Spectroscopy is the study of the quantized interaction of energy with the matter. In the electromagnetic spectrum, there are radiations of different energy which lead to a wide range of spectroscopy techniques like UV-Vis, Infrared, NMR etc. The spectral range from around 3.3 cm-1 to 333.6 cm-1 was mostly unexplored before 30 years and known as “terahertz gap” due to unavailability of Terahertz (THz) generators and detectors but in the last two decades, this has emerged as a field of great potential and various applications like THz imaging, chemical analysis and molecular spectroscopy, applications in biology, medicines, protein analysis and pharmaceuticals, in solid state where it can be an alternative to XRD, NMR, DSC, in radio astronomy, in environmental control, in explosive detection. The combination of all these applications falls under THz spectroscopy.
In this study, the development of Terahertz technology from past years to today, as well as the information and working principle about Terahertz technology are explained. In addition, various usage areas are given. Also the main topics are given below.
The general principles of the Terahertz Technology.
What is the Terahertz?
How can we generate the THz?
How can we detect it ?
Application areas of Terahertz technology
If there is a place you do not understand please contact me. (Mail, social media)
I hope you like. Please like and comment.
In this study, the development of Terahertz technology from past years to today, as well as the information and working principle about Terahertz technology are explained. In addition, various usage areas are given. Also the main topics are given below.
The general principles of the Terahertz Technology.
What is the Terahertz?
How can we generate the THz?
How can we detect it ?
Application areas of Terahertz technology
If there is a place you do not understand please contact me. (Mail, social media)
I hope you like. Please like and comment.
Photoluminescence Spectroscopy for studying Electron-Hole pair recombination ...RunjhunDutta
Description of Photoluminescence Spectroscopy: Principle, Instrumentation & Application.
Three research papers have been summarized which lay stress on Photoluminescence Study for Electron-Hole Pair Recombination for characterizing the properties of semiconductors used in Photoelectrochemical Splitting of Water.
This is a pdf file on the topic Gamow theory of alpha decay which gives description about how the scientist Gamow had solved the theory of the alpha decay via tunneling .
Basic operating principle and instrumentation of photo-luminescence technique. Brief description about interpretation of a photo-luminescence spectrum. Applications, advantages and disadvantages of photo-luminescence.
The postulates of quantum mechanics have been successfully used for deriving exact solutions to Schrodinger equation for problems like A particle in 1 Dimensional box Harmonic oscillator Rigid rotator Hydrogen atom • However for a multielectron system, the SWE cannot be solved exactly due to inter-electronic repulsion terms.
The SWE is solved by method of seperation of variables.
• However, the inter-electronic repulsion term cannot be solved because the variables cannot be seperated and the SWE cannot be solved. • Approximate methods have helped to generate solutions for such and even more complex real quantum systems. • Approximate methods have been developed for solving Schrodinger equation to find wave function and energy of the complex system under consideration. • Two widely used approximate methods are, 1. Perturbation theory 2. Variation method
Perturbation theory is an approximate method that describes a complex quantum system in terms of a simpler system for which the exact solution is known. • Perturbation theory has been categorized into, i. Time independent perturbation theory, proposed by Erwin Schrodinger, where the perturbation Hamiltonian is static. ii. Time dependent perturbation theory, proposed by Paul Dirac, which studies the effect of time dependent perturbation on a time independent Hamiltonian H0.
PERTURBATION THEOREM
FIRST ORDER PERTURBATION THEORY
FIRST ORDER ENERGY CORRECTION
FIRST ORDER WAVE FUNCTION CORRECTION
APPLICATIONS OF PERTURBATION METHOD
SIGNIFICANCE OF PERTURBATION METHOD
Photoluminescence Spectroscopy for studying Electron-Hole pair recombination ...RunjhunDutta
Description of Photoluminescence Spectroscopy: Principle, Instrumentation & Application.
Three research papers have been summarized which lay stress on Photoluminescence Study for Electron-Hole Pair Recombination for characterizing the properties of semiconductors used in Photoelectrochemical Splitting of Water.
This is a pdf file on the topic Gamow theory of alpha decay which gives description about how the scientist Gamow had solved the theory of the alpha decay via tunneling .
