A dual dispersion telescope with a plane grating primary objective was previously disclosed that can overcome intrinsic
chromatic aberration of dispersive optics while allowing for unprecedented features such as million object spectroscopy,
extraordinary étendue, flat primary objective with a relaxed figure tolerance, gossamer membrane substrate stowable as
an unsegmented roll inside a delivery vehicle, and extensibility past 100 meter aperture at optical wavelengths. The
novel design meets many criteria for space deployment. Other embodiments are suitable for airborne platforms as well
as terrestrial and lunar sites. One problem with this novel telescope is that the grazing exodus configuration necessary to
achieve a large aperture is traded for throughput efficiency. Now we show how the hologram of a point source used in
place of the primary objective plane grating can improve efficiency by lowering the diffraction angle below grazing
exodus. An intermediate refractive element is used to compensate for wavelength dependent focal lengths of the
holographic primary objective.
We present an improved model for a spectrographic survey telescope with a kilometer scale diffraction grating collector. Refining the initial public disclosures, the new model quantifies flux collection for telescopes of this type. An option in the new model allows a trade of reduced spectral bandwidth for increased flux collection. We provide experimental evidence to demonstrate an earlier prediction of Ångstrom spectral resolution with relaxed tolerances for grating flatness. This model also posits a kilometer focal length secondary parabolic mirror and details its secondary spectrometer.
Terrestrial installations for telescopes of this type can be at the ground level, presenting a near-zero wind profile despite the unprecedented kilometer scale aperture. The secondary, consisting of a parabolic reflector, is mechanically independent of the primary and completely static. The resulting open frame eliminates the need for a secondary spyder and has no obstructions in the active ray path. The grating primary can be combined with zenith tube liquid mirrors to provide full coverage of right ascension and all angles of declination. A folding mirror can be used as adaptive wave front correction. In space-based deployment, the kilometer length primary can be stowed as a membrane and unfurled in orbit using simple inertial forces.
A University/Industry/Air Force Laboratory collaboration has developed an inexpensive but innovative telescope for interferometry. It incorporates low weight mirrors, low profile tip/tilt secondary, and accelerometer based jitter control. It is built to incorporate higher order adaptive optics. A design team has striven to emphasize a low cost medium tech approach to reduce costs coupled with sturdy precision engineering. The telescopes will be sited in New Mexico and used for Academic and Defense needs.
In this paper we present results using a compact, portable adaptive optics system. The system was developed as a joint venture between the Naval Research Laboratory, Air Force Research Laboratory, and two small, New Mexico based-businesses. The system has a footprint of 18x24x18 inches and weighs less than 100 lbs. Key hardware design characteristics enable portability, easy mounting, and stable alignment. The system also enables quick calibration procedures, stable performance, and automatic adaptability to various pupil configurations. The system was tested during an engineering run in late July 2002 at the Naval Observatory Flagstaff Station one-meter telescope. Weather prevented extensive testing and the seeing during the run was marginal but a sufficient opportunity was provided for proof-of-concept, initial characterization of closed loop performance, and to start addressing some of the most pressing engineering and scientific issues.
Telescope structures are typically required to attain a certain degree of mechanical rigidity in order to achieve the desired optical performance goals, yet there are many applications where weight is either at a premium or local conditions exist that pre-empt optimal mechanical stability requirements. What is needed is a system which can sense and compensate for the opto-mechanical instabilities and correct them in real-time, preferably without "stealing" light from the optical system. We propose using tiny MEMS-based inertial reference sensors to measure the structural dynamics, and, using an appropriate model and coordinate transformations, correct in real-time the tip/tilt, focus, and possibly higher order errors of the optical system aberrations using MEMS-based deformable mirrors and/or our own tip/tilt + piston mirrors.
In many instances, mechanical vibrations, not atmospherics, are the dominant contributors to time varying optical tilts affecting both astronomical and terrestrial observations. We used a pair of inexpensive micromachined accelerometers placed on the secondary mirror mount of a 12' telescope, inferring angular deviations from twice temporally integrated acceleration signals. We then applied this result with appropriate gain to a feed-forward tip/tilt mirror correction loop with good results.
The Magdalena Ridge Observatory project has received first- year funding to complete planning and environmental work. The observatory will have three 2.4-meter telescopes that can be used individually for conventional single-telescope projects or linked to do interferometry. The layout of the observatory will allow fixed east-west baselines as long as 75 meters and may include one telescope that can be moved north-south 100 meters or more to improve coverage in the u- v plane.
Gone are the days of unfettered government spending. An affordable, high performance alternative to multi-million dollar adaptive optics systems is required by the scientific and industrial communities. We have constructed and now give early performance specifications for the 1 St ofthree low cost Adaptive Optics systems for the University of Puerto Rico Imaging Interferometer. Built in months, not years, our in-house subsystem developments include (1) a photon counting ICCD Shack-Hartmann wavefront sensor; (2) a zero latency analog wavefront reconstructor; (3) a precision 2D geometry interpolator; (4) a 700Hz bandwidth beamsteering mirror system with photon counting tracker; and (5)adata acquisition, monitoring and deformable mirror control computer. Key to the control system is a 37-element MEM electrostatic membrane deformable mirror purchased from OKO Technologies. Every element of this system is innovative in the sense of exceptionally high performance at low cost. We will discuss the applicability of using several unique 2D liquid crystal spatial light modulators as correcting elements. We will discuss feedback vs. feed-forward implementations of control law, as well as many practical considerations of full implementation. Other possible medical, industrial, and scientific applications of this affordable, high performance AO technology will be presented.
The University ofPuerto Rico, Mayaguez, in conjunction with the Deep Space Surveillance Branch (DEBS) ofthe USAF Research Laboratory (AFRL) Phillips Site (PL) in Albuquerque, NM is initiating an Adaptive Optics (AO) Interferometry program. The program will begin with four projects. We currently have finding for a three element optical interferometer, described in this paper, using Technology developed at DEBS, for a new wavefront sensor and a Liquid Crystal (LC) wavefront compensator being presented at this meeting'9.and a Low Light Level Fringe Tracker (LLLFT)"6'1"24 Michelson: Interferometer. We are also developing a program to put a similarly configured inexpensive two-element interferometer test-bed in orbit. The interferometer would have optical elements on a 10-meter boom. It will use Aperture Synthesis by rotation and motion ofthe elements along the booms. The third project under development would incorporate the initial 3-element interferometer into a larger array with the additional collaboration ofNew Mexico Tech and New Mexico State University at a 10,600' site near Socorro, NM. As part ofthe ground based interferometry effort we are trying to develop inexpensive meter class telescopes. The 0.75meter telescopes we are building for our small interferometer will serve as prototypes and system test-beds. The telescopes will be robotic, remotely operable, essentially self-orienting, and portable. We hope to produce such systems for commercial distribution for approximately $250K each. All ofthe ground-based interferometric systems will be configured for remote operation and independent use ofsub-arrays while upgrades and repairs are underway. The major thrust ofthe UPR effort will be to develop inexpensive interferometers for diverse applications with the low light level capabilities and the LC adaptive optics developed at the Phillips Site. Particular applications will be for high-resolution astronomy and satellite imaging. The adaptive optics will be such that they can be placed on the individual telescopes and are not part ofthe interferometer. They will then serve as templates fbr AO systems ofgeneral interest. As an additional part ofall ofthese projects we will try to develop the use ofoptical fibers for several applications. We would like to couple the telescopes with fiber if we can develop an efficient way to couple the output signal from the telescope to the fibers. in addition we hope to use fiber stretchers for optical path compensation to replace expensive conventional optical delay lines. Key words; adaptive optics, interferometer, Liquid Crystal wavefront compensation