Quote:
Originally Posted by Suzy_A
Hi Peter,
As you are probably aware, in SI units, Power (in watts) is defined as energy (in Joules) over time (seconds). Similarly, watt per square meter or a joule per second per square meter is power per unit area (m2).
A beam of photons at 1250 watts per square meter will carry the same amount of power per unit area and hence energy per unit time and area irrespective of the wavelength, spatial or chromatic coherence....
Am I still coherent or has the red wine and late night got to me?
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Well said Susan...as coherent as a He-Ne laser!
I see what you are saying with regard to power per unit area.....but I suspect there is also the rub...assuming a 100mw beam diverges to say 200mm after a kilometer or so (this approximates my pointer's performance) then the flux in our 1mm beam is being spread over pi*r**2 in area or about 31,000x the area....hence if a
person with say a 6mm pupil is "flashed" we'd have about 5000x less energy going into their eye than say over a few metres...about 0.02 of a milliwatt?