Industrial Applications of Lasers

John F. Ready

• Publisher: Academic Press
• Year: 1997
• Print ISBN:
  9780125839617
• Edition: 2
• eBook ISBN:
  9780080508603
• Topic: Biological Sciences
• Subtopic: Zoology
• Index: Biological Sciences

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

Chapter 1

Fundamentals of Lasers

This chapter will provide fundamental information about lasers. It will describe the basic principles of laser operation and will define some of the terminology commonly encountered in laser work. The level is elementary; the chapter is intended as an introduction for those who have not worked extensively with lasers.

A. Electromagnetic Radiation

The light emitted by a laser is electromagnetic radiation. We note here that the word “light” will be used in an extended sense, including infrared and ultraviolet as well as visible light. Also, the word “radiation” refers to radiant energy and does not imply ionizing radiation.

The term “electromagnetic radiation” includes a continuous range of many different types of radiant energy. This section will describe the spectrum of electromagnetic radiation, and it will show how laser light is related to other familiar forms of radiant energy.

Electromagnetic radiation has a wave nature. The waves consist of oscillating electric and magnetic fields. The waves can be characterized by their frequency, that is, by the number of cycles of oscillation of the electric or magnetic field per unit time. The distance between the peak amplitudes of the oscillating field is called the wavelength. The wave propagates with a characteristic velocity c (“the velocity of light”) equal to 3 × 10¹⁰ cm/sec in vacuum. The physical nature of the electromagnetic radiation is the same in all portions of the electromagnetic spectrum. It has the same wave nature and the same velocity, c. It differs only in wavelength and frequency. The different regions in the electromagnetic spectrum are characterized by different values of wavelength and frequency for the oscillation of the wave.

There is a relation between the frequency f and wavelength λ valid for all types of electromagnetic radiation:

(1.1)

According to this relation, the wavelength decreases as frequency increases.

Figure 1-1 shows the electromagnetic spectrum, with several familiar regions identified, along with a wavelength and a frequency scale. Radio waves are at the low-frequency, long-wavelength end of the spectrum. As frequency increases and wavelength decreases, we pass through the microwave, the infrared, the visible, the ultraviolet, the x-ray, and the gamma ray regions. The frequency varies by a factor of 10¹⁶ or more. The boundaries between the different regions are not sharp and distinct; rather, they are defined by convention according to how the radiation interacts with materials. We emphasize that all these types of radiation are essentially the same in their nature, differing in the frequency of the oscillation of the wave motion.

Figure 1-1 The electromagnetic spectrum, with wavelength and frequency indicated for different spectral regions.

In addition to its wave characteristics, electromagnetic radiation also has a particle-like nature. In some cases, light acts as if it consisted of discrete particle-like quanta of energy, called photons. Each photon carries a discrete amount of energy. The energy E of a photon is

(1.2)

where h is Planck’s constant, equal to 6.6 × 10⁻²⁷ erg-sec. Equation (1.2) indicates that the photon energy associated with a light wave increases as the wavelength decreases.

In many of the interactions of light with matter, the quantum nature of light overshadows the wave nature. The light can interact only when the photon energy exceeds some characteristic value. In such interactions, it is difficult to reconcile conceptually the wave and particle natures of light. In some experiments, for example, those involving diffraction and interference, the wave nature will dominate. In other experiments, like those involving absorption of light by atomic and molecular systems, the photon nature will dominate. Thus, light will be absorbed between energy levels of a molecule only when the photon energy equals the energy difference between the levels.

A classic example of the photon nature of light involves the photoelectric effect, in which electrons are emitted from a surface that absorbs light. There will be a minimum photon energy required for emission of an electron. This value is called the work function Φ of the surface and is a function of the material. If the photon energy slightly exceeds this value, that is, if the wavelength is slightly shorter than hc/Φ, electrons are emitted. But if the wavelength is slightly longer than this value, no photoelectric emission occurs, even if the light is intense.

The fact that light has both a wave and a particulate character is called the dual nature of light. This phenomenon can be conceptually troublesome. For our purposes, we simply point out that light sometimes behaves like a wave and at other times like a particle.

With lasers, we are concerned with light in the ultraviolet, visible, and infrared portions of the spectrum, that is, with wavelengths in the approximate range 10⁻⁵–10⁻² cm and frequencies of the order of 10¹³–10¹⁵ Hz. The wavelength of light is usually expressed in units of micrometers (μm) or nanometers (nm). The micrometer, equal to 10⁻⁴ cm, is sometimes called a micron, especially in older literature. The angstrom (Å), a unit equal to 10⁻⁸ cm, is also sometimes encountered. The wavelength of green light may be given as 0.55 μm = 550 nm = 5.5 × 10⁻⁵ cm = 5500 Å.

The complete range of wavelengths covered by operating lasers runs approximately from 0.01 to 1000 μm, but at the far ends of this range, the existing devices are experimental laboratory systems. The region in which useful devices for industrial applications operate is about 0.2 to 10 μm. This region is shown in Figure 1-2, which shows an expanded view of part of the electromagnetic spectrum. The wavelengths of several popular lasers are noted. The wavelength of a given laser is sharply defined; the spread in wavelength for a particular laser covers a very small fraction of the wavelength range shown in the figure.

Figure 1-2 Expanded portion of the electromagnetic spectrum, showing the wavelengths at which several important lasers operate.

Lasers can be fabricated using a variety of different materials as the activ...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Dedication
• Preface
• Acknowledgments
• Historical Prologue
• Chapter 1: Fundamentals of Lasers
• Chapter 2: Properties of Laser Light
• Chapter 3: Practical Lasers
• Chapter 4: Trends in Laser Development
• Chapter 5: Laser Components and Accessories
• Chapter 6: Care and Maintenance of Lasers
• Chapter 7: Laser Safety
• Chapter 8: Alignment, Tooling, and Angle Tracking
• Chapter 9: Principles Used in Measurement
• Chapter 10: Distance Measurement and Dimensional Control
• Chapter 11: Laser Instrumentation and Measurement
• Chapter 12: Interaction of High-Power Laser Radiation with Materials
• Chapter 13: Laser Applications in Material Processing
• Chapter 14: Applications of Laser Welding
• Chapter 15: Applications for Surface Treatment
• Chapter 16: Applications for Material Removal: Drilling, Cutting, Marking
• Chapter 17: Lasers in Electronic Fabrication
• Chapter 18: Principles of Holography
• Chapter 19: Applications of Holography
• Chapter 20: Laser Applications in Spectroscopy
• Chapter 21: Chemical Applications
• Chapter 22: Fiber Optics
• Chapter 23: Integrated Optics
• Chapter 24: Information-Related Applications of Lasers
• A Look at the Future
• INDEX