Spatial-frequency response of holographic gratings photodeposited from inorganic colloids.
Surface photodeposition is a photon-assisted process by which thin films are formed on substrates immersed in colloid solutions. We experimentally evaluate the resolution capabilities of the photodeposition process with amorphous selenium colloids by recording holographic gratings at different spatial frequencies, up to 2200 lines/mm. The experimental diffraction efficiencies are analyzed in terms of a theoretical model, which relates the spatial-frequency response to optical recording parameters and colloid particle sizes. The maximal experimental diffraction efficiency reaches 13% with a spatial frequency of f = 1100 lines/mm. The diffraction efficiencies decrease monotonically with spatial frequency, and drop to half of the maximal diffraction efficiency at f ≈ 1500 lines/mm. These resolution capabilities are achieved with colloid particle sizes extending up to 80 nm. The theoretical derivation indicates that to obtain spatial frequencies above 3000 lines/mm, one should restrict the colloid particle size to a(max) ≤ 30 nm.
Laser-Beam Direct Writing of TiO2 Channels for Fabrication of Ti:LiNbO3 Waveguides
A novel photoresist-free process used for fabrication of Ti:LiNbO3 waveguides is proposed and demonstrated. In this process, smooth waveguide patterning of TiO2 channels can be performed by laser-beam (LB) direct writing at up to 0.2 mm/s, where Ti film deposited on LiNbO3 is thermally oxidized in air by the focused Ar+ laser beam. LB writing has sufficiently high accuracy for waveguide patterning because the Ti film thickness is usually below 0.1 µm. Unlike the previously reported resist-free processes, the process demonstrated here does not require any specific tools or materials, and can provide Ti:LiNbO3 waveguides more easily. It was also confirmed that there are no marked differences in guiding properties between two Ti:LiNbO3 waveguides fabricated by the proposed resist-free process and the standard process based on waveguide patterning in photoresist as thick as 1 µm.
The Thermal Activation Compensation Effect and the isokinetic temperature relation to physical models
The "Thermal Activation Compensation Effect", reported in many temperature activated experiments, is reviewed. The effect describes the observation that in some cases, families of Arrhenius curves plotted vs. a compensation variable, intercept at a finite temperature called the compensation or isokinetic temperature T0. It is shown in this work that the effect is real, in the sense that T0 was obtained within the experimental range and not by graphical extrapolation. The case of intrinsic charge carrier concentration in semiconductors vs. temperature, with bandgap as a compensation variable allows one to probe into the origin of T0 by reference to an available detailed theory. The conclusion drawn is that the compensation temperature is mathematically a reflection of the dependence of activation energy on the temperature and compensation variable in the cases discussed. Hot carrier effects are suggested to account for this phenomenon.