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Beam Shaping and Combining of Terahe...

Chen, Ji.

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Beam Shaping and Combining of Terahertz Quantum-Cascade Laser Arrays, and Terahertz Sensing.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Beam Shaping and Combining of Terahertz Quantum-Cascade Laser Arrays, and Terahertz Sensing./
作者:	Chen, Ji.
出版者:	Ann Arbor : ProQuest Dissertations & Theses, : 2021,
面頁冊數:	160 p.
附註:	Source: Dissertations Abstracts International, Volume: 82-12, Section: B.
Contained By:	Dissertations Abstracts International82-12B.
標題:	Electrical engineering. -
電子資源:	https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=28497074
ISBN:	9798515201258

Beam Shaping and Combining of Terahertz Quantum-Cascade Laser Arrays, and Terahertz Sensing.
Chen, Ji.

Beam Shaping and Combining of Terahertz Quantum-Cascade Laser Arrays, and Terahertz Sensing. - Ann Arbor : ProQuest Dissertations & Theses, 2021 - 160 p.

Source: Dissertations Abstracts International, Volume: 82-12, Section: B.

Thesis (Ph.D.)--Lehigh University, 2021.

This item must not be sold to any third party vendors.

Terahertz (THz) quantum-cascade lasers (QCLs) are the brightest available solid-state sources of coherent THz radiation that hold immense promise for applications in THz imaging, sensing, and spectroscopy. Since the first device was invented in 2001, THz QCLs have been demonstrated with a frequency coverage from 1.2 THz to 5.4 THz, a peak output power of multiwatt, and a maximum operation temperature of 250 K. However, their use of sub-wavelength metallic cavities results in poor radiation characteristics including low out-coupling efficiencies and divergent far-field beams that deviate significantly from the ideal Gaussian beam. Also, the lack of commercial THz optical components such as lenses and gratings that could be readily utilized for THz QCLs with high focusing and diffraction efficiencies, and until recently, lack of robust techniques to achieve symmetric single-lobed beams with high output power across a broad gain spectrum for single-mode THz QCLs, limit the applications of THz QCLs and their commercialization.Single-mode THz QCLs have been realized using a wide variety of techniques to obtain a combination of large power output, good beam quality with single-lobed beam, and low far-field divergence. Beam shaping using external components has not been previously exploited due to limited commercial availability of THz optical components and also the accompanying large loss from most THz optical materials. Here, we demonstrate that excellent beam characteristics could be obtained for a THz QCL by integration of a surface-emitting distributed-feedback (DFB) QCL with a simple lens within the vacuum chamber of a cryocooler. Plano-convex lenses are made from inexpensive plastic balls and integrated in proximity with a 3.4 THz DFB QCL. With appropriately chosen lens parameters, THz laser beams with high peak intensity or low-divergence are realized at 62 K in a compact electrically operated Stirling cooler.Wavelength beam-combining of four THz DFB QCLs is demonstrated using low-cost terahertz components that include a lens carved out of a plastic ball and a mechanically fabricated blazed grating. Single-lobed beams from predominantly single-mode QCLs radiating peak-power in the range of 50-170 mW are overlapped in the far-field at frequencies ranging from 3.31-3.54 THz. Collinear propagation with a maximum angular deviation of 0.3° is realized for the four beams. The full-width at half-maximum divergence of each beam after combining is ~1° x 1°. The total power efficiency for the focused and beam-combined radiation is as high as 25%.Multi-spectral terahertz sensing of chemicals is demonstrated using four high-power DFB QCLs and sensing schemes with custom-made liquid channels. The losses of low-loss liquids in the categories of fuels, oils and lubricants and high-loss liquids such as water and alcohols are reported. The sensing of sugar and medicine dissolved solutions with different concentrations is also realized. In addition, the sensing of methanol and gasoline vapors at different pressures is achieved. This result could pave the way for future commercialization of monolithic THz QCL arrays for multispectral terahertz sensing and spectroscopy.

ISBN: 9798515201258Subjects--Topical Terms:

649834
Electrical engineering.

Beam Shaping and Combining of Terahertz Quantum-Cascade Laser Arrays, and Terahertz Sensing.
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520 $a Terahertz (THz) quantum-cascade lasers (QCLs) are the brightest available solid-state sources of coherent THz radiation that hold immense promise for applications in THz imaging, sensing, and spectroscopy. Since the first device was invented in 2001, THz QCLs have been demonstrated with a frequency coverage from 1.2 THz to 5.4 THz, a peak output power of multiwatt, and a maximum operation temperature of 250 K. However, their use of sub-wavelength metallic cavities results in poor radiation characteristics including low out-coupling efficiencies and divergent far-field beams that deviate significantly from the ideal Gaussian beam. Also, the lack of commercial THz optical components such as lenses and gratings that could be readily utilized for THz QCLs with high focusing and diffraction efficiencies, and until recently, lack of robust techniques to achieve symmetric single-lobed beams with high output power across a broad gain spectrum for single-mode THz QCLs, limit the applications of THz QCLs and their commercialization.Single-mode THz QCLs have been realized using a wide variety of techniques to obtain a combination of large power output, good beam quality with single-lobed beam, and low far-field divergence. Beam shaping using external components has not been previously exploited due to limited commercial availability of THz optical components and also the accompanying large loss from most THz optical materials. Here, we demonstrate that excellent beam characteristics could be obtained for a THz QCL by integration of a surface-emitting distributed-feedback (DFB) QCL with a simple lens within the vacuum chamber of a cryocooler. Plano-convex lenses are made from inexpensive plastic balls and integrated in proximity with a 3.4 THz DFB QCL. With appropriately chosen lens parameters, THz laser beams with high peak intensity or low-divergence are realized at 62 K in a compact electrically operated Stirling cooler.Wavelength beam-combining of four THz DFB QCLs is demonstrated using low-cost terahertz components that include a lens carved out of a plastic ball and a mechanically fabricated blazed grating. Single-lobed beams from predominantly single-mode QCLs radiating peak-power in the range of 50-170 mW are overlapped in the far-field at frequencies ranging from 3.31-3.54 THz. Collinear propagation with a maximum angular deviation of 0.3° is realized for the four beams. The full-width at half-maximum divergence of each beam after combining is ~1° x 1°. The total power efficiency for the focused and beam-combined radiation is as high as 25%.Multi-spectral terahertz sensing of chemicals is demonstrated using four high-power DFB QCLs and sensing schemes with custom-made liquid channels. The losses of low-loss liquids in the categories of fuels, oils and lubricants and high-loss liquids such as water and alcohols are reported. The sensing of sugar and medicine dissolved solutions with different concentrations is also realized. In addition, the sensing of methanol and gasoline vapors at different pressures is achieved. This result could pave the way for future commercialization of monolithic THz QCL arrays for multispectral terahertz sensing and spectroscopy.
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