G–2 231

Appendix H SPECIFIC LASER SYSTEMS Introduction H–1 233 Fielded laser systems H–2 233

Appendix I STANDARDIZATION WITH INTERNATIONAL

STANDARDS–INTERNATIONAL ELECTROTECHNICAL

COMMISSION 608.25–1.1–1998

Classification guidelines I–1 245 Federal Laser Product Performance Standard and the American National Standards Institute I–2 245 International Electrotechnical Commission I–3 246

Glossary 249 vii

List of Tables

Number Title Page

2–1 Common laser wavelengths 11 4–1 Laser classification and risk assessment 27 5–1 Control measures 37 9–1 Minimum optical density values for magnifying optical sights 84 9–2 Minimum optical density values for non-magnifying optical sights 85 11–1 Typical healthcare laser systems 97 12–1 Operational elements 102 B–1 Definitions of mathematical symbols 111 B–2 Atmospherically corrected values of nominal ocular hazard distance (NOHD) in kilometers, assuming µ = 0.05 km-1, when the NOHD, with or without optics in vacuum (NOHD(v)), is known 152 B–3 Diffuse reflection hazard from pulsed lasers in retinal hazard region (400 nanometers to 1400 nanometers) 157 B–4 Diffuse reflection hazards form visible (400 nanometers to 700 nanometers) continuous wave lasers 158 C–1 Symptoms, signs, diagnosis, and treatment of laser-induced injuries 168 D–1 Precautions/Danger areas for laser systems 185 E–1 Maximum permissible exposure for small source ocular exposure to a laser beam 208 E–2 Maximum permissible exposure for extended source ocular exposure to a laser beam for long-exposure durations 210 E–3 Parameters and correction factors 212 E–4 Maximum permissible exposure for skin exposure to a laser beam 213 E–5 Limiting apertures (irradiance and radiant exposure) and limiting cone angles γ (radiance and integrated radiance) for hazard evaluation and accessible emission limit determination 214 E–6 Measurement apertures for classification 215 F–1 Administrative and procedural control measures for all laser classes 228 F–2 Engineering control measures for all laser classes 229 G–1 Simplified method for selecting laser eye protection for small source viewing (wavelengths between 400 nanometers and 1400 nanometers) 231 H–1 Nominal ocular hazard distance (atmospheric attenuated), range safety information, and eye protection requirements for vehicle-mounted laser systems 238 H–2 Nominal ocular hazard distance (atmospheric attenuated), range safety information, and eye protection requirements for man-transportable laser systems 239 viii

Number Title Page

H–3 Nominal ocular hazard distance (atmospheric attenuated), range safety information, and eye protection requirements for aircraft-mounted laser systems 241 H–4 Nominal ocular hazard distance (atmospheric attenuated), range safety information, and eye protection requirements for ship-mounted laser systems 242 H–5 Nominal ocular hazard distance (atmospheric attenuated), range safety information, and eye protection requirements for commercial-off-the-shelf man-transportable laser systems 243 H–6 Nominal ocular hazard distance (atmospheric attenuated), range safety information, and eye protection requirements for commercial-off-the-shelf aircraft-mounted laser systems 243 H–7 Cautionary distances for eye exposure to weapons simulators and laser training devices 244 I–1 Comparison of classification schemes 246

List of Figures

2–1 The electromagnetic spectrum 6 2–2 Emission of radiation by transmission of an electron from a higher energy state to a lower energy state 7 2–3 Three-level energy diagram 8 2–4 Population inversion 9 2–5 Three typical optical cavities 10 2–6 Schematic of solid-state laser with optical pumping 12 2–7 Schematic of a liquid-dye laser with optical pumping 12 2–8 Schematic of helium-neon laser with electron collision pumping (representative of small gas lasers) 13 2–9 Schematic of carbon dioxide gas transport laser 13 2–10 Schematic of gallium arsenide laser with direct-current (electron collision) pumping (representative of semiconductor or injection lasers) 14 2–11 Pulse characteristics of several different lasers 15 2–12 Common transverse electromagnetic modes 16 2–13 Irradiance or radiant exposure at various points in the beam cross section 17 2–14 Definition of divergence angle 17 3–1 Adverse effects on eye and skin from nonionizing radiation 19 3–2 Anatomy of the eye 20 3–3 Absorption of electromagnetic radiation by the eye 21 ix

