Advanced Photonics Research最新文献

The characterization of ultrashort laser pulses is presented by using the plasma-induced frequency-resolved optical switching technique, implemented in ambient air. The recently developed method allows for a temporal reconstruction of a pulse at its focal spot by utilizing a moderately intense pump laser pulse for generating a ionization-induced ultrafast defocusing lens. When propagating through the produced plasma lens, the probe beam to characterize experiences an increase of its size in the far field. The spectrum of the defocused probe field, measured as a function of the pump-probe delay, allows for a comprehensive characterization of the temporal and spectral attributes of the pulse. Herein, the ability of this technique, initially designed for use in rare gases, is reported to operate in ambient air conditions with similar performance. The method is remarkably straightforward to implement and requires no additional optical component other than a focusing mirror while delivering laser pulse reconstructions of high reliability.

In recent years, metasurfaces composed of lumped nonlinear circuits have been reported to exhibit the capability of detecting specific electromagnetic waves, even when the waves are of the same frequency, depending on their respective waveforms or, more precisely, their pulse widths. Herein, three types of metasurface absorbers (MSAs) are presented which are composed of a square-patch structure loaded with linear circuit components, including lumped resistors or resistors in parallel with capacitors/inductors, which can mimic the waveform-selective absorption behavior in the terahertz (THz) region. By judiciously selecting suitable values for the linear circuit components, these MSAs can achieve near-perfect absorption of incident continuous waves or longer pulses while exhibiting reduced absorption of short pulses at the same THz frequency. These linear circuit structures can be referred to as pseudo-waveform-selective MSAs because their waveform-selective absorption characteristics are primarily derived from the dispersion behavior of the resonator structures, as opposed to the frequency conversion commonly observed in nonlinear circuits. These outcomes and discoveries introduce an additional degree of freedom for waveform discrimination in the THz frequency range, potentially enabling a broader range of applications, including but not limited to detection, sensing, and wireless communication.

Herein, the propagation of truncated Airyprime pulses in nonlinear optical fibers with anomalous or normal dispersion is studied. Nonlinear self-accelerating pulses generation, which is in sharp contrast to that of Airy pulses, is observed. Accelerating pulses have notable redshifted spectral notch (double peaks) or single blueshifted spectral peak depending on whether the dispersion is anomalous or normal. The emergent nonlinear self-accelerating pulses are very sensitive to the truncated coefficient. The relationship between the characteristics of such accelerating pulses and the truncated coefficient is disclosed and compared in detail. The results not only shed new light on the nonlinear propagation of Airyprime pulses, but also provide a novel method to generate nonlinear self-accelerating pulses as well as enable the realization of very efficient wavelength conversion based on the controlled frequency shift. Based on space–time duality, self-accelerating spatiotemporal nonlinear light bullets can be envisaged from the propagation of spatiotemporal Airyprime wave packets in pure Kerr medium.

Lensless imaging, as a novel computational imaging technique, has attracted great attention due to its simplicity, compactness, and flexibility. This technique analyzes and processes the diffraction of an object to obtain complex amplitude information. However, traditional algorithms such as Gerchberg-Saxton (G–S) algorithm tend to exhibit significant errors in complex amplitude retrieval, particularly for edge information. Additional constraints have to be incorporated on top of amplitude constraints to enhance the accuracy. Recently, deep learning has shown promising results in optical imaging. However, it requires a large amount of training data. To address these issues, a novel approach called dual-input physics-driven network (DPNN) is proposed for lensless imaging. DPNN utilizes two diffractions recorded at different distances as inputs and uses an unsupervised approach that combines physical imaging model to reconstruct object information. DPNN adopts a U-Net 3+ architecture with a loss function of mean absolute error (MAE) to better capture diffraction features. DPNN achieves highly accurate reconstruction without requiring extensive data and being immune to background noise. Based on different diffraction intervals, noise levels, and imaging models, DPNN exhibits superior capabilities in peak signal-to-noise ratio and structural similarity compared with conventional methods, effectively achieving accurate phase or amplitude information reconstruction.

A silicon-based room temperature (RT) continuous wave (CW) operation quantum well (QW) laser emitting at 850 nm is reported in this article. By applying the dislocation filter superlattice, the threading dislocation density of the GaAs pseudosubstrate on Si is reduced to 1.8 × 10⁷ cm⁻². The metal-organic chemical vapor deposition-grown laser structure with GaAs/GaAsP QW and InAlAs active region dislocation blocking layer are fabricated into broad-stripe Fabry–Perot laser diodes. A typical threshold current and threshold current density of 286 mA and 715 Acm⁻² are obtained with 2 mm cavity length and 20 um stripe width samples. A 94.2 mW single-facet output power lasing around 854 nm and a 0.314 WA⁻¹ slope efficiency is measured under RT CW operation. After a 10-min aging process, the tested laser can operate stably under continuous operation conditions at RT and the lifetime can be approximated using an exponential fitting curve, indicating a good life reliability of this QW laser.

