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1. UNCLASSIFIED Photonic-Crystals In Military Systems Energy Harvesting, Thermal Camouflage, & Directed Energy Leo DiDomenico3 Hwang Lee1 Marian Florescu1 Irina Puscasu2 Jonathan Dowling1 1 Department of Physics & Astronomy, Louisiana State University 2 Ion Optics Inc. 3 Xtreme Energetics Inc. Points of Contact: Dr. Leo D. DiDomenico Leoddd@XEsolar.com & Prof. Jonathan P. Dowling jdowling@lsu.edu UNCLASSIFIED

2. Contents • Introduction to Applications of Photonic Band Gap (PBG) Material • What is a Photonic Band Gap Material? • Generating Electricity from Spectral & Directional Control of IR Radiation • Controlling Thermal Radiation for IR Camouflage • Pumping Laser Weapons with Thermal Radiation from PBG Materials • Initial Experimental Studies On PBG Thermal radiation control

3. Power Generation Systems: Low-Temperature Thermophotovoltaics Problem Applications PBG Conventional TPV Systems Too Hot Performance Expectations Solution Optimize the input radiation band and propagation direction to a PV & don’t worry too much about the PV itself! TPV using PBG is relatively Low Temperature. S. Lin et al. Sandia Labs

4. Tunable IR Camouflage Systems Other Applications Problem Thermal signatures have become too easy to detect • Improved Thermal Imagers • Thermal Camouflage • Radar Signature Reduction • Low Observability and Stealth • Solar and Thermal Covers Solution Thermal Radiation Control Designs • Engineer the radiative thermal response using photonic crystals to control: • Spectral • Directional • Tunability for adaptive thermal emissivity response. • Omnidirectional IR reflectors • Broadband systems • Multi Band Operation • PBG coatings with surface effects • Smart Skin Technology for Tanks

5. High-Power Photonic Crystal Lasers for Power Beaming Problem Applications Defense against kinetic energy weapons requires repeated fast interception. Chemical lasers fail to deliver the punch over an extended fight. • High power thermally pumped PBG lasers • Replace chemical laser • Deep ammunition magazine • Other -- Point-to-point laser comm. Solution Gas Dynamic lasers require energetic chemical reactions which limit practical embodiments Convert heat gradients into A flow of incoherent narrow band pump light for laser using PBG energy funnel. Cold

6. Contents • Introduction to Applications of Photonic Band Gap (PBG) Material • What is a Photonic Band Gap Material? • Generating Electricity from Spectral & Directional Control of IR Radiation • Controlling Thermal Radiation for IR Camouflage • Pumping Laser Weapons with Thermal Radiation from PBG Materials • Initial Experimental Studies On PBG Thermal radiation control

7. Photonic Crystal Structures • Periodic dielectric • Scale of periodicity is ~l/2. • Exhibits large dielectric contrast. • Light velocity is a function of direction. • Temperature varies slowly relative to ~l/2. • Thermal radiation is selectively suppressed. • “Semiconductor” material for Light

8. Simple Photonic Crystals • Alternating materials of higher & lower refractive indices • Periodicity: on the order of wavelength of light • Functionality: semiconductors for light Joannopoulos, Meade, Winn, Photonic Crystals (1995)

9. 3-Dimensional Photonic Crystals Each scattering site contributes to the total Wave response. The math can be very complexbut the basic idea is VERY SIMPLE... Scattered waves can add destructivelyfor some frequencies and from somedirections… Therefore, certain very special PBG structures have all directions of propagation forbidden over a band of frequencies. 3D Crystal Structure with scattering plans shown

10. New Design Tools are Needed for Opto-Thermal Engineering with Photonic Crystals 2D 1D • TDOS measures the number of states {kx, ky, kz, n} that radiate. • TDOS is the number of states for a given dw about the frequency w. • Opto-Thermal applications require extending the idea of TDOS. • The TDOS must be extended to account for the overlap of • The periodic dielectric • The Radiation field. • Atoms with atomic transitions. • Temperature distribution. The fields do not always overlap the dielectric whereatoms can absorb or emit energy & heat the material. An extension of basic radiation theory, which now includes photon-phonon interactions inside a PBG material with a non-uniform temperature distribution, is being developed by the authors and with the intent of develop engineering software tools for opto-thermal PBG materials.

