I applied the Imaging Unit position correction to have the same calibration factor for a different sample thickness. Basically, this correction makes the probe spot at the Photo Detector to have the same size. We wanted to check if the size is really the same by measuring it before and after the repositioning. To measure the beam size I removed the PD and placed a blade instead, the position of the blade is the same as the surface of the detector with an accuracy of about 2 mm. The blade is mounted on a translation stage with a micrometer screw moved manually. Since the beam size is much larger than the power meter, I placed a converging lens after the blade to converge the beam on the power meter. 

I temporarily used  my personal laptop to do the measurements because the PCI laptop got windows crashed.

I wrote a script in python to read the power meter for each position of the blade. The measurements are the integral of the gaussian profile, so I took the difference array and fit it with a gaussian. The fit procedure is a polyfit of the logarithm of intensity.

I took the measurement

 

without any sample (twice).         Beam radius: 2.68±0.03 mm (plot1 and plot2)

 

 

with Tama-size sample (twice).    Beam radius: 2.04±0.03 mm (plot3 and plot4)

 

with Tama-size sample and Imaging

Unit position correction (twice).    Beam radius: 2.76±0.05 mm (plot5 and plot6)

 

With the position correction the beam size is recovered with an accuracy of 3%

 

Then I checked how the positioning error might affect the size.

The position of the blade shifted by 1mm makes a beam size change less than 1%           plot7

The position of the Imaging Unit shifted by 1mm makes a beam size change less than 1% plot8

The position of the Imaging Unit shifted by 1mm makes a beam size change less than 1% plot8I applied the Imaging Unit position correction to have the same calibration factor for a different sample 

 

thickness. Basically, this correction makes the probe spot at the Photo Detector to have the same size. 

We wanted 

 

to check if the size is really the same by measuring it before and after the repositioning. To measure the beam 

 

size I removed the PD and placed a blade instead, the position of the blade is the same as the surface of the 

 

detector with an accuracy of about 2 mm. The blade is mounted on a translation stage with a micrometer screw moved 

 

manually. Since the beam size is much larger than the power meter, I placed a converging lens after the blade to 

 

converge the beam on the power meter. 

I wrote a script on python to read the power meter for each position of the 

 

blade. The measurements are the integral of the gaussian profile, so I took the difference array and fit it with a 

 

gaussian. The fit procedure is a polyfit of logarithm of intensity.

I took the measuement

without any sample (twice). Beam radius: 2.68±0.03 mm plot1 and plot2

 

 

with tama-size sample (twice). Beam radius: 2.04±0.03 mm plot3 and plot4

 

with tama-size sample and Imaging

Unit position correction (twice). Beam radius: 2.76±0.05 mm plot5 and plot6

 

With the position correction the beam size is recovered with an accuracy of 3%

 

Then I checked how the positioning error might affect the size.

The position of the blade shifted by 1mm makes a beam size change less than 1% plot7

The position of the Imaging Unit shifted by 1mm makes a beam size change less than 1% plot8