enhanced the FID signal by remove dirt on the chamber tube. the dirt covered the laser and it was rotated, so a clean part of the tube on the laser path.
so, we measured the 30% duty again.
after we change to 20% duty. and the result disagree with old crystal. but after changed the crystal angle, the signal agrees with old crystal.
it is strange that, we has adjusted the crystal angle during 30% duty, the optimum angle is not same as 20% duty. we have to measure 30% duty again.