Handbook of Optical and Laser Scanning

Gerald F. Marshall, Glenn E. Stutz, Gerald F. Marshall, Glenn E. Stutz

• Publisher: CRC Press
• Year: 2018
• Print ISBN: 9781439808795
• eBook ISBN: 9781351834131
• Edition: 2
• Topic: Technology & Engineering
• Subtopic: Electrical Engineering & Telecommunications
• Index: Technology & Engineering

From its initial publication titled Laser Beam Scanning in 1985 to Handbook of Optical and Laser Scanning, now in its second edition, this reference has kept professionals and students at the forefront of optical scanning technology. Carefully and meticulously updated in each iteration, the book continues to be the most comprehensive scanning resource on the market. It examines the breadth and depth of subtopics in the field from a variety of perspectives.

The Second Edition covers:

• Technologies such as piezoelectric devices

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• Applications of laser scanning such as Ladar (laser radar)

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• Underwater scanning and laser scanning in CTP

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As laser costs come down, and power and availability increase, the potential applications for laser scanning continue to increase. Bringing together the knowledge and experience of 26 authors from England, Japan and the United States, the book provides an excellent resource for understanding the principles of laser scanning. It illustrates the significance of scanning in society today and would help the user get started in developing system concepts using scanning. It can be used as an introduction to the field and as a reference for persons involved in any aspect of optical and laser beam scanning.

1

Characterization of Laser Beams: The M² Model

Thomas F. Johnston, Jr.

Optical Physics Solutions

Grass Valley, California, USA

Michael W. Sasnett

Optical System Engineering

Los Altos, California, USA

CONTENTS

1.1 Introduction

1.2 Historical Development of Laser-Beam Characterization

1.3 Organization of This Chapter

1.4 The M² Model for Mixed-Mode Beams

1.4.1 Pure Transverse Modes: The Hermite-Gaussian and Laguerre-Gaussian Functions

1.4.2 Mixed Modes: The Incoherent Superposition of Pure Modes

1.4.3 Properties of the Fundamental Mode Related to the Beam Diameter

1.4.4 Propagation Properties of the Fundamental-Mode Beam

1.4.5 Propagation Properties of the Mixed-Mode Beam: The Embedded Gaussian and the M² Model

1.5 Transformation by a Lens of Fundamental and Mixed-Mode Beams

1.5.1 Application of the Beam-Lens Transform to the Measurement of Divergence

1.5.2 Applications of the Beam-Lens Transform: The Limit of Tight Focusing

1.5.3 The Inverse Transform Constant

1.6 Beam Diameter Definitions for Fundamental and Mixed-Mode Beams

1.6.1 Determining Beam Diameters from Irradiance Profiles

1.6.2 General Considerations in Obtaining Useable Beam Profiles

1.6.2.1 How Commercial Scanning Aperture Profilers Work

1.6.3 Comparing the Five Common Methods for Defining and Measuring Beam Diameters

1.6.3.1 D_pin, Separation of 1/e² Clip Points of a Pinhole Profile

1.6.3.2 D_slit, Separation of 1/e² Clip Points of a Slit Profile

1.6.3.3 D_ke, Twice the Separation of the 15.9% and 84.1% Clip Points of a Knife-Edge Scan

1.6.3.4 D₈₆, Diameter of a Centered Circular Aperture Passing 86.5% of the Total Beam Power

1.6.3.5 D_4σ, Four Times the Standard Deviation of the Pinhole Irradiance Profile

1.6.3.6 Sensitivity of D_4σ to the Signal-to-Noise Ratio of the Profile

1.6.3.7 Reasons for D_4σ Being the ISO Choice of Standard Diameter

1.6.3.8 Diameter Definitions: Final Note

1.6.4 Conversions between Diameter Definitions

1.6.4.1 Is M² Unique?

1.6.4.2 Emprical Basis for the Conversion Rules

1.6.4.3 Rules for Converting Diameters between Different Definitions

1.7 Practical Aspects of Beam Quality M² Measurement: The Four-Cuts Method

1.7.1 The Logic of the Four-Cuts Method

1.7.1.1 Requirement of an Auxiliary Lens to Make an Accessible Waist

1.7.1.2 Accuracy of the Location Found for the Waist

1.7.2 Graphical Analysis of the Data

1.7.3 Discussion of Curve-Fit Analysis of the Data

1.7.4 Commercial Instruments and Software Packages

1.8 Types of Beam Asymmetry

1.8.1 Common Types of Beam Asymmetry

1.8.2 The Equivalent Cylindrical Beam Concept

1.8.3 Other Beam Asymmetries: Twisted Beams, General Astigmatism

1.9 Applications of The M² Model to Laser Beam Scanners

1.9.1 A Stereolithography Scanner

1.9.2 Conversion to a Consistent Knife-Edge Currency

1.9.3 Why Use a Multimode Laser?

1.9.4 How to Read the Laser Test Report

1.9.5 Replacing the Focusing Beam Expander with an Equivalent Lens

1.9.6 Depth of Field and Spot-Size Variation at the Scanned Surface

1.9.7 Laser Specifications to Limit Spot Out-of-Roundness on the Scanned Surface

1.9.7.1 Case A: 10% Waist Asymmetry

1.9.7.2 Case B: 10% Divergence Asymmetry

1.9.7.3 Case C: 12% Out-of-Roundness across the Scanned Surface Due to Astigmatism

1.10 Conclusion: Overview of The M² Model

Acknowledgments

Glossary

References

1.1 INTRODUCTION

The M² model is currently the preferred way of quantitatively describing a laser beam, including its propagation through free space and lenses; specifically, as ratios of its parameters with respect to the simplest theoretical gaussian laser beam The present chapter describes the model and measuring techniques for reliably determining—in each of the two orthogonal propagation planes—the key spatial parameters of a laser beam; namely, the beam waist diameter 2W₀, the Rayleigh range z_R, the beam divergence Θ, and waist location z₀.

1.2 HISTORICAL DEVELOPMENT OF LASER-BEAM CHARACTERIZATION

In 1966, six years after the first laser was demonstrated, a classic review paper¹ by Kogelnik and Li of Bell Telephone Laboratories was published, which served as the standard reference on the description of laser beams for many years. Here the 1/e² diameter definition^1,2 for the width of the fundamental-mode gaussian beam was used The more complex transverse irradiance patterns, or transverse modes, of laser beams were identified with sets of eigen-function solutions to t...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Dedication
• Table of Contents
• Preface
• Preface to Laser Beam Scanning (1985)
• Preface to Optical Scanning (1991)
• Preface to Handbook of Optical and Laser Scanning (2004)
• Cover Image
• Acknowledgments
• Editors
• Contributors
• 1. Characterization of Laser Beams: The M2 Model
• 2. Optical Systems for Laser Scanners
• 3. Image Quality for Scanning and Digital Imaging Systems
• 4. Polygonal Scanners: Components, Performance, and Design
• 5. Motors and Controllers (Drivers) for High-Performance Polygonal Scanners
• 6. Bearings for Rotary Scanners
• 7. Pre-Objective Polygonal Scanning
• 8. Galvanometric and Resonant Scanners
• 9. Flexural Pivots for Oscillatory Scanners
• 10. Holographic Barcode Scanners: Applications, Performance, and Design
• 11. Acousto-Optic Scanners and Modulators
• 12. Electro-Optical Scanners
• 13. Piezo Scanning
• 14. Optical Disk Scanning Technology
• 15. CTP Scanning Systems
• 16. Synchronous Laser Line Scanners for Undersea Imaging Applications
• Index