The beam width parameter of a laser beam with a Gaussian profile can be measured with the knife-edge method.

This package includes a general class for plotting and fitting of beam profiles, along with more specific classes for different methods of obtaining the profiles: swinging ruler, manual micrometer positioning, my custom LEGO NXT profiler.

python setup.py develop

import knifedge as ke

For manual knife-edge measurements using the 84/16 (or 90/10) method, the easiest usage is to enter the measurements and their metadata into a YAML formatted document with the following fields:

---
label: after 150mm lens
method: '90/10'
z_offset: 313
x_error: 0
wavelength: 1550
dz: [0, 25, 50, 100, 150, 300]
measurements:
- [12.301, 13.035]
- [11.512, 12.086]
- [11.906, 12.359]
- [11.748, 11.945]
- [12.630, 12.857]
- [11.494, 12.520]

• label: Text describing the beam.
• method: '90/10' or '84/16'. Other methods will be implemented later.
• z_offset: Distance (in mm) to a fixed reference point on the table.
• x_error: Optional: Estimate of the RMS error in determining the x-values. Default value is 0 if not states.
• wavelength: Wavelength of the light in nm.
• dz: Positions along the beam (in mm) at which the beam sizes have been measured. Must be same length as measurements.
• measurements: List of two-element lists of the measured x positions of the knife-edge at which the laser beam intensity reaches the 84% and 16% levels (or 90%/10%) of its full intensity.

Multiple traces can be contained in the same file, separated by the YAML document separator ---.

Loading and fitting is done in a single line, plotting can be done afterwards:

traces = ke.traces_from_file('path/to/measurement.yml')
for trace in traces:
    ke.plot_trace(trace)