Abstract
In this paper, the influence of the bulk temperature (BT) of Polycarbonate (PC) on the occurrence and growth of Laser-induced Periodic Surface Structures (LIPSS) is studied. Ultrashort UV laser pulses with various laser peak fluence levels and various numbers of overscans were applied on the surface of pre-heated Polycarbonate at different bulk temperatures. Increased BT leads to a stronger absorption of laser energy by the Polycarbonate. For High Spatial Frequency LIPSS (HSFL), Low Spatial Frequency LIPSS perpendicular (LSFL-I) and parallel (LSFL-II) to the laser polarization were only observed on the rim of the ablated tracks on the surface but not in the center of the tracks. For , it was found that when pre-heating the polymer to a BT close its glass transition temperature (), the laser fluence to achieve similar LIPSS as when processed at room temperature decreases by a factor of two. LSFL types I and II were obtained on PC at a BT close to and their periods and amplitudes were similar to typical values found in the literature. To the best of the author’s knowledge, it is the first time both LSFL types developed simultaneously and consistently on the same sample under equal laser processing parameters. The evolution of LIPSS from HSFL, over LSFL-II to LSFL I, is described, depending on laser peak fluence levels, number of pulses processing the spot and bulk temperature.
Highlights
IntroductionIrradiating a flat surface of a solid with high intensity polarized laser light can lead to the manifestation of Laser-induced Periodic Surface Structures (LIPSS) (a list of abbreviations can be found at the end of the paper), which are nanometer-sized regular grooves [1]
Irradiating a flat surface of a solid with high intensity polarized laser light can lead to the manifestation of Laser-induced Periodic Surface Structures (LIPSS), which are nanometer-sized regular grooves [1]
The aim of this study is to investigate the LIPSS development on Polycarbonate depending on its bulk temperature
Summary
Irradiating a flat surface of a solid with high intensity polarized laser light can lead to the manifestation of Laser-induced Periodic Surface Structures (LIPSS) (a list of abbreviations can be found at the end of the paper), which are nanometer-sized regular grooves [1]. At which LIPSS can be observed on the surface already after one pulse [3], several tens to a thousand pulses are necessary for LIPSS to develop on polymers [2,4,5]. It was stated by Rebollar et al [6] that, in order for LIPSS to occur on the surface, the irradiated polymer has to reach the glass transition temperature Tg or even the melt temperature Tm. That is, the mobility of the polymer chains increases at Tg or Tm , which is required to allow surface modification. The accumulation of heat induced by laser pulses may lead to increased temperature of the surface, depending on the bulk temperature (BT), the laser pulse repetition rate ( f P ), the laser peak fluence F0 , the geometrical pulse-to-pulse overlap (OL) [7] and the number of overscans (NOS ) [8]
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