scottprahl / laserbeamsize Goto Github PK

When I use your code:

import imageio.v3 as iio
import laserbeamsize as lbs

file = "https://github.com/scottprahl/laserbeamsize/raw/master/docs/t-hene.pgm"
image = iio.imread(file)

x, y, dx, dy, phi = lbs.beam_size(image)
print("The center of the beam ellipse is at (%.0f, %.0f)" % (x, y))
print("The ellipse diameter (closest to horizontal) is %.0f pixels" % dx)
print("The ellipse diameter (closest to vertical) is %.0f pixels" % dy)
print("The ellipse is rotated %.0f° ccw from the horizontal" % (phi * 180/3.1416))

I can get the expected results.

But then I follow your instructions from the screenshot1.png:

"A visual report can be done with one function call:

lbs.beam_size_plot(beam)
plt.show() "

The code would return error: AttributeError: module 'laserbeamsize' has no attribute 'beam_size_plot'，pls see the screenshot2.png.

I wonder whether there is some trouble with my understanding on your code? And I also search the "beam_size_plot" in all the API from your link "https://laserbeamsize.readthedocs.io/en/latest/index.html",
and cannot find the "beam_size_plot" attribute.

A colleague of mine brought up that the clipping to zero done in these functions is not mentioned in the iso standard. Therefore this wouldn't be completely iso conform. Instead, negative numbers should be used for the next steps. Would you be interested in changing this?

I noticed that you have a focused_diameter function for the diffraction limited spot size. In the function, the size is not proportional to the $M^2$, but $(M^2)^2$.

This is different to what I would expect and other treatments of this. Nevertheless, I was able to dig up the equation in the referenced text and it is indeed $M^4$. Although interestingly that seems inconsistent with their own definition in their figure 12.30 which is immediately above the equation, $d_0 = M^2 d_{00}$. And also as a sanity check, consider when defined by divergence angle, $M^2$ is inversely proportional to wavelength. Then wavelengths would not cancel and you would have the situation where the focused spot size decreases as wavelength increases.

Just wondering if the equation is right or I have some confusion here.

Thank you for contributing this library and the documentation, I have found it very useful and works great so far. I shall now be able to retire my personal, much less complete beam profiling code.

When we can expect ISO 11146-2 implementation in this project ? :)

Dear Scott,

Thank you for this amazingly useful library.
I have just discovered that Gaussian fit seems to be invalid for heavily astigmatic beams, and therefore, the function returns the incorrect beam diameters. Please refer to the image below.

Is there any parameter to overcome the problem?

UPD
It seems (from the values) that dx and dy are just mixed up here

Regards

Hello!

I'm getting wrong beam diameter estimation. Here is the result of lbs.beam_size_plot(beam, pixel_size=5.2, units='µm') :

Original image: image.zip

Hi Scott Prahl,
Thanks for code. I've just used your code in data processing.
But i find data printed differs from data in plot with my experiment data.
And i cannot find what happened to this. Please help~

Here is the detailed information.

Data Printed

         laserbeamsize
M2x      1.29 ± 0.03   
M2y      1.07 ± 0.11   

d0x       152 ± 3 µm   
d0y       135 ± 14 µm  

Thetax    5.28 ± 0 mrad
Thetay    4.95 ± 0 mrad

z0x       -276 ± 1 mm  
z0y       -277 ± 3 mm  

zRx       29 ± 1 mm    
zRy       27 ± 6 mm

PLOT

Experiment data

lambda4 = 488e-9
d_scan_head = 0
f = 150
z = np.array([210, 220, 230, 240, 250, 260, 270, 280, 290, 300, 310, 320,
              760, 770, 780, 790, 800, 810, 820, 830, 840, 850]) * 1e-3
dx = np.array([397.4, 330.2, 284.4, 242.8, 192.6, 167.1, 142.1, 148.5, 180.7, 206.1, 242.3,
               287.5, 2570.9, 2622.5, 2675.6, 2726.5, 2780.2, 2832.2, 2886.8, 2939.3, 2992.1, 3024.3]) * 1e-6
dy = np.array([382.3, 329.4, 277.9, 226.1, 182.1, 149.1, 128.5, 126.3, 145.8, 178.2, 220.7,
               263.7, 2465.3, 2503.9, 2540.6, 2574.7, 2608.4, 2641.9, 2677.1, 2712.5, 2739.9, 2768.1]) * 1e-6

When specifying the phi argument of lbs.beam_size, a zero value (0.0) is not accepted.
It is, however, useful to do so, e.g., for measuring the m2 of an astigmatic beam.

Looking into the code, I'm pretty sure the reason is in line 205 of laserbeamsize/analysis.py:

phi_ = phi or phi_

There is a workaround I used, that is specifying phi as a really small but nonzero value or 180degrees, however I don't think this is elegant and yields unexpected results.

I think a robust fix would be a change to

phi_ = phi if phi is not None else phi_

in lines 205 and 223 of laserbeamsize/analysis.py.

This would require no further changes.
Would you be interested in considering this?

Thanks for this great module, I use it all the time!

Small MWE

>>> phi = 0.0
>>> phi_ =  1.0
>>> phi or phi_ # Gives phi_, even though phi is defined
1.0
>>> phi if phi is not None else phi_ # Works as expected
0.0

I like this module, as is makes analysis very easy. However, I wonder about the fitting for M2. Especially I refer to

def _beam_fit_fn_(z, d0, z0, Theta): """Fitting function for d0, z0, and Theta.""" return d0**2 + (Theta*(z-z0))**2

I understand the idea of fitting d(z)^2 = ... wwithout the sqrt. But if I change the input from d**2 to d and also the function from d0**2 + (Theta*(z-z0))**2 to np.sqrt(d0**2 + (Theta*(z-z0))**2), I get different results.

Has anyone an idea, where this change comes from and how to get the proper output? Which of the two versions is right?

Hello!

I have a highly astigmatic laser diode. At some point after a lens I getting this with lbs.beam_size_montage():

No problems with estimating the center of the beam, but axes are rotated by 45 degrees. Laser modes are aligned along x and y axes, no need to rotate them (almost).

Is there any type of workaround for this problem?

Here is the original image from Thorlabs DCC1545M: astigmatic_beam.zip

P.S. Thanks a lot for this project !!!