Spectroscopic studies of laser-induced plasma from a high-temperature superconducting material, viz., YBa2 Cu3 O7(YBCO), have been carried out. Electron temperature and electron density measurements were made from spectral data. The Stark broadening of emission lines was used to determine the electron density, and the ratio of line intensities was exploited for the determination of electron temperature. An initial electron temperature of 2.35 eV and electron density of 2.5 X 10 17 cm-3 were observed. The dependence on electron temperature and density on different experimental parameters such as distance from the target, delay time after the initiation of the plasma, and laser irradiance is also discussed in detail.

/pdf/temporal-and-spatial-behavior-of-electron-density-and-54wexewrsv.pdf

Temporal and Spatial Behavior of Electron Density and Temperature in a Laser-Produced Plasma from YBa2Cu3O7

Probe beam deflection is used for identification of the laser fluence threshold for excimer laser photoablation of various materials. The beam deflection signal due to an acoustic wave and a thermal wave are both distorted as the excimer laser beam fluence is raised through the ablation threshold.

Laser beam deflection as a probe of laser ablation of materials

Organic polymers form a class of organic molecules of considerable technological importance in the field of materials processing. For this reason, their interactions with laser radiation have attracted attention from diverse groups of scientists who have studied these interactions from perspectives that have ranged from applied physics to surgery. Since the general field of ultraviolet-laser interactions with organic polymers has been reviewed more than once in recent years, it is the intention of this review to concentrate on developments that have taken place over the last five years and to include infrared-laser interactions with polymers in order to compare results which were obtained using different wavelengths of the laser.

Interaction of Laser Radiation with Organic Polymers

Polytetrafluroethylene (PTFE) and other biocompatible polymers have been extensively used for sutures, vascular grafts and bone, and other hard tissue replacements. The use of surgical lasers for intervention on teflon-tissue interfaces has attracted a great deal of interest, as both the high intensity pulsed lasers and prosthetic biomaterials are in increasing use. The study of the ablational behaviour of PTFE films with three surgical lasers (CO2, Nd-YAG and XeCl) have been undertaken for assessing the optimal laser parameters for ablation (e.g. the absorption coefficient and the relevant threshold fluence) from ablation rate measurements.

Ultra-violet and Infra-red Laser Ablation Studies of Biocompatible Polymers

Ablation of bulk polycrystalline zinc in air is performed with single and multiple picosecond laser pulses at a wavelength of 1030 nm. The relationships between the characteristics of the ablated craters and the processing parameters are analyzed. Morphological changes of the ablated craters are characterized by means of scanning electron microscopy and confocal laser scanning microscopy. Chemical compositions of both the treated and untreated surfaces are quantified with X-ray photoelectron spectroscopy. A comparative analysis on the determination of the ablation threshold using three methods, based on ablated diameter, depth and volume is presented along with associated incubation coefficients. The single pulse ablation threshold value is found to equal 0.21 J/cm2. Using the calculated incubation coefficients, it is found that both the fluence threshold and energy penetration depth show lesser degree of incubation for multiple laser pulses.

/pdf/picosecond-pulsed-laser-ablation-of-zinc-crater-morphology-10ky0p8n80.pdf

Picosecond-pulsed laser ablation of zinc: crater morphology and comparison of methods to determine ablation threshold.

The acoustic signals generated in solids due to interaction with pulsed laser beam is used to determine the ablation threshold of bulk polymer samples of teflon (polytetrafluoroethylene) and nylon under the irradiation from a Q-switched Nd:YAG laser at 1.06µm wavelength. A suitably designed piezoelectric transducer is employed for the detection of photoacoustic (PA) signals generated in this process. It has been observed that an abrupt increase in the amplitude of the PA signal occurs at the ablation threshold. Also there exist distinct values for the threshold corresponding to different mechanisms operative in producing damages like surface morphology, bond breaking and melting processes at different laser energy densities.

/pdf/evaluation-of-laser-ablation-threshold-in-polymer-samples-3lnrcyi1dp.pdf

Evaluation of laser ablation threshold in polymer samples using pulsed photoacoustic technique

Absorption spectra of formaldehyde molecule in the gas phase have been recorded using photoacoustic (PA) technique with pulsed dye laser at various power levels. The spectral profiles at higher power levels are found to be different from that obtained at lower laser powers. Two photon absorption (TPA) is found to be responsible for the photoacoustic signal at higher laser power while the absorption at lower laser power level is attributed to one photon absorption (OPA) process. Probable assignments for the different transitions are given in this paper.

https://dyuthi.cusat.ac.in/xmlui/bitstream/handle/purl/2487/dyuthi-p0283.pdf?sequence=3

Photoacoustic detection of two photon absorption in formaldehyde using pulsed dye laser

Observation of laser induced two-photon photoemission optogalvanic (TPPOG) effect from tungsten electrode in a discharge cell using 564 nm radiation obtained from a pulsed dye laser is described. The magnitude of the POG signal is studied as a function of laser energy under various discharge parameters. Competition between one-photon and two-photon processes has been observed when nitrogen gas is used in the discharge cell.

/pdf/observation-of-two-photon-induced-photoemission-optogalvanic-1c4wl27t5y.pdf

Observation of two-photon induced photoemission optogalvanic effect

Laser induced plasma emission spectra from highTc superconducting samples of YBa2Cu3O7 and GdBa2Cu3O7 obtained with 1.06µm radiation from a Q switched Nd:YAG laser beam has been analysed. The results clearly show the presence of diatomic oxides in addition to ionized species of the constituent metals in the plasma thus produced.

Spectral features of laser induced plasma from YBa2Cu3O7 and GdBa2Cu3O7 highT c superconductors

The spectroscopic analysis of the emission from the plasma produced by irradiating a highTc superconducting GdBa2Cu3O7 target with a high power Nd:YAG laser beam shows the existence of the bands from different oxides in addition to the lines from neutrals and ions of the constituent elements. The spectral emissions by oxide species in laser-induced plasma show considerable time delays as compared to those from neutral and ionic species. Recombination processes taking place during the cooling of the hot plasma, rather than the plasma expansion velocities, have been found to be responsible for the observed time delays in this case. The decays of emission intensities from various species are found to be non-exponential.

/pdf/characteristics-of-laser-induced-plasma-from-hightc-nijqkw7fq9.pdf

G Padmaja

Papers

Evaluation of laser ablation threshold in polymer samples using pulsed photoacoustic technique

Photoacoustic detection of two photon absorption in formaldehyde using pulsed dye laser

Observation of two-photon induced photoemission optogalvanic effect

Spectral features of laser induced plasma from YBa2Cu3O7 and GdBa2Cu3O7 highT c superconductors

Characteristics of laser-induced plasma from highTc superconductor