Houghton anastigmatic telescope containing aspheric mirrors that allows corrector position as a free parameter

A family of catadioptric telescopes is investigated, characterzied with two-element, full-aperture afocal corrector lenses and aspherical, focusing, primary mirrors or primary-secondary mirror combination. Third-order aberration and design equation are provided for anastigmatic systems in which corrector position must be a free parameter, forcing the consideration of aspherics on the mirrored surfaces.     

Method for deriving the complete solution set for three-mirror anastigmatic telescopes with two spherical mirrors

The "plate-diagram" method of quantifying and manipulating the Seidel aberrations of an optical system has been used to develop a procedure that has successfully determined the complete solution set of three-mirror anastigmats in which two surfaces are left strictly spherical. The procedure also readily identified solutions in which the Petzval sum is zero, and four distinct families of flat-field three-mirror anastigmats with two mirrors strictly spherical have thus been found. The success of the method is strong support for the argument that algebraic approaches to optical design can yield results distinctly superior to currently favored optimization-based design methods, at least for some types of optical systems.     

Modification of the conventional method for determination of the focal length of convex mirrors

A simple experimental procedure is described for the precise measurement of focal lengths of medium-sized convex mirrors. This procedure is a modification of the conventional method reported in the literature. It has enabled us to minimize the errors introduced because of bench corrections and depth of focus of optical components that are generally encountered with conventional methods. The accuracy of the procedure has been found to be ±0.3%. The results of the measurements on a few test convex mirrors and experimental parameters are reported.     

Imaging performance of telescope mirrors for far-ultraviolet astronomy

We describe image testing, surface metrology, and modeling of telescope mirrors (0.5 m in diameter, f/4.3) for the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite. Laboratory image testing of wavelengths in the visible, vacuum, and midultraviolet validated a theoretical analysis by use of the Optical Surface Analysis Code (OSAC). Our modeling is based on surface metrology, including measurements of figure, midfrequency error, and microroughness. This combination of metrology, out-of-band performance testing, and modeling verified that the mirrors would meet mission requirements. We use OSAC to predict the FUSE telescope's far-ultraviolet (90-120-nm) point-spread function and assess its effect on instrument efficiency. The mirrors have a 90% encircled energy diameter of 1.5 arc sec at lambda = 100 nm. Including the effects of spacecraft pointing error, the mirrors have a predicted average slit transmission at lambda = 100 nm of approximately 87% and 96% for the 1.25- and 4-arc sec-wide spectrograph slits, respectively, where the required transmissions are 50% and 95%.     

Narrow-bandpass multilayer mirrors for an extreme-ultraviolet Doppler telescope

We have developed narrow-bandpass MoSi/Si multilayer mirrors for a Japanese sounding-rocket program. A high spectral resolution lambda/Dlambda exceeding 40 was achieved by a two-mirror telescope with a multilayer coating. The single telescope had two bandpasses in the extreme-UV range for detecting a coronal high-velocity flow; the wavelength at peak reflectance (hereafter peak wavelength) in one of the bandpasses was 210.2 A, situated on the blue side of the target's Fe xiv 211.3-A coronal emission line, and the peak wavelength in the other was 213.3 A on the red side. A high uniformity in a peak wavelength of less than 1 A was achieved over a primary (secondary) mirror surface 158 (96) mm in diameter. The ratio of the reflectance for the Fe xiv line at 211 A to that for an intense He ii line as a contaminant at 304 A in the telescope system became 2 x 10(5) owing to a wave trap consisting of a single Si layer on the MoSi/Si multilayer. The narrow-bandpass (~5-A) telescope was launched on 31 January 1998 by sounding rocket S520CN-22, and images of the whole-Sun corona at Fe xiv 211 A were successfully obtained.     

