Course entry t hz and ultrafast
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Transcript of Course entry t hz and ultrafast
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Beyond the visible: A tour to future of spectroscopy and
imaging
Barmak Heshmat
Dr. Ramesh RaskarDr. C. Barsi
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The big picture• Beyond the visible/IR spectrum (THz spec.)
– New hardware trends– New computational trends
• Beyond the line of sight (multihop imaging)– Seeing around the corners– Seeing through the diffusers
• Beyond the resolvable (subwavelength imaging) – New hardware trends(course p1)– New computational trends(course p2)
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Spectroscopy
• EM waves• Many types of spectroscopy
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Wave of spectrometers
• They were all there in the lab but now they are entering consumer market!
– Optical absorption diagnostic
– Raman food analysis– THz skin, cosmetics,
pharm.
Electronics starting to become portable
Optics starting to become portable
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Example
Just like super computers we still need the accurate lab spectrometers but portable versions can be used in limited applications.
• Raman spectrometer from lab to the key chain!
Tellspec
DeltaNu® ReporteR™
Smiths Detection RespondeR™ RCI
Microphazir™
Horiba T64000
?
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Hyperspectral and multispectral imaging
6http://www.markelowitz.com/Hyperspectral.html
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Measurement samples
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asri.technion.ac.il
www.popularmechanics.comwww.neo.no
www.bayspec.com www.perception-park.com
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Beating the diffraction limit
Superlensing Enhanced near field probes
Fluorescence imaging
Super oscillatory lenses
Diffraction limit has limited our resolution in imaging now we are learning ways to go beyond this limit.
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Seeking light after scattering• Going from imaging for human to imaging for
computers (measurement in other mathematical spaces and reconstructing the image)
• Going from single scattering imaging to multi-scattering imaging.
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2nd Bounce
1st Bounce
3rd Bounce
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Beyond visible/IR spectrum
, 11
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New hardware trends• Introductions• Applications• PC Switches
– New Materials for THz – Optimizing Excitation of PC Switches– Nanoplasmonic Structures
• Summary• Questions?
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…THz
400THz
Frequency(Hz)800THz
Unique spectroscopy capabilities
Study of THz dynamics
Faster communication
Imaging and inspection
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Why THz• Noninvasive• Water in biological systems, protein folding, disease state of
tissue• Vibrational modes for organic molecules• Picosecond time scale dynamics
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THz and tissues• Can measure absorption and refraction index together through pulsed
imaging.
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THz imaging• Security apps, (mm wave <> THz)
• More inspection and analysis apps
16See a whole gallery here: http://thznetwork.net/index.php/thz-images
Jefferson Lab Ken O, UT, Texas Startiger project
D. Mittleman Rice U Q. Hu, MITBESSY, Germany- (100um res)
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THz microscopy
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R. Kersting, THz-ANSOM 150nmEpithelial tumor cell, A. Tredicuccii, ~15umDiff
ract
ion
lim
it
Ordinary imaging
Near field imaging
Scanning probes
D. Zimdars, Picometrix, Inc,
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New trends in hardware
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THz Generation Methods
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PC Switches
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HamamatsuZomegaBATOP
Menlo SystemT-Rays
TeraView
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THz
THz
IR
THz Transmitter
IR
THz
THz
EmittingTHz
IR IR
ReceivingTHz
THz Receiver
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Tra
nsm
itter
Receiver
THz
Infrared
Infrared
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H2O,CO,HCN,Glycine, Glycerol, Thymine, Deoxycytidine,Adenosine,D-glucose, Tryptophan, L-alanine,Bacillus subtillis,And the list goes on and on…
http://thzdb.org/
Here is what is detected
Temporal profile Frequency composition
Math
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Our ultimate dream was!
Last 10 yearsin our lab
This yearin our lab
Future, in our hand
The miniaturization process
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It’s real!
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Skin quality
Lung cancer agents
Blood sugar
DrunkReally Hungry
Cold
Sam
ple
tra
nsm
itta
nce
(A
rb.
un
its)
Frequency (Terahertz)27
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New Materials for THz
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Conventional Materials The philosophy of an optical switch defines the desired properties of
the substrate material. highest level of fast photoconductivity modulations:
• high optical density• high thermal breakdown limit • high mobility, and Vb and Vsat
• short carrier lifetime (sub-picosecond)• low dark conductance
• PC switching started by Austin on Si in 1975 (D.H. Auston, Appl. Phys. Lett., 26 (3) 101 (1975))
• C.H. Lee used GaAs in 1977 (C.H. Lee, Appl. Phys. Lett., 30 (2) 84 (1977))
• M.Y. Frankel used LT-GaAs in 1990 (M.Y. Frankel, et al, IEEE Trans on Elec. Devices, 37, 2493, 1990).29
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LT-GaAs• LT-GaAs has short carrier lifetime (<1ps)• It has low mobility as well GaAsBi• Bi is a group V poor metal GaAsBi is shrinking
bandgap material
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GaAsBi Results• 500 GHz bandwidth improvement • Interesting emissions!
