home » libere » 10. quantum metrology with thz quantum cascadelasers 10. Quantum metrology with THz quantum cascade lasers
Contact person:
Miriam Vitiello
1. Free running emission linewidth of THz quantum emitters By exploiting a metrological grade system comprising a terahertz frequency comb synthesizer, we measure, for the first time, the free-running emission linewidth (LW), the tuning characteristics, and the absolute center frequency of individual emission lines of different frequency generation (DFG) THz QCLs with an uncertainty of 4 × 10−10. The unveiled emission LW (400 kHz at 1-ms integration time) indicates that DFG-QCLs are well suited to operate as local oscillators and to be used for a variety of metrological, spectroscopic, communication, and imaging applications that require narrow-LW THz sources.
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(a) Schematic diagrams of the experimental setup for measuring the beatnote signal between a free running THz comb and a THz DFG QCL; (b) A typical beat note spectrum observed on a spectrum analyzer for 2 ms integration time.
References:
L. Consolino, S. Jung, A. Campa, M. De Regis, S. Pal, J. H. Kim, K. Fujita, A. Ito, M. Hitaka, S. Bartalini, P. De Natale, M. A Belkin, M.S. Vitiello, Spectral purity and tunability of terahertz quantum cascade laser sources based on intracavity difference-frequency generation, Science Advances, 3, e1603317 (2017).
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2. Quantum limited line width of a THz laser We report experimental evidence of linewidth values approaching the quantum limit in far-infrared quantum cascade lasers. By performing noise measurements with unprecedented sensitivity levels, we demonstrate that properly designed semiconductor-heterostructure lasers can unveil the mechanisms underlying the laser-intrinsic phase noise, revealing the link between device properties and the quantum-limited line width.
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Frequency noise power spectral density. Comparison of the experimental FNPSD of the terahertz QCL (orange trace) and the contribution of the frequency noise of the CNPSD for the current driver (blue trace). The dashed green line indicates the white noise level.
References:
M.S. Vitiello, L. Consolino, S. Bartalini, A. Taschin, A. Tredicucci, M. Inguscio, P. De Natale, Quantum-limited frequency fluctuations in a terahertz laser, Nature Photonics, 6, 525-528 (2012).
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3. Quantum metrology: Phase locking and absolute frequency measurements in the far-infrared We demonstrate phase-locking of a 2.5 THz quantum cascade laser to a free-space comb, generated in a LiNbO3 waveguide and covering the 0.1–6 THz frequency range. We show that even a small fraction (< 100 nW) of the radiation emitted from the quantum cascade laser is sufficient to generate a beat note suitable for phase-locking to the comb, paving the way to novel metrological-grade terahertz applications, including high-resolution spectroscopy, manipulation of cold molecules, astronomy and telecommunications.
As a proof of concept applicationwe developed a metrological-grade THz spectroscopic system based on the combination of a THz frequency-combsynthesizer (FCS) and a THz quantum cascade laser (QCL). The achieved absolute frequency scale provides an uncertainty of a few parts in 10−11 on the laser frequency and 10−9 on the linecenter determination, ranking this technique among the most precise ever developed in the THz range.
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The scheme of the experimental setup is shown, with the diagram describing how the traceability of the primary Cs frequency standard is transferred to the THz QCL-based spectroscopy via the stabilization of the repetition rate (frep) of the pump laser and the THz FCS. The mechanism for tuning the QCL frequency (νQCL) is also sketched.
References:
L. Consolino, A. Taschin, P. Bartolini, S. Bartalini, P. Cancio, A. Tredicucci, H. E. Beere, D. A. Ritchie, R. Torre, M. S. Vitiello and P. De Natale, Phase-locking to a free-space terahertz comb for metrological-grade terahertz lasers, Nature Communications, 3, 1040 (2012).
S. Bartalini, M. S. Vitiello, P. De Natale, Quantum cascade lasers: a versatile source for precise measurements in the mid/far-infrared range, Measurement Science and Technology, 25, 012001 (2014).
S. Bartalini, L. Consolino, P. Cancio, P. De Natale, P. Bartolini, A. Taschin, M. De Pas, H. Beere, D.A. Ritchie, M.S. Vitiello, R. Torre, Frequency-Comb-Assisted Terahertz Quantum Cascade Laser Spectroscopy, Physical Review X, 4, 021006 (2014).
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