Auxiliary Mirrors Research Articles

Direct design method for holographic grating imaging spectrometer and corresponding recording system

The combination of holographic gratings with freeform surface technology has led to a significant breakthrough in terms of the performance of imaging spectrometers. In this paper, a general direct design method that is capable of designing imaging spectrometers that include holographic gratings based on a complex-shaped surface substrate and their corresponding recording systems is proposed. The most important feature of this method is that the recording and imaging systems are designed within one optical system model, thus allowing for an optimal balance to be achieved between the aberration correction capability and the manufacturability of the holographic grating. To illustrate the effectiveness of the proposed method, three imaging spectrometers were designed that used holographic gratings manufactured by a recording system without auxiliary mirrors, a system with a spherical auxiliary mirror, and a system with a freeform auxiliary mirror. Ultimately, these three systems all achieved diffraction-limited imaging quality with minimal distortion.

Optical system of aplanatic telescope with a 100 m spherical primary mirror

We propose an optical system of an extremely large telescope for ground-based or planetary use. The system comprises a segmented spherical mirror with a diameter of 100 m and f-number of f / 1. There are three annular zones on the primary mirror, which corresponds to three annular telescopes (ATs) with f-numbers f / 2, f / 3.2, and f / 5.2, all using a concave cardioidal secondary mirror with a maximum diameter of 3.18 m. This two-mirror system satisfies Fermat’s principle and the Abbe’s sine condition. The central zone of the primary mirror with a diameter of 23.8 m is used for the central three-mirror telescope, which is based on an afocal two-mirror system with a convex aspheric secondary mirror with a diameter of 3 m. Four possible configurations are presented for the central telescope, which makes it possible to vary the f-number in a wide range with design examples given for f / 1, f / 4.2, f / 14, and f / 33 systems. The ATs form three coherent images of the same astronomical object, which offers possibilities of simultaneous observations at three different wavelengths or image processing of a combined image with enhanced angular resolution. The main goal of the paper is to investigate the properties of new optical systems for ground-based and space telescopes with a fast spherical primary mirror for which aberration correction is achieved with a minimum number of auxiliary aspheric mirrors near the prime focus.

Panoramic/Dual-Surface Digital Image Correlation Measurement Using a Single Camera.

We propose a cost-effective and simple-to-implement mirror-assisted single-camera panoramic digital image correlation (DIC) method for panoramic/dual-surface profile and deformation measurement. Specifically, two planar mirrors and a single camera attached with a four-mirror adapter are used to capture stereo images of the front and rear surfaces of a test object. These stereo images can be processed by regular stereo-DIC to retrieve shape and kinematics fields of each surface. Further, with the speckle patterns prefabricated on the mirrors, reflection transformation matrices are obtained and applied to transform all reconstructed surfaces into a common world coordinate system. As such, panoramic/dual-surface shape and deformation measurements can be realized. For validation, a high-resolution smartphone camera and an industrial camera were, respectively, used to construct mirror-assisted single-camera panoramic DIC systems. Real experiments, including panoramic shape measurement of an aluminum cylinder, dual-surface shape measurement of an aluminum plate and uniaxial tensile tests of aluminum sheet specimens, were performed, confirming the feasibility and accuracy of the method. Since only a single camera and a few auxiliary reflective mirrors are required, the proposed method provides a cost-effective and convenient way for taking panoramic/dual-surface shape and deformation measurements of regular-sized cylindrical and bar samples.

Ultralight vector dark matter search with auxiliary length channels of gravitational wave detectors

Recently, a considerable amount of attention has been given to the search for ultralight dark matter by measuring the oscillating length changes in the arm cavities of gravitational wave detectors. Although gravitational wave detectors are extremely sensitive for measuring the differential arm length changes, the sensitivity to dark matter is largely attenuated, as the effect of dark matter is mostly common to arm cavity test masses. Here, we propose to use auxiliary length channels, which measure the changes in the power and signal recycling cavity lengths and the differential Michelson interferometer length. The sensitivity to dark matter can be enhanced by exploiting the fact that auxiliary interferometers are more asymmetric than two arm cavities. We show that the sensitivity to $U(1)_{B-L}$ gauge boson dark matter with masses below $7\times 10^{-14}$ eV can be greatly enhanced when our method is applied to a cryogenic gravitational wave detector KAGRA, which employs sapphire test masses and fused silica auxiliary mirrors. We show that KAGRA can probe more than an order of magnitude of unexplored parameter space at masses around $1.5 \times 10^{-14}$ eV, without any modifications to the existing interferometer.

