{TAIL ~ Apparatus} and {HEAD ~ method} for controlling tracking and focusing servo in a holographic digital data storage system 
{ TAIL ~ Apparatus } and { HEAD ~ method } for controlling tracking and focusing servo in a holographic digital data storage system
TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH