ravi ranjan physics term paper final

8/8/2019 Ravi Ranjan Physics term paper final

http://slidepdf.com/reader/full/ravi-ranjan-physics-term-paper-final 1/18

TERM PAPER

OF

PHYSICS

Topic:- Laser PlasmaInteraction.

Submitted To

Submitted By:-

Mr. Amit Bindra RaviRanjan



RF1001

RF1001A61

ACKNOWLEDGEMENT

I am a student of lovely professional university and I am preparing a term paper on topic Laser Plasma Intercation. Patience & perseverance is the part & parcel to make fulfill any desiredmotto successfully. Not only this two indispensable characters but also kind co-operation & zestful help are always required bydint of which one can be able to reach his ultimate goal after passing through a series of several incidents. Likewise I do havethe pleasure to expose that we have completed our first semester

term paper with grand success. So, at the very outset I deeplyfeel like expressing me indebtness and gratitude to allconcerned, unless who’s help, valued suggestions, guidance andmoral boosting, the pursuance of the work of mine would havenot been possible. In the beginning, I also do take theopportunity to acknowledge and honour the contribution of mylecturer and class teacher Mr. Amit Bindra, who hasguided me all along by his wise lead, benevolent direction,

suggestions and time worthy interaction with me. I’m alsothankful to the Info Tech department of the university. I wouldlike to call up all our faculty members whose essential guidance& whole hearted devotion really inspired me as well as helpedtoo in the fulfillment of my desired task.

Finally, my special thanks go to our honorable & respected

Executive Dean Mrs Rashmi Mittal for providing me with all

the facilities in pursuing my term paper.

-Ravi Ranjan



Introductio

n

Intense Laser-Plasma

Interactions... .TheInstitute's research inintense laser-plasmainteractions focuseson understanding,and eventuallycontrolling, the

plasma response,which can be usedfor compactaccelerators for fundamental researchand medicalapplications.This effort involvesdeveloping physicalmodels that representthe salient plasmafeatures, realisticallydescribing the laser structure, and

building numericalalgorithms thataccurately solve thegoverning equations.We have been the

leaders in bringingnovel approachesand fresh ideas tothese challengingquestions.

Over the last twoyears, we havedeveloped an entirely

new collisionlesskinetic model todescribe the low-temperature nature of the plasma. Our model has a finite pressure force termthat evolves in anovel way; theequations governingthe pressureevolution areconsistent withordinarythermodynamics inthe equilibrium limit, but contain highlynon-equilibriumeffects resulting fromthe collisionlessnature of the plasma.



With our new model,we are beginning tostudy the finitetemperature effects

on the evolution of the laser pulse and plasma wake; our preliminary resultsindicate that the plasma does not heatsignificant in theshort-pulse case, andthat long pulses can

heat the plasma, butnot significantly.

These results aresignificant becausethey indicate that thecold-fluidapproximation is avery good model for the plasma wake, and

that particle-in-cell(PIC) numericalmethods have verystringentcomputationalconstraints to controlthe grid-heatinginherent in themethod.

Augmenting our

physical modeling,

we have examinedseveral new

numerical methods

for solving the model

equations. We have

looked at explicit

higher-order method-

of-lines techniques

and have seen performance

improvements

anywhere from a

factor of 6 to 100,

depending on the

type of problem.

This performance

improvement arisesmostly from the

increased size of the

stability region,

allowing us to use a

much larger time

step.

We have made

extensive use of symbolic methods to

carry out our analysis

of these methods,

and we are working

to extend this work

to implicit methods.

Over the next two

years, we will usethe tools we have

developed so far to

investigate two



critical questions:

"What is the

maximum electric

field a plasma can

support?" (known asthe "wave-breaking

limit" ) and "Where

do the trapped

electrons come

from?" These

questions are

fundamental to

accelerator design because they drive

directly to the

energy, efficiency

and quality of the

beam produced.

Applications

Of Laser-

PlasmaInteractions

Recent advances inthe development of lasers with greater power and brightnessare paving the way

for importantadvances, including potential solutions tothe energy crisis.

Focusing exclusivelyon applications, this

second volume toInteraction of HighPower Lasers withPlasmas will be of interest toresearchers in boththe biologicalsciences and solid-state physics. It

analyzes differentinertial confinementschemes, and theability of lasers,while interactingwith plasmas, toefficiently producehigh power x-raysources. The high power, short pulseduration, and smalldimensions that areattainable in laser- plasma interactionslends itself to thedevelopment of sometruly uniqueapplications.

Monoenerg

etic beam

of

electrons

from laser

plasmaHigh-powerlasers that fitinto a university-



scalelaboratory1 cannow reachfocused

intensities of more than 1019W cm-2 at highrepetition rates.Such lasers arecapable of producingbeams of energeticelectrons2, 3, 4,5, 6, 7, 8, 9, 10,11, protons12and -rays13.Relativisticelectrons aregeneratedthrough thebreaking9, 10,14 of large-amplituderelativisticplasma wavescreated in thewake of the laserpulse as itpropagatesthrough aplasma, orthrough a directinteractionbetween thelaser field andthe electrons inthe plasma15.However, the

electron beamsproduced fromprevious laser–plasma

experimentshave a largeenergy spread6,7, 9, 14, limitingtheir use forpotentialapplications.

Here we reporthigh-resolutionenergymeasurementsof the electronbeams producedfrom intenselaser–plasma

interactions,showing that—under particularplasmaconditions—it ispossible togenerate beamsof relativistic

electrons withlow divergenceand a smallenergy spread(less than threeper cent).

The

monoenergeticfeatures wereobserved in theelectron energy



spectrum forplasma densities

just above athreshold

required forbreaking of theplasma wave.

These featureswere observedconsistently in

the electronspectrum,although theenergy of thebeam wasobserved to varyfrom shot toshot. If the issueof energyreproducibilitycan beaddressed, itshould bepossible togenerateultrashortmonoenergeticelectronbunches of tunable energy,holding greatpromise for thefuture

development of 'table-top'particleaccelerators.

Proton

shock

acceleratio

n

The formation of strong, highMach number(2–3),electrostaticshocks by laser

pulses incidenton overdenseplasma slabs isobserved in one-and two-dimensionalparticle-in-cellsimulations, for

a wide range of intensities, pulsedurations, targetthicknesses, anddensities. Theshockspropagateundisturbed

across theplasma,accelerating theions (protons).For adimensionlessfield strengthparameter

a0=16(Iλ2≈3×1020 Wcm-2 μm2,where I is the



intensity and λthe wavelength),and targetthicknesses of a

few microns, theshock isresponsible forthe highestenergy protons.A plateau in theion spectrumprovides a directsignature forshockacceleration.

PLASMA

LASERS

Coolcircumstellardust and gas isconstantlyaccumulatingaround a starwhich is rapidly

ejecting plasma;the rapid coolingof the plasmawhen itencounters thisshell cansignificantlyenhance the

non-equilibriumeffects of adiabaticexpansion. Gas

contact is soeffective atproducing rapidcooling that Oda

et al. (1987)havesuccessfullyoperated anextremeultravioletplasma laserusing thismechanismalone, withoutthe slightestamount of expansion :

Gas-Contact Cooling Plasma Laser (TPD-I) : Magnetically

stationary helium plasma lasing in XUV 164 nm when th

cooled by hydrogen gas -contact. (Institute of Plasma Ph

Nagoya, Japan).

Another advantage instellar atmospheresare the typically verylarge distance scales,a small populationinversion producesradiation whoseintensity would

exponentially growin amplitude over thelarge distances to the point where itdominates the



spectrum with astrong broademission line. Thestrongest

manifestation of natural lasers occur in quasars.

Another disadvantage of laboratory plasmalasers is erosiondamage.

