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Energy transfer has been proven to be an effective method to optimize optoelectronic conversion efficiency by improving light absorption and mitigating nonradiative losses. We prepared 2D/3D CsPbBr3 hybrid assemblies at different reaction temperatures using the hot injection method and found that the photoluminescence quantum yields (PLQYs) of these hybrids were greatly enhanced from 53.4% to 72.57% compared with 3D nanocrystals (NCs). Femtosecond transient absorption measurements were used to study the PLQY enhancement mechanisms, and it was found that the hot carrier lifetime improved from 0.36 to 1.88 ps for 2D/3D CsPbBr3 hybrid assemblies owing to the energy transfer from 2D nanoplates to 3D NCs. The energy transfer benefits the excited carrier accumulation and prolonged hot carrier lifetime in 3D NCs in hybrid assemblies, as well as PLQY enhancement in materials. [ABSTRACT FROM AUTHOR]

In semiconductor‐based microlasers, the generated excited carriers can affect both the optical absorption coefficient and refractive index, influencing the lasing behavior and device performance. In this study, the lasing behavior of individual MAPbBr3 microrods pumped by femtosecond laser pulses is investigated using an ultrafast optical Kerr gating technique. By analyzing the spectral and temporal evolution of the lasing behavior, it is found that the band‐filling (BF) effect can cause a significant change in the refractive index of the material, which results in an unfavorable red‐shift and broadening of the resonant modes, deteriorating the laser linewidth and quality factor. The hot carrier cooling process can provide a buffer for alteration of the energy level occupation state, resulting in a small transient refractive index change and slight red‐shift. These results offer insights into the lasing behavior driven by photogenerated carrier dynamics and provide an optimization strategy for semiconductor‐based microlasers. [ABSTRACT FROM AUTHOR]

Nonlinear optical limiting (OL) properties of carboxyl-functionalized Ti3C2 nanosheets (COOH-MXene) were studied using the nanosecond laser Z-scan technology. COOH-MXene showed excellent broadband OL properties with OL thresholds of 0.34 J/cm2 at 532 nm and 0.58 J/cm2 at 1064 nm, and the OL mechanism was mainly attributed to the reverse saturable absorption effect. Femtosecond time-resolved transient absorption measurements were used to clarify the ultrafast carrier dynamics in the OL process, and the results revealed that excited states absorption (ESA) in MXene was enhanced by introducing more carboxyl group terminations. When COOH-MXene was irradiated by laser pulses, excited electrons in the conduction band of MXene could transfer to the carboxyl groups and induce the ESA in the surface functional groups, resulting in the excellent OL property of COOH-MXene. [ABSTRACT FROM AUTHOR]

Two-dimensional molybdenum disulfide (MoS2) has been proved to be a good candidate in photodetectors, and MoS2/graphene (MoS2/G) heterostructure has been widely used to expand the optical response wavelength of MoS2. To clarify the carrier transfer dynamics in the MoS2/G heterostructure, time-resolved transient absorption and two-color pump–probe measurements are performed. By comparing the carrier dynamics in MoS2 and MoS2/G under different pump wavelengths, we find that interfacial excitons are formed in the heterostructure, and fast hot carriers transfer (<200 fs) from graphene to MoS2 are observed. The results indicate that the formed heterostructure with graphene can not only expand the optical response wavelength of MoS2 but also improve the response time of the device in the near-infrared region. [ABSTRACT FROM AUTHOR]

In this paper, we propose a demodulation method for refractive index (RI) sensing with tilted fiber Bragg gratings (TFBGs). It operates by monitoring the TFBG cladding mode resonance “cut-off wavelengths.” The idea of a “cut-off wavelength” and its determination method are introduced. The RI sensitivities of TFBGs are significantly enhanced in certain RI ranges by using our demodulation method. The temperature-induced cross sensitivity is eliminated. We also demonstrate a parallel-double-angle TFBG (PDTFBG), in which two individual TFBGs are inscribed in the fiber core in parallel using a femtosecond laser and a phase mask. The RI sensing range of the PDTFBG is significantly broader than that of a conventional single-angle TFBG. In addition, its RI sensitivity can reach 1023.1 nm/refractive index unit in the 1.4401–1.4570 RI range when our proposed demodulation method is used. [ABSTRACT FROM AUTHOR]

We studied the photoluminescence (PL) from black silicon that was fabricated using an 800 nm, 250 kHz femtosecond laser in air. By changing the scan velocity and the fluence of the femtosecond laser, the formation of the PL band between the orange (600 nm) and red bands (near 680 nm) could be controlled. The red band PL from the photoinduced microstructures on the black silicon was observed even without annealing due to the thermal accumulation of high-repetition rate femtosecond laser pulses. The orange band PL was easily quenched under 532 nm cw laser irradiation, whereas the red band PL was more stable; this can be attributed to 'defect luminescence' and 'quantum confinement', respectively. [ABSTRACT FROM AUTHOR]

All‐inorganic lead halide perovskite nanocrystals (NCs) have been widely applied in optoelectronic devices owing to their excellent photoluminescence (PL) properties. However, poor stability upon exposure to water, UV light or heat strongly limits their practical application. Herein, CsPbBr3@Pb‐MOF composites with exceptional stability against water, UV light, and heat are synthesized by ultrasonic processing the precursors of lead‐based MOF (Pb‐MOF), oleylammonium bromide (OAmBr) and cesium oleate (Cs‐OA) solutions at room temperature. Pb‐MOF can not only provide the lead source for the in situ growth of CsPbBr3 NCs, but also the protective layer of perovskites NCs. The formed CsPbBr3@Pb‐MOF composites show a considerable PL quantum yield (PLQY) of 67.8%, and can maintain 90% of the initial PL intensity when immersed in water for 2 months. In addition, the outstanding PL stability against UV light and heat is demonstrated with CsPbBr3 NCs synthesized by the conventional method as a comparison. Finally, a green (light‐emitting diode) LED is fabricated using green‐emitting CsPbBr3@Pb‐MOF composites and exhibits excellent stability without packaging when immersed in water for 30 days. This study provides a practical approach to improve the stability in aqueous phase, which may pave the way for future applications for various optoelectronic devices. [ABSTRACT FROM AUTHOR]

All-optical control of the noncentrosymmetry of azodye-doped polymer films was demonstrated by nonresonant dual-frequency coherent excitation. Three kinds of noncentrosymmetries of the polymer films were optically tailored using appropriate combinations of the writing beam polarizations, linearly polarized, and circularly polarized light. The tensor analysis of the photoinduced noncentrosymmetry was performed by monitoring second harmonic generation (SHG) of the samples. The quadratic dependence of SHG on film thickness was observed, indicating that a χ[sup (2)] grating satisfying the phase-matching condition for SHG was optically induced in the polymer films and that this nonresonant all-optical poling can be used to tailor the symmetry of bulk samples. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Phase-matched second-harmonic generation (SHG) in azodye-doped polymethylmethacrylate films was demonstrated using the nonresonant optical poling technique. During the seeding process, samples were irradiated simultaneously by coherent superposition of the fundamental and the second-harmonic light of a femtosecond laser. Optical poling experiments were performed at three wavelengths of 1500, 1320, and 1300 nm, respectively. The quadratic dependence of SHG on the film thickness showed that a χ[sup (2)] grating that satisfied the phase-matching condition for SHG was optically induced in the polymer films. The SHG conversion efficiency of a 105 μm thick film was estimated to be about 2%. A relaxation retardation effect of the photoinduced χ[sup (2)] was also observed in the thick films. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Provides information on a study which used two kinds of polymers in a thermal-assisted optical poling to improve the photostability of the optically induced polar orientation of molecules. Description of the experiments; Results and discussion; Conclusion.

Performs a comparison of temperature-dependent optical poling between two azopolymers, a side-chain and a guest-host polymer, at various poling temperatures. Factors affecting the efficiency of all-optical poling; Experimental design and methodology; Results and discussion; Conclusions.

The nonlinear optical response of gold nanoparticles/reduced graphene oxide (AuNPs/rGO) nanocomposites prepared by laser ablation method was studied using a femtosecond laser open-aperture (OA) Z-scan method, and an enhanced nonlinear absorption effect was observed. Using the femtosecond time-resolved pump-probe measurements, the nonlinear response mechanism in the hybrid was studied. When graphene was excited by an ultrashort laser pulse, the bleaching of valence band (VB) and the filling of conduction band (CB) took place, causing a saturable absorption (SA) effect. When decorated with gold nanoparticles, the excited carriers from the CB of graphene could transfer to the sp band of the metal before returning to the VB of graphene. This process would take place in a much longer time scale (∼50 ps) than the direct relaxation in pure graphene, causing the enhancement of the SA effect. The excited carrier dynamics were further demonstrated using femtosecond time-resolved transient absorption spectroscopy, and the interband relaxation of the excited electrons from the sp band of AuNPs to the CB of graphene was observed, resulting in the further filling of the CB of graphene and enhancement of the SA effect. [ABSTRACT FROM AUTHOR]

Single‐crystal halide perovskites are among the most promising semiconductor candidates for highly efficient optoelectronic devices due to their higher stability against moisture and light radiation and lower trap density than their polycrystalline counterparts. In this work, single‐crystal MAPbBr3 microcavities with controllable geometries and sizes are fabricated using a template‐limited method combined with an anti‐solvent diffusion growth method. The single‐crystal microcavities emit lasers around 550 nm under femtosecond laser excitation, with a lasing threshold of ≈35 µJ cm−2 and a quality factor of 1135, as well as excellent long‐term operation stability. The temporal‐spatial evolution of the lasing process in an individual microcavity is achieved by the microscopic optical Kerr‐gating technique. The temporal behaviors including pulse duration and build‐up time, emission spectra shift, and lasing mode evolution as a function of pump fluence are unveiled, and the complex relationship between the light‐induced carrier dynamics and lasing properties is clarified. Spatial heterogeneous lasing dynamics are also observed in an individual microdisk, which is attributed to the non‐uniform optical losses and carrier densities driven by structural imperfections. This study can provide a fabrication strategy for perovskite on‐chip optoelectronic devices, as well as a deeper understanding of the carrier‐density‐driven lasing dynamics in microcavities. [ABSTRACT FROM AUTHOR]