Basic operating principle and instrumentation of photo-luminescence technique. Brief description about interpretation of a photo-luminescence spectrum. Applications, advantages and disadvantages of photo-luminescence.
The postulates of quantum mechanics have been successfully used for deriving exact solutions to Schrodinger equation for problems like A particle in 1 Dimensional box Harmonic oscillator Rigid rotator Hydrogen atom • However for a multielectron system, the SWE cannot be solved exactly due to inter-electronic repulsion terms.
The SWE is solved by method of seperation of variables.
• However, the inter-electronic repulsion term cannot be solved because the variables cannot be seperated and the SWE cannot be solved. • Approximate methods have helped to generate solutions for such and even more complex real quantum systems. • Approximate methods have been developed for solving Schrodinger equation to find wave function and energy of the complex system under consideration. • Two widely used approximate methods are, 1. Perturbation theory 2. Variation method
Perturbation theory is an approximate method that describes a complex quantum system in terms of a simpler system for which the exact solution is known. • Perturbation theory has been categorized into, i. Time independent perturbation theory, proposed by Erwin Schrodinger, where the perturbation Hamiltonian is static. ii. Time dependent perturbation theory, proposed by Paul Dirac, which studies the effect of time dependent perturbation on a time independent Hamiltonian H0.
PERTURBATION THEOREM
FIRST ORDER PERTURBATION THEORY
FIRST ORDER ENERGY CORRECTION
FIRST ORDER WAVE FUNCTION CORRECTION
APPLICATIONS OF PERTURBATION METHOD
SIGNIFICANCE OF PERTURBATION METHOD
Compact Photonic Transmitter Based on Annular Ring Antenna for THz ApplicationsTELKOMNIKA JOURNAL
This paper presents the design of Continuous Wave Terahetz photonic transmitters based on photodector which convert the light signal to electrical signal, THz antenna, low-pass filter (LPF) and DC Probe. In the design of the CW THz photonic transmitter System, we begin with the matching input impedance and validation of THz antenna using an EM solver Momentum integrated in ADS “Advanced Design System”. Then we pass to the optimization of a low-pass filter which had the role of inductance, blocking the RF signal providing from the antenna to reach the DC probe. Finally, we associate the previous structures with a DC probe and simulate the whole circuit until validating the CW THz photonic transmitter circuit. The three structures are based on multi-layers GaAs substrate, which is the most widely used for THz circuit design. The dimensions of the whole circuit are 819.071×164.10 휇푚2.
Electro-optic Dendrimer is used to generate milliwatts of terahertz power by difference frequency
method. A terahertz time-domain spectrometer (THz-TDS) has been designed around this source that
exhibits wide broadband terahertz range, 0.1 to 35 THz. Examples of molecular characterization are discussed
for three common explosives and the vibrational states of Fullerenes. The explosives’ spectra are
unique for each explosive that allow detection and identification of the species. The Fullerenes C60 and
H2@C60 also exhibit distinctively different spectra and absorbance states indicating that the THz-TDS is
suitable for probing increased number of vibrational states expected from molecular vibrations.
2011 Elsevier B.V. All rights reserved.
2019-06-07 Characterization and research of semiconductors with an FTIR spect...LeonidBovkun
2019-06-07 Educational seminar at EP-3 University of Wuerzburg
I will present particular experiments and related results with FTIR spectrometer, so one may consider these experiments complimentary for you research.
Safalta Digital marketing institute in Noida, provide complete applications that encompass a huge range of virtual advertising and marketing additives, which includes search engine optimization, virtual communication advertising, pay-per-click on marketing, content material advertising, internet analytics, and greater. These university courses are designed for students who possess a comprehensive understanding of virtual marketing strategies and attributes.Safalta Digital Marketing Institute in Noida is a first choice for young individuals or students who are looking to start their careers in the field of digital advertising. The institute gives specialized courses designed and certification.
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June 3, 2024 Anti-Semitism Letter Sent to MIT President Kornbluth and MIT Cor...Levi Shapiro
Letter from the Congress of the United States regarding Anti-Semitism sent June 3rd to MIT President Sally Kornbluth, MIT Corp Chair, Mark Gorenberg
Dear Dr. Kornbluth and Mr. Gorenberg,
The US House of Representatives is deeply concerned by ongoing and pervasive acts of antisemitic
harassment and intimidation at the Massachusetts Institute of Technology (MIT). Failing to act decisively to ensure a safe learning environment for all students would be a grave dereliction of your responsibilities as President of MIT and Chair of the MIT Corporation.
This Congress will not stand idly by and allow an environment hostile to Jewish students to persist. The House believes that your institution is in violation of Title VI of the Civil Rights Act, and the inability or
unwillingness to rectify this violation through action requires accountability.
Postsecondary education is a unique opportunity for students to learn and have their ideas and beliefs challenged. However, universities receiving hundreds of millions of federal funds annually have denied
students that opportunity and have been hijacked to become venues for the promotion of terrorism, antisemitic harassment and intimidation, unlawful encampments, and in some cases, assaults and riots.
The House of Representatives will not countenance the use of federal funds to indoctrinate students into hateful, antisemitic, anti-American supporters of terrorism. Investigations into campus antisemitism by the Committee on Education and the Workforce and the Committee on Ways and Means have been expanded into a Congress-wide probe across all relevant jurisdictions to address this national crisis. The undersigned Committees will conduct oversight into the use of federal funds at MIT and its learning environment under authorities granted to each Committee.
• The Committee on Education and the Workforce has been investigating your institution since December 7, 2023. The Committee has broad jurisdiction over postsecondary education, including its compliance with Title VI of the Civil Rights Act, campus safety concerns over disruptions to the learning environment, and the awarding of federal student aid under the Higher Education Act.
• The Committee on Oversight and Accountability is investigating the sources of funding and other support flowing to groups espousing pro-Hamas propaganda and engaged in antisemitic harassment and intimidation of students. The Committee on Oversight and Accountability is the principal oversight committee of the US House of Representatives and has broad authority to investigate “any matter” at “any time” under House Rule X.
• The Committee on Ways and Means has been investigating several universities since November 15, 2023, when the Committee held a hearing entitled From Ivory Towers to Dark Corners: Investigating the Nexus Between Antisemitism, Tax-Exempt Universities, and Terror Financing. The Committee followed the hearing with letters to those institutions on January 10, 202
Honest Reviews of Tim Han LMA Course Program.pptxtimhan337
Personal development courses are widely available today, with each one promising life-changing outcomes. Tim Han’s Life Mastery Achievers (LMA) Course has drawn a lot of interest. In addition to offering my frank assessment of Success Insider’s LMA Course, this piece examines the course’s effects via a variety of Tim Han LMA course reviews and Success Insider comments.
Macroeconomics- Movie Location
This will be used as part of your Personal Professional Portfolio once graded.
Objective:
Prepare a presentation or a paper using research, basic comparative analysis, data organization and application of economic information. You will make an informed assessment of an economic climate outside of the United States to accomplish an entertainment industry objective.
Francesca Gottschalk - How can education support child empowerment.pptxEduSkills OECD
Francesca Gottschalk from the OECD’s Centre for Educational Research and Innovation presents at the Ask an Expert Webinar: How can education support child empowerment?
Introduction to AI for Nonprofits with Tapp NetworkTechSoup
Dive into the world of AI! Experts Jon Hill and Tareq Monaur will guide you through AI's role in enhancing nonprofit websites and basic marketing strategies, making it easy to understand and apply.
3. !3
What is spectroscopy?
• Study of the quantised interaction between matter and electromagnetic radiation.
Image courtesy: hyperphysics.phy-astr.gsu.edu
4. What is Terahertz(THz)?
• Ranges from 0.1 to 10THz
• 1THz = 1012 Hz
• wavelength: 3mm to 0.03mm
Chem. Soc. Rev., 2012, 41, 2072–2082
Anal. Chem., 2011, 83, 4342–4368 !4
• Wavenumber: 3.3cm-1 to 333.6cm-1
• Energy: 0.41 to 41 meV
• Temperature: 1 to 100K
5. What is Terahertz Gap?
Appl. Phys. A, 2010, 100, 591–597
• Non availability of THz generators and Detectors
• Non availability of stable femtosecond lasers
This restricts the application of THz in science and industry, offering complementary or
even alternative methods of material characterization.
