An Introduction to Terahertz Electromagnetic Waves
Generation, Detection, Properties and Applications
Michael R. Boersma, Member IEEE
Abstract –Electromagnetic waves spectrum contains
waves containing wavelengths from 30 cm down to .3
nm. Terahertz waves are in the area of 300 m and the
terahertz gap is generally considered to be between 300
GHz and 10 THz. What makes terahertz waves
interesting is there possible applications because of their
interesting properties. They are less harmful then Xrays when used for medical imaging, and when used for
spectroscopy they provide information other waves
cannot. In this paper the nature of terahertz waves will
be examined, focusing on their generation, detection,
properties, and their applications.
Index Terms –Applications,
Terahertz waves.
I.
Detection Properties,
INTRODUCTION
Terahertz waves are quickly gaining attention and
research funding. These waves are in the 100 GHz to 10
THz frequency range, this range is also know as the
“terahertz gap,” as demonstrated in figure 1. This gap exists
because until recently effective methods of generating
controlled THz waves, and methods for detection of THz
waves, were not available. Today there are two basic
methods by which terahertz waves are produced. The first
method is to use solid-state electronics, but this proves
difficult for many reasons. The second method is optical
generation, in which high-speed lasers are pulsed as certain
semi-conductor surfaces. It is this second method that is
receiving the most research attention.
Terahertz waves have found applications in many
different fields, such as physics, material science, electrical
engineering, chemistry, forensics, and new research
potential are being discovered in biology and medicine.
The area of focus in this paper will be spectroscopy and
medical imaging applications.
The generation and detection of terahertz waves
will also be discussed in this paper. The properties of
terahertz that make them the focus of current studies will
also be presented. Finally, some of the applications for
terahertz waves, such as medical imaging, will be discussed.
Figure 1: Electromagnetic spectrum showing the THz band gap.
II. PURPOSE
The need for this kind of study is justified by the
potential benefits terahertz waves poses. The field that is
currently receiving the most attention is medical imaging
and spectroscopy. THz waves have different absorption and
reflective indices in different tissues. Using terahertz waves
abnormalities could be detected sooner then currently
possible. THz could also make it possible to distinguish
between tissues more effectively. THz waves also provide
an advantage over x-rays because they are less harmful to
living tissue. This is because they carry less power then xrays.
The purpose of this paper it to provide an
introduction into THz imaging and research possibilities.
By giving an overview of the field the goal it to provide a
paper which is accessible yet provides a through
understanding of the challenges and successes that have
come from THz research.
III. GENERATION
Beginning in the early 1990’s two basic techniques
for generating THz waves were being developed, solid state
and optical methods as mention earlier. Optical generation
can be subdivided into photoconduction and optical
rectification. The following section provides an overview
of these two generation methods.
A. Solid-State Generation
For years, solid-state electronics have generated
infrared light by using a layered semiconductor structure,
such as in diodes that emit infrared light or lasers that
operate in the infrared range. But this principle is not easily
extended down to the THz band. Interband diode lasers,
which operate at a wavelength of 3 m, operate on the
principle that conduction band electrons will recombine
with valance band holes across a gap of active material. In
doing so light, or electromagnetic waves are emitted. But
this type of laser cannot be used to emit THz wave simply
because suitable semiconductors for this type of excitation
are not available.
A new kind of laser, called the quantum cascade
concept has been used in research. Here, the transition
between semiconductor layers is used to emit light. The
idea is that the thickness of these layers can be changed to
manipulate the electrons path. The theory is that it is
possible to engineer many different wavelengths using this
method. Again, however, a problem arises; the active
regions must be very large to accommodate THz
frequencies. This is because the active region grows as the
square of the wavelength [1]. Below 10 THz the generation
of waves becomes impossible for room temperate emitters.
However, 4.4 THz has been achieved at cryogenic
temperatures. It is these difficulties that have led to the
development and excitement about optical techniques for
generating THz waves.
then optical rectification [7]. Photoconductive antennas are
discussed in detail later in this report.
2. Optical rectification
This is also a simple and well-understood process,
which now can be applied to the generation of THz waves
because of the availability of suitable semiconductors.
Optical rectification is a second-order non-linear process
[1]. When the laser pulse hits the semiconductor the
semiconductor is polarized. The voltage that results is
proportional to the strength of the laser beam. The
“envelop” of the laser pulse is all that remains. Figure 2
demonstrates this process. The equation governing this
reaction is shown in equation 1.


P  THz


 0    E vis1  E  vis2
2
Eq. 1
Where THz = |vis1 – vis2| and is the receptiveness of
the semiconductor.
B. Optical Generation
The optical generation method does away with the
need for a solid-state emitter in the THz band. Instead,
optical generation uses a laser that pulses as 10 to 200 fs,
which is in the visible or infrared spectrum. This laser is
pointed at what is known as a THz generator, often GaSe,
GaP, or GaAs. This semiconductor generator will either
reflect the pulses or propagate them through itself. What
results are THz waves. This is possible because here the
semiconductor is no longer emitting the light. Instead they
are simply being used to conduct or refract the light.
Photoconduction and rectification are the two different
variations of optical generation that result from the
propagation or reflection of the incident laser pulses.
1. Photoconduction
Photoconduction is a commonly understood
process and has been used in other applications.
Photoconduction is the process by which current is
generated from a photoconductive semiconductor. All
materials have a valance band of electrons and a conduction
band, which is at a higher energy level. The “gap” in
between these bands is knows as the forbidden energy gap.
In insulators this gab is very large. In conductors it does not
exist because the valance electron band and the conduction
band overlap. In semiconductors the gap is small. It is
possible to over come the gap by applying a sufficient
amount of energy, such as electromagnetic energy from the
incident waves.
When such a process is applied to certain
semiconductors, like GaSE small bursts of current result.
This current provides the energy for radiating antennas.
This process generally provides higher-powered THz waves
Figure 2: Example of optical rectification: the laser pulse is shown
before and after it strikes the semiconductor [11].
The shorter wavelengths of visible or inferred light that are
emitted from the pulsing laser are filtered out. The rectified
signal of the pulse that remains is in the THz frequency
range provided that the laser was pulsed with the
appropriate timing.
C. Processes of Semiconductor Sources
The semiconductors that are used as THz
generators in conjunction with femtosecond laser pulses use
one of two methods to generate THz waves. Bulk electrooptic rectification or ultra fast charge transport.
1. Bulk Electro-Optic Rectification
This is a version of optical rectification. In the
rectification process the large electric field from the laser
pulses allows the non-linear receptiveness of a
semiconductor to generate the THz waves. A polarization
in the THz range occurs which is proportional to the
intensity of the laser pulses.
Bulk electro-optic rectification differs from simple
optical rectification because here two laser pulses are
incident on the semiconductor. A special variety of crystals
are used, called NLO crystals. NLO crystals either combine
or separate incoming electromagnetic waves [8]. The two
types of combining NLO crystals are sum frequency
generation (SFG) or differential frequency generation
(DFG).
1
1
eff( k) 0.5
7
2.57310
0
10
0
10
 10
k
10
Figure 4: Graph of conversation efficiency, demonstrating how
smaller phase mismatching numbers lead to height conversion
efficiency’s.
Figure 3: Diagram of how waves enter an NLO crystal.
For SFG NLO crystals the resulting wavelength is given in
Eq. 2, and Eq. 3 gives the resulting wavelength for a DFG
NLO crystal [8].
1  2
1  2
3
3
Eq. 2
Eq. 3
The efficiency of the conversion from the visible or
near infrared spectrum to THz is determined by the
effectiveness phase matching (PM) between the pulses
entering the NLO crystal and the resulting field [1]. The
conversation efficiency depends on phase mismatching.
Phase mismatching, k, is described in Eq. 4. From phase
mismatching the PM effectiveness can be found. PM
effectiveness is shown in Eq. 5.
k
 n3
2  
 3

