- Email: [email protected]
The physics of laser fusion
ferometry through single-mode optical fibres. Applications include such varied topics as a study of the vibration of tympanic membranes of various mammals to a sophisticated differential interferometer with a claimed height sensitivity of 0.001 A used to study Stoneley waves and the use of a modified Michelson interferometer to measure the movement of timber roof trusses under load. To summarize, a session that is a veritable pot-pourri with something of interest for most readers and likewise a book of considerable interest to all practising interferometrists. K. L. Birch
In my opinion this volume is of a very high standard and matches that set by the first two volumes. Although expensive it is good value for money compared to many other books and will form a valuable reference work in the library of any institution in which laser work is being carried out. 1 hope that Volume IV will appear before 1988! A. F. Purdie
The physics of laser fusion H. Motz
Laser handbook
Academic,
Edited
The inertial confinement approach to nuclear fusion based on the laser compression technique has reached a critical stage in its development. With the pulse energy now believed to be necessary for break-even about 100 times the 1 kJ thought sufficient in the optimistic days of 1972, other drivers, in particular heavy-ion beams, are becoming highly competitive alternatives. It is with such a background that this book, one of the first dealing with the basic physics of laser initiated fusion, introduces the novice to this developing field.
by M. L. Stitch
Volume III, North Holland, 1979, pp IX + 878, $ 122 The Laser Handbook is intended as an authoritative and centralized source of information covering the entire laser field. It consists of a series of review articles intended for workers in related fields and advanced students. The first two volumes appeared in 1972 and covered fairly basic theory, classes of laser and application. This one deals with more specialized and recently developed lasers and applications. The laser technology section has six articles on unstable resonators; waveguide gas lasers; high power, efficient, electrically excited CO lasers; excimer lasers; chemical and gasdynamic lasers; and pulsed dye lasers. The articles vary in length from 38 to 90 pages with an average of around 60 pages. The laser applications sections also has siz articles on bandwidth limited ultrashort pulse generation; high average power efficient second harmonic generation; laser induced chemical reactions and isotope separation; pulsed holographyc; advanced lasers for fusion; and continuous picosecond spectroscopy of dyes. These articles vary from 50 to 120 pages with an average of around 80 pages. There are subject and author indexes at the end of the book. The length variation of each chapter reflects the complexity of the subject rather than different levels of coverage. I had the feeling while reading this book (unlike some others) that each author felt free to develop a logical review of his subject from early work right through to the most recent developments. Thus each chapter is easy to follow and leaves one well able to tackle the literature. The choice of subject matter is good, on the whole. Some gaps mentioned in the Optics and Laser Technology review of the first two volumes are well plugged. Some readers may feel that the space devoted to advanced fusion lasers (120 pages) is excessive in view of the limited number of people building Shiva Nova’s in their garden sheds, but there is much interesting background information. The overall standard of production is high with clear diagrams and type. The aims of the handbook are ambitious. Comprehensive coverage of a large, still expanding field can lead to the ‘Forth Bridge effect’; by the time it has all been written down it is necessary to start over again updating the material. Considering the length of this book it is remarkably up to date; the latest reference cited at the end of each chapter were published in 1978 and the dye laser review has a random list of extra references up to 1979 added in proof.
