For the picosecond pulse width range, the ripple formation can be based on any or a combination of the acoustic wave, surface tension gradient and interference between the incident light/surface wave mechanisms. The primary theory we used to explain the creation of ripples in the femtosecond regime was the Boson Condensation Hypothesis since mechanical and thermal forces are deemed to be negligible. In our experiments, the ripples formed at a lower laser fluence range 1.56–4.66 J/cm 2, whereas the grains were created at a higher laser fluence range 3.34–6.77 J/cm 2.
Also, this report strides to identify the mechanisms that lead to ripple and grain formation at different pulse durations.
A unique high repetition rate femtosecond fiber laser system was used to study the effect of pulse width, repetition rate and pulse energy on the spacing of ripples as well as diameter of grains created during the surface patterning operations. Surface patterning using femtosecond laser can be utilized for the fabrication of MEMS/NEMS, CMOS, 3D-microstructures, microtrenches, microchannels, microholes, periodical submicron gratings and nanophotonics. Preliminary observations seem to confirm the condensation. The proposed experiment involves observation of the single plasmon mode by diffraction or from the appearance of linear ripples left on the solid surface and the rotation of this pattern. An experiment is proposed that is argued to be both easy to perform and to offer a conclusive demonstration of boson condensation. If not, it does not exhibit perfect diamagnetism and the Meissner effect. In addition to the practical problems associated with such a test, there are theoretical questions such as whether or not the bipolar plasma ought to be able to expel a magnetic field within the 100 ns or so that it persists in the proposed boson condensed phase. At this writing no magnetic experiment has been completed to test this proposition further. Lattice temperatures for the material during this phase have beeb measured by Raman scattering to lie in the range from 500 to 1000 K. The condensed state is described in the same form as the BCS superconductor and has many of the properties of the superconducting state. Van Vechten and Compaan and, independently, Nagy and Noga have proposed that the high reflectivity state observed in pulsed laser/electron/ion beam annealing of Si and other semiconductors results when the electron-hole plasma created by the initial absorption of the ionizing radiation undergoes a boson condensation.