Topics in applied physics: Volume 1 — dye lasers

energy lepton pair processes. In session 3 Gamo and Chuang present some detailed and interesting measurements of the super-radiance from xenon at 3.5 pm, which show significant non-Gaussian effects. Session 4 includes a summary by Gilmore of coherent state situations in physics. Also, the unifying concept of a coherent state as the result of a particular operation, within a Lie Algebra defined by the Hamiltonian, on the ground state is demonstrated. The same approach is used by this author, Courtens, and Thomas to arrive at ‘atomic coherent states’ for the ensemble of N two-level atoms. The value of these further steps forward in the theory of coherence seems mainly aesthetic at the moment, but this is no condemnation of such work. In session 5 there are substantial contributions from Birman on the theory of resonant light scattering processes in solids, and by Lax and Nelson on light scattering in anisotropic media. In session 8 there are articles by Pate1 on the spin-flip Raman laser, which he has pioneered, and by Hencher and Snavely on dye lasers, in which field they are equally expert. The final session on quantum noise includes an interesting article by Graham on fluctuations far from equilibrium. In this, a new entropy variable is postulated. There are also in this session two thoughtful papers by Rousseau and Benard on different types of incoherent source. It would be invidious to dwell too much on papers at the other end of the spectrum but, unfortunately, there is no lack of them. It seems to be a current sickness of optics to attract more than its fair share of amateur theorists. Even Clauser, who one feels from his previous work may not disbelieve the quantum theory, puts forward in a postdeadline paper the most complete nonsense regarding the localization of photons. He states that ‘the most conspicuous difference between particles and waves is that only particles may be localized.’ The entire literature of quantum field theory, in which it is shown that particles of spin one and zero mass cannot be localized, has clearly passed him by. Some of the experimental papers also raise similar awkward questions. I will diffidently mention here the one by Davis and Mandel in session 2 on the time delay statistics of photoelectric emissions. This exact experiment was done, shamefacedly, one dark afternoon many years ago in the corner of my own laboratory when no-one of importance was looking. With relief, the expected result was obtained. I do remember someone mentioning that perhaps the American Journal of Physics might have been interested! Surely only in the atmosphere engendered in session 2 of this conference could such an experiment be taken seriously in the present era. Another experimental paper, this time from session 6, entitled ‘two-photon time distributions in mixed light beams’ turns out not to be about non-linear optics at all. Instead it is only another heterodyne correlation experiment with apparently no knowledge whatsoever of the very precise theories and experimental verifications which have existed in the literature for some years. In a third experimental paper we have yet more photon statistics of a laser at threshold. These were obtained using a six-stop home-made timing device of a type devised by White at Harwell in the mid-sixties. It was abandoned in this reviewer’s laboratory some six years ago. All this makes me wonder whether more conference organizers should adopt the attitude of our own Institute of Physics and not, in the main, go in for publication of Conference

OPTICS AND LASER TECHNOLOGY.

OCTOBER 1974

Proceedings? The worthy science presented at our conferences wilI certainly find its way into the regular scientific literature. In so doing it will be selected and refereed much more carefully than is obviously the case for these proceedings. Although there is a good deal of interesting material in this volume, my general impression is that I am grateful another six years will elapse before the next meeting. E. R Pike

Topics in applied physics: Volume

1 - dye lasers

Edited by F. P. Schafer Springer-Verlag,

1973, pp 285, $26.70

In his introduction to this new series H. K. V. Lotsch points out that recent progress in pure and applied research has produced vast quantities of results. There can be few areas where this is more true than in research with dye lasers. It is thus fitting that the first volume should cover just this subject, The five chapters of the book are more or less self contained review articles covering the principles of dye laser operation (Schafer), cw dye lasers (Snavely) modelocked dye lasers (Shank and Ippen), structure and properties of laser dyes (Drexhage), and dye laser applications (Hansch). Of particular interest is the chapter by Drexhag which describes clearly and in a fascinating way some of the least well reported aspects of laser dye chemistry and dye engineering. This was, for me, by far the most interesting section of the book and I would have liked it to have been longer. A rather surprising omission is a discussion of the chemistry of triplet quenching. It would be almost impossible to find any omissions in Hansch’s chapter on dye laser applications, quite a few of which the author was responsible for initiating. From nonlinear spectroscopy to biology the dye laser is presenting research workers with an invaluable aid, and this chapter reflects the enthusiasm felt in a developing field. One of the advantages of the book’s rapid publication schedule is that it has the flavour, and anticipation of the future, of a research review rather than a textbook. It can be read, however, as a textbook since the introductory chapters include many of the theoretical and experimental details presently available. It is a pity that the jet’stream cw dye laser, now used a great deal, appeared too late to warrant much discussion. There are small errors to be found but nothing of substance. The transfer from a notation in which S, + S1 indicates absorption and S1 + S, indicates emission, as iri Chapter 1, to one in which S, + S, indicates absorption and S, 6 S1 indicates emission, as in Chapter 2, I found annoying. This was probably simply a personal problem which anyone, if they felt similarly, could resolve with a few strokes of the pen. It in no real sense detracts from the overall excellent quality of the book. I have no hesitation in recommending this book to anyone who may be in the field, or just entering it. I would even say that it could make fascinating reading for someone who was not especially interested in dye lasers at all. M J. Colles

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