276
1979, pp. ix + 290,&19.40
It does, in general, a good job of describing the various complex and some quite subtle processes that are (possibly) contributing to the attempts at igniting a thermonuclear burn by laser irradiation. Some of these mechanism are equally relevant to the alternative, non-laser, pellet compression approaches: For example, the physics of fusion and power generation covered in the first two chapters; shocks, implosions and their stability described in chapters 9 and 10 and the basic plasma physics of chapters 4 and 11. In between these the remainder of the book concentrates mainly on the laser-plasma interaction specifically. The general emphasis is on the theory of the various phenomena with the experimental aspects limited to two short chapters on the laser systems and the results of laser compression experiments. This is probably a correct choice, by the author judging by the somewhat misleading remarks about glass-laser amplifier rods of ‘up to 20 cm’ and saturable dyes to ‘define’ the oscillator power. The author’s background is also apparent in the emphatically British, or more specifically Oxfordshire, view of the subject. In this respect the book does not give a wholly balanced view of international work on laser initiated fusion. This, however, is not such a bad attribute as organizations, such as the Lawrence Livermore Laboratory in the States, are quite capable of publicising their own work with considerable vigour ! One important function of a book of this sort is that it should explain and expand on the jargon commonly used by the experts so that the newcomer can appreciate the fundamental basis of the subject and thus understand its associated problems. To test this the reviewer looked up a few topics in the index. There are two main classes of pellet compression: The ablative mode and the exploding pusher mode. The former is not indexed while the latter is, though only referring one to the many experiments using this mode with no explamation of the mechanism. However, buried in the chapter 8 on energy transport there is a brief discussion of these two approaches and their relative merits. Further, isentropic
OPTICS
AND
LASER
TECHNOLOGY.
OCTOBER
1980
compression, the ideal form of the ablative mode, is dealt with in excellent detail and clearly indexed. Concepts such as ‘hot electrons’, ‘filamentation’ and ‘wave-breaking’ are all explained clearly and properly indexed. On the topic of light absorption, however, there is again the possibility of leaving the novice confused. For example, the term ‘resonance absorption’ is used a number of times throughout the book but in chapter 7, where it is actually described, the mechanism is not named. Further, this important absorption process does not appear in the index. ‘Parametric absorption’ is mentioned, somewhat surprisingly, in the section of (linear) inverse Bremsstrahlung absorption and not under parametric processes or non-linear absorption. Again, it is not indexed. Other similar inconsistencies lead one to conclude that the book, in isolation, is not the ideal basic introduction to the field. On the other hand for researchers with some familiarity already with the subject, or newcomers with experienced colleagues available for further discussion, it does indeed cover the many ‘branches of physics relevant to laser fusion’ and ‘draws the various strands together’. Indeed for such a reader the book does an excellent job of reviewing the important processes and their theories, giving a fresh insight into the subject. It also gives a very useful introduction to the papers published on each topic which themselves will refer the investigator to the large quantity of other relevant literature. In conclusion, despite the various criticisms made - and the many printing and proof-reading errors (where is the first Fig. 16 of chapter 13?) - the book remains a valuable addition to the material published on this subject. It is recommended for anyone working in the general field of laserplasma interactions in addition to those more specifically studying the application of lasers to inertial-confinement fusion. A.C. Walker Free electron generators of coherent radiation Edited by S. F. Jacobs, H.S. Pilloff, 4.4.Sargent, M.O. Scully and R. Spitzer Physics of quantum electronics, volume 7, AddisonWesley Publishing Company, 1980, pp. xix t 813, $36.50 The goal is immense - the production of very high power radiation, tunable from the millimeter to the x-ray region. The problems are commensurate but hopes are high! A whole new discipline of research is beginning to take shape formed by forward looking researchers drawn from various fields and who approach the problem from different perspectives. The book contains the proceedings of the second workshop on free electron generators of coherent radiation held at Telluride, Colorado from 13 - 17th August, 1979. It is essentially an updating of the first workshop two years previously but concentrating on free electron lasers themselves, with particular emphasis on those aspects relating to operation in the optical region and on the consideration of novel concepts. The present volume is divided into four sections; tutorial, general interest, variable wigglers and research interests. Thankfully, for those like me, with a passing interest but no great expertise in the field, the tutorial section succeeds, as
OPTICS AND LASER TECHNOLOGY.
