1.Using Metamaterials as Optical Perfect Absorbers Sepehr Ahmadzadeh University of Tehran 1

2. 2 Outline 1. Introduction to Electromagnetic Wave Perfect Absorber 2. Theory 3. Metamaterial Perfect Absorbers (MPA) 4. Optical Perfect Absorbers 5. Recent Papers 6. Conclusion 3. 3 Introduction Electromagnetic wave Absorber Absorption of Incident Electromagnetic Wave In Operating Frequency Frequency Microwave to Optical Regime Types Resonant Absorbers Broadband Absorbers 4. 4 Resonant Absorbers Radar Absorber Material Stealth Technology Reduce RCS Crossed Grating Absorber Metal Plane with an Etched Shallow Periodic Grid [1] [1] 5. 5 Broadband Absorbers Geometric Transition Absorbers Lossy materials using shapes such as pyramids [1] 6. 6 Near Unity Absorber All Incident Wave is Absorbed at the Operating Frequency Transmissivity, Reflectivity and scattering are disabled. Unity absorption Zero Reflection Zero Transmission Transparency in Optical Regime !? 7. 7 Electromagnetic Wave Absorption Theory Electromagnetic Wave Incidence Reflection Transmission Absorption Scattering Excite Surface Electromagnetic Waves Average Roughness Ignore Scattering Effects Propagation Length SEW (mostly plasmons) 8. 8 Electromagnetic Wave Absorption Theory (Contd) In order for an incident EM wave to couple to a surface wave we must have 1. Matching between incident wavevector and dispersion of surface 2. The loss of the surface for propagation of our SEW 9. 9 Electromagnetic Wave Absorption Theory (Contd) If is sufficiently large, SEW may be a form of loss. Re-radiation is possible too, e.g. our surface is curved. Finally Reflection ( ) Transmission ( ) Absorption ( ) 10. Case I Consider a slab of thickness d of magneto-dielectric medium backed by a highly conductive metallic ground plane. 10 NO TRANSMISSION For 11. 11 Case I (Contd) Reflection from metallic ground plane ? Sufficient thickness of d Sufficient loss 12. 12 Case II Consider a slab of thickness d of magneto-dielectric medium embedded in vacuum. 13. 13 a. Magneto-dielectric medium backed by a metallic ground plane b. Permittivity and Permeability of the magneto-dielectric material c. Magneto dielectric medium of thickness d [1] Adv. Mater. 2012, 24, OP98OP120 14. 14 Metamaterial Perfect Absorbers (MPA) Arrays of structured subwavelength elements Typically highly conductive metals such as copper, gold, or silver MMs are geometrically scalable (Self-Scaling) 15. 15 (Continued)Metamaterial Perfect Absorbers (MPA) As an effective medium By manipulating resonances in & Absorb both electric and magnetic field By matching & Impedance matching to free space Minimizing reflectivity 16. 16 [2]Wide-angle infrared absorber based on negative index plasmonic metamaterial Yoav Avitzor, Yaroslav Urzhumov, Gennady Shvets Physical Review January 13, 2009 17. 17 Wide-angle absorber of infrared radiation Based on anisotropic impedance matched negative index material 100% Absorption up to to the normal Constructed from plasmonic wires Characteristics PIMNIM Structure [2]Wide-angle infrared absorber based on negative index plasmonic metamaterial Physical Review December 2009 18. 18 Theoretical Background Semi-infinite slab of a lossy MM Incident in the x-z plane Relevant components Engineered structure ( diagonal tensors) 19. 19 Theoretical Background (Contd) At normal incidence in the x-z plane absorbers material impedance = At specific wavelength if the structures impedance is matched to that of vacuum Assuming that and we find that 20. 20 Angular dependence of the absorption Dashed Line Dashed Dotted Line [2]Wide-angle infrared absorber based on negative index plasmonic metamaterial Physical Review December 2009 21. 21 [2]Wide-angle infrared absorber based on negative index plasmonic metamaterial Physical Review December 2009 Extracted effective dielectric permittivity and magnetic Permeability of the PIMNIM structure. Reflectance vanishes at because nm scale Results 22. 22 Reflectance, transmittance and absorbance at normal incidence of a single PIMNIM layer. Simulation Results [2]Wide-angle infrared absorber based on negative index plasmonic metamaterial Physical Review December 2009 nm scale 23. 23 [3] Optically thin composite resonant absorber at the near infrared band: a polarization independent and spectrally broadband configuration Kamil Alici, Adil Turhan, Ekmel Ozbey 18 July 2011 / Vol. 19, No. 15 / OPTICS EXPRESS 14267 24. 24 Electrical and magnetic impedance matching at the near-infrared regime. Consist of four main layers : 1. A metal back plate 2. Dielectric spacer 3&4. Two artificial layers Polarization independent broad band perfect absorber Wide angle incidence due to the subwavelength unit cell Applications in Thermal photovoltaic , Sensors , ... Characteristics 25. 25 Transmission Reflection Spectroscopy Using Ocean Optics Spectrometer Visible Regime 600nm 1000nm Near IR 900nm 1700nm [3] Optically thin composite resonant absorber at the near infrared band: a polarization independent and spectrally broadband configuration Structure 26. Up to this point Normal incidence OK Single Polarization OK Gold-only SRR 26 Results [3] Optically thin composite resonant absorber at the near infrared band: a polarization independent and spectrally broadband configuration Center Freq. of Operation 250 THz 27. 27 Adding resistive sheet (thin titanium) Between the MM and dielectric 1. Resistive sheet resonant absorber 2. MM absorber [3] Optically thin composite resonant absorber at the near infrared band: a polarization independent and spectrally broadband configuration 28. 28 Simulated Results Oblique Incidence Absorption remains more than 70% up to 60 deg angle of incidence [3] Optically thin composite resonant absorber at the near infrared band: a polarization independent and spectrally broadband configuration 29. 29 [4] Optical metamaterial absorber based on leaf-shaped cells Weiren Zhu, Xiaopeng Zhao, Boyi Gong Longhai Liu, Bin Su Applied Physics A 102: 147151 (2011) 30. 30 Characteristics IR MM Absorber composed of metallic leaf-shaped cells, dielectric substrate, and continuous metallic film Absorptivity of 99.3% at the IR frequency of 126.7 THz fabricated with an electrochemical deposition technique Support different incident angles and radiation modes Applications such as IR imaging systems, thermal bolometers, Optical bi-stable switches 31. Structure 31 Numerical simulations Using CST Microwave Studio Silver leaf-shaped cells [4] Optical metamaterial absorber based on leaf-shaped cells 32. 32 Results Simulated Results of the structure in the Optical Regime [4] Optical metamaterial absorber based on leaf-shaped cells 33. 33 [4] Optical metamaterial absorber based on leaf-shaped cells Angular dependence of the absorptivity of the infrared metamaterial absorber 34. 34 [5] Perfect absorbers on curved surfaces and their potential applications Rasoul Alaee , Christoph Menzel , Carsten Rockstuhl, and Falk Lederer 30 July 2012 / Vol. 20, No. 16 / OPTICS EXPRESS 18376 35. 35 Perfect metamaterial absorber applied on curved surfaces 1. Suppression of back-scattered light from the covered objects 2. Rendering it cloaked in reflection 3. Optical black holes suppression of spurious back-scattered light for example in Radar absorbers Characteristics Flexible polymer film structure 36. 36 Omni directional Perfect Absorber Perfect Absorber on Planar Surface Ground plane and metallic wire made from silver [5] Perfect absorbers on curved surfaces and their potential applications Anti symmetric current distribution in the nanowire and the ground plane 37. 37 Hz- component at resonance for a plane wave incident at an absorber on curved surface [5] Perfect absorbers on curved surfaces and their potential applications 38. 38 Conclusion 1. Theory of EM absorbing materials 2. What is Perfect Absorber ? 3. Two specific types of PA 4. Using Metamaterial as a PA 5. Recent papers and applications 39. 39 References [1] Metamaterial Electromagnetic Wave Absorbers ; Adv. Mater. 2012, 24, OP98OP120 [2] Y. Avitzour, Y. A. Urzhumov, and G. Shvets, Wide-angle infrared absorber based on a negative-index plasmonic metamaterial, Phys. Rev. B79, 045131 (2009) [3] Optically thin composite resonant absorber at the near infrared band: a polarization independent and spectrally broadband configuration ; July 2011 / Vol. 19, No. 15 / OPTICS EXPRESS 14267 [4] Optical metamaterial absorber based on leaf-shaped cells Applied Physics A 102: 147151 (2011) [5] Perfect absorbers on curved surfaces and their potential applications ; 30 July 2012 / Vol. 20, No. 16 / OPTICS EXPRESS 40. 40 [6] N. I. Landy, S. Sajuyigbe, J. J. Mock, D. R. Smith, and W. J. Padilla, Perfect metamaterial absorber, Phys. Rev. Lett. 100, p. 207402, 2008 [7] Jiaming Hao, Jing Wang, Xianliang Liu, Willie J. Padilla, Lei Zhou, and Min Qiu,High performance optical absorber based on a plasmonic metamaterial, Appl. Phys. Lett.96, 2010 [8] Design of highly absorbing metamaterials for Infrared frequencies 30 July 2012 / Vol. 20, No. 16 / OPTICS EXPRESS 17508 41. 41