!5
6. Properties of THz radiations:
• Terahertz waves can penetrate through materials opaque to other parts of the EM
spectrum
• Packaging materials as plastics, ceramic, wood etc. are transparent to some degree
• Does not initiate any changes in chemical structure, as opposed to other forms of
spectroscopy
• Can create images and transmit information
• It lies in the region of rotational transitions of many gas molecules and the
vibrational transition of weak bond.
!6
Image source: Science, 2002, 297 5582, 763
7. !7
Generation of THz radiation:Chapter 3. Generation and detection of THz radiation 29
Figure 3.5. Source [2]: THz radiation from accelerating electrons by frequency up conver-
sion.
accelerators produce extremely bright THz radiation. The process of generating the THz
radiation from accelerating electrons results in both broadband and continuous wave THz
radiation as indicated below;
1. Femtosecond laser pulse incident on the electron source, triggers the electron source,
and sets in motion ultrashort pulses of electrons. The generated electrons are accel-
erated to relativistic speeds, smashing them into a metal target or forcing them into
circular motion by a magnetic field. It is the acceleration of these transient electrons
that generates coherent broadband THz radiation [2].
2. CW THz radiation can be generated using Backward Wave Oscillators (BWOs) and
Stellenbosch University http://scholar.sun.ac.za
THz radiation are mainly two types Broadband and Continuous wave (CW)THz radiation
Principles of terahertz, science and technology. Springer, 2009
3.2.2.1 Photocurrent in semiconductors
THz generation from photocurrent in semiconductors utilising a biased photoconductive
antenna excited by laser beams. Two techniques utilising this process are summarised
in Figure 3.4. In the first technique a femtosecond laser pulse produces broadband THz
radiation by using transient photoconductive switching of the PC antenna. The other
technique is referred to as photomixing, where two laser beams with different frequencies
are mixed forming an optical beat which generates CW THz radiation at the beat frequency
via a PC antenna. More information about the structure and operation of a PC antenna
is given in Section 3.3.
Figure 3.4. Source [2]: THz radiation from accelerating electrons by frequency down
conversion.
THz radiation from
accelerating electrons by
frequency down
conversion
THz radiation from
accelerating electrons
by frequency up
conversion
10. !10
Photoconductive antenna (PC):
Mounted on a hemispherical substrate lens
electrical switch in which
the increase in electrical
conductivity of semiconductors
and insulators when they are
exposed to light
• Most commonly used THz emitter and detector
• Examples: LT-GaAs, RD-SOS, Cr-GaAs, InP, amorphous Si
Int. J. Infrared Millimeter Waves, 2006 , 27, 531–546.
PC emitter antenna PC detector antenna
12. !12
Detection of THz using PC:
Chapter 3. Generation and detection of THz radiatio
Figure 3.9. Schematic representation of THz puls
silicon, as will be summarised in Subsubsection 3.4.1
PC antenna excited by femtosecond laser.
Schematic diagram of detection of THz radiations
Int. J. Infrared Millimeter Waves, 2006 , 27, 531–546.
13. !13
3.4.1 Materials for Photoconductive switches
A wide variety of materials have been used for the construction of photoconductive anten-
nas. Some examples are shown in Table 3.2. Of all these materials, the most commonly
Photoconductive ma-
terials
Carrier
lifetime
(Ps)
Mobility
(cm2
/(V.s))
Resistivity (⌦.cm)
(Breakdown field, V/cm)
Band gap
(ev at R.T)
Cr:doped SI-GaAs 50 100.0 ' 1000 107
1.43
LT-GaAS 0.3 150 200 106
(5 ⇥ 105
) 1.43
SI-InP 50 100.0 ' 1000 4 ⇥ 107
1.34
Ion-Implanted InP 2 4.0 200 > 106
1.34
RD-SOS 0.6 30 1.10
Amorphous Si 0.8 20.0 1 107
1.10
MOCVD CdTe 0.5 180 1.49
LT-In0.52Al0.48As 0.4 5 1.45
Ion-Implanted Ge 0.6 100 0.66
Table 3.2. Characteristics of ultra fast photoconductive materials [32].
