Laser Plasma Interaction - Science topic

This seems like an odd question. There is no physical quantity that is the average of the orthogonal fields, so why would you want to plot that? In two dimensions (for example if you have a planar wave front) the field must be described by two linearly independent components. Those could be Ex and Ey, or some other basis. However, whatever the choice of basis, the two components are orthogonal and completely independent. Any physical behavior that depends linearly on the field generally has to be evaluated twice using the independent quantities. Jones vectors and matrices provide a convenient notation for keeping the two calculations together (and handling components that link them, such as retarders) through linear algebra. Scalar quantities, like intensity, are single valued combinations of the two independent fields, but they are never linear in the field, so they are never built from the average of the two fields.

in three dimensions (say, in the case of a non-planar wave front). Things are more complicated. However, at the root, that is just adding in another independent orthogonal dimension to the field description.

Anyhow, assuming you have a reason to want to plot the average the field, you should have no trouble plotting it. Once you perform the average the result is just a 2D matrix of values. You can plot a 2D map where the color scale represents the value using “imagesc “. Or you can plot a contour map using “contour”.

On the other hand, if you don’t want to average and want to plot something more meaningful, a common choice is a polarization pupil map. At points on a regular grid across the beam you plot ellipses representing the field strength and polarization at each point. There isn’t a super simple function for this, but it’s not too hard. Use “hold” to allow multiple plots on the same plot. “annotate(‘ellipse‘, …) is one approach. Another is to make your own sub function to parametrically describe an ellipse as a pair of x, y vectors which you then plot using “plot”. Some people let the size of the ellipses represent the field strength. Others normalize the ellipse size to make the polarization state more clear and plot the ellipses on top of an intensity map. (I.e. Calculate and plot the intensity with “imagesc”, and then use “ hold” to plot the ellipses on the same axes.

Dear

You can benefit from this valuable article about your topic:

"Create Your Own Plasma PIC Simulation (With Python)"

@https://medium.com/swlh/create-your-own-plasma-pic-simulation-with-python-39145c66578b

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Also this one:

"2D laser step by step tutorial in python"

@https://smileipic.github.io/tutorials/advanced_wakefield.html

I hope it will be helpful..

Best wishes...

Hello,

If you want to study electron acceleration in plasma, as Laser Wakefield Acceleration, using PIC code, I suggest the following open-source code:

- SMILEI: https://github.com/SmileiPIC/Smilei

- Large number of PIC code from UCLA group: https://github.com/UCLA-Plasma-Simulation-Group

Thanks

You can see the database of the Paris obervatory (Stark-B):

http://stark-b.obspm.fr

LIBS is a spectroscopic technique capable of doing many tasks. As already stated in the previous answers, it can measure plasma temperature and electron density. They can give a good characterization figures of the plasma. This plasma (LIBS) can be used to perform the direct chemical characterization of solid samples without prior sample preparation. LIBS can also be used for nano-material preparation under liquid to be an environmentally friend preparation procedure. LIBS has many other applications in science and technology.

Forget it. The packages available do not have the kinetic physics to model an intense laser-plasma interaction.  For this you need something like LSP (http://www.lspsuite.com/LSP/index.html) a PIC code which can do fluid and kinetic together. Pure kinetic should work, but does not scale up well (lots of processor time needed). How big is your problem (physical size and temporal scale)? This will determine what type of code you can run.

There are several other PIC (particle in cell) codes out there, many groups might let you use it for free, just ask the developer. Groups that develop and maintain their own codes are UCLA (OSIRIS), Berkeley (OOPIC, free), UNR (PICLS), Berkeley Lab (WARP and others), HZDR (PIConGPU) . LANL (VPIC), Tech-X (VORPAL) and many others.  Or you can write you own! :-) https://arxiv.org/ftp/arxiv/papers/1104/1104.3163.pdf 

Good luck!

Dear Mauro:

Thanks for answer.

Do you know a formula to calculate pulse duration after stretching?

I have studied the ablation of metallic targets (see my articles if you want) , what I can tell that to produce thin films without droplets you have to avoid phase explosion and to choose fluence above the threshold of evaporation. Thin films with good quality are synthesize in evaporation regime.

In phase explosion you have an homogeneous nucleations of bubbles on the surface target that lead to the formation of droplets on the thin films.

In PLD the stoichiometry is conserved generally. There are several articles proving that. YBaCu is the most cited in the litterature for congruent transfer between the target and the thin film.

In general every plasma can be inhomogenious and thus have spatial dependent refractive index fields (I was assuming a homogenious plasma, because if the plasma is inhomogenious the trivial answer is that you cannot do anything about focussing or defocussing as the electron density changes from point to point and hence also the refractive index - that can usually be not compensated by any power modulation of your beam).

Secondly not every nonlinearity does automatically lead to a refraction of your beam. Furthermore first you wrote that the beam has to have enough energy that the non linearities of the plasma come into play and then you claim that it is this non linearities, which (de)focus the laser beam - this is not really stringent.

The power and the timescale of the laser beam are also correlating, because due to energy conservation it holds that the shorter the beam temporally (at a given pulse energy) the higher is the power, you can deposit. However, non linearities come into play per definition at high amplitudes of your electromagnetic fields (the type of non linearity is hereby secondary).

So, you cannot say that you have just to go to higher laser powers in order to avoid self (de)focusing of your beam. Also the power density per unit area of the beam is proportional to the |E|² of your laser, which I also covered in my first post here.

So, in conclusion I want to emphasise again, the straight forward way to avoid optical effects in a plasma is to use a laser beam with small wavelength, low energy and a profile with maximum homogenity.

1. The Physics of Laser Plasma Interactions by W. L. Kruer, Westview, 2003, ISBN 0813340837, 9780813340838.

2. A Superintense Laser-Plasma Interaction Theory Primer, Andrea Macchi, Publisher Springer Science & Business Media, 2013, ISBN 9400761252, 9789400761254

I may have an explaination.  When laser light processing metal specimen, photon "hit"  electron at the surface first. Electron got hited get kinetic energy which drive it away from surface to inner part of the metal specimenor just emit. During which, the running elctron will hit other electron or lattice. The hitting will accrelrate both electron and lattice vibration. that is how energy of laser turn into heat. There are free electron inside metal. so the hitting between electrons play the major role in enery transpot.

The ground (earth) could be considered as a very large negative electrode which will provide infinite amont of (cold, slow moving) electron.

PS： if my theory fit, the smaller specimen is ,the bigger difference  maybe detected.

I hope this wil help.

Hi Sajjad!

The method of polymerization you're talking about involves free radical polymerization wherein a free radical is generated, and such radical initiates the polymerization reaction. You could easily find the mechanism online.

To answer your question, free radical polymerization can involve many unwanted side reactions such as chain transfer reactions where there is a premature termination of polymerization due to the radical interacting with the solvent, other radical initiators, or even molecules in the air.

As such, the main concern in conducting such grafting technique would be to minimize these side reactions and increase chances that the free radical formed would interact with the monomer of your choice.  This might include atmosphere and temperature control.

Going back, for the first method, wherein you irradiate the polymer with the monomer (simultaneous), you form free radicals and the radicals allow for polymerization of the monomer and polymers.

For the second method, wherein you irradiate the polymer, then submerge the irradiated polymer in a monomer solution (consecutive), you form free radicals in the polymer first (preirradiation), then allow for the radicals to interact with monomers in solution after.

Both methods have their own advantages and disadvantages, depending on your system.  Just remember to keep your focus on the radicals formed and making sure it reacts with the right molecules.

I also found an article which you might find helpful. 

Cheers! :)

The vertikal and horizontal size of the source depends on your geometry, e.g. the incident angle of the laser, the observation angle and also the roughness of your targetmaterial.