5–1 Sample warning sign for Class 3b laser 39 5–2 Sample warning sign for Class 4 laser 39 5–3 Sample warning sign for Class 4 double neodymium:yttrium aluminum garnet laser 40 5–4 Sample warning sign for Class 4 neodymium:yttrium aluminum garnet laser 40 5–5 Sample warning sign for Class r carbon dioxide laser 41 5–6 Sample International Electrotechnical Commission warning sign 42 5–7 Sample warning sign for temporary laser controlled area 43 6–1 Laser range terrain profiles with backstop 46 6–2 Diffuse and specular reflections 47 6–3 Specular reflection from water or horizontal flat glass on laser range 47 6–4 Reflected intrabeam viewing 48 6–5 Sample laser range warning sign 50 6–6 Sample range backstop 51 6–7 Buffer zones 52 6–8 Laser safety danger zones 53 6–9 Buffer zone for a laser designator with a ground-based target 57 6–10 Laser maintenance test range 58 6–11 Visual interference flight zones 60 6–12 Critical and laser free zones 61 6–13 Laser free zone 62 7–1 Commercially available laser eye protectors 64 7–2 Relative spectral luminous efficiency (normalized) curves for photopic (daylight) and scotopic (night) vision 68 7–3 Examples of damage to laser protective devices 69 7–4 Ballistic and laser protective spectacles 71 7–5 Special protective eyewear, cylindrical system 72 7–6 Sun, wind, and dust goggles 72 7–7 M40/M42 gas mask laser/ballistic outsert 73 9–1 Exemption label 1 83 9–2 Exemption label 2 83 9–3 Example of a label for Class 1 lasers 86 9–4 Example of a warning label for Class 2 lasers 86 9–5 Example of a warning label for Class 3a visible (400 nanometers to 700 nanometers) lasers 87 9–6 Example of a warning label for Class 3a infrared (> 700 nanometers) and ultraviolet (< 400 nanometers) lasers 87 9–7 Example of a warning label for Class 3b lasers 88 9–8 Example of a warning label for Class 4 lasers 88 x

9–9 Example of typical International Electrotechnical Commission warning labels 89 9–10 Example of an interlock label 89 B–1 Specular reflectance from both surfaces of plate glass having an index of refraction of 1.5 115 B–2 Hazard envelopes created by a laser beam incident upon a vertically oriented flat (30 centimeter x 15 centimeter) glass surface 116 B–3 Intrabeam viewing–direct beam (primary beam) 119 B–4a Intrabeam viewing–specularly reflected from flat surface (secondary beam) 119 B–4b Intrabeam viewing–specularly reflected from curved surface (secondary beam) 120 B–5 Viewing a diffuse reflection–“r” represents the distance from the laser to the diffuse target, and r1 represents the distance from the target to the eye 120 B–6 Beam expansion with distance from the laser 145 B–7 Using the laser range equation to determine nominal ocular hazard distances 150 C–1 Laser injury evaluation matrix 169 E–1 Maximum permissible exposures for visible and near infrared (400 nanometers to 1400 nanometers) for pulsed small sources 216 E–2 Maximum permissible exposures for small and extended source ultraviolet radiation for exposure durations from 10-9 to 30,000 seconds for ocular exposures and 10-9 to 10-3 second for skin exposure 217 E–3 Maximum permissible exposures for ultraviolet (315 nanometers to 400 nanometers) and infrared (1400 nanometers to 1 millimeter) for single pulses or continuous exposure to small or extended sources 218 E–4 Maximum permissible exposures for ocular exposure to visible laser radiation (400 nanometers to 700 nanometers) for single pulses or continuous exposure (small or extended sources) 219 E–5 Small source ocular maximum permissible exposures (α ≤ 1.5 milliradian) for visible and near infrared (400 nanometers to 1400 nanometers) (Solid lines are maximum permissible exposures based on thermal effects, and dashed lines are maximum permissible exposures based on photochemical effects) 220 E–6 Extended source ocular maximum permissible exposures (α = 3 milliradian) for visible and near infrared (400 nanometers to 1400 nanometers) (Solid lines are maximum permissible exposures based on thermal effects, and dashed lines are maximum permissible exposures based on photochemical effects) 221 xi

E–7 Extended source ocular maximum permissible exposures (α = 11 milliradian) for visible and near infrared (400 nanometers to 1400 nanometers) (Solid lines are maximum permissible exposures based on thermal effects, and dashed lines are maximum permissible exposures based on photochemical effects) 222 E–8 Extended source ocular maximum permissible exposures (α = 25 milliradian) for visible and near infrared (400 nanometers to 1400 nanometers) (Solid lines are maximum permissible exposures based on thermal effects, and dashed lines are maximum permissible exposures based on photochemical effects) 223 E–9 Extended source ocular maximum permissible exposures (α = 50 milliradian) for visible and near infrared (400 nanometers to 1400 nanometers) (Solid lines are maximum permissible exposures based on thermal effects, and dashed lines are maximum permissible exposures based on photochemical effects) 224 E–10 Extended source ocular radiance maximum permissible exposures (α ≥ 110 milliradian) for visible and near infrared (400 nanometers to 1400 nanometers) (Solid lines are maximum permissible exposures based on thermal effects, and dashed lines are maximum permissible exposures based on photochemical effects) 225 E–11 Extended source ocular radiance maximum permissible exposures (α ≥ 100 milliradian) for visible and near infrared (400 nanometers to 1400 nanometers) for pulsed or continuous wave exposures less than 1 second 226 xii

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CHAPTER 1

BACKGROUND

1–1. Purpose

a. This bulletin provides guidelines and establishes procedures for personnel protection from laser radiation within the framework of currently documented experimental evidence. Medical guidance is limited to biological data available. This bulletin encompasses the portion of the electromagnetic spectrum in which laser radiation can be produced including: ultraviolet (UV), visible light, and infrared (IR) radiation.

b. This bulletin applies to those activities established and operated at active Army, Army National Guard/Army National Guard of the United States, U.S. Army Reserve, Department of the Army (DA) personnel, and Corps of Engineers facilities.

c. Provisions of this publication are subject to the latest editions of three international standardization agreements (STANAG): STANAG 2900, STANAG 3606, and STANAG 3828 found in appendix A.

d. It is Army policy to follow guidance in the American National Standards Institute (ANSI) Z136 series of standards. Additional guidance is contained in this document for U.S. Army laser systems used both indoors and outdoors for laser research, training, and tactical and strategic applications. Consult Military Handbook (MIL–HDBK)–828A for specific guidance on fielded military laser systems found in appendix A.

e. The evaluation of laser hazards often requires highly technical calculations by experienced individuals. See appendix B for sample calculations of potential hazards. Detailed technical information for highly specialized laser applications may be found in MIL–HDBK–828A.

Assistance in the control of laser hazards on a range is available from the Laser/Optical Radiation Program (LORP) at the U.S. Army Center for Health Promotion and Preventive Medicine (USACHPPM), ATTN: MCHB–TS–OLO, 5158 Blackhawk Road, Aberdeen Proving Ground, MD 21010-5403 or electronically at:

http://chppm-www.apgea.army.mil/laser/laser.html.

1–2. References Required and related publications and prescribed and referenced forms are listed in appendix A.

Use of trademarked names does not imply endorsement by the U.S. Army but is intended only to assist in identification of a specific product.

1–3. Explanation of abbreviations and terms Abbreviations and special terms used in this bulletin are explained in the glossary.

1–4. Responsibilities

a. The Surgeon General will evaluate potential health hazards to personnel operating, testing, or associated with lasers. (See Army Regulation (AR) 10–5.)

b. The installation Laser Safety Officer (LSO) and/or Radiation Safety Officer (RSO) will

(1) Be trained in laser safety by taking a laser hazards course such as offered by the

USACHPPM LORP.

(2) Ensure that the medical surveillance guidance provided in appendix C is followed.

c. The Commander, USACHPPM will

(1) Provide a team to investigate an alleged exposure to laser radiation when directed to do so by The Surgeon General.

(2) Establish the nominal ocular hazard distance (NOHD) of the standard fielded lasers.

(3) Determine minimum necessary optical density (OD) requirements for standard fielded lasers.

d. The USACHPPM LORP will

(1) Provide specific guidance for all Force-on-Force training exercises for hazard assessment to ensure safety of personnel if Class 3b or Class 4 lasers are used. Contact the USACHPPM LORP at http://chppm-www.apgea.army.mil/laser/laser.html for guidance on Force-on-Force training operations.

(2) Evaluate any health hazards associated with the development of Army materiel including commercial off-the-shelf (COTS) laser devices.

(3) Perform any necessary health hazard analyses in order to minimize any potential hazardous exposures to laser/optical systems. Effective 28 November 1995, the USACHPPM was appointed lead agent for the Army Health Hazard Assessment Program. (See AR 40–10).

e. The Director, U.S. Army Medical Research Detachment - Walter Reed Army Institute of Research (USAMRD–WRAIR), Ocular Hazards Research will conduct research and development to obtain data on biomedical effects of laser radiation.

f. Installation commanders will perform responsibilities set forth in AR 11–9 and

AR 385–63.

g. The command safety manager will perform responsibilities set forth in AR 385-10 and

AR 385–63.

h. Firing/lasing unit commanders will perform responsibilities set forth in AR 11–9, AR 385–63, Department of the Army Pamphlet (DA Pam) 385–63, MIL–HDBK–828A, and Joint Publication (JP) 3–09.1.

i. The laser range safety officer/laser range safety noncommissioned officer (LRSO/LRSNCO) will ensure that all personnel authorized to participate in the laser operation are thoroughly instructed regarding safety precautions to be followed. See appendix D for safety guidelines to―

(1) Ensure that established target areas, with buffer zones around the target area as defined by the greatest laser-to-target distance, are observed.

(2) Provide adequate surveillance of the target area to ensure that unauthorized personnel do not enter the target area.

(3) Ensure that communication with personnel in the target area is maintained and that required protective eyewear is worn during the operation of the laser system.

(4) Report immediately to the LSO/RSO any suspected eye injury due to laser radiation so that an examination and care can be provided as soon as possible (within 24 hours of the exposure).

See appendix C for information concerning medical surveillance.

CHAPTER 2

INTRODUCTION TO LASERS

2–1. Background

a. The term Laser is an acronym derived from Light Amplification by Stimulated Emission of Radiation. The effects of laser radiation are essentially the same as optical radiation that is generated by more conventional UV, IR, and visible optical sources. The biological implications attributed to laser radiation usually result from the very high beam collimation, beam intensities, and monochromaticity of many lasers. Lasers differ from conventional sources of optical radiation primarily in their ability to attain highly coherent radiation (that is, light waves in phase). The increased directional intensity of the optical radiation generated by a laser results in concentrated optical beam irradiances at considerable distances.

b. Recent developments in laser technology have resulted in an increase in the use of these devices for military research and field use. Field military lasers are used primarily for target acquisition, training, and fire control. These lasers are termed rangefinders, target designators and direct-fire simulators. The widespread use of laser systems increases the probability of personnel exposure to injurious levels of laser radiation. Although lasers have useful characteristics, they are potentially hazardous, and adequate safeguards must be provided. Laser radiation should not be confused with ionizing radiation (that is, X-ray and gamma rays).

c. Lasers also perform a variety of non-military functions and come in many shapes and forms.

Dangerous lasers can be smaller than a pen or larger than a truck and can be every size and shape in between. Lasers are also being used in communications, precision distance measurements, guidance systems, metalwork, photography, holography, and medicine.

d. The term laser is applied to devices that operate from stimulated emission with an output wavelength usually between approximately 100 nanometers (nm) and 1 millimeter (mm). Most lasers operate in one or more of the following output temporal modes (para 2–9):

(1) Continuous wave (CW).

(2) Pulsed, including: single-pulsed, Q-switched, mode-locked, and repetitively pulsed.

2–2. Nature of light

a. The word light as properly used refers to that portion of the electromagnetic spectrum that produces a visual effect. It was first shown by James Clerk Maxwell in 1873 that light is electromagnetic radiation that propagates at approximately 3 108 meters per second (m/s) in vacuum. Albert Einstein later postulated that the velocity of light in vacuum was constant and independent of the frame of reference throughout the universe and is the ultimate speed at which energy may be transmitted. The independence of the speed of light in vacuum has been verified experimentally numerous times.

b. Quantum mechanics was developed to describe the experimentally observed phenomenon that energy interacts with matter in discrete steps. Energy can be considered to consist of quanta (packets) of energy, called photons. The amount of energy (Q), represented by one photon, is proportional to the electromagnetic wave frequency ( ), with the proportionality constant being Planck's constant (h)

Q = h

c. Scientists have made use of almost the entire electromagnetic spectrum from zero hertz (Hz) (such as direct current from storage batteries) to 1024 hertz (Hz) (the very hard X-rays used for nondestructive inspection of metal parts). Figure 2–1 shows the electromagnetic spectrum and some of its uses and properties.

Figure 2–1. The electromagnetic spectrum

2–3. Production of light

a. Electromagnetic radiation, in the form of photons, is emitted whenever a charge is accelerated. This happens, for example, every time an electron drops from a higher energy state to a lower energy state in an atom, ion, or molecule (see figure 2–2). The energy of the photon is proportional to the change in energy of the atom, ion, or molecule.

Figure 2–2. Emission of radiation by transmission of an electron from a higher energy state to a lower energy state

b. In ordinary light sources, electron transitions from higher energy states to lower energy states occur randomly and spontaneously, and one photon has no correlation with another. In a laser, however, these transitions are stimulated by other photons of exactly the same energy, wavelength, phase, and direction.

c. Electrons must be raised to higher energy levels before they can make the transition to lower energy levels and emit photons. There are many ways in which electrons can be raised to higher energy levels or become "excited," such as

(1) Heating, as in the filament of an incandescent lamp.

(2) Collisions with other electrons, as in a fluorescent lamp discharge or in a television picture tube.

(3) Absorbing energy from photons, as in luminescent paint on a watch dial.

(4) Chemical reactions, as in a flame.

d. In addition to the familiar electronic energy levels, laser action can also result from vibrational and rotational energy levels of molecules, as in the carbon dioxide laser.

2–4. Components of a laser

a. A laser has three basic components

(1) A lasing medium.

(2) A “pumping” system (that is, supplying the energy to excite the molecules).

(3) A resonant optical cavity.

b. Lenses, mirrors, cooling systems, shutters, and other accessories may be added to the system to obtain more power, shorter pulses, or special beam shapes, but only the above three basic components are necessary for laser action.

2–5. Lasing medium

a. A medium, to be suitable for a laser, must have at least one excited energy state, which is meta-stable where electrons can be "trapped" and cannot immediately and spontaneously transition to lower energy states. Electrons may remain in these metastable states from a few microseconds ( s) to several milliseconds (ms). When the medium is exposed to the appropriate pumping energy, the excited electrons are trapped in these metastable states long enough for a "population inversion" to occur (that is, a condition where there are more electrons in this excited state than in the lower state to which these electrons decay when stimulated emission occurs).

b. Figure 2–3 shows a simplified three-level energy diagram for a laser material. This is just one of the many possible configurations of energy levels. Although laser action is possible with only two energy levels, most such actions involve four or more levels.

2–6. Pumping system

a. To raise atoms or molecules to a higher energy level, lasers employ pumping systems (figure 2–4).

b. These systems pump energy into the laser material, increasing the number of atoms or molecules in the metastable energy state. When the number of atoms or molecules in the metastable energy state exceeds those in the lower level, a population inversion exists, and laser action becomes possible. Several different pumping systems are used—

Figure 2–3. Three-level energy diagram

Note: E: electron energy states

Figure 2–4. Population inversion

c. These systems pump energy into the laser material, increasing the number of atoms or molecules in the metastable energy state. When the number of atoms or molecules in the metastable energy state exceeds those in the lower level, a population inversion exists, and laser action becomes possible. Several different pumping systems are used

(1) Optical pumping uses an intense light source, such as an xenon flashtube or another laser (for example, an argon laser or diode).

(2) Electron collision pumping is accomplished by passing an electric current through the laser material or by accelerating electrons from an electron gun to impact on the laser material (for example, helium neon laser).

(3) Chemical pumping is based on energy released in the making and breaking of chemical bonds (for example, hydrogen fluoride lasers).

2–7. Optical cavity

a. A resonant optical cavity is formed by placing a mirror at each end of the laser material so that the photons of light may be reflected from one mirror to the other, passing back and forth through the laser medium (figure 2–5 - simple flat mirror system (top); rotating prism Q-switch system (middle); confocal mirror system (bottom)).

b. Lasers are constructed in this way so that the photons pass through the medium many times and are continuously amplified each time. One of the mirrors is only partially reflecting and permits a fraction of the beam energy to be transmitted out of the cavity.

Figure 2–5. Three typical optical cavities

2–8. Types of lasers

a. Lasers are often designated by the type of laser material in the optical cavity. Lasers can produce radiation in the UV, IR and visible regions of the spectrum.

b. Table 2–1 lists several common laser wavelengths and the medium used to produce the laser.

Table 2–1 Common laser wavelengths1

CIE band Wavelength nm

Medium Typical Operation

UV-C, B, A2

UV-A

UV-A

UV-A

Visible light Visible light Visible light Visible light Visible light Visible light Visible light Visible light Visible light

IR-A3

IR-A

IR-A

IR-A

IR-A

IR-B6

IR-B

IR-C

IR-C7

193, 222, 248, 308, 351 441.6 458 ,488 ,514.5 568, 647 511-578 632.8 694.3 560-640 700-800 10,600

Excimer Helium-cadmium Nitrogen Argon Helium-Cadmium Argon Krypton Nd:YAG frequency-doubled Copper vapor Helium-neon Diode Ruby Rhodamine 6G dye Alexandrite GaA1As4

Gallium-arsenide Nd:glass Nd:YAG5

Erbium:YAG Hydrogen fluoride Deuterium fluoride Carbon dioxide

CW/Pulsed

CW

Repetitively pulsed

CW

CW

CW

CW

Pulsed Repetitively pulsed

CW

CW

Pulsed CW/Pulsed Repetitively pulsed Repetitively pulsed Repetitively pulsed Pulsed Pulsed Pulsed Pulsed Pulsed

CW

Notes:

1 Source: Modified from Field Manual (FM) 8-50, table A-1 2 Ultraviolet radiation:

(a) UV–C (100 nm–280 nm)

(b) UV–B (280 nm–315 nm)

(c) UV–A (315 nm–400 nm) 3 IR–A (700 nm–1400 nm) 4 GaA1As: Gallium Aluminum Arsenide 5 Nd:YAG: Neodymium:Yittrium Aluminum Garnet 6 IR–B (1400 nm–3 micrometer (µm)) 7 IR–C (3 µm–1000 µm)

c. Solid-state lasers employ a glass or crystalline material (figure 2–6) and commonly employ optical pumping.

Figure 2–6. Schematic of solid-state laser with optical pumping

d. Liquid lasers employ an active material in a liquid solution or suspension, usually a dye (figure 2–7). Liquid lasers commonly employ optical pumping, although some types of liquid lasers have employed chemical-reaction pumping.

Figure 2–7. Schematic of a liquid-dye laser with optical pumping

e. Gas lasers employ a pure gas or a mixture of gases (figures 2–8 and 2–9). Figure 2–9 represents the larger type of flowing gas laser. A still larger type of gas laser, known as a gas dynamic laser (not shown), employs a combustion chamber and supersonic nozzle for population inversion. Gas lasers usually employ electron collision pumping, although some types of gas lasers have employed chemical-reaction pumping.

