Fangfang Luo

Redistribution of elements in glass induced by a high-repetition-rate femtosecond laser.

The redistribution of elements in a multicomponent oxyfluoride glass is induced by a 250 kHz femtosecond laser. Elemental distribution in the cross section of the modified region along the laser propagation axis is analyzed by an electron microprobe analyzer. The results indicate that the relative concentrations of network formers of the glass are higher in the central area of the modified region and lower in the periphery of the modified region compared with the unirradiated areas. However, the relative concentrations of network modifiers are as opposed to that of network formers. Fluorescence spectra confirm that the distribution of fluorescence intensity of Yb(3+) in the modified region is consistent with that of its concentration. The effects of spherical aberration of the incident beam on the elemental redistribution are also discussed.

Femtosecond laser-induced inverted microstructures inside glasses by tuning refractive index of objective’s immersion liquid

We report the formation of inverted microstructures inside glasses after femtosecond laser irradiation by tuning the refractive index contrast between the immersion liquid and the glass sample. By using water as well as 1-bromonaphthalene as immersion liquids, microstructures with similar shape but opposite directions are induced after femtosecond laser irradiation. Interestingly, the elemental distribution in the induced structures is also inverted. The simulation of laser intensity distribution along the laser propagation direction indicates that the interfacial spherical aberration effect is responsible for the inversion of microstructures and elemental distribution.

Space-selective precipitation of Ge crystalline patterns in glasses by femtosecond laser irradiation

Crystalline Ge was induced space selectively inside a borosilicate glass by 800 nm, 250 kHz femtosecond laser irradiation. Micro-Raman spectra and x-ray diffraction analysis confirmed that the laser-induced crystals were cubic Ge. A periodic structure consisting of Ge crystalline lines was inscribed in the glass sample by continuously moving the focal point of the laser beam. Large third-order nonlinear optical properties and ultrafast response time were observed from the crystallization region owing to highly optical nonlinearity of Ge crystals. These results may find some applications in fabrication of functional optical and photonic devices, such as optical circuits.

Nd-doped phosphate glass microstructured optical fiber laser

We experimentally demonstrated a single-mode laser at 1056 nm with Nd-doped phosphate glass microstructured optical fiber (MOF), which was fabricated with conventional stack-and-draw method. The laser action was observed from a Fabry-Perot cavity formed by placing two dichroic mirrors of ∼100 and 85% reflectivity, to the two end facets of MOF. Pumped by CW laser diodes (LDs) at 808 nm, the MOF laser yielded a maximum output power of 8.5 mW and a slope efficiency of 2%.

Different refractive index change behavior in borosilicate glasses induced by 1 kHz and 250 kHz femtosecond lasers

We report on different refractive index change (RIC) behavior in borosilicate glasses induced by focused 1 kHz and 250 kHz femtosecond (fs) laser irradiation. The influence of fs laser irradiation condition and annealing temperature on RIC was examined. Absorption, electron spin resonance and Raman spectra, and transmission electron microscope were used to clarify the mechanisms of the RIC. Smaller RIC (up to 10−4) was observed after 1 kHz fs laser irradiation, while larger RIC (up to 10−1) was detected after 250 kHz fs laser irradiation, which were ascribed to the formation of color centers and precipitation of nanocrystals, respectively. The result highlights that the mechanisms of RIC induced by fs laser can be very different depending on the irradiation conditions.

Mechanism of femtosecond laser inducing inverted microstructures by employing different types of objective lens

In this paper, an interesting inverted structure, fabricated by focusing femtosecond laser pulses through two different objective lenses (an oil-immersion objective lens and a dry objective lens), is reviewed. According to the interface spherical aberration theory, reasonable models are built and the simulated laser fluence in the focal region is given. The distribution of laser fluence agrees with the structural characteristics of the experimentally obtained void array. We propose that the monotonic tendency that the aberration function changes with the azimuth angle determines the final ?growth? direction of the void array.

Shape- and size-controllable microstructure on glass surface induced by femtosecond laser irradiation

Controllable microstructures are formed on a glass surface after irradiation of a focused 800 nm, 250 KHz femtosecond laser beam. Field-emission scanning electron microscope and 3D measuring laser microscope images reveal that the induced structures are circular and linear protuberances and can be controlled from 10 microm to hundreds of micrometers in width, and from 1 microm to tens of micrometers in height. The protuberance structure is proposed to be formed as a consequence of the laser-induced high temperature and pressure owing to linear and nonlinear absorption near the laser focal point, and low softening and melting temperature of the glass sample.

Recent Research Progress on Femtosecond Laser Induced Microstructures in Glasses

The availability of laser pulses with femtosecond duration allows materials to be subjected to higher light intensity than ever before, opening the door to the study of laser/material interactions in a new regime. Various microstructures induced by femtosecond laser have been reported, such as color centers, voids, and refractive index change. In this article, we review our recent research findings on the femtosecond laser induced microstructures in glasses, which are not only helpful for understanding the interaction process between the ultrafast laser and the glassy materials, but also valuable for the fabrication of integrated optical elements.