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   SUBJECT: SETI OPTICAL SEARCH BEST ?                          FILE: UFO1001        
                   
      
   PART 1                      
                         
                      SETI How and Where?   
      
       Copying or reprinting of the EJASA, in part or in whole, is   
       encouraged, provided clear attribution is made to the Astronomical   
       Society of the Atlantic, the Electronic Journal, and the author(s).   
       Opinions expressed in the EJASA are those of the authors' and not   
       necessarily those of the ASA.  This Journal is Copyright (c) 1993   
       by the Astronomical Society of the Atlantic, Incorporated.   
      
      
                                 CONFERENCE PREVIEW   
      
                 THE SEARCH FOR EXTRATERRESTRIAL INTELLIGENCE (SETI)   
                               IN THE OPTICAL SPECTRUM   
      
                              by Dr. Stuart A. Kingsley   
                      Fiberdyne Optoelectronics, Columbus, Ohio   
      
           From the author of the January 1992 six-part EJASA (THE ELECTRONIC   
       JOURNAL OF THE ASTRONOMICAL SOCIETY OF THE ATLANTIC) article (Vol. 3,   
       No. 6A-6F) on Optical SETI (OSETI).   
      
           The author would like to acknowledge that this Electronic Journal   
       has been instrumental in the organization of this conference, for   
       without last January's publication, this author would not have been   
       invited by SPIE to put this conference together.   
      
           You are encouraged to remail this material to anyone you know with   
       interests in SETI or to print it out and pin it up on your astronomical   
       society, company, faculty, or school notice board.  Some of the   
       following material was featured in the October 1992 issue of EJASA   
       (Vol. 4, No. 3) and the December 1992 issue of SPIE's OE REPORTS:   
      
      
           Almost three years ago I began "lobbying" the scientific community   
       to reconsider the optical approach to the electromagnetic search for   
       extraterrestrial intelligence (SETI), first described by Nobel laureate   
       Charles Townes (1964 - masers/lasers) in 1961.  Unfortunately, many of   
       the strongest proponents for electromagnetic SETI have become dogmatic   
       and will not countenance open discussion of alternatives to microwave   
       SETI, believing that the issue of the relative efficiencies of microwave   
       and optical SETI was settled years ago in favor of microwaves.  Optical   
       SETI has received very poor press ever since the skewed ETI laser   
       transmitter assumptions in the Project Cyclops report, two decades ago.   
       This NASA design study report described a microwave array consisting of   
       up to nine hundred 100-meter diameter dishes which if fully built would   
       have occupied an area 6.4 kilometers in diameter and cost, in 1970s   
       currency, some ten billion dollars.  This grand project was never fun-   
       ded but the report itself has had a profound effect on SETI thinking.   
      
           In the comparison table that appeared on page 50 of that report, the   
       optical system modeled described an interstellar laser communication   
       system that employed a 1.06 micron Nd:YAG laser, and a 22.5 cm diameter   
       transmitting telescope.  There were various reasons for limiting the   
       aperture of the ETI transmitter.  One reason arose out of unnecessarily   
       constraining both parts of the system to operate on a planetary surface,   
       within an atmosphere, and thus be limited by the atmospheric coherence   
       cell size.  Another reason was to avoid the production of beams that   
       were smaller than the zones of life around nearby targeted stars.   
       However, the net effect was to cripple the potential very high Effective   
       Isotropic Radiated Power (EIRP) of the optical transmitters.   
      
           It would be far better to build larger transmitting telescopes and   
       defocus them when targeting nearby stars, if, in the unlikely event,   
       the ETI civilization did not possess the technical prowess to aim narrow   
       beams into nearby stars.  In this way, the long-range EIRP would not be   
       unnecessarily degraded.  The modeled "toy" ETI uplink telescopes put   
       the onus on the young and technically immature receiving civilization   
       (humanity) to build very large and expensive telescopes to receive weak   
       signals from mature ETI civilizations, instead of the converse.  It   
       was this part of an otherwise excellent report that so distorted its   
       conclusions concerning the efficacy and relative cost (to us) of the   
       optical approach to SETI.   
      
           If we allow for transmitting and receiving apertures to be 10 meters   
       in diameter or larger, it can be shown for transmitter powers comparable   
       to those for microwave systems that relatively small diffraction-   
       limited laser systems are capable of supporting far higher signal-to-   
       noise ratios and data rates than the much larger microwave systems.  The   
       extremely high gains of optical antennas more than make up for the   
       additional quantum noise and stellar background radiation noise.  The   
       lack of (currently) easily identifiable "magic optical frequencies",   
       equivalent to the microwave waterhole between 1.420 and 1.662 GHz, save   
       for the major CO2 transition at 10.6 microns, is not a reason to   
       conclude that ETIs would not use lasers to signal Earth.  Indeed, the   
       effectiveness of pulsed laser signals is so high that there is less   
       need to be concerned about the exact laser frequency.   
      
           Indeed, from the viewpoint of communications with extraterrestrial   
       intelligences (CETI), which is not presently being proposed, terrene SDI   
       lasers of the late Twentieth Century are certainly capable of "reaching   
       out and touching ETIs" across one thousand or more light years.  The   
       problem today is that we do not know where to point our lasers and we   
       lack the means to provide precise forward predictive targeting of   
       extrasolar planets.  Even more basic to this problem is that direct   
       visual observations of other planets around nearby star systems await   
       the technological developments of the next century.  In the meantime,   
       we must take the passive and perhaps safer approach of listening for   
       ETI signals.   
      
           Let it be noted here that the word "optical" is used in a manner   
       familiar to optoelectronics (photonics) engineers and scientists, as   
       an umbrella term.  It is a superset of both "visible" and "infrared."   
       The word "optical" is not to be taken as being synonymous with the word   
       "visible", since the former (for communication engineers) covers all   
       electromagnetic frequencies from the far-infrared to the ultra-violet.   
      
             
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