Sorry, I left out the the transmission/reflection plot. http://dug.im/ea6c8
Marian ----- Original Message ----- From: mf <[email protected]> To: Steven G. Johnson <[email protected]>; meep-discuss Discuss <[email protected]> Cc: Sent: Friday, July 29, 2011 5:43:35 PM Subject: Re: [Meep-discuss] PML at oblique incidence, or diffuse light Hi Steven, I have increased the PML to 100 units (sample size 20x20, PAD 6, and I had to reduce the resolution to 20). The amplitude of the oscillations decreases, but they do not vanish (see the plot below). http://dug.im/803e6 I have also exported the field for a frequency at the center of the gap (I attach the animated gifs, last two zooming around the source position; on the images I have separately generated some guiding lines for the position of the source and reflection and transmission detectors and the PML is the gray area). It seems that I was wrong is not diffuse light, but some rather strange residual field bouncing between the periodic boundaries (and propagating at almost 180 wrt to the PML surface). I fail to understand if this is a real effect or a artifact of the boundary condition. http://dug.im/a33c5 http://dug.im/803e6 http://dug.im/a70a6 Also, I am a bit surprised that the T+R goes over one. Is the sources too close sample and sees a larger LDOS ? Thank you, Marian ----- Original Message ----- From: Steven G. Johnson <[email protected]> To: meep-discuss Discuss <[email protected]> Cc: Sent: Thursday, July 21, 2011 4:07:52 PM Subject: Re: [Meep-discuss] PML at oblique incidence, or diffuse light On Jul 21, 2011, at 4:00 PM, mf wrote: >> The decay coefficient within any PML is well-known to have a cos(theta) >> factor, where theta is the incidence angle, which makes the decay become >> slower as you approach glancing incidence. However, this is true even at >> infinite resolution, so if you are seeing an effect that decreases with >> increasing resolution then it is something different. e.g. it may be >> transition reflections, which you can also decrease by making the PML >> thicker instead of increasing the resolution. >> Transition reflections also increase as you approach glancing incidence, >> because at glancing incidence the phase-velocity mismatch between incident >> and reflected waves goes to zero. See e.g. equation (13) in our paper: >> http://www.opticsinfobase.org/abstract.cfm?URI=oe-16-15-11376 > I realize this, and that is what I was afraid of. However the effect seems > rather strong: at a resolution of 64, the amplitude is .02 and I can not run > resolutions higher than 128 (where the oscillations are still clearly > visible). Is there anything I can do ? (modify the functional absorption in > the PML ?) My guess is that what I see are reflections from the first PML > layers (the results seem to do not depend on the PML thickness). If it is transition reflections, I don't see how they could fail to depend on PML thickness. As you make the PML thicker and thicker, the PML turns on more and more gradually (the same quadratic profile, but shallower and more stretched out). Asymptotically for large thicknesses, the transition reflections must vanish. The only caveat is that the decrease with thickness does not occur until the PML is sufficiently thick to be in the asymptotic regime -- normally, this is true whenever the PML reflections are low, but maybe at your glancing angles the reflection is currently so high that you are not yet in the regime where you can see the thickness dependence. (See e.g. our paper, mentioned previously, for some graphs.) Try increasing the PML thickness by a factor of 10 to see if that improves things. If it doesn't, I would begin to suspect that something else is going on, although I'm not sure what it could be. _______________________________________________ meep-discuss mailing list [email protected] http://ab-initio.mit.edu/cgi-bin/mailman/listinfo/meep-discuss _______________________________________________ meep-discuss mailing list [email protected] http://ab-initio.mit.edu/cgi-bin/mailman/listinfo/meep-discuss _______________________________________________ meep-discuss mailing list [email protected] http://ab-initio.mit.edu/cgi-bin/mailman/listinfo/meep-discuss
