# Laser basics

1. Jul 30, 2017

### joslaz90

Hey guys!

I am currently working on some tasks to improve and expand my skills,
but I can not go on with the following task

An Nd-YAG laser (D=5mm diameter) is focussed with a lens (f = 200mm).

I: How big is the laser beam at its waist? (Solved)

II: What is the largest bundle behind the lens occurring in the optical axis (beam axis)? (Solved)

III: How long is the zone around the waist in which the beam is smaller than 0.2mm? (Solved)

IV: What is the average power density? (P= 3 Watt)

V: What is the peak power when the laser delivers the 3 watts in the form of 10000 pulses per second, each of which is 20 ns long?

To I:

(1060nm wavelength)

With
d= 2,44 α x f / D
I get as size for the laser beam at a waist of 1.035x10-4m

((2,44x1.06x10-6m x 2 x 10-1m)/5x10-3m)

To II:

tan α = 0,5D - 0,5 d /f

= 2,5 x 10-3m - 0,5 x 1.035 x 10 -4m / 2 x 10 -1m
= 0,01225
tan -1(0,01225)=0,702
α = 0,7°

To III:

tan α = 0,2mm / a
a = 0,2mm / tan α
=16,3mm

To IV:
I = P / A =

P = 3 W

I= 3W / 0,5 x 1.035 x 10-4m2Pi

Am I right with these considerations / approaches?

Can you help me with the last two tasks?

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Last edited by a moderator: Jul 30, 2017
2. Aug 4, 2017

### PF_Help_Bot

Thanks for the thread! This is an automated courtesy bump. Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post? The more details the better.