Mirror-assisted Multi-view Digital Image Correlation with Improved Spatial Resolution

Accurate measurements of panoramic/dual-surface kinematic fields are essential to elastoplastic mechanics for the determination of true stress-strain curves, through-thickness strain and the identification of 3D anisotropic parameters. Recently, a novel mirror-assisted multi-view digital image correlation (DIC) method that uses only a two-camera stereo-DIC system and two auxiliary planar mirrors was proposed. It has been convincingly demonstrated to be a cost-efficient and effective technique for measuring 360-deg panoramic/dual-surface kinematic fields. Nevertheless, in this method, the mirrors need to be partly decorated with speckle patterns and the latter clearly captured by the cameras to estimate the reflection transformation of both mirrors. Capturing the speckle patterns on the two mirrors occupies a part of the precious spatial resolution of the cameras, considerably reducing the effective spatial resolution left for the DIC measurement. In this work, an alternative method for estimating the reflection transformation is proposed to improve the spatial resolution of the mirror-assisted multi-view DIC. This method estimates the reflection transformation of the two mirrors by adjusting the mirrors to three or more diverse poses, thus eliminating the need of speckling the mirrors. A set of real tests were carried out, and the results well demonstrated the accuracy and effectiveness of the proposed method.

Absolute interferometric characterization of an x-ray mirror surface profile

An approach to achieve absolute planarity characterization of an x-ray mirror through an interferometric method is presented. With three measurements and two nominally flat auxiliary mirrors, the radius of curvature and the slope profile of a nominally flat x-ray mirror are retrieved. The height profile is then calculated through integration of the slope profile and merging this information with the radius of curvature knowledge. The method is explained in detail and a measurement example is provided. A comparison with a state-of-the-art deflectometric method is shown, with an agreement level of about 0.14 nm rms.

A Method of Phasing the Segmented Main Mirror of the Millimetron Space Observatory Radio Telescope

The effect of errors in positioning the segments of the parabolic mirror of the Millimetron space observatory radio telescope on the point scattering function is analyzed. A method of monitoring the phasing of the segmented paraboloid, based on the use of auxiliary conical mirrors connected constructively with the paraboloid segments, is developed. A method of monitoring the shape of the central part of the paraboloid is proposed.

Measuring coalignment of retroreflectors with large lateral incoming-outgoing beam offset

A method based on phase-shifting Fizeau interferometry is presented with which retroreflectors with large incoming-outgoing beam separations can be tested. The method relies on a flat Reference Bar that is used to align two auxiliary mirrors parallel to each other to extend the aperture of the interferometer. The method is applied to measure the beam coalignment of a prototype Triple Mirror Assembly of the GRACE Follow-On Laser Ranging Interferometer, a future satellite-to-satellite tracking device for Earth gravimetry. The Triple Mirror Assembly features a lateral beam offset of incoming and outgoing beam of 600 mm, whereas the acceptance angle for the incoming beam is only about ±2 mrad. With the developed method, the beam coalignment of the prototype Triple Mirror Assembly was measured to be 9 μrad with a repeatability of below 1 μrad.

Edge-emitting quantum well heterostructure laser diodes with auxiliary native-oxide vertical cavity confinement

Data are presented demonstrating edge-emitting laser diode operation of AlyGa1−yAs– GaAs–InxGa1−xAs quantum well heterostructures modified by the formation of a buried native-oxide distributed Bragg reflecting (DBR) mirror adding vertical confinement to the longitudinal laser cavity. The bottom DBR mirror, combined with the highly reflective top p-contact metallization (Ag), forms a thin broadband vertical cavity. The auxiliary vertical mirrors are tuned to improve the coupling of the spontaneous emission to the longitudinal lasing mode, resulting in reduced threshold currents and modified emission characteristics below threshold.

