On Sun, 11 Mar 2007, Andrew Andrew wrote:
I write a ctl according to some codes that Steven have given on this
list, but I can't change the position of the waist of a gaussian beam.
(define ( (my-amp sigma k x0) x)
(exp (- (* 0+2i pi (vector3-dot k (vector3+ x x0) ))
(/ (vector3-dot (vector3+ x x0) (vector3+ x x0)) (* 2 sigma sigma)))))
(set! sources (list
(make source
(src (make continuous-src (frequency fcen) (fwidth df)))
(component Hz)
(center 0 0) ;
(size 0 10)
(amp-func (my-amp 1 k (vector3 -15 0 0))))))
This isn't going to work because you put the center of your beam at -15,
but your source only extends from -5 to 5. You need to make the size of
your source bigger.
PS: The width of waist seems larger than what I have specified, i.e. 1
unit. What's wrong?
Look at the beam definition you are using. According to your definition,
at the beam "waist", i.e. at x = -x0 +/- sigma/2, the field amplitude is
exp(-0.5^2 / 2) = 0.883. It's not surprising that the beam looks wider
than this, since visually you would tend to define the beam width as where
the amplitude drops a lot more than 12%.
Steven
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