A metasurface composed of silver nanoflower arrays, which exhibit asymmetrical absorption and surface-enhanced Raman scattering (SERS) due to hybrid plasmonic effects, is reported. The silver nanoflowers are fabricated by oblique deposition of silver on a polymer nanohole array on a glass substrate, forming petal-like semicontinuous thin films on the inner walls of the holes. Depending on the deposition angle, three- or five-petal nanoflowers are obtained. The nanoflower arrays show strong reflection from the air side and broadband and wide-angle absorption from the glass side, as a result of transmission surface plasmon resonance and localized surface plasmon resonance, respectively. The three-petal structure, which absorbs most of the incident light from the glass side, induces a localized enhancement of electric field in the center of each nanohole, providing a high-sensitivity SERS substrate. The SERS performance of the metasurface by direct measurement and near-field simulation is demonstrated.

SiGe-SiO₂-based structures present high interest for their high photosensitivity from visible to short-wavelength infrared. Herein, two postdeposition annealing procedures, that is, rapid thermal annealing (RTA) and rapid-like furnace annealing (FA), are compared. Both RTA and FA are performed at 600 °C for 1 min for SiGe nanocrystals (NCs) formation in SiO₂ matrix in Si/SiO₂/SiGe/SiO₂ structures deposited by magnetron sputtering. The FA imitates RTA resulting in enhanced spectral response. X-ray diffraction, transmission electron microscopy, and Raman spectroscopy are carried out showing Ge-rich SiGe NCs with 11.3 ± 1.2 nm size for RTA and 9.4 ± 0.8 nm for FA. Photocurrent spectra for both structures show several peaks that are annealing dependent. The photocurrent intensity for FA samples is ≈7 times higher than RTA samples while cutoff wavelengths are slightly different, that is, 1365 nm for FA and 1375 nm for RTA. The FA structures show (at −1.5 V) over 4 A W⁻¹ responsivity at 730 nm, 6.4 × 10⁷ Jones detectivity at 735 nm, and 2.2 × 10⁷ Jones at about 1210 nm. FA structures contain small SiGe NCs with incorporated residual strain, while RTA ones are formed of columnar SiGe NCs separated by SiGeO_x amorphous regions and show increased tensile strain in the SiGe.

Thermally activated delayed fluorescence (TADF) emitters potentially can provide organic light-emitting diodes with 100% internal quantum efficiency by harvesting triplet excitons. Generally, TADF emitters are small molecules that are not applicable for solution processability. The addition of tert-butyl groups to the periphery of TADF emitters has proven to improve their solubility in various organic solvents, reduce aggregation-induced quenching, and enhance the photoluminescence quantum yield (PLQY). This article studies the photophysical influence of the tert-butyl group attached to an emitter with a carbazole acceptor and a triazine donor. The resulting t3CzTrz-F is a blue–green TADF emitter, in which the addition of a tert-butyl group increases the rate of reverse intersystem crossing (rISC), while simultaneously decreasing the nonradiative decay rate substantially. In addition, dilution of t3CzTrz-F in a host matrix in film results in an enhanced PLQY, which is associated with a decrease in the nonradiative decay constant, while there is no change in the rISC rate. Through a solid-state NMR study, the change in rISC and nonradiative rate upon tert-butylation by enlarged intermolecular spacing and reduced vibrational and rotational freedom is rationalized, resulting in improved photophysical performance.

Tuning the color of Au has been a longstanding problem in the luxury industry. Conventional approaches, involving Au alloying, compromise purity and demand distinct alloy compositions for each hue. This study demonstrates a lithography-free method for generating structural colors on a gold surface by adjusting the thickness of titanium dioxide, a high-index dielectric. While color tuneability is limited if TiO₂ is coated directly on the Au surface, a range of vivid colors can be generated if a 50−100 nm thick AuAl₂ underlayer is used. AuAl₂, an accepted alloy for purple gold, broadens the color gamut, providing a protective coating without diminishing gold purity. The reflectance dip of the bilayer structure exhibits a significant red shift with increasing thickness of the TiO₂ layer, allowing diverse colors by TiO₂ insulator tuning. Simulation studies corroborate experimental results, affirming that coating a TiO₂ layer on the AuAl₂ underlayer yields a wide range of colors. This method, based on thin-film interference, shows promise for widespread use, offering a broad spectrum of structural colors in an industry striving for diverse Au color representation.

Recent reports of upconversion and white light emission from graphitic particles warrant an explanation of the physics behind the process. A model is offered, wherein the upconversion is facilitated by photoinduced electronic structure modification allowing for multiphoton processes. As per the prediction of the model, it is experimentally shown that graphite upconverts infrared light centered around 1.31 μm (0.95 eV) to broadband white light centered around 0.85 μm (1.46 eV). The results suggest that upconversion from shortwave infrared (≈3 μm, 0.45 eV) to visible region may be possible. The experiments show that the population dynamics of the electronic states involved in this upconversion process occur in the timescale of milliseconds.