The effect of an oxygen atmosphere on the expansion dynamics of a laser-produced vanadium-oxygen plasma has been investigated using a fast intensified charged-coupled device camera. We find regimes of the plasma plume expansion ranging from a free plume at vacuum and low oxygen pressures, through collisional and shock-wave-like hydrodynamic regimes at intermediate oxygen pressure, finally reaching a confined plume with subsequent thermalization of the plume particles at the highest pressure of the oxygen gas. Vanadium oxide nanostructures thin films were synthesized from this plasma and the resulting vanadium oxide phases studied as a function of the plume dynamics. We found monoclinic vanadium dioxide (VO2) (M1) and VO2 (B) nanoparticles in thin films deposited at 0.05 mbar. Pure phases of vanadium trioxide (V2O3) smooth and pentoxide (V2O5) nanorods thin films were detected at 0.01 and 0.1 to 0.2 mbar, respectively. Thin films containing VO2 (M1) were found to have a reversible metal-to-insulator transition at 61°C. This work paves the way to VO phase control by judicious choice of laser and plasma conditions.
Fast imaging plasma plume study have been carried out on vanadium-oxygen plasma generated using 248 nm, 25 ns pulses from an excimer KrF laser under oxygen atmosphere. The plume expansion dynamics of an ablated VO<sub>2</sub> target was investigated using a fast-imaging technique. The free expansion, splitting, sharpening and stopping of the plume were observed during these oxygen pressures, 0.01, 0.05, 0.10 and 0.20 mbar. The influence of the plume dynamics study on the properties of the obtained vanadium oxide thin films were examined using X-Ray Diffraction method. A vanadium dioxide phases were deposited at 0.05 mbar oxygen pressure for target-substrate distance of 40 mm and 50 mm. Mixed phases of vanadium oxide were deposited at 0.01, 0.10 and 0.20 mbar oxygen pressure for target-substrate distance of 40 mm. Transition temperatures of around 60.9<sup>o</sup>C have been measured from sample deposited at 0.05 mbar oxygen pressure for target-substrate distance of 50 mm. We observe mixed nanostructures for thin film prepared at 0.05 mbar for target-substrate distance of 40 mm, while the thin film prepared at 0.05 mbar for target-substrate of 50 mm shows an uniform nanostructure film.
We outline an all-optical and noncontact approach for controlled laser heating and measurement of the resultant temperature distribution at the surface of a material, respectively. We show how the boundary conditions of the heating problem may be controlled optically through shaping of the pump light and use the examples of both Gaussian and flat-top beams. These two beams, together with appropriate nonoptical boundary control, allow for the laser-induced thermal study of materials with and without thermal stress. We illustrate the technique on an industrial diamond sample where a gradient and uniform temperature profile on the surface of the diamond was successfully created and measured. We use the technique to study the thermally induced degradation of industrial diamond in a controlled manner.
This paper presents an implementation of a laser beam shaping system for both heating a diamond tool and measuring
the resulting temperature optically. The influence the initial laser parameters have on the resultant temperature profiles is
shown experimentally and theoretically. A CO<sub>2</sub> laser beam was used as the source to raise the temperature of the
diamond tool and the resultant temperature was measured by using the blackbody principle. We have successfully
transformed a Gaussian beam profile into a flat-top beam profile by using a diffractive optical element as a phase
element in conjunction with a Fourier transforming lens. In this paper, we have successfully demonstrated temperature
profiles across the diamond tool surface using two laser beam profiles and two optical setups, thus allowing a study of
temperature influences with and without thermal stress. The generation of such temperature profiles on the diamond tool
in the laboratory is important in the study of changes that occur in diamond tools, particularly the reduced efficiency of
such tools in applications where extreme heating due to friction is expected.