February 2004 Charles A. DiMarzio, Northeastern University ECEG287 Optical Detection Course Notes Part 10: More on the Detector as a Circuit Element Profs. Charles A. DiMarzio and Stephen W. McKnight Northeastern University, Spring 2004

February 2004 Charles A. DiMarzio, Northeastern University Topics PMT Dynode Circuits –Conventional Voltage Divider –Cockroft-Walton Dynode Modulation –Application –Technique

February 2004 Charles A. DiMarzio, Northeastern University PMT Concept

February 2004 Charles A. DiMarzio, Northeastern University PMT Dynode Chain Currents (1) V 0 =-HV icic G 12 i c G 13 i c G 14 i c R 01 R 12 R 23 R 34 V1V1 V2V2 V3V3 Assumption is made that all V/R are much larger that corresponding Gi c.

February 2004 Charles A. DiMarzio, Northeastern University PMT Dynode Chain Currents (2) V 0 =-HV icic G 12 i c G 13 i c G 14 i c R 01 R 12 R 23 R 34 V1V1 V2V2 V3V3 At high cathode currents, higher dynode currents modify dynode voltages.

February 2004 Charles A. DiMarzio, Northeastern University Cockroft-Walton Divider Emitter-follower-like circuit maintains the dynode voltages without high power consumption.

February 2004 Charles A. DiMarzio, Northeastern University DOT: Using Modulated Light Laser Demod t P t P

February 2004 Charles A. DiMarzio, Northeastern University Physical Reason for Dispersion Imaginary part of diffusive wavenumber increases with frequency Easy to understand in terms of multiple paths. m100574a.m

February 2004 Charles A. DiMarzio, Northeastern University TECHNOLOGY Near-infrared light Fiber optics Computed Tomography ADVANTAGES Optical contrast Portable - bedside, ambulance Continuous Inexpensive DISADVANTAGES Resolution Depth penetration From David A. Boas - MGH NMR Center DOT Instrumentation at MGH

February 2004 Charles A. DiMarzio, Northeastern University Detectors Sources 6 cm 4 cm Mid-line Data Set I At Rest Passive movement of right arm Passive movement of right arm From David A. Boas - MGH NMR Center Functional Imaging of a Neonate

February 2004 Charles A. DiMarzio, Northeastern University Demodulation Techniques Laser t P t P Transmitter LO MHz MHz 10kHz Ref 10kHz Sig DC Out 300MHz Sig

February 2004 Charles A. DiMarzio, Northeastern University PMT Time Delay and Bandwidth Dynode Paths Transit Time Variations

February 2004 Charles A. DiMarzio, Northeastern University Long and Short Paths in PMT

February 2004 Charles A. DiMarzio, Northeastern University Mixing at the Dynode V 0 =-HV icic G 12 i c G 13 i c G 14 i c R 01 R 12 R 23 R 34 V1V1 V2V2 V3V3 V2V2 t

February 2004 Charles A. DiMarzio, Northeastern University PMT Dynode Modulation Example V 2, Dynode Voltage, Volts G 13, Two-Stage Gain Operating Point m10464_10a.m