Two-dimensional Surface-relief Gratings Research Articles

Dual Amplified Spontaneous Emission and Lasing from Nanographene Films.

Chemically synthesized zigzag-edged nanographenes (NG) have recently demonstrated great success as the active laser units in solution-processed organic distributed feedback (DFB) lasers. Here, we report the first observation of dual amplified spontaneous emission (ASE) from a large-size NG derivative (with 12 benzenoid rings) dispersed in a polystyrene film. ASE is observed simultaneously at the 685 and 739 nm wavelengths, which correspond to different transitions of the photoluminescence spectrum. Ultrafast pump-probe spectroscopy has been used to ascertain the underlying photophysical processes taking place in the films. DFB lasers, based on these materials and top-layer nanostructured polymeric resonators (i.e., one or two-dimensional surface relief gratings), have been fabricated and characterized. Lasers emitting close to either one of the two possible ASE wavelengths, or simultaneously at both of them, have been prepared by proper selection of the resonator parameters.

The investigation of the two-dimensional surface relief grating on dye-doped polymer film

Two-dimensional surface relief grating (2D-SRG) on azo-dye doped polymer film (DDPF) was fabricated using the two-step of holographic writing technique. The groove structure of the 2D-SRG was dependent on the rotational angle of the two-step of writing, and the depth of the groove could be enhanced about 2~3 times by using nematic liquid crystal as the interface. The surface modulation of groove on DDPF with or without the interface of nematic liquid crystal depending on the polarization of the writing beams is also discussed. As the rotational angle between the two steps of writing was increased, the depth of the groove was gradually decreased for the writing beams with the S-polarization in the second step of writing, while increasing for the writing beams with the P-polarization.

Study of surface relief gratings on azo organometallic films in picosecond regime

Materials for optical data storage and optical information processing must exhibit good holographic properties. Many materials for these applications have been already proposed. Here we describe a grating inscription process characterized by short inscription time and long-time stability. A series of ruthenium-acetylide organometallic complexes containing an azobenzene fragment were synthesized. Photo-induced gratings were produced by short pulse (16 ps, 532 nm) laser irradiation. The surface relief gratings formed at the same time were observed by atomic force microscope. In this work, we highlight the short inscription times brought into play as well as the good temporal stability of these gratings stored at room temperature. We study the influence of the polarization states and the light intensity of writing beams on the dynamics of the surface relief gratings formation and we compare these results with those of a known representative of azobenzene derivative (Disperse Red 1). Lastly, we show that it is possible to write two-dimensional surface relief gratings.

Emission properties of an organic light-emitting diode patterned by a photoinduced autostructuration process

The photoluminescence properties of a periodically structured organic light-emitting diode are presented. Patterning is achieved using an original single-step autostructuration technique based on photoinduced effects in azo-polymer films. We show that single beam laser irradiation can lead to the induction of regular two-dimensional surface relief gratings. The waveguide properties of these microstructures as well as their effect on the emission properties of a light-emitting material are studied. We demonstrate a new straightforward technique to improve external light emission efficiency by outcoupling part of the light that was initially guided into the different diode layers.

Thermophotovoltaic generation with selective radiators based on tungsten surface gratings

Two-dimensional surface-relief gratings with a period of 1.0–0.2μm composed of rectangular microcavities were fabricated on single crystalline W substrates to develop spectrally selective radiators for thermophotovoltaic generation. The radiators displayed strong emission in the near-infrared region where narrow-band-gap photovoltaic cells could convert photons into electricity. The enhancement of thermal emission was attributed to the microcavity effect. Power generation tests were carried out and the W gratings showed more than two times higher generation efficiency, compared to a SiC radiator. The results showed that the microstructured W radiators behave as good selective radiator, with both high efficiency and high power density.

Vector coupled-wave analysis of hemispherical grid gratings for visible light

With the rapid development of modern science, the techniques of fabricating two-dimensional surface-relief gratings with a hemispherical grid for visible light by chemical methods are proving to be successful. In this paper, we use a multi-level structure to simulate this kind of grating and adopt the Lagrange multiplier method to minimize the volume error, and the rigorous coupled-wave method is employed to analyse the vector diffraction properties of this kind of grating. By computer simulation and calculation, the relations between the reflectivity and the structure parameters of the gratings are presented, and the antireflective characteristics are also studied when visible light is incident upon them. The results show that this kind of grating is capable of reducing reflections, and could achieve very low reflectivity over a wide field of view and a wide waveband by choosing appropriate parameters. The results also show that the errors can be neglected when and the results are proved to be credible.

High-Density Optical Storage with Nanospheres on Surface Relief Structure

We report optical storage media using fluorescent nanospheres on a surface relief structure. By using a nanosphere as one recording bit, we can carry out high-density recording. We have developed a new recording medium by arranging and fixing a large number of nanospheres on a two-dimensional surface relief grating (SRG).