Originally Posted by 2ndServe
are there any good videos of advanced high level slice technique?
There probably are lots. Rosewall, Federer, Wawrinka, Youzny, and Haas come to mind. I think you might find lots more of what you're asking about by checking out vids of players from the '70s and '80s.
Anyway, below is a video of one way that I hit it. Yes, I know, contrary to your request, these are low level and not very advanced at all, but it works for me, and I didn't feel like searching for relevant pro vids.
What some posters said about not hitting it too choppy, hitting it almost flat, slightly undercut, with forward body movement if possible is good advice I think. Hitting it deeper and faster (penetration) is just a matter of the forward momentum you impart to the ball. A deep, hard hit, slightly undercut ball that skids real low can be tough for anybody to handle. But slices that hit in no mans land near the sidelines can be very effective also. (as I suppose you know, which is why you started the thread)