Actually it depends on the beam type. For a gaussian beam laser Inverse law applies but after the photons reach to a specific amount of density they will get out of the resonance cavity from the less reflecting end. Till here, inverse law applies but after the beam is out it will be degrading less than an isotropic common source due to regeneration of photons emerging from the applied electric field to lasing material (YAG). Assuming the same conditions, laser beam intensity will be very close as if it obeys the inverse square law but this is not a practical consideration. In theory it differs and can be explained by Michelson Interferometer but due to very small lengths in the cavity it will not be a practical issue. On Thu, Jun 23, 2011 at 5:34 PM, Kerry Wentworth wrote: > Carey Fisher wrote: >> On Thu, Jun 23, 2011 at 9:31 AM, Michael Watterson wr= ote: >> >> >>> On 23/06/2011 13:15, Yigit Turgut wrote: >>> >>>> Intensity of light is reduced by inversely proportional to >>>> square of the distance. >>>> >>> not true with a laser. That would imply the spot doubles in diameter >>> with double distance. many don't >>> -- >>> >>> >>> The Inverse Square Law only applies to a point (or equivalent) source >>> >> radiating energy in "all" directions - "all" directions meaning a spheri= cal >> surface subtending an angle of 4pi steradians. >> Carey >> > Correct me if I'm wrong, but here is my understanding of it: > > Any beam of electromagnetic waves must be diverging or converging, as it > would be physically impossible to make them exactly parallel. =A0If the > energy density is measured at distance d from the focal point, and also > at distance 2d from the focal point, the energy density at 2d will be > 1/4 the energy density at d. =A0At 3d, it will be 1/9 what it is at d. > The inverse square law applies, you just need to measure from the right > starting point. > > Kerry > > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .