Recent developments

Recent developments

Recent developments Liquid filled fibre losses down to 10 dB km-’ A team under Professor W. A. Gambling of Southampton University’s Electronics Depa...

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Recent

developments

Liquid filled fibre losses down to 10 dB km-’ A team under Professor W. A. Gambling of Southampton University’s Electronics Department has developed liquidfilled fibre-optic waveguides with the very low transmission loss of 10 dB km-‘. These fibres which have an internal diameter of 50pm, are being made by Mr. D. N. Payne in lengths approaching 1 km and there is no reason to doubt that much longer fibres can be produced by extending the filling time. The transmission is more than twice as good as the best previously claimed by groups at Bell Telephone Laboratories, USA, (13.5 dB km-‘) and CSIRO, Australia (17.5 dB km-r). The low-loss region extends to longer wavelengths than those previously reported. At 0.96 pm where the Bell group recently reported a loss of more than 80 dB km-r due to an absorption peak, the Southampton group’s fibre has a loss of only 14 dB km-r. In fact the loss in the Southampton fibre is below 20 dB km-i over the wavelength range 0.8 ym to well above 1 .l pm. The Southampton achievement is notable not only for the low transmission loss but also because it has been achieved with cheap, easily obtainable materials which are more flexible and adaptable than the combination of specially-selected silica tubing with the tetrachloroethylene filling liquid used by the two other groups. The materials used are the subject of a patent application. The Southampton research team, which also includes J. P. Dakin, H. Sunak, H. Matsumura and M. W. McGeoch, have claimed several other important successes. Firstly, lower a;tenuations have been obtained in cladded-glass fibres than any reported elsewhere. Secondly, they have measured pulse broadening over lengths approaching 200 m of multi-mode fibre corresponding to bandwidths of 100 MHz and if this can be maintained over kilometre distances then multi-mode fibres will become competitive with single-mode ones. They have also proposed a modefiltering technique for suppressing higher-order modes.

As a result of these developments there is now greatly increased interest in multi-mode tibres. Initially, research centred on the single-mode, solid-core fibre where the core diameter is about 1 pm because it was thought to be the best method of obtaining a reasonable bandwidth. Interest was heightened a year or so ago by the advent of a fibre having an attenuation of 20 dB km-‘. Unfortunately the material used was silica (in the form of a pure silica cladding with a doped silica core) which has a high working temperature and is not easy to process. The fibre, which is reputedly rather brittle, was not commercially available at time of going to press. Launching from semiconductor lasers, and jointing between adjacent sections, are further difficulties which have not yet been adequately solved for single-mode fibres. Multimode fibres were not thought to be suitable for long-distance communications because existing attenuations were high and the bandwidth was expected to be small due to mode conversion effects. The value of the work of Professor Gambling’s group is in showing that multi-mode tibres may well be worthy of serious consideration as optical waveguides particularly since jointing and launching present far fewer difficulties. The work is being carried out in collaboration with the Signals Research and Development Establishment. Mr. Payne has been drawing claddedglass fibres in lengths of several kilometres with core diameters in the range 20 m to 100 pm as well as singlemode fibres. A simple manufacturing method based on the rod-and-tube technique has been used to give great precision in tibre production. Department of Electronics, University of Southampton, Southampton, UK A simple optical test for surface quality A simple optical method of testing surfaces has been developed at Philips Research Laboratories, Eindhoven It uses the optical interference occurring when the wedge-shaped edge of a

Principles

of the Philips droplet

test

method

S Interference ferroxcube

pattern

of a surface of a

sample with

scratches at S (Depth

polishing

O.lpm;

h = 546 nm)

drop of transparent liquid on the surface under test is illuminated by monochromatic light. The new inspection method, discovered and worked out by J. P. M. Verbunt, requires no precision optical components other than a microscope, and can detect surface irregularities of less than 1 pm. A drop of transparent liquid is put on the surface to be tested (See Figs). If a droplet of appropriate surface tension is used, it will wet the surface under test and flow out so that its thickness at the edge gradually decreases to zero. This wedge-shaped edge is than illuminated with monochromatic light A, B. Part of this light is reflected at the upper surface of the liquid, part of it at the lower surface. The interference between these two reflections C, D leads to a pattern of almost parallel fringes. Since the upper surface of the drop of liquid does not exhibit any irregularities, imperfections in the surface under test are shown up immediately as irregularities in the fringes. The wavelength of the monochromatic light and the optical index of refraction of the liquid being known, the magnitude of the observed irregularities can at once

