Wadsworth mount redux: paraboloidal versus spherical gratings.

In this work, based on the diffraction principle of reflective blazed grating, the structure size of the convex spherical blazed grating unit is determined, the machining accuracy of the convex spherical blazed grating is formulated, the effects of tool nose radius and Poisson burr on the diffraction efficiency of the convex spherical blazed grating are analyzed, and the performances of cutting convex gratings with microcrystalline aluminum RSA6061 and RSA6061+ chemically plated NiP for two workpiece materials are compared. A convex spherical blazed grating with a radius of curvature R = 41.104 mm, substrate diameter 14 mm, grating density 53.97 line/mm, and blaze angle of roughly 3.8° is turned by a four-axis ultra-precision machining system by adjustment of the cutting tool, workpiece material, and cutting parameters, as well as modification of the layouts of the blazed grating on the convex sphere. The results of the testing of convex spherical blazed grating elements in both layouts show that the size error of the grating period is close for both layouts, the size error of grating height is smaller in the equal-along-arc layout, the blaze angle error in the equal-along-projection layout is only 0.74%, and the average roughness of the blazed surface is less than 5 nm to meet the processing quality requirements of the reflective convex spherical blazed grating. The greater the blaze angle accuracy of the blazed grating, the higher its diffraction efficiency, so the grating element with an equal-along-projection layout has a higher diffraction efficiency than the grating element with an equal-along-arc layout. RSA6061+ chemically plated NiP material is superior to RSA6061 material in Poisson burr height and blazed surface roughness, which is more suitable for Offner-type imaging spectrometers in the spectral range 0.95–2.5 μm (SWIR).

The diffraction gratings are widely used in Space-flight satellites for spectrograph instruments or in ground-based telescopes in astronomy. The diffraction gratings are one of the key optical components of such systems and have to exhibit very high optical performances. HORIBA Jobin Yvon S.A.S. (part of HORIBA Group) is in the forefront of such gratings development for more than 40 years. During the past decades, HORIBA Jobin Yvon (HJY) has developed a unique expertise in diffraction grating design and manufacturing processes for holographic, ruled or etched gratings. We will present in this paper an overview of diffraction grating technologies especially designed for space and astronomy applications. We will firstly review the heritage of the company in this field with the space qualification of different grating types. Then, we will describe several key grating technologies developed for specific space or astronomy projects: ruled blazed low groove density plane reflection grating, high-groove density holographic toroidal and spherical grating, and finally transmission Fused Silica Etched (FSE) grism-assembled grating. We will not present the Volume Phase Holographic (VPHG) grating type which is used in Astronomy.

A dispersive transform spectral imager named FAROS (FAst Reconfigurable Optical Sensor) has been developed for high frame rate, moderate-to-high resolution hyperspectral imaging. A programmable digital micromirror array (DMA) modulator makes it possible to adjust spectral, temporal and spatial resolution in real time to achieve optimum tradeoff for dynamic monitoring requirements. The system’s F/2.8 collection optics produces diffraction-limited images in the mid-wave infrared (MWIR) spectral region. The optical system is based on a proprietary dual-pass Offner configuration with a single spherical mirror and a confocal spherical diffraction grating. FAROS fulfills two functions simultaneously: one output produces two-dimensional polychromatic imagery at the full focal plane array (FPA) frame rate for fast object acquisition and tracking, while the other output operates in parallel and produces variable-resolution spectral images via Hadamard transform encoding to assist in object discrimination and classification. The current version of the FAROS spectral imager is a multispectral technology demonstrator that operates in the MWIR with a 320 x 256 pixel InSb FPA running at 478 frames per second resulting in time resolution of several tens of milliseconds per hypercube. The instrument has been tested by monitoring small-scale rocket engine firings in outdoor environments. The instrument has no macro-scale moving parts, and conforms to a robust, small-volume and lightweight package, suitable for integration with small surveillance vehicles. The technology is also applicable to multispectral/hyperspectral imaging applications in diverse areas such as atmospheric contamination monitoring, agriculture, process control, and biomedical imaging, and can be adapted for use in any spectral domain from the ultraviolet (UV) to the LWIR region.

