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Message ID: 1888     Entry time: Thu Jan 7 09:44:52 2021
Author: Paco 
Type: DailyProgress 
Category: Optics 
Subject: Shaping the OPO cavity mode 

Summary of solution number 2 (from previous post). 

After installing the lenses, mirrors and some minor alignment, took the beam profile around the expected minimum waist position (~102" from laser head). The beam profile is astigmatic as can be seen from the plot below (red / blue = x / y), so the mode matching will be suboptimal from the start. 

Taking the geometric mean of the waists (w = sqrt(wx * wy)) we represent our nominal mode and find a min waist of 36.8 um (shaded region in the plot).

The OPO cavity model targets a min waist of 35.5 um (for an optimal Boyd--Klein parameter of ~2.7), but solutions exist with slightly shorter cavities and slightly larger waists which would only compromise the optimal Boyd--Klein parameter to ~2.55 for the sake of better mode matching. I think this is a good place to move out of calculation-land and see how well we can make the cavity work in reality.

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