Industrial Applications of Lasers (eBook)

John F. Ready (Autor)

eBook Download: PDF

1997 | 2. Auflage
599 Seiten
Elsevier Science (Verlag)
978-0-08-050860-3 (ISBN)

Infos

A practical book with a variety of uses, this book can help applications engineers spark problem-solving techniques through the use of lasers. Industrial Application of Lasers, Second Edition takes the reader through laser fundamentals, unusual properties of laser light, types of practical lasers available, and commonly used accessory equipment. The book also applies this information to existing and developing applications. Current uses of lasers, including laser welding and cutting, electronic fabrication techniques, lightwave communications, laser-based applications in alignment, surveying, and metrology are all covered as well as discussing the potential for future applications such as all-optical computers,remote environmental monitoring, and laser-assisted thermonuclear fusion.

Key Features
* Explains basic laser fundamentals as well as emphasizing how lasers are used for real applications in industry
* Describes the importance of laser safety
* Discusses potentially important future applications such as remote environmental monitoring
* Includes rare expert lore and opinion

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A practical book with a variety of uses, this book can help applications engineers spark problem-solving techniques through the use of lasers. Industrial Application of Lasers, Second Edition takes the reader through laser fundamentals, unusual properties of laser light, types of practical lasers available, and commonly used accessory equipment. The book also applies this information to existing and developing applications. Current uses of lasers, including laser welding and cutting, electronic fabrication techniques, lightwave communications, laser-based applications in alignment, surveying, and metrology are all covered as well as discussing the potential for future applications such as all-optical computers,remote environmental monitoring, and laser-assisted thermonuclear fusion. - Explains basic laser fundamentals as well as emphasizing how lasers are used for real applications in industry- Describes the importance of laser safety- Discusses potentially important future applications such as remote environmental monitoring- Includes rare expert lore and opinion

