Hi, the degree of monochromaticity of the source is inversely proportional to the simulation time. You can suppress spectral ringing by slow onset of the source, and possibly by applying a smooth window to the time recorded function. Consequently, there is nothing like a fully monochromatic source.
If you need an efficient monochromatic computation, you can use the frequency-domain solver built in meep. Filip 2015-05-05 12:29 GMT+02:00, Eoin Murray <em...@cam.ac.uk>: > Does anyone have a solution to this, to make a fully monochromatic light > source, it seems like a fairly typical use case for an electromagnetic FDTD > library. > > I have found that a mono-source can be made if you run the simulation for a > long time, like 1500 periods, but there must be a more efficient way to do > this. I will post my solution as soon as I find one. > > >> On 2 May 2015, at 14:30, Eoin Murray <em...@cam.ac.uk> wrote: >> >> Hi Filip, >> >> Thanks for the swift reply and for recommending the solution. I have tried >> what was suggested in Gib's post - where a smooth turn on function of >> around two periods should narrow down the linewidth of the source spectrum >> (or power spectrum) - however this does not seem to work for me, >> >> I have made a sample repo on github to show the issue, I am using a >> frequency of 1.1 and a continuous-src with a 2 period turn on time (I have >> tried unto 20 periods turn on and little changes), I would expect the >> linewidth of this source to be approaching zero. I understand that there >> would be some numerical broadening, but still the source is far to broad >> for me at the moment with a width of 0.05, this should be much smaller to >> simulate a close-to-monochromatic light source like an atomic dipole >> (which a continuous wave src should do). >> >> The field does become more spectrally narrow if I run for a long time >> (like 1500 periods), but I expect I should be able to achieve same after >> 20 periods or something, why do the transients take so long to die out.? >> >> The attached repo contains a _test.ctl file with my code and graphs in the >> _test-out/ folder. >> >> https://github.com/eoinmurray/meep-test.git >> <https://github.com/eoinmurray/meep-test.git> >> >> Thanks again for the help. >> Eoin >> >>> Begin forwarded message: >>> >>> Date: 1 May 2015 20:59:41 BST >>> Subject: Re: [Meep-discuss] flux spectrum of continuous source >>> From: Filip Dominec <filip.domi...@gmail.com >>> <mailto:filip.domi...@gmail.com>> >>> To: Eoin Murray <em...@cam.ac.uk <mailto:em...@cam.ac.uk>> >>> >>> Hi, Eoin, >>> everything suggests you have the same problem (which is actually not a >>> problem per se) as Gib: >>> https://www.mail-archive.com/meep-discuss@ab-initio.mit.edu/msg05374.html >>> <https://www.mail-archive.com/meep-discuss@ab-initio.mit.edu/msg05374.html> >>> >>> Regards, >>> Filip >>> >>> 2015-05-01 14:17 GMT, Eoin Murray <em...@cam.ac.uk >>> <mailto:em...@cam.ac.uk>>: >>>> >>>> >>>> Begin forwarded message: >>>> >>>> From: Eoin Murray <em...@cam.ac.uk <mailto:em...@cam.ac.uk>> >>>> Subject: flux spectrum of continuous source >>>> Date: 1 May 2015 15:14:20 BST >>>> To: meep-discuss@ab-initio.mit.edu >>>> <mailto:meep-discuss@ab-initio.mit.edu> >>>> >>>> I want to create a monochromatic continuous source, in air, and measure >>>> the >>>> flux through some plane, so I use the following code: >>>> >>>>> (set! sources (list >>>>> (make source >>>>> (src (make continuous-src (wavelength wv) (width 0))) >>>>> (component Ez) >>>>> (center 0 0) (size 0 0)))) >>>> >>>> I thought that the flux spectrum would look like a dirac delta >>>> function, >>>> instead it is quite broad, why is this? >>>> How can I create a continuous wave monochromatic source in meep? >>>> Attached are links to the flux spectrum I measured through a plane north >>>> of >>>> the source, and also an image of the field. >>>> >>>> http://i.imgur.com/xeAZCte.png <http://i.imgur.com/xeAZCte.png> >>>> <http://i.imgur.com/xeAZCte.png <http://i.imgur.com/xeAZCte.png>> >>>> >>>> http://i.imgur.com/Dza8deC.png <http://i.imgur.com/Dza8deC.png> >>>> <http://i.imgur.com/Dza8deC.png <http://i.imgur.com/Dza8deC.png>> >> >> _______________________________________________ >> meep-discuss mailing list >> meep-discuss@ab-initio.mit.edu >> http://ab-initio.mit.edu/cgi-bin/mailman/listinfo/meep-discuss > > _______________________________________________ meep-discuss mailing list meep-discuss@ab-initio.mit.edu http://ab-initio.mit.edu/cgi-bin/mailman/listinfo/meep-discuss
