Fast imaging of laser-blow-off plume:Lateral confinement in ambient environment

The dynamics of plasma plume, formed by the laser-blow-off of multicomponent LiF-C thin film under various ambient pressures ranging from high vacuum to argon pressure of 3 Torr, has been studied using fast imaging technique. In vacuum, the plume has ellipsoidal shape. With the increase in the ambient pressure, sharp plume boundary is developed showing a focusing-like confinement in the lateral space behavior in the front end, which persists for long times. At higher ambient pressure (> 10−1 Torr ), structures are developed in the plasma plume due to hydrodynamic instability/turbulences.

Influence of ambient gas on the temperature and density of laser produced carbon plasma

The effect of ambient gas on the dynamics of the plasma generated by laser ablation of a carbon target using 1.06 μm radiation from a Q-switched Nd:YAG laser has been investigated using a spectroscopic technique. The emission characteristics of the carbon plasma produced in argon, helium and air atmospheres are found to depend strongly on the nature and pressure of the surrounding gas. It has been observed that hotter and denser plasmas are formed in an argon atmosphere rather than in helium or air as an ambient.

Twin peak distribution of electron emission profile and impact ionization of ambient molecules during laser ablation of silver target

Laser-induced plasma generated from a silver target under partial vacuum conditions using the fundamental output of nanosecond duration from a pulsed Nd:yttrium aluminum garnet laser is studied using a Langmuir probe. The time of flight measurements show a clear twin peak distribution in the temporal profile of electron emission. The first peak has almost the same duration as the laser pulse while the second lasts for several microseconds. The prompt electrons are energetic enough ('60 eV) to ionize the ambient gas molecules or atoms. The use of prompt electron pulses as sources for electron impact excitation is demonstrated by taking nitrogen, carbon dioxide, and argon as ambient gases.

Effect of ambient gas on the expansion dynamics of plasma plume formed by laser blow off of thin film

A study has been carried out to understand the influence of ambient gases on the dynamics of laser-blow-off plumes of multi-layered LiF–C thin film. Plume images at various time intervals ranging from 100 to 3000 ns have been recorded using an intensified CCD camera. Enhancement in the plume intensity and change in size and shape occurs on introducing ambient gases and these changes are highly dependent on the nature and composition of the ambient gas used. Velocity of the plume was found to be higher in helium ambient whereas intensity enhancement is greater in argon environment. The plume shapes have maximum size at 10−2 and 10−1 Torr of Ar and He pressures, respectively. As the background pressure increases further (>10−2 Torr: depending on the nature of gas), the plume gets compressed/focused in the lateral direction. Internal structure formation and turbulences are observed at higher pressures (>10−1 Torr) in both ambient gases.

Induction of mitotic aberrations by Argon ion lasers in Vicia faba L. and Allium cepa L.

A comparat ive study of the effect oflaser in inducing chro mosomal aberrat ions at 4gg nm was done in View j aba L. (faba bean) and Allium ccpa L. (onion) with Argon ion laser (Spectra Physics Model 171). Seeds and bulbs of V.jaba and A. eepa were subjected to laser irra diation by 4gg nm excitations from Argon ion laser source at power levels 200 and 400 mW with power densities 2.25 mW em" and 4.49 mW em" and ditTerent exposure times (10, 20, 30 & 40 minutes). Similar to the effect of oth er physical and chemical mutagens, laser caused a dose dependent decrease in mitotic index and a rise in mitotic aberrations when compared to the control. In both plant species, mutations were observed in all stages of mitotic cell cycle. The total percentage of aberrations was two fold higher at 400 mW than at 200 mW exposure.