It's interesting to note the immediate difference between a short nap (less than 45 mins) and one longer. I've never heard the pre nap coffee suggestions! I take naps frequently and hate when I over sleep or wake up from one longer than an hour and a half due to the groggy/grumpy side effects.
Try this - immediately before closing your eyes say to yourself "I need to wake up in 15 minutes". In exactly 15 minutes you will feel a subtle mental nudge that you need to act upon and open your eyes. You can as easily ignore it, in which case you will go right back to sleep. YMMV, of course, but it works for many people and it is seriously amazing.
The body's own clock is amazing. I've done this to wake myself up in the mornings successfully too!
I do it like this: when laying in bed right before falling asleep I imagine a flip-card clock and the whole thing is spinning, just spinning, then I imagine it stopping suddenly on the time that I want to wakeup. The really cool part is when you wake up at exactly that time the next morning with NO alarm clocks!
I once had a study partner who took quite precise power naps. I remember one occasion when he asked to be woken up after 16 minutes. At the end of the 16 minutes I was mid-paragraph so I finished the paragraph and then woke him (after probably 18 minutes). His comment was, "That wasn't 16 minutes."
Yep, I noticed I had this ability when I was a kid. Of I tell myself I've got to awake at a specific time then I always wake seconds before my alarm in the morning. Mysterious intuitive knowing by the sleeping-consciousness.
Really interesting and insightful piece!