Residual thermal effects in Al following single ns- and fs-laser pulse ablation

Thermal response and optical absorptance of metals under femtosecond laser irradiation

“…To explain those enhanced thermal energy coupling, it has been suggested that energy transferring to a metal sample from laser-induced plasmas plays a key role [31]. Previously, we have found that the behavior of residual thermal energy coupling shows a similar general trend between nanosecond-and femtosecond-laser pulse ablation [28], and this suggests that the physical mechanism used to explain the long-pulse REC enhancement may also account for the behaviors of residual heating in femtosecond laser ablation. In general, two types of plasmas can be produced during a femtosecond laser pulse: 1) solid-density plasma in the skin layer of the sample and 2) ambient gas plasma.…”

“…We note that the generation of air plasma prior to the hydrodynamic motion of the ablated material has been observed in the past in picosecond laser ablation [38]. The difference between plasmas produced in air and in vacuum can clearly be seen from the plasma plume images in Figure 11, which are taken using an open-shutter camera [28]. We can see that the size of hot plasma generated following ablation in air is larger than that in vacuum.…”

“…To measure E R , we apply a calorimetric technique that has been described in our previous studies [28,29]. Briefly, we measure the bulk temperature rise ΔT R with a thermocouple battery following ablation and determine E R calorimetrically as E R = mCΔT R , where m is the mass and C is the known specific heat capacity of the sample.…”

“…Although femtosecond laser ablation have been extensively studied in the past [21][22][23][24][25][26][27], many of the physical mechanisms remain unclear. For example, recent studies have shown that the residual thermal energy in an irradiated metal sample abruptly increases following both single-pulse and pulse-train femtosecond laser ablation in a gas medium when the laser fluence is above a certain threshold [28,29]. In the case of pulse-train ablation [29], it was found that one contributing factor to the enhanced thermal coupling following a large number of applied pulses is an increase of sample absorptance due to surface structural modifications.…”

Experimental study on femtosecond laser micromachining of grooves in stainless steel

“…In the case of steel, even for highest repetition rates applied for groove machining experiments being discussed in this paper, the local heat accumulation is considered negligible. However this model does not take into account residual sample heating, described in [26], and neglects effects present particularly in 2D machining. As such the change of erosion front and modification of absorbing material together with damage accumulation [25] must be noted.…”