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Single Point THz Imagery

Single Point THz Imagery. Jaewook Ahn KAIST - physics. Image encryption and decryption through THz waveforms. Thanks to collaborators Kanghee Lee Kyung Hwan Jin Prof. Jong Ye ( Kaist – biosystem ). Funding. Postech , March 2010. Visible. THz. Radio. Microwave. Infrared. UV.

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Single Point THz Imagery

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  1. Single Point THz Imagery Jaewook Ahn KAIST - physics Image encryption and decryption through THz waveforms. • Thanks to collaborators • Kanghee Lee • Kyung Hwan Jin • Prof. Jong Ye (Kaist – biosystem) • Funding Postech, March 2010

  2. Visible THz Radio Microwave Infrared UV X-rays 108 109 1010 1011 1012 1013 1014 1015 1016 1017 Frequency (Hz) Source: Terahertz waves n = 1 THz T = 48 K hn = 33 cm-1 THz waves l = 300 mm Pulsed THz Ultrafast laser based 4.1 meV THz ultrasonic BWO Photomixing CO2 pumped FIR QCL FEL accelerator ~100 fs nW-mW 10-100 kV/cm KAIST

  3. What’s special about THz Optics ? • Wavelength = ~100 mm • MEMS fabrication • Laser micro-machining • Extremely broad bandwidth : df/f=1 • Dispersion engineering • Sub-diffraction limit optics ~l/100 • Coherent Emission and Detection • Laser Induced Terahertz Emission • Amplitude and Phase measurement

  4. The First Terahertz Imaging First THz imaging ???

  5. Far-Infrared Imagery Source: 0.3-1THz (Commercial HCN laser, etc) 1-10mW Detector: liquid helium –cooled GaAs. Future direction: coherent detection, “Rapidly advancing FIR technology indicates that an FIR imaging system can be developed for industrial, military, law enforcement, and medical applications in the next few years.” T. S. Hartwick, D. T. Hodges, D. H. Barker, and F. B. Foote, Applied Optics 15, 1919 (1976).

  6. The First Terahertz Imaging They predicted …

  7. Hu and Nuss : Future Directions • “In future implementations, the THz beam could be scanned across the sample instead.” • “With current microelectronics fabrication technology, one should be able to fabricate a 100 x100 focal-plane array of photo-conducting dipole antennas to replace the single dipole detector that we used.” • “An obvious future improvement of the T-ray imaging technology will include the use of speech recognition algorithms for recognition of the THz waveforms in amplitude and phase.” “Imaging with Terahertz Waves” Hu and Nuss, OL 20, 1716 (1995). THz beam over the sample …

  8. Single-Pixel THz Camera • 300번(30%)600번(60%) “A single-pixel THz imaging system based on compresssed sensing” Chan, Charan, Takhar, Kelly, Baraniuk and Mittleman, APL 93, 121105 (2008) Array detector imaging…

  9. Real-Time THz Imaging : QCL • Standoff operation (>25 m) • Real-time operation • QCL 50 mW power : bright source • uncooledmicrobolometer camera : low sensitivity • To use atmospheric windows at 4.9 THz, 1.5 THz, etc. • Images taken with 1 s (20 frames) : Res. <0.75 mm “Real-time terahertz imaging over a standoff distance” Lee, Qin, Kumar, Willams and Hu, APL 89, 11125 (2006). THz beam over the sample …

  10. THz Reciprocal Imaging • Single detector to read out 2D target. • 2D signals are separated in timed sequence. • To avoid crosstalk : mod. freq. are prime numbers. • Need source array with each modulated at a different frequency. “Terahertz wave reciprocal imaging” Xu and Zhang, APL 88, 151107 (2006). Still needs a lot of development …

  11. Fresnel Lens THz tomography Targets are along the beam line. z= 3, 4, 7cm. Patterns are images at z’=6cm. The corresponding focal lengths are achieved at 0.75, 1.24, and 1.57 THz. Wang and Zhang (2002). KAIST

  12. None of these have spectroscopic capability, and THz beams were used as a simple wave. Simple wave Complex wave Image encryption and decryption through THz waveforms ??? Here is how. KAIST - Physics THz CDMA imaging…

  13. Image encryption and decryption through EM waveforms. + = Analog Optical Computing KAIST - Physics Digital Image Recovery Signal Processing KAIST

  14. THz Single point Imagery : First Look (a) (b) (c) (d) (e) (f) (1) Fourier mask selects spatial frequencies of the object and maps into THz spectrum. E(kq)  E(w) (2) Temporal waveforms deliver object function. E(x,y) -> E(t, q) (3) Single waveforms for 2D imaging ? (a) Target (b) E(t, q) (c) E(w, q) (d) Sinogram (e) dq=p/10 (f) dq=p/15 (g) dq=p/30 (h) Simulation (g) (h) KAIST - Physics Anatomy of the procedure…

  15. Images Encrypted in Waveforms (a) (b) (a) Target (b) E(t, q) (c) (d) (c) E(w, q) (d) Sinogram KAIST - Physics Sinogram : A visual representation of the raw data obtained in a computed axial tomography (CAT) scan. (wikipedia)

  16. Images Decrypted from Waveforms (e) (f) (h) (g) (h) (e) dq=p/10 (f) dq=p/15 (g) dq=p/30 (h) Simulation KAIST - Physics

