Crystal Clear

One of the toughest challenges facing faculty in physics and engineering departments today is how best to educate students who seek a breadth of information in the field of solid-state lasers.

Several renowned texts address strictly the engineering principles of lasers, or the theoretical and experimental aspects of photophysical processes, but few tutorial texts have been specifically directed toward advanced undergraduate- or graduate-level courses encompassing many of the complexities required to understand, design, and advance both the physics and engineering of solid-state lasers.

Based strongly upon his well-received short courses offered throughout the past decade at the SPIE Photonics West and Photonics Europe symposia, The Physics and Engineering of Solid State Lasers (SPIE Press 2006) by Yehoshua Kalisky, of the Chemistry Division of the Negev Nuclear Research Center in Israel, presents an overview of many of the greatest breakthroughs in solid-state lasers during the past two decades.

Kalisky's text starts with a historical overview of the evolution of solid-state laser materials and associated technology, and moves into the basic elements of laser resonators. While this is typical for most books addressing solid-state lasers, it is here within the first three chapters that Kalisky provides readers with an integration of principles and technologies for which most readers have previously had to rely upon multiple treatises for similar information.

He very succinctly addresses a multitude of topics that are necessary for those entering the field of solid-state lasers who desire a more complete understanding of the complexities required to design not only the laser resonator but also the materials and transitions required for specific applications.

"My biggest challenge was to integrate several key processes developed independently in other texts so that the desired audience of students in both the sciences and engineering fields could see the relationships between photochemistry, nonradiative processes, energy transfer, and laser physics. The goal was to bring photophysical processes to the forefront, as some previous texts have taken these for granted," explains Kalisky.

Why should the interrelationship of these areas be so critical to the modern laser engineer? Kalisky stresses from his experience that "it is quite important for laser engineers to have a foundation to be able to predict performance capabilities of new laser materials based upon an understanding of the thermal properties and overall efficiencies observed in similar hosts and with previously characterized transitions."

This breadth in the evaluation of complex laser materials is examined in a very understandable manner throughout Chapter 8: Lasing Efficiency and Sensitization. Here, Kalisky uses as a working example chromium-sensitized garnets that incorporate thulium and holmium ions as the activation pair to emit in the 2-µm region of the infrared.

He very skillfully examines energy transfer, thermal effects, concentration-dependant effects, and the laser performance impact of host and sensitizer/activator ion selection, which will assist in providing the novice laser engineer with a comprehendible overview of these complexities that define whether a laser material will have the capability of being both efficient and feasible.

The review of the evolution of the ytterbium lasers illustrates the materials development path to reach acceptance and maturity in the field. As with many solid-state lasers, a 10- to 15-year full maturity cycle can be clearly seen through the research outlined in this chapter. After examining the optical properties and thermal considerations of these ytterbium-doped lasers, Kalisky summarizes the various excitation techniques, such as the thin-disk laser concept, face-pumping, and various waveguide designs.

When asked about such revolutionary technologies witnessed during this past decade, Kalisky remarked that he believes the three leading technologies are "the demonstration of multi-kilowatt lasers based upon ytterbium, thin-disk technology, the evolution of high-power fiber lasers based upon breakthroughs in glass and diode technologies, and finally, the exploitation of polycrystalline materials currently under investigation for ultrafast and high-energy laser platforms."

Kalisky went on to expound that "by applying the energy gap laws, an understanding of phonon interactions, and the various photophysical laws examined in the text, one is able to apply this understanding to other growing fields such as high-power fiber lasers and materials engineering, such as with the rare-earth activated orthovanadates."

Another strength of The Physics and Engineering of Solid State Lasers is that it provides not only a strong selection of seminal references, but it also provides readers with extensive tables that highlight and compare the pertinent physical and optical properties of a variety of mature and new solid-state laser material. Many of the engineers and scientists utilizing this text will find these tabulations invaluable resources as they attempt to model and design future laser systems.

In fact, these parameters evolve directly from the source of the strength of this tutorial: the integration of both the theoretical and practical engineering aspects of solid-state lasers based upon photophysical processes.