# Homework Help: Fresenel Diffraction

1. Apr 25, 2010

### grothem

1. The problem statement, all variables and given/known data
A point source of monochromatic light (500 nm) is 50 cm from an aperture plane. The detection point is located 50 cm on the other side of the aperture plane.

a) The transmitting portion of the aperture plane is an annular ring of inner radius .5 mm and outer radius .935 mm. What is the irradiance at the detector relative to the irradiance there for an unobstructed wavefront?

b) Answer the same question if the outer radius is 1.00 mm

c) How many half-period zones are included in the annular ring in each case?

2. Relevant equations
Rn = (n*ro*lambda)^1/2

3. The attempt at a solution
I don't even know where to start on this problem. I know R1 and R2 but I don't know how I can go from there to determine the irradiance. I know that irradiance is proportional to the electric field squared, but I'm still confused by this problem.
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution