arXiv subjects

Akio Ito

Publications and source records attributed to Akio Ito.

3 recordsLinked to original sources

arXiv2026

Twisted Gradient Flow Approach to Vegetation-Rainfall-Bushfire Interactions Model

We consider a vegetation-rainfall-bushfire interaction model consisting of two partial differential equations describing the evolutions of bushfire intensity and water availability, together with an ordinary differential equation governing the vegetation density. The main feature of the model is that the ODE contains a nonlocal coefficient multiplying the vegetation density, which makes the mathematical analysis highly nontrivial. In this paper, we regard this nonlocal coefficient as the generator of a deformation of the metric structure of the underlying real Hilbert space. This interpretation enables us to formulate the ODE as a twisted gradient flow on state-dependent Hilbert spaces and to establish the existence of strong solutions to the associated initial-boundary value problem.

math.AP↗

arXiv2021

Direct observation of terahertz frequency comb generationin difference-frequency quantum cascade lasers

Terahertz quantum cascade laser sources based on intra-cavity difference frequency generation from mid-IR devices are an important asset for applications in rotational molecular spectroscopy and sensing, beingthe only electrically pumped device able to operate in the 0.6-6 THz range without the need of bulky andexpensive liquid helium cooling. Here we present comb operation obtained by intra-cavity mixing of adistributed feedback laser at λ = 6.5 μm and a Fabry-Pérot device at around λ = 6.9 μm. The resultingultra-broadband THz emission extends from 1.8 to 3.3 THz, with a total output power of 8 μW at 78K.The THz emission has been characterized by multi-heterodyne detection with a primary frequencystandard referenced THz comb, obtained by optical rectification of near infrared pulses. The down-converted beatnotes, simultaneously acquired, confirm an equally spaced THz emission down to 1 MHzaccuracy. In the next future this setup can be used for Fourier transform based evaluation of the phaserelation among the emitted THz modes, paving the way to room-temperature, compact and field-deployable metrological grade THz frequency combs.

physics.optics↗

arXiv2018

Unveiling spectral purity and tunability of terahertz quantum cascade laser sources based on intra-cavity difference frequency generation

Terahertz sources based on intra-cavity difference-frequency generation in mid-infrared quantum cascade lasers (THz DFG-QCLs) have recently emerged as the first monolithic electrically-pumped semiconductor sources capable of operating at room-temperature (RT) across the 1-6 THz range. Despite tremendous progress in power output, that now exceeds 1mW in pulsed and 10 μW in continuous-wave regime at room-temperature, knowledge of the major figure of merits of these devices for high precision spectroscopy, such as spectral purity and absolute frequency tunability, is still lacking. Here, 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 frequency of individual emission lines of these sources with an uncertainty of 4 x 10-10. The unveiled emission LW (400 kHz at 1ms 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 requiring narrow-linewidth THz sources.

physics.app-ph↗