Date of this Version
Patent Number: 5,847,825
A method and apparatus for in situ detection and concentration measurement of trace elements in an analysis Sample is disclosed. The invention uses laser induced breakdown spectroscopy (LIBS) wherein femtosecond pulsed laser energy is employed to produce the plasma. The femtosecond pulsed laser energy is focused on the analysis Sample to produce the plasma and the resulting emission is delivered for spectral analysis. Because the method and apparatus of the present invention allow breakdown of the analysis Sample without propagation of energy to the Sample-air interface, a plasma is produced that consists essentially of Sample materials without being contaminated by air plasma formation. Thus, the background emission is reduced and there is no need to wait for the plasma to cool down over time before detecting the spectral lines of the Sample. Because there is no need to wait for cooling before spectral measurement, lower detection limits are possible. Furthermore, concentration measurement accuracy is improved using intensity rationing techniques Since a calibration curve produced using the method and apparatus of the present invention is Substantially more linear than those using the conventional nanosecond pulsed LIBS.