The nonlinear optical limiting (OL) property of tin phthalocyanine porous organic frameworks (Sn-Pc-POFs) dispersion in the nanosecond regime was studied, which showed excellent dispersibility and stability as well as a low OL threshold. To clarify the nonlinear optical response mechanisms in the material, the energy level structure of Sn-Pc-POFs was simulated using the density functional theory calculation, and the photoinduced carrier dynamics was studied using femtosecond time-resolved transient absorption spectroscopy. The results indicated that the large absorption cross section and long lifetime of the excited state were responsible for the excellent OL property of the material. [ABSTRACT FROM AUTHOR]

Transient energy transfer effect might occur in femtosecond pump-probe optical Kerr gate (OKG) measurements. Using time- and frequency-resolved two-dimensional pump-probe imaging spectroscopy, we are able to obtain the OKG spectra as a function of the delay time between pump and probe pulses. By analyzing the pump power dependence of the OKG spectra at different delay time, we find that due to the effect of transient energy transfer, the short-wavelength components of the OKG spectra are enhanced when the delay of the probe to pump pulse is positive, while the long-wavelength components increase when the delay is negative. [ABSTRACT FROM AUTHOR]

Carbon nanodots (C-dots) are promising substitutes for the present fluorescent nanomaterials of various applications due to their unique combination properties of intense photoluminescence (PL), low toxicity, and high aqueous solubility. However, the origin of the fascinating PL in C-dots is still a matter of current debate. Due to their complex and uncontrollable structures, the contributions of surface chemicals and carbogenic-core to their PL are poorly understood. Here, a facile two-step method combining laser ablation and UV light irradiation has been developed, in which non-fluorescent C-dots are prepared by ablating graphite powders in water using nanosecond laser, and the PL intensities are enhanced by UV light irradiation in oxygen atmosphere. Using this strategy, we are able to control the size and the surface functional groups of C-dots independently. By detailed characterization and comparison of different C-dots, we find that the intense PL in C-dots is originated from abundant surface functional groups on its surface rather than its carbogenic-core. One kind of surface functional group forms a single surface state energy level and becomes an isolated emission center with specific carrier dynamics on the surface site of C-dots. The energy gap of each surface state exhibits carbogenic-core size independent and is characterized by distinct central energies, such as C O group at 335 nm, and C O group at 430 nm. [ABSTRACT FROM AUTHOR]

Feedback-based wavefront shaping for focusing light through scattering media is an established method. In conventional feedback-based wavefront shaping, the incident light is divided into N input modes that are modulated by a spatial light modulator (SLM) using N segments, each of which has the same number and size of pixels. Here we propose light intensity-dependent feedback-based wavefront shaping using a genetic algorithm to achieve the desired wavefront shaping in less time and with fewer iterations than the conventional method. In our method, a phase mask is divided into several regions, each being allocated different phase modulation units according to the distribution of light intensity, with the pixels of the SLM being grouped non-uniformly to modulate the incident light. Compared with the conventional method, the experimental response time of our method using four subregions decreased by 15.6% and the enhancement factor increased by 30.4%. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) periodic structures were fabricated on silicon surfaces by femtosecond laser irradiation in air and water, with the assistance of a microlens array (MLA) placed in the beam's path. By scanning the laser beam along the silicon surface, multiple grooves were simultaneously fabricated in parallel along with smaller laser-induced ripples. The 2D periodic structures contained long-periodic grooves and perpendicular short-periodic laser-induced ripples, which had periods of several microns and several hundred nanometers, respectively. We investigated the influence of laser power and scanning velocity on the morphological evolution of the 2D periodic structures in air and water. Large-area grid-like structures with ripples were fabricated by successively scanning once along each direction of the silicon's surface, which showed enhanced optical absorption. Hydrofluoric acid was then used to remove any oxygen and laser-induced defects for all-silicon structures. [ABSTRACT FROM AUTHOR]

Since their discovery, carbon nanodots (C-dots) have attracted great interest due to their strong photoluminescence (PL). Yet a full understanding of the mechanisms for PL from C-dots is still under debate. In this work, we analyzed the evolution of the time-resolved PL spectra of C-dots using picosecond time-resolved spectroscopy to explore the carrier dynamics in C-dots. Our results suggest two different pathways of electron–hole radiative recombination, each with distinct relaxation time scales: a relaxation of carriers from carbogenic core onto the surface states with a slow decay (>14 ns) and direct radiative recombination of carriers on the surface states with a fast decay (∼1.3 ns). The slow decay at short-wavelength emissions is dominant due to the effective relaxation from the carbogenic core onto the surface states, while the fast decay is dominant at long-wavelength emissions. An explanation for the excitation-dependent and independent PL properties of C-dots is also presented here using this carrier dynamic model. [ABSTRACT FROM AUTHOR]

