Recent Advances of Efficient Design of Terahertz Quantum-Cascade Lasers
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Recent Advances of Efficient Design of Terahertz Quantum-Cascade Lasers Rajesh Sharma1
· Harpreet Kaur1 · Manjot Singh1
Received: 23 April 2020 / Accepted: 25 September 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Terahertz (THz) quantum cascade lasers (QCLs) are electrically pumped and heterostructure based semiconductor laser sources with intersubband transitions of electrons in different layers of the quantum wells and barriers. The THz QCLs have high output power in THz region which make them important from application point of view. Recently intensive research has been carried out by researchers for obtaining efficient designs of THz sources. Most of the researchers have investigated the THz frequency range between 0.1 and 3 THz; however, the output power of the THz sources in the frequency range 3–5 THz is small because of transit time and resistance-capacitance effects. Nevertheless, the present review is focused for the development of efficient THz QCL sources in the frequency range from 3 to 5 THz where one of the major problem of thermal backfilling of the carriers has to be overcome by engineering the heterostructure. Keywords Terahertz radiation sources · Intersubband transitions · Heterostructure · Superlattice · Quantum wells and barriers · Terahertz quantum-cascade laser · Waveguides
Introduction Terahertz (THz) domain is related to the electromagnetic radiations having frequency between the infrared and microwave region. These are radiations of high frequency and are referred as T-rays in connection with imaging techniques. THz name comes from metric prefix “T” which means trillions, so THz represent frequencies in the trillion of a cycle per second (1 THz = 1012 Hz). The wavelength of THz radiations is shorter than the microwave and longer than the infrared rays which specifies that the range of the wavelength in electromagnetic spectrum is from 30 μm to 3 mm (0.1 to 10 THz). THz radiations are invisible rays that can penetrate through materials which are opaque to visible radiations such as clothes, cardboard, wood, papers, and non-conducting materials; however, these radiations have limited penetration through fog, clouds, metals etc. Water is such a strong absorber of T-rays because the absorption coefficient of THz radiations in water is very high owing to polar nature of water molecules. These Rajesh Sharma
sharma [email protected] 1
Department of Physics, University Institute of Sciences, Chandigarh University, Mohali, Punjab, 140413, India
radiations have low energy around 0.413 to 41.3 meV so they cannot penetrate deeply into the tissues of the human body, which makes them suitable for various medical applications. The propagation range of THz radiations in air is limited to tens of meters due to strong absorption in earth’s atmosphere, which makes them unsuitable for low altitude communications. The spectroscopic applications of THz radiations started from 1970s [1–4] which were followed by various reports of advanced techniques in photocondu
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