Artificial nanograting woven by self-assembled nanowires

We report on a new simple route to realize a high resolution nanograting. By adopting an InAlGaAs matrix and strain-compensated technique, we have proved that a uniform self-assembled InAs nanowire array can be fabricated by molecular beam epitaxy (MBE). A nanograting woven by self-assembled semiconductor nanowires shows a conspicuous diffraction feature. The good agreement between the theoretical and experimental values of diffraction peak positions indicates that a uniform nanowire array is a promising nanograting. This simple one-step MBE growth method will open exciting opportunities for the field of clever optics design.

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 250 kHz. 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 Bragg-like grating is formed by moving the sample at a speed of 10 mu m/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.

Coherent linking of periodic nano-ripples on a ZnO crystal surface induced by femtosecond laser pulses

We demonstrate the coherent linking of periodic nano-ripples formed on the surface of ZnO crystals induced by femtosecond laser pulses. By adjusting the distance between two laser scanning zones, the periodic nano-ripples induced by two separated laser writing processes can be coherently linked and the ZnO nanograting with much longer grooves is therefore produced. The length limitation of this kind of nanograting previously set by the laser focus size is thus overcome. The micro-Raman mapping technique is used to evaluate the quality of coherent linking, and the underlying physics is discussed. The demonstrated scheme is promising for producing large-size self-organized nanogratings induced by femtosecond laser pulses.

Formation of nanogratings on the surface of a ZnSe crystal irradiated by femtosecond laser pulses

Two collinear femtosecond laser pulses, one at wavelength of 800 nm and the other at 400 nm (double frequency), simultaneously irradiated the surface of ZnSe crystal, which resulted in regular nanograting with period of 180 nm on the whole ablation area. We attribute the formation of the nanograting to be due to the interference between the surface scattered wave of 800 nm lasers and the 400 nm light. The period of the nanograting Lambda is about lambda/2n, where n is refractive index of the sample, and lambda, the laser wavelength. This mechanism is supported by observation of rotation of the nanograting with the polarization of 400 nm light, and by the dependence of Lambda similar to lambda of the nanoripples on the surface of semiconductors and dielectrics.

Femtosecond pulse laser-induced self-organized nanogratings on the surface of a ZnSe crystal

Periodic nanostructures are observed on the surface of ZnSe after irradiation by a focused beam of a femtosecond Ti:sapphire laser, which are aligned perpendicular to the laser polarization direction. The period of self-organized grating structures is about 160 nm. The phenomenon is interpreted in terms of interference between the incident light field and the surface scattered wave of 800-nm laser pulses. With the laser polarization parallel to the moving direction we produce long-range Bragg-like gratings by slowly moving the crystal under a fixed laser focus. The nanograting orientation is adjusted by laser polarization and the accumulation effect.

Three-dimensional micro- and nano-fabrication in transparent materials by femtosecond laser

Femtosecond pulsed lasers have been widely used for materials microprocessing. Due to their ultrashort pulse width and ultrahigh light intensity, the process is generally characterized by the nonthermal diffusion process. We observed various induced microstructures such as refractive-index-changed structures, color center defects, microvoids and microcracks in transparent materials (e.g., glasses after the femtosecond laser irradiation), and discussed the possible applications of the microstructures in the fabrication of various micro optical devices [e.g., optical waveguides, microgratings, microlenses, fiber attenuators, and three-dimensional (3D) optical memory]. In this paper, we review our recent research developments on single femtosecond-laser-induced nanostructures. We introduce the space-selective valence state manipulation of active ions, precipitation and control of metal nanoparticles and light polarization-dependent permanent nanostructures, and discuss the mechanisms and possible applications of the observed phenomena.