'IT IS ALL

DONE WITH

MIRRORS':-

In laboratoryplasma lasersthe lasingmedium is of necessity limitedto small scalescompared toastrophysical

lasers. Thisdrawback ispartlycompensated bythe advantagethat we canplace mirrors atboth ends of the

lasing mediumto produce alaser whichseems to be

much longer ineffective 'virtual'extent. Byrepeatedly

bouncing off themirrors thephotons makemany back andforth passes,effectivelylengthening thelasing medium.Place yourself between a pairof parallelmirrors and seeinfinitelyrepeated imagesof yourself, untilyou can nolonger see theimages due tothe greenishabsorption of theglass and finitereflectivity of themirrors.

Placing the lasingmedium within a pair of mirrorsalso produces a

Fabry-Perotresonant cavitywhose spectralresponse is



equivalent is theAiry functionconsisting of asequence of cavity'modes'.

Each modecorrespond to anelectromagneticstanding wavewhich can occupythe cavity. With

careful design, thelaser can be madeto oscillate in onlyone of thesemodes whichresults in a highlymonochromaticcollimated beam

with extremelysharp spectralresponse.

NATURALLY

OCCURING,

FUSION

POWERED

PLASMALASERS:-

The maximumnumber of passes than aphoton canmake within a

mirroredlaboratory lasercavity is limitedby absorption

and upper leveldepletion, whichis ultimatelylimited by the

finite amount of energy pumpedinto thepopulationinversion. Theshorter thewavelength thefaster theenergy must bepumped into theupper levels.

Although thereare no mirrors inouter space, nosuch powerrestrictionsoccur inastrophysicalplasma lasers,which arepumped by anenormouslypowerful fusionfurnace.

AMPLIFIED

SPONTANEOUS

EMISSION:-

Even though most

commercial lasers



are designed to

operate within a

cavity and produce

very sharp emission

lines; this is notnecessarily so for

lasers without

mirrors, especially in

astrophysical

environments where

usually the spectral

line is broadened by

Doppler effects,turbulence and rapid

plasma ejections.

The stimulated

emission occurs from

many spontaneous

emissions 'seeds'

simultaneously, i.e.

amplifiedspontaneous

emission; a technical

name for the

phenomena of

cooperative photon

emission in the

absence of mirrors.

Since the

amplification is

exponential over

distance the gain is

strongest along an

axis through which

the longest path

through the plasmacan be attained. If

the plasma is very

elongated the

emission occurs

almost exclusively

along that axis.

100 kilowatt Homebuilt Air Laser : pumped byelectrical gasdischarge, it

produces coherent 337 nm UV radiation

from a molecular nitrogen transition.There are no mirrors

so the laser emitsamplified

spontaneousemission both in the

forward and backward direction simultaneously.(Scientific American

June 1974)



PRACTICAL

USES OF

PLASMA

LASERS:-

HIGH-

POWER,

HIGH-

EFFICIEN

CY

LASERS:-

The simplefact the lasingmedium is a

highly ionizedplasma readilylends itself tovirtually

unlimitedpoweramplification.

High Power

Continuous highpower lasing ispossible byusing thegeometry of aplasmaexpanding awayfrom a nozzle;

since the decayof different partsof the plasmaoccur atdifferent timesthe active lasingportion of the jetis constantly

beingreplenishedwhilesimultaneouslythe depletedlasant is rapidlycarried out of the active zone.

This dualcombination aretwo crucialingredient in



most high powerlasers,

1. Rapid

overpopulation of theupperquantumlevelrelative tothe lowerlevel.

2. Rapid de-

populationof the lowerlasing levelbytransport of depletedplasma outof theactive

lasingmedium.

High

Efficienc

y:-

High power can

be achievedsimultaneouslywith highefficiency by asuitable choiceof initial plasmaparametersbefore the rapid

cooling takesplace : In certaintemperatureranges the

thermodynamicpopulation of certain ionspecies is almost

exclusivelydominated bythe ionconsisting of aclosed electronshell.

