ULTRAQCL

THz roadmap

Sukhy — 2019-05-02T17:48:54Z

Future directions in THz quantum cascade laser research has been presented in "The 2017 terahertz science and technology roadmap" issue in Journal of Physics D: Applied Physics. This highlights the impact of QCLs to the THz domain and future directions related to modelocking.

The full publication can be found here

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Yann Colin — 2019-05-02T15:18:29Z

- Milestones and Deliverables

Multi-Watt high-power THz frequency quantum cascade lasers

Sukhy — 2019-04-30T07:44:59Z

Multi-Watt high-power terahertz (THz) frequency quantum cascade lasers are demonstrated, based on a single, epitaxially grown, 24-μm-thick active region embedded into a surface-plasmon waveguide. The devices emit in pulsed mode at a frequency of ∼4.4 THz and have a maximum operating temperature of 132 K. The
maximum measurable emitted powers from a single facet are ∼2.4 W at 10 K and ∼1.8 W at 77 K.

The full publication can be found here

Bow-Tie Cavity for Terahertz Radiation

Sukhy — 2019-04-29T22:26:01Z

We report on the development, testing, and performance analysis of a bow-tie resonant cavity for terahertz (THz) radiation, injected with a continuous-wave 2.55 THz quantum cascade laser. The bow-tie cavity employs a wire-grid polarizer as input/output coupler and a pair of copper spherical mirrors coated with an unprotected 500 nm thick gold layer. The improvements with respect to previous setups have led to a measured finesse value F = 123, and a high quality factor Q. The resonator performances and the relevant parameters are theoretically predicted and discussed, and a comparison among simulated and experimental spectra is given.

The full publication can be found here

QCL-based frequency metrology from the mid-infrared to the THz range: a review

Sukhy — 2019-04-29T22:20:16Z

Quantum cascade lasers (QCLs) are becoming a key tool for plenty of applications, from the mid-infrared (mid-IR) to the THz range. Progress in related areas, such as the development of ultra-low-loss crystalline microresonators, optical frequency standards, and optical fiber networks for time and frequency dissemination, is paving the way for unprecedented applications in many fields. For most demanding applications, a thorough control of QCLs emission must be achieved. In the last few years, QCLs' unique spectral features have been unveiled, while multifrequency QCLs have been demonstrated. Ultra-narrow frequency linewidths are necessary for metrological
applications, ranging from cold molecules interaction and ultra-high sensitivity spectroscopy to infrared/THz metrology. A review of the present status of research in
this field is presented, with a view of perspectives and future applications.

The full publication can be found here

Heterogeneous, terahertz quantum cascade lasers with thermally tunable frequency comb operation

Sukhy — 2019-04-29T22:10:40Z

We report on the engineering of broadband quantum cascade lasers (QCLs) emitting at Terahertz (THz) frequencies, which exploit a heterogeneous active region scheme and have a current density dynamic range (Jdr) of 3.2, significantly larger than the state of the art, over a 1.3 THz bandwidth. We demonstrate that the devised broadband lasers operate as THz optical frequency comb synthesizers in continuous-wave, with a maximum optical output power of 4 mW. Measurement of the intermode beatnote map reveals a clear dispersion-compensated frequency comb regime with a corresponding emission bandwidth of ≈ 1.05 THz and a stable and narrow (4.15 KHz) beatnote. Analysis of the electrical and thermal beatnote tuning reveals a current-tuning coefficient ranging between 5 MHz/mA and 2.1 MHz/mA and a temperature-tuning coefficient of –4 MHz/K. The ability to tune the THz QCL combs over their full dynamic range by temperature and current paves the way for their use as a powerful spectroscopy tool that can provide broad frequency coverage combined with high
precision spectral accuracy.

The full publication can be found here

Advanced GaAs/AlGaAs ICP-DRIE etching for optoelectronic applications

Sukhy — 2019-04-29T21:58:27Z

We investigate the parameter optimization for micron-scale etching by Inductive Coupled Plasma - Deep Reactive Ion Etching (ICP-DRIE) of GaAs/AlGaAs semiconductor heterostructures. Although dry etching approaches have been reported in the literature using a broad variety of plasma etch tools, there is still need to meet the majority of microsystems dry etching requirements. The desired etch characteristics for GaAs/AlGaAs heterostructures can be achieved by controlling the various process parameters with good reliability, high selectivity, and – simultaneously – high etch rates and sidewall verticality. Etch rates from 1 to over 5.5μm/min have been obtained. The selectivity with optical photoresist varies from 2.3 to 16. The presented results can be
valuable for a wide range of applications involving fabrication of micro-electro-mechanical-systems or Micro Optoelectronic Mechanical Systems.

The full publication can be found here

Waveguided Approach for Difference Frequency Generation of Broadly-Tunable Terahertz Radiation

Sukhy — 2019-04-29T21:47:25Z

The spectral features of stabilized telecom sources can be transferred to the THz range by difference frequency generation. In this paper we extensively discuss the role of Lithium Niobate (LN) channel-waveguides in the experimental accomplishment of a room-temperature continuous wave (CW) spectrometer, with μW-range power levels and a spectral coverage of up to 7.5 THz. To this purpose, and looking for further improvements, a thought characterization of specially-designed LN waveguides is presented, whilst discussing its nonlinear efficiency and its unprecedented capability to handle high optical power on the basis of a three-wave-mixing theoretical model.

The full publication can be found here

Room-Temperature Frequency-Referenced Spectrometer up to 7.5 THz

Sukhy — 2019-04-29T21:27:33Z

High-precision frequency measurements of molecular transitions in the THz range are crucial but remain an open challenge. Here, room-temperature generation and detection of continuous-wave, broadly tunable, narrow-linewidth THz radiation are presented, and their application to high-resolution spectroscopy in the broad 1–7.5 THz spectral range is demonstrated. This result has been achieved by implementing a Cherenkov phase-matching scheme into a channel waveguide in a nonlinear crystal. This simple approach, entirely based on robust telecom technology, unprecedently merges in a single source an ultra-broad continuous-wave spectral coverage and a state-of-the-art accuracy in molecular-transition-center determination.

The full publication can be found here

Ultrafast two-dimensional field spectroscopy of terahertz intersubband saturable absorbers

Sukhy — 2019-04-29T21:18:35Z

Intersubband (ISB) transitions in semiconductor multi-quantum well (MQW) structures
are promising candidates for the development of saturable absorbers at terahertz (THz)
frequencies. Here, we exploit amplitude and phase-resolved two-dimensional (2D) THz spectroscopy on the sub-cycle time scale, to observe directly the saturation dynamics and coherent control of ISB transitions in a metal-insulator MQW structure. We demonstrate that this behavior is a fingerprint of THz-driven carrier-wave Rabi flopping. A microscopic model allows us to design tailored MQW structures with optimized dynamical properties for saturable absorbers that could be used in future compact semiconductor-based single-cycle THz sources.

The publication can be found here here