Inhalt

Cover 1
Contents 8
Preface 16
Acknowledgments 18
Historical Prologue 20
Chapter 1. Fundamentals of Lasers 24
A. Electromagnetic Radiation 24
B. Elementary Optical Principles 27
C. Energy Levels 32
D. Interaction of Radiation and Matter 34
E. Laser Materials 35
F. Population Inversion 38
G. Resonant Cavity 45
Selected References 53
Chapter 2. Properties of Laser Light 54
A. Linewidth 54
B. Collimation 59
C. Spatial Profiles of Laser Beams 63
D. Temporal Behavior of Laser Output 69
E. Coherence 76
F. Radiance 81
G. Focusing Properties of Laser Radiation 82
H. Power 86
References 86
Selected Additional References 86
Chapter 3. Practical Lasers 89
A. Gas Lasers 89
B. Solid State Lasers 112
C. Semiconductor Lasers 125
D. Organic Dye Lasers 143
References 152
Selected Additional References 152
Chapter 4. Trends in Laser Development 154
A. Semiconductor Lasers 155
B. Diode-Pumped Solid State Lasers 156
C. Chemical Lasers 159
D. Free Electron Lasers 160
E. X-Ray Lasers 162
F. Optical Parametric Oscillators 163
G. Tunsble Lasers 164
References 166
Selected Additional References 166
Chapter 5. Laser Components and Accessories 167
A. Mirrors 167
B. Optics 171
C. Polarizers 172
D. Infrared Materials 174
E. Detectors 175
F. Modulators 188
G. Light Beam Deflectors 194
H. Q-Switches 199
I. Nonlinear Optical Elements 202
J. Optical Isolators 205
K. Raman Shifters 206
L. Injection Seeders 207
M. Beam Profilers 208
N. Optical Tables 210
O. Spatial Light Modulators 212
P. Beam Homogenizers 213
Selected References 214
Chapter 6. Care and Maintenance of Lasers 216
A. Damage and Deterioration of Lasers 216
B. Care and Maintenance 231
References 236
Selected Additional References 237
Chapter 7. Laser Safety 238
A. Physiological Effects 239
B. Laser Safety Practices and Standards 247
References 254
Selected Additional References 254
Chapter 8. Alignment, Tooling, and Angle Tracking 255
A. Position-Sensitive Detectors 256
B. Laser Tooling 258
C. Angle Tracking 265
D. Lasers in Construction 267
References 270
Selected Additional References 270
Chapter 9. Principles Used in Measurement 271
A. The Michelson Interferometer 272
B. Beat Production (Heterodyne) 274
C. The Doppler Effect 275
D. Coherence Requirements 276
Selected References 278
Chapter 10. Distance Measurement and Dimensional Control 279
A. Interferometric Distance Measurement 280
B. Laser Doppler Displacement 293
C. Beam Modulation Telemetry 293
D. Pulsed Laser Range Finders 297
E. A Laser Interferometer Application in Mask Production: A Specific Example of Distance Measurement and Dimensional Control 299
References 299
Selected Additional References 300
Chapter 11. Laser Instrumentation and Measurement 301
A. Velocity Measurement 301
B. Angular Rotation Rate 310
C. Diffractive Measurement of Small Dimension: Wire Diameter 318
D. Profile and Surface Position Measurement 320
E. Measurement of Product Dimension 326
F. Measurement of Surface Finish 328
G. Particle Diameter Measurement 330
H. Strain Measurement 332
I. Vibration 333
J. Cylindrical Form Measurement 333
K. Defect Detection 334
L. Surface Flaw Inspection Monitor: A Specific Example 335
M. Summary 336
References 336
Selected Additional References 336
Chapter 12. Interaction of High-Power Laser Radiation with Materials 338
References 357
Selected Additional References 357
Chapter 13. Laser Applications in Material Processing 358
Selected References 365
Chapter 14. Applications of Laser Welding 366
A. Seam Welding: Subkilowatt Levels 368
B. Welding with Multikilowatt Lasers 376
C. Spot Welding 386
D. Specific Examples of Laser Welding Capability 390
E. Summary 392
References 395
Selected Additional References 395
Chapter 15. Applications for Surface Treatment 396
A. Hardening 396
B. Glazing 403
C. Laser Alloying 403
D. Laser Cladding 404
E. Specific Examples of Laser Heat Treating Capability 405
References 406
Selected Additional References 406
Chapter 16. Applications for Material Removal: Drilling, Cutting, Marking 407
A. Laser-Induced Material Removal 407
B. Hole Drilling 410
C. Cutting 418
D. Scribing 432
E. Marking 434
E. Balancing 436
G. Paint Stripping 438
H. Laser Deposition of Thin Films 438
I. Specific Examples of Material Removal 439
References 440
Selected Additional References 440
Chapter 17. Lasers in Electronic Fabrication 442
A. Established Applications in Electronics 442
B. Applications in Integrated Circuit Fabrication 449
C. Summary 455
D. A Specific Example: Laser-Based Photomask Repair 457
References 458
Selected Additional References 459
Chapter 18. Principles of Holography 460
A. Formation of Holograms 460
B. The Holographic Process 465
C. Hologram Types and Efficiency 474
D. Practical Aspects of Holography 479
References 486
Selected Additional References 486
Chapter 19. Applications of Holography 487
A. Holographic Interferometry 487
B. A Miscellany of Applications 503
C. Holographic Optical Elements 509
D. An Example of Holographic Application 510
References 512
Selected Additional References 513
Chapter 20. Laser Applications in Spectroscopy 514
A. Lasers for Spectroscopic Applications 515
B. Types of Laser Spectroscopy 516
C. Applications of Laser Spectroscopy 522
References 532
Selected Additional References 532
Chapter 21. Chemical Applications 533
A. Laser-Initiated Reactions 534
B. Laser-Altered Reactions 535
C. Laser Monitoring of Chemical Dynamics 539
D. Isotope Separation 542
References 552
Selected Additional References 552
Chapter 22. Fiber Optics 553
A. Structures 553
B. Losses 556
C. Manufacture of Optical Fibers 560
D. Connectors, Splicing, and Couplers 561
E. Fiber Amplifiers 563
F. Infrared-Transmitting Fibers 563
G. Fiber Optic Sensors 565
H. Summary 567
References 568
Selected Additional References 568
Chapter 23. Integrated Optics 569
A. Optical Waveguides 570
B. Components for Integrated Optics 574
C. Integrated Optic Circuits 577
D. Applications 580
References 581
Selected Additional References 581
Chapter 24. Information-Related Applications of Lasers 582
A. Lightwave Communications 582
B. Optical Data Storage 589
C. Optical Data Processing 596
D. Laser Graphics 606
E. Consumer Products 608
References 612
Selected Additional References 612
Epilogue A Look at the Future 613
References 616
Selected Additional References 616
INDEX 618

Textauszug

Chapter 2

Properties of Laser Light

The applications of lasers depend on the unusual properties of laser light, ones that are different from the properties of light from conventional sources. The properties that will be discussed in this chapter include monochromaticity (narrow spectral linewidth), directionality (good collimation of the beam), the spatial and temporal characteristics of laser beams, coherence properties, radiance (or brightness), the capability to focus to a small spot, and the high power levels available. These properties are not all independent: for example, the focusability depends on the collimation to a large extent. Still, it is convenient to discuss these different aspects separately. These characteristics of laser light, which can be very different from light produced by ordinary sources, enable lasers to be used for the practical applications, which will be described later.

A. Linewidth

Laser light is highly monochromatic, that is, it has a very narrow spectral width. The spectral width is greater than zero, but typically it is much less than that of conventional light sources. The narrow spectral linewidth is one of the most important features of lasers. Early calculations [1] indicated that the linewidth could be a small fraction of 1 Hz. Of course, most practical lasers have much greater linewidth.

In discussing linewidth, we must distinguish between the width of one mode of the resonant cavity and the width of the total spectrum of the laser output. As Chapter 1 described, many lasers operate simultaneously in more than one longitudinal mode, so that the total linewidth may approach the fluorescent linewidth of the laser material. Figure 2-1 illustrates the situation. The evenly spaced cavity modes are illustrated in part (a). The frequency spacing is c/2nD, with D the distance between the two mirrors and n the index of refraction of the material. For a gas, the index of refraction is close to unity, and the spacing becomes c/2D. This spacing is equivalent to a wavelength spacing of λ2/2D, where λ is the wavelength. Figure 2-1b shows the gain and the loss as functions of frequency. The gain curve has the same shape as the fluorescent line, and the loss is essentially independent of frequency, at least over a reasonably small range. All modes for which the gain is greater than loss can be present in the laser output. Thus, the spectral form of the output can be as shown in Figure 2-1c.

Figure 2-1 Frequency spectrum of laser output. Part (a) shows the resonant modes of a cavity for a gas laser, with c the velocity of light and D the mirror separation. Part (b) shows the gain curve for the fluorescent emission, with the cavity loss, which is relatively constant with respect to frequency, also indicated. Part (c) shows the resulting frequency spectrum, in which all the modes for which gain is greater than loss are present.

Some typical values are shown in Table 2-1 for representative lasers. The fluorescent linewidth varies considerably for different laser materials. The table presents the operating wavelength and frequency of the laser, the fluorescent linewidth of the laser material, and the typical number of longitudinal modes present in the output of the laser. The number of modes is calculated as the fluorescent linewidth divided by the quantity c/2D, the spacing between longitudinal modes. In most cases this will be an overestimate, because near the edges of the fluorescent line, the gain will not be high enough to sustain laser operation. Thus, for typical commercial helium–neon lasers, perhaps three or four modes will be present, rather than ten as the calculation indicates. CO2 lasers present an interesting case, because at low gas pressure the fluorescent linewidth is narrow, of the order of 60 MHz. As the pressure increases to near atmospheric, the fluorescent linewidth broadens. Atmospheric pressure CO2 lasers may operate in several modes. Neodymium:glass has an unusually wide fluorescent linewidth, and an Nd:glass laser can have hundreds or even thousands of longitudinal modes present in its output. In particular, in mode-locked operation (to be described later) the emission spectrum can fill the fluorescent linewidth.

Table 2-1

Linewidth for Common Lasers

In summary, the total spectral width covered by many practical lasers will be almost as wide as the fluorescent linewidth, often around 109 Hz. We note that this is still much smaller than the operating frequency, around 1015 Hz. Even a laser with many longitudinal modes present in its output is still almost monochromatic.