OCTOBER
1980
its name implies, to get across many of the principles and illustrates the field from various perspectives, while only being partially successful in not getting too bogged down with mathematics. For those who require to grasp a simple explanation of how such systems operate, the first free electron laser at Stanford University in 1977 generated radiation by the passage of electrons through a spatially varying magnetic field which causes the electron beam to “wiggle” and hence radiate. The large Doppler upshift due to relativistic electron velocities can be adjusted and this results in emission at tunable optical frequencies. Generally, the understanding of free electron generators concerns the interaction of three components on the dynamical system; electromagnetic wave, electron beam and some natural or artificially created medium. It draws heavily on such areas as plasma physics, accelerator physics and technology, and optical physics. One of the main problems encountered in the book is the seemingly inevitable use of different languages by workers from these diverse fields to describe the same phenomena. The book contains 32 articles from 58 contributors and while no attempt is made here to review them in detail or invidiously select one or two for particular attention, an indication of the fields covered is given. Individuals are left to get hold of the book and use it as suggested by the editors in their preface as a ‘source book and as a road map to future research literature’. The tutorial section reviews the fundamentals of the electronphoton interaction via energy and momentum requirements plus a laser physics analysis of free electron devices. A good discussion on Cerenkov and Cerenkov-Raman radiation sources is given. The general interest section begins with two papers on the interaction of electrons at superluminal velocities and its implications for ‘stimulated electromagnetic shock radiation’ concepts, a coherent pulse treatment of the fel from the pendulum picture, and various problems associated with the storage ring and numerical simulation of the fel in singleparticle and collective regimes. Electron pre-bunching and klystron-like enhancement of the radiation gain in twoelement fel’s are discussed. In part three, the variable wiggler concept is described and several different approaches to the problem are presented. Finally, in part four, a broad range of research contributions is put forward, from far infra-red to possible x-ray production via fel devices. Of special interest is the possibility of controlling the spread of electron velocities via the transverse gradient in the magnetic wiggler field. It is evident that the field of free electron lasers is not one an individual department can take up, except in a peripheral sense, without considerable resources. This subject will probably remain one requiring large central shared facilities. The sort of experiments that can be done were summarized by Szoke, Weil and Prosnitz. Using either RF linac, electron storage ring, electrostatic generator or induction linac, one can demonstrate trapping and deceleration of electrons, bunching of electrons, gain of signal field, energy extraction, etc. Free electron lasers are design tunable and will probably find most importance in the vuv and soft x-ray region and the far infra-red, with competition from existing or newly developed simpler systems in the visible and near infrared proving to be too strong for normal applications.
277
In my opinion this volume is of a very high standard and matches that set by the first two volumes. Although expensive it is good value for money compared to many other books and will form a valuable reference work in the library of any institution in which laser work is being carried out. 1 hope that Volume IV will appear before 1988! A. F. Purdie
The physics of laser fusion H. Motz
Laser handbook
Academic,
Edited
The inertial confinement approach to nuclear fusion based on the laser compression technique has reached a critical stage in its development. With the pulse energy now believed to be necessary for break-even about 100 times the 1 kJ thought sufficient in the optimistic days of 1972, other drivers, in particular heavy-ion beams, are becoming highly competitive alternatives. It is with such a background that this book, one of the first dealing with the basic physics of laser initiated fusion, introduces the novice to this developing field.
