The document discusses terahertz (THz) radiation, covering its history, properties, generation, detection methods, and applications. THz waves, which exist between microwaves and infrared in the electromagnetic spectrum, have significant potential in non-invasive imaging and secure communications, especially in medical and defense fields. The document highlights the challenges in generating and detecting THz waves and the advancements made in related technologies.

1. Kutluhan Utku TUMEN
2018 / 2019
TERAHERTZ EMISSION

2. 1- History of Terahertz
2- Introduction about Terahertz Emission
3- Properties of Terahertz
4- Terahertz Generation and Detection
5- Applications of Terahertz
K.U.TUMEN 2018/2019 1
Outline

3. K.U.TUMEN 2018/2019 2
History of Terahertz
•It has been several decades since electromagnetic radiation in the THz band was first
scientifically studied.
•In the beginning, such radiation was called far-infrared waves or millimeter/submillimeter
waves.
•It was through the development of ultrafast optoelectronics, which led to the successful
generation and detection of THz pulses in the middle 1980s, that interest in this particular
electromagnetic wave widely emerged.
•Early researchers were focused on developing technologies in generating, detecting, and
manipulating THz waves.
•Lately, interest has become more focused on the real-world application of THz waves.
https://en.wikipedia.org/wiki/Terahertz_radiation

4. K.U.TUMEN 2018/2019 3
Introduction about Terahertz
Various frequencies are spaced along the frequently used electromagnetic spectrum.
• Microwaves
• Infrared Radiations
• Visible Lights
• Ultraviolet
• X-Rays
Between the microwave and infrared frequencies lies terahertz (THz) radiation.
https://en.wikipedia.org/wiki/Terahertz_radiation

5. K.U.TUMEN 2018/2019 4
Introduction about Terahertz
•Terahertz radiation is also known as submillimeter radiation.
•Terahertz waves, tremendously high frequency (THF), T-rays, T-waves, T-light, T-lux or Thz
is consists of electromagnetic waves within the designated band of frequencies from 0.3
to 30 terahertz.
•Wavelengths (𝞴) of radiation in the terahertz band correspondingly range from 1 mm to
0.1 mm.
•If we take generally Radiation at 1 THz has;
i. Period of 1 ps,
ii. Wave number (hv) of 33 cm¯¹,
iii. Photon Energy of 4.1 meV,
iv. Equivalent Temperature (T) of 47.6 K .
https://en.wikipedia.org/wiki/Terahertz_radiation

6. K.U.TUMEN 2018/2019 5
Introduction about Terahertz
•1 THz : 10¹² Hz
https://en.wikipedia.org/wiki/Terahertz_radiation

7. Interactions of Terahertz waves with matter :
• Rotation of molecules
• Bond vibrations
• Stretching and torsion
• Phonons
• Free carrier acceleration
K.U.TUMEN 2018/2019 6
Introduction about Terahertz
https://en.wikipedia.org/wiki/Terahertz_radiation

8. K.U.TUMEN 2018/2019 7
Properties of Terahertz
•Terahertz radiation travels in a line of sight.
•It is non-ionizing.
•Like microwave radiation, terahertz radiation can penetrate a wide variety of non-conducting materials.
•Terahertz radiation can pass through
I. Clothing
II. Paper,
III. Cardboard,
IV. Wood,
V. Plastic and ceramics.
•Terahertz radiation has limited penetration through fog and clouds and can not penetrate liquid water
or metal.
•Due to extreme water absorption, THz waves cannot penetrate into the human body like microwaves
can. Therefore, even if THz waves do cause any harm, it is limited to skin level.
https://en.wikipedia.org/wiki/Terahertz_radiation

