An extended use of two crossed Babinet compensators as a wavefront sensor for adaptive optics applications is proposed. This method is based on the lateral shearing interferometry technique in two directions. A single record of the fringes in a pupil plane provides the information about the wavefront. The theoretical simulations based on this approach for various atmospheric conditions and other errors of optical surfaces are provided for better understanding of this method. Derivation of the results from a laboratory experiment using simulated atmospheric conditions demonstrates the steps involved in data analysis and wavefront evaluation. It is shown that this method has a higher degree of freedom in terms of subapertures and on the choice of detectors, and can be suitably adopted for real-time wavefront sensing for adaptive optics.
The plane grating monochromator is to be used with the 480 MeV ((lambda) c equals 61 angstroms) consists of a, plane grating, plane mirror (500 mm X 50 mm) and an ellipsoidal mirror (300 mm X 50 mm, & semi-major axis 39935.7 mm, semi-minor axis 378.84 mm and eccentricity is 0.999955 viz center of the mirror x equals 38433.772 mm, y equals 102.920 mm). The technology for fabricating the plane mirror and the ellipsoidal mirror is being developed at Photonics Division, Indian Institute of Astrophysics. The optical requirement for these mirrors in terms of tangent error better than 1 sec of arc and the micro roughness better than 5Ao is dictated by the design parameters of the monochromator. With these specifications in mind Zerodur substrate material has been chosen in the first phase of the development. For the fabrication of the ellipsoidal mirror a new machine has been designed and fabricated for different stages of grinding, polishing and figuring. The flat and the ellipsoidal mirror are in the final stages of figuring. The paper presents the technology development for manufacturing of these mirrors and the measurement procedures adopted during the fabrication. Problem areas have also been discussed.
The high-resolution EUV spectroheliometer (HiRES) is our first step towards the 0.1 arc sec angular resolution goal at EUV wavelengths. The HiRES instrument consists of a Gregory telescope with a 45-cm-diameter primary mirror, and an imaging EUV spectrometer, employing a single-reflection toric diffraction grating in a Rowland circle mounting and an imaging pulse-counting multi-anode microchannel array (MAMA) detector system. The MAMA detector covers the spectral range from 560 to 631 angstrom with a spectral resolution of 70 mAngstrom. A Pt/Ne lamp impresses a wavelength calibration spectrum on the upper part of the detector while the solar spectrum is recorded simultaneously on the lower part. The times-of-arrival and addresses of the detected photons are transmitted directly to the ground to allow correction of the SPARCS pointing jitter. The HiRES spectrometer slit is pointed to a specific location using real-time control of the SPARCS, and SPARCS can be commanded to execute a linear (push broom) scan across the sun. Two EUV photodiodes are used to measure the absolute sola irradiances and the atmospheric extinction profiles in wavelength bands centered at 304 angstrom and 584 angstrom respectively.
India is planning to build a large Optical/Infrared Telescope of 4 to 5 M in size. This telescope will adopt most of the features of the New Technology Telescope including active and adoptive optics corrections for achieving improved image quality. Keeping this in view a prototype active optics system for a 27 inch thin mirror is being developed at Indian Institute of Astrophysics. A new digital polarization shearing interferometer will be used for wavefront sensing. The paper describes in detail the procedure for wavefront sensing and the approach for the active correction.
The HiRES sounding rocket payload has been described in detail in previous SPIE Proceedings. Here, optical design of the toroidal grating spectrograph is presented and discussed. Ray tracing results are presented which outline the extreme ultraviolet (EUV) performance theoretically attainable with the HiRES instrument. Effects of optical system misalignment on the spectrograph image quality are investigated. Laboratory test results of two f/15 toroidal diffraction gratings using a 1 meter vacuum spectrograph and a multi-anode microchannel array detector are presented and discussed. The test toroidal gratings are fabricated using the elastic substrate replication technique from a ruled master grating with either a 3600 lines/mm or 1800 lines/mm density. EUV images of 10 25 micrometers pinholes with 250 micrometers center-to-center spacing taken with a hollow cathode discharge lamp are presented. Interferometric studies of toroidal figure accuracy as well as optical and electron microscopy investigations into surface quality are presented and discussed. It is found that the current toroidal gratings exhibit good imaging characteristics across a wide wavelength range but suffer from excessive EUV scatter and spectral ghosting.