by M. L. Stitch
Volume III, North Holland, 1979, pp IX + 878, $ 122 The Laser Handbook is intended as an authoritative and centralized source of information covering the entire laser field. It consists of a series of review articles intended for workers in related fields and advanced students. The first two volumes appeared in 1972 and covered fairly basic theory, classes of laser and application. This one deals with more specialized and recently developed lasers and applications. The laser technology section has six articles on unstable resonators; waveguide gas lasers; high power, efficient, electrically excited CO lasers; excimer lasers; chemical and gasdynamic lasers; and pulsed dye lasers. The articles vary in length from 38 to 90 pages with an average of around 60 pages. The laser applications sections also has siz articles on bandwidth limited ultrashort pulse generation; high average power efficient second harmonic generation; laser induced chemical reactions and isotope separation; pulsed holographyc; advanced lasers for fusion; and continuous picosecond spectroscopy of dyes. These articles vary from 50 to 120 pages with an average of around 80 pages. There are subject and author indexes at the end of the book. The length variation of each chapter reflects the complexity of the subject rather than different levels of coverage. I had the feeling while reading this book (unlike some others) that each author felt free to develop a logical review of his subject from early work right through to the most recent developments. Thus each chapter is easy to follow and leaves one well able to tackle the literature. The choice of subject matter is good, on the whole. Some gaps mentioned in the Optics and Laser Technology review of the first two volumes are well plugged. Some readers may feel that the space devoted to advanced fusion lasers (120 pages) is excessive in view of the limited number of people building Shiva Nova’s in their garden sheds, but there is much interesting background information. The overall standard of production is high with clear diagrams and type. The aims of the handbook are ambitious. Comprehensive coverage of a large, still expanding field can lead to the ‘Forth Bridge effect’; by the time it has all been written down it is necessary to start over again updating the material. Considering the length of this book it is remarkably up to date; the latest reference cited at the end of each chapter were published in 1978 and the dye laser review has a random list of extra references up to 1979 added in proof.
276
1979, pp. ix + 290,&19.40
It does, in general, a good job of describing the various complex and some quite subtle processes that are (possibly) contributing to the attempts at igniting a thermonuclear burn by laser irradiation. Some of these mechanism are equally relevant to the alternative, non-laser, pellet compression approaches: For example, the physics of fusion and power generation covered in the first two chapters; shocks, implosions and their stability described in chapters 9 and 10 and the basic plasma physics of chapters 4 and 11. In between these the remainder of the book concentrates mainly on the laser-plasma interaction specifically. The general emphasis is on the theory of the various phenomena with the experimental aspects limited to two short chapters on the laser systems and the results of laser compression experiments. This is probably a correct choice, by the author judging by the somewhat misleading remarks about glass-laser amplifier rods of ‘up to 20 cm’ and saturable dyes to ‘define’ the oscillator power. The author’s background is also apparent in the emphatically British, or more specifically Oxfordshire, view of the subject. In this respect the book does not give a wholly balanced view of international work on laser initiated fusion. This, however, is not such a bad attribute as organizations, such as the Lawrence Livermore Laboratory in the States, are quite capable of publicising their own work with considerable vigour ! One important function of a book of this sort is that it should explain and expand on the jargon commonly used by the experts so that the newcomer can appreciate the fundamental basis of the subject and thus understand its associated problems. To test this the reviewer looked up a few topics in the index. There are two main classes of pellet compression: The ablative mode and the exploding pusher mode. The former is not indexed while the latter is, though only referring one to the many experiments using this mode with no explamation of the mechanism. However, buried in the chapter 8 on energy transport there is a brief discussion of these two approaches and their relative merits. Further, isentropic
OPTICS
AND
LASER
TECHNOLOGY.
OCTOBER
1980
compression, the ideal form of the ablative mode, is dealt with in excellent detail and clearly indexed. Concepts such as ‘hot electrons’, ‘filamentation’ and ‘wave-breaking’ are all explained clearly and properly indexed. On the topic of light absorption, however, there is again the possibility of leaving the novice confused. For example, the term ‘resonance absorption’ is used a number of times throughout the book but in chapter 7, where it is actually described, the mechanism is not named. Further, this important absorption process does not appear in the index. ‘Parametric absorption’ is mentioned, somewhat surprisingly, in the section of (linear) inverse Bremsstrahlung absorption and not under parametric processes or non-linear absorption. Again, it is not indexed. Other similar inconsistencies lead one to conclude that the book, in isolation, is not the ideal basic introduction to the field. On the other hand for researchers with some familiarity