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be recalculated as differences in height on the surface under inspection. With this very simple method, Verbunt was able to measure quantitatively differences in height down to 0.05 pm. A further advantage is that the observed pattern immediately reveals whether the irregularities are small protrusions or scratches in the surface. In the latter case the interference lines are convex towards the edge of the droplet. Philips Research Laboratories, Eindhoven. The Netherlands

Bright future for Bell ‘chip’ camera Bell Laboratories engineers have produced a prototype model of a solid-state video camera claimed to be potentially superior to existing video cameras. The new device which uses a process termed ‘charge coupling’, does not need the electron scanning beam, high voltages, and vacuum envelope needed by conventional video cameras to

convert an optical image into an electrical signal in a video format. The camera needs none of the complex integrated circuits used in other solid state cameras, and does not suffer from electron damage associated with conventional vidicon tubes. The basic element of the device is a p-type silicon chip measuring about 3 mm X 5 mm and covered with a two dimensional array of 13568 (I 28 X 106) electrodes. The electrodes are each 9 mm wide and 2 pm from each other. Light focused on the silicon chip generates free electrons within the silicon, more where the light is brightest, and less in areas of shadow. These free electrons collect at the surface of the silicon under the electrodes with high positive potential in the area where they were generated. These charge pockets are then transferred along the surface of the silicon chip by decreasing the potential of the electrode holding the charge while applying a more positive potential to the next electrode. This causes the charge pocket to move from under one electrode to under the next. This process is repeated until the pockets of charge reach the end of the device and are read out through a serial register. The present prototype model generates an image with about one quarter of the detail of Bell’s Picturephone camera, now in production. Engineers say construction of devices capable of greater detail is quite feasible.

Adjusting the image quality of the Bell charge-coupled camera against an IEEE test chart “I

“2

“3

“I

The new charged coupled device (CCD) area-imaging system may some day be used in the Bell System Picturephone station set, a CCD linear imaging device for slow-scan transmission of very high resolution images, and a CCD analogue shift register whose potential uses include echo suppression in transmission links, bandwidth reduction in video transmission, filter network synthesis, and other electronic signal processing. Bell Telephone Laboratories, Mountain Avenue, Murray Hill, NJ. 07974, USA

New photographic film requires no processing stage Three

phase charge-coupled

used in the transfer

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device

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A method of recording images on film with the result ready for projection in under a second, without chemical

August 7972

processing, is being offered for licensing by the General Electric Company, USA. The technique which has been under development for several years, is called photo-plastic recording. The brightness and clarity of the image have recently been greatly improved by the development of a thin metallic layer added to the film. The film is insensitive to light until just before it is used, at which time it is ‘charged’ by connecting it to a high voltage power supply. When light strikes the film, the electrical charges on the surface are redistributed, and as a source of heat softens one layer of film, its surface is distorted. When the film cools, a fraction of a second later, the ridges are frozen into a pattern that reproduces the image being recorded. Additional information can be added a number of times without erasing the original image. The absence of a chemical processing stage makes the film suitable for use in computer-related microfilming, computers with graphic display outputs, military photography, and industries where holograms are used to study the performance of parts that may become distorted by vibration. Studies conducted recently by General Electric indicate that some vibration studies on complex parts can be reduced from months to days by the use of photoplastic recording. Complete research packages of film, equipment, and know-how are being made available with an option to license. General Electric Company USA, Research and Development Dept., Schenectady, N. Y. 12305, USA

f0.5 million boost for optoelectronics research A prize fund of 2500 000 has been set up by the Rank Organization for ‘The advancement and promotion for the public benefit, of knowledge, education and learning in the interface between the science of optics and the science of electronics and nearly related phenomena’. There will be three categories of awards: 1

Prizes to persons who have made notable advances in or towards any of the sciences covered by the Trust

2

3

Scholarships or fellowships for the purpose of research in any of the sciences and the dissemination of the results of such research Financial support for seminars or conferences for scientists from all parts of the world for the discussion of any aspects of any of the above-mentioned sciences and paying or reimbursing all travelling, hotel and other expenses incurred by them.