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Effect of GaAsBi growth condition• THz emission with variation of different parameters
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Carbon nanotubes
Increasing the performance with carbon nanotubes
between the gold electrodes of the chip
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So we made samples.
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Nanoplasmonic Structures
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Nanoplasmonics
• Engineering surface electron density waves in the metallic nanostructures to achieve an enhanced optical response.
• A key property of nanoplasmonics is its capability to efficiently couple light into subwavelength structures.
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Nanoplasmonics: An Example
Tuning annular nano-apertures
B. Heshmat, D. Li, T. E. Darcie, R. Gordon, " Tuning plasmonic resonances of an annular aperture in metal plate "Optics Express, Vol. 19, Iss. 7, pp. 5912–5923 (2011). 37
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Nanoplasmoincs for THz PC Switches
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Nanoplasmoincs in THz PC switches
B. Heshmat, H. Pahlevaninezhad,Y. Pang, M. Masnadi, R. Lewis, T. Tiedje, R. Gordon and T. E. Darcie "Nanoplasmonic Terahertz Photoconductive Switch" Nano letter, accepted. 39
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Results of Using Nanoplasmonic Structures
Peak-to-peak response enhancements of 40×, 10×, and 2×, compared to GaAs, LT-GaAs and Commerical device.
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Past, Present, Future
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Challenges• THz waves have long wavelength; biological structures, many
important ones, are small…• Living things need water: THz radiation and water are not
“best friends”…• Unless you work hard, no clear spectroscopic features at THz
are visible for many samples.• Some solutions to above problems are coming out.
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Summary of new trends in hardware• 100 GHz to 10THz region of EM waves are called THz, have
been unexplored, but we are finally closing the gap.
• Main challenge is detection and generation.
• Major sources and QCLs, schottky diodes, PC switches and nonlinear crystals.
• There is room for enhancement through material, optics and nanoplasmonics.
• Many exciting applications from early cancer detection to inspection of organic materials and faster telecommunication.
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New computational trends
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• They also investigated the difference between a random mask and an optimized one.
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The optimal block size for the block-based CS is a function of the local image characteristics, and different block sizes can be assigned to
different regions.
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Summary of computational trends
• Compressive measurements, where you measure the minimum amount of points to reconstruct an image with known priors.
• Layer separation based on pulse features• Reference-free measurements in THz imaging• Here is a demo:
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Beyond the line of sight
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Time-of-flightIn Situ remote sensing
Require direct path between objects sensor
JPL
Hyperspectral Imaging
SpectroscopicMonterrey Bay Aquarium Research Institutehttp://www.mbari.org/coastal/
http://earthobservatory.nasa.gov/Features/Lidar/
http://aviris.jpl.nasa.gov/html/aviris.freedata.html
Optical remote sensing
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What if there is no direct path?
Receiver
Source
?
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Computation + optics
J. Bertolotti, et al. Nature 491 (2012).S. M. Popoff, et al. Nat. Commun. 1 (2010)
• Relies on coherence/correlation
• Small field of view
• Short standoff distance
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60Nature Photonics 6, 549–553 (2012)
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A. Velten, et al. Nat. Commun. 3 (2012).
Time is a parameter for imaging
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x
t Hyperbola
x
Laser
Streak camera
Diffuser
Object
Time-resolved image formation
Source: Ti:Sapph (λ0 =795nm, but could use other wavelengths)Detector: Streak Camera (δt ≈2ps)Different ray paths register at different times hyperbolic impulse response (x – ct)
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Time-resolved image formation
Geometry Diffuser Object Reflectance
Time constraint
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1)(0for ,ˆˆ1minarg
12(.)),(
xRIIL
L
l
numll
measl
NxR
Inverse problem
Given a set of streak images
Find the unknown reflectance R(x)
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Streak Image
Experimental setup
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Visible volume
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Experimental setup
• Need to know something about diffuser
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Unknown reflectance
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Unknown reflectance
• Assume object geometry known (can get from previous work)
• Wide field reconstruction
• Works for incoherent light
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Moving on to the miniaturization
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Time of flight camera• Continuous wave instead of pulsed• Cheaper, safer, more compact, but less accurate.
R. Raskar, et al., “Coded Time of Flight Cameras: Sparse Deconvolution to Address Multipath Interference and Recover Time Profiles”, SIGGRAPH Asia 2013.
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3d imaging through turbulence
Solving occlusion problems
www.picassodreams.com/photos/nyc_skyscrapers/
http://www.nasa.gov/vision/earth/lookingatearth/h2005_katrina.html
http://www.fjellandfjord.com/article.php?id=166
http://www.soest.hawaii.edu/GG/HCV/loihi.html
Generalizations for remote imaging
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Summary of time of flight imaging• Moving from single scattering to multiscattering
(multihop) imaging
• Different reconstruction techniques that rely on previous optimization techniques can be used.
• Moving from expensive ultrafast hardware to cheaper slow hardware that operates on modulated light
• Now we can recover what is in the visible volume of these cameras
N. Naik, C. Barsi, A. Velten, R. Raskar.“Estimating spatially varying reflectance through scattering layers using time-resolve inversion.” JOSA A.
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Two picosecond time resolution
Streak camera details