Riju, C Issac; Harilal, S S; Bindhu, C V; Geetha K, Varier; Nampoori, V P N; Vallabhan, C P G(Elsevier, 1997)
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Abstract:
A laser produced plasma from the multielement solid target YBa2Cu3O7 is generated using 1.06 μm, 9 ns pulses from a Q-switched Nd:YAG laser in air at atmospheric pressure. A time resolved analysis of the profile of the 4554.03 Å resonance line emission from Ba II at various laser power densities has been carried out. It has been found that the line has a profile which is strongly self-reversed. It is also observed that at laser power densities equal to or exceeding 1.6×1011 W cm−2, a third peak begins to develop at the centre of the self-reversed profile and this has been interpreted as due to the anisotropic resonance scattering (fluorescence). The number densities of singly ionized barium ions evaluated from the width of the resonance line as a function of time delay with respect to the beginning of the laser pulse give typical values of the order of 1019 cm−3. The higher ion concentrations existing at smaller time delays are seen to decrease rapidly. The Ba II ions in the ground state resonantly absorb the radiation and this absorption is maximum around 120 ns after the laser pulse.
Riju, C Issac; Vasudevan Pillai, K; Harilal, S S; Geetha K, Varier; Bindhu, C V; Pramod, Gopinath; Radhakrishnan, P; Nampoori, V P N; Vallabhan, C P G(Elsevier Science, 1998)
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Abstract:
Laser produced plasma from silver is generated using a Q-switched Nd:YAG laser. Optical emission spectroscopy is used
to carry out time of flight (TOF) analysis of atomic particles. An anomalous double peak profile in the TOF distribution is
observed at low pressure. A collection of slower species emerge at reduced pressure below 4 X lO-3 mbar and this species
has a greater velocity spread. At high pressure the plasma expansion follows the shockwave model with cylindrical
symmetry whereas at reduced pressure it shows unsteady adiabatic expansion (UAE). During UAE the species show a
parabolic increases in the expansion time with radial distance whereas during shock wave expansion the exponent is less
than one. The angular distribution of the ablated species in the plume is obtained from the measurement of optical density of
thin films deposited on to glass substrates kept perpendicular to the plume. There is a sharp variation in the film thickness
away from the film centre due to asymmetries in the plume.
Harilal, S S; Issac, Riju C; Bindhu, C V; Nampoori, V P N; Vallabhan, C P G(Pramana, September , 1997)
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Abstract:
Time resolved optical emission spectroscopy is employed to study the expansion
dynamics of C2 species in a graphite plasma produced during the Nd : YAG ablation. At low laser
fluences a single peak distribution with low kinetic energy is observed. At higher fluences a twin
peak distribution is found. It has been noted that these double peak time of flight distribution splits
into a triple peak structure at distances >_ 17mm from the target surface. The reason for the
occurrence of multiple peak is due to different formation mechanisms of C2 species
Geetha K, Varier; Issac, Riju C; Harilal, S S; Bindhu, C V; Nampoori, V P N; Vallabhan, C P G(Elsevier, 1997)
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Abstract:
The laser produced plasma from the multi-component target YBa2CU3O7 was analyzed using Michelson interferometry and time resolved emission spectroscopy. The interaction of 10 ns pulses of 1.06 mum radiation from a Q-switched Nd:YAG laser at laser power densities ranging from 0.55 GW cm-2 to 1.5 GW cm-2 has been studied. Time resolved spectral measurements of the plasma evolution show distinct features at different points in its temporal history. For a time duration of less than 55 ns after the laser pulse (for a typical laser power density of 0.8 GW cm-2, the emission spectrum is dominated by black-body radiation. During cooling after 55 ns the spectral emission consists mainly of neutral and ionic species. Line averaged electron densities were deduced from interferometric line intensity measurements at various laser power densities. Plasma electron densities are of the order of 1017 cm-3 and the plasma temperature at the core region is about 1 eV. The measurement of plasma emission line intensities of various ions inside the plasma gave evidence of multiphoton ionization of the elements constituting the target at low laser power densities. At higher laser power densities the ionization mechanism is collision dominated. For elements such as nitrogen present outside the target, ionization is due to collisions only.