M. S. Komlenok

Heat accumulation effects in short-pulse multi-pass cutting of carbon fiber reinforced plastics

The formation of a matrix evaporation zone (MEZ) in carbon fiber reinforced plastics during multi-pass laser cutting with picosecond laser pulses is studied for a wide range of pulse frequencies (fp = 10–800 kHz) and feed rates (vf = 0.002–10 m/s). Three regimes of the formation of the MEZ are found and related with different heat accumulation effects: (i) small MEZ (<2 μm) with negligible heat accumulation, (ii) moderate-size MEZ (up to a few hundred microns) determined by heat accumulation between pulses, and (iii) large MEZ (up to a few millimeters) caused by heat accumulation between scans. The dependence of the size of the MEZ on the number of scans and the scan frequency was studied to distinguish the two heat accumulation effects (between pulses and between scans), which occur on different time-scales. A diagram to illustrate the boundaries between the three regimes of the formation of the MEZ as a function of feed rate and pulse frequency is proposed as a promising base for further studies and as ...

Nonlinear photooxidation of diamond surface exposed to femtosecond laser pulses

We present an experimental investigation of photooxidation of a diamond surface exposed to femtosecond laser pulses that induce transient high concentrations of free carriers (>1022cm−3) while the lattice stays cold. Etching rate measurements and a laser-induced plasma study indicated that the rate of desorption of carbon species is proportional to the square of the induced plasma density, which contrasts with previous investigations of diamond etching by nanosecond pulses. We discuss how laser-induced ionization of diamond occurs and how it affects the photoreaction mechanism.

Oxygen-assisted multipass cutting of carbon fiber reinforced plastics with ultra-short laser pulses

Deep multipass cutting of bidirectional and unidirectional carbon fiber reinforced plastics (CFRP) with picosecond laser pulses was investigated in different static atmospheres as well as with the assistance of an oxygen or nitrogen gas flow. The ablation rate was determined as a function of the kerf depth and the resulting heat affected zone was measured. An assisting oxygen gas flow is found to significantly increase the cutting productivity, but only in deep kerfs where the diminished evaporative ablation due to the reduced laser fluence reaching the bottom of the kerf does not dominate the contribution of reactive etching anymore. Oxygen-supported cutting was shown to also solve the problem that occurs when cutting the CFRP parallel to the fiber orientation where a strong deformation and widening of the kerf, which temporarily slows down the process speed, is revealed to be typical for processing in standard air atmospheres.

Resonant ablation of single-wall carbon nanotubes by femtosecond laser pulses

The thin 50 nm film of bundled arc-discharge single-wall carbon nanotubes was irradiated by femtosecond laser pulses with wavelengths 675, 1350 and 1745 nm corresponding to the absorption band of metallic nanotubes E11 M , to the background absorption and to the absorption band of semiconducting nanotubes E11 S , respectively. The aim was to induce a selective removal of nanotubes of specific type from the bundled material. Similar to conducted thermal heating experiments, the effect of laser irradiation results in suppression of all radial breathing modes in the Raman spectra, with preferential destruction of the metallic nanotubes with diameters less than 1.26 nm and of the semiconducting nanotubes with diameters 1.36 nm. However, the etching rate of different nanotubes depends on the wavelength of the laser irradiation. It is demonstrated that the relative content of nanotubes of different chiralities can be tuned by a resonant laser ablation of undesired nanotube fraction. The preferential etching of the resonant nanotubes has been shown for laser wavelengths 675 nm (E11 M ) and 1745 nm (E11 S ).