time period between bursts the two lines of photocharge for each event stored in storage region 102 can be transferred to a read out means represented in fig1 as a first horizontal charge coupled device 104 and a second separate horizontal charge coupled device 106 in accordance with an exemplary embodiment the first horizontal charge coupled device 104 can be used to store a first photocharge accumulated by the accumulating means during a first sample time e g including a laser pulse superimposed on background illumination while the second horizontal charge coupled device 106 can be used to store a second photocharge accumulated by the accumulating means during a second sample time i e background illumination alone photocharge transferred form the storage region to each of the first and second horizontal charge coupled devices can be subsequently transferred to a means for generating a differential output proportional to a difference between the first photocharge and the second photocharge for example in accordance with the exemplary fig1 embodiment the generating means can include a first buffer output amplifier 108 and a second buffer output amplifier 110 and a third differential amplifier 111 for differentially combining the first and second photocharges in accordance with the.