This issue is devoted to a variety of papers describing work in the general field of optical engineering which has been carried out recently in the United Kingdom. The titles included were among those submitted as a result of an invitation extended to a wide range of organisations known by your guest editor to be working in this field. A considerable number of offers to prepare historical reviews of achievements at various centers were received but were excluded in favour of 'contributions describing more recent work.
Photofabrication is the manufacture of devices through the action of light on a photosensitive material. In its most usual form an image is projected onto a layer of photoresist which, when developed, acts as a mask for the selective processing of the underlying substrate. In coherent photofabrication the pattern to which the photo-resist is exposed is generated in situ as a pattern of interference fringes, produced by the interaction of coherent beams of light. The device is then an interferogram recorded as a modulation in the surface of the photoresist layer and may either be used as it stands or may require further processing. Items which have successfully been made in this way include spectroscopic diffraction gratings of very high quality, grid polarisers for the near infrared, a novel type of antireflection surface, grating couplers for thin film integrated optics and a selectively absorbing surface which may be useful for the harnessing of solar energy.
A new technology is described for making transparent thermo-setting plastic replica mouldings of optical quality. The finished mouldings are sufficiently accurate for a wide range of applications in image-forming lenses, and particularly for the manufacture of quantities of identical aspheric lenses. The moulded lenses are made in the form of a thin layer of plastic of suitably chosen properties bonded during the moulding process onto one or both faces of a prepared glass substrate. The substrate is first ground and polished to a convenient flat or spherical form. An accurate optically worked negative glass block is used as a mould tool to form the plastic to the correct shape, and the plastic is then polymerised before the finished lens is removed from the tool. The difference in profile between the mould tool and the glass substrate is taken up by variations in thickness of the plastic layer.
The Royal Aircraft Establishment has an extensive programme of work on the application of coherent optical methods to problems arising in aerospace research. In addition to the use of both real-time and double-pulse holographic interferometry in the non-destructive testing of experimental aircraft components, techniques have been developed for the investigation of the mechanical properties of new composite materials and for studies of the behaviour of these and of more conventional materials under stress. Results obtained using a moire-type method for the determination of in-plane strain are presented; and an interferometric system is described which, incorporates an image-converter camera for study ing the surface deformation of a metal bar during the passage of a shockwave front. A simple interferometric method is being applied to the measurement of vibration amplitudes in the subnanometer range; some typical results showing the behaviour of a piezo-electric transducer at frequencies up to 1 megahertz are given. Current work in connection with aerial photography is described, including the incorporation of holographic optical elements into a very large Fizeau interferoscope being constructed for the examination of aircraft camera window. Laser anemometry techniques for supersonic wind tunnel applications using an argon laser and a photon-correlator have been developed. Results obtained in laminar and turbulent air flows at transonic and higher Mach numbers are discussed.
This paper considers the nature and magnitude of the influence of the spectral bandwidth on the MTF of a night vision objective as measured during testing and quality control and the relationship between this and the MTF values applying during the actual use of the objective. It is shown that the practical constraints which must be applied to the quality control procedures, and variations in spectral characteristics, may lead to widely differing MTF values in these two situations. The origins of these differences are also discussed.
The limitations of displays for visual flight simulation are described and the need for a collimated display demonstrated. The results of a comprehensive investigation into methods of achieving collimated displays for flight simulation are given and the subsequent development of the Touview' display, which gives an undistorted view from all parts of the cockpit, is described and the performance indicated.
Exceptionally smooth glass, vitreous silica and metal surfaces are required for a variety of purposes in industrial and scientific laboratories. A variety of defects may mar the perfection of an optically polished surface. In a supersmooth surface, significant imperfections may have heights of about 1 nm and the principal defects which are difficult to eliminate are sleeks and fine undulations. No single method of assessing surface quality has adequate sensitivity to characterise all types of defect and the instruments and inspection techniques employed include optical microscopy, optical scatter and interferometry, bire-fringence, ellipsometry, electromechanical stylus, electron microscopy and X-ray scatter and reflection. The ability to detect and measure surface imperfections of atomic dimensions may enable the origin of the defect to be traced. In this way polishing technology may be improved systematically, in contrast to the traditional empirical approach.