n2
2

n1 

1

Eq. 4
Where ni is the refractive index, and i is the wavelength.
eff ( k)  

sin ( k) 
k


2
Eq. 5
What is shown from these equations is that the
smaller the phase mismatching is, or in other words the
closer the refractivity and wavelength of the resulting wave
is to the incoming waves the better conversation efficiency
is. Figure 4 shows conversion efficiency with respect to
phase mismatching.
In other words, for the best result the group
velocity of the laser pulse should be matched to the phase
velocity of the THz wave pulse [1]. This is difficult to
accomplish.
Yet this method has been successfully
employed in a wide variety of semiconductors, including
GaAs, GaP, GaSe, and ZnTe as all as by using certain
organic compounds.
2. Ultra-Fast Charge Transport
Ultra-fast charge transport earns its name from
electron-hole pairs that are formed on the surface of the
semiconductor. Again a laser pulse of around 100 fs in the
visible to near infrared wavelength range is used. This
pulse of photon energy is greater then the bandgap of the
semiconductor resulting in the creation of the electron-hole
pairs on the surface of the semiconductor. The changing
dipole moments from an applied electric field cause the
generation of THz waves [1].
One method for applying the electric field was
developed by D. H. Auston. Auston’s method was to imbed
two electrodes into the semiconductor surface. Which
applied a large electric field and accelerated the electronhole pairs.
Ultra-fast
charge
transport
is
receiving
considerable attention. It is allowing the development of
many new applications of THz technology.
D. Semiconductor Sources Properties
As mentioned earlier, some of the common
semiconductors used in terahertz generation are GaSe,
GaAs, GaP, and ZnTe. By far the most common are the Ga
crystal varieties. Experiments that have been conduction on
Ga crystals and the properties that have been demonstrated
are presented here.
1. GaSe Semiconductor Sources
Experiments conducted, such as that described in
[5], have demonstrated the properties of tunable terahertz
waves generated with GaSe. The waves were generated
using optical rectification. The laser used as a 1.064 m
YAG laser. The crystals used were 2 mm thick of undoped
GaSe. Because this was intended for spectroscopy use over
a wide range these short crystals where used because power
would not be limited. Long crystals would also have made
the setup more difficult because displacement of the THz
signals caused by the orientation of the crystals could not be
neglected as with the short crystals.
The experiment in [5] was done using a DFG NLO.
The efficiency of which for GaSe can be found by a
different method then the one described above. Taking the
cosine squared of PM () and the cosine of the azimuthal
() angle, as shown in Eq. 6.
eff
d22  cos     cos  3 
2
generated was bulk electro-optic rectification. A 140 fs
pump laser was used. The experiments in [13] were done to
compare the response of GaAs and InAs to differing
magnetic fields. A summery of their findings is presented
in figure 5. For both GaAs and InAs the highest power
around or just below 2 THz.
Eq. 6
This means that NLO conversation efficiency is optimized
at any particular PM when |cos(3)| = 1. In [5] they held
the azimuthal angle such that that condition was met,
allowing them to study the effect of changing PM on
maximum power and frequencies generated.
Using 2 mm GaSe crystals frequencies from 0.3 to
4.9 THz could be generated that produced at least 3% of the
maximum power possible. The highest power wave was
found at 3 THz. The lowest power was at 0.48 mW at the
lower side of the spectrum. The power was maintained at
about 15 mW over 2.4 to 3.1 THz. The power dropped back
off to 0.48 mW at 4.9 THz, and no signal could be detected
at 5.1 THz [5].
2. GaP Semiconductor Sources
Experiments done on GaP, using the same general
set up as those conducted with GaSe have shown that they
are tunable over a 0.5 to 7 THz range [6]. The differences
included using 2.6, 5, and 20 mm crystal but again used
DFG and a 1.064 m YAG laser.
It was shown that the power ranges greatly over the
tunable spectrum. At 0.5 THz the power was 10mW. This
increased all the way up to 300 mW at 2.5 THz for the 20
mm crystal. The semiconductor showed a power of 67 mW
at 1.3 THz, which rose to 100 mW at 2.5 THz. Interestingly
the power maximum occurred at the same frequency as the
20 mm crystal. Unlike the 20 mm crystal the 5 mm crystal
held that 100 mW over a wide range, 2.5 – 4.5 THz. The
smallest crystal size was able to maintain a higher power
level at frequencies above 7 THz then the 5 mm crystal [6].
Overall, GaP was tunable over a larger then GaSe,
as well as provides higher-powered waves. But there are
advantages to GaSe because the configuration for GaSe is
easier for spectrometer applications [5].
3. GaAs and InAs Semiconductor Sources
GaAs and InAs are being compared together
because of there seminaries, and because [13] used the same
experimental setup for each of these semiconductors in their
experiments. The process by which the THz waves were
Figure 5: Power vs. frequency for GaAs and InAs semiconductor
THz generation.
IV. DETECTION
It is obvious that the generation of THz waves is
pointless without an effective means of detection. The
general process by which THz waves are detection follows
