Participants: Yuhang, Matteo, Yuefan, Marc, Emil

 

We designed and set up the mode-matching telescope for the green mode cleaner. First measurements indicate a very good mode matching and alignment to the mode cleaner.

 

To get good starting parameters we did a new beam profiling measurement of the green beam after the first 50:50 beamsplitter. An old measurement from last year (entry 613) could not be used, because the beam was changed in the meantime. The measured parameters varied quite significantly between minor and major axis (probably a measurement artefact, not strong indication of real astigmatism), but we could confirm that this does not significantly effect the mode matching solution. As a result we get a waist of 26µm roughly 10cm before the 50:50 beamsplitter (7cm after the EOM).

 

We did the beam fitting and and telescope optimization with the MATLAB toolbox 'a la mode'. There are several possible solutions with the available lens set and we chose one based on overall beam size (not too large) and by minimizing the sensitivity of the mode overlap to the lens position.

 

While setting up the beam path we reconfirmed the beam parameters with another profiling measurement while one of the two lenses was installed.

 

With the mode cleaner in place we performed a mode scan to do the final alignment. Both paths of the Mach-Zehnder interferometer were aligned individually to achieve very good contrast (first measurement indicates >95%).

 

Based on the mode scan, the final misalignment is <1% and the 2nd-order mode mismatch is about 1%.

 

During our work we had noticed that the beam shape was not quite Gaussian (some interference fringes and indication of clipping). This was traced back to a point before the first green Faraday, so it probably originates inside the SHG. We still need to see wether this significantly affects the mode cleaner transmission. This could be done by measuring the reflected power on and off resonance.

During our work we had noticed that the beam shape was not quite Gaussian (some interference fringes and indication of clipping). This was traced back to a point before the first green Faraday, so it probably originates inside the SHG. We still need to see wether this significantly affects the mode cleaner transmission. This could be done by measuring the reflected power on and off resonance.Participants: Yuhang, Matteo, Yuefan, Emil

 

 

We designed and set up the mode-matching telescope for the green mode cleaner. First measurements indicate a very good mode matching and alignment to the mode cleaner.

 

To get good starting parameters we did a new beam profiling measurement of the green beam after the first 50:50 beamsplitter. An old measurement from last year (entry 613) could not be used, because the beam was changed in the meantime. The measured parameters varied quite significantly between minor and major axis (probably a measurement artefact, not strong indication of real astigmatism), but we could confirm that this does not significantly effect the mode matching solution. As a result we get a waist of 26µm roughly 10cm before the 50:50 beamsplitter (7cm after the EOM).

 

We did the beam fitting and and telescope optimization with the MATLAB toolbox 'a la mode'. There are several possible solutions with the available lens set and we chose one based on overall beam size (not too large) and by minimizing the sensitivity of the mode overlap to the lens position.

 

While setting up the beam path we reconfirmed the beam parameters with another profiling measurement while one of the two lenses was installed.

 

With the mode cleaner in place we performed a mode scan to do the final alignment. Both paths of the Mach-Zehnder interferometer were aligned individually to achieve very good contrast (first measurement indicates >95%).

 

Based on the mode scan, the final misalignment is <1% and the 2nd-order mode mismatch is about 1%.

 

During our work we had noticed that the beam shape was not quite Gaussian (some interference fringes and indication of clipping). This was traced back to a point before the first green Faraday, so it probably originates inside the SHG. We still need to see wether this significantly affects the mode cleaner transmission. This could be done by measuring the reflected power on and off resonance.