used materials for THz emitters and detectors are, radiation-damaged-silicon-on sapphire
(RD-SOS) and low-temperature grown gallium arsenide (LT-GaAs) [2, 32]. RD-SOS is pre-
pared by implanting argon, silicon or oxygen ions into SOS samples. Implanting results in
Materials for Photoconductive switches:
Terahertz optoelectronics. Springer, 2005
14. !14
THz time-domain spectroscopy
It uses THz pulsed tradition and consists of an Emitter stimulated by femtosecond laser, a
beam forming optics consisting of focuses lenses and mirrors, a sample holder and optical
delay line and a Detector which uses a femtosecond laser.
Nanotechnology, 2015, 26 (31), 5203
Difference absorption
spectra technique,THz
pulse is measured with and
without the sample.
The absorption and
dispersion of the sample
obtained by Fourier
transformation.
THz-TDS determines both
the amplitude and the phase
Pump Pulse
REVIEW ARTICLES
Femtosecond laser Half mirror
Emitter
Excitationpulses
Off-axis
paraboloidal mirror
Detector
Time delay
Detection pulses
THz
1.0
0.8
–0.2
–0.4
0.0
0.2
0.4
0.6
DAST
p-InAs
DAST
p-InAs
100
10–1
10–2
Normalizedamplitude(a.u.)
1,560 nmc
Probe Pulse
Schematic diagram of THz time domain spectrometer
15. !15
Material Type Optical property
Liquid Water High absorption (α = 250 cm−1 at 1
THz)
Metal High reflective (> 99.5 % at 1 THz)
Plastic
Low absorption (α < 0.5 cm−1), low
refractive index (n ∼= 1.5)
Semiconductor Low absorption (α < 1 cm−1 at 1
THz), high refractive index
Optical properties of condensed matter in the THz band:
Principles of terahertz, science and technology. Springer, 2009
17. !17
Opt. Commun. 2012, 285, 1868
IR-Spectra THz-Spectra
Chemical Analysis and Molecular Spectroscopy:
1. Differentiating the molecules:
18. !18
Chemical Analysis and Molecular Spectroscopy:
Due to low energy of THz radiation many vibrational and rotational modes fall within this region.
2. Tracing illegal drugs/ narcotics:
REVIEW ARTICLES
to study the behaviour of light at longer wavelengths. Examples
include the study of multiple diffraction and propagation in
random media84,85
and the group-velocity anomaly of propagating
Figure 6 MOSFET damage detection by LTEM. a, Laser-reflection image of a
series of MOSFETs. Three MOSFETs as indicated by yellow circles have interrupted
connection lines cut by a focused ion beam. One MOSFET is shown magnified
in the large yellow circle. b,c, LTEM images of the normal and damaged sample,
respectively. The negative and positive amplitude of the THz waves, when the delay
time is fixed at the time which gives maximal intensity, are denoted by black and
white respectively. The blue and red boxes indicate p- and n-type respectively.
200 µm
a b c a
Visible THz-reflection mode
b
Codeine Cocaine Sucrose
(60 mg each)
Every explosive and narcotic has a
distinct signature in its THz spectra,
making THz spectroscopy valuable
for security applications.
Nat. Photon., 2007, 1 97105
rtz spectroscopy of explosives and drugs
a range of common drugs-of-abuse. The samples are prepared as compressed pellets, diluting the pure drugs with PTFE powder;
ht) is indicated. A refractive index measurement is shown for cocaine free base, as an example. The cocaine free base and cocaine
s shown in Fig. 2.
