arXiv subjects

Ermanno F. Borra

Publications and source records attributed to Ermanno F. Borra.

26 records · Page 2Linked to original sources

arXiv2001

Optical Tests of a 3.7-m diameter Liquid Mirror: Behavior under External Perturbations

We have built and tested a 3.7-m diameter liquid mirror that rotates on a ball bearing. We have carried out extensive optical tests. We find that although the ball bearing has a poor quality, the quality of the mirror, with mercury layers 1-mm thick, is surprisingly good. Taken at face values the instantaneous Strehl ratios indicate a mirror, that is not quite diffraction limited but usable for astronomical applications. However, the large coning error of the bearing (1.5 arcseconds P-V) induces an excessive wobble, considerably worsening the time averaged PSF. The most interesting result of the interferometry is that we do not see any evidence of the strong astigmatism that may have been expected from Coriolis forces.

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arXiv2001

Strip Searching for Supernovae

The survey of a strip of sky carried out with a zenith-observing 4-m liquid mirror can discover and observe several thousand supernovae/year to z = 1, making it quite competitive with other proposed surveys. Because LMs are inexpensive, and easy to build, a SNeIa survey can begin rapidly. As documented in the published literature, the present technology, and its cost, has been proven in both the laboratory and in observatory settings and is ready, at a very modest cost, for a 4-m class telescope. As a bonus, the coadded data would survey 150 square degrees of sky to magnitudes > 27, as deep as the deepest optical surveys but in a far larger area of sky. There presently is a window of opportunity to make fundamental discoveries by exploiting the cost advantage of this powerful novel technology.

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arXiv1999

Ultra-Thin Floating Mirrors

We discuss a new technology that promises large inexpensive mirrors. We argue that it should be possible to tilt a rotating viscous liquid by perhaps as much as a few tens of degrees. The tilted liquid parabolic surface is used as the support for a thin reflecting metallic film. We demonstrate two critical steps: that a viscous liquid mirror can be tilted and that an optical quality metallic film can be deposited on a liquid. The advent of astronomically useful tilted floating mirror telescopes is contingent on the development of high-viscosity high-reflectivity liquids. It is a good omen that we already have identified two classes of such liquids; however there remain technical challenges to overcome before such liquids can be used in viable telescopes.

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arXiv1997

Optical Tests of a 2.5-m diameter Liquid Mirror: Behavior under External Perturbations and Scattered Light Measurements

Interferometric tests of a f/1.2 2.5-m diameter liquid mirror show RMS surface deviations about wave/20 and Strehl ratios of order 0.6, showing that it is diffraction limited. The mirror is certainly better than implied by the data because of aberrations introduced by the auxiliary testing optics. We have made detailed studies of the scattered light of the mirror. We have studied the behavior of the mirror under external perturbations. With this article we have reached an important milestone since we now have a good understanding of liquid mirrors.

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arXiv1997

Detection of Gravitational Lenses and Measurement of Time Delays from Classical Electromagnetic Radiation Fluctuations

I suggest that measurements of intensity fluctuations caused by classical wave interactions can be used to find unresolved gravitational lenses and determine time delays of essentially arbitrary length among the images formed by a gravitational lens. No interferometry i s needed, the time delays can be measured by analyzing the intensity signal alone. The technique works with lensed sources that have constant luminosities and is capable of measuring very long time delays. I suggest interferometric techniques, capable of measuring time delays of arbitrary length, that can be used to refine the measurements.

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arXiv1997

A corrector design using active vase mirrors that allows a fixed telescope to access a large region of the sky

We investigate whether a three-mirror system, having secondary and the tertiary mirrors with surfaces warped by Zernike polynomials generated by active vase mirrors, is suitable to do the corrections of a fixed parabolic mirror observing at large angles from the zenith. We obtain designs of correctors with remarkable images and control of the distortion of the field of the view contained within a field greater than 15 Deg.

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arXiv1996

Liquid Mirror Telescopes: A progress report

We review the present status of liquid mirror telescopes. Interferometric tests of liquid mirrors (the largest one having a diameter of 2.5 meters ) show excellent optical qualities. The basic technology is now sufficiently reliable that it can be put to work. Indeed, a handful of liquid mirrors have now been built that are used for scientific work. A 3.7-m diameter LMT is presently being built in the new Laval upgraded testing facilities. Construction of the mirror can be followed on the Web site: http://astrosun.phy.ulaval.ca/lmt/lmt- home.html. Finally we address the issue of the field accessible to LMTs equipped with novel optical correctors. Optical design work, and some exploratory laboratory work, indicate that a single LMT should be able to access, with excellent images, small regions anywhere inside fields as large as 45 degrees.

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arXiv1994

Liquid Mirrors: A Review

The surface of a spinning liquid takes the shape of a paraboloid that can be used as a reflecting mirror. This very old and nearly forgotten concept has recently been revived and I review its present status. Extensive interferometric tests of liquid mirrors (the largest one having a diameter of 2.5-meters ) show excellent optical qualities. I discuss the factors that can limit the optical quality of liquid mirrors, how to minimize them as well as the basic technology. A handful of liquid mirrors have now been built that are used for scientific work. I show representative data obtained from 2.65-m diameter liquid mirror telescopes used for astronomy and the atmospheric sciences (lidar). Section 5, of particular interest to cosmologists, or astronomers using surveys, examines the expected performance of 4-m liquid mirror telescopes dedicated to cosmological surveys. It is rather impressive, due to the fact that the instruments work full- time on four-year surveys: Spectrophotometry reaches B=24 for all objects within over 100 square degrees and wide-band photometry reaches about B=28. I consider the future of liquid mirror telescopes: limits to their sizes, engineering issues as well as speculations on lunar or space LMTs. I briefly mention the possibility of non-rotating GRIN liquid mirrors. Finally I address the issues of the field accessible to LMTs equipped with novel optical correctors. Optical design work, and some exploratory laboratory work, indicate that a single LMT should be able to access, with excellent images, small regions anywhere inside fields

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