Pump light

Retroreflector

output hm

111111

Mini-F P L laser slab

3 Pump light

Schematic diagram of the Mini-FPL

laser

An advisory committee is being set up, chaired by Dr. F. E. Jones, Managing Director of Mullard. The other six members of the committee are: Prof. D. J. Bradley, Professor of Physics, Queens University, Belfast; Prof. J. D. McGee O.B.E., Emeritus Professor of Applied Physics, Imperial College, London; Prof. A. F. Huxley, Royal Society Research Professor, University College, London; Dr. T. P. Maclean, Deputy Chief Scientific Officer, Royal Radar Establishment, Malvern; Dr. P. Schagen O.B.E., Head of Vacuum Physics Division, Mullard Research Laboratories, Redhill; and Dr. R A. Smith C.B.E., Principal and ViceChancellor, Heriot-Watt University, Edinburgh. Funds will become available and prizes will be awarded in the Spring of 1973. The Trustees include Joseph Rank, Chairman of Ranks Hovis McDougal Limited. Dr. l? E Jones, M&lard Ltd, M&lard House, Torrington Place London WCI, UK

Glass laser as oscillator or amplifier A new family of glass lasers which can be used as oscillators or amplifiers, and claimed free of thermally induced optical distortion was announced by General Electric at an IEEE Conference in Montreal in May. Other advantages claimed are high brightness and high power operation. In the basic mini-face pumped laser (Mini-FPL) a laser beam enters at one end of a glass plate, zig-zags down between the top and bottom surfaces of the plate, and leaves by the other end. The glass plate is sandwiched between rows of pumping flash lamps. As the laser beam passes down the plate, it goes through a wide variety of con-

Mini-FPL

laser

ditions of temperature and energy distribution. Consequently the effective average temperature is uniform across the output beam. Thus a high degree of internal self-compensation for thermal effects is obtained. Narrow slab models have been operated as oscillators to produce IS and 20 W average power in Q-switched and normal pulse operation respectively at 20 pulses per second. The wide slab model (designated ‘Big-Mini-FPL’, slab dimensions 4 in X 9 in X $4in) although designed primarily as a multipass laser amplifier, has, in the oscillator configuration produced an average power of 105 Win three pulses per second operation. In Q-switched operation, it has produced 47 W average power. Average powers of several hundred watts are theoretically obtainable with an amplifier system composed of these lasers. One problem encountered so far has been a lens effect in the slab due to thermal geometry distortions near

the edges of the slab. This has been compensated for in the ‘Big-Mini-FPL by increasing the width of the slab in the regions where the effect is most marked Other lasers in the GE range include the ‘Open-Slab-FPL’, used in high energy plasma physics experiments, and the Zig-Zag-FPL, one version of which is being used in picosecond pulse experiments at the Laboratory for Laser Energetics, University of Rochester General Electric Company USA, Research and Development Dept. Schenectady, N. Y. 12305, USA

USSR looks at laser street lighting Scientists working under Professor Y. Raizer at the Institute of Problems of Mechanics, Moscow, are seriously studying the possibility of using laserpumped plasma light sources as street lamps.

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In experiments carried out at the Institute, a small pressure chamber was filled first with xenon and subsequently argon to a pressure of 3-5 atmospheres. The beam from a C.W. laser was introduced into the chamber via a glass window and focused at its centre. The plasma reaction was induced by passing pulses of radiation from a more powerful pulsed laser through the focus. The Russian team is confident that plasma ‘blobs’ working on these lines could be used to illuminate main roads, but stressed that much work needs to be done before practical installations are brought into operation. The Russian newspaper ‘Molodezh Estonii’, which recently published a short article on the technique, hints that there are no theoretical obstacles to forming plasma lamps in the atmosphere at normal atmospheric pressures. Such a ‘street lamp’ could be sustained at any height without any lighting fittings except the lasers themselves.

cover the principal optical characteristics of fibre-optic components to be used in typical electro-optical systems such as image intensifiers, x-ray systems, cathode ray tubes and television cameras. Sira Institute, South Hill, Chislehurst, Kent,

Military application dye lasers

UK

for BAC’s

Laser-guided missiles are all too easily confused and misdirected when using a discreet wavelength laser such as a He-Ne or neodymium laser. All the enemy has to do is to determine the type of laser being used (and therefore the wavelength used), point a laser using the same wavelength away from the target, and the missile is decoyed.

