# Determine the intensity profile and fwhm for gaussian beam.

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1. Nov 27, 2015

### Aerozeppelin

1. The problem statement, all variables and given/known data

A beam of wavelength 600 nm has initially an intensity profile of Gaussian shape with a
fwhm of 1 mm. Determine the intensity profile and fwhm 10 meter away.

2. Relevant equations

FWHM = λ/(2NA√(1 + I/Is))

3. The attempt at a solution

FWHM1 = 1mm = 600 nm/(2NA√(1 + I/Is))

(2NA√(1 + I/Is)) = 0.0006m
NA2(1+ I/Is) = 0.00015

10meters away :

NA2(1+ I/Is) = (0.00015)/10 = 0.000015

2. Nov 27, 2015

### blue_leaf77

Where is the initial information are given? Is it at the beam waist?

3. Nov 28, 2015

### Aerozeppelin

This is all the information given!

4. Nov 28, 2015

### blue_leaf77

You have to know either the beam waist diameter or the distance between the initial plane and the beam waist. Without these information you can only guess what the question maker means with "initially" in the question's wording.

5. Dec 2, 2015

### Aerozeppelin

There must be a solution as it was on an exam?

6. Dec 2, 2015

### blue_leaf77

If I were to face such a problem in an exam, exactly worded as you have written, I would be most likely not overwhelmed by shyness to ask the prof for a greater detail about the initial plane.