Figure 2–8. Schematic of helium-neon laser with electron collision pumping

(representative of small gas lasers)

Note: DC: Direct Current

Figure 2–9. Schematic of carbon dioxide gas transport laser

f. Semiconductor lasers employ diode materials (figure 2–10). Semiconductor lasers may be optically pumped by another laser beam, electron-collision pumped by an electron beam or an applied potential difference over a diode junction resulting in an electric current.

Figure 2–10. Schematic of gallium arsenide laser with direct-current (electron collision) pumping (representative of semiconductor or injection lasers)

2–9. Temporal modes of operation The different temporal modes of operation of a laser are distinguished by the rate at which energy is delivered.

a. Some lasers are able to operate continuously. This mode of operation is called continuous wave or CW. In this temporal mode of operation, the peak power is equal to the average power output (that is, the beam power is constant with time).

b. Lasers operating in the normal-pulse mode have pulse durations of microseconds to a few milliseconds. This mode of operation is sometimes referred to as long-pulsed. The length in time of a pulse is called the pulse width.

c. The resonance quality of the optical cavity of a laser can be changed by placing special optics within the laser. These optics enable the beam to be turned on and off rapidly and normally create pulses with a duration of a few nanoseconds to a few tenths of a microsecond.

This mode of operation is normally called Q-switched. The "Q" refers to the resonant quality of the optical cavity. A laser operating in the Q-switched mode delivers less energy than the same laser operating in the normal-pulse mode, but the energy is delivered in a much shorter time period. Thus, Q-switched lasers are capable of delivering very high peak powers of several megawatts or even gigawatts. Most military lasers are Q-switched with pulse durations of 1 to 30 nanoseconds (ns) and are used in target acquisition and fire control.

d. When the phases of different frequency modes are synchronized (that is, "locked together"), the different modes will interfere with one another to generate a beat effect. The result will be a laser output that is observed as regularly spaced pulsations. Lasers operating in this fashion, mode-locked, usually produce trains of pulses, each having duration of a few picoseconds to a few nanoseconds. A mode-locked laser can deliver higher peak powers than the same laser operating in the Q-switched mode.

e. Pulsed lasers can be operated to produce repetitive pulses. The pulse repetition frequency (PRF) of a laser is the number of pulses that the laser produces in a second, measured in hertz.

Lasers are now available with PRFs as high as several million pulses per second. Pulse characteristics, as shown in figure 2–11, are important in laser hazard evaluations. Target designators and direct-fire simulators illuminate a target with a series of precisely spaced pulses.

Training devices have laser pulse trains that contain information on the weapon type.

2–11. Pulse characteristics of several different lasers

2–10. Spatial transverse electromagnetic modes of operation

a. Certain beam geometries have transverse wave patterns, which are identified by transverse electromagnetic modes (TEM) numbers.

b. A laser operating in the TEM00 mode emits a beam that is circularly symmetric in shape.

Figure 2–12 illustrates how several of the more common TEM modes would look in cross section.

Figure 2–12. Common transverse electromagnetic modes

2-11. Beam diameter

a. The exit laser beam diameter is measured at the exit aperture of the cavity. For an approximately circular beam, the edge of the beam is defined using different criteria. Often it is defined to be the diameter of a circle where the irradiance (E) or radiant exposure falls off to 1/e or 1/e2 of the maximum (figure 2–13); the laser’s beam diameter will contain 63 percent and 86 percent of the beam energy respectively.

b. In this bulletin, the diameter is defined at 1/e of maximum. For a circularly shaped beam, 63 percent of the laser’s output energy is within the circular area defined by this beam diameter.

Figure 2–13. Irradiance or radiant exposure at various points in the beam cross section

2–12. Divergence

a. The beam divergence ( ) is the increase in beam diameter with increase in distance (that is, how fast the beam spreads out over distance). Although lasers are unable to produce perfectly collimated beams due to the wave nature of light, the divergence can be made much smaller than with any other source of optical radiation available.

b. When determining the beam diameter or beam divergence, the beam should be defined at 1/e of peak irradiance points. It is expressed as an angle and given in radians. For example, a laser beam that is 1 meter (m) in diameter at a distance of 1 kilometer (km) would have a divergence of 1 milliradian (mrad) (1/1000 of a radian). (See figure 2–14.)

Figure 2–14. Definition of divergence angle

2–13. Hot spots

a. “Hot spots” are defined as localized areas of the beam where the beam irradiance is much greater than the average across the beam. There are several sources of hot spots:

inhomogeneities in the laser cavity or areas where more energy is emitted than in other areas, imperfections in the mirrors and lenses of the laser system, and changes caused by atmospheric conditions.

b. Atmospheric inhomogeneities, or regions of different air density along the beam path, produce lenticular effects (scintillation), which are responsible for atmospheric hot spots. Fog, rain, snow, dust, smoke, or other obscuring haze absorb and/or scatter the laser beam but do not cause hot spots; in fact, such scattering reduces the effect of hot spots.

