Large area uniform femtosecond-laser-induced periodic surface structures fabricated on heated LiNbO3:Fe

The influence of laser fluences and scanning speeds on the morphologies of laser-induced periodic surface structures(LIPSS) on heated LiNbO3:Fe(1000○C) surfaces was investigated under femtosecond(fs) laser scanning irradiation. Laser fluence of 8.5 kJ/m2 and scanning speed of 1 mm/s were found to be optimum process parameters, and large-area fs-LIPSS on LiNbO3:Fe with an area of 8 mm×8 mm were fabricated with these parameters. The wettability of laser-textured LiNbO3:Fe changed to be hydrophilic, and the absorptance was improved substantially in the spectral range of 400-2000 nm. This technique is efficient, and environmentally friendly, which will attract tremendous interest in nano-photoelectron and nano-mechanics.

Femtosecond lasers for eye surgery applications: historical overview and modern low pulse energy concepts

This review provides an overview of the historical development and modern applications of femtosecond (fs) lasers in ophthalmology, with a focus on the optical concepts involved. fs-Laser technology is unique because it allows very precise cutting inside the eye through optically transparent tissue, without a need for any mechanical openings. fs-Lasers were historically first used for refractive cornea surgery, later also for therapeutic cornea procedures and lens surgery. Further new areas of ophthalmic application are under development. The latest laser system concept is low pulse energy and high pulse frequency: by using larger numerical aperture focusing optics, the pulse energy required for optical breakdown decreases, and athermal tissue cutting with minimal side effects is enabled.

Phase-Type Fresnel Zone Plate with Multi-Wavelength Imaging Embedded in Fluoroaluminate Glass Fabricated via Ultraviolet Femtosecond Laser Lithography

Herein, we report a novel optical glass material, fluoroaluminate (AlF3) glass, with excellent optical transmittance from ultraviolet to infrared wavelength ranges, which provides more options for application in optical devices. Based on its performance, the phase-type Fresnel zone plate (FZP) by ultraviolet femtosecond (fs) laser-inscribed lithography is achieved, which induces the refractive index change by fs-laser tailoring. The realization of ultraviolet fs-laser fabrication inside glass can benefit from the excellent optical performance of the AlF3 glass. Compared with traditional surface-etching micro-optical elements, the phase-type FZP based on AlF3 glass exhibits a clear and well-defined geometry and presents perfect environmental suitability without surface roughness problems. Additionally, optical focusing and multi-wavelength imaging can be easily obtained. Phase-type FZP embedded in AlF3 glass has great potential applications in the imaging and focusing in glass-integrated photonics, especially for the ultraviolet wavelength range.

Competing processes in generation of the third optical harmonic in air under femtosecond infrared repetitively pulsed excitation

Parametric interaction of electromagnetic and gravitational waves with the radiation generation at the third harmonic wavelength is one of the ways to detect gravitational interaction in a material medium. To implement the effect in question, superstrong fields must be used, but in this case competing nonlinear processes arise, leading to the generation of the third harmonic as a result of laser radiation filamentation. This paper investigates the characteristics of the radiation recorded for femtosecond (250 fs) laser pulses with a wavelength of λ = 1032 nm focused in air. The threshold pump power made it possible to observe the formation of a filament with concomitant generation of narrow-band radiation at the focus of the lens at the third harmonic wavelength λ = 344 nm. The research presents spectral and spatial dependences of ultraviolet radiation (λ = 344 nm) at pumping power of infrared radiation (λ = 1032 nm) of 500 mW. Energy dependences of the third harmonic generation efficiency in the power range from 150 to 1750 mW are obtained.

