Subtarget effect on laser plasma generated by Transversely Excited Atmospheric CO2 laser at atmospheric gas pressure

An experimental study has been carried out on the dynamical process taking place in the laser plasma generated by Transversely Excited Atmospheric CO2 laser (100 mJ, 50 ns) irradiation of a soft sample at surrounding helium p ressure of 1 atm. It is shown that the presence of a copper subtarget behin d the soft sample is crucial in raising the gushing speed of the atoms to t he level adequate for the generation of shock wave laser plasma even at atm ospheric pressure. It is also found that the time profiles of spatially int egrated emission intensity of the target's atoms and gas atoms exhibit a ch aracteristic dynamical process that consists of successive excitation and c ooling stages even at such a high pressure, which is typical of shock wave laser plasma. It is therefore suggested that the generation of the laser pl asma at atmospheric pressure is more likely due to the shock wave mechanism than to the widely known breakdown mechanism. Initial spectrochemical anal ysis of water from the blow off of a boiler system was also can icd out, sh owing a detection limit of as low as 5 ppm for calcium.