1. Beyond the visible: A tour to
future of spectroscopy and
imaging
Barmak Heshmat
Dr. Ramesh Raskar
Dr. C. Barsi
1
2. 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)
2
4. 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
5. 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
?
9. Beating the diffraction limit
9
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.
10. 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.
10
2nd Bounce
1st
Bounce
3rd
Bounce
12. New hardware trends
• Introductions
• Applications
• PC Switches
– New Materials for THz
– Optimizing Excitation of PC Switches
– Nanoplasmonic Structures
• Summary
• Questions?
12
14. Why THz
• Noninvasive
• Water in biological systems, protein folding, disease state of
tissue
• Vibrational modes for organic molecules
• Picosecond time scale dynamics
14
15. THz and tissues
• Can measure absorption and refraction index together through pulsed
imaging.
15
16. THz imaging
• Security apps, (mm wave <> THz)
• More inspection and analysis apps
16
See 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)
17. THz microscopy
17
R. Kersting, THz-ANSOM 150nmEpithelial tumor cell, A. Tredicuccii, ~15um
Diffractionlimit
Ordinary
imaging
Near field
imaging
Scanning
probes
D. Zimdars, Picometrix, Inc,
29. 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
30. 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
30
36. 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.
36
37. 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
39. 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
40. Results of Using Nanoplasmonic
Structures
Peak-to-peak response enhancements of 40×,
10×, and 2×, compared to GaAs, LT-GaAs and
Commerical device.
40
42. 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.
42
43. 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
51. 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.
52.
53.
54.
55. 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:
55
57. Time-of-flight
In Situ remote sensing
Require direct path between objects sensor
JPL
Hyperspectral Imaging
Spectroscopic
Monterrey Bay Aquarium Research Institute
http://www.mbari.org/coastal/
http://earthobservatory.nasa.gov/Features/Lidar/
http://aviris.jpl.nasa.gov/html/aviris.freedata.html
Optical remote sensing
59. 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
64. Il R(x), N(qin,out ){ }
1)(0for,ˆˆ1
minarg
1
2(.)),(
xRII
L
L
l
num
ll
meas
l
NxR
Inverse problem
Given a set of streak images
Find the unknown reflectance R(x)
71. 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.
72. 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
73. 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.
