Re: Can you photograph a light beam stopping midair?

Taking a picture of a laser pulse (easier than a beam) going through some material is hard, since light travels close to 30cm per nanosecond in most materials. So to get some good resolution (that is, see it halfway through a ~1cm frame), you only have a few picoseconds of leeway.

This kind of timing is possible using today's femtosecond lasers, and some of the "quantum computing" experiments you may have heard about do this exact thing, in effect. The timing is so fast, though, that a traditional "photograph" isn't possible to take in the usual sense. You need to be able to send an "imaging" pulse through the material and collide with the "travelling" pulse half-way through, and record the differences in the properties of the material where the travellin pulse has passed and where it hasn't.

For something similar, try this link: http://kemi.aau.dk/research/femtolab/ion_imag.html

-Greg Billock

[Moderator note: The light pulse is only detectable if it is traveling through some medium that scatters the pulse or that is changed by the pulse. In a vacuum, there is no way to see the light pulse unless the detector intercepts the pulse.]