Now BAC is investigating tunable dye lasers for weapons guidance systems. Using a dye laser makes it very difficult for an enemy to decoy the missile Predictably, the report neither compares because using the new system it is the overall efficiency of the proposed possible to change the wavelength of system with that of conventional operation several hundered times a methods, nor discusses the environmenta 11 second. problems. BAC is also considering using fibreUnless Professor Raizer’s team has optics for communication on board developed an exceptionally efficier? aeroplanes and in military applications. laser, there seem little future for the As well as advantages of stopping intersystem. In addition the presence of ference which often worries designers laser beams pointing vertically or of radio communication equipment, BAC claim that crew-to-crew fibreobliquely into the air would present dangers to low flying aircraft and birds. optic communication gear is also very Another objection is the high capital light in weight. A BAC experimental cost of powerful lasers which must fibre-optic communication set is to be drop before such a scheme could be installed on board Concorde 01. considered. Optics Research at BAC was discussed at length at a recent meeting of the Novosti Information Service, Institute of Physics’ Optical Group. 3 Rosary Gardens, London SW7 4NW

British Aircraft Corporation, Weapons Division,

Guided

Group 02 Group 03

Vision and colour terminology Lighting technology terminology.

Co-operating organizations assisting in the preparation of this standard are the British Optical Association, the Institute of Physics and the National Physical Laboratory, together with UK Government departments and other research and industrial organizations. BSI Sales Branch, 101 Pentonville Rd, London Nl YND, UK

Gas laser miniaturized A Bell Laboratories’ scientist has developed waveguide gas lasers measuring only about two inches long by 0.02 in in diameter. These miniature lasers have been operated with different gases at several wavelengths in the visible and near infra-red parts of the spectrum. The first successful model used a He-Ne discharge and operated at 632.8 nm in the visible region. Gains of 2.7 dB m-’ were measured in a glass capillary tubing with a 430 pm bore. Laser output powers of I mW were measured with a 20 cm length of the same waveguide material. R.F. excitation was necessary to maintain a stable discharge. Recently, a 5 cm laser tube was produced that uses a cold cathode, has no gas return path, and requires only d.c. excitation. This tube had a gain in excess of 2.5% at 632.8 nm, and 10 db at 3.39 pm. Due to the high gas pressures used in these laser tubes, gas collision effects produce essentially homogeneous line broadening. For

Stevenage, Herts, UK

Assessing fibre-optic

faceplates

Instrumental techniques have been developed at Sira Institute to measure o.t.f., veiling glare and the ‘chicken wire’ effect in fibre-optic faceplates. These new developments are the outcome of a group-sponsored project concerned with the specification and assessment of faceplates, the first stage of which has just been successfully completed. The project is about to enter its next stage at Sira Institute - the preparation, in Collaboration with the sp&s&s, of a set of agreed test procedures and performance specifications. These will

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Coming to terms with light The last group of a new British Standard glossary of terms (BS 4727 part 4) on lighting and colour has now been published. The new Standard replaces BS 233: Glossary of terms in illumination and photometry. BS 472 7: Glossary of electrotechnical power, telecommunications electronics, lighting and colour terms; part 4; terms particular to lighting and colour, is

published in three volumes: Group 01

August 1972

Radiation and photometry terminology

Miniature

gas laser in operation

this reason, these lasers have been observed to operate at a single frequency that stays within half a longitudinal mode spacing of the atomic line centre when the laser length is varied. Bell Telephone Laboratories, Mountain Avenue, Murray Hill, N. J. 0 79 74, USA

ERA to report on information display systems

radar signals in real-time, telemetered from the aircraft. In the former case it will be employed when the aircraft is too far away for communication with the ground. In these instances the information will be stored on the film and processed when the aircraft returns to its base.

CBS Laboratories, High Ridge Rd, Stamford, Connecticut 06905, USA

The recorder is being built by RCA Government Communications Systems, under a $1.4 million contract from Westinghouse.

New paint gives improved optical performance

A Which? type evaluation report on the whole range of information display systems is to be brought out by the Electrical Research Association’s Applied Electronics Department.

