Localized Temperature Engineering Enables Writing of Heterostructures in Glass for Polarized Photoluminescence of Perovskites.

Metal halide perovskite (MHP) structures that exhibit polarized photoluminescence (PL) have attracted significant interest in fabricating light field regulation elements for display, imaging, and information storage applications. We report a three-dimensional direct lithography of heterostructures for controllable polarized PL inside glass by laser-induced localized temperature engineering. The heterostructures consisted of oriented periodic structures (OPSs) and MHP nanocrystals, and the mechanism for hierarchical distribution of heterostructures was illustrated. The patterning of heterostructures for manipulable polarized PL can be used for information encryption, wave-plate, and polarized micro-LEDs.

Nonlinear optical response and ultrafast all-optical modulation of Nb4C3.

MXenes exhibit a variety of unique electronic, optical, chemical, and mechanical properties. In this work, the nonlinear optical (NLO) properties of Nb4C3Tx are systematically investigated. The Nb4C3Tx nanosheets exhibit saturable absorption (SA) response from visible region to near-infrared region and better saturability under 6 ns pulse excitation than that under 380 fs excitation. The ultrafast carrier dynamics show a relaxation time of ∼6 ps, which suggests a high optical modulation speed of ∼160 GHz. Consequently, an all-optical modulator is demonstrated by transferring the Nb4C3Tx nanosheets to the microfiber. The signal light can be modulated well by pump pulses with a modulation rate of 5 MHz and an energy consumption of 12.564 nJ. Our study indicates that Nb4C3Tx is a potential material for nonlinear devices.

Femtosecond laser-induced phase transition in VO2 films.

VO2 is a very promising material due to its semiconductor-metal phase transition, however, the research on fs laser-induced phase transition is still very controversial, which greatly limits its development in ultrafast optics. In this work, the fs laser-induced changes in the optical properties of VO2 films were studied with a variable-temperature Z-scan. At room temperature, VO2 consistently maintained nonlinear absorption properties at laser repetition frequencies below 10 kHz while laser-induced phase transition properties appeared at higher repetition frequencies. It was found by temperature variation experiments at 100 kHz that the modulation depth of the laser-induced VO2 phase transition was consistent with that of the ambient temperature-induced phase transition, which was increased linearly with thickness, further confirming that the phase transition was caused by the accumulation of thermal effects of a high-repetition-frequency laser. The phase transition process is reversible and causes substantial changes in optical properties of the film, which holds significant promise for all-optical switches and related applications.

Microscopic optical nonlinearities and transient carrier dynamics in indium selenide nanosheet.

This work systematically investigates the third-order nonlinear optical (NLO) properties and ultrafast carrier dynamics of layered indium selenide (InSe) obtained by mechanical exfoliation (ME). The two-photon absorption (TPA) effect of layered InSe was tested using micro-Z/I-scan techniques. The results indicate that InSe flakes undergo the TPA response under the excitation of both 520 nm and 1040 nm fs pulses, and that InSe is more likely to achieve TPA saturation under visible light excitation. Furthermore, ultrafast carrier dynamics revealed that InSe flakes in the visible region undergo a transition from photoinduced absorption to photobleaching and exhibit a fast recombination time of ∼0.4-1ps, suggesting a high optical modulation speed as high as ∼1-2.5 THz.

Nonlinear absorption and integrated photonics applications of MoSSe.

This study explores the wavelength-dependent and pulse-width-dependent nonlinear optical properties of liquid-phase exfoliated molybdenum sulfide selenide (MoSSe) nanosheets. The saturable absorption response of MoSSe nanosheets in the visible region is better than that in the near-infrared region, and the response under 6-ns pulse excitation is better than that of a 380-fs pulse. Furthermore, based on the first-principles calculations, we designed a phase modulator and optimized its structure by integrating a monolayer MoSSe into a silicon slot waveguide. The simulation results revealed that the phase shift could achieve a high optical extinction. Consequently, MoSSe exhibits satisfactory nonlinear optical properties and an excellent potential for applications in optoelectronic devices.

All-Organic Composite Films for High Flexibility and Giant Nonlinear Optical Limiting Responses.

Given the substantial π-electron delocalization observed in 4-N,N-dimethylamino-4'-N'-methyl-stilbazolium tosylate (DAST), a high third-order nonlinear optical response can be expected that might manifest itself in various ways for potential applications. To probe the possibility and assess its potential, all-organic DAST-polymethyl methacrylate (PMMA) composite films were prepared by a simple solution casting method, and their nonlinear absorption performances were measured by an open-aperture Z-scan system. The results reveal that under irradiation by a 380 fs laser pulse at 520 nm or a 6 ns laser pulse at 532 nm, the DAST-PMMA composite films with a DAST concentration of 0.125 wt % exhibit similar giant optical limiting (OL) responses with OL threshold of 7.84 or 0.37 GW cm-2, both superior to those of most organic and inorganic OL materials measured under similar conditions. These all-organic composite films show high flexibility, and interestingly, their OL responses can remain stable even after exposure to air for 3 months. The superior OL behaviors of such materials in the femtosecond and nanosecond regimes are attributed to the two-photon absorption and the combination of two-photon absorption and excited-state absorption, respectively. The simple preparation, high flexibility, giant OL responses, and excellent environmental stability suggest that such novel all-organic composite films hold great potential for applications in flexible OL devices.

Anisotropic Raman scattering and intense broadband second-harmonic generation in tellurium nanosheets.

Tellurium (Te) is a novel elementary material, which has recently attracted extensive attention due to its intriguing physical properties, such as topological, thermoelectric, and photoelectric properties. Further study on Te crystal structures will help to understand its properties and facilitate its application. Here, the angle-resolved polarized Raman spectroscopy has been employed to study Te crystal symmetry. Three different Raman vibration modes were obtained, each of which possess a different polarization dependence. Furthermore, it is revealed that Te nanosheets show a second-order harmonic response over a wide spectrum and have the greatest conversion efficiency at an excitation wavelength of 880 nm. Its second-order nonlinear susceptibility is estimated to be 2049pmV-1. This substantial nonlinear optical response endows Te nanosheets with the potential for developing nonlinear photonic and optoelectronic nanodevices with high efficiency.

Surface-State Assisted Carrier Recombination and Optical Nonlinearities in Bulk to 2D Nonlayered PtS.

Cooperite, or platinum sulfide (PtS), is a rare mineral that generally exists as microscale, irregularly shaped crystallites. The presence of impurities, in both naturally occurring and synthesized samples, has hindered the study of its optical properties in the past. In this work, we prepare large-scale, uniform PtS films in bulk to two-dimensional form through the thermally assisted conversion method. An abnormal trend is observed in linear spectral studies whereby the optical bandgap narrows as the film thickness decreases. A model based on the continuous distribution of carriers in real space, which can be regarded as a quantum well normal to the plane, is used to describe the thickness-dependent carrier recombination phenomenon. In the nonlinear optical measurements, PtS exhibits ultrafast saturable absorption and self-defocusing properties in the visible region, which are dominated by the resonant electronic nonlinearities.