Figure 1. Schematic of 3D tracking system. The 2D-EOD ( EOD1 & EOD2 ) and the TAG lens ( TAG ) deflect the laser along the XY and Z directions, respectively. The APD ( APD ) is used to collect fluorescence photons, which are sent to the FPGA ( FPGA ). FPGA is used for the position calculation algorithm, photon counting, control of the 2D-EOD as well as control and readout of piezoelectric nanopositioner ( NSxy and NZz ). Other components labeled in the figure: mirrors ( M ); lenses ( L# ); pinhole ( PH ); Glan-Thompson polarizer ( GP ); half-wave plate ( W1 ); dichroic filter ( DC ); objective lens ( OL , 100X NA = 1.49); fluorescence emission filter ( F ); beam splitter ( BS ); XY micropositioner stage ( MSxy ); Z micropositioner stage ( MSz ). Please click here to view a larger version of this figure.