single point thz imagery
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
Single Point THz Imagery
Jaewook AhnKAIST - physics
Postech, March 2010
Thanks to collaborators• Kanghee Lee• Kyung Hwan Jin• Prof. Jong Ye (Kaist – biosystem)
Funding
Image encryption anddecryption through THz waveforms.
KAIST
Source: Terahertz waves
THz waves Pulsed
THzUltrafast
laser basedFEL
accelerator
THzRadio Microwave Infrared UV X-rays
Visible
Frequency (Hz)108 109 1010 1011 1012 1013 1014 1015 1016 1017
n = 1 THz
l = 300 mm
hn = 33 cm-1
T = 48 K
4.1 meVTHz ultrasonicBWOPhotomixingCO2 pumped FIRQCL ~100 fs
nW-mW10-100 kV/cm
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 ~ /100l
Coherent Emission and Detection Laser Induced Terahertz Emission Amplitude and Phase measurement
The First Terahertz Imaging
First THz imaging ???
Far-Infrared Imagery
T. S. Hartwick, D. T. Hodges, D. H. Barker, and F. B. Foote, Applied Optics 15, 1919 (1976).
Source: 0.3-1THz (Commercial HCN laser, etc) 1-10mWDetector: 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.”
The First Terahertz Imaging
They predicted …
Hu and Nuss : Future Directions
“Imaging with Terahertz Waves”Hu and Nuss, OL 20, 1716 (1995).
1. “In future implementations, the THz beam could be scanned across the sample instead.”
2. “With current microelectronics fabrication technology, one should be able to fabricate a 100 x100 focal-plane array of photo-con-ducting dipole antennas to replace the single dipole detector that we used.”
3. “An obvious future improvement of the T-ray imaging technology will include the use of speech recognition algorithms for recogni-tion of the THz waveforms in amplitude and phase.”
THz beam over the sample …
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…
Real-Time THz Imaging : QCL
“Real-time terahertz imaging over a standoff distance”Lee, Qin, Kumar, Willams and Hu, APL 89, 11125 (2006).
Standoff operation (>25 m) Real-time operation
QCL 50 mW power : bright source uncooled microbolometer 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
THz beam over the sample …
THz Reciprocal Imaging
“Terahertz wave reciprocal imaging”Xu and Zhang, APL 88, 151107 (2006).
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.
Still needs a lot of development …
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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).
fzz
1
'
11
2
2p
v
rf
None of these have spectroscopic capability, and THz beams were used as a simple wave.
Image encryption anddecryption through THz waveforms ???
Here is how.
Simple wave Complex wave
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THz CDMA imaging…
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Image encryption and decryption through EM wave-forms.
+ =
Analog Optical Computing
Signal ProcessingDigital Image Recovery
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THz Single point Imagery : First Look
(a) Target(b) E(t, q)(c) E( , w q)(d) Sinogram(e) d = /10q p
(f) d = /15q p(g) d = /30q p
(h) Simulation
(a) (b)
(c) (d)
(e) (f)
(g) (h)
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(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 ?
Anatomy of the procedure…
(a) (b)
(c) (d)
Images Encrypted in Waveforms
(a) Target
(c) E( , w q)
(b) E(t, q)
(d) Sinogram
Sinogram : A visual representation of the raw data obtained in a computed axial tomography (CAT) scan. (wikipedia)
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(e) d = /10q p (f) d = /15q p(g) d = /30q p (h) Simulation
(e) (f)
(g)(h)
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(h)
Images Decrypted from Waveforms
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To understand how it works, we go back to the introductory optics textbook.
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).
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f D
(x/f, h/f)
St SiSo
U(x,y)U’( ,x h)
V(x’,y’)S2
S1
S0
S-1
S-2
(x’/D, y’/D)
dxdyeyxUCUyf
xf
ik
),(),(' 1
Spatial filtering
THz Broadband ?
E( )w
E(x)
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dxxUexV f
xxik
)()'('
(a) Conventional imaging (b) Broadband imaging
dxxUeV f
xx
ci
x )()('
'
Broadband nature may allow single point imagery.
