Doppler-free spectroscopy with a terahertz quantum-cascade laser

Wienold, Martin; Alam, Tasmim; Schrottke, L.; Grahn, H. T.; Hübers, Heinz‐Wilhelm

doi:10.1364/oe.26.006692

Cited by 26 publications

(13 citation statements)

References 23 publications

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“…Despite the very low generated power (generally tens of nW, requiring liquid-He cooled detectors), such a wide-tunability approach has produced, in about fifteen years, plenty (several tens) of significant spectroscopic results (e.g., [6,[18][19][20][21][22][23]). However, after a comparable time-span, THz QCLs have provided mostly proof-of-principle spectroscopic results [10,[24][25][26] to date, thus paying the price for insufficient tunability in regard to spectroscopy.…”

Section: Introductionmentioning

confidence: 99%

“…The current accuracy (∼10 −9 ) , achieved in a direct-absorption configuration, was limited by the Doppler linewidth of the measured absorption profiles. However, improvement of the order of magnitude is possible by implementing more advanced setups [26,37]. To this purpose, higher THz power levels, in the order of a few µW and not yet available with our source, are desirable.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2018

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The 1–10 terahertz (THz) spectral window is emerging as a key region for plenty of applications, requiring not yet available continuous-wave room-temperature THz spectrometers with high spectral purity and ultra-broad tunability. In this regard, the spectral features of stabilized telecom sources can actually be transferred to the THz range by difference frequency generation, considering that the width of the accessible THz spectrum generally scales with the area involved in the nonlinear interaction. For this reason, 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 (107 W/cm2), on the basis of a three-wave-mixing theoretical model.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

et al. 2018

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“…This further limitation can be overcome using sub-Doppler spectroscopic techniques, that are precluded to DC-FCs-based DCS, but can be implemented in our spectrometer, thanks to the significantly higher output power provided by a QCL-FC. Indeed, saturation effects and pump and probe setups have been implemented with QCLbased spectrometers 59,60 , although no metrological-grade measurements have been obtained yet. Finally, although having low finesse values, newly developed THz resonant cavities 61 Fig.…”

Section: Discussionmentioning

confidence: 99%

Quantum cascade laser based hybrid dual comb spectrometer

et al. 2020

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Four-wave-mixing-based quantum cascade laser frequency combs (QCL-FC) are a powerful photonic tool, driving a recent revolution in major molecular fingerprint regions, i.e. mid-and far-infrared domains. Their compact and frequency-agile design, together with their high optical power and spectral purity, promise to deliver an all-in-one source for the most challenging spectroscopic applications. Here, we demonstrate a metrological-grade hybrid dual comb spectrometer, combining the advantages of a THz QCL-FC with the accuracy and absolute frequency referencing provided by a free-standing, optically-rectified THz frequency comb. A proof-of-principle application to methanol molecular transitions is presented. The multi-heterodyne molecular spectra retrieved provide state-of-the-art results in line-center determination, achieving the same precision as currently available molecular databases. The devised setup provides a solid platform for a new generation of THz spectrometers, paving the way to more refined and sophisticated systems exploiting full phase control of QCL-FCs, or Doppler-free spectroscopic schemes.

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“…Full control of FCs, i.e., of linewidth and phase of teeth and spacing between them, as well as of their shape, that means getting control on the overall number and on the intensity pattern of the manifold [51] is the key challenge to widen the application spectrum of FCs. In particular, phase control and a significant increase of the intensity of each tooth (e.g., hundreds µW power range), together with the assessment of a stable FC operation over the entire operational range of the QCL, will make it easier to access the nonlinear interaction regime [52]. Saturation of gas-phase molecular lines is a straightforward example of application that could be accompanied by cavity-enhanced setups, although the cavity finesse reported to date, at THz frequencies, is very limited [53,54].…”

Section: Applications and Perspectivesmentioning

confidence: 99%

Toward new frontiers for terahertz quantum cascade laser frequency combs

et al. 2020

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Broadband, quantum-engineered, quantum cascade lasers (QCLs) are the most powerful chip-scale sources of optical frequency combs (FCs) across the mid-infrared and the terahertz (THz) frequency range. The inherently short intersubband upper state lifetime spontaneously allows mode proliferation, with large quantum efficiencies, as a result of the intracavity four-wave mixing. QCLs can be easily integrated with external elements or engineered for intracavity embedding of nonlinear optical components and can inherently operate as quantum detectors, providing an intriguing technological platform for on-chip quantum investigations at the nanoscale. The research field of THz FCs is extremely vibrant and promises major impacts in several application domains crossing dual-comb spectroscopy, hyperspectral imaging, time-domain nanoimaging, quantum science and technology, metrology and nonlinear optics in a miniaturized and compact architecture. Here, we discuss the fundamental physical properties and the technological performances of THz QCL FCs, highlighting the future perspectives of this frontier research field.

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Doppler-free spectroscopy with a terahertz quantum-cascade laser

Cited by 26 publications

References 23 publications

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

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

Quantum cascade laser based hybrid dual comb spectrometer

Toward new frontiers for terahertz quantum cascade laser frequency combs

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