Laser beam diffraction

  • #1

Homework Statement



A scientist needs to focus a helium-neon laser beam (lamda = 633nm) to a 10 micrometre diameter spot 8.0 cm behind the lens.

a) What focal-length should she use?
b) What minimum diameter should she use?

Homework Equations



w = (2.44lambda * focal length) / diameter

theta = 1.22lamda/diameter

Wmin is apprx equal to 2.5lambda....apparently, but if you have a seperate method ignore this.

The Attempt at a Solution



i attempted to calculate w through 2.5lambda, then use that to calculate the focal length. the answer i got was 0.001cm.
 

Answers and Replies

  • #2
I cannot seem to find any modification of this equation anywhere, but it seems that this is the only equation that is used to solve this problem
 
  • #3
4
0
Oh! So did you get the right answer using that formula?
 
  • #4
nope, still nothing, anyone know anything??
 

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