This book provides a comprehensive overview of the important technologies for photon detection from the millimeter-wave through the ultraviolet spectral regions. The reader should gain a good understanding of the similarities and contrasts, the strengths and weaknesses of the multitude of approaches that have been developed over a century of effort to improve our ability to sense photons. The emphasis is always upon the methods of operation and physical limits to detector performance. Brief mention is sometimes made of the currently achieved performance levels, but only to place the broader physical principles in a practical context.

Writing is a process of successive approximations toward poorly defined goals. A second edition not only brings a book up to date, it also allows reconsideration of the goals and permits a new series of approximations toward them. Specific goals for this edition are to:

• Provide a bridge from general physics into the methods used for photon detection;

• Guide readers into more detailed and technical treatments of individual topics;

• Give a broad overview of the subject;

• Make the book accessible to the widest possible audience.

Based on the extensive survey of the literature that accompanied preparation of this edition, these goals have led to a unique book.