M. Aslam Baig

A comparative study of single and double pulse laser induced breakdown spectroscopy

A comparative study of single and double pulse laser induced breakdown spectroscopy (LIBS) using the fundamental (1064 nm) and the second harmonics (532 nm) of Nd:YAG lasers is presented. The double pulse collinear configuration yields more than three hundred times signal enhancement in the singly ionized aluminum lines as compared to the single pulse LIBS spectrum. The effect of interpulse delay between the two laser pulses and the laser pulses energies ratio in the double pulse spectrum are studied. A comparison of variations of plasma parameters along the plume axis in the single and the double pulse has also been studied.

Effects of laser wavelengths and pulse energy ratio on the emission enhancement in dual pulse LIBS

We present new studies on the effects of laser wavelengths, pulse energy ratio and interpulse delay between two laser pulses in the collinear dual pulse configuration of laser-induced breakdown spectroscopy (LIBS) on an iron sample in air using the fundamental (1064 nm) and the second harmonics (532 nm) of Nd:YAG lasers. In the dual pulse LIBS, an optimum value of interpulse delay with an appropriate combination of laser wavelengths, and laser pulse energy ratio, yields a 30 times signal intensity enhancement in the neutral iron lines as compared with single pulse LIBS. A comparison in the spatial variations of electron temperature along the axis of the plume expansion in single and double pulse LIBS has also been studied.

An inexpensive technique for the time resolved laser induced plasma spectroscopy

We present an efficient and inexpensive method for calculating the time resolved emission spectrum from the time integrated spectrum by monitoring the time evolution of neutral and singly ionized species in the laser produced plasma. To validate our assertion of extracting time resolved information from the time integrated spectrum, the time evolution data of the Cu II line at 481.29 nm and the molecular bands of AlO in the wavelength region (450–550 nm) have been studied. The plasma parameters were also estimated from the time resolved and time integrated spectra. A comparison of the results clearly reveals that the time resolved information about the plasma parameters can be extracted from the spectra registered with a time integrated spectrograph. Our proposed method will make the laser induced plasma spectroscopy robust and a low cost technique which is attractive for industry and environmental monitoring.

Determination of transition probabilities for the 3p → 3s transition array in neon using laser induced breakdown spectroscopy

We present here a study of the optical emission spectra of the laser produced neon plasma generated by a Nd:YAG laser at 1064 nm. The spectra were recorded using the laser induced breakdown spectroscopy 2000 detection system comprising of five spectrometers covering the entire visible region. The observed spectra yield all the optically allowed transitions between the 2p53p upper and 2p53s lower configurations based levels. The relative line strengths of all the dipole allowed transitions have been determined using the intensity ratios and compared with the J-file sum rule. The absolute transition probabilities have been calculated by using the lifetimes of the upper levels and the intensities of the observed spectral lines and show good agreement with the literature values.

Two-step laser excitation and ionization from the 7p 2P3/2 state of potassium

New measurements of photoionization cross-sections from the 7p 2P3/2 excited state of potassium near the first ionization threshold are presented using a two-step laser excitation/ionization technique in conjunction with a time-of-flight (TOF) mass spectrometer. The absolute values of photoionization cross-sections have been determined as (3.52?????0.52)?Mb, (2.21?????0.33)?Mb, (1.35?????0.22)?Mb and (0.54?????0.08)?Mb at four ionizing laser wavelengths; 1064?nm, 643.61?nm, 532?nm and 355?nm respectively whereas the number density has been determined as (1.6?????0.31)???1010?cm?3. The presently measured experimental values of photoionization cross-sections are in good agreement with the literature experimental and theoretical values.