Papers by Keyword: Femtosecond Laser Ablation

Abstract: Thermodynamics effects generated by femtosecond laser ablation are very important. In this work, the numerical simulation of high-energy femtosecond laser ablation especially the electro-phonon coupling coefficient influence of high-energy femtosecond laser ablation on metal target was studied. A new two-temperature model (TTM) which considered the effects of electron density of states (DOS) on electron-phonon coupling coefficient was first established, then the temperature evolvement for electron and lattice in different electro-phonon coupling coefficient G, and the effect of G on electron temperature and lattice temperature and electron-phonon coupling time were emphatically analyzed. The results showed that the electron-phonon coupling coefficient strongly affected the surface electron temperature and coupling time in the femtosecond laser ablation. The smaller the electron-phonon coupling coefficient was, the more the energy transmission from electronic to ion subsystem. As a result, the smaller the value of electron-phonon coupling coefficient, a more rapid decline for the temperature of electronic sub-system achieved. This work will offer help for the future investigation of material fabrication by femtosecond laser ablation.

Abstract: We fabricated Si Nano-columns by a femtosecond laser with various wavelengths and process parameters, whilst the specimen was submerged in water. The experiments were carried out by three types of wavelengths i.e. 1030 nm, 515nm, 343nm, with 500 fs laser pulses. The scales of these spikes are much smaller than micro spikes that are constructed by laser irradiation of silicon surface in vacuum or gases like SF6, Cl2. The Si nano-columns of 300 nm or less in width were characterized by SEM measurements. The formation of these Si Nano-columns that were revealed by SEM observation, indicates chemical etching with laser ablation occurred when surface exposed by laser beam. We observed 200 nm spikes height at the center of laser beam profile and the ones uniform in height at lateral incident area.

Abstract: In order to research the ablation of 0Cr18Ni9 stainless steel films whose thickness is 20μm, stainless steel films were ablated and micro-cut by fs laser in the paper. Firstly, the ablation threshold of 0Cr18Ni9 stainless steel films and the beam waist radius of fs laser were obtained based on the functional relation between ablation area and the laser energy. And, experimental results indicate that the waist radius of fs laser is 10.416μm and the ablation threshold of stainless steel films whose thickness is 20μm is 0.455J/cm2. Secondly, in order to observe the heat-affected zone, metallographic phase and electrical resistivity of stainless steel films ablated by fs laser were researched in detail. And through the experimental results, we can deduce that metallographic phase of specimens which were cut by fs laser was in recovery process and the metallographic was not change. Finally, in order to research the composition of stainless steel films phase affected by fs laser ablation, specimens were tested by XRD. And through the XRD test, it can be deduced the composition of stainless steel films phase was not affected by fs laser cut and the content of phase was affected by it.

Abstract: The numerical simulation of high-energy femtosecond laser ablation on metal target is studied in this paper. Based on the two-temperature model (TTM), a new model considering the effects of the electron density of states (DOS) on electronic heat capacity, electron-phonon coupling coefficient and electronic thermal conductivity is established. As an example of gold target, the relationship between the melting threshold and the thickness of gold films is numerically calculated. Our result is more consistent with the experimental datum in contrast to the results without considering the DOS effects. This shows that the revised TTM of high-energy femtosecond laser ablation (i.e. DOS-TTM) is more reasonable compared with general used TTM.

Abstract: The role of multi-pulse feedback in self-organized nanostructure (ripples) formation on silicon surface upon femtosecond laser ablation is investigated. For irradiation at constant intensity and pulse repetition rate, the previously postulated feedback effect of accumulated dose with in¬creasing number of pulses is confirmed and investigated in detail: both the modified surface area as well as the complexity and feature size of generated nanostructures increase with accumulated dose. More interestingly, at constant total incident dose (number of pulses times pulse energy) accumu¬lation and feedback depend strongly on temporal pulse separation. The feedback becomes increas¬ingly weaker with increasing time intervals between successive pulses, involving times up to one second and more before individual pulses act independently. In a first attempt to model this long-lived coupling, we find that conduction band electrons, produced by the preceding laser pulse, can provide, indeed, such feedback by facilitating coupling of subsequent pulses for substantial delays. However, the achieved time span of about a millisecond is still significantly shorter than observed experimentally.