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Create short pulses in Comsol

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Hi Everybody

The purpose of the simulation:

Illuminate a cylindrical shaped quarz with a pulsed laser for 1 second.

So I created the following functions under definitions:
a "Gaussian Pulse" function gp1
an "Analytic" an1 with the expression (amplitude*gp1(x)) and the argument x
a "Waveform" wv1
an "Analytic" an2 with the expression (wv1(t)+1)/2 and the argument t
an "Analytic" an3 with the expression (an1(x)*an2(t)) and the arguments x, t

Now what I don't understand are the following points:
when I change the duty cycle DC of wv1, then the length of an2 changes.
by length I mean how long the signal is.
i.e.
DC = 0.1 -> length of an2 = 50 sec
DC = 0.01 -> length of an2 = 5 sec

And when I change the CD of wv1, also the plot of an3 changes drastically:
CD = 0.1 -> an3 shows 10 pulses. They are in the range of 0.5 sec
CD = 0.01 -> an3 shows only 2 pulses. They are in the range of 1 sec
CD = 0.5 -> an3 shows 20 pulses (10 of them have a wider shape than the other 10). They are in the range of 1 sec
CD = 0.2 -> an3 shows 20 similar pulses. They are in the range of 1 sec

So my first questions:
Why and how do an2 and an3 change because of DC?

And the second question:
Also with the "smoothing" check box in wv1 disabled, there is a transition zone of the step with a fixed width of 0.0001. This will cause a problems as I want to simulate 1.5 ns pulses with a pulse frequency of
20 Hz.

Could someone give me some advices / answers?

Best regards

Gabriel

0 Replies Last Post 25 nov. 2016, 09:57 UTC−5
COMSOL Moderator

Hello Gabriel Voirol

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