Individual longitudinal modes have much narrower spectral width. To provide better monochromaticity, lasers are sometimes constructed so as to operate in only one longitudinal mode.

One method for providing single-mode operation involves construction of short laser cavities, so that the spacing between modes (c/2D) becomes large and gain can be sustained on only one longitudinal mode. Other longitudinal modes will fall outside the fluorescent line. This is illustrated in Figure 2-2. This approach is most commonly applied in helium–neon lasers. Commercial single-mode helium–neon lasers have spectral widths of the order of 107 Hz, much reduced from the 109 Hz range of multimode lasers. But this reduction is achieved at a sacrifice in output power. The short cavity limits the power that can be extracted.

Figure 2-2 Relation of line shape and resonant modes of a short cavity. Only one mode lies within the width of the line, which allows laser operation in a single longitudinal mode.

A second method for obtaining single-mode operation involves use of multiple mirrors, as illustrated in Figure 2-3a. This defines cavities of two different lengths, D1 and D2. The length of the short cavity D1 is chosen so that only one mode lies within the fluorescent linewidth. The laser must operate in a mode that is simultaneously resonant in both cavities. This is illustrated in Figure 2-3b. The lengths of the two cavities must be adjusted carefully, so that there is an overlap of two resonant modes. This places stringent requirements on mirror position and stability. However, this arrangement allows operation of single-longitudinal-mode lasers with higher power. It is used most often with solid state lasers.

Figure 2-3 Three-mirror method for obtaining operation in a single longitudinal mode. Part (a) shows the positioning of the mirrors so as to define cavities of two different lengths, D1 and D2. Part (b) shows the gain of the laser transition superimposed on the longitudinal mode spectra of the long cavity and the short cavity. The laser can operate in only the one mode that is under the gain curve and that is simultaneously a mode of both cavities.

Another method for providing a long cavity and a short cavity involves insertion of a device called an etalon into the laser cavity. The etalon is a short resonant cavity, which may be formed from a piece of glass with its two faces polished to a high degree of parallelism. Figure 2-4 shows how an etalon may be inserted into a laser cavity. The etalon generally is tilted with respect to the axis of the cavity in order to provide tuning, as we will discuss. The surfaces of the etalon form a short cavity. The etalon produces loss at wavelengths that are not modes of its cavity. The longitudinal modes in the laser output must be simultaneously modes of the etalon and of the cavity that defines the laser. Generally, only one mode of the laser will satisfy this condition. This forces the laser to operate in only one of its longitudinal modes. The use of an intracavity etalon is perhaps the most common method for producing single-mode operation.

Figure 2-4 Laser cavity with an etalon.

Usually the etalon is mounted so that its surfaces are tilted with respect to the axis of the laser. As the etalon is rotated, its effective length along the axis changes. The allowed wavelength then changes slightly, so that it is possible to tune the wavelength of the laser by a small amount within the gain curve of the laser material.

Another method for forcing the output of a pulsed laser into a single longitudinal mode is injection seeding. One directs the output of a small, stable, single-frequency laser, called the seed laser, into the laser cavity of the larger laser, which provides the output pulse. The seed laser is usually a continuous laser. The frequency of the seed laser must lie within the linewidth of the larger laser. When the pulse of the larger laser develops, it occurs at the longitudinal mode that is closest to the frequency of the seed laser. This longitudinal mode builds up rapidly by stimulated emission and saturates the gain of the laser before the other longitudinal modes have a chance to develop from noise. Thus, the output of the pulsed laser will be at a single frequency, rather than in a number of longitudinal modes at different frequencies.

Even when operating in a single longitudinal mode, a laser still has a finite spectral linewidth. Because the width of a single mode is much less than the intermode spacing, it will be much smaller than for multimode operation.

Further, the...

Produkt-Details

• Erscheint lt. Verlag: 25.4.1997
• Sprache: englisch
• Themenwelt: Mathematik / Informatik ► Informatik
• Themenwelt: Naturwissenschaften ► Physik / Astronomie ► Elektrodynamik
• Themenwelt: Technik ► Elektrotechnik / Energietechnik
• ISBN-10: 0-08-050860-X / 008050860X
• ISBN-13: 978-0-08-050860-3 / 9780080508603