1. Photonic Crystal Fiber for Radiation Sensors Feng Wu Khalid Ikram Sacharia Albin Feng Wu Khalid Ikram Sacharia Albin Photonic Laboratory Old Dominion University Department of Electrical & Computer Engineering Kaufman Hall Norfolk, VA 23529 Workshop on Innovative Fiber Sensors, CNU, Newport News, May 20, 2003

2. Outline  Introduction  Various Fiber Optic Radiation Sensors  Stimulated Electronic Transition  Microstructured Fibers  Radiation Sensing Mechanism  Summary

3. Introduction  Wavelength, Intensity, Phase & State of Polarization  Sensors for thermal, mechanical, electrical, magnetic and chemical effects  Fiber optic sensors: small size, low weight and low power  Distributed and multiplexed fiber optic sensor systems: low cost and high performance

4. Various Fiber Optic Radiation Sensors  Radiation sensors: ionization chambers, Geiger-Mueller counters, photographic emulsions,scintillators, and semiconductor junctions (temporary or permanent changes in conductivity)  Discrete devices: e.g., radiation safety badges- accumulate the total dose received during a known period of time. Location of radiation unknown if there are many sources  Dosimetry using radiation induced effects which increase the optical absorption in a fiber  Fiber scintillators: emitted light guided to a remote location  Distributed & Multiplexed Sensors: space and weight constraints, e.g., the space station

5. Stimulated Electronic Transition (SET) for Optical Memory  Large bandgap indirect semiconductor  Dope to create trap and recombination levels  Radiation excites electrons from the valence band to the conduction band through these levels-Writing  The traps store electrons-Optical Storage  Radiative recombination centers give photons-detection  The capture rates depend on their respective probabilities and densities  Optical stimulation of trapped electrons to produce photons- Reading

6. hv 1 hv 1 > (E r -E v ) hv 1 SET Process for Optical Storage Valance Band, E V hv 1 hv 3 hv 2 Conduction Band, E C EgEg ErEr EtEt hv 1 hv 1 > (E c -E r ) Optical Writing Optical Storage

7. hv 1 hv 1 > (E r -E v ) hv 1 SET Process for Optical Storage Valance Band, E V hv 1 hv 3 hv 2 Conduction Band, E C EgEg ErEr EtEt hv 1 hv 1 > (E c -E r ) Optical Writing Optical Reading hv 2 > (E c -E t ) hv 2

8. hv 1 hv 1 > (E r -E v ) hv 1 SET Process for Optical Storage Valance Band, E V hv 1 hv 3 hv 2 Conduction Band, E C EgEg ErEr EtEt hv 1 hv 1 > (E c -E r ) Optical Writing Optical Reading hv 2 > (E c -E t ) hv 2 hv 3 Detect hv 3 Optical Storage

9. Band Diagram model for SrS doped with Eu and Sm Valance Band, E V Conduction Band, E C Fermi Level Eu 2+ (Excited State) (Ground State) Eu 3+ (Ground State) (Excited State) Eu 3+ Sm 2+ Sm 3+ ~1.1eV ~0.85eV ~2eV Thermal Traps

10. SET Materials: MgS and SrS doped with Eu and Sm impurities The absorbtance spectra of MgS and SrS doped with Eu and Sm impurities

11. The writing (488 nm) and the stimulation (1064 nm) spectra

12. Infrared exhaustion curves for Mg and SrS doped with Eu and Sm impurities Sensor Refreshing Time

13. Storage times of Sm 2+ electrons for MgS and SrS 138days for MgS (588 nm) and 20 days for SrS (615 nm)

14. Writing intensity variation versus photoluminescence for MgS and SrS doped with Eu and Sm impurities MgS: 588 nm & SrS: 615 nm

15. Writing intensity variation versus stimulated emission intensity for MgS and SrS doped with Eu and Sm impurities Reading by 1064 nm: 588 nm for MgS and 615 nm for SrS

16. Reading intensity variation versus stimulated emission intensity for MgS and SrS doped with Eu and Sm impurities Reading by 1064 nm

17. Possible sulfide material combinations for an SET medium

18. Nanoparticle (SET) Infiltrated Microstructured Fibers What type of microstructured fibers will be useful? From U. Bath

19. Microstructured Fiber  Triangular lattice  Red circles : air holes  Blue region : fiber core  d: diameter of the air hole   : lattice constant

20. Microstructured Fiber- Intensity distribution in the air holes

21. Microstructured Fiber Confinement in the core

22. Parameters for SET Radiation Sensor  Reading wavelength: 1064 nm  Emission wavelength : 588 nm  Lattice constant : 1.2  m & d/  : 0.23 Field intensity extended to the air holes : 1.5% (1064 nm) Field intensity confined in the core : 70% (588 nm)

23. Microstructured Fiber Intensity Distribution Profile

25. Other Issues: Remote Sensing Long distance transmission.  = 1.7 or 2.2  m is better. Extension: ~ 0.7% (1064 nm) Confinement : ~ 85% (588 nm)

26. Other Issues: High Delta Fiber

27. Other Issues  Coupling of light emitted from nano particles to the core

28. Radiation Sensing Mechanism Reading Source (0.80 - 1  m) Detector Cross Section of SET Fiber t Radiation SET Fiber t1t1 t2t2 L L1L1 L2L2 v t1=t1= L1L1 v t2=t2= 2L 2 + L 1

29. Summary  Concept of SET based radiation sensing  Incorporate SET into microstructured fibers  Dose and location measurements  Distributed sensing  Refreshable sensor