Thermal expansion uniformity of materials for large telescope mirrors

Uniformity of thermal expansion has been measured for fused quartz (Heraeus-Amersil TO8E) and borosilicate glass (Schott Duran and Ohara E6). The variation of expansion coefficient for three melts of TO8E was 5 x 10(-9)/K over a temperature range of 300 to 100 K and was found to vary linearly with position in the melt. This spatial gradient averaged 3.5 x 10(-11)/K cm. The room-temperature thermal expansivity variation of Duran (Tempax) glass was approximately 27 x 10(-9)/K, while that of E6 glass was approximately 52 x 10(-9)/K.     

空间太阳望远镜成像镜调焦机构设计与分析

 根据空间太阳望远镜成像调焦的要求，设计了一成像镜调焦机构。给出了设计的基本原理及设计方法，即步进电机驱动滚珠丝杠，丝杠通过连接杆和转向关节带动内筒，并根据设计加工制作了实物缩尺模型，进行了误差分析，最后给出了机构在锁定状态，16g重力加速度作用下的力学分析。     

Medium-precision null-screen testing of off-axis parabolic mirrors for segmented primary telescope optics: the large millimeter telescope

The feasibility of using null screens for testing the segments of a parabolic segmented telescope mirror for the Large Millimeter Telescope (LMT) is analyzed. An algorithm for designing the null screen for testing the off-axis segments of conic surfaces is described. Actual screen designs for the different classes of segments of the LMT are presented. The sensitivity of the test and the required accuracies for the fabrication and positioning of the screen are analyzed. A measuring accuracy of approximately 12 microm in surface sagitta is within the reach of the technique.     

Imaging with three spherical mirrors

Unobstructed, plane-symmetric systems of three spherical mirrors are investigated. Twelve parameters are necessary to specify the configuration of such a system. Constraints are determined to eliminate four of these parameters as independent degrees of freedom. These constraints ensure appropriate first-order behavior and are used to aid in two example design studies-one for a class of systems with the object at infinity and another for a class of finite conjugate projection systems. For the first study, a portion of the associated merit-function space is systematically evaluated and plotted, and the results are compared with those obtained when a global optimizer is used. For the second study, a global optimizer is employed as the primary search tool. Example systems from both studies are presented.     

Experimental study of an off-axis three mirror anastigmatic system with wavefront coding technology

Wavefront coding (WFC) is a kind of computational imaging technique that controls defocus and defocus related aberrations of optical systems by introducing a specially designed phase distribution to the pupil function. This technology has been applied in many imaging systems to improve performance and/or reduce cost. The application of WFC technology in an off-axis three mirror anastigmatic (TMA) system has been proposed, and the design and optimization of optics, the restoration of degraded images, and the manufacturing of wavefront coded elements have been researched in our previous work. In this paper, we describe the alignment, the imaging experiment, and the image restoration of the off-axis TMA system with WFC technology. The ideal wavefront map is set to be the system error of the interferometer to simplify the assembly, and the coefficients of certain Zernike polynomials are monitored to verify the result in the alignment process. A pinhole of 20 μm diameter and the third plate of WT1005-62 resolution patterns are selected as the targets in the imaging experiment. The comparison of the tail lengths of point spread functions is represented to show the invariance of the image quality in the extended depth of focus. The structure similarity is applied to estimate the relationship among the captured images with varying defocus. We conclude that the experiment results agree with the earlier theoretical analysis.     

Alternative method for measuring effective focal length of lenses using the front and back surface reflections from a reference plate

We present a simple method for measuring the effective focal length without determining the location of principle plane of the lens. The method is based on the measurement of confocal backreflection axial responses from the front and back surfaces of a reference plate with known refractive index and thickness. We proved the concept by measuring the effective focal lengths of thin singlet lenses and complex microscope objectives. The theoretical limit of measurement precision varies depending on the numerical aperture of the lens. This method can provide an alternative focal length measurement method for complex lenses or lenses that are permanently attached to other structures. Measurement errors were analyzed theoretically and improvements in measurement accuracy were discussed.     

