詳細

Laser beam quality is more complicated and subtle than is usually assumed, a fact that has caused no end of frustration and misunderstanding between laser manufacturers, users, and acquirers. Laser Beam Quality Metrics guides the reader through the subtleties of laser beam quality analysis and requirements synthesis, arming the reader with the tools to understand beam quality specifications and to write custom specifications that are traceable to the intended application.

The book is geared toward engineers and laser physicists involved in the development of laser-based systems, especially laser systems for directed energy applications. It begins with a review of basic laser properties and moves to definitions and implications of the various standard beam quality metrics such as M2, power in the bucket, brightness, beam parameter product, and Strehl ratio. The practical aspects of beam metrology, which have not been sufficiently addressed in the literature, are amply covered here.

For those who are only interested in measuring Gaussian beams from commercial lasers, a reading of Chapter 1, Chapter 2 “What Your Laser Beam Analyzer Manual Didn’t Tell You,” and the first three sections of Chapter 6 “Cautionary Tales” will be sufficient. For those working in more off-the-map fields such as unique lasers, unstable resonators, multikilowatt lasers, MOPAs, or requirements generation and development, a reading of the entire text is recommended.

Sample Pages (PDF)

Preface
Acknowledgment
List of Acronyms, Symbols, and Notation
1 Introduction
　1.1 First Rule of Laser Beam Quality Metrics
　1.2 History, Resources, and State of Laser Beam Quality
　1.3 Anatomy of a Laser
　　1.3.1 Generic laser resonator
　　1.3.2 Stable resonator
　　1.3.3 Unstable resonator
　　1.3.4 Master oscillator power amplifier (MOPA)
　　1.3.5 Temporal behavior of lasers
　　1.3.6 Types of lasers
　1.4 Basic Properties of Laser Radiation
　　1.4.1 Near field versus far field
　　1.4.2 Special shapes
　1.5 Laser Modes and Modal Analysis
　　1.5.1 Hermite?Gaussian modes
　　1.5.2 Laguerre?Gaussian modes
　　1.5.3 Unstable resonator modes
　　1.5.4 Fiber laser modes
　1.6 Common Measures of Beam Centroid
　　1.6.1 First moment
　　1.6.2 Peak irradiance
　　1.6.3 Transmission maximization
　　1.6.4 Geometrical center/cutoff
　1.7 Common Measures of Beam Radius and Divergence Angle
　　1.7.1 Second moment
　　1.7.2 Best fit to Gaussian
　　1.7.3 First null
　　1.7.4 Hard cutoff measures
　　1.7.5 Mode maximization
　1.8 Common Sources of Beam Quality Degradation
　　1.8.1 Resonator modes
　　1.8.2 Physical nonuniformities
　　1.8.3 Unstable resonator
　　1.8.4 Thermal nonuniformities
　　1.8.4 Diffraction effects
　1.9 Common Measures of Beam Quality
　　1.9.1 M2
　　1.9.2 Power in the bucket
　　1.9.3 Strehl ratio
　　1.9.4 Wavefront error
　　1.9.5 Central lobe power
　　1.9.6 Beam parameter product
　　1.9.7 Brightness
　　1.9.8 Times the diffraction limit
　　1.9.9 Summary: What each metric is designed to determine
2 What Your Beam Analyzer Manual Didn't Tell You: How to Build Your Own M2 Device (or Understand Theirs)
　2.1 Preparing to Purchase a Commercial Beam Analyzer
　2.2 Resources
　　2.2.1 Summary of the ISO standards on laser beam quality
　2.3 Equipment
　　2.3.1 Camera selection
　　2.3.2 Stage tradeoffs
　　2.3.3 Filters
　2.4 Dark Current Noise and Zeroing
　2.5 Data Windowing
　　2.5.1 Noise equivalent aperture (NEA)
