Calculating Focal Length and Minimum Diameter for Laser Beam Diffraction

AI Thread Summary
To calculate the focal length for focusing a helium-neon laser beam to a 10 micrometre diameter spot at 8.0 cm, the relevant equations involve the parameters of wavelength and diameter. The equation w = (2.44lambda * focal length) / diameter is central to the calculations. An attempt to solve for focal length using 2.5lambda yielded an answer of 0.001 cm, but this result was not confirmed by others in the discussion. Participants expressed difficulty in finding modifications or alternative methods for the equations provided. Clarification on the correct application of these formulas is needed to resolve the calculations.
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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 separate 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.
 
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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
 
Oh! So did you get the right answer using that formula?
 
nope, still nothing, anyone know anything??
 

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