Design of microlenses with long focal depth based on the general focal length function

A general focal length function is proposed to design microlenses with long extended focal depth and high lateral resolution. The focal performance of the designed microlenses, including the actual focal depth, the focal spot size, and the diffraction efficiency, is calculated by rigorous electromagnetic theory and the boundary-element method for several f-numbers. In contrast to conventional microlenses, the numerical results indicate that the designed microlenses can exhibit long extended focal depth and good focal performance. It is expected that the long focal length function will be widely used to design microlenses with long focal depth characteristics.     

Measurement of focal length with phase-shifting Talbot interferometry

Phase-shifting interferometry with a Fourier fringe analysis technique is implemented to analyze Talbot interferometric fringes and to evaluate the focal length of a lens. A four-step algorithm is used to obtain the phase map of the lens. The slope of the phase map is related to the focal length, and it is from this relationship that we evaluate the focal length. Experimental results are presented. Our experimental study suggests that phase-shifting Talbot interferometry combined with a Fourier fringe analysis technique can be advantageously used to improve the accuracy of measurement.     

Calibration method for high-accuracy measurement of long focal length with Talbot interferometry

In this paper, a new calibration method for accurate long focal-length measurements, based on Talbot interferometry, is presented. Error analysis is derived in detail by the numerical method, and an effective way to improve the accuracy is proposed. By this method, the systematic errors that are the main factors effecting accuracy are calibrated and reduced. Both simulation and experiments have been carried out to prove the effectiveness and advantages of the proposed method as compared to conventional approaches. The experimental results reveal that the relative error is lower than 0.02%, and the repeatability is better than 0.05%. This method is especially useful for measuring long focal-length lenses.     

X-ray telescope onboard Astro-E: optical design and fabrication of thin foil mirrors

X-ray telescopes (XRT's) of nested thin foil mirrors are developed for Astro-E, the fifth Japanese x-ray astronomy satellite. Although the launch was not successful, the design concept, fabrication, and alignment procedure are summarized. The main purpose of the Astro-E XRT is to collect hard x rays up to 10 keV with high efficiency and to provide medium spatial resolution in limited weight and volume. Compared with the previous mission, Advanced Satellite for Cosmology and Astrophysics (ASCA), a slightly longer focal length of 4.5-4.75 m and a larger diameter of 40 cm yields an effective area of 1750 cm(2) at 8 keV with five telescopes. The image quality is also improved to 2-arc min half-power diameter by introduction of a replication process. Platinum is used instead of gold for the reflectors of one of the five telescopes to enhance the high-energy response. The fabrication and alignment procedure is also summarized. Several methods for improvement are suggested for the reflight Astro-E II mission and for other future missions. Preflight calibration results will be described in a forthcoming second paper, and a detailed study of images will be presented in a third paper.     

Corrector design with active vase mirrors that allows a fixed telescope to access a large region of the sky

We investigate a family of two-mirror correctors to compensate for the aberrations of a parabolic mirror observing at a large angle from the zenith. We constrain our designs to optical elements that can be built with currently available technology. The secondary and the tertiary mirrors are warped by Zernike polynomials, which we know can be generated with active vase mirrors. The performances of these corrector designs are usable for imagery.     

Vibrating knife-edge technique for measuring the focal length of a microlens

A vibrating knife-edge technique is proposed for measuring the focal length of a microlens. The technique is based on the propagation properties of Gaussian beams. A laser beam with a Gaussian intensity profile is focused in front of the microlens under test. After being transmitted through the microlens, the beam propagates toward a detector, which consists of a photodiode that is half blocked by a knife-edge. The photodiode integrates approximately half the intensity of the transmitted beam. The knife-edge vibrates sinusoidally with small amplitude in a plane normal to the direction of propagation. Our analysis shows that the output signal at the photodiode consists of a dc component plus a temporal sinusoidal signal whose amplitude is proportional to the focal length of the microlens. After system calibration, the focal length is measured with an envelope detector or a lock-in amplifier.