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Atomic gas laser transition data: a critical evaluation
BOOKS Optical and infra-red detectors Edited by R.J. Keys Springer-Verlag,
1980, pp 325 t xi, $26.50
Almost all of this book is about infra-red detectors, but ‘optical’ has been included in the title to cover the chapter on photoemissive detectors (photomultipliers) which cover the visible and uv part of the spectrum and only the very near infra-red. Each chapter is written by a recognized authority, and the editor has contributed a short introduction as well as Chapter 8, on recent developments. This last chapter has been added to the first edition published in 1977. It is not a book on technology. Nowhere is there a picture or a diagram showing what form the detectors finally take and little on how they are used. Methods of obtaining the low temperatures necessary for the operation of many infra-red detectors are not discussed. The book is published as volume 19 of Springer’s ‘Topics in applied physics’. It gives an up-to-date survey of what is known of the physical processes underlying infra-red detector operation. Detectors of historical interest are covered briefly within a general and wide-ranging survey (Chapter 2). Three chapters concentrate in much more detail on the physical processes underlying the operation of the different kinds of detectors which are in use today. Thermal detectors cover the broadest spectral range and often operate at ambient temperature. Photovoltaic and photoconductive detectors have been developed especially for the 3-5 nm and 18-l 3 ,um wavebands most favoured for infra-red imaging devices. The HgCdTe alloy system allows the wavelength cut-off to be controlled by adjusting the proportions of the first two components in the alloy. In the case of photoemissive detectors, the classic alkali low work function surfaces have been replaced by the more recent negative electron affinity (NEA) devices using a single crystal of semiconductor, typically GaAs, with a caesium oxide monolayer. Dramatic improvements in quantum efficiency and extended red response are the result. The performance of modern detectors has come close to that of ideal detectors, limited only by photon noise in the radiation which they receive. Further improvement in infrared imaging is to be expected mainly from the use of large detector arrays in place of, or in addition to, mechanical scanning. A chapter on charge coupled devices (CCDs) shows how multiplexing for parallel arrays, and time delay and integration for serial arrays, can be carried out in a single focal plane device consisting of detector array and underlying CCDs. A chapter on non-linear heterodyne detection is more mathematical than other parts of the book. A heterodyne receiver in a communication channel can be made immune to the effect of unknown Doppler shifts by means of a two-frequency transmitter. One unmodulated frequency provides the Doppler information. Several variants of this idea are analysed.
160
The organization of the book is good. Each chapter starts with a summary of its content and contains, on average, a bibliography of about a hundred references at the end. It is well printed and can be recommended to those who wish to follow modern infra-red detector developments. W.R . Bradford Atomic gas laser transition evaluation
data: a critical
W. R. Bennett Plenum, 1979, pp 293 t vii, $75 All relevant papers dealing with atomic gas laser transitions in fifty one elements published to July 1979 have been critically assessed, and the data tabulated by the author of this labour of love. In his introduction to this book Professor Bennett describes his motive as a desire to return something useful to the system which produced Charlotte Moore’s famous volumes on ‘Atomic energy levels’. The volume is divided into two main parts - the tables themselves arranged alphabetically by element, and an annotated bibliography of the 432 references from which data has been drawn. The tables list ion species, wavelengths, upper and lower states, and whether observed under pulsed or cw operation. Also given are computed wavelengths, wavenumber and energy levels in cm-’ . The author has assessed the reliability of each reference by examining details of the experimenters’ work. The method used to determine whether ‘oscillation’ has occurred and the possibility that the author has mistakenly observed grating ‘ghosts’ have been examined before giving a ‘reliability’ rating of ‘dubious’, ‘probable’ or ‘certain’. The accuracy of wavelength measurement of atom and atomic species designation and of transition identification have likewise been critically examined and reliability indicated in the tables. The annotated references give more detail; this section alone occupies some 120 pages, on average of about 150 words comment on each one of more than 400 papers! Although much of the compilation has been achieved by computer, the author was unable to devise a method of performing the critical evaluation semi-automatically. The result is a work which exhibits a thoroughness all too rare in these time-obsessed days. Certainly it contrasts most refreshingly with that other genus of computer-compiled book in which a vast collection of references and ‘key words’ have been uncritically strung together in narrative form by an almost certainly uncomprehending author. This is a work which compels admiration for the dedication which has been lavished upon it. It will certainly be of value to workers in the laser field; the only pity is that it is unlikely to be updated for a long time. B.A. Tozer
