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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]

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-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 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]

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]

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]

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]

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 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]

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]

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]

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]

Microchannel plates (MCPs) are widely utilized as key device components in various photomultipliers; however, the performance of MCPs cannot be further improved by traditional processing. Atomic layer deposition (ALD) is a promising route to prepare a composite conductive layer and secondary electron emission (SEE) layer structure on the inner wall of the MCP. Moreover, ZnO is an essential component of a composite conductive layer, which is located at the bottom of the SEE layer and significantly influences the SEE coefficient, which, in turn, affects the gain performance of MCPs. Herein, ALD is used to deposit different thicknesses of ZnO films (1–50 nm) on an Si substrate, resulting in an ZnO/Si double-layer film structure. The relationship between the SEE coefficient and the primary electron energy of ZnO films with different thicknesses was established. The maximum secondary electron yield value of 2.04 is achieved at a film thickness of 30 nm. Moreover, Dionne's SEE model and theory of semiconductors are used to simulate and verify the experimental results. These results provide useful guidelines for the development of ALD-MCPs. [ABSTRACT FROM AUTHOR]

An ultrafast optical Kerr gate of Bi2O3–B2O3–SiO2 oxide glass (BI glass) was used in an ultrafast time-resolved imaging system for shape measurement of objects. The experimental results showed that the longitudinal resolution of the imaging system using the ultrafast optical Kerr gate was less than 20 μm and the measurements of object shape using the ultrafast optical Kerr gate of BI glass had more advantages compared with that using CS2. [ABSTRACT FROM AUTHOR]

All-optical control of the noncentrosymmetry of azodye-doped polymer films was demonstrated by nonresonant dual-frequency coherent excitation. The tensor analysis of the photoinduced noncentrosymmetry was performed by monitoring second harmonic generation (SHG) of the samples. The quadratic dependence of SHG on the film thickness showed that a χ[sup (2)] grating satisfying the phase-matching condition for SHG was optically induced in the polymer films, indicating this nonresonant all-optical poling can be used to tailor the symmetry of bulk samples. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The temperature dependence of optical poling of a side-chain azobenzene–polyimide film with high glass transition temperature was experimentally investigated. With the increase of the sample temperature the light-induced second-harmonic generation increased first, and then decreased as the temperature was near its glass transition temperature. The light-induced second-order nonlinear optical coefficient d[sub 33] for the optimum temperature was determined to be 6.9 pm/V, which was about 2.7 times that obtained at room temperature. Compared with optical poling at room temperature, this thermal-assisted optical poling not only enhanced d[sub 33] of the polyimide film, but also improved the polar order stability of molecules. Optical storage based on optical poling was also demonstrated experimentally. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have developed an ultrafast time-resolved imaging technique for the propagation dynamics of ultrashort laser pulses in transparent media. This method utilizes the optical polarigraphy technique and a chirped supercontinuum as the probe light. The supercontinuum senses the instantaneous birefringence induced by the propagation of an intense pulse, and a polarigraphy image with different color distributions could be obtained. Using this method, we performed a space-time characterization of the filament induced by a femtosecond laser pulse in CS2, indicating that this technique could be used for the single-shot imaging of pulse propagation dynamics. [ABSTRACT FROM AUTHOR]

We demonstrated the controllable acquisition of optical gated spectra from a chirped supercontinuum (SC) pulse based on ultrafast transient lens (TrL) effect. Comparing with CS2, the gated spectra had much narrower spectral bandwidths using tellurite glass (Te glass) as the nonlinear medium due to its ultrafast nonlinear response. Experimental results showed that the chirp structure of the SC pulse measured by TrL method was quite accordant with that measured by femtosecond optical Kerr gate method. [ABSTRACT FROM AUTHOR]

High-aspect-ratio grooves have been fabricated in silicon by a single pass of femtosecond laser pulses in water and ambient air. Scanning electron microscopy and energy dispersive x-ray spectroscopy were employed to image for the morphology of the photoinduced grooves and analyze the chemical composition in the surrounding of the grooves. It was observed that the sidewall of the grooves fabricated in water was much smoother than that in ambient air, and there were homogeneous nano-scale protrusions on the sidewall of the grooves fabricated in water. Meanwhile, oxygen species, which was incorporated into the grooves fabricated in air, was not observed in those in water. [ABSTRACT FROM AUTHOR]

