Camilla, Sophie

The previous unit on the table, 0922, was measured to have a very nongaussian profile and the measure beam at the output of the table was not agreeing with modelling so we chose to switch it out for the spare unit, 0970. The Thorlabs beam profile measurements showed this unit to have a far more gaussian beam shape which was confirmed later in profiling. 

0922 was removed from the set up and returned to a box of CHETA spares. 0970 has been installed in the laser mount and initial profiling has begun. 
To find the q-factor at the laser we profiled the beam in the operation state, TEC = 25C and I=1A, using the nanoscan beam profiler. To reduce the possibility of any damaging back reflections off the profiler or dump we placed the 99:1 BS at 45 deg to QCL and profiled the reflection. The 99% beam was dumped. Additionally, the laser was turned off each time the beam profiler was moved. A photo of the set up is attached

The beam was profiled over the region 99mm to 469mm after the output and was a q-factor was found using a non-linear where M^2 = 1. This fit was worse then expected so a linear fit with a variable M^2 was also completed which fit much better but M^2 was 0.88 and 0.81 for x and y slices. Both plots are attached and the fitted q-factors are:

Nonlinear fit

qx: -233+/-5 + 120+/-6i mm
qy: -288+/-7 + 116+/-10i mm

Linear fit

qx: -221+/-20 + 113+/-61i mm,     M^2 = 0.88 ± 0.25
qy: -297+/-21 + 104+/-66i mm,     M^2 = 0.81± 0.25

We think the bad fit is due to the low power incident on the nanoscan effecting SNR and a slight angle of incidence onto the profiler, ≈ 3deg. We plan to run this measurement again tomorrow using a different beam splitter with a greater reflection coefficient and with more careful alignment.