Huh??? Pardon my ignorance, my experience with laser internals is quite=20 limited. Almost exclusively Excimers, KrF 248nm, and not particularly=20 deep even with them. I was referring to electromagnetic waves in a=20 vacuum or equivalent, outside of the laser. Kerry Yigit Turgut wrote: > 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: > =20 >> Carey Fisher wrote: >> =20 >>> On Thu, Jun 23, 2011 at 9:31 AM, Michael Watterson w= rote: >>> >>> >>> =20 >>>> On 23/06/2011 13:15, Yigit Turgut wrote: >>>> >>>> =20 >>>>> Intensity of light is reduced by inversely proportional to >>>>> square of the distance. >>>>> >>>>> =20 >>>> 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 >>>> >>>> =20 >>> radiating energy in "all" directions - "all" directions meaning a spher= ical >>> surface subtending an angle of 4pi steradians. >>> Carey >>> >>> =20 >> 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. If 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. At 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 > > =20 --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .