You can aslo use isopropyl alcohol (99%) and if you use a cotton swab, pull the tip a bit and roll it between your fingers so that the alcohol-soaked material enters the window and then turn gently... do the same this time with the dry tip to pick-up any fibers left and finally a quick blast of compressed air to loosen any prticles of dust and microfibers.
I hope that the gunk hasn't literally "cooked" on the diode window... there's little to be done then...
- Robert