Null testing using the virtual conjugates satisfying the Herschel condition

Utilizing the Herschel condition, a method is presented for null testing most refractor doublet objectives, including the Baker air-spaced design with equal internal radii, and Maksutov corrector plates using auxiliary spherical mirrors. A special Baker air-spaced objective is offered that utilizes a spherical mirror in null testing that is generated by silvering the front face of the doublet's crown lens or immersing it into mercury. The classical Schmidt corrector is found to deny null testing using the technique.

Comparison of grating designs for the Lyman Far-Ultraviolet Spectroscopic Explorer spectrograph

Various grating designs have been proposed by several investigators for possible use with the Lyman/Far-Ultraviolet Spectroscopic Explorer mission. The image quality, the feasibility, and the efficiency of five designs are compared, each using a distinct type of grating: (1) a grating ruled on a deformed ellipsoidal or toroidal blank, (2) an ellipsoidal grating recorded holographically with two auxiliary spherical mirrors, (3) a spherical holographic grating recorded with two auxiliary spherical holographic gratings, (4) a spherical ruled grating with variable spacing and straight grooves, and (5) a spherical ruled grating with a groove pattern that is determined theoretically (hybrid grating). From a purely theoretical viewpoint, grating (5) provides the finest images, followed by gratings, (3), (1), (4), and (2). In view of the current technological limitations, the order of practical importance is gratings (4), (1), (2), (3), and (5).

A Vacuum Féry Polarizing Monochromator

A vacuum double monochromator with two crystalline quartz prisms was designed and constructed. The monochromator is capable of providing plane-polarized light down to 170 nm using a conventional D2 lamp. The prisms are of the Féry type, so they are able to focus themselves without auxiliary mirrors, improving the efficiency of the monochromator. The monochromator has already been used in the study of the electro-optic effects in KDP and ADP, and is now being used in the study of depolarizers in the near-vacuum region.

Lasing regimes and emission characteristics of a ring iodine photodissociation laser

An experimental investigation was made of the energy, space-time, and polarization characteristics of an atomic iodine photodissociation laser with a four-mirror ring resonator. The direction of lasing was governed mainly by weak reverse signals which could originate, in the absence of auxiliary mirrors, from parasitic reflections or scattering. Under flashlamp pumping, an influence of dynamic inhomogeneity waves on the lasing threshold was manifested in the space-time structure of the near-field pattern. It was established that the polarization of the emitted radiation was linear in the absence of external magnetic fields. It was shown that one can use a ring-laser oscillator for investigations on amplifying systems, and that this approach ensures suppression of amplifier self-excitation by reflection from the resonator mirrors.

Ebert Spectrometers Free of Astigmatism and Coma

A ray-tracing computer programme has been developed to analyse and design Ebert spectrometers. Using this programme the author has found families of spectrometers that have no astigmatism or coma. In general these spectrometers are usable over only a narrow spectral range, but special cases were found that are suitable for use as scanning monochromators. The monochromators are corrected for these aberrations at all wavelengths, but they require auxiliary folding mirrors. The good performance of the monochromators is due to zero incidence angles of the chief ray at both reflections from the spherical mirror.

Optical design for beam-foil experiments

We consider the threshold signal-to-noise ratio for several optical designs appropriate to beam-foil spectroscopy. Calculation of signal-to-noise ratios is complicated by the strong Doppler effect associated with the high unidirectional velocity of the emitting ions. The Doppler effect introduces an unusual coupling of spectral resolution and signal strength which requires modifications to the accepted methods for optimizing these parameters for weak sources. The discussion includes results on the side-on, end-on, and axicon systems, as well as modifications to the side-on system using anamorphic elements or auxiliary mirrors.

