Radiative cooling of laser ablated vapor plumes: Experimental and theoretical analyses

Abstract

A study was made of the cooling of the laser induced vapor plume in background air.The temperature and size variations of the vapor plume were determined from spectroscopic measurements during the first few tens of micro-seconds after the laser pulse. Experiments were carried out over a range of laser spot sizes and energies ------------------------------------------------------------------------------------------- Keywords Laser ablation, plasma cooling, thermal radiation decrease of the vapor plume was independent of the plume size, shape, and position. For 1 larger optical thicknesses of the vapor plume, the calculations showed that the reflectivity of the sample surface and the size of the vapor plume would dramatically affect cooling of the vapor plume.2

Experimental and theoretical studies of particle generation after laser ablation of copper with a background gas at atmospheric pressure

“…However, since the average temperature of the vapor plume was high and the thermal radiation was strong during the first few microseconds, condensation is limited only in the region close to the contact surface (between the vapor plume and the background gas) where significant cooling occurred. Afterwards, the temperature is lower than ~5500K and conduction and mass diffusion dominate the heat transfer from the vapor plume to the background gas, causing the temperature of the vapor plume to decrease [13].…”

“…From previous studies [11][12][13], the time interval when condensation occurs within the vapor plume with a background gas has been determined to be greater than tens of microseconds after the laser pulse; during this time interval the pressure of the vapor plume is close to the background gas pressure. This work excludes the external shockwave expansion, internal shockwave reflection, and radiative cooling during the first tens of microseconds after the laser pulse.…”

“…Pure copper was chosen as the sample to continue the sequence of our previous studies [11][12][13]. In addition, compared to other materials, copper is inexpensive, easy to obtain and prepare for the experimental purpose.…”

“…Both quantities are functions of the cooling rate of the vapor plume. The cooling rate of the vapor plume is generally very fast (>~10,000 K/s) [11][12][13]. Consequently, the critical radius of the particles generated by homogeneous nucleation is very small (<~10nm), and the duration for particle growth is very short (<0.1s).…”

“…This difficulty results from the complexity of the laser ablation process. The laser induced vapor plume experiences significant changes in size, shape and temperature before and during the condensation process [11][12][13]. The size, shape and temperature of the vapor plume are complex functions of the laser energy, physical properties of the background gas and the alignment of the ablation system (chamber size and the sample position).…”