Space-selective precipitation of ZnO crystals in glass by using high repetition rate femtosecond laser irradiation

Mid-infrared ridge waveguides fabricated in CaF2 crystal by the technique of O5+ ion irradiation

The fabrication of ridge waveguides in calcium fluoride (CaF₂) crystal working at the mid-infrared wavelength was studied. First, the planar waveguide was fabricated by using O⁵⁺ ion irradiation, and then the ridge waveguide structure was manufactured by precise diamond blade dicing. The propagation loss was measured by end-face coupling arrangement, and then annealing treatment was implemented to optimize the waveguide performance, and the propagation loss was finally reduced to 0.5 dB/cm. We measured the Raman spectra of the waveguide and substrate to observe the damage to the material lattice caused by O⁵⁺ ion irradiation technology.

A strategy for fabrication of controllable 3D pattern containing clusters and nanoparticles inside a solid material

Directly controlling the growth process of clusters and nanoparticles is an effective way to tune their specific properties, which has been considered as a significant issue lying at the heart of nanotechnology. For technological applications, great strides have been made in the assembly of clusters and nanoparticles. However, controllable synthesis of clusters and nanoparticles inside a bulk solid-state medium remains a tremendous challenge, which is important for integrated devices. Here we report a strategy for space-selective control of elemental tellurium (Te) precipitation as clusters or nanoparticles in glass by femtosecond (fs) laser irradiation. After irradiation by a 1 kHz fs laser at 800 nm, Te₂ clusters, which emit near-infrared (NIR) light, are observed at the focal point of the laser beam inside the glass sample. By shifting the repetition rate to 250 kHz, a temperature field forms around the focal area that facilitates transformation of Te clusters into nanoparticles. Raman mapping shows that the clusters are localized in the center of the laser-induced microstructure, while the nanoparticles exhibit an annular distribution. The possible mechanisms of generation and distribution of different species are discussed. We have also demonstrated optical data storage and embedded micro-grating by using this technique.

Saturable absorber: transparent glass-ceramics based on a mixture of Co:β-Zn2SiO4 and Co:ZnO nanocrystals

We report on the development of novel saturable absorbers for erbium lasers based on transparent glass-ceramics (GCs) containing a mixture of cobalt-doped β-willemite, Co²⁺:β-Zn₂SiO₄, and zinc oxide, Co²⁺:ZnO, nanosized (10-14 nm) crystals. The structure of the parent glass and GCs is studied by x-ray diffraction, differential scanning calorimetry, transmission electron microscopy, and Raman spectroscopy. Variations of absorption spectra with heat-treatment reveal that Co²⁺ ions from the parent glass enter the crystals of ZnO and β-willemite. GCs are characterized by a broad absorption band due to the A₂4(F4)→T₁4(F4) transition of Co²⁺ ions in tetrahedral sites spanning up to ∼1.74  μm, relatively low saturation fluence, F_S=0.75  J/cm² at 1.54 μm, short recovery time, τ=830  ns, and high laser damage threshold, ∼14  J/cm². By using the developed GCs in a diode-side-pumped Er, Yb:glass laser, 0.77 mJ/45 ns pulses are generated.

Gold-film coating assisted femtosecond laser fabrication of large-area, uniform periodic surface structures

A simple, repeatable approach is proposed to fabricate large-area, uniform periodic surface structures by a femtosecond laser. 20 nm gold films are coated on semiconductor surfaces on which large-area, uniform structures are fabricated. In the case study of silicon, cross-links and broken structures of laser induced periodic surface structures (LIPSSs) are significantly reduced on Au-coated silicon. The good consistency between the scanning lines facilitates the formation of large-area, uniform LIPSSs. The diffusion of hot electrons in the Au films increases the interfacial carrier densities, which significantly enhances interfacial electron-phonon coupling. High and uniform electron density suppresses the influence of defects on the silicon and further makes the coupling field more uniform and thus reduces the impact of laser energy fluctuations, which homogenizes and stabilizes large-area LIPSSs.