i had a diode that had terrible spotting (probably due to an unclean work environment), the spot constantly looked blurry and out of focus.
A q-tip and rubbing alcohol worked great. Also, I found that after cleaning the diode, let the diode sit (in its module) face down. this keeps any additional ipurities from pooling on the window.
Using the q-tip method it took me several tries to figure this out. After cleaning the window when i turned on the laser the alcohol would evaporate but leave additional spotting. So remember to clean, test to see that it is clean, and then leave the diode alone for an hour or so to completely dry.