A combined optical parametric oscillator (OPO) with continuous tuning of the radiation wavelength in the spectral range 2.5–10.8 μm, optically pumped with the radiation from a Q-switched Nd : YLF laser (1.053 μm), is developed and tested. The oscillation is provided by an OPO1 based on a MgO : PPLN ‘fan-out’ structure in the spectral region 2.5–4.5 μm and by an OPO2 based on HgGa2S4 nonlinear crystals in the spectral region 4.18–10.8 μm, respectively. The angles of phase matching are measured for the HgGa2S4 crystals in the spectral range 4.18–10.8 μm for the type II conversion (eo-e), which virtually coincide with the calculated ones. The experimental absorption spectra of a gas mixture in the range 2.5–10.8 μm obtained using a gas-filled sealed-off photoacoustic cell are presented.

SUMMARY We see from the data that 5.2% of the group of 500 definitely accept a new-axis for near and that 4.6% of the group accept a different cylinder strength at near point. Part of the above percentages probably would be able to wear their distance correction at near point comfortably after becoming accustomed to it; however, a few cases do exist whpre it mould be more advisable to prescribe a separate prescription for near work. The dynamic retinoscope should be used as a method for checking change in power and axis after convergence in every refraction as it furnishes a quick method for detection of whether a change in cylindrical power or axis takes place between distance and near. When a notable difference is detected, a refining of the finding can be made with the Jackson cross cylinder and the subjective at near point. The change of cylinder power and axis at near point would also have a bearing on the cross cylinder findings at near in which a grid is used. This could partially account for the inability of some patients to obtain equality of the vertical and horizontal lines of the cross cylinder grid, even after sufficient plus has been added to bring equality. The discrepancy between distance and near cylinder is usually compensated for in uncorrected pre-presbyopes by the accommodative action of the crystalline lens, which with the added cylinder, establishes a conus of least confusion about the retina. An experiment illustrating this may be performed by placing a + 1.50 times 90 cylinder before the corrected eye of the non-presbyope and viewing the print at twenty feet. As a result, the letters on the chart will be blurred several lines. However, upon viewing the print at near through the same + 1.50 times 90, corresponding change cannot be noted in the clarity of the near print. This indicates that a compensating spherical action by the crystalline lens must have taken place; an action which forms a circle of least confusion with the amount of axis of the new cylinder found at near. As indicated by the above experiment, quite a bit of cylinder power change can take place upon convergence, yet still go unnoticed in the subjective answers of the patient. For this reason, the examiner might be inclined to believe that no change had taken place. However, as these cylindrical power changes are slight, it is quite possible that they are masked under the spherical component added by the crystalline lens in the form of a circle of least confusion which is preferred to a point focus. This may account for the frequent change in axis of cylinder with no apparent associated power change. The preceding experiment may be conversely borne out by placing a 2.50 diopter lens before the corrected eye and viewing a near point card placed at the focal length of the 2.50 diopter lens, so that accommodation is completely relaxed. When a + 1.50 times 90 cylinder is placed before the 2.50 diopter, a blur in the print of the near point card is obtained which approximates that obtained on the distance chart with the 2.50 diopter lens removed. This further supports the contention that a conus of least confusion is formed between the spherical component added by the crystalline lens and the total cylindrical error present. The compensating action of the lens, in itself, probably changes the amount and axis of the near cylinder a slight amount. In any case, however, a spherical balance with the total cylindrical error is formed, which places a conus of least confusion about the retina. In the resultant finding at near (Table II), it may be noted that some cases prefer less cylinder on near findings than on distance findings, while others show more cylinder at near than at distance. It is probable that the patients showing more cylinder on the distance prescription than on the near prefer a conus of least confusion at the near point, while those showing less cylinder at distance than at

Research of depth of field (DOF) for capsule endoscope is important for the reason that the shapes of the object plane of the intestine or the stomach are curve surfaces of "<" shape or "c" shape. The depth of field is dependent on following factors: focal length, circle of confusion, aperture, and subject distance. The first three factors are improved for wide view angle in prior paper and determined by the chosen sensor, and it is not going against depth of field. Last factor, subject distance, is the more freedom to enlarge the depth of field. However, depth of field is the range between near depth of field limit and far depth of field limit that are acceptably sharp. The fraction of the depth of field behind the focus is always large then the one in front of the focus distance. The depth of field does change with object distance, and it is increasing as object distance is increasing. But the object distance of the design for capsule endoscope is short. The object distance setting in front of the dorm is more efficient to use the depth of field than the one setting at the dome top. Therefore there is an appropriate design of object distance to make depth of field be used efficiently to inspect curve surface of intestine and stomach. The more vision information of inspect digestive system is get and is compared easily to diagnose patients' condition under wide and efficient range of depth of field.

We have developed new, Mg/SiC multilayer coatings with corrosion barriers which can be used to efficiently and simultaneously reflect extreme ultraviolet (EUV) radiation in single or multiple narrow bands centered at wavelengths in the spectral region from 25 to 80 nm. Corrosion mitigation was attempted through the use of Al-Mg or Al thin layers. Three different multilayer design concepts were developed and deposited by magnetron sputtering and the reflectance was measured at near-normal incidence in a broad spectral range. Standard Mg/SiC multilayers were also deposited and measured for comparison. They were shown to efficiently reflect radiation at a wavelength of 76.9 nm with a peak reflectance of 40.6% at near-normal incidence, the highest experimental reflectance reported at this wavelength for a narrowband coating. The demonstration of multilayer coatings with corrosion resistance and multiple-wavelength EUV performance is of great interest in the development of mirrors for space-borne solar physics telescopes and other applications requiring long-lasting coatings with narrowband response in multiple emission lines across the EUV range.

Principles for the design of pendulum-type ruling engines and their potential application for the fabrication of non-classical ruled diffraction gratings with large apertures are considered. For spherical diffraction gratings, the derivation of the analytical dependences for the determination of the geometrical shape of the curvilinear projections of their grooves, their curvature radii, and variable pitch is presented. Expressions for the coefficients of first–third-order aberrations are obtained.

Holographic gratings are widely used in spectrographs and monochromators, since they make it possible to control the most important aberrations. However, there are at most three degrees of freedom in determining the positions of the two mutually coherent point sources relative to the grating substrate for a planar recording system. Recording in an aspheric wavefront by means of ellipsoidal mirrors has been used to provide a larger number of free parameters. The aspherical optics approach, with its production and testing, is a complex task, and this solution is not suitable for optical production. Recording by means of spherical diffraction gratings was proposed for apparatus operating on a Rowland circle. Since only recording in copropagating beams was considered, the application of the method was limited to certain particular optical systems. The recording of concave gratings in counterpropagating beams by means of a complex system consisting of several lenses was proposed in Ref. 3. The use of such refractive optics with any holographic recording increases the scattered light level and degrades the quality of the final grating. Recording by means of a spherical diffraction grating and counterpropagating recording beams is free from all the disadvantages mentioned above. The holographic recording apparatus using counterpropagating beams proposed in Ref. 7 is more workable. However, from the standpoint of correcting aberrations, the use of this system is extremely limited.

This is a proposal and description of a new configuration for an Offner imaging spectrometer based on the theory of aberrations of off-plane classical-ruled spherical diffraction gratings. This new spectrometer comprises a concave mirror used in double reflection and a convex reflection grating operating in quadrature, in a concentric layout. A very simple procedure obtains designs that are anastigmatic for a given point on the entrance slit and a given wavelength. Specific examples show that the performance of this type of system improves the performance of analogous conventional in-plane systems, when compactness and/or high spectral resolution is of fundamental importance.

An analytical method to calibrate a camera's extrinsic parameters and effective focal lengths is presented. We used a single image with four coplanar control lines. Unique solutions of the camera's extrinsic parameters and the two effective focal lengths are derived linearly and analytically. If the effective focal lengths are known, unique solutions of the extrinsic parameters can be derived more easily. Our method can easily be implemented and has better precision than the analogous method by use of control points. The results of simulated experiments are presented.