19. !19
Chemical Analysis and Molecular Spectroscopy:
3. Tracing explosive:
Absorption
THz absorption spectra of a range of
common explosives. The pure
explosive samples (PETN and RDX)
were diluted with PTFE powder to a
30:70 (explosive: PTFE) ratio by
weight, and compressed into pellets
range of common explosives. The pure explosive samples (PETN and RDX) were diluted with PTFE powder to a 30:70 (explosive:
essed into pellets. The plastic explosives (Metabel, Semtex, and SX2) were cut into thin slices and measured without further
x and SX2, several spectra are shown, each arising from a different sample batch. A refractive index measurement is shown for
Mater. Today 2008, 11(3)
20. !20
Biology and Medicine:
Water is strong observer of
THz radiations in 1-3THz.
So THz radiation can
detect the difference in
water content and density
of a tissue.
Image Source: teraview.com
21. !21
Diabetic foot measurement studies using THz. (A) Photograph of the measurement set-up. THz images
plotting the calculated water volume for (B) a control and (C) a diabetic patient. (D) Calculated water
volume for control and diabetic patients using data from the centre of the big toe.
Quant Imaging Med. Surg. 2017;7(3):345-355
Biology and Medicine:
23. !23
Chem. Phy. Lett. 2004, 390, 20–24
rahertz absorption spectra for
orms of CBZ, EM, IM, and FC
from the figures that differences
or all four compounds give rise
he terahertz absorption spectra
ectra of CBZ forms III and I
t are polymorph-distinct. The
ibits major peaks at 41, 60 and
eak at 47 cmÀ1
while the form I
peaks at 31, 44, 52 and 70
ty peak at 23 cmÀ1
. The mid-
n spectra of forms III and I are
tive absorptions however, can
d 1680 cmÀ1
in the IR spectra
udies have shown that these
ith the CONH2 moiety. Both
mation with hydrogen-bonding
Fig. 3. Absorbance spectra of EM form I (solid line) and form II
(dashed line) 25% in PE.
10 20 30 40 50 60 70
0.0
0.5
1.0
1.5
2.0
2.5
Absorbance(decadic)
Wavenumber / cm
-1
Fig. 4. Absorbance spectra of IM crystalline (solid line) and amor-
phous (dashed line) 75% in PE.Indomethacin (anti-inflammatory drug)
Amorphous(dotted line) and Crystalline(solid)
Pharmaceuticals:
24. !24
THz imaging:
Concealed knife under the sole of shoe
Check before you buy next time..
Crack in ceramic
Image sources: Terasense and Teraview
25. !25
Visible image of an integrated circuit THz image of an integrated circuit
Electronic devices:
Opt. Lett. 1995, 20 (16)
27. !27
Current wireless systems utilise carrier waves less than 5 GHz which restrict their
maximum data rate, 100’s Mbps typically. Higher frequency carriers enable high data rates
and therefore 1000’s Gbps dates rates are on offer with terahertz carrier waves.
J. Phys. D: Appl. Phys. 2017, 50, 043001
Wireless technology:
46 Gbps..😳
using a carrier frequency of 400 GHz
28. !28
Read through a book without opening it..
flections of the E-field from the layered
me resolution. The sample consists of nine
single character written on each page. The
the velocity extracted from the waveform, with high energy
corresponding to large amplitudes and low velocities (Supple-
mentary Fig. 2a). This corresponds to candidate points being
Sample
n2n1n0n1n0
1,
92,..2,..
1,
Layered sample
Motorized
stage
z
y
x
THz-TDS
d< , g <0.1
g~20 µm d~300 µm
ba
geometry and sample schematics. (a) Confocal THz time-domain (THz-TDS) measurement is used in reflection geometry. x–y–z
n coordinate system that is kept consistent throughout this study. The 9-page sample is held on an x–y-motorized stage that
r scanning in x–y plane. A THz pulse is transmitted. The electric field is a bipolar pulse as shown schematically in blue. The
n red) has a series of dense reflections (usually more than nine) from the layered sample that provides time-of-flight information
n z. (b) The layered sample is composed of nine packed paper layers. Each layer is 300 mm thick and the non-uniform gaps
B20 mm after pressing the pages together.