　　2.5.2 Error terms due to data windowing
　2.6 Curve Fitting
　2.7 Error Determination in M2 Measurements
　　2.7.1 Error estimation
　　2.7.2 Variance of second-moment radius due to discretization error
　　2.7.3 Variance of second-moment radius due to dark current noise
　　2.7.4 Error in NEA estimation
　　2.7.5 Variance of second-moment radius due to NEA estimation error
　　2.7.6 Total variance in second-moment radius measurements
　　2.7.7 Effect of averaging multiple shots on second-moment radius variance
　2.8 Knife-Edge Measurements
　　2.8.1 ISO two-point knife-edge method
　　2.8.2 Single-point variable-aperture method
　2.9 Conclusions: M2
3 How to Design Your Own Beam Quality Metric
　3.1 Overview: Synthesis, Analysis, and Comparison
　3.2 Requirements Synthesis
　　3.2.1 Determining the nature of application requirements: producing a minimally effective beam
　　3.2.2 Propagating minimally effective beams backward from target to aperture produces the best Strehl　　 ratio
　　3.2.3 Propagating a filled aperture forward from aperture to target produces the best spot size
　　3.2.4 Bounding plausible aperture?target?beam combinations
　　3.2.5 Choosing and documenting the metric
　3.3 Specification Analysis
　　3.3.1 Determining the reference beam
　　3.3.2 Determining the basis of comparison between the actual beam and the reference beam
　　3.3.3 Determining the definition of beam radius
　　3.3.4 Completely specifying key metrics for measurement of beam quality
　　3.3.5 Obtaining programmatic, technical, and contractual buy-in
　　3.3.6 Fully documenting the beam quality specification
　3.4 Comparative Beam Quality Metrics
　3.5 Example: Generic VPIB-related Specifications
　3.6 Example: Requirements Area
　3.7 Example: System Beam Quality Metric
　3.8 Example: Core and Pedestal Metrics
4 Beam Quality Metric Conversion
　4.1 Gaussian Beam Quality Conversions
　　4.1.1 Gaussian conversion: VPIB
　　4.1.2 Gaussian conversion: HPIB
　　4.1.3 Gaussian conversion: Strehl ratio
　　4.1.4 Gaussian conversion: Phase aberration
　　4.1.5 Gaussian conversion: Brightness
　4.2 General Beam Quality Conversions
　　4.2.1 Beam quality metrics versus uncorrelated Gaussian phase noise
　　4.2.2 Beam quality metrics versus uncorrelated Gaussian amplitude noise
5 Arrays
　5.1 Sources of Beam Quality Degradation
　　5.1.1 Fill factor considerations
　　5.1.2 Phasing errors
　　5.1.3 Misalignment errors
　　5.1.4 Emitter degradation
　5.2 Adapting Beam Quality Metrics for Array Use
　　5.2.1 Radius metrics in the near and far field
　5.3 Thought Experiment: Loss of an Emitter
6 Cautionary Tales
　6.1 Three Viewpoints on Gaussian Beam Propagation
　6.2 Non-Gaussian Gaussians
　6.3 The Effect of Truncation on Gaussian Beam Quality
　6.4 Case Studies
　　6.4.1 Fast cameras (jitter)
　　6.4.2 Ever-changing near-field diameter (inscribed, circumscribed, square versus round, cutoffs, etc.)
　　6.4.3 Creative time gating (taking only the good part)
　　6.4.4 Gaming the beam profile (annular)
　　6.4.5 Let's be fair to the laser (elliptic)
　　6.4.6 Power and beam quality mismatch
　　6.4.7 Adjusting data to get a "proper" PIB curve
　6.5 What to Look for in Advertising
7 Conclusions
Appendix
　A.1 Derivation of M2 from Gaussian modes
　　A.1.1 Hermite?Gaussian
　　A.1.2 Laguerre?Gaussian
　A.2 Deconvolving the ISO Standard
　　A.2.1 ISO propagation equation
　A.3 Beam Waist Versus Focal Plane
References
Index