already with the subject, or newcomers with experienced colleagues available for further discussion, it does indeed cover the many ‘branches of physics relevant to laser fusion’ and ‘draws the various strands together’. Indeed for such a reader the book does an excellent job of reviewing the important processes and their theories, giving a fresh insight into the subject. It also gives a very useful introduction to the papers published on each topic which themselves will refer the investigator to the large quantity of other relevant literature. In conclusion, despite the various criticisms made - and the many printing and proof-reading errors (where is the first Fig. 16 of chapter 13?) - the book remains a valuable addition to the material published on this subject. It is recommended for anyone working in the general field of laserplasma interactions in addition to those more specifically studying the application of lasers to inertial-confinement fusion. A.C. Walker Free electron generators of coherent radiation Edited by S. F. Jacobs, H.S. Pilloff, 4.4.Sargent, M.O. Scully and R. Spitzer Physics of quantum electronics, volume 7, AddisonWesley Publishing Company, 1980, pp. xix t 813, $36.50 The goal is immense - the production of very high power radiation, tunable from the millimeter to the x-ray region. The problems are commensurate but hopes are high! A whole new discipline of research is beginning to take shape formed by forward looking researchers drawn from various fields and who approach the problem from different perspectives. The book contains the proceedings of the second workshop on free electron generators of coherent radiation held at Telluride, Colorado from 13 - 17th August, 1979. It is essentially an updating of the first workshop two years previously but concentrating on free electron lasers themselves, with particular emphasis on those aspects relating to operation in the optical region and on the consideration of novel concepts. The present volume is divided into four sections; tutorial, general interest, variable wigglers and research interests. Thankfully, for those like me, with a passing interest but no great expertise in the field, the tutorial section succeeds, as
OPTICS AND LASER TECHNOLOGY.
OCTOBER
1980
its name implies, to get across many of the principles and illustrates the field from various perspectives, while only being partially successful in not getting too bogged down with mathematics. For those who require to grasp a simple explanation of how such systems operate, the first free electron laser at Stanford University in 1977 generated radiation by the passage of electrons through a spatially varying magnetic field which causes the electron beam to “wiggle” and hence radiate. The large Doppler upshift due to relativistic electron velocities can be adjusted and this results in emission at tunable optical frequencies. Generally, the understanding of free electron generators concerns the interaction of three components on the dynamical system; electromagnetic wave, electron beam and some natural or artificially created medium. It draws heavily on such areas as plasma physics, accelerator physics and technology, and optical physics. One of the main problems encountered in the book is the seemingly inevitable use of different languages by workers from these diverse fields to describe the same phenomena. The book contains 32 articles from 58 contributors and while no attempt is made here to review them in detail or invidiously select one or two for particular attention, an indication of the fields covered is given. Individuals are left to get hold of the book and use it as suggested by the editors in their preface as a ‘source book and as a road map to future research literature’. The tutorial section reviews the fundamentals of the electronphoton interaction via energy and momentum requirements plus a laser physics analysis of free electron devices. A good discussion on Cerenkov and Cerenkov-Raman radiation sources is given. The general interest section begins with two papers on the interaction of electrons at superluminal velocities and its implications for ‘stimulated electromagnetic shock radiation’ concepts, a coherent pulse treatment of the fel from the pendulum picture, and various problems associated with the storage ring and numerical simulation of the fel in singleparticle and collective regimes. Electron pre-bunching and klystron-like enhancement of the radiation gain in twoelement fel’s are discussed. In part three, the variable wiggler concept is described and several different approaches to the problem are presented. Finally, in part four, a broad range of research contributions is put forward, from far infra-red to possible x-ray production via fel devices. Of special interest is the possibility of controlling the spread of electron velocities via the transverse gradient in the magnetic wiggler field. It is evident that the field of free electron lasers is not one an individual department can take up, except in a peripheral sense, without considerable resources. This subject will probably remain one requiring large central shared facilities. The sort of experiments that can be done were summarized by Szoke, Weil and Prosnitz. Using either RF linac, electron storage ring, electrostatic generator or induction linac, one can demonstrate trapping and deceleration of electrons, bunching of electrons, gain of signal field, energy extraction, etc. Free electron lasers are design tunable and will probably find most importance in the vuv and soft x-ray region and the far infra-red, with competition from existing or newly developed simpler systems in the visible and near infrared proving to be too strong for normal applications.
277