Modern microwave methods in solid state inorganic materials chemistry: from fundamentals to manufacturing

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Real-time imaging using a 4.3-THz quantum cascade laser and a 320×240 microbolometer focal-plane array

Abstract: We report on the development of a compact, easy-to-use terahertz radiation source, which combines a quantum-cascade laser (QCL) operating at 3.1 THz with a compact, low-input-power Stirling cooler. The QCL, which is based on a two-miniband design, has been developed for high output and low electrical pump power. The amount of generated heat complies with the nominal cooling capacity of the Stirling cooler of 7 W at 65 K with 240 W of electrical input power. Special care has been taken to achieve a good thermal coupling between the QCL and the cold finger of the cooler. The whole system weighs less than 15 kg including the cooler and power supplies. The maximum output power is 8 mW at 3.1 THz. With an appropriate optical beam shaping, the emission profile of the laser is fundamental Gaussian. The applicability of the system is demonstrated by imaging and molecular-spectroscopy experiments. Hübers, "Sub-megahertz frequency stabilization of a terahertz quantum cascade laser to a molecular absorption line," Appl. Phys. Lett. 96(7), 071112 (2010). ©2010 Optical Society of Americ

Molecular spectroscopy with a multimode THz quantum-cascade laser

A terahertz absorption spectrometer for highresolution molecular spectroscopy is realized. The spectrometer is based on a multimode quantum-cascade laser. The design and performance of the spectrometer are presented. Three aspects are discussed: sensitivity, frequency calibration, and frequency multiplexing

A compact, continuous-wave radiation source for local oscillator applications based on a THz quantum-cascade laser

Heterodyne spectroscopy of molecular rotational lines and atomic fine-structure lines is a powerful tool in astronomy and planetary research. It allows for studying the chemical composition, the evolution, and the dynamical behaviour of many astronomical objects. As a consequence, current and future airborne as well as spaceborne observatories such as SOFIA, Herschel or Millimetron are equipped with heterodyne spectrometers. A major challenge for heterodyne receivers operating above approximately 2 THz is the local oscillator, which should be a compact source requiring little electrical input power. THz quantum-cascade lasers (QCLs) have the potential to comply with these requirements. However, until now, THz QCLs operate at rather low temperatures so that cooling by liquid helium or using large cryo-coolers becomes necessary. While these cooling approaches might be acceptable for laboratory experiments, they either result in too many restrictions on airborne or spaceborne heterodyne receivers or are completely unacceptable. We report on the development of a compact, easy-to-use source, which combines a QCL operating at 3.1 THz with a compact, low-input-power Stirling cooler. The QCL, which is based on a two-miniband design, has been developed for high output powers and low electrical pump powers [1]. Efficient carrier injection is achieved by resonant longitudinal-optical phonon scattering. At the same time, the operating voltage can be kept below 6 V. The amount of generated heat complies with the cooling capacity of the Stirling cooler of 7 W at 65 K with 240 W of electrical input power. Special care has been taken to achieve a good thermal coupling between the QCL and the cold finger of the cryostat. The whole system weighs less than 15 kg including cooler, power supplies etc. The output power is well above 1 mW at 3.1 THz. With an appropriate optical beam shaping, the emission profile of the laser becomes a fundamental Gaussian one. In addition to the performance of the QCL in the Stirling cooler, we will present results of the application of this source to highresolution molecular spectroscopy

Molecular spectroscopy with a multimode THz quantum-cascade laser

High-resolution molecular spectroscopy is a powerful tool for investigations of the structure and energy levels of molecules and atoms. In addition to scientific utilization, terahertz (THz) spectroscopy is of interest for detection and identification of gases in safety and security applications. While for frequencies below 2 THz many different methods have been developed, spectroscopy above 2 THz is hampered by the lack of frequency-tunable, continuous-wave, powerful, and narrow-linewidth radiation sources. For this frequency range, THz quantum-cascade lasers (QCLs) are promising radiation sources. We report on a THz absorption spectrometer, which combines a grating monochromator, a QCL, and a microbolometer camera. The QCL used for these experiments is based on a single-plasmon waveguide and a Fabry-Pérot cavity with both facets uncoated and is optimized for a low electrical pump power. It operates on several modes centered around 3.4 THz. The laser is mounted in a compact air-cooled cryocooler (model K535 from Ricor). The emitted beam is focused with a TPX lens and guided through a 27 cm long absorption cell onto the monochromator, which spectrally resolves the laser modes. The modes are imaged onto the microbolometer camera. The absorption spectrum of methanol around 3.4 THz is measured by detecting simultaneously the signal of each of the laser modes as a function of the laser driving current

Broadband molecular spectroscopy with a multi-mode THz quantum cascade laser (QCL)

High-resolution molecular spectroscopy is a powerful tool for investigations of the structure and energy levels of molecules and atoms. In addition to the scientific interest, terahertz (THz) spectroscopy is also of interest for the detection and identification of gases in safety and security applications. While for frequencies below 2 THz many different methods have been developed, spectroscopy above 2 THz is hampered by the lack of frequency-tunable, continuous-wave, powerful, and narrow-linewidth radiation sources. For this frequency range, THz quantum-cascade lasers (QCLs) are promising radiation sources. We report on a THz absorption spectrometer, which combines a grating monochromator, a QCL, and a microbolometer camera. The QCL used in these experiments contains a single-plasmon waveguide and a Fabry-Pérot cavity with both facets uncoated. It is optimized for low electrical pumping powers an emits several modes centered around 3.4 THz. The laser is mounted in a compact air-cooled cryocooler (model K535 from Ricor). The emitted beam is focused with a TPX lens and guided through a 27 cm long absorption cell onto the monochromator, which spectrally resolves the laser modes. The modes are imaged onto the microbolometer camera. The absorption spectrum of methanol around 3.4 THz is measured by detecting simultaneously the signal of each of the laser modes as a function of the laser driving current. By this means, frequency multiplexing is achieved

A compact, continuous-wave terahertz source based on a quantum-cascade laser and a miniature cryocooler

We report on the development of a compact, easy-to-use terahertz radiation source, which combines a quantum cascade laser (QCL) operating at 3.1 THz with a compact, low input-power Stirling cooler. The QCL, which is based on a two miniband design, has been developed for high output and low electrical pump power. The amount of generated heat complies with the nominal cooling capacity of the Stirling cooler of 7 W at 65 K with 240 W of electrical input power. Special care has been taken to achieve a good thermal coupling between the QCL and the cold finger of the cooler. he whole system weighs less than 15 kg including the cooler and power supplies. The maximum output power is 8 mW at 3.1 THz. With an appropriate optical beam shaping, the emission profile of the laser is fundamental Gaussian. The applicability of the system is demonstrated by imaging and molecular-spectroscopy experiments