The ionization

energy of aninert-gas likeelectronconfiguration ismuch largerthan the energyrequired toionize less stable

configurations. The inert gas-like stage of ionizationpersists over amuch largerrange of temperatures,

and for certainparticulartemperaturesthe competingionic stageshave negligibleconcentrations.

During the rapidcooling stage, almostall of these stable'parent' ions withinthe plasma contribute



to the rapid three- body recombinationof the free-electronsinto the upper laser

level. This meansthat every ion inthe plasma can potentiallycontribute astimulated photonto theamplification

process.The extent towhich the excitedions cancoherentlyamplify the lightis limited only byunwantedspontaneousemissions, and therequirement of maintaining asuitable inversionrate for thespecific ratio of stimulatedemission versusspontaneousemissions that the particular applicationrequires.

The potential for high efficiency,unlimited power lasers isenormous, and its practical uses inindustry are toonumerous tomention here.

Laser Plasma

Interactions &

Related

Diagnostic

s:-

Thomson scattering

is widely used tomeasure plasmatemperature, density,and flow velocity inlaser-produced plasmas at Trident,and is also used todetect plasma wavesdriven by unstable

and nonlinear processes. A typicalconfiguration uses alow intensity laser beam (2nd, 3rd, or 4th

harmonic of 1054-nm) to probe a plasma volume.

The Thomson

scattered light iscollected by a lensand is measuredusing a spectrometer



coupled to a gated or streaked camera. Therange of plasmawave numbers

probed is determined by the Thomson probe beamwavelength andscattering geometry.

Thomson scatteringis routinely used atTrident in variousconfigurationsincluding self-Thomson scattering,imaging Thomsonscattering, streakedThomson scattering,and to obtain “ω-k” plasma wavedispersion. TheThomson scattered

spectrum can bemeasured withtemporal resolution ~10 ps, spatialresolution ~ 10-µm,and spectralresolution ~ 0.5 Å

Streaked Thomsonscattering fromelectron plasmawaves in a gas jetlaser produced plasma. The probelaser is a 1-ns pulse,followed by three

100-ps pulses. Thetime-dependent plasma density can be deduced from thespectral shifts.

Time-resolved backscattered spectrafrom a N2H2 gas jet plasma experiment,shot number 20040.The narrow spectrumnear 527-nm is fromstimulated Brillouinscattering, and the

broad spectrum between 650 – 730nm is fromstimulated Ramanscattering.

Coupling of

the laser beam

energy to agiven target isimportant inboth

fundamental andapplied laser-matterinteraction



experiments. The intense laserbeam can driveparametric

instabilitieswhich scatterlaser lightprimarily in thebackwarddirection,resulting in aloss of laserenergy in thetarget.Measurementsof thebackscatteredlight include thereflected energy,time-resolvedspectra, andtime-integratedangulardistribution of the lightscattered justoutside the lens(nearbackscatter).Backscattereddiagnostics canbe deployedboth

for randomphase platesmoothed laserbeams, and the

near-diffraction-limited singlehot spot laserbeam. The

backscatteredlight can bemeasured withtemporalresolution ~ 10ps, and spectralresolution ~ 0.5Å.

Applications

of Laser

Produced

Plasmas:-

The Division hasalso carried out anumber of studieson applications of laser producedplasmas of technological

interest. Theseinclude :characterization of x-ray source for contact imaging, x-



ray microscopicimaging of biological cells andphysical

microstructureswith a spatialresolution better than 200nm,developingstereoscopic x-rayimaging techniqueusing twin laser produced plasmas,

spectral distributionof keV x-ray yieldfrom gold plasma,laser drivenmonochromatic x-ray point source of short-pulseduration in a diodeconfiguration,generation of high

current densityelectron pulsesfrom laser drivenferroelectrics, laser driven vacuumdischarge, andanalysis of isotopicenhancement inlaser plasma

plumes.



Refrences:- 1. Wikipedia.org2. Answers.com

ravi ranjan physics term paper final

Documents