9. K.U.TUMEN 2018/2019 8
Properties of Terahertz
•The penetration depth is typically less than that of microwave radiation.
•THz is not ionizing yet can penetrate some distance through body tissue, so it is of interest as a
replacement for medical X-rays.
•However, due to their specific location on the electromagnetic spectrum, THz waves are much more
difficult to handle than waves adjacent to them.
•THz waves have low photon energies and thus can not lead to photo-ionization in biological tissues as
can X-rays.
•As a result, THz waves are considered safe for both the samples and the operator.
•The earth's atmosphere is a strong absorber of terahertz radiation, so the range of terahertz radiation in
air is limited to tens of meters, making it unsuitable for long-distance communications.
https://en.wikipedia.org/wiki/Terahertz_radiation

10. K.U.TUMEN 2018/2019 9
Terahertz Sources
•There generation and detection is still not as good as it should have.
•We can not measure terahertz via electronic counters. Generation and detection become
impossible by conventional electronic devices. So we require new devices and techniques.
•Tera-Hertz Sources are divided into two sources :
1 - Natural :
Naturally terahertz frequencies are emitted by black bodies with above 2K Temperature.
We measure these frequencies from objects like cold matter, dust particle and distant starburst
galaxies.
2- Artificial :
Gyrotron Oscillator, Backward wave oscillator
Organic gas far infrared laser, Free electron laser (FEL)
Schottky diode multipliers, Quantum cascade laser
https://en.wikipedia.org/wiki/Terahertz_radiation

11. K.U.TUMEN 2018/2019 10
Terahertz Generation&Detection
•We detect tera hertz pulses by two methods.
1)Photoconductive Antennas
Operation principle of photoconductive antennas is
the laser beam is focused on the dipole gap which
generating electron-hole pairs, and the transient
current conditioned by the applied voltage emits an
electromagnetic pulse of sub picosecond duration
into the free space. (the THz pulse) The emitted
wavelengths are much longer compared to the size
of their source, the dipole; hence, they diffract
strongly in the form of a wide cone filling out almost
the whole solid angle behind the antenna (dark grey
area marked THz).
http://entsphere.com/pub/pdf/%5BYun-Shik_Lee%5D_Principles_of_Terahertz_Science_and(BookFi.org).pdf

12. K.U.TUMEN 2018/2019 11
•We detect terahertz pulses by two methods.
2)Electro-Optic Sampling
The laser pulses of some tens of femtoseconds width pass through the scanning delay enabling a
time-resolved acquisition of the electric field of the THz pulse over multiple shots. The analyzer
consists of a retarder and a Wollaston beam splitter. The photodetectors acquire the modulated
intensities of the laser pulses depending on the phase retardation.
Terahertz Generation&Detection
http://entsphere.com/pub/pdf/%5BYun-Shik_Lee%5D_Principles_of_Terahertz_Science_and(BookFi.org).pdf

13. K.U.TUMEN 2018/2019 12
Terahertz Applications
•X-rays can see shapes within the human body so Terahertz waves (also called as T-rays) can create
pictures and transmit information.
•With T-rays that do not harm biological tissues, it will be possible for the passengers to be screened
without leaving their belongings.
https://www.slideshare.net/lodro-ahmed/tera-hertz-electromagnetic-waves?from_action=save

14. K.U.TUMEN 2018/2019 13
•It has also been shown that it is possible to detect landmines at a distance of up to 30 m using T-ray
reflection spectroscopy.
https://www.slideshare.net/lodro-ahmed/tera-hertz-electromagnetic-waves?from_action=save

15. K.U.TUMEN 2018/2019 14
•The THz Band can also enable ultra-broadband secure communication links in the military and
defense fields.
https://en.wikipedia.org/wiki/Terahertz_radiation

16. • 5G Cellular Networks
• Terabit Wireless Local Area Networks (T-WLAN)
• Terabit Wireless Personal Area Networks (T-WPAN)
• Secure Terabit Wireless Communication
• Health Monitoring Systems
• Nuclear, Biological and Chemical Defenses
• The Internet of Nano-things
• Ultra-high-speed On-chip Communication
K.U.TUMEN 2018/2019 16
Also another axamples are;
https://en.wikipedia.org/wiki/Terahertz_radiation
Macroscale
Nanoscale

17. THANK YOU
FOR
PARTICIPATING AND LISTENING
K.U.TUMEN 2018/2019