Course entry t hz and ultrafast
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 Raskar
Dr. 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
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http://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
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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
Bounce3rd
Bounce
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Beyond visible/IR spectrum
,
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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
400
THz
Frequency(Hz)
800
THz
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
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See a whole gallery here: http://thznetwork.net/index.php/thz-images
Jefferson Lab Ken O, UT, Texas Startiger project
D. Mittleman Rice UQ. Hu, MITBESSY, Germany- (100um res)
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THz microscopy
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R. Kersting, THz-ANSOM 150nmEpithelial tumor cell, A. Tredicuccii, ~15umDiffr
actio
n li
mit
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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Hamamatsu
ZomegaBATOP
Menlo SystemT-Rays
TeraView
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THz
THz
THz Transmitter
THz
THz
Emitting
THz
Receiving
THz
THz Receiver
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Tra
nsm
itte
r
Receiv
er
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H2O,
CO,
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
agentsBlood
sugar
DrunkReally
Hungry
Cold
Sam
ple
tra
nsm
itta
nce (
Arb
. u
nit
s)
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).
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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 wavesin 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. 43
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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
Spectroscopic
Monterrey 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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Il (x, t) = I0 G(xl, x, ¢x )N(qin )N(qout )R( ¢x )d ct - (rl ( ¢x )+ rc( ¢x ))( )d ¢xò
Time-resolved image formation
Geometry Diffuser Object
Reflectance
Time
constraint
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Il R(x),N(qin,out ){ }
1)(0for ,ˆˆ1minarg
12(.)),(
xRIIL
L
l
num
ll
meas
lNxR
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