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Message ID: 162     Entry time: Wed Jul 8 17:29:46 2009
Author: Connor Mooney, Michelle Stephens 
Type: Laser 
Category: Fiber 
Subject: Beam Divergence of 495mW NPRO 

We made a set of beam width measurements of the 495 mW laser using the Beamscan. All values were taken at (1/e^2) of the peak intensity, in micrometers. The distances were taken in units of inches (no metric-based rulers).

Here is our data: 

Distances (in inches): [2 3 4 5 6 7 8 9 10 12 14 16 18 20 22]

Beam Diameters (in micrometers): [357 364 413 448 528 608 690 758 854 1043 1216 1403 1624 1812 1999]

Again, we least-squared fit the data to the characteristic curve parametrized by the waist location and size, and found that the waist size is 178 micrometers, located 4.6 cm. in front of the aperture.

THINGS TO NOTE:

First, DMass mentioned he suspects that the beamscan is impaired, so we're not sure how well it is acting.

Second, Rana noted that the best indicators of the parameters of interest are data points taken far from the waist, where the beam width grows close to linearly with distance.  We took  lots of data points in the nonlinear regime, as seen on the attached plot. It might be a good idea to take more data points further away and refit our data.

Lastly, this laser is more stable than the 1W NPRO, with fluctuations of only 1-3 micrometers around the reported beam width values rather than the 40-50 we saw for the 1W.

The directory for our code is /users/cmooney/Beamscan_495mW.m

Here is the code:

%This is a graphical representation of beam width data taken for the 495 mW NPRO
%Laser, taken on July 8, 2009.

%W1 is the full width at 1/(e^2)*(peak intensity) taken at 1.00A driving
%current (around 150 mW) for the axis A1 as labelled on the BeamScan. Measurements are
%in micrometers.

W1 = [357 364 413 448 528 608 690 758 854 1043 1216 1403 1624 1812 1999];

%S1 is the standard deviation of the measurements given in W1.

S1 = [0.3 0.3 0.4 0.4 0.4 1.2 0.8 0.8 1 1 2.7 2.9 1.6 1.6 2.2];

d = 2; %distance from laser aperture to its base, from which it is easier to measure distance
D = [0 1 2 3 4 5 6 7 8 10 12 14 16 18 20]; %distances (in inches) at which measurements were taken
Ds = 2.54*(D+2)/100; %conversion to meters

W1s = 0.5*W1/(10^6);
S1s = S1/(10^6);

errorbar(Ds,W1s,S1s,'.')
title('Beam Width vs. Distance from Laser');
xlabel('Distance (m)');
ylabel('Beam Width (m)');

%This is a brief program to assist in the measurement of width of a
%Gaussian beam. Its wavelength is 1064 nm.

xdata = Ds;
ydata = W1s;
 
a0 = [.0001, .2]  % Starting guess
[a] = lsqcurvefit(@myfun,a0,xdata,ydata)

w_0 = a(1);
Zo = a(2)
L = 1064*10^(-9);
Dmax = 1;
sh = 0.35;
dt = (Dmax+sh)/10000;
Z = -sh:dt:Dmax;

Wt = w_0*(1+(((Z+Zo).*L)/(pi*w_0^2)).^2).^(1/2);

hold on;
plot(Z,Wt);

Attachment 1: beamdiv495mW.pdf  7 kB  | Hide | Hide all
beamdiv495mW.pdf
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