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Spie Press Book

Laser Systems Engineering
Author(s): Keith J. Kasunic
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Book Description

While almost all of the books that have the word "laser" in their title focus on the development of the lasers themselves, Laser Systems Engineering emphasizes the design and engineering of optical systems that incorporate these unique sources of light. Taking the perspective of the laser systems engineer, this book reviews the concepts and components required for the development of laser-based systems for manufacturing, biomedical applications, laser radar, sensors, metrology, laser-based displays, directed energy, etc. Emphasizing practical design problems and the first-order equations and commercial off-the-shelf components used to solve them, this book is for engineers, scientists, and managers who want to quickly master the principles of laser system development.

Covered topics include:
• a review of the various types of lasers, with an emphasis on laser specifications unique to specific applications;
• propagation of ideal, aberrated, and higher-order Gaussian beams;
• selection of laser system optics and critical specifications for their use;
• requirements on the scan technologies, optical components, and system trades for beam scanning;
• radiometry of laser-based systems; and
• selection of detectors appropriate for laser systems, as well as the performance limitations of noise sources and their effects on overall architecture.

“This book will be a valued tool for the laser professional who either has a broad experience and is looking to architect an integrated system or one who has great depth in a particular area and is looking to transition into the systems-engineering realm.”
--Tim J. Valle, Staff Consultant, Ball Aerospace & Technologies Corporation


Book Details

Date Published: 2 December 2016
Pages: 328
ISBN: 9781510604261
Volume: PM271

Table of Contents
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Table of Contents

Preface

1 Introduction
1.1 Laser Systems
1.2 Laser Engineering
      1.2.1 Temporal coherence
      1.2.2 Spatial coherence
      1.2.3 Pulse generation
      1.2.4 Wavelength conversion
1.3 Laser Systems Engineering
1.4 Problems
Notes and References

2 Laser Selection
2.1 Laser Specifications
      2.1.1 Wavelength
      2.1.2 Temporal coherence
      2.1.3 Spatial coherence
      2.1.4 Power: CW, QCW, and pulsed
      2.1.5 Pulse width
      2.1.6 Pulse energy
      2.1.7 Pulse repetition frequency
      2.1.8 Power and energy stability
      2.1.9 Frequency stability
      2.1.10 Pointing stability
      2.1.11 Wall-plug efficiency
      2.1.12 Polarization
2.2 Laser Types
      2.2.1 Semiconductor lasers
      2.2.2 Solid-state lasers
      2.2.3 Fiber lasers
      2.2.4 Gas lasers
2.3 Laser selection
2.4 Problems
Notes and References

3 Beam Propagation
3.1 Gaussian Beams
3.2 Beam Quality
3.3 Beam Imaging
3.4 Problems
Notes and References

4 Laser System Optics
4.1 Windows and Filters
4.2 Lenses
      4.2.1 Focusing
      4.2.2 Beam truncation
      4.2.3 Aberrations
      4.2.4 Surface figure (irregularity)
      4.2.5 Surface ripple ("quilting")
      4.2.6 Surface finish (roughness)
      4.2.7 Surface quality (scratch-dig)
4.3 Beam Expanders and Collimators
4.4 Homogenizers
4.5 Miscellaneous
      4.5.1 Material absorption
      4.5.2 Backreflections
      4.5.3 Optical coatings
      4.5.4 Laser damage threshold
      4.5.5 Polarization
4.6 Problems
Notes and References

5 Beam Scanning
5.1 Scan Technologies
      5.1.1 Galvanometers
      5.1.2 Polygon scanners
      5.1.3 MEMS scanners
      5.1.4 Miscellaneous technologies
5.2 Scan Optics
      5.2.1 Scan mirrors
      5.2.2 f-θ lenses
5.3 System Design and Trades
      5.3.1 Mirror speed, angle, and aperture trades
      5.3.2 Resolvable spots
      5.3.3 Scan velocity and PRF
      5.3.4 Entrance pupils
5.4 Problems
Notes and References

