Lasers continue to be an amazingly robust field of activity, one of continually expanding scientific and technological frontiers. Thus today we have lasing without inversion, quantum cascade lasers, lasing in strongly scattering media, lasing in biomaterials, lasing in photonic crystals, a single atom laser, speculation about black hole lasers, femtosecond-duration laser pulses only a few cycles long, lasers with subhertz linewidths, semiconductor lasers with predicted operating lifetimes of more than 100 years, peak powers in the petawatt regime and planned megajoule pulse lasers, sizes ranging from semiconductor lasers with dimensions of a few microns diameter and a few hundred atoms thick to huge glass lasers with hundreds of beams for inertial confinement fusion research, lasers costing from less than one dollar to more than one billion dollars, and a multibillion dollar per year market.
In addition, the nearly ubiquitous presence of lasers in our daily lives attests to the prolific growth of their utilization. The laser is at the heart of the revolution that is marrying photonic and electronic devices. In the past four decades, the laser has become an invaluable tool for mankind encompassing such diverse applications as science, engineering, communications, manufacturing and materials processing, medical therapeutics, entertainment and displays, data storage and processing, environmental sensing, military, energy, and metrology. It is difficult to imagine state-of-the-art research in physics, chemistry, biology, and medicine without the use of radiation from various laser systems.
Laser action occurs in all states of matter—solids, liquids, gases, and plasmas. Within each category of lasing medium there may be differences in the nature of the active lasing ion or center, the composition of the medium, and the excitation and operating techniques. For some lasers, the periodic table has been extensively explored and exploited; for others—solid-state lasers in particular—the compositional regime of hosts continues to expand. In the case of semiconductor lasers the ability to grow special structures one atomic layer at a time by liquid phase epitaxy, molecular beam epitaxy, and metal-organic chemical vapor deposition has led to numerous new structures and operating configurations, such as quantum wells and superlattices, and to a proliferation of new lasing wavelengths. Quantum cascade lasers are examples of laser materials by design.
The number and type of lasers and their wavelength coverage continue to expand. Anyone seeking a photon source is now confronted with an enormous number of possible lasers and laser wavelengths. The spectral output ranges of solid, liquid, and gas lasers are shown in Figure 1 and extend from the soft x-ray and extreme ultraviolet regions to millimeter wavelengths, thus overlapping masers. By using various frequency conversion techniques—harmonic generation, parametric oscillation, sum- and difference-frequency mixing, and Raman shifting—the wavelength of a given laser can be extended to longer and shorter wavelengths, thus enlarging its spectral coverage.
This volume seeks to provide a comprehensive, up-to-date compilation of lasers, their properties, and original references in a readily accessible form for laser scientists and engineers and for those contemplating the use of lasers. The compilation also indicates the state of knowledge and development in the field, provides a rapid means of obtaining reference data, is a pathway to the literature, contains data useful for comparison with predictions and/or to develop models of processes, and may reveal fundamental inconsistencies or conflicts in the data. It serves an archival function and as an indicator of newly emerging trends.