CHAPTER 3

EFFECTS OF LASER EXPOSURE

3–1. Introduction

a. Laser radiation should not be confused with ionizing radiation (such as, X and gamma rays), although very high irradiances have been known to produce ionization in air and other materials.

The biological effects of laser radiation are essentially those of UV, IR, or visible radiation upon tissues. However, radiant intensities typically produced by lasers are of magnitudes that could previously be approached only by the sun, nuclear weapons, burning magnesium, or arc sources.

This is one of the important properties that makes lasers potentially hazardous. A laser radiation incident upon biological tissue will be reflected, transmitted, and/or absorbed.

b. Absorption is selective. As in the case of visible light, colored material such as melanin or other pigmented tissue will absorb more energy than unpigmented tissue. Adverse effects may be caused by the heating (see figure 3–1.) Low-level adverse visual effects from visible lasers are also possible (see para 3–6).

Notes:

1 UV–C (100 nm–280 nm) 2 UV–B (280 nm–315 nm) 3 UV–A (315 nm–400 nm) 4 IR–A (700 nm–1400 nm) 5 IR–B (1400 nm–3µm) 6 IR–C (3 µm–1000 µm)

Figure 3–1. Adverse effects on eye and skin from nonionizing radiation

3–2. Skin

a. Adverse thermal effects resulting from exposure of the skin to radiation from 315 nm to 1 mm may vary from mild reddening (erythema or sunburn) to blistering and charring. This depends upon the exposure dose rate (power), the dose (total amount of energy) transferred, and the conduction of heat away from the absorption site.

b. Adverse photochemical skin effects resulting from exposure to actinic UV radiation (180 nm–315 nm) vary from erythema to blistering, depending upon the wavelength and total exposure dose.

3–3. Eye

a. Anatomy of the eye. Figure 3–2 shows the anatomy of the eye and those areas as they relate to the interaction with electromagnetic radiation. In almost all situations, the eye is the organ most vulnerable to injury.

Figure 3–2. Anatomy of the eye

b. Absorption of electromagnetic radiation. Figure 3–3 provides a schematic representation of absorption of electromagnetic radiation by the eye―

(1) Most higher energy X-rays and gamma rays pass completely through the eye with relatively little absorption.

(2) Absorption of far ultraviolet (UV–B and UV–C) and far-infrared (IR–B and IR–C) radiation occurs principally at the cornea.

(3) Near ultraviolet (UV–A) radiation is primarily absorbed in the lens.

(4) Light (380 nm–780 nm) is refracted at the cornea and lens and absorbed at the retina; near infrared (IR–A) radiation is also refracted and is absorbed in the ocular media and at the retina.

(See chapter 7 for a discussion on laser eye protective devices.)

Figure 3–3. Absorption of electromagnetic radiation by the eye

c. Middle and far-infrared radiation (IR–B and IR–C)(1400 nm–1 mm) (see figure 3–3b).

Absorption of far-IR radiation produces heat with its characteristic effect on the cornea and the lens of the eye. Middle-infrared radiation (1400 nm–3000 nm) penetrates deeper into skin or corneal tissue than radiation of longer wavelengths. Consequentially, optical energy from middle-infrared wavelengths delivered in short pulses is absorbed in a volume of tissue rather simply at the cornea surface. Consequentially, tissue damage occurs at radiant exposure levels much higher than far-infrared wavelengths. When multiple pulsed exposures are involved, thermal heating from the combination of pulses determines the hazard, and little difference in hazard exists for middle infrared and far infrared. For example, the 10,600 nm wavelength from the carbon dioxide laser is absorbed by the surface of the cornea and conjunctiva and may cause severe pain and destructive effects.

d. Ultraviolet radiation (180 nm–400 nm) (figures 3–3b and 3c). Actinic UV radiation, UV–B, and UV–C (180 nm–315 nm) can produce symptoms similar to those observed in arc welders. It may cause severe acute inflammation of the cornea and conjunctiva. UV–B and UV–C radiation do not reach the retina. Near UV radiation (UV–A) is absorbed principally in the lens, which causes the lens to fluoresce. Very high doses can cause corneal and lenticular opacities (clouding). Insignificant levels of UV–A reach the retina.

e. Light (380 nm–780 nm) and near-infrared (IR–A) radiation (780 nm–1400 nm) (figure 3–3d). Adverse laser effects are generally believed to be limited to the retina in this spectral region. The effect upon the retina may be a temporary reaction without residual pathological changes, or it may be more severe with permanent pathological changes resulting in a permanent scotoma (blindspot). The mildest observable reaction may be a simple reddening, but as the retinal irradiance is increased, lesions may occur, which progress in severity from edema (swelling) to hemorrhage and additional tissue reaction around the lesion. Very high radiant exposures will cause gases to form near the site of absorption, which may disrupt the retina and may alter its physical structure. Portions of the eye, other than the retina, may be selectively injured depending upon the region where the greatest absorption of the specific wavelength of the laser energy occurs and the relative sensitivity of tissue affected. Chronic low-level exposure to blue light at wavelengths between 400 nm–600 nm may produce photochemical retinal damage.