11. Photonic Crystals: Examples Butterfly Wing Opal Inverted Opal Silicon Pillars Photonic Crystal Fiber Woodpile

12. A Dizzying Array ofPotential Applications Semiconductors for Light • Band Gap: Optical Switching & Routing • Band-Gap Shift: • Local Field Enhancement: Strong Nonlinear Optical Effects • Anomalous Group Velocity Dispersion: Negative index metamaterials for stealth applications and super-prism dispersion, true time delay lines Photodetectors, LED • Micro-cavity Effects: Low-Threshold Lasers

13. Contents • Introduction to Applications of Photonic Band Gap (PBG) Material • What is a Photonic Band Gap Material? • Generating Electricity from Spectral & Directional Control of IR Radiation • Controlling Thermal Radiation for IR Camouflage • Pumping Laser Weapons with Thermal Radiation from PBG Materials • Initial Experimental Studies On PBG Thermal radiation control

14. PV Cells Need a Matched Spectrum TPV Cell There are 2 potential solutions Using Photonic Crystals … Heat Generated! Out of band energy from PV cell,creates waste heat but no electricity !

15. Method 1: Thermal Gradients Allow Rethermalization Heat Source Photonic Crystal Hot Cold Band GapLight Cone To TPV RethermalizeOut of Band Energy

16. Thermal Radiation in PBG Material RECALL: Photon-PhononInteraction in Non-PBG Now extend principles to a PBG material • Spectral Intensity: position, direction, & frequency • Absorptivity: T(r), direction, # of levels, & frequency • Energy velocity depends on PCS • Total density of atom-connected photon states

17. TPV Energy Conversion:PBG Spectral Control TPV Cell Device Spectral Funnel(Not a Filter) Broad BandHeat Source

18. TPV Energy Conversion State-of-the-art Improve conversion efficiency: • Recycling the unused photons to heat the Emitter/absorber • Intermediate Absorber/Emitter • Filter: Only the photons with right energy • Keep operating temperatures lower • Recycle: Heat the absorber with the unused photons Incorporate PBG into a Classic TPV Design

19. Method 2: TPV Energy Conversion:Using PBG Directional Control absorber cell Solid angle for absorber Solid angle for the sun 85% Temp of the thermal source Temp of absorber TA = 2500 K Temp of the cell T Kelvin Instead of increasing WS (concentration), decrease the solid angle of the intermediate absorber, WA. Full concentration

20. Novel PBG Angle-Selective Absorber Novel Design of an efficient angle-selective PBG absorber • a wave-guide channel in 2D PBG embedded in a 3D PBG structure • single-mode (uni-directional) operation for a wide range of frequency • alternative structures can be designed to achieve a prescribed efficiency • LSU patent application 3D PBG 2D PBG 1D Channel 3D PBG

21. Photonic crystal radiation Blackbody input radiation Filter output radiation Filter output radiation Funneling of the Thermal Radiation • For a given blackbody input power, T= 400 K (area under the red curve) • Filter • only eliminates lower and higher spectral components, selecting incident radiation in a narrow range • Appreciable amount of energy is wasted • Photonic crystal • funnels the incident energy into a narrow spectral range • runs at a higher effective temperature (defined by the blackbody with the same maximum peak power) Proposed Current 5 % Transfer efficiency 20 % Transfer efficiency Blackbody input radiation

22. Contents • Introduction to Applications of Photonic Band Gap (PBG) Material • What is a Photonic Band Gap Material? • Generating Electricity from Spectral & Directional Control of IR Radiation • Controlling Thermal Radiation for IR Camouflage • Pumping Laser Weapons with Thermal Radiation from PBG Materials • Initial Experimental Studies On PBG Thermal radiation control

23. Hiding Thermal Signatures

24. Doubly-Periodic Photonic Crystals:Dual-Band Optical Properties (I) • “On demand” optical transmission and reflection spectra • three characteristic length scales: radius of the cylinders, distance between the cylinders and width of the rectangular veins (optimum values: r/a=0.078, L/a=0.194 and w/a=0.38) • full photonic band gap (both polarizations) of /c=18.25% centered on c/0=0.83 • presents spectral regions with high reflection concomitant with a large number of modes at lower frequencies (high transmission) Photonic crystal structure Photonic band structure

25. Doubly-Periodic Photonic Crystals:Dual-Band Optical Properties (II) • “On demand” field distribution • depending on the frequency the field can be localized in different regions of the high-index of refraction dielectric or in the air fraction • spatial field distribution can be used to optimize the coupling to absorbers placed into the structure in order to enhance thermal emission Electromagnetic field distribution for TM modes for the first three bands at the M-point

26. Dynamical Tuning of Spectral Emissivity Normalized emission from photonic crystal test structure at 325 C under different gas conditions: different concentration values for CO2 and N2. (right side-zoom in) Possibility of tuning the emissivity of the structure by gas choice and by controlling its gas concentration

27. Contents • Introduction to Applications of Photonic Band Gap (PBG) Material • What is a Photonic Band Gap Material? • Generating Electricity from Spectral & Directional Control of IR Radiation • Controlling Thermal Radiation for IR Camouflage • Pumping Laser Weapons with Thermal Radiation from PBG Materials • Initial Experimental Studies On PBG Thermal radiation control

28. Light Spectral Distribution vs Position Phonons Hot Cold Narrow BandPhotons Laser GainMedium Energy Separation - I Schematic of energy flow: • Temperature gradient moves phonons left to right & Rethermalizes. • Photonic Band Gap restricts photons to move downward. Three types of insulators are possible: electrical, thermal, & light. We are using the light insulating properties of Photonic Crystals to force the desired narrow-band photons into the Lasing gain medium & rethermalizing the remaining out-of-band photons into the desired band for further extraction.

29. Energy Separation - II Photonic Crystal Cold Designing thespectral and directionalProperties of PCS is ahard synthesis problem. LasingMedium Hot

30. Contents • Introduction to Applications of Photonic Band Gap (PBG) Material • What is a Photonic Band Gap Material? • Generating Electricity from Spectral & Directional Control of IR Radiation • Controlling Thermal Radiation for IR Camouflage • Pumping Laser Weapons with PBG & Thermal Radiation • Initial Experimental Studies On PBG Thermal radiation control

31. 512 node, dual-processor IA32 Linux cluster with 3.06 GHz Intel Pentium IV Xeon processors and 2 GB RAM Super- Mike LSU New, $4.6M, world-class, JEOL JBX-9300FS e-beam lithography system (third of its kind) MDL JPL Spectral and angular optical FTIR characterization facilities Ion Optics Inc. Photonic Crystals: Thermal Radiation Control in IR Enhancement and suppression of thermal emission by a three-dimensional photonic crystal, Lin et al. (2000) Sandia Labs Photonic-crystal enhanced narrow-band infrared emitters, Pralle et al. (2002) Ion Optics Three-dimensional photonic crystal emitter for thermophotovoltaic power generation, Lin et al.,(2003) Sandia Labs Thermal emission and absorption of radiation in finite inverted-opal photonic crystals, Florescu et al.,(2005) JPL&LSU Direct calculation of thermal emission for three-dimensionally periodic photonic crystal slabs, Chan et al.(2006) MIT

32. Funneling of the Thermal RadiationExperimental Results BB, Pin = 315 mW, T2 = 420.1 oC BB (273.4oC) and PC (273.4oC) plots have the same input power while the photonic crystal produces lower wavelength photons PC, Pin = 130 mW, T2 = 420.1 oC BB, Pin = 130 mW, T1 = 273.4 oC BB (420.1oC) and PC (273.4oC) plots have the same peak power wavelength • Funneling of thermal radiation of larger wavelength (orange area) to thermal radiation of shorter wavelength (grey area). JPL (micro-fab), Ion Optics (testing), LSU (analysis)

33. Conclusions • TPV cell efficiencies can be dramatically improved by employing the spectral and angular control provided by photonic crystals • Dual-band spectral radiation management systems using doubly-periodic photonic crystals are now being designed using a restricted set of “practical” structures • Experimental results confirm the photonic crystal ability to control the thermal radiation properties • New vistas exist for using photonic crystals in lasers, IR thermal signature suppression, and high-power ( non-chemical ) lasers for communications and weapons.