Following our research group's efforts to measure the nonlinear properties of CdTe, CdS, and CdTe/CdS quantum dot nanoparticles (QD NPs), we deposited these QD NPs on ITO metal-oxide substrates to characterize their thin-film nonlinearities, such as nonlinear refraction (NLR) and nonlinear absorption (NLA). The layers were deposited through the electrodeposition (ED) method and were analyzed by a Z-scan optical setup, together with employing FESEM, AFM imaging, XRD, and UV-Vis spectroscopy techniques. in exposure by a 655nm laser. NLA (beta) coefficients were determined as -2.99, 1.35, and -9.69cm/GW with reverse saturable absorption (RSA) for ITO-CdS and saturable absorption (SA) for ITO-CdTe and ITO-CdTe/CdS. Hence, with a 632.8nm laser, with slightly 20 nm further excitation wavelength, their NLA(beta) were measured as -18.44, -7.52, and -38.02cm/GW as SA for ITO-CdTe, ITO-CdS, and ITO-CdTe/CdS, respectively. For measuring the NLR, self-focusing and defocusing mechanisms were evaluated for layers throughout different excitations. Extreme, tunable, and identical nonlinearities against different wavelengths make these thin films promising candidates for optical limiter devices that safeguard delicate optical detectors from pulse or beam spikes, biological tissue protectors, and all-optical switching behavior near epsilon near zero (ENZ) wavelengths.
In this paper, we numerically investigate an all-fiber chirped pulse amplification (CPA) system operating at 2.86 mu m, where the stretcher, Er3+-doped amplifier, and a tapered photonic crystal fiber (TPCF) compressor are all ZBLAN based, enabling a fully integrated mid-IR solution. Numerical outcomes of the proposed CPA show that 0.0011pJ energy of a 1ps pulse with 1mW power is amplified to 1.245pJ with a duration of 1.0111ps, achieving a peak power of 1,086mW, which is almost 1,000 times greater than the input pulse.
Employing the first-principles density functional theoretical approach, this study first reports a systematic investigation of the electronic and topological properties and nonlinear optical phenomena of Ge-doped graphene. These include energy band spectra, valley Hall effect, second-harmonic generation (SHG), and the Berry curvature. The substitutionally doped graphene supercells of the functional quantum materials were modeled with Ge concentrations of 12.5%, 5.5%, 3.125%, and 2%. The computed results show that Ge doping breaks the inversion symmetry of graphene and opens a tunable bandgap ranging from 0.17eV to 1.06eV. The calculated Berry curvature exhibits opposite signs at the K and K ' valleys, indicating valley-contrasting transportation and the emergence of a valley Hall effect. Pronounced valley polarization is observed for the 12.5% and 3.125% doped Ge-graphene quantum systems, while the 5.5% doped structure exhibits weakened valley contrast associated with a nearly closed bandgap. Spin-orbit coupling (SOC) lifts band degeneracies near the valley points, whereas the calculated Chern numbers remain close to zero, confirming a topologically trivial phase. Furthermore, inversion-symmetry breaking induces strong second-order nonlinear optical responses and pronounced SHG peaks correlated with the optical absorption spectra. These findings demonstrate that Ge doping is an effective strategy for tailoring the valleytronic and nonlinear optical properties of graphene.
Nonlinear optical (NLO) limiting materials are essential for laser protection and advanced photonic applications. Metals, semiconductors, carbon-based nanomaterials, and organic macrocycles (e.g., porphyrins and phthalocyanines) exhibit distinctive limiting effects through mechanisms such as plasmon resonance, two-photon absorption, and excited-state absorption processes. Composite systems further enhance performance via interfacial coupling, achieving broadband operation, reduced thresholds, and ultrafast response dynamics. However, challenges remain, including the scarcity of broadband materials, poor dispersion stability, and the use of toxic fabrication methods. Future progress will rely on interdisciplinary strategies integrating molecular engineering, interface control, and device integration to realize efficient, stable, and environmentally sustainable optical limiting technologies.
Optical frequency combs underpin precision metrology and broadband photonics, yet analytic models that tie their formation directly to modulation instability remain scarce. We address this gap in the ℂP 2 sine-Gordon system, a coupled optical model in which a real field and a complex field evolve on a nonzero background. We show that this background is linearly unstable across a finite band of modulation wavenumbers, and we construct in closed form, through a Darboux transformation, the breather that carries the instability into its nonlinear stage. The spatial spectrum of this breather is a discrete frequency comb whose growth rate coincides exactly with the linear gain evaluated at the comb spacing, providing a transparent analytic bridge between the linear and nonlinear regimes. We further find that the fastest growing mode and the widest comb arise at distinct wavenumbers, a separation that directly constrains comb design. Iterating the transformation produces a second order breather with a richer spectral structure. Guided by the requirements of practical optical platforms, we translate the dimensionless results into physical comb line spacings and gain lengths, we show that a weak dissipative perturbation lowers the instability gain by its own rate and sets a threshold below which the comb still forms, and we show that the comb spacing that emerges from broadband noise is fixed by the gain peak rather than by the noise itself. These exact results establish the ℂP 2 sine-Gordon system as a tractable platform for supercontinuum generation and optical frequency comb engineering.
