Laser Cooling and Trapping Harold J. Metcalf and Peter van der Straten Springer-Verlag, New York, 1999. $69.95, $29.95 paper (323 pp.). ISBN 0-387-98747-9, ISBN 0-387-98728-2 paper
For the past 15 years, the rapid rate at which laser-cooling and atom-trapping techniques were being invented and applied to new problems scared off most would-be textbook writers. The thought was that the field should settle down a bit before a textbook could present it in a proper perspective. As a result, the introduction to cooling and trapping to date has been left to special issues of journals, review articles, conference texts, isolated book chapters, and a few PhD theses.
The spawning of the new field of Bose–Einstein condensation of atomic gases, the awarding of the 1997 Nobel Prize in Physics for laser cooling, and the advent of extensive applications, including the incorporation of laser cooling into the fundamental time standard, and plans to put cold, trapped atoms into space, have all contributed to a changed perspective. The field is established; why isn’t there a textbook?
There has certainly been a need: Students entering the field must first understand a core of specialized atomic theory. Then they are faced with the impressive number of ways the theory has been applied to achieve mechanical control over atoms. For instance, the widely known Doppler cooling technique is but one of roughly a dozen distinct laser cooling mechanisms that have been demonstrated. Similarly, there are more than a score of variants on magnetic, optical, and electric field atom traps and a comparable number of atom optical elements. It is a lot to pick out of primary sources without a guide. Hal Metcalf and Peter van der Straten’s Laser Cooling and Trapping provides the guide.
Laser Cooling and Trapping is divided into three parts. The first part is an introduction that summarizes general physics relevant to cooling and trapping. It presents the background topics a student must understand to read the cooling and trapping literature. I find it remarkable that, besides being thorough, it contains essentially no extraneous topics. Despite what must have been a strong temptation to give a little more background here and there, the introduction is consistently on message. Most of its space is used to discuss two-level atoms, optical Bloch equations, and light–atom interactions. The brief discussion of atomic structure is just what you need to know for most laser cooling. The miniprimer on thermodynamics hits only those concepts that tend to crop up in cooling and trapping, such as random walks, the Fokker–Planck equation, and Liouville’s theorem. In all, the material in this introduction would typically be gleaned from at least four different texts. It’s nice to have it all in one place. Although the discussions in the book are self-contained, students will often need to supplement them with more specialized texts. I think that a chapter-by-chapter annotated bibliography would significantly help students to use the extensive array of references.
The next two parts discuss cooling and trapping and their applications. This array of experiments and technologies is special, in that most of the physical phenomena are exactly calculable. Everything comes down to electromagnetic fields interacting with atoms, or atoms interacting with each other at low energy. Experimental situations may get complicated, but the complete Hamiltonians are known, and the equations of motion can usually be solved.
The book provides the framework for understanding this aspect of laser cooling, but does not dwell on it. Instead, the authors usually opt for simple models and pictorial explanations. Much of the time, cold atoms are batted around by fields as if they were little balls, or they are ideal wavefunctions navigating textbook potentials. And it was the right approach for the authors to take. This flavor of explanation is common in the field, allowing the introduction of a huge range of techniques and applications. Most important: Students should find this approach to physics compelling.
I would be somewhat uneasy if Laser Cooling and Trapping, despite its protestations to the contrary, comes to be viewed as a definitive, archival review of past work. It may take on this cast because it does cover so much ground, but the book is not complete; it leaves out some relevant work of comparable importance. Further, the explicit mention of names of scientists and institutions in the text is rather erratic. But for its intended use, which is to guide newcomers into the field of laser cooling and trapping, the book does a superb job. It is organized so as to facilitate updates and additions, and even now, developments since the text was written could probably extend the book by half. Accordingly, I look forward to the second edition. This book is well placed to evolve with the field for many years to come.