  17. To understand how it works, we go back to the introductory optics textbook. KAIST

  18. Abbe’s Theory of Image Formation • Double diffractions of the object at So do form a spatial-frequency filtered image at Si. • Fraunhoffer Formula • Spatial frequencies : (kx,ky)=k(x/f, h/f). U’(x,h) S2 U(x,y) V(x’,y’) (x’/D, y’/D) S1 (x/f, h/f) S0 S-1 S-2 f D So Si St KAIST - Physics Spatial filtering

  19. THz Broadband ? E(x) Broadband nature may allow single point imagery. The question is how. E(w) (a) Conventional imaging (b) Broadband imaging KAIST - Physics

  20. Coherent Optical Computer TM Lt Li U(x,y) M(x,h) V(x’,y’) (x/f, h/f) So St Si f f f f KAIST - Physics Tricks:

  21. Coherent Optical Computer Lt Li U(x,y) M(x,h) V(x’,y’) (x/f, h/f) So St Si f f f f KAIST - Physics M(x,h) Spectrum at the image plane delivers the object shape.

  22. Image encrypted in THz waveform (b) (c) (c) (b) E(t, q) (c) E(w, q) KAIST - Physics

  23. Single-Point THz Imagery (a) (b) (c) (d) (e) (f) (1) Fourier mask selects spatial frequencies of the object and maps into THz spectrum. E(kq)  E(w) (2) Temporal waveforms deliver object function. E(x,y) -> E(t, q) (3) Single waveforms for 2D imaging ? (a) Target (b) E(t, q) (c) E(w, q) (d) Sinogram (e) dq=p/10 (f) dq=p/15 (g) dq=p/30 (h) Simulation (g) (h) KAIST - Physics “Coherent Optical Computing for T-ray Imaging” K.Lee et al, submitted (2009).

  24. KAIST

  25. Decryption of Image from Waveform Sinogram E’(x,y) Target Images are reconstructed by Inverse Radon transformation Angular resolution p/Dq=1,3,5, ... ,120 KAIST - Physics

  26. Field of View (a) (b) (b’) , where KAIST - Physics KAIST

  27. THz Bandwidth & Image Resolution Inverse Radon Transformation is used to reconstruct the image. Image Resolution KAIST - Physics Terahertz Bandwidth: wmax=0-1.8 THz

  28. THz C(F?)DMA Imaging : proposal Dq N sets of spectral combs for diff. angular measurements. S1=Dw{1, Nq+1, 2Nq+1, 3Nq+1, ...} S2=Dw{2, Nq+2, 2Nq+2, 3Nq+2, ...} S3=Dw{3, Nq+3, 2Nq+3, 3Nq+3, ...} … SNq=Dw{Nq, 2Nq, 3Nq, 4Nq, ...} Total # of combs = wmax/(Dw) # of combs In each set = MT Dw : frequency comb width NqDw : comb width in each set Simple mask CDMA mask NqDw wmax KAIST - Physics

  29. THz CDMA Imaging : Simulation ~4cm one set of combs With 45waveforms 3 sets of combs With 15waveforms object KAIST - Physics 5 sets of combs With 9waveforms 15 sets of combs With 3waveforms 45 sets of combs With 1 waveform Using frequency: up to 1.8 THz Frequency resolution: 10GHz

  30. THz CDMA Imaging : Simulation ~4cm one set of combs With 45waveforms 3 sets of combs With 15waveforms object KAIST - Physics 5 sets of combs With 9waveforms 15 sets of combs With 3waveforms 45 sets of combs With 1 waveform Using frequency: up to 1.8 THz Frequency resolution: 1GHz

  31. THz CDMA Imaging : Simulation ~4cm one set of combs With 45waveforms 3 sets of combs With 15waveforms object KAIST - Physics 5 sets of combs With 9waveforms 15 sets of combs With 3waveforms 45 sets of combs With 1 waveform Using frequency: up to 1.8 THz Frequency resolution: 100MHz

  32. Simulation : Field of View ~4cm N=p/Dq=45 M=wmax/(NDw)=40 1GHz combs N=p/Dq=45 M=wmax/(NDw)=400 100MHz combs object 50 x 50 pixels Nyquist-Shannon sampling theorem limits the field of view. KAIST - Physics

  33. Simpler variations (a-2) (a-1) (b) THz CDMA Imaging KAIST - Physics Waveforms could measured at once by (a-1) time separation with dense materials (a-2) frequency separation with multi-layers or modulations (b) Integrated array detector

  34. Summary Single-pixel THz imagery has been demonstrated. THz waves finds new applicationsin broadband coherent optical computing. Code division multiple access protocol for “real” single-point THz imagery is under development. p/Dq=10 p/Dq=15 p/Dq=30 KAIST - Physics

  35. Thanks to collaborators and students • THz System Development • Prof. Jong C. Ye (Kaist-biosystem) • Prof. Kihoon Jeong (Kaist-biosystem) • Dr. D.S. Yi (KRISS) • Laser Terahertz Emission Microscope • Prof. Y. D. Cho (Gist-IC) • Students • 이강희, THz CDMA imaging • 이민우, LTEM • 한대훈, THz metamaterials KAIST - Physics

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