Characterization of excimer laser ablation generated pepsin particles using multi-wavelength photoacoustic instrument

Abstract

Preparation of organic thin layers on various special substrates using the pulsed laser deposition (PLD) technique is an important task from the point of view of bioengineering and biosensor technologies. Earlier studies demonstrated that particle ejection starts during the ablating laser pulse resulting in significant shielding effects which can influence the real fluence on the target surface and consequently the efficiency of layer preparation. In this study, we introduce a photoacoustic absorption measurement technique for in-situ characterization of ablated particles during PLD experiments. A KrF excimer laser beam (λ = 248 nm, FWHM = 18 ns) was focused onto pepsin targets in a PLD chamber; the applied laser fluences were 440 and 660 mJ/cm 2 . We determined the wavelength dependence of optical absorption and mass specific absorption coefficient of laser ablation generated pepsin aerosols in the UV-VIS-NIR range. On the basis of our measurements, we calculated the absorbance at the ablating laser wavelength, too. We demonstrated that when the laser ablation generated pepsin aerosols spread through the whole PLD chamber the effect of absorptivity is negligible for the subsequent pulses. However, the interaction of the laser pulse and the just formed particle cloud generated by the same pulse is more significant.B

Microphysical properties of carbonaceous aerosol particles generated by laser ablation of a graphite target

“…The sample was placed and irradiated in an ablation chamber (Fig. 1), which was a modified version of a PLD (pulsed laser deposition) chamber described in detail earlier (Ajtai et al, 2010;Hopp et al, 2012). The cylindrically shaped ablation chamber was made of stainless steel with an inner diameter and length of 3 and 10 cm, respectively.…”

Investigation of Artificially Generated and Ambient Carbonaceous Particulate Matter

“…The graphite disc was placed and irradiated in an ablation chamber ( Fig. 12), which was a modified version of a PLD (pulsed laser deposition) chamber described in detail earlier (Ajtai et al, 2010b;Hopp et al, 2012). The cylindrically shaped ablation chamber is made of stainless steel with an inner diameter and length of 3 and 10 cm.…”

“…The laser beam was focused into the chamber through a fused silica window at an angle of 45° with respect to the surface of the irradiated sample. To improve the stability of particle yield, the target was placed onto a rotating sample holder and the angular speed of rotation was matched with the repetition rate of the laser and the dimension of the irradiated spot to ensure uniform sample etching, i.e., quasi-homogeneous ablated target surface structure and consequently uniform material ejection over a prolonged period (Ajtai et al, 2010b;Hopp et al, 2012). This way stable particle production could be realized for several hours.…”

“…Above the ablation threshold value, aerosol yield depends mostly on the thermochemical properties of the target material. It is proportional to the whole ablation volume determined by the penetration depth of the laser pulses (Ajtai et al, 2010b;Hopp et al, 2012). Thus, increasing fluence results in higher aerosol yield.…”