With the aid of an infrared thermograph technique, we directly observed the temperature variation across a bulk copper specimen as it was being ablated by multiple femtosecond laser pulses. Combining the experimental results with simulations, we quantified the deposited thermal power into the copper specimen during the femtosecond laser ablation process. A substantial amount of thermal power (more than 50%) was deposited in the copper specimen, implying that thermal effect can be significant in femtosecond laser materials processing in spite of its ultrashort pulse duration.

The interaction of high-intensity laser pulses with matter releases instantaneously ultra-large currents of highly energetic electrons, leading to the generation of highly-transient, large-amplitude electric and magnetic fields. We report results of recent experiments in which such charge dynamics have been studied by using proton probing techniques able to provide maps of the electrostatic fields with high spatial and temporal resolution. The dynamics of ponderomotive channeling in underdense plasmas have been studied in this way, as also the processes of Debye sheath formation and MeV ion front expansion at the rear of laser-irradiated thin metallic foils. Laser-driven impulsive fields at the surface of solid targets can be applied for energy-selective ion beam focusing.

Stochastic instabilities are studied considering the motion of one particle in a very high intensity wave propagating along a constant homogeneous magnetic field, and in a high intensity wave propagating in a nonmagnetized medium perturbed by one or two low intensity traveling waves. Resonances are identified and conditions for resonance overlap are studied. The part of chaos in the electron acceleration is analyzed. PIC code simulation results confirm the stochastic heating.

The effects of multiple pulses of a CO2 laser with energy of 2.5 J and pulse duration of 200 ns on the surface morphology of ion irradiated CR-39 is investigated in light of the modification in its track registration properties. For this purpose, a CR-39 was exposed by a CO2 laser generated hydrogen, argon, cadmium, air molecular ions (N2 and O2, etc.), high energy (300 KeV) proton beam from Cock Croft Walton accelerator, and α (5 MeV) from 0.5 μCi Pu239 source. The registered tracks were enlarged after 6 h of 6.25 N NaOH etching. These etched detectors were then exposed to different number of CO2 laser shots. The etched detectors were then analyzed by a computer controlled optical microscope (Lexica DMR series). It was observed that even a single shot of CO2 laser, irrespective of the registered ions tracks, can change the track registration properties of CR-39, and can remove the vaporization resistant skin present on the polymer (CR-39). A significant change in track density and track shaping regardless of the ions is observed. At the outside of the focal area, the ion density of different registered tracks is compared graphically before and after laser irradiation. Laser ablation of unexposed CR-39 is also done with multiple pulses CO2 laser. In this regard, the coherent and non-coherent structures, diffraction patterns, circular fringes with corrugations and ripples, droplets, chain like structures with cluster formation, chain folded crystallites, and hole drilling were observed. The irradiation induced ablation of the polymer is of great importance in electronics industry, lithography, etc.

This article appeared in Volume 24, Number 3, Pages 421–425.