All,
I made a bunch of test cuts in 5mm acrylic with and without PPI. I cut 4 samples. The "control" was the system setup without any PPI, only on/off as is typical. Then I tested PPI with 3 different pulse widths, 2.5ms, 3ms, and 5ms and did my best to analytically and quantitatively compare them.
First the control (no PPI). In order to make this as comparative as possible, I reduced the power level of the constant on laser to just barely on. I'm not sure how others laser systems compare, but that is setting my power level pot to just past 9 o-clock, about 25% of the way around. This produced cut depths that were comparable to PPI at the same feed rates. I don't really know what power level that equates to in a quantitative way because I can't measure that, but this allowed me to compare the results.
For each test, I ran the laser at 400, 200, 100, 50, 25, and 12.5 mm/min. For the PPI tests, I set the PPI to 400, 800, 1600, 3200, 6400, and 12800 respective to the feed rate so that the "cut energy density" would remain the same. The power setting for all PPI tests was 100%. For each test I set up 25 x 120 x 5 mm acrylic piece set up on end so the laser was cutting into the face with dimensions of 5x120 mm. I made 15mm cuts for each test and spaced them on 18mm centers.
To evaluate each cut, I measured the maximum penetration, the minimum penetration, and did something like an "eyeball average" which was more or less a median penetration. Then I did several semi-quantitative measures of heat effects. I counted the number of bubbles on the side of the cut. Bubbles indicate sublimation/boiling of the solid/melted-solid which is not good and makes cuts look ugly. I also looked at the flat manufacturers sides and looked for distortions. I gave them a grade of 0, 1, or 2 with sub-grades of vs, s, or m. Grade 0 means no distortion by visible light reflection. I reflected light from our blinds (which are repeated strait light and dark regions) off of the flat manufacturers face into my eye. That way I could see with high sensitivity if there were any distortions of the flat face. Grade 1 meant that there was a distortion detectable by light reflection, and grade 2 meant that I could feel the distortion via tactile sense. The sub grades are vs (very slight effect), s (slight effect), or m (major/unmistakable). I also made a bunch of qualitative observations and recorded them as notes.
First the profile pictures. The pictures were taken at the same magnification, but the pieces wouldn't fit in the widest zoom with the macro lens I have so there are 2 for each.
1) control:

- Control Profile 1

- Control Profile 2
2) PPI at 2.5 ms

- PPI 2.5ms Profile 1

- PPI 2.5ms Profile 2
3) PPI at 3 ms

- PPI 3ms Profile 1

- PPI 3ms Profile 2
4) PPI at 5 ms

- PPI 5ms Profile 1

- PPI 5ms Profile 2
I also wanted to show the kerf at the top and be able to show the width. I colored the top with a sharpie to make the kerf show up better.

- Kerfs 1

- Kerfs 2
The order of the samples in kerf pictures is Control, 2.5ms, 3ms, and 5ms from top down. The feed rates are 400 to 12.5 from left to right for each.
** Post Continued, Out of Picture Space **