A portion of the light emitted by laser 850 passes through a lens , the semi reflective layer, or coating, 822 and is reflected by highly reflective layer, or coating, 834 and sensed by detector 852, which senses modulations in {HEAD ~ light intensity} based on the presence or {TAIL ~ absence} of a pit or land in a particular spot on the highly reflective layer or coating 822 
based on
A portion of the light emitted by laser 850 passes through a lens , the semi reflective layer , or coating , 822 and is reflected by highly reflective layer , or coating , 834 and sensed by detector 852 , which senses modulations in { HEAD ~ light intensity } based on the presence or { TAIL ~ absence } of a pit or land in a particular spot on the highly reflective layer or coating 822
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH