1. February 2004 Charles A. DiMarzio, Northeastern University 10464-10-1 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

2. February 2004 Charles A. DiMarzio, Northeastern University 10464-10-2 Topics PMT Dynode Circuits –Conventional Voltage Divider –Cockroft-Walton Dynode Modulation –Application –Technique

3. February 2004 Charles A. DiMarzio, Northeastern University 10464-10-3 PMT Concept

4. February 2004 Charles A. DiMarzio, Northeastern University 10464-10-4 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.

5. February 2004 Charles A. DiMarzio, Northeastern University 10464-10-5 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.

6. February 2004 Charles A. DiMarzio, Northeastern University 10464-10-6 Cockroft-Walton Divider Emitter-follower-like circuit maintains the dynode voltages without high power consumption.

7. February 2004 Charles A. DiMarzio, Northeastern University 10464-10-7 DOT: Using Modulated Light Laser Demod t P t P

8. February 2004 Charles A. DiMarzio, Northeastern University 10464-10-8 Physical Reason for Dispersion Imaginary part of diffusive wavenumber increases with frequency Easy to understand in terms of multiple paths. m100574a.m

9. February 2004 Charles A. DiMarzio, Northeastern University 10464-10-9 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

10. February 2004 Charles A. DiMarzio, Northeastern University 10464-10-10 Detectors Sources 6 cm 4 cm Mid-line Data Set I - 98-05-14 At Rest Passive movement of right arm Passive movement of right arm From David A. Boas - MGH NMR Center Functional Imaging of a Neonate

11. February 2004 Charles A. DiMarzio, Northeastern University 10464-10-11 Demodulation Techniques Laser t P t P Transmitter LO 300.00MHz 300.01MHz 10kHz Ref 10kHz Sig DC Out 300MHz Sig

12. February 2004 Charles A. DiMarzio, Northeastern University 10464-10-12 PMT Time Delay and Bandwidth Dynode Paths Transit Time Variations

13. February 2004 Charles A. DiMarzio, Northeastern University 10464-10-13 Long and Short Paths in PMT

14. February 2004 Charles A. DiMarzio, Northeastern University 10464-10-14 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

15. February 2004 Charles A. DiMarzio, Northeastern University 10464-10-15 PMT Dynode Modulation Example -900-850-800-750-700 0 2 4 6 8 10 V 2, Dynode Voltage, Volts G 13, Two-Stage Gain Operating Point m10464_10a.m