X-Message-Number: 19391 From: Date: Tue, 2 Jul 2002 15:37:02 EDT Subject: Re: #19388 --part1_196.9365c60.2a535ade_boundary Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit > > Unfortunately, 100 Ghz sampling rates are NOT a possibility. Remember, > light > is a particle as well as a wave, and if you're sampling at higher than the > rate photons are arriving, most of your samples will be empty. Naturally, > the dimmer the source, the lower the rate at which photons arrive... > > Brett Bellmore > > Allows me a small computation: From memory, the Sun has a magnitude near -26 (between minus 26 and minus 27). Adding five magnitudes divide energy by 100 in round numbers. Now the solar constant is 1.3 kJ per second per sq. meter at the Earth's orbit distance. Typical optical photons have an energy of 3 electron-volts and 1 eV = 1.6 x 10^-19 Joule, that is, the Sun light is a shower of 1300/(3 x 1.6 x 1O^-19) = 2.7 x 10^21 photons per sq. meter per second. Take a 4th magnitude star as an example, this is 30 mag. under the Sun or 6 x 5, as 5 mag divide the number of photons by 100, 30 mags. divide it by 10^12. So, a 4th magnitude star send us a shower of 2.7 x 10^9 photons by sq. meter by second. The Narrabri interferometer light collectors was 7 m in diameter or 38 sq. m. So they collected something as 100 billions photons per second from a 4th magnitude star. With a sampling rate of 100 Ghz, there would be one photon per bin, this is the most efficient way to detect bunching. Beyond that frequency indeed we would gain nothing as all bunch would be resolved. So I maintain what I have said: for a typical ii observation a 100 Ghz sampling rate is not only possible, it is too the best possible. Sorry, I like computing and giving definite values :-) Yvan Bozzonetti. --part1_196.9365c60.2a535ade_boundary Content-Type: text/html; charset="US-ASCII" [ AUTOMATICALLY SKIPPING HTML ENCODING! ] Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=19391