Cascaded Parametric Amplification for Highly Efficient Terahertz Generation

A highly efficient, practical approach to high-energy terahertz (THz) generation based on spectrally cascaded optical parametric amplification (THz-COPA) is introduced. The THz wave initially generated by difference frequency generation between a strong narrowband optical pump and optical seed (0.1-10% of pump energy) kick-starts a repeated or cascaded energy down-conversion of pump photons. This helps to greatly surpass the quantum-defect efficiency and results in exponential growth of THz energy over crystal length. In cryogenically cooled periodically poled lithium niobate, energy conversion efficiencies >8% for 100 ps pulses are predicted. The calculations account for cascading effects, absorption, dispersion and laser-induced damage. Due to the coupled nonlinear interaction of multiple triplets of waves, THz-COPA exhibits physics distinct from conventional three-wave mixing parametric amplifiers. This in turn governs optimal phase-matching conditions, evolution of optical spectra as well as limitations of the nonlinear process.Comment: 5 pages, double colum

Large Time Behavior of Solutions to the Neumann Problem for a Quasilinear Second Order Degenerate Parabolic Equation in Domains with Noncompact Boundary

AbstractWe investigate the optimal rate of stabilization at large time of a solution to the Neumann problemut=∑i=1N∂∂xi(ai(x, t, ∇u))−b(x, t, u),inΩ×(0, T),T>0∑i=1Nai(x, t, ∇u)ni=0,on∂Ω×(0, T)u(x, 0)=u0(x)x∈Ω,u0(x)⩾0inΩ,where Ω⊂RN, N⩾2, is an unbounded domain with sufficiently smooth noncompact boundary ∂Ω satisfying certain isoperimetrical inequality and n=(ni) is the outward normal to ∂Ω

Anti-inflammatory activity of Citrus bergamia derivatives: Where do we stand?

Inflammatory diseases affect a large portion of the worldwide population, and chronic inflammation is a major risk factor for several dangerous pathologies. To limit the side effects of both synthetic and biological anti-inflammatory drugs, the use of herbal medicines, nutraceuticals and food supplements has increased tremendously as alternative and/or complementary medicine to treat several pathologies, including inflammation. During the last decades, the biological properties of Citrus bergamia (bergamot) derivatives have obtained important scientific achievements, and it has been suggested their use in a context of a multitarget pharmacological strategy. Here, we present an overview of the anti-inflammatory properties of bergamot extracts that could represent the scientific basis for develop novel and alternative strategies to improve health status and attenuate inflammatory conditions

Unilateral problems with degenerate coercivity

In this note we prove some existence and regularity results for unilateral problems with degenerate coercivity

Parametric Waveform Synthesis: a scalable approach to generate sub-cycle optical transients

The availability of electromagnetic pulses with controllable field waveform and extremely short duration, even below a single optical cycle, is imperative to fully harness strong-field processes and to gain insight into ultrafast light-driven mechanisms occurring in the attosecond time-domain. The recently demonstrated parametric waveform synthesis (PWS) introduces an energy-, power- and spectrum-scalable method to generate non-sinusoidal sub-cycle optical waveforms by coherently combining different phase-stable pulses attained via optical parametric amplifiers. Significant technological developments have been addressed to overcome the stability issues related to PWS and to obtain an effective and reliable waveform control system. Here we present the main ingredients enabling PWS technology. The design choices concerning the optical, mechanical and electronic setups are justified by analytical/numerical modeling and benchmarked by experimental observations. In its present incarnation, the PWS technology enables the generation of field-controllable mJ-level few-femtosecond pulses spanning the visible to infrared range.Comment: 34 page

La Lingua Matematica: un'esperienza didattica nel Liceo Matematico

In questo lavoro si presenta un modulo didattico dal titolo La Lingua Matematica, rivolto a studenti del primo anno di scuola secondaria di secondo grado.Il modulo è stato presentato in classi di Liceo Matematico, ma può essere proposto anche in altri contesti. Esso ha un duplice obiettivo: introdurre questioni relative a matematica e linguaggio da un lato e introdurre i concetti di teorema e dimostrazione dall'altro. Il percorso ha permesso di introdurre nozioni di aritmetica modulare e ha condotto gli studenti a confrontarsi, elaborare ipotesi, produrre argomentazioni e generare nuovi teoremi

