In the Heart of Femtosecond Laser Induced Nanogratings: From Porous Nanoplanes to Form Birefringence

It is demonstrated that the form birefringence related to the so-called nanogratings is quantitatively correlated to the porosity-filling factor of these nanostructures. We reveal that matters surrounding the nanopores exhibit significant refractive index decrease which is likely due to the fictive temperature increase and/or the presence of a significant amount of interstitial O2. The control of the porosity was achieved by adjusting the laser pulse energy and the number of pulses/micron i.e. the overlapping rate. Applications can be numerous in fast material processing by the production of nanoporous matter, and photonics by changing the optical properties.

Regular uniform large-area subwavelength nanogratings fabricated by the interference of two femtosecond laser beams via cylindrical lens

Inhomogeneity and low efficiency are two important factors that hinder the wide application of laser-induced periodic surface structures. Two-beam interference is commonly used to fabricate gratings with interference periods. This study reports regular and uniform periodic ripples fabricated efficiently by the interference of two femtosecond laser beams via a cylindrical lens. The interference period is adjusted to be an integer multiple of the wavelength of a surface plasmon polariton. Regular and uniform subwavelength nanogratings(RUSNGs)on a silicon wafer of a diameter of 100 mm are fabricated with a scanning velocity of 6–9 mm/s. Bright and pure colors(including purple, blue, and red) are demonstrated on different patterns covered with RUSNGs.

Exciton polaritons based on planar dielectric Si asymmetric nanogratings coupled with J-aggregated dyes film

Optical cavity polaritons,originated from strong coupling between the excitons in materials and photons in the confined cavities field,have recently emerged as their applications in the high-speed lowpower polaritons devices,low-threshold lasing and so on.However,the traditional exciton polaritons based on metal plasmonic structures or Fabry-Perot cavities suffer from the disadvantages of large intrinsic losses or hard to integrate and nanofabricate.This greatly limits the applications of exciton poalritons.Thus,here we implement a compact low-loss dielectric photonic–organic nanostructure by placing a 2-nm-thick PVA doped with TDBC film on top of a planar Si asymmetric nanogratings to reveal the exciton polaritons modes.We find a distinct anti-crossing dispersion behavior appears with a 117.16 meV Rabi splitting when varying the period of Si nanogratings.Polaritons dispersion and mode anti-crossing behaviors are also observed when considering the independence of the height of Si,width of Si nanowire B,and distance between the two Si nanowires in one period.This work offers an opportunity to realize low-loss novel polaritons applications.

Single femtosecond laser beam induced nanogratings in transparentmedia - Mechanisms and applications

Single femtosecond laser beam induced nanograting structure in transparent media has attracted extensive attention in many fields of science and technology in the past decades.Considering the excellent physicochemical properties and promising applications,it will continue to be a hot topic in the field of laser-matter interaction in the future.Over the recent ten years,both fundamental research and practical application have gained tremendous advances.We have witnessed the finding of novel fresh phenomena,imaginative physical models and promising technologies related to femtosecond laser induced nanogratings in transparent materials.However,despite those achievements,numerous issues related to mechanism,material dependence and process are still far from completely solved.This review will focus on recent research progress including basic properties,theory models,control methods and potential applications.Achievements in recent five years are discussed in detail and several core issues are specially commented.The future developing trend is also prospected.©2019 The Chinese Ceramic Society.

A high figure of merit localized surface plasmon sensor based on a gold nanograting on the top of a gold planar film

We investigate the sensitivity and figure of merit （FOM） of a localized surface plasmon （LSP） sensor with gold nanograting on the top of planar metallic film. The sensitivity of the localized surface plasmon sensor is 317 nm/RIU, and the FOM is predicted to be above 8, which is very high for a localized surface plasmon sensor. By employing the rigorous coupled-wave analysis （RCWA） method, we analyze the distribution of the magnetic field and find that the sensing property of our proposed system is attributed to the interactions between the localized surface plasmon around the gold nanostrips and the surface plasmon polarition on the surface of the gold planar metallic film. These findings are important for developing high FOM localized surface plasmon sensors.

Femtosecond pulse laser-induced self-organized nanostructures on the surface of ZnO crystal

This paper reports self-organized nanostructures observed on the surface of ZnO crystal after irradiation by a focused beam of a femtosecond Ti：sapphire laser with a repetition rate of 250kHz. For a linearly polarized femtosecond laser, the periodic nanograting structure on the ablation crater surface was promoted. The period of self-organization structures is about 180 nm. The grating orientation is adjusted by the laser polarization direction. A long range Bragglike grating is formed by moving the sample at a speed of 10μm/s. For a circularly polarized laser beam, uniform spherical nanoparticles were formed as a result of Coulomb explosion during the interaction of near-infrared laser with ZnO crystal.