6 Radiometry
6.1 Laser Brightness
6.2 Power-in-Bucket
6.3 Laser Intensity
6.4 Power Budgets
      6.4.1 Reflected power and radiance
      6.4.2 Power collection
      6.4.3 Atmospheric transmission
      6.4.4 Background and stray light
      6.4.5 The range equation
6.5 Problems
Notes and References

7 Detectors
7.1 PIN Photodiodes
      7.1.1 Photon detectors
      7.1.2 Reverse-bias PINs
      7.1.3 PIN detector specifications
7.2 Avalanche Photodiodes
      7.2.1 Linear-mode APDs
      7.2.2 Geiger-mode APDs
7.3 Photomultiplier Tubes
7.4 Focal Plane Arrays
      7.4.1 Sampling
      7.4.2 FPA technologies
      7.4.3 FPA specifications
7.5 Noise, Sensitivity, and Selection
      7.5.1 Signal-to-noise ratio
      7.5.2 Detector sensitivity
      7.5.3 Detector selection
7.6 Problems
Notes and References

Glossary of Symbols and Acronyms
Index

Preface

How did it happen that more than 50 years after the invention of the laser, almost all of the books that have the word "laser" in their title emphasize the design of the lasers themselves, rather than the development of optical systems that incorporate these unique sources of light? A quick web search reveals thousands of books that focus on laser design; very few books, however—Building Electro-Optical Systems by Hobbs, Laser Communications in Space by Lambert and Casey, Field Guide to Lidar by McManamon, and Electro-Optical Instrumentation by Donati, for example—address aspects of the design and engineering of laser systems.

As a result, and aside from the many books available for fiber-optic communication systems, the design of laser systems that use free-space optics—manufacturing, biomedical systems, laser radar, laser displays, and so on—is still a hit-or-miss proposition, with little systematic guidance available. The purpose of this book is to take an initial step in addressing this gap.

The perspective taken to do this—that of the laser systems engineer—is sometimes thought of as "designing the right laser" versus "designing the laser right." Unfortunately, this approach is both incomplete and overly centered on the laser designer's goal of designing the laser right. Designing (or selecting) the right laser—i.e., one that meets system-level requirements—is certainly key, but designing the right optical, scanning, and detector subsystems is equally important.

Starting with a description of what the "right" laser might look like, this book addresses all of these topics. Laser selection will depend on the application, with Chapter 2 reviewing the available laser types (semiconductor, solid-state, fiber, and gas) in the context of what makes them uniquely suited to meet specific requirements such as average power, peak power, linewidth, power consumption, cost, size, and so on.

Chapter 3 then looks at Gaussian beam propagation and associated nonidealities for aberrated and higher-order beams; Chapter 4 uses these concepts to develop the details of the optical subsystem, including the unique properties of Gaussian-beam focusing, as well as truncation, aberrations, surface figure, surface ripple, surface roughness, surface quality, material absorption, backreflections, optical coatings, and laser damage threshold.

In addition to the laser and optical subsystems, scanning and beam control are required for directing photons onto a biomedical specimen, manufacturing workpiece, projection screen, or target. The scanning technologies, optical components, and system trades for these subsystems are covered in Chapter 5.

Finally, many laser systems require the use of a detector—single-pixel or focal plane array—to collect an image or otherwise obtain information about the beam. Before we can measure photons, however, we first need to understand how many are expected, their wavelengths, and their spatial distribution. This is reviewed in Chapter 6, where we examine the notion of laser brightness, and then use the concept to estimate the power collected by the optical and detector subsystems. Chapter 7 then ties everything together from the point of view of photon detection, including detector types, geometries, sensitivities, and selection.

The emphasis in all chapters is on real-world design problems and the first-order equations and commercial off-the-shelf components used to solve them. As with any book, not every topic can be included; however, readers may also find my previous books useful for understanding the many differences between lasers and incoherent sources [Optical Systems Engineering (McGraw-Hill, 2011)] or obtaining additional details on the optomechanical aspects of building laser systems [Optomechanical Systems Engineering (John Wiley & Sons, 2015)].

Keith J. Kasunic
August 2016


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