We demonstrated the time-gated ballistic imaging technique using a femtosecond optical Kerr gate (OKG) of bismuth–plumbum oxide glass, the nonlinear optical properties of which were also investigated. The third-order nonlinear refractive-indexn2of the bismuth–plumbum oxide glass was measured to be 2.19?×?10?15?cm2/W, and the nonlinear response time was estimated to be shorter than 180?fs. For the time-gated ballistic imaging, the maximum measurable optical density of turbid media using the OKG of bismuth–plumbum oxide glass was 9.3, while only 7.0 for the OKG of quartz glass. And the intensities of the images for the bismuth–plumbum oxide glass were approximately two orders of magnitude higher than that for the quartz glass. The experimental results indicated that the bismuth–plumbum oxide glass was an excellent optical material for nonlinear optical applications. [ABSTRACT FROM AUTHOR]

A femtosecond pulse laser was used to fabricate carbon nanodots (CDs), of which the particle size and photoluminescence (PL) properties could be effectively controlled by adjusting ambient pressure. By increasing the reaction pressure, the particle size of CDs gradually decreased and finally reached less than 1 nm at 4 MPa. Simultaneously, the fluorescence intensity of the CDs first increased and then decreased by further increasing the pressure. By examining the PL dynamics and the chemical structure of the CDs, we found that the PL change of products was attributed to the quantity change of functional groups attached to the CDs due to the surface area change of the carbonic core. [ABSTRACT FROM AUTHOR]

We investigated the ultrafast time-resolved single-shot imaging of femtosecond pulse propagation using a supercontinuum and optical polarigraphy in transparent liquids. The probe supercontinuum senses the instantaneous birefringence induced by the laser pulse, and a polarigraphy image with different color distributions could be obtained. By comparing the wavelength distributions and the saturation variation of the images, the recorded polarigraphy images in two samples with different response time were analyzed. In the fast response sample, N-methyl-2-pyrrolidone (NMP), the spectral widths and the saturation values of the polarigraphy image at fixed positions were narrower and higher than those in CS2. Due to the slow response of CS2, the probe light sensed a long-lived birefringence and the polarigraphy image contained more wavelength components at every position along the pump pulse propagation direction. [ABSTRACT FROM AUTHOR]

Abstract: We design a novel plasmonic lens consisting of multiple nano-metal slits surrounded by dielectric air slot waveguides. The surface plasmon polaritons (SPPs) are excited from the metal slits. The slot waveguides provide desired phase retardations of light focusing. Numerical simulations with finite-difference time-domain (FDTD) method show that the transmitted fields through the design example can generate light focusing and deflection by altering the width or length of slot waveguides. The focal spot size is far narrower than the incident wavelength and the focal length can be controlled in several micrometers, which agree with our theoretical analysis. [Copyright &y& Elsevier]

The electromagnetic induced transparency (EIT) effect originates from the destructive interference in an atomic system, which contributes to the transparency window in its response spectrum. The implementation of EIT requires highly demanding laboratory conditions, which greatly limits its acceptance and application. In this paper, an improved harmonic spring oscillation (HSO) model with four oscillators is proposed as a classical analog for the tunable triple-band EIT effect. A more general HSO model including more oscillators is also given, and the analyses of the power absorption in the HSO model conclude a formula, which is more innovative and useful for the study of the multiple-band EIT effect. To further inspect the analogizing ability of the HSO model, a hybrid unit cell containing an electric dipole and toroidal dipoles in the metamaterials is proposed. The highly comparable transmission spectra based on the HSO model and metamaterials indicate the validity of the classical analog in illustrating the formation process of the multiple-band EIT effect in metamaterials. Hence, the HSO model, as a classical analog, is a valid and powerful theoretical tool that can mimic the multiple-band EIT effect in metamaterials. [ABSTRACT FROM AUTHOR]

In order to diagnose the high-speed compressible turbulent flow field, a two-dimensional (2-D) multi-parameters measurement method based on multi-beam interferometric Rayleigh scattering (IRS) technique was proposed. Under the beam splitting of etalon, the Rayleigh scattering signals generated by the interaction between multi-beam laser probes and the flow field gas molecules formed 2-D interference measurement lattice. Each measurement point contained the thermodynamic and velocity information of the flow field corresponding to a specific spatial location. By calibrating the effective finesse and transmittance of the etalon at different incident angles, the measurement accuracy of temperature and density of high-order interferometric points was improved. A 2-D IRS measurement system was established by combining multi-beam laser probes, amplification imaging system and solid quartz etalon. A high speed jet was used to verify the technology. The distributions of temperature, density and velocity at different positions along the radial direction and axial direction of the nozzle were obtained. The results shown that the technique could be used to simultaneously measure the 2-D multi-parameter information of the flow field. [ABSTRACT FROM AUTHOR]

Abstract: We show an inorganic–organic hybrid silica gel glass with remarkable femtosecond optical Kerr effect in the order of the time-resolution of the experiment (∼200fs) based on doped lead phthalocyanine. In our materials, self-diffraction of the pumping beam by ultrafast transient gratings dominates the Kerr signal, ensuring ultrafast response happens. By the replacement of inorganic or polymeric matrix with inorganic-organic hybrid, many practical advantages can be gained. Our results demonstrate a critical role for the design of novel ultrafast optical Kerr shutters in such low-cost silica based-nanocomposites with great flexibility. [Copyright &y& Elsevier]