Enhancing light absorption for organic solar cells using front ITO nanograting and back ultrathin Al layer

To address the discrepancy between carrier collection and light absorption of organic solar cells caused by the limited carrier mobility and optical absorption coefficient for the normally employed organic photoactive layers,a light management structure composed of a front indium tin oxide(ITO)nanograting and ultrathin Al layer inserted in between the photoactive layer and the electron transport layer(ETL)is introduced.Owing to the antireflection and light scattering induced by the ITO nanograting and the suppression of light absorption in the ETL by the inserted Al layer,the light absorption of the photoactive layer is significantly enhanced in a spectral range from 400 nm to 650 nm that also covers the main energy region of solar irradiation for the normally employed active materials such as the P3HT:PC_(61)BM blend.The simulation results indicate that comparing with the control device with a planar configuration of ITO/PEDOT:PSS/P3HT:PC_(61)BM(80-nm thick)/ZnO/Al,the short-circuit current density and power conversion efficiency of the optimized light management structure can be improved by 32.86%and 34.46%.Moreover,good omnidirectional light management is observed for the proposed device structure.Owing to the fact that the light management structure possesses the simple structure and excellent performance,the exploration of such a structure can be believed to be significant in fabricating the thin film-based optoelectronic devices.

Development of the Biopolymeric Optical Planar Waveguide with Nanopattern

This paper demonstrates for fabricating the biopolymric optical planar waveguide. Gelatin and chitosan were mixed with ratio of 9 to 1 and stirred at 70°C with 1300 rpm. The blended biopolymer was spincoated on silicon substrate with 500 rpm and then dried in the oven at 50°C. The refractive indices of the prepared biopolymer clad and core layers of the waveguide were measured by the ellipsometry. The measured refractive indices of the two layers were obtained to be 1.516 and 1.52, respectively. The nanograting was successfully imprinted on surface of the biopolymeric waveguide.

Decoding the future:opportunities and challenges in next-generation optical data storage[Invited]

The ongoing quest for higher data storage density has led to a plethora of innovations in the field of optical data storage.This review paper provides a comprehensive overview of recent advancements in next-generation optical data storage,offering insights into various technological roadmaps.We pay particular attention to multidimensional and superresolution approaches,each of which uniquely addresses the challenge of dense storage.The multidimensional approach exploits multiple parameters of light,allowing for the storage of multiple bits of information within a single voxel while still adhering to diffraction limitation.Alternatively,superresolution approaches leverage the photoexcitation and photoinhibition properties of materials to create diffraction-unlimited data voxels.We conclude by summarizing the immense opportunities these approaches present,while also outlining the formidable challenges they face in the transition to industrial applications.

Demonstration of a ZnO-Nanowire-Based Nanograting Temperature Sensor

In this study,we experimentally demonstrate a miniature fiber thermometer based on tip-integrated ZnO-nanowire-nanograting.The sensor has a diameter less than 1μm and the length of the Bragg grating is sub-10μm.The ZnO-nanowire-nanograting is sensitive to the environmental temperature change.Thus,the intensity of the light whose wavelength is in the rising or falling region of the nanograting spectrum will vary with the shift in wavelength due to change in temperature.Taking one wavelength(655 nm)in the rise linear region of the nanograting spectrum,a sensitivity of 0.066nW/℃in the air is achieved experimentally.The proposed temperature sensor has the superiorities of compactness,stableness,and easy fabrication compared to regular fiber grating sensors,offering great potential for detecting inside minimal volume environments.

Label-free fiber nanograting sensor for real-time in situ early monitoring of cellular apoptosis

The achievement of functional nanomodules for subcellular label-free measurement has long been pursued in order to fully understand cellular functions.Here,a compact label-free nanosensor based on a fiber taper and zinc oxide nanogratings is designed and applied for the early monitoring of apoptosis in individual living cells.Because of its nanoscale dimensions,mechanical flexibility,and minimal cytotoxicity to cells,the sensing module can be loaded in cells for long term in situ tracking with high sensitivity.A gradual increase in the nuclear refractive index during the apoptosis process is observed,revealing the increase in molecular density and the decrease in cell volume.The strategy used in our study not only contributes to the understanding of internal environmental variations during cellular apoptosis but also provides a new platform for nonfluorescent fiber devices for investigation of cellular events and understanding fundamental cell biochemical engineering.

Scanning and Splicing Atom Lithography for Self-traceable Nanograting Fabrication

Atom lithography is a unique method to fabricate self-traceable pitch standards and angle standards,but extending its structure area to millimeter-level for application is challenging.In this paper,on the one hand,we put forward a new approach to fabricate a full-covered self-traceable Cr nanograting by inserting and scanning a Dove prism in the Gaussian beam direction of atom lithography.On the other hand,we extend the structure area along the standing-wave direction by splicing two-step atom deposition.Both nanostructures manufactured via scanning atom lithography and splicing atom lithography demonstrate good pitch accuracy,parallelism,continuity,and homogeneity,which opens a new way to fabricate centimeter-level full-covered self-traceable nanograting and lays the basis for the application of square ruler and optical encoders at the nanoscale.

Design and fabrication of an embedded wire-grid nanograting

An embedded wire-grid nanograting was designed and fabricated for using as a broadband polarizing beam splitter to reflect s-polarized light and transmit p-polarized light. A protected cladding layer of the same material as the grating＇s was deposited on the ridge, whereas the wire-grid is deposited in the grating trenches, which makes it more firm during application. High polarization extinction ratios of above 40 and 20 dB for transmission and reflection, respectively, with a broad wavelength range for the whole optical communication bandwidth （850 -1700 nm） and a wide angular tolerance （〉 ±20 °） are obtained by optimization of the designed structures, and the grating period is 200 nm.