NATURE COMMUNICATIONS | 7:12665 | DOI: 10.1038/ncomms12665 | www.nature.com/naturecommunications
timization software. Figure 3c shows that
pite the presence of significant shadowing
deeper layers. The CCSC optimization is
ary Note 7.
n. The proposed three steps work together
deep as possible (Supplementary Movie).
uperior performance (about an order of
dB—SNR is 20log(|Es|.|En|À 1)) of PPEX
of standard deconvolution techniques
Es is the signal component of the mea-
plitude and En is the noise component.
th edge detection techniques and CLEAN
n in Supplementary Figs 4a–e and 5a–d
plied to the data before feeding it to the
4a comparison. The induced dispersive
omain is not because of the dispersion in
itself as in the case of optical waveguides.
ve behaviour induced by the frequency-
the detection process. Water vapour-induced ripples in the
electric field can be partially compensated for deconvolution
methods as well, but the strong reference dependency of these
techniques means that any change in the humidity level can
negatively impact the deconvolution.
Figure 4b shows the difference between amplitude mapping in
the time domain and the time-gated Fourier transform. The time-
gated spectral analysis based on kurtosis provides up to 18 times
more contrast for the eighth layer. For the ninth layer, the signal
level is too low to accurately estimate the contrast improvement
(our estimation is B10.5). However, in Fig. 4b, we see that the
character is now completely recognizable to both the human eye
and the CCSC algorithm.
The signal loss with depth is a major burden on reading deeper
layers. This loss is caused by consecutive reflections at the
material interfaces (both the back and the front of each layer) and
also by the exponential Lambertian absorption of the layers
themselves. The reflected signal level is not the bottleneck to
content extraction at deeper layers (we can detect 15 pages with
the first step of time-gated spectral imaging; PPEX), it is rather
Page number
0
1
0.51
0
5
10
15
20
20100
25
30
30
35
40
40
2 3 4 5 6 7 8 9
x(mm)
t (ps)
a b
c
ontent extraction with THz time-gated spectral imaging. (a) Layers are identified in time based on the statistics of the
ignal. Image is binary. (b) The technique uses kurtosis of the time-gated Fourier transform to contrast the content. Grey scale
rmalized amplitude of the averaged frequency components in arbitrary units that is output from the contrast enhancement
malized separately, and horizontal and vertical axes are omitted for simplicity. (c) Convex cardinal shape composition (CCSC)
uded characters through THz noise down to page 9. The detected letters are highlighted with light orange.
a
c
0
17
0
Page 1 Page 2 Page 3
Page 4 Page 5 Page 6
Page 7 Page 8 Page 9
x (m
y(mm)
Figure 2 | Sample description and raw measurements overview. (a) Nine
are then stacked on top of each other, respectively. The orange highlighted a
NATURE COMMUNICATIONS | DOI: 10.1038/ncomms12665
Nine roman letters T, H, Z, L, A, B, C,
C and G are written on nine pages
(a) THz-TDS measurement is used in reflection geometry
(b) layered sample is composed of nine packed paper layers
uniform thickness
(a) Layers are identified in time based on the
statistics of the reflected bipolar THz field
signal.
(b) Then converted the time-gated Fourier
transform to contrast the content.
(c) Convex cardinal shape composition
algorithm extracts the occluded characters
through THz noise down to page 9.
Nat. Comm. 2016, 7, 12665
29. !29
THz technology
Plasmonics
Metamaterials
MEMS
Semiconductor technology
Material properties
Nano- and microtechnology
Electromagnetic wave simulation
Spectroscopic and imaging equipment
Optical components (lenses, filters, polarizers,
waveguides, modulators)
Sensing devices
Superconductor technologyLaser technology
Small light sources (laser-excited radiation devices, electronic devices)
Medium and large light sources (gyrotrons, synchrotron, FELs)
Detectors (bolometers, superconductive detectors, single-electron
transistors, arrays)
Information communications
Security
Materials science Analysis science
Biology
Medical care
Agriculture
Industries
Space technologies
Environment
Drug development
Preservation of
cultural assets
Quantum
information
Nuclear fusion plasma diagnosis
Materials development
Fig. 15. (Color online) Peripheral technologies and applications of THz technology.
54, 120101 (2015) COMPREHEN
Jpn. J. Appl. Phys. 2015, 54, 120101
Conclusions