Thermally Resilient Planar Waveguides in Novel nc-YSZ Transparent Ceramic by fs Laser Pulses

We report on thermally resilient planar waveguides fabricated on nc-YSZ by direct fs-laser inscription in transparent nc-yttria stabilized zirconia (nc-YSZ) polycrystalline ceramic. The waveguides consisted of rectangular sections (4.5 × 2 mm2) on the surface of the sample. Optical characterization at 633 and 810 nm was performed. We estimate a laser-induced refractive index contrast of 10–4. Post-waveguide-fabrication thermal annealing treatments at 750°C for 24 h were carried out to test the resilience of the waveguides and to further reduce the waveguide losses. Both micro-Raman spectroscopy and XPS characterization revealed unmodified lattice and steady chemical features, which are consistent with the waveguide thermal resilience. Our results suggest a promising potential use of nc-YSZ in harsh and high temperature demanding photonic environments.

Laser-ablative synthesis of stable size-tunable Bi nanoparticles and their functionalization for radiotherapy applications

Nanoformulations of high-Z elements can improve therapeutic outcome in radiotherapy-based treatment of tumors, but current nanomedicine implementations in radiotherapy still need biocompatible, non-toxic nano-agents exhibiting low polydispersity and high colloidal stability. Here, we elaborate methods of femtosecond (fs) laser ablation in water and organic solvents to fabricate stable aqueous colloidal solutions of ultrapure elemental Bi nanoparticles (NPs) and characterize them. We show that fs laser ablation of Bi target leads to the formation of spherical elemental Bi NPs having 25 nm mean size and wide size-dispersion. NPs prepared in water undergo fast conversion into 400-500 nm flake-like nanosheets, while NPs prepared in acetone demonstrate a high colloidal stability. We then employ methods of fs laser fragmentation to control mean size and size dispersion of Bi NPs. Stable aqueous solution of Bi NPs suitable for biomedical applications can be obtained by coating with Pluronic® F-127. We finally show that surface modification of Bi NPs increases its colloidal stability in phosphate buffer saline (PBS) solution by more than 6 fold. Exempt of any toxic synthetic by-products, laser-ablated Bi NPs present a novel appealing nanoplatform for image-guided combination photo- and radiotherapy.

Nanoscale-Precision Removal of Copper in Integrated Circuits Based on a Hybrid Process of Plasma Oxidation and Femtosecond Laser Ablation

Copper (Cu) is the main interconnect conductor for integrated circuits (IC), and its processing quality is very important to device performance. Herein, a hybrid process of plasma oxidation and femtosecond laser (fs-laser) ablation was proposed for the nanoscale precision removal of Cu in integrated circuits. In this hybrid process, the surface layer of Cu was oxidized to the copper oxide by plasma oxidation, and then the fs-laser with a laser fluence lower than the Cu ablation threshold was used to remove the copper oxide without damaging the underlying Cu. Theoretically, the surface temperature evolutions of Cu and copper oxide under the femtosecond laser were studied by the two-temperature model, and it was revealed that the ablation threshold of copper oxide is much lower than that of Cu. The experimental results showed that the ablation threshold of copper oxide is lower than that of Cu, which is consistent with the theoretical analysis. Using the hybrid process, a surface roughness of 3 nm and a removal accuracy of 4 nm were obtained in the process of Cu film processing, which were better than those obtained by fs-laser ablation. This demonstrated that the hybrid process has good application potential in the field of copper micromachining.

Miniature Fabry-Perot Cavity Based on Fiber Bragg Gratings Fabricated by Fs Laser Micromachining Technique

Fabry-Perot cavity (FPC) based on Fiber Bragg gratings (FBGs) is an excellent candidate for fiber sensing and high-precision measurement. The advancement of the femtosecond laser micromachining technique provides more choices for the fabrication of FBGs-based FPCs. In this paper, we fabricate miniature FBGs-based FPCs, using the femtosecond laser line-by-line scanning writing technique for the first time. By this method, the FBGs can be limited to a specific area in the fiber core region. The grating length, position, and the distance between two successive FBGs can be conveniently controlled to achieve the desired transmission spectrum. For future applications in sensing, the temperature and strain responses of the fabricated FBGs-based FPCs were studied experimentally. This work provides a meaningful guidance for the fabrication and application of miniature FPCs based on FBGs.