Question

Q1. (2pts) A ImW laser beam has a 2 mm diameter operating at wavelength near 600 nm. traveling in air. Calculate the irradiance of the source I, and determine the amplitude of the electric field Eo assuming all the wavefronts are homogeneous. Type to enter text 02. (2pts) For a given laser power P and beam area A formulate the beam energy density if the divergence of the beam is negligible? Using the formula you obtain, calculate the beam energy density for Questionl and confirm your result for Question I Type to enter text Q3. (Ipts) Assume now you have I mW point source not a laser, what is the irradiance le. 0.5 m away from your the source. Compare this number with the answer in Question 1 and explain the reason for such difference in the order of magnitude. Type to enter text

Answer 1

Question 1 :

P = power of the laser = 1 mW = 0.001 Watt

d = diameter = 2 mm = 0.002 m

r = radius = diameter/2 = d/2 = 0.002/2 = 0.001 m

A = area = 4$\pi$r² = 4 (3.14) (0.001)² = 12.56 x 10^-6 m²

Irradiance is given as

I = P/A

I = 0.001/(12.56 x 10^-6 )

I = 79.6 W/m²

E_o = amplitude of electric field

using the equation

I = (0.5) $\epsilon _{o}$ c E_o²

79.6 = (0.5) (8.85 x 10^-12) (3 x 10⁸) E_o²

E_o = 244.87