S. U. Haq

Oscillator strength measurements of the highly excited 4s4p 3 P 1 o →4snd 3 D 2 transitions of zinc

We report experimentally determined oscillator strength distribution in the bound region of zinc corresponding to the 4s4p 3P1o→4snd 3D2 (23≤n≤55) transitions. The absolute photoionization cross section from the 4s4p 3P1o excited state at the 4s 2S1/2 ionization threshold has been determined as 54±8 Mbarns by using the saturated absorption technique. The measured value of the photoionization cross section at threshold is used to calibrate the oscillator strengths of the above-mentioned Rydberg transitions.

Quantitative analysis of Al-Si alloy using calibration free laser induced breakdown spectroscopy (CF-LIBS)

The quantitative analysis of the standard aluminum-silicon alloy has been performed using calibration free laser induced breakdown spectroscopy (CF-LIBS). The plasma was produced using the fundamental harmonic (1064 nm) of the Nd: YAG laser and the emission spectra were recorded at 3.5 μs detector gate delay. The qualitative analysis of the emission spectra confirms the presence of Mg, Al, Si, Ti, Mn, Fe, Ni, Cu, Zn, Sn, and Pb in the alloy. The background subtracted and self-absorption corrected emission spectra were used for the estimation of plasma temperature as 10 100 ± 300 K. The plasma temperature and self-absorption corrected emission lines of each element have been used for the determination of concentration of each species present in the alloy. The use of corrected emission intensities and accurate evaluation of plasma temperature yield reliable quantitative analysis up to a maximum 2.2% deviation from reference sample concentration.

Electron temperature and density measurements of laser induced germanium plasma

The germanium plasma produced by the fundamental harmonics (1064 nm) of Nd:YAG laser in single and double pulse configurations have been studied spectroscopically. The plasma is characterized by measuring the electron temperature using the Boltzmann plot method for neutral and ionized species and electron number density as a function of laser irradiance, ambient pressure, and distance from the target surface. It is observed that the plasma parameters have an increasing trend with laser irradiance (9–33 GW/cm2) and with ambient pressure (8–250 mbar). However, a decreasing trend is observed along the plume length up to 4.5 mm. The electron temperature and electron number density are also determined using a double pulse configuration, and their behavior at fixed energy ratio and different interpulse delays is discussed.

Characterization of laser produced plasma using laser induced breakdown spectroscopy

The plasma parameter studies of the Nd:YAG (neodymium-doped yttrium aluminum garnet, Nd:Y3Al15O12) crystal by using the fundamental (1064 nm) and second (532 nm) harmonics of Nd:YAG laser are reported. The electron temperature (Te) and electron number density (Ne) were determined using the Boltzmann plot method and the Stark-broadened line profile, respectively. An increase in the plasma parameters have been observed with an increase in the laser irradiance for both laser modes. The electron temperatures were calculated in the range of 0.53–0.66 eV for 1064 nm and 0.47–0.60 eV for 532 nm, and the electron number densities were determined in the range of 7.43 × 1015–3.27 × 1016 cm−3 for 1064 nm and 1.35 × 1016–3.97 × 1016 cm−3 for 532 nm in the studied irradiance range of 1.19–12.5 GW/cm2. However, the spatial evolution of the plasma parameters investigated up to 2.75 mm away from the target surface at a fixed laser irradiance of 6.51 GW/cm2 showed a decreasing trend. In addition, the estimated values of the inverse bremsstrahlung (IB) absorption coefficients at both laser wavelengths showed that the IB process is dominant for the 1064-nm laser.

Photoionization from the 5p {sup 2}P{sub 3/2} state of rubidium

We report two-step photoionization studies from the 5p {sup 2}P{sub 3/2} excited state of rubidium using two dye lasers simultaneously pumped by a common Nd:YAG laser in conjunction with a thermionic diode ion detector. The photoionization cross section at the first ionization threshold is measured as 18.8 {+-} 3 Mb and at excess energies of 0.013, 0.106, 0.229, and 0.329 eV is measured as 15, 13.6, 12.6, and 12.5 Mb, respectively. The measured value of the photoionization cross section at the threshold is used to calibrate the oscillator strengths of the 5p {sup 2}P{sub 3/2}{yields}nd {sup 2}D{sub 5/2} (22 {<=}n{<=} 52) Rydberg transitions.

Photoionization from the 6p {sup 2}P{sub 3/2} state of neutral cesium

We report the photoionization studies of cesium from the 6p {sup 2}P{sub 3/2} excited state to measure the photoionization cross section at and above the first ionization threshold, oscillator strength of the highly excited transitions, and extension in the Rydberg series. The photoionization cross section at the first ionization threshold is measured as 25 (4) Mb and at excess energies 0.02, 0.04, 0.07, and 0.09 eV as 21, 19, 17, and 16 Mb, respectively. Oscillator strength of the 6p {sup 2}P{sub 3/2} {yields} nd {sup 2}D{sub 5/2} (23 {<=} n {<=} 60) Rydberg transitions has been extracted utilizing the threshold value of photoionization cross section and the recorded nd {sup 2}D{sub 5/2} photoionization spectra.