Abstract: Multiphoton-induced two-dimensional periodic microstructures were fabricated in dye-doped bulk transparent materials by four-beam interference of femtosecond pulses at a wavelength of 800nm. Observations of optical microscopy show that two-dimensional microstructures are realized in the samples through nonresonant absorption process. The photoinduced refractive index modulation, resulted from the multiphoton-induced photodecomposition, is responsible for the periodic microstructures. These results suggest that this method can be applied to a wide variety of transparent materials and that the materials co-doped with different dyes and with photoinduced microstructure may be possible to make the distributed feedback lasers with novel properties. [Copyright &y& Elsevier]

Abstract: ZrO2–SiO2 binary films for active optical waveguides were prepared by the sol–gel method with zirconium oxychloride and tetraethoxysilane as precursors. The main factors that influence the film thickness and refractive index have been found. The relationship between the film refractive index composition and heat treatment temperature has been determined. The continuous tuning of the thickness and refractive index of the thin films has also been achieved, which will open up new possibilities in the development of active optical waveguides. [Copyright &y& Elsevier]

Abstract: We report on multiphoton-induced periodic microstructures inside bulk polymers by multibeam interference of femtosecond laser pulses at a wavelength of 800 nm, which is out of the linear absorption range of the polymer sample. Two-dimensional structures and three-dimensional periodic microstructures were fabricated inside bulk azodye-doped polymethylmethacrylate by four-beam interference and five-beam interference, respectively. The Raman spectra measurements for the photomodified area of the sample before and after irradiation with the writing light showed that the periodic microstructures probably arose from photoinduced decomposition reaction of azodye molecules through multiphoton absorption. [Copyright &y& Elsevier]

Azodye-doped vinyl group substituted bulk silica materials were prepared by a sol–gel method. Photoinduced noncentrosymmetry in these initially centrosymmetric rigid matrixes was demonstrated first using nonresonant all-optical poling with a fundamental light at wavelength of 1500 nm and its second-harmonic light. The largest photoinduced second-order nonlinear optical coefficient d33 was estimated to be 8×10−3 pm/V. The characteristic kinetics of decay of the induced second-order susceptibility was measured by second-harmonic generation. Although the signal decay was fast and the coefficient d33 was low, we found that increasing the power of the seeding beams could improve the second-harmonic signal decay process. [Copyright &y& Elsevier]

The photoinduced birefringence induced by a femtosecond laser through two-photon absorption was studied in bulk azodye-doped hybrid inorganic–organic materials. The probe transmittance for the induced birefringence was estimated to be 92% after irradiating disperse red 1-doped silica materials with the femtosecond writing beam. The relaxation characteristic of the induced birefringence was also investigated. Although the signal decay process was fast, these photoinduced birefringence materials might have wide applications in optical image storage. [Copyright &y& Elsevier]

Germanium diselenide (GeSe2) has recently emerged as a promising material for high‐performance optoelectronic devices due to its high absorption coefficient, wide direct bandgap, and anisotropic electronic properties. For the future applications, it is necessary to understand the dynamic evolution of carriers with ultrafast response. In this work, the transient absorption spectroscopy measurements are performed to study the anisotropic dynamic evolution of GeSe2 under the polarized photoexcitation. It is find that the dynamics exhibit linear dichroism and show a significant Auger recombination process when the photoexcitation is perpendicular to the b‐axis of GeSe2. Using first‐principle and transition dipole moment calculations, it is confirmed that the more carrier localization at Γ point along the Γ‐X (perpendicular to the b‐axis) and increase the Auger recombination. In addition, the Auger recombination coefficient ≈ 1.1×10−31 cm6 s−1 is determined and demonstrated that the defect‐assisted indirect Auger recombination plays a key role in the carrier relaxation process. Through time‐resolved transient absorption spectra, it is further revealed that the ultrafast dynamical evolution of excited state absorption peaks under polarized photoexcitation. These results have implications for improving the quantum efficiency of high‐field polarization‐sensitive optoelectronics. [ABSTRACT FROM AUTHOR]

Phase-matched second-harmonic generation (SHG) in thermal-cross-linking polyurethane films was demonstrated using a thermal-assisted nonresonant optical poling technique. During the seeding process, samples heated in an oven were irradiated simultaneously by coherent superposition of the 1300 nm fundamental and 650 nm second-harmonic lights of a femtosecond laser. The photoinduced second-order optical nonlinearity of the polymer films seeded at elevated temperatures kept stable at room temperature. The measurements for the dependence of SHG on the film thickness showed that a χ(2) grating that satisfied the phase-matching condition for SHG was optically induced in the polymer films. [ABSTRACT FROM AUTHOR]

Permanent holographic gratings were fabricated in bulk azodye-doped polymethylmethacrylate by the coherent field of a femtosecond laser. Optical microscopy and atomic force microscopy observations revealed that the gratings consist of two parts, surface relief gratings on both surfaces and refractive index modulated volume gratings in the interior of the polymers. The diffraction efficiency of the first-order Bragg for the gratings was estimated to be 90%. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We demonstrate an environmentally stable femtosecond laser for industrial application based on all polarization‐maintaining Yb‐doped laser and experimentally explore the effect of the net cavity dispersion (NCD) on output characteristics. The oscillator emits pulses with 5.1 ps and a 23 nm spectral bandwidth, then the pulse is compressed to 88 fs. The instabilities over 120 h gives 0.32% relative root mean square noise, indicating high stability of the pulse laser. With effective regulation of NCD, we obtained the maximum spectral bandwidth of 27 nm. Such broadband oscillator with compact all‐fiber configurations provide extremely high stability should be very attractive for long‐term industrial application. [ABSTRACT FROM AUTHOR]

Controlled sequential crystallization of donors and acceptors is a critical factor for achieving enhanced phase separation and efficient charge transfer performance in polymer solar cells (PSCs). In this study, a comprehensive investigation of a structurally simple solvent additive, 1‐fluoro‐2‐iodobenzene (OFIB) is conducted, which efficiently controls the morphology of the active layer, resulting in fibrous assembly and significantly enhancing the power conversion efficiency from 16.34% to 18.38% based on the PM6:L8‐BO system. Density functional theory, molecular dynamics simulations, and grazing incidence small‐ and wide‐angle X‐ray scattering techniques reveal that the addition of OFIB to the processed blend aligns the orientation of the acceptor molecules, thereby enhancing the overall π–π stacking in the active layer. OFIB establishes nearly equal‐strength π–π interactions with the conjugated frameworks of both the donor and acceptor materials, benefiting from the multiple electron conjugation between its iodine atom and the conjugated framework in the active layer. Femtosecond‐timescale photophysical studies demonstrate that the OFIB‐optimized active layer shows reduced exciton losses at the donor–acceptor interface. This study offers a new perspective on the mechanism underlying the function of solvent additives and presents a comprehensive research methodology that will guide the development of next‐generation non‐fullerene acceptors for efficient PSCs. [ABSTRACT FROM AUTHOR]

With the wide application of intense lasers, the protection of human eyes and detectors from laser damage is becoming more and more strict. In this paper, we study the nonlinear optical limiting (OL) properties of porous carbon with a super large specific surface area (2.9 × 103 m2/g) using the nanosecond Z-scan technique. Compared to the traditional OL material C60, the porous carbon material shows an excellent broadband limiting effect, and the limiting thresholds correspond to 0.11 J/cm2 for 532 nm and 0.25 J/cm2 for 1064 nm pulses, respectively. The nonlinear scattering experiments showed that the OL behavior was mainly attributed to the nonlinear scattering effect, which is caused by the rapid growth and expansion of bubbles in the dispersion induced by laser irradiation, and the scattered light distribution is consistent with the results of Mie's scattering. These results suggest that porous carbon materials are expected to be applied to the field of laser protection in the future to further protect the human eye and precision optical instruments. [ABSTRACT FROM AUTHOR]

The molecular hyperpolarizability γ(-ω;ω,ω,-ω) of a supramolecule, zinc 4,4[sup ′] ,4[sup ′′] ,4[sup ′′′] -tetrasulfonato-phthalocyanine/N-butyl-N[sup ′] -methylanthraquinone-4,4[sup ′] -bipyridinum dibromide assembly (ZnTsPc-V-AQ), was observed to be enhanced by ten times when the sample was optically pumped by a 355 nm pump beam. The enhancement of the nonlinearity was found to be due predominantly to the charge transfer between the two monomers of the supramolecule after optical excitation. [ABSTRACT FROM AUTHOR]

Light-induced enhancement of the third-order nonlinear optical susceptibility of a heterodimer consisting of two different porphyrin monomers, a zinctetra(4-sulfonatophenyl)porphyrin and a zinctetra(4-N-methyl-pyridyl)porphyrin, was observed when the sample was optically pumped by a 30 ps, 532 nm pump pulse. The temporal behavior of the enhancement was studied. It was found that the enhancement was due predominantly to the population of the charge-separated state with a large electronic third-order nonlinear optical susceptibility © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The advancement of carbon‐based electronics is reliant on the development of semiconducting carbon nanotubes with high purity and yield. We developed a new extraction strategy to efficiently sort SWCNTs with superior yields and purity. The approach uses two polymers, poly[N‐(1‐octylnonyl)‐9H‐carbazol‐2,7‐diyl](PCz) and poly(9,9‐n‐dihexyl‐2,7‐fluorene‐alt‐9‐phenyl‐3,6‐carbazole)(PDFP), and two sonication processes to eliminate surface polymer contamination. PCz selectively wraps large‐diameter s‐SWCNTs, with PDFP added as an enhancing molecule to increase sorting efficiency at 4‐fold compared to the efficiency of only PCz alone sorting. The purity of the sorted s‐SWCNTs was confirmed to be above 99 % using absorption and Raman spectra. Field‐effect transistors and photodetectors made from the sorted s‐SWCNTs exhibited excellent semiconductor properties and broad‐spectrum detection, with good long‐term stability. Furthermore, a photodetector using large‐tube diameter s‐SWCNTs achieved broad‐spectrum detection, which the photoresponsivity is 0.35 mA/W and the detectivity is 4.7×106 Jones. The s‐SWCNTs/graphene heterojunction photodetector achieved a photoresponsivity of 3 mA/W and a detectivity of 6.3×106 Jones. This new strategy provides a promising approach to obtain high‐purity and high‐yield s‐SWCNTs for carbon‐based photodetectors. [ABSTRACT FROM AUTHOR]

Recently, molybdenum disulfide (MoS 2) nanosheets have been used in passively mode-locked laser due to excellent saturable absorption (SA) property. To enhance their optical nonlinearity, some heterostructures such as MoS 2 /Graphene (MoS 2 /G) have been designed, but the carrier dynamics in the materials have rarely been reported. Here, the nonlinear response of MoS 2 and MoS 2 /G heterostructures nanosheets with different thickness are studied via nanosecond laser Z-scan and femtosecond time-resolved transient absorption (TA) technique. The results reveal that the ground state bleaching take place under intense laser excitation, which would block the further absorption of incident light, causing a strong SA effect of the materials. With increasing the thickness of MoS 2 , electron diffusion take place between adjacent layers, resulting in a slow recombination of excited carriers and the enhancement of SA effect in MoS 2. In MoS 2 /G, excited electrons could transfer from MoS 2 to graphene and the interlayer carrier diffusion in MoS 2 could be enhanced, prolonging the decay time of ground state bleaching effect. The slower carrier relaxation time in MoS 2 would lead a stronger SA effect for nanosecond laser pulse. This work could provide an effective strategy for designing saturable absorbers in mode-locked lasers using MoS 2 heterostructures. Image 1 [ABSTRACT FROM AUTHOR]

We demonstrated a linear-cavity fiber laser using a fiber Bragg grating (FBG) fabricated by femtosecond laser and a Sagnac loop as cavity mirrors. The temperature sensing response of the fiber laser was characterized by placing the FBG in a high-temperature environment. The stability of the fiber laser at high temperature was improved after the FBG was annealed at 1100 °C. The fiber laser can work stably as a temperature sensor at 1000 °C and its temperature sensing sensitivity is approximately 15.9 pm/°C from 300 °C to 1000 °C. • A fiber laser based on an FBG fabricated by femtosecond laser and a Sagnac loop as cavity mirrors is demonstrated. • The fiber laser can work stably as a temperature sensor at 1000 °C after the FBG was annealed at 1100 °C. • The wavelength of the fiber laser had a quadratic dependence on temperature from room temperature to 1000 °C. • The temperature–wavelength had a good linear relationship from 300 °C to 1000 °C. Its sensing sensitivity was about 15.9 pm/°C. [ABSTRACT FROM AUTHOR]

The feedback-based wavefront shaping method can be used to focus light behind or inside strongly scattering media. In this study, we investigated several characteristics of the focus after optimization to evaluate the enhancement effect of the wavefront shaping method, including the spot size, the intensity, and two types of enhancement factor. In addition, we studied the influences of various experimental parameters on these characteristics, including the number of controlled segments N, diameter of the irradiated area at the front of the scattering medium D, and distance between the expected focusing spot and scattering medium Z. A larger N and smaller Z provided a smaller focus spot. For a brighter focus spot, a larger N and smaller D and Z were required, while for a high-resolution focus spot, larger N, D, and Z were required. [ABSTRACT FROM AUTHOR]

Gold nanorod (GNR) and reduced graphene oxide (rGO) hybrids are synthesized using photochemical method based on femtosecond laser ablation without the usage of strong chemical reducing agents. The products are characterized by absorption spectra, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The formed GNR are well located on the surface of rGO sheets. By adjusting the laser ablation time, the aspect ratio and optical properties of GNR can be well controlled. The produced nanocomposites exhibited an excellent near-infrared (NIR) photothermal performance with a photothermal conversion efficiency of 77.8%, suggesting that the hybrids have large potential as agents in photothermal therapy. • Gold nanorod and graphene hybrids are synthesized using femtosecond laser. • The aspect ratio of gold nanorod can be well controlled by adjusting laser ablation time. • The produced hybrids exhibited an excellent photothermal performance at 808 nm. [ABSTRACT FROM AUTHOR]

A strong coherent effect was observed in the monochromatic optical Kerr effect (OKE) experiment of a Bi2O3-B2O3-SiO2 oxide glass (BI glass). To eliminate the influence of the coherent effect, we proposed a simple femtosecond two-color OKE measurement method with wavelength tunability using a supercontinuum. In the two-color OKE measurement the third order nonlinear susceptibility of the BI glass was measured to be 1.64 × 10-13 electrostatic units (esu), in which the influence of the coherent effect was eliminated. The result is smaller than that obtained in a previous monochromatic OKE experiment. In addition, we discuss the discrepancies between the result obtained in this paper and those reported in other studies. [ABSTRACT FROM AUTHOR]

Lead halide perovskites (LHPs) have excellent semiconductor properties. They have been used in many applications such as solar cells. Recently, the hot carrier dynamics in this type of material have received much attention as they are useful for enhancing the performance of optoelectrical devices fabricated from it. Here, we study the ultrafast hot carrier dynamics of a single CsPbBr3 microplate using femtosecond Kerr-gated wide-field fluorescence spectroscopy. The transient photoluminescence spectra have been measured under a variety of excitation fluences. The temporal evolution of bandgap renormalization and the competition between hot carrier cooling and the recovery of the renormalized bandgap are clearly revealed. [ABSTRACT FROM AUTHOR]

Zinc oxide (ZnO) nanoparticles (NPs) are synthesized by one-step femtosecond laser ablation of zinc powders in n-methyl pyrrolidone (NMP) at room temperature. The as-prepared ZnO NPs are fairly stable, water-soluble and have abundant surface functional groups resulting in a strong fluorescence in the visible region. By further annealing the ZnO NPs in the reacting solvent up to 120∘C, the photoluminescence (PL) intensity of material can be significantly enhanced. Besides, the PL of ZnO NPs can change from blue to green by controlling the annealing temperature. The products exhibit excellent temperature sensing with high temperature sensitivity and a 1.3% change per ∘C response over a linear temperature sensing range (6–84 ∘ C) in aqueous buffer, which matches well with the physiologically relevant temperatures. Hence, the ZnO nanoparticle system can serve as a promising candidate for practical fluorescent temperatures nanosensors which can be used for accurate temperature monitoring within biological systems. Water-soluble and photoluminescent ZnO NPs are synthesized by femtosecond laser ablation of zinc powders at room temperature. By further annealing, the photoluminescence intensity of the products can be significantly enhanced. The ZnO NPs exhibit excellent temperature sensing with a high sensitivity of 1.3% change per ∘C over a linear range of 6–84∘C in aqueous buffer, which can serve as a promising candidate for fluorescent temperature nanosensors to be used for accurate temperature monitoring within biological systems. [ABSTRACT FROM AUTHOR]

Degenerate four-wave-mixing was performed in azobenzene-doped polymethyl methacrylate film under a low power continuous-wave laser at 632.8 nm with a pulsed pump laser of 532 nm. Different temporal profiles of the degenerate four-wave-mixing signal were observed under different pump energies, which originated from the relaxation processes between the energy levels of azobenzene during the photoisomerization, especially the transferring processes between the triplet states of the two isomers, trans and cis. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

All-inorganic lead halide perovskites nanocrystals (NCs) have been demonstrated to be promising candidates for optoelectronic devices, but preparing perovskite NCs with high photoluminescence quantum yields (PLQYs) and excellent stability has been a challenge. In this work, CsPbBr 3 /Cs 4 PbBr 6 core/shell NCs with a PLQYs of 87.23% and long-term stability in ambient environments was prepared by room temperature inverse microemulsion method. The excellent stability of the sample was attributed to the protection of Cs 4 PbBr 6 , and higher PLQYs could be owing to the passivation effect of the core/shell structure. To illustrate the distribution of photogenerated carrier in the core/shell structure, a confined excitons model was proposed based on time-resolved PL and temperature dependent PL measurements. Femtosecond time-resolved transient absorption spectra measurements were performed upon different excitation wavelength to unveil the photogenerated carrier dynamics in core/shell NCs. Upon 300 nm excitation, a carrier transfer process with the time of 3.18 ps from shell to core layer was observed. Furthermore, both two- and three-photon absorption PL was discovered in core/shell NCs, further verifying the carrier transfer process. [Display omitted] • Fabrication of strongly luminescent and highly stable CsPbBr 3 /Cs 4 PbBr 6 core/shell NCs. • A confined excitons model proposed for illustrating the higher PLQY in core/shell NCs. • A carrier transfer process from shell to core layer was observed in core/shell NCs. • Multi-photon absorption PL was observed further verifying the carrier transfer process. [ABSTRACT FROM AUTHOR]

Argon dielectric barrier discharge driven by the dual frequency at atmospheric pressure has been investigated by a 1D fluid model. Temporal evolutions of voltage and charge density on dielectric surface, fluxes of electrons and ions on the surface, the spatiotemporal distribution of electron generation rate, and the spatial distribution of electron density are studied with various low-frequency (LF) voltages. Minimum sustained discharge amplitude of high frequency (HF) voltage and spatiotemporal mean electron density over one LF period varying with sheath voltage (α → γ) are also discussed. Results show that in α mode, the electron flux on the dielectric surface decreases significantly when the LF voltage amplitude is lower while the ion flux is less affected. The positive charge density on the surface increases, causing the surface voltage waveform to shift upward. When the LF voltage amplitude is 40 V and that of HF voltage is 87 V, the positive and negative values of voltage amplitude of dielectric surface are 182 and 32 V. As the LF voltage amplitude increases further, the sheath formation time is significantly delayed and the discharge terminates, and the rate of electron generation decreases significantly. The discharge is extinguished when the amplitude of LF voltage is 68 V while it regains when the amplitude reaches up to 750 V. In γ mode, when the amplitude of HF voltage reaches or exceeds its minimum sustained discharge value, the generation and distribution of electrons are almost unaffected by the amplitude of LF voltage. [ABSTRACT FROM AUTHOR]