I have studied this issue for many years. There were also many studies that have all made different partial responses. You will find a review of these studies in the article that was reported by G. Ermolaeev earlier in this discussion, and references attached to it. To answer the original question by R. Seidgazov, and trying to be brief, I will say that the improvement of the penetration depth is mainly the result of two phenomena: the first one is the decrease in the evaporation temperature (which is the order of 1000K) when the ambient pressure is reduced. This is of course a result of the equilibrium between the metal vapor and liquid (the well-known Clausius Clapeyron law). It is easy to show (using heat balance equations) that when the evaporation temperature decreases (which corresponds to the temperature of the walls of the keyhole), the incident laser power can be distributed over a greater depth.

The second effect explaining the increase of the keyhole depth is due to the decrease of the screening processes of the laser radiation through the metallic vapors (inside of the keyhole and externally, in the vapor plume) generated by the evaporation process: When a CO2 laser is used (10.6 micron wavelength), the laser radiation is absorbed by the effects of Inverse Bremsstrahlung, because the metal vapor is hot and ionized, and the wavelength is large (see reference 4 the aforementioned paper). When using the present solid state lasers (1.06 micron wavelength), absorption by Inverse Bremsstrahlung becomes negligible, but it is then the scattering processes (Rayleigh and Mie) that appear on the aggregates, clusters or micro-droplets inside the vapor, which become dominant and cause the propagation of laser radiation to be limited. When the ambient pressure decreases, such adverse effects decrease because of the decrease of the vapor density (electronic, for CO2 lasers or aggregates for solid state lasers), and therefore we gain a deeper penetration keyhole.  

I can also tell you about the limitation of the observed increase in the keyhole depth with the reduction of ambient pressure or the increase of the welding speed. These results are the subject of a paper that I will present to the next Icaleo Conference in October (I can send it to those who are interested, but I will also put it on RG).

1)  In the literature, the generation of x-ray hotspots due to Small Scale Filamentation Instabilities (SSFI) are reported in the laser intensity regime 10^14-15 W/cm^2. References below

R1_ Observations of instabilities in the corona of laser produced plasmas by Willi.O et al 41 110 (1982)

R2. An important effect of filamentation instability on laser fusion,  Z.Lin et al.  High Power Laser Sci and Engg 1 110-122 (2013).

These works report and explain generation of  >1.5 keV X-ray hotspots (for 10¹³ W/cm²)  in the plasma / corona  region .

2)  It is also known that the x-ray radiation from these hotspots will travel towards the target. This is seen in the rear side x-ray emission studies in case of foil targets by Herbst et al

R3_ Evidence from X-ray, 3/2 wo and 2wo Emission for Laser Filamentation in a Plasma in PRL 46 328 (1981).

Probably (thinking) the channels seen in our experiments are caused because of these x-rays. As the intensity goes to 2x10¹⁴ W/cm² the energy of x-ray hot spots may go up to 10 keV which will have attenuation lengths of few hundreds of microns.  This looks like a possibility.

3) In the shadowgram given below some indications are present (not in all snaps) showing a mild diverging trend is seen if you take the whole bundle of channels as a whole. And as you proceed further you see only the central part (on axis) indicating higher energy x-ray component where as on the periphery, it is getting attenuated faster indicating slightly lower energies.

This looks like a possibility at present. But I will appreciate if   some other advice / opinion / suggestion about this.

Shamim Ahsan, it's not true in general. Your objective may not match your input beam size or not antireflection coated for your wavelength. Power is not disappearing without a good reason ;)

Square root rule works good for nanosecond range. For femtosecond range it gives wrong results. LIDT (in J/cm2) reduces more slow, than square root rule predict. For 80-200 fs LIDT is about 0.1-0.5 J/cm2. You could surf scientific journals rather than ask people at researchgate.net.

This is quite a difficult task and is topic of current reseasch efforts.

First of all, it must be said that for a plasma jet propagating freely, without interaction with a substrate, there will be no "beam" of ions with a defined energy, but actually it will be better described by a distribution of energy. When a substrate is put in contact with the jet, an accelerating sheat may be formed, and the ion energy distribution function may be distorted. So the first thing one must have in mind in this case is that what should be measured is the ion energy distribution function (IEDF). It may happen to be sharp and peaked, but this is not always the case.