RCA Government and Commercial Systems, Moorestown, N.J., USA

In certain areas, the department says, incandescent lamps, cathode ray tubes and gas discharge tubes may have been superseded by light emitting devices. Cathode ray tubes, however, have recently been improved and may meet the challenge of the new technology

Photochemistry launched

The enquiry was initiated in response to heavy demand following ERA’s report No 7 l-l 15 which examined the suitability and economic viability of liquid crystals. Electrical Research Association, Cleeve Rd, Leatherhead, Surrey, UK.

Laser recorder used in radar system Plans for the development of highresolution laser imager/recorder that will enable signals from an airborne radar system to be converted into photographic quality views, have been announced by RCA. The laser recorder receives signals from a conventional radar, and traces its frequency response on 23 cm wide photographic film. The laser is used as the light source to scan across and expose the film, using a light modulator to vary the laser beam’s intensity to match the radar output. Photographic film is used to record the signal because the wide bandwidth of the radar’s return signal is incompatible with magnetic tape characteristics. Images of photographic quality are claimed. The laser recorder which will be used with the U.S. Air Force’s AN/UPD-5 radar reconnaissance system can be used either in the aircraft or at a ground station where it will receive

journal to be

A new journal on photo-chemistry is to be launched by Elsevier Sequoia S.A. of Switzerland. The journal will be entitled Journal of Photochemistry International Journal devoted to the study of the quantitative aspects of photochemistry and energy transfer. Editor of the journal is to be Dr. R. P. Wayne, of Oxford University. The international editorial board consists of 32 experts from six different countries - 13 from the UK, 11 from USA, five from Canada and one each from West Germany, France and New Zealand. Journal of Photochemistry will be published six times a year and the first issue should appear this year. Papers should be submitted to: Dr. R. P Wayne, Physical Chemistry Laboratory, South Parks Road, Oxford OX1 3QZ, UK

New art form based on holography Following in the footsteps of Leonardo Da Vinci who achieved fame in both science and the arts, Professor Dennis Gabor made his debut in the world of art recently. Professor Gabor has now teamed up with artist Salvador Dali to produce a new art form based on holography. The new Dali-inspired holograms include one showing basketball players being transfigured into angels; another features beer drinkers and a detail from the Velasquez painting ‘Les Meninas’. The holograms were displayed at a recent exhibition the Knoedler Galleries, New York.

Professor Gabor who was awarded the Nobel Prize in Physics in 1971, for his development of the hologram, is a research scientist with CBS.

Since writing their article ‘The study of vibration patterns using real-time hologram interferometry, (p. 167) the authors have been experimenting with a new retro-reflective material, supplied to them by the 3M Company. The material which is to be supplied in spray and adhesive backed tape versions, is not yet commercially available. Improvements in light reflection of around forty times over Codit paint (used in the original study), have been obtained. Using the new paint, the authors have successfully studied vibrating objects 1 m in length with a 1 mW He-Ne laser. An interesting feature is that the reflected light has less depolarization than Codit, enabling the beam intensity ratios to be widely varied. Matt white painted object hologram interferometers usually have reference/ object beam intensity ratios of 3: 1 to 10: 1. Using the new retro-reflective material reference/object intensity ratios of 1:s to 1O:l have been successfuly used. Ratios have been switched around since the noise level in the non-depolarized reflected beam is very low. The photographic plate thus sees two beams of equal polarization and noise content and cannot differentiate between them. The significance behind the discovery is that the greater part of the laser energy, i.e. 80%, can illuminate the object and only 20% go into the reference beam. The authors have also evolved a method of eliminating the need for a large viewing beam-splitter and simultaneously doubling the amount of reflected light. Large light losses occur due only to a portion of the reflected light being transmitted throug the splitter to the spot. The point has been reached where l-2 mW He-Ne lasers can comfortably illuminate a large range of sizes of rectro-reflective models. It is hoped to publish the work in the near future. Mechanical Engineering Dept, University of Stathclyde, Glasgow, UK

