In: Physics
A 225 mW horizontally polarized laser beam passes through a polarizing filter whose axis is 23° from vertical. What is the power of the laser beam as it emerges from the filter?
answer units must be in mW
if you consider that a vertical polariser, in an ideal world,
stop 100% of a horizontally polarised beam and if it were at 90° to
vertical (i.e. horizontal) then it would pass 100% of the beam. So
if you turn it just 23° from vertical it will be passing a possible
100% divided by 90° and multiplied by 23°, which gives 25.55%
If the input beam was 225mW then 25.55% of that is
57.5mW
This assumes perfect world scenario, that the polariser is 100%
transmissive when aligned, and 100% opaque when misaligned (not the
case in the real world)
Or
Method2)
The plane of polarization of the laser beam is vertical, so it
makes an angle of 90⁰- 23⁰ = 67⁰ with the polarizing filter
plane.
I = I₀cos²(67⁰)
= 225mW x 0.39²
= 34.35mW