Hi Paolo, It’s still not completely clear to me, but I’m gonna take a gamble . First of all, see my first email (with link to paper). What I think you’re calculating is the spontaneous emission enhancement factor. By putting a source inside a resonant cavity, you limit the number of modes to which the source can transfer its energy. The emission rate (and thus its flux) of the source is therefore strongly enhanced with respect to the situation without cavity. If you divide the spectrum of the structure with cavity by the spectrum of the structure without cavity, you calculate by which factor the emission rate of your source is enhanced. Hence a value larger than 1 (can be any value > 1 really, depending on the situation)
For the case of the source outside the cavity, there might not be any mode to which your source can radiate its energy. The emission rate is therefore reduced, hence a value smaller than 1. Hope this helps. Best regards, Milan From: [email protected] [mailto:[email protected]] On Behalf Of paolo bettotti Sent: maandag 24 januari 2011 17:36 To: [email protected] Subject: [Meep-discuss] normalization Thanks a lot Marell and Steven, but I am still confused. I am trying to put sources inside a PC cavity. It's difficult but it's not science fiction (Appl. Phys. Lett., 89, 211117 (2006)). I am interested in coherent nonlinear phenomena, thus I need to be sure about normalization procedures. And I'd like to get information about the source emission spectra form inside the cavity. I designed a PC "stripe" composed by 7 periods in the direction normal to light propagation, with a cavity in the middle. I use exactly the same simulation window and I move the light source inside and outside the PC cavity, keeping the monitor fixed. With source outside the cavity, there are no problem: things running fine and normalization works as expected (one simulation with PC and one with bulk homogeneous material - no PC). If I put the source inside the cavity I always get a kind of light amplification that it is not expected to be there. Probably things are clearer with the attached image that shows the two spectra with source inside (narrower red peak) and outside the cavity (wider black data). Y Scales differ for one order of magnitude, and if I normalize the spectra things get even worse, clearly... Why I get this signal amplification? Is it because I am running a pure 2D simulation? Thanks for any suggestions! Paolo. Here below the revelant ctl code: (define-param res 10) (define-param rad 0.3) (define-param numlayers 15) (define-param dpml 3) (define-param pad 2) (define-param freq 0.4397) (define-param defreq 0.2) (define-param nfreq 1000) (define-param fcen_h freq) (define-param df_h defreq) (define-param sx 24) (define-param sy sx) (define-param runtime 500) (define-param sourcex (/ sx -3.5)) (define-param sourcey 0) (define eps-averaging? true) (set! pml-layers (list (make pml (thickness dpml)))) (set! resolution res) (set! default-material (make dielectric (epsilon diel_slab))) (set! geometry-lattice (make lattice (size sx sy no-size))) (set! geometry (append (geometric-objects-duplicates (vector3 (/ (sqrt 3) 2) 0.5) (* -1 numlayers) numlayers (geometric-objects-duplicates (vector3 (/ (sqrt 3) 2) -0.5) (* -1 numlayers) numlayers (list (make cylinder (center 0 0)(radius rad)(height infinity)(material (make dielectric(epsilon diel_hole)))) ))))) (set! geometry (append geometry (list (make cylinder (center 0 0)(radius (* 1 rad))(height infinity)(material (make dielectric (epsilon diel_slab)))) (make cylinder (center 0 1) (radius (* 1 rad))(height infinity)(material (make dielectric (epsilon diel_slab)))) (make cylinder (center 0 -1)(radius (* 1 rad))(height infinity)(material (make dielectric (epsilon diel_slab)))) (make block (center (- (/ sx 2) 3.5) 0) (size (+ dpml (* 4 pad)) sy) (material (make dielectric (epsilon diel_slab)))) (make block (center (+ (/ sx -2) 3.5) 0) (size (+ dpml (* 4 pad)) sy) (material (make dielectric (epsilon diel_slab)))) ))) (set! geometry (list (make block (center 0 0) (size sx sy)(material (make dielectric (epsilon diel_slab)))); for normalization )) (set! sources (list (make source (src (make gaussian-src (frequency freq)(fwidth defreq))) (component Ex) (center sourcex sourcey) (size 0 0)))) (define trans (add-flux freq defreq nfreq (make flux-region (center (- (/ sx 2) dpml pad) 0) (size 0 (- sy dpml dpml pad)))) ) (run-sources+ runtime (at-beginning output-epsilon) ; (at-every 25 output-efield-x) (after-sources (harminv Ex (vector3 (+ 0 sourcex) (+ 0 sourcey)) fcen_h df_h) ) ) (display-fluxes trans) ________________________________ Da: Steven G. Johnson <[email protected]> A: MEEP Discuss <[email protected]> Inviato: Mer 19 gennaio 2011, 02:18:31 Oggetto: Re: [Meep-discuss] normalization What property of the cavity are you trying to simulate? e.g. are you simulating and experiment? In an experiment, the light source is probably not within the photonic crystal. e.g. it may be coming from the air outside a finite photonic crystal. In that case, you would normalize by the incident power, which is the power measured in a simulation when you remove the cavity AND the photonic crystal. Other simulation golas will call for other normalizations. --SGJ _______________________________________________ meep-discuss mailing list [email protected]<mailto:[email protected]> http://ab-initio.mit.edu/cgi-bin/mailman/listinfo/meep-discuss
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