Background subtraction
X-ray patterns measured through diamond-anvil cell often have very intense background. PeakPo provides background subtraction function to reveal weak peaks better.
Background subtraction is a convenient feature but also you need to be careful. Because of this concern, default setting for the Bg sub checkbox in the Plot control box in the Main tab is uncheck.
The parameters used for background subtraction can be found in the Bkgn tab. If you leave mouse pointer more than 1 s within a widget, it will show tooltips (balloon help). The numbers in the parenthesis in the label are the recommended values: N Points = 20, N Order = 10, N Iteration = 20.
When the Bg sub checkbox is not checked, you will find a raw base pattern plotted together with a dashed line, which is the background fit by the PeakPo. You need to carefully inspect if the background does not take away any intensities from diffraction peaks and if the background introduces any artifacts in the subtracted pattern. Some strange background fitting behavior is quite common mostly at the edge of the range you chose (ROI, region of interest).
(Recommendation) When you begin a new dataset, play with the different sets of background parameters. The most important parameters to optimize for your diffraction pattern are ROI Min and ROI max. Once you find satisfactory results you can perhaps use the same background parameters for the rest of your dataset as long as the background and the two theta range remain similar.
(Tip) For better result, it is a good idea to set ROI min and max values at an area without peaks. This way you can avoid strange structures near the edge of the ROI.
(Note) If your min or max values for two theta is outside of the range of the data, you will see that PeakPo tries to make background fitting for the entire two theta range. Please make sure your min and max values are within the two theta range of your data.