Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Patent
1997-07-29
2000-07-04
Le, Que T.
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
356121, G01J 120
Patent
active
06084227&
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to the imaging of objects which have been distorted or blurred, and more particularly relates to a method and apparatus for creating clear wide field images after first characterizing and then compensating for the distortion. The distortion is characterized by being both spatially and time variant.
BACKGROUND AND SUMMARY OF THE INVENTION
The limitations on imaging system performance imposed by a turbulent media, most simply described as `blurring,` are well known, particularly in applications using medium to large aperture telescopes in the open atmosphere. These limitations have not only led to a variety of system solutions that will be discussed as prior art, but have played a major role in the decision to launch space based telescopes and have led to serious postulations of lunar based observatories.
For a large aperture telescope--generally greater than a 10 centimeter diameter for the visible light region--which is otherwise constructed to a precision commonly referred to as "near diffraction limited," the overall ability to resolve objects obscured by a turbulent atmosphere is limited by the turbulence rather than by the instrument. For the visual band of light once more, it is quite typical for a 1 meter aperture telescope to have ten times worse resolving power due to the turbulence, while a 10 meter aperture telescope can be 100 times or more worse than its innate "diffraction limit." The exact numbers for any given telescope on any given night are a function of many variables, but this general level of degradation is widely recognized. As importantly, this atmospheric blurring directly leads to a loss in effective sensitivity of these large aperture imaging systems, which either renders dim objects just too dim to be seen or forces greatly extended exposure times, ultimately limiting the number of objects that can be imaged during a given length of usage time.
The prior art for addressing this problem and trying to alleviate it can be generally categorized into the following well known areas: 1) Telescope Placement; 2) Adaptive Optics Systems; and 3) Speckle Inferometric Systems. It would not be unfair to say that the system disclosed herein is best summarized as a fundamental expansion to the third category, though this is only in a most general sense.
Regarding the first category, that of simply finding locations of minimal turbulence, the placement of telescopes at high elevations has been known and practiced since Isaac Newton's area. This typically adds some expense, but more critically, it is well known that this only goes a small way toward reaching diffraction limited performance, and moreover, imaging performance is still quite subject to the varying atmospheric conditions of a given site. The space age has brought about the "obvious" solution of launching telescopes above the atmosphere, through at considerable expense and complexity.
The second category of adaptive optics has been well known for decades and has seen significant physical realizations over the last two decades. A brief technical summary of such a system is that after a telescope primary mirror has collected the light waves emanating from a given object, it splits the light wave into two "beams." One beam goes into an instrument known as a wavefront sensor and the other beam enters an ordinary imaging system or camera. The wavefront sensor derives information about the phase distortion (caused by the atmosphere) of the incoming light wave and in less than hundredths or even thousandths of a second, sends control signals to mirror actuators which advance and retard primary beam mirror surfaces in cancelling opposition to the incoming phase distortion. There are two critical problems with these systems, however. First, they are expensive to build and expensive to maintain. Second, they can only increase the resolving power within an extremely small angle about the nominal central (paraxial) ray of the telescope, typically on the order of 2 to 10 arc seconds in the vis
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Conwell William Y.
Le Que T.
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