LASER PRODUCED

PLASMASMuhammad Adeel

09050610-041

What is Plasma?

• Quasi neutral gas which exhibits collective behaviour.

• it is believed to comprise more than 99% of our visible

universe.

• Plasma can also be formed when an exterior source of

energy, like an electromagnetic field, is so strong that it

tears electrons free from originally neutral atoms. The

conversion of a neutral gas into a plasma can occur

extremely quickly.

Shielding of a Plasma by a Magnetic Field

Laser Produced Plasma Technology

Basic concepts

Typical temperature, density and expansion velocity profiles

of a plasma generated by irradiation of a solid target by a

nanosecond laser pulse focused on target at an irradiance of

10^14 W/cm2

• The propagation of laser light in the plasma is dominated by the presence of free electrons, and

follows the dispersion relation

• Where

• The group velocit decreases as the electron density increases

• An estimate of the temperature of laser produced plasmas can be obtained by equating

the absorbed laser intensity I absto the electron heat flux

• Solving for the temperature gives

that for typical parameters I abs = 10^13

W/cm^2 , f = 0.1 , ne=10^21cm^-3, gives

Te=0.6keV

• blow-off velocity is roughly equal to the

local sound speed

Typical values for the blow-off velocity range

between 10^7and 10^8 cm/sec

. In the general case, such a scale length is given by

where T and phi are the laser length and the focal spot diameter on the target

The Debye screening length,

the Debye sphere is very high,

Applications Of Laser Produced Plasmas:

• Laser-produced plasmas in medicine

• Laser-produced plasmas as unique x-ray souces for

industry and astrophysics

• Application of laser produced plasma K alpha x-ray

probe in radiation biology.