3–4. Medical surveillance See appendix C for proper medical surveillance information and procedures for potential laser injuries.

3–5. Overexposure reporting For any known or suspected overexposure to laser radiation, contact the installation LSO and RSO. Laser accident reporting procedures are described in AR 40–400, AR 11–9, and AR 385–40. In addition, contact the following as soon as possible after getting the accident victim immediate medical attention:

a. The USAMRD–WRAIR, Ocular Hazards Research at USAMRD–Ocular Hazards Research Branch, DNS 240–4620/4621; commercial (410) 536–4620/4621 or at http://army.brooks.af.mil/.

b. The USACHPPM LORP at DSN 584–3931; commercial (410) 436–3932 or at http://chppm-www.apgea.army.mil/laser/laser.html.

c. The USACHPPM Tri-Service Vision Conservation and Readiness Program (TVCRP) at DSN 584-2714; commercial (410) 436–2714 or at:

http://chppm-www.apgea.army.mil/doem/vision.

d. For further medical surveillance information, see appendix C.

3–6. Low-level adverse visual effects At exposure levels below the maximum permissible exposure (MPE), several adverse visual effects from visible laser exposure may occur. The degree of each visual effect is strongest at night and may not be disturbing in daylight. These visual effects are

a. Afterimage. A reverse contrast, shadow image left in the visual field after a direct exposure to a bright light, such as a photographic flash. Afterimages may persist for several minutes, depending upon the level of adaptation of the eye (that is, the ambient lighting).

b. Flashblindness. A temporary visual interference effect that persists after the source of illumination has been removed. This is similar to the effect produced by a photographic flash and can occur at exposure levels below those that cause eye injury. In other words, flashblindness is a severe afterimage.

c. Glare. A reduction or total loss of visibility in the central field of vision, such as that produced by an intense light from oncoming headlights or from a momentary laser pointer exposure. These visual effects last only as long as the light is actually present. Visible laser light can produce glare and can interfere with vision even at exposure levels well below those that produce eye injury.

d. Dazzle. A temporary loss of vision or a temporary reduction in visual acuity.

e. Startle. Refers to an interruption of a critical task due to the unexpected appearance of a bright light, such as a laser beam.

CHAPTER 4

LASER HAZARD CLASSIFICATION AND EVALUATION

4–1. Introduction

a. A practical means for both evaluation and control of laser radiation hazards is to first classify laser devices according to their relative hazards and then to specify controls for each classification. (See chapter 5 for indoor control measures.) Due to the unique nature of military tactical and training devices, the USACHPPM LORP will classify U.S. Army military lasers and assign NOHDs. The classification scheme presented here is similar to that used in Standards Z– 136.1–2000 and Z136.6–2000. The MPEs are provided in this document for convenience. The most current ANSI Z136 standards are used when performing laser hazard classifications and evaluations. The classification scheme presented here is also similar to the Federal Laser Product Performance Standard (FLPPS) in Title 21, Code of Federal Regulations Part 1040 (21 CFR 1040) and the International Electrotechnical Commission (IEC) 60825–1, edition 1.2 (2001–2008). The federal classification already appears on commercial laser products manufactured after July 1976. Laser classifications performed using the IEC standard are now accepted by the U.S. Food and Drug Administration (FDA).

b. Three aspects of the application of a laser or laser system influence the total hazard evaluation and, thereby, influence the application of control measures

(1) The laser or laser system’s capability of injuring personnel or interfering with task performance.

(2) The environment in which the laser is used.

(3) The personnel who may use or be exposed to laser radiation.

c. The laser classification scheme is based on aspect (1). All three aspects should be considered during hazard evaluation, although aspects two and three are not easily standardized due to a laser’s potential varying application. Visual interference levels are based on aspects contained in paragraphs b(1) and b(2) above. Any laser or laser system should be classified according to its accessible radiation during operation.

d. For laboratory, medical, and non-military lasers, classification conforming to the FLPPS may be used to satisfy the classification requirements of this standard; although it should be noted that in some cases differences exist. If the manufacturer has modified the laser subsequent to classification, non-military lasers may be reclassified according to ANSI Z136.1 under the supervision of the LSO. The LSO should then ascertain whether any changes in control measures are required.

e. Lasers that are used for combat, combat training, or are classified in the interest of national security may be exempted from the FLPPS (see FDA Exemption 76 EL–01 DOD (21 CFR 1010.5)). The laser manufacturer must obtain an exemption letter prior to the sale of the laser from an authorized Department of Defense (DOD) procuring agency to allow the use of the

DOD exemption for that specific product. A manufacturer violates federal law if it sells a laser system not in compliance with the FLPPS to the DOD or falsely labels a laser product as exempt without a written DOD exemption letter. Further information on this process can be found in Laser Notice No. 52 issued by the FDA. These U.S.