At about 1345, I flipped the helicity of the laser light.
Did not do a degree of circular polarization check as the angles are very well known and previous measurements have affirmed the repeatibility of such flips.
The λ/4 plates angles are now 135° (double-pass beam) and 105° (single-pass beam).
Target operators note that this will flip the direction on the NMR peaks (and also change the EPR from "hat" to "well").
Also note that this has nothing to do with the beam helicity or
the beam half wave plate (BHWP).