X-ray gratings have been developed for use in the wavelength region of 0.01 to 20 nm, where it is required to employ a grazing incidence configuration. Both laminar and blazed gratings have been produced by conversion of a ruled or photo-fabricated grating, using various etching procedures. The X-ray gratings are formed in a vitreous silica substrate and are relatively robust. Absolute diffraction efficiencies in the first order range from about 5% in the 0.15 to 0.3 nm region to nearly 20% for wavelengths greater than 1 nm. A new precision focusing spectrometer for use in the wavelength range 0.05 to 0.5 nm has been developed. The spectrometer design is based on the polar coordinate principle and the spectrometer can cater for concave gratings of various radii between 5 and 15 m.
Leading British manufacturer of optical products and zoom lenses is Rank Optics-Taylor Hobson who carry on the tradition of Taylor, Taylor & Hobson of Leicester, England who made the 'Cooke' lens on which the film industry grew up. This tradition of optical manufacture owes much to William Taylor who also did pioneering work on standards and gauging. The present day zoom lens is a complex combination of optics, mechanisms and electronics which requires a unique combination of traditional skills and modern technology to meet the demands made on it. The mechanical components have to be made to close tolerances and a tradition of machine adaptation has enabled very high standards of finish to be achieved under production conditions. Air-bearing spindles combined with special diamond cutters produce finishes better than 0.025 micrometres Ra. Thread chasing comprises a considerable proportion of turning and machines with automatic chasing attachments produce threads in ferrous and non-ferrous materials at high outputs. And the employment of numerically controlled milling machines substantially reduces tooling costs. Nevertheless, the skill and experience of the craftsmen still play an essential part in lens production.
The ability to obtain quantitative measurements from the visual analysis of specimens is a growing requirement in many branches of science and engineering. The following paper describes the opto-electronic system used in the Ealing-Beck Histotrak and Optomax image analysis instruments. The system incorporates a CCTV system linked to an optical input device for formatting the image of the specimen for analysis onto a TV camera and an electronic processing sys-tem for analysing the resulting video information. A light pen and associated 80K bit store is included in the system. The light pen, which is used to 'draw' on a video monitor displaying the TV camera image, may either define the boundary of an area of the displayed specimen within which analysis is required or be used to program the movement of the specimen stage. The system store may also be used to retain detected feature information over the whole field of view, allowing comparison of subsequent features with previously detected and stored information.
An instrument for the nondestructive measurement of attenuation in fibres for optical communications and for checking the system laser and detector in situ is described. The instrument is the first of a range of instruments designed to cover all test requirements on optical fibres and incorporates its own gallium aluminium arsenide laser source. The attenuation of fibres with a range of core sizes, and whose losses may be as much as 60 d may be measured to within ±1 dB accuracy. The method involves comparison with a short (zero dB loss) piece of similar fibre. The system detector can be checked for golno go performance and the instrument's detector can be calibrated to read the mean output power of the system laser.
A laser scanning inspection gauge has been designed which enables quick objective assessment of optically polished surfaces to be carried out by relatively unskilled operators. The gauge is suitable for batch inspection of optical flats, windows and lenses over a wide range of sizes and powers. It is capable of detecting and measuring surface defects such as scratches, digs, poor polish and surface contamination and inclusions in the body of the glass, or in a cement layer. It is possible to modify the gauge to permit inspection of lenses on the block, and reflecting surfaces, including semiconductor wafers.