Secondary electron emission (SEE) plays a crucial role in the gain performance of devices, such as electron multipliers and microchannel plates (MCPs). Gain performance could be improved by increasing the secondary electron yield (SEY) of device surface. Al2O3 coating is an ideal material for SEE, benefiting from its high SEY. The Al2O3 coating deposited on inner device walls by atomic layer deposition (ALD) can improve the gain performance of devices. In this study, the SEE characteristics of Al2O3 coatings were investigated experimentally. A series of Al2O3 coatings with thicknesses of 1-30 nm were prepared on Si substrate through the ALD method. Then, the SEY of the coatings were quantified as a function of primary electron energy in the range of 100∼1500 eV. Furthermore, an equation describing the true SEY as a function of thickness was established by applying theory of Dionne's SEE model. This work presents potential approach for controlling the SEE level of Al2O3 coatings through thickness adjustment and is crucial for comprehending the SEE of composite materials. [ABSTRACT FROM AUTHOR]

Microlens arrays on curvilinear surfaces are highly desirable for wide field-of-view imaging and sensing systems. However, it is technically challenging to fabricate these structures. This letter reports a simple method to machine close-packed microlenses on curvilinear surfaces as inspired by the insect eyes, which involves a femtosecond-laser-based microfabrication and a thermomechanical bending process. Over 7600 hexagonal-shaped microlenses with a diameter of 50 μm were fabricated on a hemispherical poly (methyl methacrylate) shell, which is similar to the compound eyes of insects. The optical performances of the microlens array were demonstrated by the abilities of high-resolution imaging and large view-angle focusing. [ABSTRACT FROM AUTHOR]

Here, the authors demonstrate a unique technique to form dense dislocations locally inside a single crystal with a rocksalt-type structure using femtosecond laser irradiation for the first time, to our knowledge. Cross-shaped patterns of micrometer size, originating from densely introduced dislocations, are formed around the focal point. The authors controlled three-dimensional propagation of dislocations by adjusting the pulse energy of femtosecond laser and numerical aperture of objective lens. [ABSTRACT FROM AUTHOR]

We report the precipitation and control of metal nanoparticles inside transparent glasses. An Ag[sup +]-doped silicate glass sample was first irradiated by using an 800 nm femtosecond laser at room temperature and then annealed at 550 °C. The area near the focal point of the laser beam became gray after laser irradiation and yellow after further annealing at 550 °C for 10 min. Absorption and electron spin resonance spectra of the glass sample showed that a portion of silver ions near the focused part of the laser beam inside the glass were reduced to silver atoms after the laser irradiation. These silver atoms aggregated to form nanoparticles after further annealing at temperatures above 500 °C. A mechanism is suggested that consists of multiphoton reduction, which is induced by the fundamental light of the laser beam and supercontinuum white light, and diffusion of silver atoms driven by heat energy to form nanoparticles. The observed phenomenon may have promising applications for the fabrication of three-dimensional multicolored images inside a transparent material and for integrative micro-optical switches. [ABSTRACT FROM AUTHOR]

We report the observation of space-selective oxidation of Mn[sup 2+] to Mn[sup 3+] in a transparent and colorless Mn and Fe ions codoped silicate glass at room temperature by using an 800-nm-femtosecond laser. Difference absorption spectrum of the glass after and before the irradiation of the focused infrared femtosecond pulsed laser showed that a portion of Mn[sup 2+] ions near the focused part of the laser beam inside the glass were oxidized to Mn[sup 3+] ions after the laser irradiation. Mn[sup 3+] ions were stable at the temperatures below 300 °C. It is suggested that Mn[sup 2+] ions act as hole trapping centers while Fe[sup 3+] ions as well as active sites in the glass matrix act as electron trapping centers. A promising application was demonstrated for the fabrication of three-dimensional colored image inside a transparent material. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report the observation of memorized polarization-dependent light scattering in a Eu[sup 2+]-doped fluoroaluminate glass sample. Anisotropic light scattering along the plane of the light polarization was observed in the glass sample after the excitation of a focused 800 nm, 150 fs laser beam at a repetition rate of 200 kHz. When we changed the direction of the light polarization and irradiated the same location, we observed an anisotropic light-scattering pattern identical to the original one at the beginning, but then observed a new pattern along the new direction of the light polarization while the original light-scattering pattern disappeared gradually with the passage of time. This observed phenomenon was considered to be due to the light scattering of the polarization-dependent permanent microstructure induced by the polarized ultrashort pulsed laser itself. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]