A 2 mW laser shines vertically polarized red light (lambda = 650 x 10^-9 m) from

Question

A 2 mW laser shines vertically polarized red light (lambda = 650 x 10^-9 m) from left to right through two polaroid filters whose axes of polarization are shown below as DOTTED LINES. The light wave emerging from the last polaroid has a maximum electric field of 51 V/m. a) P: What is the maximum value of the magnetic field of the light wave emerging from the last polaroid? b) P: What is the intensity of the light wave emerging from the last polaroid? c) P: What is the diameter of the laser beam hitting the first polaroid. d) P: Repeat part c) if the laser were replaced with a 2 mW unpolarized spotlight.

Explanation / Answer

apply Intensity I = power/area = Emax^2/2uoC

where Emax = EF max = 51 V/m

uo is 4pi e-7

C is Speed of light = 3e8 m/s

so

Area A = P * uoC/Emax^2

Area = 2e-3 * 4*3.14 e-7 * 3e8/(51*51)

Area A = 2.89 e -4 m^2

Area A = pi r^2 = 2.89 e-4

r^2 = 2.89 e-4/3.14

r^2 = 92.27 e-6

r = 9.6 mm

diameter = d = 2r = 19.21 mm or 1.921 cm

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