In the conventional femtosecond laser direct writing with a Gaussian beam, the focus is an ellipsoid with the long axis along the beam propagation direction, resulting in the ellipsoidal fabricated dot. Due to the simple shape of the dot, complex three-dimensional (3D) nano/microstructures should be written dot by dot by the focus scanning, which is usually time-consuming. Therefore, a rapid nano/microfabrication technique is becoming highly desired to achieve arbitrary 3D nano/microstructures. By 2D phase modulation of the Gaussian beam, multi-focuses were generated for the direct writing of several same nano/microstructures simultaneously to save fabrication time, and donut and other 2D intensity distributions were produced for the single exposure fabrication of 2D microstructures. Here, we demonstrate the single-exposure two-photon polymerization of a 3D microstructure via the 3D focal field engineering by using the 2D phase-only spatial light modulation. With a single exposure, a whole 3D microstructure like a double-helix is polymerized simultaneously, whose configuration is controlled by the designed 3D focal intensity distribution. In addition, a longitudinal circular intensity distribution is generated for the multi-photon inscription of a depressed cladding waveguide inside glass with single scan transverse writing.
This paper reports ex-situ preparation of conductive polymer/single-walled carbon nanotubes (SWNTs) nanocomposites by adding high conductive SWNTs to the polymer matrix. Sonication methods were used to disperse the SWNTs in the polymer. The conductivity of the nanocomposites is tuned by increasing the concentration of SWNTs. Furthermore, we present two-photon polymerization (2PP) method to fabricate structures on the basis of conductive photosensitive composites. The conductive structures were successfully generated by means of 2PP effect induced by a femtosecond laser.
Fano resonances, sometimes behaving like electromagnetic induced transparency (EIT)-like resonances in whisperinggallery-
mode (WGM) microcavities are attracting much attention due to the important applications in high-sensitivity
biosensing, optical switch, and slow light. In this paper, Fano resonances in several WGM systems are reported,
including in a single WGM photonic microcavity and in coupled WGM microcavities. Specifically, in a single WGM
microcavity system, Fano or EIT-like resonances in both polydimethylsiloxane (PDMS) coated silica microtoroid and
bare silica microtoroid are experimentally investigated. In coupled microcavity system, we report a theoretical study of
EIT-like resonance in an array of microcavities indirectly coupled through a parallel waveguides system. Finally, we
experimentally investigate the Fano resonance in two microcavities indirectly coupled via a single fiber taper.
We have realized three-dimensional micromachining and microfabrication in transparent materials with femtosecond
laser pulses, including water-assisted drilling by ablation, hologram encoding by microexplosion, waveguide writing by
refractive index increase, and nanoline and nanotip polymerization via two-photon absorption. With the water-assisted
drilling, we showed that not only longitudinal holes in the laser beam propagation direction but also transverse holes
perpendicular to laser beam could be drilled when the sample's rear surface was in contact with water. True three-dimensional
microchannels and microchambers were fabricated. In addition, three-dimensional cutting of glass was
realized with the water assistance. By using tightly focused pulse to induce microexplosion, permanent computer-generated
holograms were directly written inside glass and the stored data were reconstructed by a He-Ne laser beam. A
waveguide array was written inside glass by the laser induced refractive index increase, and coupling between these
waveguides was observed. Nanoline and nanotips with sub-30nm feature-size were fabricated using resin SCR500 by
We present the microfabrication of high refractive index-modulated structures written by line scan inside bulk of fused silica with a femtosecond laser at wavelength of 810 nm. The femtosecond laser beam, with duration between 130 fs and 500 fs at a repetition rate of 1 kHz, was focused through a microscope objective with numerical aperture (NA) of 0.10 or 0.25 into the sample. To fabricate high refractive index-modulated structures in fused silica, we investigated the dependence of refractive index change on laser pulse energy, pulse duration, scan speed, and scanning repetitions. The results showed a "triangle region", with pulse duration of 130 fs to 230 fs and pulse energy of 0.35 μJ to 1.5 μJ, for the fabrication of refractive index modulation structures. The refractive index modulation was increased to 3×10-3 after several scanning passes. Diffractive optical components such as grid, square, circle gratings and Fresnel zone plates have been fabricated by direct writing technique. The structures could be used as diffractive beam splitters, beam shaper and micro-lens.