Dear Danila,

yes you got that correctly.

The line

  const double PULSE_LENGTH_SI = 5.0e-15; //25.0e-15 / 1.17741;

are confusing comments behind "//" and are *outdated*. I will remove
those for the next release.

Thanks!
Axel

On 04.05.2016 11:45, Khikhlukha Danila wrote:
> Dear Axel,
> thank you for your replay and clarification!
>
> Indeed I'm using release-0.1.2 version. So just to double check let me repeat your answer.
> So PULSE_LENGHT in the laserConfig.param file is the intensity sigma. Which means that for 25fs of intensity FWHM, PULSE_LENGHT = 25fs/k, where k = 2*sqrt(2*log(2))=2.3548. So PULSE_LENGHT = 10.616fs. This matches your answer and comments in the code. However, there is a  line
>  60             const double PULSE_LENGTH_SI = 5.0e-15; //25.0e-15 / 1.17741;
> which is a bit confusing, cause I don't understand the number 1.1774 (and 25.0e-15 / 1.17741 will not give 5.0e-15).
> I'm sorry for being picky however I just want to have a clear picture of the initialization procedure and reading the comments is a good way to get familiar with unknown code.
>
> Once again thanks for your support!
>
> Cheers,
> Danila.  
> ________________________________________
> From: picongpu-users@hzdr.de [picongpu-users@hzdr.de] on behalf of Huebl, Axel [a.huebl@hzdr.de]
> Sent: Wednesday, May 04, 2016 11:05 AM
> To: picongpu-users@hzdr.de
> Subject: Re:  [PIConGPU-Users] laserGaussianBeam initialization
>
> Dear Danila,
>
>
> we cross-checked our implementation and it looks correct.
> We will reference the full derivation in our wiki in the next days.
>
> To give you a non-latex explanation for now:
>
> *laserConfig.param*
>   defined in laserConfig.param you found correctly the variable
> "PULSE_LENGHT" which is as described the sigma of a standard gaussian of
> the intensity.
> (For the experimentalist conversion to FWHM of intensity, see conversion
> factor in the comment.)
>
> *laserGaussianBeam.hpp*
>   In the implementation (great you found it on your own! :) ) we set the
> electric field.
>
> the relation of electric field and intensity sigma's are:
>     sig_Ex^2 = 2 sig_I^2   | * 2
>   2 sig_Ex^2 = 4 sig_I^2
>
> So instead of converting into sig_Ex by sqrt(2) we just implemented
>   ( 2 sig_I) ^ 2 == 4 sig_I^2
>
> for setting the E-field component.
>
>
> Cheers,
> Axel
>
> On 03.05.2016 19:42, Huebl, Axel wrote:
>> Hi Danila,
>>
>> thanks for the question!
>>
>> Which version of PIConGPU you are using?
>> The latest release, 0.1.2, changed the documentation in the
>> laserConfig.param a bit because it was not precise before it.
>>
>>
>> I got your question regarding the temporal envelope (pulse length) of
>> the Gaussian Beam. I actually just fixed it for 2D last year but we can
>> double check tomorrow if the documentation is up-to-date.
>>
>>   https://github.com/ComputationalRadiationPhysics/picongpu/pull/1090
>>
>> So far, great you found the implementation yourself! :) I am missing the
>> sqrt on the first view, too but let us check tomorrow.
>>
>>
>> Cheers,
>> Axel
>>
>> On 02.05.2016 13:06, Khikhlukha Danila wrote:
>>> Hi
>>> all,
>>>
>>>
>>>
>>> I have a couple of short questions regarding the Gaussian beam
>>> initialization.
>>>
>>>
>>> 1. As far as I understood from the code comments
>>> (simulation_defines/param/laserConfig.param)
>>> the initialization for laser pulse is done based on the sigma of the
>>> intensity envelope. However in the code
>>> (src/picongpu/include/fields/laserProfiles/laserGaussianBeam.hpp) it
>>> looks like PULSE_LENGTH is the sigma of electrical field envelope.
>>> I also wasn't able to find any conversion (namely
>>> sqrt(2))
>>>
>>>
>>> 2. So at the moment I'm assuming that the initialization of the Gaussian
>>> beam is done based on the sigma of an electrical field envelope.
>>> So if we consider k = 2*sqrt(2*log(2))=2.3548 as a coefficient between
>>> FWHM and sigma of the Gaussian curve
>>> then the coefficient between sigma of an electrical field and FWHM of
>>> the intensity becomes sqrt(2)/k = 0.6006.
>>> However, in comments for laserGaussianBeam it is stated the number
>>> 1./1.17741 = 0.8493 and I'm not sure what is it.
>>>
>>>
>>> Can you please double check if comments are up-to-date? Otherwise I got
>>> something wrong in the description.
>>>
>>>
>>> Thank
>>> you,
>>>
>>> Danila.
>>
>
> --
>
> Axel Huebl
> Phone +49 351 260 3582
> https://www.hzdr.de/crp
> Computational Radiation Physics
> Laser Particle Acceleration Division
> Helmholtz-Zentrum Dresden - Rossendorf e.V.
>
> Bautzner Landstrasse 400, 01328 Dresden
> POB 510119, D-01314 Dresden
> Vorstand: Prof. Dr.Dr.h.c. R. Sauerbrey
>           Prof. Dr.Dr.h.c. P. Joehnk
> VR 1693 beim Amtsgericht Dresden
>
>
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--

Axel Huebl
Phone +49 351 260 3582
https://www.hzdr.de/crp
Computational Radiation Physics
Laser Particle Acceleration Division
Helmholtz-Zentrum Dresden - Rossendorf e.V.

Bautzner Landstrasse 400, 01328 Dresden
POB 510119, D-01314 Dresden
Vorstand: Prof. Dr.Dr.h.c. R. Sauerbrey
          Prof. Dr.Dr.h.c. P. Joehnk
VR 1693 beim Amtsgericht Dresden