The history of the optical micrometer is briefly traced from its invention by James Watt about 1770. Attention is drawn to errors that can arise when it is used to produce calibrated displacements to be observed with a photoelectric detection system. These errors are caused mainly by stray reflections, and can be much reduced by antireflection treatment of the optical micrometer plate and other components. For a tungsten filament source at 2900°K and with silicon photocells the effective refractive index to be used in the optical micrometer formula is that of the micrometer plate at about 760nm; this should then be made the peak of the antireflection coating. Displacements calibrated to 1 nm can be reliably made. The optical micrometer may also be used in a servo-control system to stabilize the position at which a laser beam crosses any desired plane.
The paper describes a fully portable test set for use in the field for checking the performance of a wide range of night vision equipments and their associated image tubes. Vehicle mounted equipments may be checked without removal from their mounting. Techniques are described for measurement of Luminous Gain, Infrared Gain and Equivalent Background Illumination of tubes and night vision equipments, together with the checking of equipment power supplies.
An infrared spectrophotometer is described for observation of airglow. Ranges 1.26. to 1.28u and 1.55u to 1.62u are scanned. The simple rugged design facilitated installation in Concorde 001 on its flight along the path of totality during the total eclipse of 1973.
The scale invariance of the Mellin transform and its optical synthesis in real-time are discussed. An initial off-line demonstration of an optical Mellin transform is presented. A scale invariant correlation and a combined Fourier-Mellin transform that is both scale and shift invariant are discussed. Applications of these transforms in optical data processing and optical pattern recognition are emphasized.
Image space scanners are often avoided because of off-axis defocus problems. However, there are areas where their application would be useful: when the object distance is small (microscopes), or the optics diameter large (air-and space borne scanners).
This paper summarizes development of large, lightweight, beryllium optical components pursued for nearly three years under a U.S. Air Force contract. The entire process of large beryllium optical technology is described, beginning with materials development, through the design and fabrication process, and final optical surface figuring. The results achieved to date are presented, and finally, the future direction and expectations of ultralightweight optical technologies that will eventually derive from this initial effort are addressed.
It is well known that speckle reduction can be achieved by the noncoherent addition of independent image samples. Sampling can occur at either an image plane or at a Fresnel or Fraunhofer plane of a coherent imaging system. In the literature various comparisons have been made between continuous and discrete sampling methods which take place at a Fraunhofer plane. Because of difficulties in obtaining general closed form expressions in these calculations, no sampling function with optimum characteristics has been specified. This paper shows that continuous sampling at a Fresnel or Fraunhofer plane is precisely equivalent to image plane sampling, provided certain simple criteria are satisfied. This result is valuable since the degree of speckle reduction for a given resolution loss in image plane sampling can be easily calculated and optimized.
In this paper we show that annular source and dynamic coherent phase contrast viewing systems are equivalent. Experimental results which demonstrate the equivalence by showing the bandwidth doubling are included. The additional noise reduction and the continuous tone capability of these systems is also shown experimentally.
In a recent paper, Zambuto and Hanafyl have described a method for holographic interferometry of vibrating objects in which two equal exposures are made; during the first the object is at rest, while during the second it is made to vibrate after having been subjected to a uniform step-displacement of a quarter wavelength.
In the late 1960s, a number of congressional committee hearings were held on the problem of medical radiation exposure in this country. In these hearings, considerable testimony was delivered by selected radiation experts concerning excessive use of medical radiation under conditions which created unwarranted hazards to patient and operator. These hazards were documented by data such as that presented in the 1964 X-Ray Exposure Study conducted by the United States Public Health Service (USPHS). In the 1964 USPHS study, the genetically significant dose (GSD) was computed as 55 mrems for medical radiation exposure in this country, as compared to a medical GSD on the order of 20 mrems for other countries of similar technical sophistication. This difference. in IGSDs was represented as illustrative of unwarranted exposure of U.S. residents to medical radiation, and contributed significantly to establishment by Congress of Public Law 90-602: The Radiation Control for Health and Safety Act of 1968.