four steps. First the waves are focused onto a detection
medium or photoconductive antenna, which will be
discussed later. Second, the birefringence can be read using
a visible or inferred pulse, usually split off of the laser used
to generate the waves. Third, the probe beam is measured
with a quarter wavelength plate. Finally, the time delay
between the probe pulse and the THz signal can be
measured to obtain the electric field in the time domain.
A. Photoconductive Antennas
Photoconductive antennas were the first key to
effective THz detection, as well as emissions. They are
commonly made from either Si or GaAs. Laser pluses split
off from the pump laser pulses probe the antenna. The time
delay from pump and probe pulses are measured, as well as
the chance in DC current form the antenna to determine the
THz waveform [12].
The common structure is shown in figure 6. It is
shown with a GaAs substrate, but other semiconductors
such as GaSe may be used. The whole in the middle,
labeled D on the diagram, is biased by a DC voltage, A, and
is probed by laser pulses slit off from the laser pump in the
case of detection. It is normally on the order of 5 to 10 m.
The over all size of the antenna is generally 10-20 (W) m
by 30-50 (L) m [12].
waves with the sample is measured by recording the
waveform of the THz wave.
V. APPLICATIONS
The study of terahertz waves applies to many
areas, from forensics to 3D imaging, medical imaging and
spectroscopy. Medical imaging however presents many
areas of study. Terahertz wave poses many properties that
make them perfect for such imaging, but also contain many
challenges.
A. THz Imaging and Tomography
Figure 6: Photoconductive antenna structure [12].
The THz waves strike the antenna they cause slight
transient current changes. These current changes J(t)
describe the incident electromagnetic field by the simple
relation shown below:
ETHz
d
J( t)
dt
Eq. 7
d
The maximum
ETHz THz
J( t)wave that is capable of being measured
by the photoconductive
antenna is:
dt
Emax
1  R  Pin  Vb
 D
 hv 
e    
Eq. 8
In eq. 8,  is the mobility of the carriers, R is the reflectance
of the substrate, hv is the photon energy form the laser, P in
is the average laser power, and Vb is the biasing voltage
[12].
The bandwidth of the antenna is affected by several
factors. The key factors are the physical structure of the
antenna, the carrier scattering time, the THz beam optics.
However, what is the key factor according to [12] is the
duration of the laser pulse.
B. Electro-Optic Sampling
Electro-Optic sampling was first presented in 1995
and offers several benefits over a single photoconductive
antenna. It is able to provide a higher bandwidth and has
parallel imaging capabilities.
The birefringence caused by the electric field
applied will polarize an optical probe beam that is passed
through the crystal. This polarization can be analyzed to
determine the amplitude and phase of the THz field. If a
thinker crystal is used the sensitivity of the system is
increased because the length of the interaction between the
field and electro-optic probe is increased. To image a
sample, the sample is placed in-between the THz. Wave
source and the sensing crystals. The interaction of the THz
Just As other electromagnetic waves are used in
imaging so can THz waves. This is the single most
important application of THz waves and most other
applications draw from THz imaging. THz imaging has
been demonstrated on leaves, semiconductors, IC packages,
floppy disks, biological material, and teeth. THz imaging
possibilities has been demonstrated on such a wide range of
material because THz waves penetrate almost all nonmetallic or polarizing substances [12].
What is the benefit of THz waves over X-rays
though? X-rays are capable of penetrating nearly all
materials, and the technology is well developed. X-rays are
limited however in what they can image. If the material as a
low index materials x-rays cannot provide clear images.
THz waves could be used to supplement x-rays in this case
[12].
There are other properties of THz waves that have
clear benefits over other imaging techniques. One benefit
of using THz time-domain spectroscopy (THz-TDI) is that
THz-TDI provides a measurement of the electric field
produced by THz waves, of the intensity of the wave [9].
Through this phase information is maintained and a Fourier
transform can reveal the imaginary and real components of
the THz wave. When THz waves are applied to a sample
the structure of the sample can be determined.
Another benefit of THz imaging is that is it also
possible to gain spectroscopic information along with the
structural information. This is because THz waves contain
all the necessary frequency information [9]. Other benefits
include improved safety and non ionizing radiation [12].
A disadvantage of THz imaging however is the
resolution. Because THz waves have large wavelengths
then visible light or x-rays they cannot provide as high was
a resolution [12]. This will be discussed more in depth
later.
1. Relevant Wave Equations for THz Imaging
When a THz passes through, or is reflected off it,
the waves amplitude and phase is altered and scattered.
This is a result of the refractive indexes of the samples.
Maxwell’s equations may be used to describe this process
[9,10]. Eq. 8 is an extension of Maxwell’s electric field
equation shown in eq 7.
del  E
2
Eq. 7
0
del  E 
 ( r)  ( r)
c

2
d2
dt
2
E  del  ln   ( r)   ( del  E)
+ del   E  del ln  ( r)  
are the Nyquist criterion. Nyquist criterion, often applied to
digital sampling, says that in order to reconstruct the sample
the sampling rate must be at least twice that of the highest
frequency being sampled. [2] provides an example, if the
area of the sample is 400 mm2, then no less than 128 x 128
(rounded to the nearest power of two) samples should be
taken. And this is just for the special dimensions. In order
to represent spectral
Eq. 8
0
Here c is the speed of light, r is a point in space, (r) is
dielectric constant, and (r) is the magnetic permeability of
the sample [9].
Assuming that  and  are changing slowly a
simplification may be made. If it is indeed the case that 
and  are changing slowly then del natural log of and 
will be approximately 0, as shown is eq. 9.
del  ln ( r) 
del  ln ( r) 
0
Eq. 9
0
Eq. 10
Applying this to eq. 8 we are left with
2
del  E 
 ( r)  ( r)
c
2

d2
dt
2
E
Figure 7: Standard tomography measurement setup [9].
Going one step further and neglecting polarization effects
eq. 10 can be shown to be the scalar Helmholtz equation [9].
del  u ( r)  k0  n    r  u ( r)
2
2
2
0
Eq. 11
n

Here, n is the refractive index, u(r) is the amplitude
function, and k0 is the wavenumber. Eq. 11 is the basis of
imaging techniques [9]. The general goal in THz imaging is
to determine the n(,r) and u(r) functions from the
measured THz wave.
information many more points are need in the time domain.
If the emitter is putting out 3 THz waves then the sampling
rate in the time domain is about 100 fs. In all at least 10 6
points are needed. Since it is a mechanical system that
scans across the sample data taking can be a lengthy process
[2].
C. Capabilities and Difficulties
Many difficulties have arisen in the THz imaging
process. Not the least of which is image resolution.
B. THz Tomography
As said previously, in order to obtain valid
tomography the diffraction and scattering of the THz waves
needs to be resolved by finding the n(,r) and u(r)
functions. Max Born solved this problem in 1925 [9]. The
resulting equation is
u s ( r)









 G( r  r') V( r') u ( r') d r' d r' d r'
0


Eq. 12
G(r-r`) represents the Green function, and u(r) = us(r) +
u0(r). Figure 7 shows the general method of tomographic
measurements. The waves are measured by a wave that by
a plate perpendicular to the incoming waves [9]. By
performing a Fourier transform the sample can be
reconstructed.
Once the waves have been measured this data must
be handled. One of the factors that limits the amount of
data that must be recorded in order to reconstruct the sample
Figure 8: THz image of a melanoma sample under different
conditions. a) Transmittance at .5 THz b) Transmittance at 2 THz
c) Phase angle at 1 THz d) e) dispersion at 1 THz f) dual frequency
image, 1 THz and 1.5 THz. There images were interpolated to cut
down on pixelation [2].
B. Medical Imaging
The need and desire for medical imaging is clear,
there is always a desire for earlier detection and improved,
non-invasive imaging. Currently, in the detection of cancer
medical professionals look for tumors or anatomic location,
but if instead doctors could detect pre-malignant cell
growth, tumor cell markers, or genetic alterations cancer
detection, treatment, and survival would greatly increase
[7].
With THz imaging technology diagnoses could
occur much earlier then current technology allows. It could
provide a multi-spectral 3D image of the tissue or living
abnormal tissue. This would lead to a better understanding
of diseases and how they spread [7]. Indeed, the potential
for THz imaging and spectroscopy technology is nearly
endless in the medical field.
An example of what is possible with THz medical
imaging is shown in Figure 8. From each of the six
different images something unique can be learned. The
sample was prepared according to standard practices; it was
dehydrated, formalin fixed, and then wax embedded. The
difference between pictures (a) and (b) is due to the higher
absorption rates are higher frequencies.
Image (c)
demonstrates a time delay. It points to the refraction
differences between the melanoma and the normal skin,
giving a very clear indicator to the nature of the sample.
The final two images, (e) and (f) also show that the
absorption rate of THZ waves is higher in the melanoma
then he surrounding tissue [2]. Again, demonstrating how
THz imaging could be employed to gain faster and earlier
diagnosis of diseases such as melanoma.
In the next section the current technology for
medical imaging is presented. As well as the current
challenges. This is the main application focus for this
paper.
1. Medical Imaging Systems
A typical medical imaging system is shown in
figure 9. The laser beam is split into two; one beam is for
the THz generation, the other is for detection. THz waves
are optically generated by either photoconduction or optical
rectification. From the generator, parabolic mirrors focus
the THz waves onto the sample.
The detection beam
crosses a detector and acts as a time indicator for the THz
waves being detected [2]. The data can be handled in
several waves as described in the imaging section.
2. Concerns and Challenges
In developing imaging technology for medical
purposes there are additional challenges above the
challenges presented by generating and detecting THz
waves. Foremost is safety, which involves signal power. In
addition to safety concerns there are challenges presented
by absorption rates, size, and cost
Figure 9: Layout for a typical THz imaging system [2].
a. Safety
When THz waves are used for medical imaging it
is very important that that radiation levels to not exceed
safety protocols. Electromagnetic radiation levels are given
in terms of the maximum permissible exposure, or MPE.
This is calculated from the root mean square value of the
peak electric and magnetic fields [2]. Factors that effect the
MPE value are pulse repetition frequency, exposure length,
total number of pulses, the area of the incident beam, and
the duration of the pulse itself. As recommended by the
American National Standard Institute the maximum average
power for a pulsed THz imaging system is
MPEPW
A  MPECW
F t
Eq. 13
Where MPEPW is the maximum average power, A is the
area of the incident beam, MPECW is the maximum allowed
continues exposure power level, F is the pulse frequency,
and t is the pulse duration [2].
Using standard values from other pulsed imaging
technologies MPEPW is 94 W. As discussed in the
generation section earlier, current power in THz wave
systems are on the order of mW, well below what safety
regulations require. It should be noted however, that these
values are typically used for shorter wavelengths. As will
be discussed THz waves have high absorption rates with
water and this could lead to more tissue damage then
expected [2].
b. Absorption rates
This is perhaps the most challenging hurdle to
medical imaging. Water and other polar liquids present a
high absorption rate for THz waves, on the order of 150cm-1
at 1 THz [7]. This limits the depth at which THz waves can
be effective because most THz applications rely on THz
passing though the samples. Therefore, most current
applications in medical imaging rely on skin conditions [7].
The impressions, however, should not be that
absorption of THz waves is a complete limiting factor and
something that needs to be completely resolved. As
mentioned at the beginning of this section, melanoma
absorbs more THz radiation then the surrounding tissue.
This is due to the composition of melanoma. If it were not
for differences in absorption rates some of the effectiveness
of THz imaging would be lost.
c. Size and Cost
A THz wave imaging set up requires a few square
meters. One possible simplification of the process is that
the same semiconductor could be used to both generation
and detection. This is because of the inverse relationship
between optic rectification and electro-optic detection. This
would allow transceivers to be made that are much smaller
[7].
Currently THz systems cost up to $300,000 total,
this is for sensing and imaging of THz waves. Before THz
imaging can be adopted by the mainstream medical
community the cost my have to reduce. Currently THz
imaging systems are limited to research application [7].
d. Specific Medical Applications
The process of THz imaging and medical imaging
processes and concerns have been presented. In order to
clearly demonstrate the need for this technology, presented
are a few specific applications for medical imaging.
Dermatology is the first and obvious application.
Skin is not only the most accessible part of the human body
for observation but some of the difficulties having to due
with THz absorption rates are removed from the picture. It
is already well known that using ultrasound for MRI reveals
differences between normal healthy skin and diseased skin.
THz imaging offers the potential to gain further
understanding into skin diseases, and provide a way to
monitor them more effectively then with large MRI
machines [2].
Specific applications within dermatology include,
monitoring healing, measuring scar tissue, and perhaps most
important, cancer detection. This could lead to a better
understanding of the healing process. It could also be used
to test the effectiveness of drugs designed to suppress the
formation of scar tissue.
Dentistry also has a lot to gain from THz imaging.
There are fewer options currently for dental imaging.
Primarily the introductory relies on x-ray imaging. A new
imaging technique that is emerging besides THz imagining
is optical coherence tomography. It has been shown
however that THz imaging can detect caries in the tooth’s
enamel layer earlier then the other techniques [2].
VI. SUMMARY PROPERTIES IN SPECTOSCOPY
SYSTEMS
When used for biomedical purposes, several
properties of THz waves are important. These include
power, wavelength, signal to noise rations, signal
absorption, and bandwidth.
The typical power for a THz wave is from 0.1 W
to 100W. For real time applications however, a higher
power is required. Amplifiers are used to boost the output
to the mA range and in some cases as high as kW.
A key factor in determining the usefulness of
medical imaging is the resolution that can be obtained. The
resolution is limited by the wavelength of the wave, which
is around 300 m. This means that imaging cellular
structure is not possible. However, research is being done
in order to improve the resolution of THz waves.
VII. CONCLUSTION
More research is needed to continue developing
THz wave applications. As the equipment become more
readily available and lower in cost they systems are likely to
become more available. Particularly, in the medical field
great potential exists. Once some of the challenges are met
THz will become a true, practical benefit.
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Michael R Boersma( M’03) was born in Grand Rapids, MI,
on March 10, 1982. He attended Calvin College in Grand
Rapids in 2000. He graduated with a BS in engineering
with a concentration in electrical engineering in 2004. He is
currently seeking employment in the west Michigan area.