The HiRES High-Resolution EUV Spectroheliometer is a sounding rocket instrument yielding very high spatial, spectral, and temporal resolution images of the solar outer atmosphere, on the basis of a 45-cm Gregorian telescope feeding a normal-incidence stigmatic EUV spectrometer with imaging multianode microchannel-array detector system, as well as an IR spectrometer with imaging CCD detector system. Attention is given to the expected performance of this system, including the effects of vibrational misalignments due to the sounding rocket flight environment.
We describe the design of a high-resolution stigmatic extremeultraviolet (EUV) spectroheliometer, configured for flight on a Black Brant sounding rocket, which consists of a 45-cm Gregory telescope coupled to a spectrometer employing a single toroidal diffraction grating in a normalincidence Rowland circle mounting and an imaging pulse-counting multianode microchannel array (MAMA) detector system. The toroidal diffraction grating is fabricated by a technique employing an elastically deformable submaster grating that is replicated in a spherical form and then mechanically distorted to produce the desired aspect ratio of the toroidal surface for stigmatic imaging over the selected wavelength range. The spectroheliometer will produce spatially resolved spectra of the chromosphere, transition region, and corona with an angular resolution of 0.4 arcsec or better, a spectral resolution λ/Δλ of about 104 in first order, and a temporal resolution of the order of seconds. Because of the geometric fidelity of the MAMA detector system, the spectroheliometer will be able to determine Doppler shifts to a resolution of at least 2 mÅ at wavelengths near 600 Å (~1.0 km s-1), depending on the level of the accumulated signal. The unique characteristics of the spectroheliometer will be used in combination with plasma-diagnostic techniques to study the emperature, density, and velocity structures of specific features in the solar outer atmosphere.
We describe the design of a high-resolution stigmatic extreme-ultraviolet (EUV) spectroheliometer, configured for flight on a
Black Brant sounding rocket, which consists of a 45-cm Gregory telescope coupled to a spectrometer employing a single
toroidal diffraction grating in a normal-incidence Rowland circle mounting and an imaging pulse-counting Multi-Anode
Microchannel Array (MAMA) detector system. The toroidal diffraction grating is fabricated by a new technique employing an
elastically-deformable sub-master grating which is replicated in a spherical form and then mechanically distorted to produce the
desired aspect ratio of the toroidal surface for stigmatic imaging over the selected wavelength range. The spectroheliometer will
produce spatially-resolved spectra of the chromosphere, transition-region and corona with an angular resolution of 0.4 arc sec or
better, a spectral resolution AII of about 1O in first order, and a temporal resolution of the order of seconds. Because of the
geometric fidelity of the MAMA detector system, the speciroheliometer will be able to determine Doppler shifts to a resolution
of at least 2 mA at wavelengths near 600 A (-1.0 km s1), depending on the level of the accumulated signal. The unique
characteristics of the spectroheliometer will be used in combination with plasma-diagnostic techniques to study the temperature,
density and velocity structures of specific features in the solar outer atmosphere.
This paper describes a method for testing a right angle prism, or any other optical component having a right angle, to subarcsecond accuracy. The method makes use of Haidinger fringes and is simple to use. Unlike autocollimation and Fizeau interferometer methods, it does not involve an expensive optical setup and has no aperture restriction. The sensitivity of the method can be suitably modified by changing the test setup parameters.
Indian Institute of Astrophysics (IIA) has recently completed building of 2.34 M
TelescopeS Optics for the same was fabricated in the Optical shop of the Institute. The
paper describes the technology used in making 2.34 M Telescope Optics. A polarisation
shearing interferometer developed for the testing of large mirrors has also been discussed.
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