In a similar editorial written one year ago for the December 1987 issue of Optical Engineering, I expressed my amazement at how quickly 1987 had seemed to pass. However, my attitude about 1988 is considerably different. Why? Because it was a presidential election year in the United States, which happens to be where I live. Those of you who either do not live in the U.S. or do not follow our election process that closely may not fully appreciate my state of mind, but it seems to me that it has now been several years since the beginning of 1987 and remember that 1987 was quite short.
"Why do you have to keep designing new lenses? Aren't they all designed?" (see Hopkins p. 1019). This question is one of the reasons for having a special issue on Optical Design. The optical designer's answer is very simple: No, not all lenses have been designed yet! In fact, each day we encounter new problems requiring optical solutions that truly test our understanding and ingenuity. We are being asked to design systems in response to telecommunications needs and consumer products. We also design systems for research in physics, geology, astronomy, and medicine. Perhaps it is because lenses are used as tools for other's work, that their design is sometimes not appreciated.
Abstract. By today's standards, lens design and fabrication were primitive during the period from 1937 to 1950, but even today, with all the power of modern computer programs, many of the original techniques are needed. The damped least squares method has been established as the most common method for the optimization process. Several large optical design programs are available commercially. They can handle almost any problem required. They do need many added features, but these can be added to the basic shells. The lens design task today is that of starting with an appropriate understanding of the requirements, a reasonable configuration, and the judgment to be able to make wise trade-offs between conflicting conditions. It is unfortunate that with all our design and manufacturing know-how there are essentially no large production facilities available in the United States. It appears that our skills are being directed primarily to small numbers of units for military or space applications. Most business applications are being produced overseas. This situation probably cannot be changed, so we should attempt to excel in building prototypes of precision optical systems. We can do this at competitive prices but not without some consensus on a plan.
This paper describes the procedure followed in reoptimizing a laser scan lens to eliminate two undesirable elements of the concentric-meniscus type. The continual reappearance of two weak meniscus elements during several reoptimizations had suggested that there were unneeded elements in the lens. When we reduced the number of elements from six to five and reoptimized, both meniscus elements became ordinary elements, and diffraction-limited performance was obtained. Fitting the existing lens into the optimum minimum region of the Los Alamos National Laboratory optimization code was the most difficult part of the procedure.
Nonlinearities infesting optical systems keep Spencer's optimization method from operating in an orderly manner. Experiments with simple nonlinear functions give some insight into peculiarities that are often hidden by the complexity of the design problem.
Numerous designs for triplet lenses, in addition to the well-known Cooke triplet and the inside-out triplet design, are possible. All are difficult to find on the computer because the starting point has to be very close to the final solution for the computer to find it. This paper describes a number of triplet solutions. All but the Cooke and inside-out triplet designs contain at least one thick element.
A monocentric element, that is, one whose surfaces are concentric, can be valuable in an optical design. Such elements are, however, very difficult to fabricate. A departure from exact monocentricity can make the fabrication problem more tractable and can usually be achieved without loss of design performance. A relationship is derived that indicates the minimum departure from monocentricity necessary to make fabrication feasible.
The design of a 360 mm focal length, f/3.6 camera objective to be installed on a Cassegrain spectrograph is described. The system, which is a four-eleMent, all-quartz arrangement with no aspheric surfaces, has a useful Spectral range from 350 to 1000 nm and an equivalent field of view of 4°.
Two coincident-optical-axis, three-mirror telescopes have been designed that feature relatively low focal ratios (f/2.3 and f/3), unobscured optical aperture, large circular fields of view (6° and 8°), good resolution, flat field, reimaging with accessible field stop, Lyot or glare stop, effective stray light suppression, and ease of spectral filter integration. The design for the f/3 telescope with 8° field of view has been fabricated and validated using single-point diamond turned optics.
Some design examples are presented that illustrate the design of null correctors for the testing of strong aspherical surfaces such as those that are of interest in astronomical instrumentation. The design and analysis of an Offner corrector for an f/1 paraboloid is given. Also presented are a zoom null corrector and a null lens that can correct positive as well as negative spherical aberration. A configuration for the testing of convex surfaces is suggested.
Various methods of testing hyperbolic secondary mirrors are reviewed, and their applicability to testing large secondaries is assessed. Traditional methods are found wanting, and a combination of tests is suggested for large, high quality, astronomical secondaries.
This paper presents the optical description of a white light radial shear interferometer for use in the control of segmented mirror systems. White light from a segment of the mirror under control is caused to interfere with light from other segments. The resulting white light fringe position is modulated so that an error signal corresponding to wavefront offset may be generated.
Abstract. A technique has been developed to design single laser rod, multiple flash lamp pump cavities that allow all of the energy generated by the lamp to pass through the laser rod before entering another lamp cavity. The effective lamp and rod perimeters are matched, guaranteeing maximal concentration and uniformity of pumping.
This paper deals with the structural analysis of the optical system of four sets of coaxial mirror concentrators planned for the Italian Satellite for X-ray Astronomy (SAX). Possible damage to the grazing incidence optical surfaces could be induced by the harsh environment during launch, so holographic nondestructive testing was adopted to obtain reliable data about amplitude and shape of the vibrational modes at some critical expected frequencies (from 1 to I 500 Hz). Computer simulation carried out by the finite element approach showed good agreement with holographic analysis in both resonance frequencies and mode shaping, so it is possible to complete the simulation with the attenuation factor obtained from holographic measurements.
A technique for measuring wavefront errors in an optical system that receives light from a spatially extended, arbitrarily structured, incoherent source is described. If we place a suitable transparent mask at an image plane of the system, the structure in the light source serves as a tracer for wavefront errors. The slope of the wavefront error can be detected in the form of intensity variations in a pupil image that follows the mask. One-dimensional numerical simulations of the method as well as the analytical treatment of the proposed principle are presented. The application of the technique as a wavefront sensor in an adaptive optical system for solar observations, in which aberrations are caused by atmospheric turbulence in the light path, is discussed as an example.
A high finesse piezoelectrically controlled and scanned Fabry-Perot interferometric system has been developed for high resolution studies of spectral lines from extended astronomical objects such as comets and diffuse nebulae. The instrument has a resolving power (at Ha) of ~4x10 4 and is superior to conventional pressure scanned Fabry-Perot spectrometers in its finesse, range of scanning, and ease of operation. This paper describes the basic design and operation of the instrument.
Abstract. A new approach for characterizing resolution and depth of focus (DOF) in optical microlithography is introduced. By examination of the interaction of the aerial image with the photoresist process, a metric of image quality is defined. The variation of this metric with feature size and defocus can be used to measure the resolution and DOF. The effects of various imaging parameters on DOF can then be determined. To further study focus effects in submicrometer imaging, the lithography simulation program PROLITH (the positive resist optical lithography model) is modified to account for defocus within the photoresist film.