Qualitative properties of solutions of some quasilinear equations related to Bingham fluids

We consider a quasilinear parabolic equation and its associate stationary problem which correspond to a simplified formulation of a Bingham flow and we mainly study two qualitative properties. The first one concerns with the Absence and, respectively, disappearance in finite time, of the movement. We show that there is a suitable balance between the L1-norm of the forcing datum f∞ and the measure of the spatial domain Ω (essentially saying that the forcing daum must be small enough) such that the corresponding solution u∞(x) of the stationary problem is such that u∞ ≡ 0 a.e. in Ω (even if f∞ ≠ 0). Moreover, if f∞ is also the forcing term of the parabolic problem, and if the above mentioned balance is strict, for any u0 ∈ L(Ω) there exists a finite time Tu0,f∞ > 0 such that the unique solution u(t,x) of the parabolic problem globally stops after Tu0,f∞, in the sense that u(t,x) ≡ 0 a.e. in Ω, for any t ≥ Tu0,f∞. The second property concerns with the Formation of a positively measure “solid region”. We show that if the above balance condition fails (i.e., when the forcing datum is large enough) then the solution u∞(x) of the stationary problem satisfies that u∞ ≠ 0 in Ω and its “solid region” (defined as the set S(u∞) = {x ∈ Ω : ∇u∞(x) = 0}) has a positive measure. Similar results are obtained for the symmetric solutions u(t) of the parabolic problem. In addition the convergence u(t) → u∞ in H10 (Ω), as t → +∞, does not take place in any finite time

Terahertz Generation in Lithium Niobate Driven by Ti:Sapphire Laser Pulses and its Limitations

We experimentally investigate the limits to 800 nm-to-terahertz (THz) energy conversion in lithium niobate at room temperature driven by amplified Ti:Sapphire laser pulses with tilted-pulse-front. The influence of the pump central wavelength, pulse duration, and fluence on THz generation is studied. We achieved a high peak efficiency of 0.12% using transform limited 150 fs pulses and observed saturation of the optical to THz conversion efficiency at a fluence of 15 mJ/cm2. We experimentally identify two main limitations for the scaling of optical-to-THz conversion efficiencies: (i) the large spectral broadening of the optical pump spectrum in combination with large angular dispersion of the tilted-pulse-front and (ii) free-carrier absorption of THz radiation due to multi-photon absorption of the 800 nm radiation.Comment: 4 pages, 6 figure

Effectiveness of Citrus Fruits on Helicobacter pylori

It is known that Helicobacter pylori infection is associated with chronic gastritis, peptic ulcer, and gastric carcinoma. Due to the increased side effects of the treatment regimens and the development of antimicrobial resistance, a number of natural compounds have been tested as potential alternatives. In this review, we will examine the current knowledge on the effect of Citrus fruits and their derivatives against H. pylori, highlighting the remaining outstanding questions on the development of novel therapeutic strategies

Coherent pulse synthesis: Towards sub-cycle optical waveforms

The generation of sub-optical-cycle, carrier–envelope phase-stable light pulses is one of the frontiers of ultrafast optics. The two key ingredients for sub-cycle pulse generation are bandwidths substantially exceeding one octave and accurate control of the spectral phase. These requirements arevery challenging to satisfy with a single laser beam, and thus intense research activity is currently devoted to the coherent synthesis of pulses generated by separate sources. In this review we discuss the conceptual schemes and experimental tools that can be employed for the generation, amplification, control, and combination of separate light pulses. The main techniques for the spectrotemporal characterization of the synthesized fields are also described. We discuss recent implementations of coherent waveform synthesis: from the first demonstration of a single-cycle opticalpulse by the addition of two pulse trains derived from a fiber laser, to the coherent combination of the outputs from optical parametric chirped-pulse amplifiers