# How to find the FWHM-diameter of the SH beam?

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1. Nov 7, 2016

### telekom90

1. The problem statement, all variables and given/known data
Assume a Gaussian laser beam ( 1064 nm wavelength) having an FWHM-diameter(intensity) of 5 mm. By transmission through a thin nonlinear crystal, a new wave is generated that is proportional to the square of the incoming field (and therefore radiates at twice the frequency, or 532nm wavelength). This second harmonic (SH) beam co-propagates with the fundamental laser beam. What is the FWHM-diameter of the SH beam?

2. Relevant equations

dFWHM = ω(z)√2ln2

3. The attempt at a solution
λ =1064nm, dFWHM=5 mm$,$ λSH=532 nm .
I can't solve this problem because I don't know how to relate this equation "dFWHM=ω(z)√2ln2= 5mm " with the FWHM-diameter of second harmonic (SH) beam?!

2. Nov 11, 2016

### blue_leaf77

The key word is
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