The question is how.
Coherent Optical Computer TM
)}],({),([)','( 1 yxUMyxV FF
f
(x/f, h/f)
SiSt
U(x,y) M( ,x h) V(x’,y’)
f f f
So
Lt Li
Tricks:
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Coherent Optical Computer
)}],({),([)','( 1 yxUMyxV FF
f
(x/f, h/f)
SiSt
U(x,y) M( ,x h) V(x’,y’)
f f f
So
Lt Li
M( ,x h)
ddxdydeyxUMCVyf
xf
ik
),(),()0,0( 1
ddxdydeyxUCVy
f
dx
f
d
ci
sincos
1 ),(),(
Spectrum at the image plane delivers the object shape.
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Image encrypted in THz waveform
ddxdydeyxUCVy
f
dx
f
d
ci
sincos
1 ),()(),(
dxdytd
fcyxyxUtV )sincos(),(),(
~
(c) E( , w q)(b) E(t, q)
(b)
(c)
(c)
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Single-Point THz Imagery
(a) Target(b) E(t, q)(c) E( , w q)(d) Sinogram(e) d = /10q p
(f) d = /15q p(g) d = /30q p
(h) Simulation
(a) (b)
(c) (d)
(e) (f)
(g) (h)
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(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 ?
“Coherent Optical Computing for T-ray Imaging”K.Lee et al, submitted (2009).
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Decryption of Image from Waveform
Angular resolution / =1,3,5, ... ,120p Dq
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Target Images are reconstructed byInverse Radon transformation
E’(x,y)Sinogram
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Field of View
dxdyeyxUCVy
f
dx
f
d
ci
sincos
1 ),()(),(
ddxdydeyxUMCVyf
xf
ik
),(),()0,0( 1(a)
(b)
(b’) , where fka
fkaJyxUayxU
/
)/(2),(),(' 12
22 yx
maxmax
/215.2
afc
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THz Bandwidth & Image Resolution
Inverse Radon Transformation is used to reconstruct the image.
Terahertz Bandwidth: wmax=0-1.8 THz
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fc
d
f
dk maxmax
Image Resolution
THz C(F?)DMA Imaging : proposal
Simple mask CDMA mask
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 widthNq : Dw comb width in each set
NqDw
wmax
Dq
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Using frequency: up to 1.8 THzFrequency resolution: 10GHz
one set of combsWith 45waveforms
object 3 sets of combsWith 15waveforms
5 sets of combsWith 9waveforms
15 sets of combsWith 3waveforms
45 sets of combsWith 1 waveform
~4cm
THz CDMA Imaging : SimulationK
AIS
T -
Ph
ys
ics
Using frequency: up to 1.8 THzFrequency resolution: 1GHz
one set of combsWith 45waveforms
object 3 sets of combsWith 15waveforms
5 sets of combsWith 9waveforms
15 sets of combsWith 3waveforms
45 sets of combsWith 1 waveform
~4cm
THz CDMA Imaging : SimulationK
AIS
T -
Ph
ys
ics
Using frequency: up to 1.8 THzFrequency resolution: 100MHz
one set of combsWith 45waveforms
object 3 sets of combsWith 15waveforms
5 sets of combsWith 9waveforms
15 sets of combsWith 3waveforms
45 sets of combsWith 1 waveform
~4cm
THz CDMA Imaging : SimulationK
AIS
T -
Ph
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Simulation : Field of View
= / =45N p Dq
=M wmax/
(NDw)=401GHz combs
object50 x 50 pixels
~4cm
= / =45N p Dq
=M wmax/
(NDw)=400100MHz combs
Nyquist-Shannon sampling theorem limits the field of view.
)number pixel(max
NM
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Simpler variations
(a) 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
(a-1) (a-2)
(b)
THz CDMA Imaging
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Summary
/ =10p Dq / =15p Dq / =30p Dq
1. Single-pixel THz imagery has been demonstrated.
2. THz waves finds new applicationsin broadband coherent optical computing.
3. Code division multiple access protocol for “real” single-point THz imagery is under development.
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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
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