Laser Wavelength Selection and Output Coupling by a Grating

The principles of use of gratings as laser wavelength-selective end reflectors are reviewed. A useful output beam can be derived from a grating's zeroth-order reflection. This beam moves when the grating is rotated to select various laser wavelengths, but can be made stationary by the addition of auxiliary mirrors. The grating-mirror combination has been applied to a CO(2) laser in the in and to a dye laser in the visible.

Surveyor 7 Lunar Mission

The spacecraft Surveyor 7 landed on the outer rim of the crater Tycho on January 10, 1968. The landing area was selected to provide contrast with the mare sites of previous Surveyor landings. The surface at this highland site, associated with a major crater, was expected to consist of material that came from depth in relatively recent times. Surveyor 7 carried an alpha-particle backscattering instrument, a soil mechanics surface sampler, a television camera, and auxiliary mirrors and magnets. Data were obtained on the following properties of the lunar surface: topography and geology of the site; character, variety, density, size, distribution, and erosion of rocks; photometry and optical polarization associated with rock surfaces; nature and depth of the surface layer of fine particles; density, bearing capacity, bearing load-penetration relations, cohesion, adhesion, photometry and optical polarization of the fine particulate material; elemental composition and magnetic behavior of fine material and rocks; infrared brightness temperature; thermal inertia; microwave reflectivity. Microwave Doppler measurements were made of the motion of the landing site relative to earth. Pictures were taken of earth through polarizing filters, of lasers on earth, and of the solar corona.

A solar furnace for research in nonferrous metallurgy

Pyrometallurgical and physical metallurgical research often require high temperatures, controlled atmospheres, and freedom from contamination. To obtain such conditions at the Kennecott Research Center, a high temperature solar furnace was constructed using the 60-in. rhodium-plated mirror from an Army surplus searchlight. For maximum flexibility in sample handling, a modified heliostat-type mounting with two auxiliary mirrors was used. A traversing mechanism for zone refining experiments and a totally enclosed sample chamber have been provided. The installation and its characteristics as well as some of its projected uses are described.

Economic factors in furnace design

The theoretical and practical factors which affect the specific performance characteristics and costs of solar furnaces are reviewed in detail. Technical and economic considerations indicate that the best design for a large solar furnace should incorporate the following features: 1.(1) a parabolic concentrator consisting of adjustable curved-mirror segments,2.(2) a stationary concentrator with its axis horizontal, using an auxiliary movable mirror to follow the sun,3.(3) an angle between the image area and the rim of the concentrator of between 50° to 70°,4.(4) a reflecting surface consisting of back-silvered glass. The actual heat flux available at the target is expressed as p=46.1×103EP0 sin2θ where E is the over-all efficiency factor of the solar furnace, p0 is the solar constant, and θ is the rim angle. E is defined as = eta;aηrηsγ where ηa accounts for loss of radiant energy due to the atmosphere, ηr is the combined reflectivity coefficient of the reflecting surfaces of the concentrator and auxiliary mirrors, η8 accounts for the nonreflecting portions of the concentrator because of shadowing and open areas between mirror segments, and γ is an index which represents the degree of geometrical perfection of the parabolic concentrator. A tabulation of calculated E and γ values for a number of actual solar furnaces is presented.The design study and cost estimate, given in Appendix A, include a preliminary structural design and relative cost estimates for a solar furnace system having a 100-ft parabolic concentrator with a movable auxiliary mirror to follow the sun. The results of this study were extrapolated to give cost curves for furnace systems having concentrators with diameters from 50 to 200 ft.

Electrical features of the 200-inch telescope

BRIEFLY, the function of the Palomar Mountain 200-inch telescope is to collect light from celestial objects and concentrate it at the prime focus, or, by a series of additional reflections from auxiliary mirrors, bring the light to other focal points both on and off the telescope. The major advantages of the 200-inch telescope over other large telescopes are: (1) its considerably larger light-gathering capacity, permitting reduction in time of exposures and the photographing of more distant objects; (2) its design, permitting astronomical work directly on the telescope at the prime focus, thus avoiding the loss of light through additional reflections: (3) its flexibility by remotely operated auxiliary mirror combinations; and (4) its automatically corrected drive and setting controls.