[FLASH-USERS] How Laser Break through the Target

[Daniel Barnak]

Hello,

Jonathan Davies, Po-Yu Chang, and I have measured laser burn through of
plastic windows using both FLASH and our own in-house rad-hydro code DRACO.
Specifically, I want to address the idea that the disk undergoes uniform
expansion. This is correct in the model, however empirically has been shown
not to be the case. As a good check, it might be worth your while to read
the paper, simulate a plastic window that's a bit thicker, and compare to
our experimental results. It should give you a good idea as to the
limitation of the predictive capabilities of FLASH.

https://aip.scitation.org/doi/full/10.1063/1.5030107

Cheers,

Dan

Daniel Barnak
Assistant Scientist
Laboratory for Laser Energetics
University of Rochester
250 E River Rd
Rochester, NY 14623-1299
W: 585-276-4332


On Mon, Feb 17, 2020 at 5:26 PM Scott Feister <sfeister at gmail.com> wrote:

> I will *also *add something relevant to FLASH: given the inverse
> Bremsstrahlung physics model for laser energy absorption in FLASH, light
> will mostly reflect from a steep density interface until expansion from
> that interface has started -- and so, you may either (1) need to verify
> that your energy absorption has converged by increasing and decreasing cell
> resolution, or (2) don't use a steep density interface. This effect will
> cause more and more trouble as the pulse duration shortens, since less time
> is given for expansion before the pulse is "gone".
>
> On Mon, Feb 17, 2020 at 2:19 PM Scott Feister <sfeister at gmail.com> wrote:
>
>> Zhang,
>>
>> Temporal dynamics can matter! I will just add a comment that two lasers
>> with the *same *amount of energy but *different *pulse durations aren't
>> necessarily expected to do the same thing. The 0.4 ps pulse has 10x less
>> time for the same amount of energy to dissipate into the target, for
>> example.
>>
>> I haven't looked at the specific parfile, and maybe something else is
>> going on here as well!
>>
>> -Scott
>>
>> On Mon, Feb 17, 2020 at 2:40 AM Zhang Shizheng <
>> zsz526654434 at stu.xjtu.edu.cn> wrote:
>>
>>>
>>> Hi all,
>>>
>>>    I am trying to simulate a single laser beam with energy 400 mJ
>>> illuminating a solid Al disc, of which the thickness is 0.8 um.
>>>
>>>
>>>    (1) When the pulse is 4ps and the laser power is 10^11 W, the laser
>>> will break through the Al disc and a hole will appear
>>>
>>>    (2) When the pulse is 0.4 ps and the laser power is 10^12 W, the disk
>>> will expand evenly and there will be no hole in the disc.
>>>
>>>
>>>    In my opinion， the moment of light is only related to the energy, so
>>> the light in both (1) and (2) should break through the Altarget, *what
>>> might cause the difference between these two results?*  The .par file
>>> is in attachment, and I have changed nothing but pulse and laser power to
>>> get these two results, and the total energy is a constant 400 mJ.
>>>
>>>
>>> Best Wishes
>>> ------------------------------
>>>
>>> Zhang Shizheng
>>>
>>> PHD
>>>
>>> Xi'an Jiaotong University
>>>
>>> Institute for Science and Technology of Laser and Particle Beams
>>>
>>
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