Hi, Bathgate
The Diag you mentioned in a previous post (see below) should work fine, The reflective media should be 0.150 thou. away and the length of about 3/4 to 1" to give Mach time to see the puls.
I'm Using a 5" disk hear with a optical window pickup with a slot length of 3/4", Works up to 3,000+ rpm, Longer slot higher rpm.
Hope this Helps, Chip