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1972

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Geneva Conference and Exhibition plans forge ahead In spite of the recent decision by ISC Management to hold an electro-optics exhibition in the USA at the same time as the 1st European Electra-Optics Markets and Technology Conference and Exhibition in Geneva, both conference papers and bookings for exhibition space in Geneva are coming in rapidly. This degree of interest ~ shown in the face of competition - is an important measure of the recent growth of the electro-optics industry. Confirmation of this upward trend is to be found in the large amount of space now devoted to electro-optics in the national, trade and technical press, glowing reports of the electro-optics industry in a survey carried out earlier this year in the USA ~- and, incidentally, in the recent heavy influx of papers into our journal. There is little point in encouraging this development of a highly advanced technology unless the principles behind this technology can find applications. What is needed now is a heavy marketing effort on the part of the companies who have been carrying out this research. Although researchers must carry on looking for solutions to problems ~ and grants from organizations like the Rank Prize Fund will ensure that this is the case ~ companies with problems must now be shown more forcibly that electro-optic solutions can provide the answers. Exhibition organizers Mack Brooks believe that this is where the Geneva Conference - firmly marketoriented ~ fits into the present trend. Optics and Laser Technology will be giving special coverage to the Geneva Conference and Exhibition in the September issue of the Journal (brought forward one month from October to meet the deadline for the Conference). In the meantime, here is some advance information on a few of the stands:

Jodon is showing the latest additions to a complete industrial holography system. These products fall in line with the Company’s policy of taking holography out of the R & D department and onto the shop floor. lnnovations include an electronic shutter system; an automatic plate processor, magnetic bases for optical elements; and a high power He-Ne laser with additional HF excitation. Oriel Optik is introducing a range of radiometers and photometers, an optical benchtop interferometer, a pulse holography power meter and a range of interference filters. Two other new products to be shown at Geneva include a far infra-red polarizer and a spectrum analyser for CO2 and CO lasers. The 1st European Electra-Optics Markets and Technology Conference and Exhibition will be held at the Palais des Expositions, Geneva, between 12th and 15th September 1972. Carriers for the event are Swissair. Copies of the conference proceedings will shortly be available from NonSerial Publications Dept., IPC Science and Technology Press Ltd., 32 High Street, Guildford, Surrey. Mack Brooks Exhibitions, 7 London Rd, St Albans, Herts, UK

Simultaneous

viewing microscope

A new microscope just announced by the Taylor-Hobson Optics division of Rank Precision Industries has a dual eyepiece system that allows two people to view simultaneously.

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Optics and Laser Technology

Two alternative magnifications are available: X 1.5or X 30, and changes from one to the other are made simply by changing the eyepieces. Price about E275. Rank Precision Industries, PO Box 64, Taylor-Hobson OQtiCS, Stoughton St,, Leicester LE2 OSP, UK

Aerial viewing system uses rotating screen An aerial image projection system which uses a rotating screen to enlarge the exit pupil artificially has been announced by Vision Engineering. One version ~ for use on a compound microscope - uses a conventional objective and eyepiece projection system to focus an image on a screen. This screen is made of aluminized plastic material, the surface of which is covered by a large number of adjacent lenticules, or curved ‘lumps’. The screen can be viewed via field lenses. The reflecting ‘lumps’ produces a series of dots of light in the field of view. These dots move across the field of view as the observer moves his eye, but when the disc rotates, the focal plane is scanned and a composite image is formed. Advantages claimed for the Vision Dynascope are the elimination of ‘microscope fatigue’ experienced with small exit pupils and the absence of ‘eye debris’ in the image plane. Group viewing is possible with wide-angle models. Another version, used in the transmission mode, incorporates a transparent lenticular disc instead of an opaque screen. Vision Engineering L td, Serld Rd, Send, Woking, Surrey, UK

A.S. Akers Electronics, of Norway are showing a range of electronic and optoelectronic components, including a liquid nitrogen cooled infra-red detector, photo-diodes, photo-field effect transistors, and a range of associated circuits. The company points out that a high proportion of its products are custom-built, so there is little point in giving detailed specifications here. Cryophysics are introducing a tunable dye laser to add to the range of lasers they are currently marketing.

Each user can focus his or her own set of eye-pieces independently, and the distance between the two eyepieces can be adjusted to gain the maximum three dimensional effect.

Video proceedings published The proceedings of a symposium on video cartridge, cassette and disc player systems from the 110th SMPTE Conference, held in October 197 1 has now been published.

Dual eyepiece

August 1972

microscope

SMPTE, 9, East 41 St, New York, N. Y. 10017, USA