OPTICS AND LASER TECHNOLOGY
. JUNE 1981
1980, pp 325 t xi, $26.50
Almost all of this book is about infra-red detectors, but ‘optical’ has been included in the title to cover the chapter on photoemissive detectors (photomultipliers) which cover the visible and uv part of the spectrum and only the very near infra-red. Each chapter is written by a recognized authority, and the editor has contributed a short introduction as well as Chapter 8, on recent developments. This last chapter has been added to the first edition published in 1977. It is not a book on technology. Nowhere is there a picture or a diagram showing what form the detectors finally take and little on how they are used. Methods of obtaining the low temperatures necessary for the operation of many infra-red detectors are not discussed. The book is published as volume 19 of Springer’s ‘Topics in applied physics’. It gives an up-to-date survey of what is known of the physical processes underlying infra-red detector operation. Detectors of historical interest are covered briefly within a general and wide-ranging survey (Chapter 2). Three chapters concentrate in much more detail on the physical processes underlying the operation of the different kinds of detectors which are in use today. Thermal detectors cover the broadest spectral range and often operate at ambient temperature. Photovoltaic and photoconductive detectors have been developed especially for the 3-5 nm and 18-l 3 ,um wavebands most favoured for infra-red imaging devices. The HgCdTe alloy system allows the wavelength cut-off to be controlled by adjusting the proportions of the first two components in the alloy. In the case of photoemissive detectors, the classic alkali low work function surfaces have been replaced by the more recent negative electron affinity (NEA) devices using a single crystal of semiconductor, typically GaAs, with a caesium oxide monolayer. Dramatic improvements in quantum efficiency and extended red response are the result. The performance of modern detectors has come close to that of ideal detectors, limited only by photon noise in the radiation which they receive. Further improvement in infrared imaging is to be expected mainly from the use of large detector arrays in place of, or in addition to, mechanical scanning. A chapter on charge coupled devices (CCDs) shows how multiplexing for parallel arrays, and time delay and integration for serial arrays, can be carried out in a single focal plane device consisting of detector array and underlying CCDs. A chapter on non-linear heterodyne detection is more mathematical than other parts of the book. A heterodyne receiver in a communication channel can be made immune to the effect of unknown Doppler shifts by means of a two-frequency transmitter. One unmodulated frequency provides the Doppler information. Several variants of this idea are analysed.
160
The organization of the book is good. Each chapter starts with a summary of its content and contains, on average, a bibliography of about a hundred references at the end. It is well printed and can be recommended to those who wish to follow modern infra-red detector developments. W.R . Bradford Atomic gas laser transition evaluation
data: a critical
W. R. Bennett Plenum, 1979, pp 293 t vii, $75 All relevant papers dealing with atomic gas laser transitions in fifty one elements published to July 1979 have been critically assessed, and the data tabulated by the author of this labour of love. In his introduction to this book Professor Bennett describes his motive as a desire to return something useful to the system which produced Charlotte Moore’s famous volumes on ‘Atomic energy levels’. The volume is divided into two main parts - the tables themselves arranged alphabetically by element, and an annotated bibliography of the 432 references from which data has been drawn. The tables list ion species, wavelengths, upper and lower states, and whether observed under pulsed or cw operation. Also given are computed wavelengths, wavenumber and energy levels in cm-’ . The author has assessed the reliability of each reference by examining details of the experimenters’ work. The method used to determine whether ‘oscillation’ has occurred and the possibility that the author has mistakenly observed grating ‘ghosts’ have been examined before giving a ‘reliability’ rating of ‘dubious’, ‘probable’ or ‘certain’. The accuracy of wavelength measurement of atom and atomic species designation and of transition identification have likewise been critically examined and reliability indicated in the tables. The annotated references give more detail; this section alone occupies some 120 pages, on average of about 150 words comment on each one of more than 400 papers! Although much of the compilation has been achieved by computer, the author was unable to devise a method of performing the critical evaluation semi-automatically. The result is a work which exhibits a thoroughness all too rare in these time-obsessed days. Certainly it contrasts most refreshingly with that other genus of computer-compiled book in which a vast collection of references and ‘key words’ have been uncritically strung together in narrative form by an almost certainly uncomprehending author. This is a work which compels admiration for the dedication which has been lavished upon it. It will certainly be of value to workers in the laser field; the only pity is that it is unlikely to be updated for a long time. B.A. Tozer
OPTICS AND LASER TECHNOLOGY
. JUNE 1981