[Laser] Re: Can anyone explain what a Steradian

[steve kavanagh]

A steradian is a measure of "solid angle".  There are
4 x Pi steradians in a sphere.  There are about 3283
square degrees in a steradian.

So if a diode emits a beam with a square cross-section
10 degrees by 10 degrees the beam subtends a solid
angle of 100 square degrees or about 0.03 steradian.

A measure in W/sr is simply the radiated power per
unit of solid angle.  In the above example if the
diode emits a power of 5 mW then it can be described
as producing about 164 mW/sr (assuming the intensity
across the beamwidth is constant for sake of
simplicity).  

If the beamwidth (in each of two planes) one quarter
as much, then for the same power the power per unit of
solid angle is 16 times as high.

Steve VE3SMA

______________________________________________________________________ 
Post your free ad now! http://personals.yahoo.ca