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Spectroscopic Applications of Terahertz Quantum-Cascade Lasers

Alam, Tasmim (2020) Spectroscopic Applications of Terahertz Quantum-Cascade Lasers. Dissertation, Ferdinand-Braun-Institut, Leibniz-Institut für Hochfrequenztechnik.

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Abstract

Quantum cascade lasers (QCLs) are attractive for high-resolution spectroscopy because they can provide high power and a narrow linewidth. They are particularly promising in the terahertz (THz) range since they can be used as local oscillators for heterodyne detection as well as transmitters for direct detection. However, THz QCL-based technologies are still under development and are limited by the lack of frequency tunability as well as the frequency and output power stability for free-running operation. In this dissertation, frequency tuning and linewidth of THz QCLs are studied in detail by using rotational spectroscopic features of molecular species. In molecular spectroscopy, the Doppler effect broadens the spectral lines of molecules in the gas phase at thermal equilibrium. Saturated absorption spectroscopy has been performed that allows for sub-Doppler resolution of the spectral features. One possible application is QCL frequency stabilization based on the Lamb dip. Since the tunability of the emission frequency is an essential requirement to use THz QCL for high-resolution spectroscopy, a new method has been developed that relies on near-infrared (NIR) optical excitation of the QCL rear-facet. A wide tuning range has been achieved by using this approach. The scheme is straightforward to implement and, the approach can be readily applied to a large class of THz QCLs. The frequency and output stability of the local oscillator has a direct impact on the performance and consistency of the heterodyne spectroscopy. A technique has been developed for a simultaneous stabilization of the frequency and output power by taking advantage of the frequency and power regulation by NIR excitation. The results presented in this thesis will enable the routine use of THz QCLs for spectroscopic applications in the near future.

Item URL in elib:https://elib.dlr.de/140018/
Document Type:Thesis (Dissertation)
Title:Spectroscopic Applications of Terahertz Quantum-Cascade Lasers
Authors:
AuthorsInstitution or Email of AuthorsAuthor's ORCID iD
Alam, Tasmimtasmim.alam (at) dlr.deUNSPECIFIED
Date:17 August 2020
Refereed publication:Yes
Open Access:No
Gold Open Access:No
In SCOPUS:No
In ISI Web of Science:No
Status:Published
Keywords:Molecular spectroscopy, Terahertz Quantum cascade laser, high-resolution spectroscopy, rotational spectroscopy, spectral lines.
Institution:Ferdinand-Braun-Institut, Leibniz-Institut für Hochfrequenztechnik
Department:Electrical Engineering and Computer Science
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space
HGF - Program Themes:other
DLR - Research area:Raumfahrt
DLR - Program:R - no assignment
DLR - Research theme (Project):R - no assignment
Location: Berlin-Adlershof
Institutes and Institutions:Institute of Optical Sensor Systems
Deposited By: Alam, Tasmim
Deposited On:07 Jan 2021 08:10
Last Modified:07 Jan 2021 08:10

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