A method for computing the polychromatic MTF of hybrid refractive - diffractive elements is described taking into consideration the effects of not only the primary diffraction order but also the effects of additional parasitic diffraction orders. The results of this approach are compared with the more conventional single order calculation and with actual measured performance.
For certain markets and applications the cost of infrared lenses are critical in order to achieve customer expectations. Two possible methods of realising this requirement are the use of moulded optics or the use of multiple kinoform optics with no refractive power. Examples of such lenses are given along with discussion of the merits and limitations that each approach entails.
In this paper, the design of a dual field-of-view optical system for 3-5 μm infra-red focal-plane arrays is described. Preliminary calculations are done to determine the first-order parameters of the narrow and the wide-field modes. To achieve a switchable dual field-of-view system, two different optical configurations, one based on the axial motion of a lens group and the other based on a roate-in motion of two separated lens groups, are studied and compared. Diffractive and conic surfaces are used to control the color and the monochromatic aberrations with less number of total lenses used. Paraxial and real-ray modelling of the Narcissus effect is described. It is shown that the rotate-in scheme achieves better optical performance in both the narrow and the wide-fifeld modes. The axial-motion scheme suffers from poor lateral color in the wide-angle mode. The final optical designs along with the aberrations curves and MTF plots are presented showing excellent performance.
In our digital age, digital cinematography is gaining importance. Therefore the camera lens division of Carl Zeiss decided to extend its conventional cine lenses with a set of digital prime lenses, the DigiPrimes. These lenses are designed for High Definition Television (HDTV) cameras with three 2/3-inch format CCD-Chips and a beamsplitter HDTV prism. There are six lenses with an effective focal length from 5mm to 40mm. The lenses have a telecentric design on the image side, because of the color separating prism. We will discuss some aspects of the mechanical and optical design and their influence on each other.
The quality of high performance microscope objectives is usually verified by interferometric measurement of the wave front. However, a non-interferometric method might be preferable, when appropriate light sources of sufficient coherence length or an interferometric setup are difficult to realize. Under these circumstances, the complex pupil function of an optical system can also be determined from its intensity point spread function (PSF), i.e. from the image of a sub-resolution point object. We present a system that can determine the pupil function of high-NA microscope objectives from defocused images of an artificial point source. An extended version of the "Misell" algorithm is used, which utilizes 4 or more PSF images to overcome the Fourier phase ambiguity and which generally converges rapidly to the correct pupil function both in phase and amplitude. The algorithm can also compensate small errors in the x-, y- and z-positions of the images, which might be caused by vibrations, thermal drift or the limited accuracy of the z-drive.
We have measured the wavefront aberrations of fused silica and silicon microlenses using a Shack-Hartmann wavefront sensor system. The Shack-Hartmann sensor uses a combination of a microlens array and a CCD camera to measure wavefront local tilts with respect to a reference wavefront. Data reduction software then reconstructs the wavefront and expresses it in various forms such as Seidel or Zernike. We measured a series of our custom microlens arrays by placing a fiber source at a distance of one focal length behind the array to create a series of collimated beams from the individual lenslets. We then observed the quality of the collimated beams from single lenslets by using different aperture converters (for different sized lenslets) to expand the individual beams so that they filled a significant portion of the CCD area. For these microlens arrays, the P-V OPD was found to be less than λ/4 and the RMS wavefront error less than λ/20.
Most conventional imaging systems suffer from unwanted and unexpected stray light that is often caused by reflections and scattering from optics and opto-mechanical features. This problem is easily missed during a design procedure that concentrates on improvement of imaging performance. The problem becomes apparent at the final step of production in most cases. If an imaging system consists of micro-optics, a stray light problem may become more difficult to solve due to the system's micro-scale size.
The purpose of this stray light analysis is to improve imaging performance of the multi-modal miniature microscope (4M). The 4M device is a complete microscope on a chip, including optical, micro-mechanical, and electronic components. The 4M device is potentially a useful tool for early detection of pre-cancer due to its very compact size and capability for microscopic-scale imaging. Before actual fabrication of this device, however, we built the same geometry as the real 4M device in a commercial non-sequential ray tracing code and implemented stray light analysis of 4M device.
Our findings indicate that most of the stray light in a 4M device is created by reflection from optics that are nominally supposed to be transparent. Due to a low signal level associated with the object, it is required to add high quality anti-reflection coatings on optics to achieve reasonable SNR.
We have developed a star sensor with a short baffle of 140 mm. Our baffle provides a Sun rejection angle of 35 degrees with stray light attenuation less than the intensity level of a visual magnitude of Mv = +5 for a wide field of view lens of 13x13 degrees. The application of a new light shielding technique taking advantage of total internal reflection phenomena enables us to reduce the baffle length to about three fourths that of the conventional two-stage baffle. We have introduced two ideas to make the baffle length shorter. The one is the application of a nearly half sphere convex lens as the first focusing lens. The bottom surface reflects the scattering rays with high incident angles of over 50 degrees by using the total internal reflection phenomena.
The other is the painting of the surface of the baffle with not frosted but gloss black paint. The gloss black paint enables most of the specular reflection rays to go back to outer space without scattering. We confirm the baffle performance mentioned above by scattering ray tracing simulation and a light attenuation experiment in a darkroom on the ground.
The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument is a 10-channel earth limb-viewing sensor that measures atmospheric emissions in the spectral range of 1.27 μm to 16.9 μm. SABER is part of NASA's Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics (TIMED) mission, which was successfully launched in December 2001. Uncommon among limb-viewing sensors, SABER employs an on-axis telescope design with reimaging optics to allow for an intermediate field stop and a Lyot stop. Additional stray light protection is achieved by an innovative inner Lyot stop, which is placed conjugate to the secondary obscuration and support structure. Presented in this paper is the off-axis response of SABER as measured in the Terrestrial Black Hole off-axis scatter facility at the Space Dynamics Laboratory. The measurement was made at visible wavelengths; thus, the response is only representative of SABER's short wavelength channels. The measurement validated the stray light design and complemented the APART software model, which predicts that mirror scatter is the dominant stray light mechanism at short wavelengths. In addition, estimates of the mirror bi-directional reflectance distribution function (BRDF) were made. The off-axis response measurement indicates that SABER is an exceptional stray light suppression telescope.
Results of measurements of the total hemisphere reflectance (THR), emissivity ε and solar radiation absorption factor αs of the Al-Cr stray-light-absorptive coating are reported. This coating was designed to reduce the stray sunlight background in aerospace instruments. Generally, this problem arises when a density of instruments installed on the satellite is high and it is difficult to avoid getting to instrument the light reflected by neighboring devices. The THR, ε, and αs measurement results are presented for 10 wavelengths within a range from 400 to 927 nm, and also at 121.6 nm, the most intensive line of the solar UV spectrum, which is able to create considerable contribution to the detector noise in space devices. The goal of present experiments was to test an idea that by providing the electron scattering in the coating skin layer, it is possible to reduce the THR. To have the samples with increased electron scattering intensity, the samples of the Al-Cr coating were manufactured. As in teh Al-Cr alloy the d-band of chromium electrons is located in the vicinity of the Fermi energy of Al, in this alloy a considerable electron scattering takes place. Therefore, within the skin layer of such coating, the electrons excited by photons transfer their energies and momenta to the lattice and other electrons instead of releasing the secondary photons. Hence, the reflectivity of the Al-Cr coating might be reduced. The prepared samples and performed experiments confirmed this assumption. According to the measurement results, the chromium appears to be an acceptable additional admixture to provide a further reflectivity reduction in the previously sutdied promising Al-N coating.
For the first time, developed are sphere-shaped precision diamond micropowders ASMV-RM having a number of unique properties - advanced, ordered crystal structure, improved surface morphology, maximal hardening of crystals with increase wear-resistant, with high uniformity of grains and in physico-mechanical properties, with absence of needle, sharp-angled crystals. These exclusive properties enable to provide the considerable increase of productivity of processes at essential improvement of surface quality during thin grinding and polishing of products by these micropowders. They are outside of a competition to the standard marks of diamonds of general purpose as were created for new highly perspective areas of applications focused on high technologies in electronics, optics and other branches of modern engineering. In precision micropowders ASMV-RM enormous potential of diamonds is realized.
The technology of precision diamond micropowders preparation is based on results of the scientific school by Academician of the National Academy of Sciences of Ukraine V.I. Trefilov and complex approach directed on deepened influence on a material with application of modern effective technologies and the optimum technical solutions.
The technology of their manufacture is referred to high technologies, and precision micropowders have created a new direction in diamond branch.
Real conditions for realization of technical revolution in creation and use of a new class precision diamond micropowders are now created.
We first consider the potential impact of a technology that could deliver polished, accurate aspheric surfaces in a routine and automated manner. We then summarise the technical challenge, and present an appraisal of the performance of the novel 'Precessions' process, which is a major advance in this direction. We outline the design concepts behind the productionized CNC polishing machines which executes the process, and then describe the progress developing strategies to preserve form when polishing ground surfaces, and to correct form on both pre-ground and polished surfaces. Particular consideration is given to resolving the inherent difficulties of control of centres on rotationally-symmetric parts. We then report on experimental results achieved with the machines. Finally, we present our programme to extend the control-algorithms to handle fully free-form surfaces, and draw conclusions about the effectiveness and generality of the 'Precessions' technique.
PLEXISS (Planetary Exospheres from the International Space Station) is a proposed small instrument dedicated to the coronagraphic imaging in the Na yellow doublet (5890 and 5896 A) and in the K red doublet (7665 and 7699) A of the transient lunar atmosphere from the International Space Station (ISS). The scientific return of PLEXISS can give important information for the understanding of the transient atmospheres of several other bodies of the Solar System; in particular, the European cornerstone mission Bepi-Colombo to planet Mercury can greatly benefit from PLEXISS.
This paper describes the two concepts of coronagraphic telescope design (one totally reflecting and one totally refractive) we have developed for this very challenging application, that requires occulting the lunar disk and providing a clear field of approximately ± 2° around it, with a resolution of about 30 arcsec per pixel.
The Laser Interferometer Space Antenna (LISA) for the detection of Gravitational Waves is a very long baseline interferometer which will measure the changes in the distance of a five million kilometer arm to picometer accuracies. As with any optical system, even one with such very large separations between the transmitting and receiving telescopes, a sensitivity analysis has to be performed to see how, in this case, the far field phase varies when the telescope parameters change as a result of structural stress relief or temperature changes. The results of the sensitivity analysis are presented.
A miniaturized instrument for systematic planetary mineralogy is presented, and the optical design of the component parts is discussed. The instrument combines the following capabilities: wide field color imaging, confocal imaging at two different resolution/range levels, reflectance spectroscopy in the 400-2500 nm region with a resolution of 10nm, and Raman spectroscopy over 4000 cm-1 with an average resolution of 3.3 cm-1. The instrument can also serve as an expandable platform for adding fluorescence spectroscopy, or for examining samples from a distance of several meters while using the same spectrometer.
Helicopter mounted optical systems require compact packaging, good image performance (approaching the diffraction-limit), and must survive and operate in a rugged shock and thermal environment. The always-present requirement for low weight in an airborne sensor is paramount when considering the optical configuration. In addition, the usual list of optical requirements which must be satisfied within narrow tolerances, including field-of-view, vignetting, boresight, stray light rejection, and transmittance drive the optical design. It must be determined early in the engineering process which internal optical alignment adjustment provisions must be included, which may be included, and which will have to be omitted, since adding alignment features often conflicts with the requirement for optical component stability during operation and of course adds weight. When the system is to be modular and mates with another optical system, a telescope designed by different contractor in this case, additional alignment requirements between the two systems must be specified and agreed upon. Final delivered cost is certainly critical and "touch labor" assembly time must be determined and controlled. A clear plan for the alignment and assembly steps must be devised before the optical design can even begin to ensure that an arrangement of optical components amenable to adjustment is reached. The optical specification document should be written contemporaneously with the alignment plan to insure compatibility.
The optics decisions that led to the success of this project are described and the final optical design is presented. A description of some unique pupil alignment adjustments, never performed by us in the infrared, is described.
We have developed a new method other than traditional technique based on ray tracing and optimization algorithm to design arbitrary aspherics. Analytic definition of the aspheric surfaces is done away with and numerical solution of nonlinear difference equations called Aspheric Intrinsic Equations (AIE) is implemented instead. Simulation results compared with traditional optical design software are presented, which prove that this new method is more effective and reliable in designing aspheric surfaces.
Analysis of aberration performance of two-mirror lens allowed revealing an interesting relationship between them and the central obscuration coefficient ε and the distance δ of the focal plane from the vertex of the primary mirror and introducing the coefficient of complexity of Cassegrain lens.
Several types of telescopes are used for free space telecommunications. The most common are Cassegrain and Gregorian telescopes. The main difference between Cassegrain and Gregorian optical systems is that Gregorian telescopes employ a concave secondary mirror located beyond the focus of the primary mirror. This results in longer tube lengths, as the distance between mirrors is slightly more than the sum of their focal lengths, which is the reason Cassegrain systems are the most common. In addition, Gregorian telescopes produce an upright image, while Cassegrain telescopes produce an inverted image.
FSONA is presenting a new compact optical system, which can be described as a modified Gregorian telescope. This telescope is ideally suited for free space optical communications but also has many other applications. The compact telescope is created from a standard Gregorian system by flipping the secondary mirror over a folding mirror installed approximately in the middle of the optical path between primary and secondary mirrors. In this manner, the primary mirror is constructed with a concentric "double curved" geometry, and a central obscuring folding mirror which matches the diameter of the smaller curve of the primary is mounted a short distance in front. This "double curved" geometry is easily produced using diamond turning technology, and the result is a compact telescope approximately 1/2 the length of a regular Gregorian telescope and roughly 2/3 the length of a Cassegrain telescope.
There are several advantages to using this type of telescope:
1. The system is very compact. Telescope can be as short as 1/7 of the focal length of the system.
2. For Cassegrain and Gregorian systems it is very critical to keep tight tolerances on the centration between primary and secondary mirrors. The modified Gregorian telescope will always have perfect centration because both curved surfaces are machined at the same time on a diamond turning lathe. The folding mirror is flat so no centration is required
3. The modified Gregorian system is inexpensive. Instead of two curved mirrors, there is one mirror with two curves, and one inexpensive flat folding mirror.
4. The folding mirror can be used as a steering mirror for a tracking system.
5. If the modified Gregorian telescope is constructed out of one material (ie. aluminum), it is completely a-thermal and insensitive to changes in temperataure.
We present real-time measurements of the wave front distortion induced by a variable focal lens. This lens, called Varioptic, is made of a transparent cell filled with twin liquids. We submit a 4.5mm in diameter lens upon a 110V voltage step inducing a optical power shift of about 25 dioptries (m-1) . Characteristic response time is shown to be of the order of a few 1/100s, the lens recovering its full quality after 5/100s. We present a scaling analysis of this response time versus lens size.