The objective of this study was to evaluate the antibacterial activity of argon fluoride (ArF) excimer laser radiation on clinically important strains of gram-negative bacteria. The antibacterial activity of ArF excimer laser radiation was evaluated on two Acinetobacter baumannii, one Enterobacter cloacae, three Escherichia coli, two Helicobacter pylori, one Klebsiella pneumoniae and two Pseudomonas aeruginosa strains. The strains were isolated from clinical specimens and typed by the usual biochemical procedures. Square agar plates of 12 x 12 cm were divided into rectangular (2 x 3 cm) regions and spread with 0.5x 10(4) colony forming units (CFU)/ml of bacterial suspension. The excess liquid was removed and the plates were allowed to dry for 30 min. A total of 96 rectangular (2x3 cm) regions were used for each strain, in order to test an equal number of laser parameters. Each rectangular region was irradiated with different laser parameters, using a 193 nm ArF excimer laser, linked with a simple Galilean afocal system and a rectangular diaphragm of the same dimensions as the original laser beam cross-section, at a distance of 10 cm from the irradiated surface. This system was used in order to keep the laser pulse energy under 80 mJ and to cut-out the non-transverse electromagnetic mode branches of the laser beam. We then studied the bacterial survival ratio versus the number of laser pulses, the repetition frequency and the total laser beam fluence. Our results showed that the total laser beam fluence was the most important parameter to consider in evaluating the bactericidal effect of ArF excimer laser radiation. A critical value of the total fluence was determined for each strain, such that, for laser beam fluences greater than this critical value, no colonies appeared to survive while, for laser fluences less than this critical value, the survival ratio did not exceed 2 x 10(7) CFU (2 x 10(-5)%). These critical values were found to vary between 8 J/cm2 and 16 J/cm2 for the bacterial species studied. Under these conditions, ArF laser irradiation is promising for the sterilisation of hard surfaces and for in situ application.

No abstract

The shock wave generation in stapes models during laser ear surgery is experimentally investigated The intensity absolute measurements of shock waves generated by excimer laser in the treated bone is performed. It is shown that the roughness of the crater bottom profile depends on the laser beam fluence. it is revealed that in pulse repetition regime of bone drilling there exists an optimal laser beam fluence, which provides as high rate of drilling as smooth bottom of crater. For ArF and KrF excimer lasers the optimal fluence is equal to about 0.4-0.5 i/cm2 at the repetition rote 5 Hz. The amplitude of shock wave induced at these parameters of laser beam in the back side of the bone sample of 1.1 mm thickness was measured to be about 25 bar. For 0.5 mm thick bone sample the amplitude of such a shock wave was measured to be about 60 bar and the corresponding pressure gradient 0.35 bar/pm.