In order to optically vary the magnification of an imaging system, continuous mechanical zoom lenses require multiple optical elements and use fine mechanical motion to precisely adjust the separations between individual or groups of lenses. By incorporating active elements into the optical design, we have designed and demonstrated imaging systems that are capable of variable optical magnification with no macroscopic moving parts. Changing the effective focal length and magnification of an imaging system can be accomplished by adeptly positioning two or more active optics in the optical design and appropriately adjusting the optical power of those elements. In this application, the active optics (e.g. liquid crystal spatial light modulators or deformable mirrors) serve as variable focal-length lenses. Unfortunately, the range over which currently available devices can operate (i.e. their dynamic range) is relatively small. Therefore, the key to this concept is to create large changes in the effective focal length of the system with very small changes in the focal lengths of individual elements by leveraging the optical power of conventional optical elements surrounding the active optics. By appropriately designing the optical system, these variable focal-length lenses can provide the flexibility necessary to change the overall system focal length, and therefore magnification, that is normally accomplished with mechanical motion in conventional zoom lenses.

This paper presents a Lobster Eye (LE) X-ray telescope developed for the Water Recovery X-ray Rocket (WRX-R) experiment. The primary payload of the rocket experiment is a soft X-ray spectroscope developed by the Pennsylvania State University (PSU), USA. The Czech team participates by hard LE X-ray telescope as a secondary payload. The astrophysical objective of the rocket experiment is the Vela Supernova of size about 8deg x 8deg. In the center of the nebula is a neutron star with a strong magnetic field, roughly the mass of the Sun and a diameter of about 20 kilometers forming the Vela pulsar. The primary objective of WRX-R is the spectral measurement of the outer part of the nebula in soft X-ray and FOV of 3.25deg x 3.25deg. The secondary objective (hard LE X-ray telescope) is the Vela neutron star observation. The hard LE telescope consists of two X-ray telescopes with the Timepix detector. First telescope uses 2D LE Schmidt optics (2DLE- REX) with focal length over 1m and 4 Timepix detectors (2x2 matrix). The telescope FOV is 1.5deg x 1.5deg with spectral range from 3keV to 60keV. The second telescope uses 1D LE Schmidt optics (1D-LE-REX) with focal length of 25 cm and one Timepix detector. The telescope is made as a wide field with FOV 4.5deg x 3.5deg and spectral range from 3keV to 40keV. The rocket experiment serves as a technology demonstration mission for the payloads. The LE X-ray telescopes can be in the future used as all‐sky monitor/surveyor. The astrophysical observation can cover the hard X-ray observation of astrophysical sources in time-domain, the GRBs surveying or the exploration of the gravitational wave sources.

The nutrition of grazing ruminants can be optimized by allocating pasture according to its nutritive characteristics, provided that nutritive concentrations are determined in near-real time. Current proximal spectrometers can provide accurate predictive results but are bulky and expensive. This study compared an industry standard, ‘control’, proximal spectrometer, often used for scientific estimation of pasture nutrient concentrations in situ (350–2500 nm spectral range), with three lower-cost, ‘next-generation’, handheld spectrometers. The candidate sensors included a hyperspectral camera (397–1004 nm), and two handheld spectrometers (908–1676 nm and 1345–2555 nm respectively). Pasture samples (n = 145) collected from two paddocks on a working Australian dairy farm, over three timepoints, were scanned in situ by each instrument and then analysed for eight nutritive parameters. Chemometric models were then developed for each nutrient using data from each sensor (split into 80:20 calibration and validation sets). According to Lin’s Concordance Correlation Coefficient (LCCC) from independent validation (n = 29), the hyperspectral camera was the best candidate instrument (LCCC from 0.31 to 0.85, and 0.67 on average), rivalling the control sensor (LCCC from 0.41 to 0.84, and 0.67 on average). Consideration was given to whether the hyperspectral camera’s success was due to spectral range or data type/capture method. It was found that the 400–920 nm (trimmed) spectral region was slightly less sensitive in principle to nutrient concentrations than higher spectral ranges. Therefore, the predictive performance of the camera was attributed to the advantage of gathering data as hyperspectral images as opposed to single spectra.

Focus on lasers and imaging