The second part to this answer is more practical: can I measure this IEDF? Yes, it is possible, and I know at least one method, but which have its drawbacks. The plasma jet may be put in contact with a very small sampling orifice, whose diameter should be not larger than 10 \mu m. The plasma particles are collected and then expanded trough some differential pumping stages, focused and accelerated into a energy analyzer in a UHV environment. In order to analyze only helium particles, one should place a mass filter after it. A SEM detector would suffice to count the particles. Many details and cautions must be taken when building such apparatus or even using commercial equipment, such as Hiden products. One of the main drawbacks of this apparatus is the fact that the sampling material interacts with the plasma, producing a sheath and distorting the IEDF. One may try to use a dielectric material similar to the substrate of the application of interest.

Any other idea or method to measure the plasma IEDF would be welcome and would surely give an important contribution to the field of plasma diagnostics.

fs lasers have very small energy per pulse, making it only possible to ablate very small spots, making very small plasma with little emission. You need a good optical setup and high sensitivity spectrometer, compared to ns LIBS. But the small ablation per pulse can be advantage in some cases like thin layer depth profiling etc. I dont have experience with attosecond laser but I guess its the same

1-  Rayleigh Range: RR ~D²/ lambda, and is proportional to light frequency.

2- Rayleigh Length: Z_R=pi.(W₀)2 / lambda, the distance where area of cross-section is doubled. Area at Z_R is 2 pi W₀. Area  of beam waist is pi W_0. W₀ is  t he beam waist.

Both definition 1 and 2  are the same.

The threshold of SRS is much higher than SBS, hence SBS is most likely occurs. Please check the threshold values available in Boyd - Nonlinear Optics.

Thanks a lot Prof. Vita and  Prof. Sheikhdom-Sabzevari for your responses,  I am researching about what factors can increase the absorption in laser fusion.

I don't think COMSOL can do LPI properly (kinetic effects are not included in the multi-physics package for instance that I know of).  Depending on what you are trying to model, you really need a PIC (particle in cell) code, or a hybrid like Lsp, or a rad-hydro code with a laser package (Draco [http://www.lle.rochester.edu/media/publications/presentations/documents/APS99/Keller_APS99.pdf] or Hydra [http://arxiv.org/pdf/astro-ph/9603116v3.pdf]) . Comsol is for fluids and mechanics applications with RF or low-power lasers  (like industry, not basic science). Look a the modules: (http://www.comsol.com/plasma-module) this one is for plasma processing, or the Optics module (http://www.comsol.com/wave-optics-module), which is clearly suited for low-power non-linear optics, but not high-power laser-matter interactions, nor parametric instabilities. So it clearly depends on your application.  For the later I would recommend LSP (http://www.lspsuite.com/) if you can afford it, or freeware like xoopic if you can't (runs on Ubuntu! :-) http://langmuir.nuc.berkeley.edu/pub/codes/xoopic/), or try collaborating with someone who built their own code.  Or in the end write one yourself, it's not that hard ;-) , though energy conservation is a b*tch. :-) Nice thesis work tho. :-P

I quite agree with the submission of dr. Ikubanni.

please read Atzeni book, the inertial confinement, i think in chapter of 10, EOS was described.

So first SHG can in principle always happen if the material the light is passing has the right nonlinear dipole interaction. The problem is usually the probability is quite small, therefore intensity of the light has to be quite high. With the TEM00* mode it should in principle be possible.

Density and temperature of the plasma are the main parameters to consider, in the past we implemented some very simple models about this:

Laser Ablation of Metals: A 3D Process Simulation for Industrial Applications

Giovanni Tani, Leonardo Orazi, Alessandro Fortunato and Gabriele Cuccolini

J. Manuf. Sci. Eng. 130(3), 031111 (May 12, 2008) (11 pages)

doi:10.1115/1.2917326

G. TANI, L. ORAZI, A. FORTUNATO, G. CUCCOLINI (2007). The influence of plasma plume in laser milling for mold manufacturing. JOURNAL OF LASER MICRO NANOENGINEERING, vol. 2, p. 225-229, ISSN: 1880-0688