Benm
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- Aug 16, 2007
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Looking at the video, and the website that now seems to work, i can see where the difference/problem is:
They use a LED with a bigass lens compared to a laser with a tiny output beam diameter, increasing atmospheric problems for the latter.
The comparison would have been fair if they used a beam expander on the laser to create and exit beam comparable of that of the led + lens system used. In that case any difference caused by coherence or lack of it would be visible.
Also, this was taken in the dark. If you did this experiment in the daytime it'd be impossible to see a led with a 20 cm lens 24 km away. If you took a laser and expanded its beam to 20 cm (say a 100x beam expander) it would likely be visible to the naked eye.
They use a LED with a bigass lens compared to a laser with a tiny output beam diameter, increasing atmospheric problems for the latter.
The comparison would have been fair if they used a beam expander on the laser to create and exit beam comparable of that of the led + lens system used. In that case any difference caused by coherence or lack of it would be visible.
Also, this was taken in the dark. If you did this experiment in the daytime it'd be impossible to see a led with a 20 cm lens 24 km away. If you took a laser and expanded its beam to 20 cm (say a 100x beam expander) it would likely be visible to the naked eye.
