Journal of Nonlinear Optical Physics & Materials

Transition metal oxides (TMOs) are distinguished by their thermal and chemical stability as well as excellent optical, electrical, and magnetic properties. Moreover, the 3$d$-orbital electrons of the transition metal ions in TMOs have a strong $d-d$ Coulomb interaction, enabling them to exhibit a variety of unusual physical phenomena, dramatically different from conventional metals and semiconductors. Additionally, TMOs possess excellent nonlinear optical properties, such as third-order nonlinear response and saturation absorption, which make them broadly applicable for ultrafast photonics devices. Herein, a review is presented of the nonlinear optical properties of typical TMOs, as well as their employment as saturable absorbers in near-infrared pulsed fiber lasers in recent years. Finally, some challenges and promising prospects for nonlinear ultrafast photonic devices based on TMOs are discussed.

Direct growth of large-area uniform graphene films on insulating materials could facilitate the applications of graphene in optoelectronic devices. The ultrafast photocarrier relaxation and saturable absorption of direct chemical vapor deposition-grown graphene glasses, with lots of defects, are studied by using femtosecond time-resolved pump–probe and Z-scan techniques at 800 nm. We find that both the relaxation times associated with hot carrier cooling and the hot phonon effect are greatly suppressed in these defect-rich graphene glasses, which further leads to the increase of both saturation intensity and anisotropy in transient optical response for graphene glasses as compared with defect-free graphene. And, both the suppression effect and saturation intensity increase with the thickness of graphene film. The dominance of defect-assisted carrier-acoustic phonon scattering (i.e., supercollision, the collision of a carrier with both an acoustic phonon and defects) in the cooling process of hot carriers is responsible for the suppression of relaxation time.

The modulation of electrostatic potential and optoelectronic characteristics of Janus MoSSe/MX₂ (M $=$ Mo, X $=$ S, Se) van der Waals (vdW) heterostructures with strain engineering were studied by first principles. Based on the effection of uniaxial strain, the electronic properties of heterostructures not only are induced to form direct band gap and indirect band gap and even semiconductor-metal transformation, but also lead to strong interface-built electric field and excellent optical adsorption properties in the range of IR-visible. This work reveals the photophysical properties of MoSSe/MX₂ vdW heterostructures as well as shows their strong potential for applications in novel optoelectronic devices and photocatalysis.

In this work, the nonlinear optical response and the ultrafast carrier dynamics in the visible region of NbSe₂ are investigated. The transient absorption (TA) spectra reveal the relaxation process, including electron–phonon scattering and phonon–phonon scattering. These results contribute to an in-depth understanding of the light-matter interactions and carrier dynamics in NbSe₂ and will establish a foundation for its applications in nonlinear photonic and optoelectronic devices.

This paper explores the role of spatial extension of impurity (SEI) on two nonlinear optical (NLO) properties and two other related properties of impurity doped GaAs quantum dot (QD). The NLO properties include the electro-optic effect (EOE) and the third-order nonlinear optical susceptibility (TONOS) whereas the other two related properties being total optical dielectric function (TODF) and the intraband transition lifetime (ITL). The study also involves Gaussian white noise (GWN) which has been introduced to the doped QD through additive and multiplicative pathways. The investigation unveils the subtle interplay between GWN and SEI which ultimately fine-tunes the said NLO properties. TODF, EOE and TONOS manifest red-shift with enhancement of SEI both with and without GWN. The ITL, on the other hand, exhibits monotonic growth with increase in SEI under all conditions. Moreover, the application of GWN causes noticeable quenching of the NLO properties. And the quenching becomes more stringent in presence of multiplicative noise than its additive counterpart.

Monolayer transition metal dichalcogenides are a class of atomically thin semiconductors that have a direct bandgap, making them promising candidates for optoelectronic and photonic devices. However, the low quantum yield at high charge injection levels significantly limits their applicability in optoelectronic devices that function under high current densities, such as light-emitting diodes and lasers. To address this issue, we demonstrate the use of hexagonal boron nitride encapsulation as a means of tuning the photoluminescence properties in monolayer transition metal dichalcogenides. Our results show a several-fold enhancement in the photoluminescence quantum yield at high exciton densities. This improvement is attributed to the suppressed exciton–exciton annihilation, which is supported by experimental time-resolved photoluminescence spectra and theoretical analysis. Our findings provide a simple and effective method for achieving highly efficient optoelectronic devices based on monolayer transition metal dichalcogenides.

Electrochemical modulation of nonlinear optical (NLO) absorption has recently garnered significant attention. In this work, we demonstrate the effective modulation of the third-order NLO absorption of layered molybdenum trioxide (MoO₃) by cation intercalation. Upon application of different negative voltages to samples in different electrolytes, we observe varying degrees of enhancement in MoO₃’s nonlinear absorption corresponding to different cations and different electrochemical processes. Cation intercalation of H${}^{+}$, Li${}^{+}$, Na${}^{+}$, K${}^{+}$, and Mg${}^{2+}$ is found to be more effective in enhancing the nonlinear absorption of MoO₃ than electrochemisorption of Al${}^{3+}$ cations. Notably, Li${}^{+}$ intercalation leads to the most significant performance improvement, with an enhancement of 11.6 times and a nonlinear absorption coefficient of $-79.88\pm 11.21$cmGW${}^{-1}$. This improvement is ascribed to the increasing number of defect states in MoO₃ during ion intercalation, which strengthens its saturation absorption behavior. Our work provides valuable insights into the electrically controlled NLO performance of MoO₃ and can be applied to other similar materials.

In this paper, we present the structural and photoluminescence (PL) spectra of 2D-MoS₂ and we report a theoretical investigation of the influence of Ag- and Au-doping on the transmission in 2D-MoS₂ photonic crystal structure (PCS). A finite-difference time-domain (FDTD) technique and plane wave expansion method (PWE) have been introduced and adapted for periodic and aperiodic structures to extract the PC-bandgap and study the behavior of the transmission spectrum. The impact of the size of defects, the Ag- and Au-doping on the 2D-PC band structure and transmission spectrum has been visualized under the inclusion of the distribution of electromagnetic fields and the associated field maps. It has been shown that the Au-doping changes significantly the 2D-MoS₂ PCS and as a result the transmission spectrum increases considerably. We can predict that 2D-MoS₂ PC doped with Au is more convenient than doped with Ag in most applications involving optical transmission and waveguides for optoelectronics devices.