Dr. Johnson,
Is this true when just the complex part of epsilon is negative? I was
aware of the instability for non-dispersive negative epsilon, but
thought it was only for the real part. I know the FD-TD method can model
non-dispersive gain situations, but is there a limit on the value of the
gain? I have found some work that suggests the time step must be
reduced when modeling complex epsilon to ensure stability, but that
didn't seem to fix my issue. I tried cutting the Courant number in half
and the results were the same in my simulation.
Regards,
Nathan
Steven G. Johnson wrote:
On Mar 5, 2009, at 12:12 PM, Ian Buss wrote:
I had a similar problem when simulating real metals - it turns out
that Meep will not accept negative permittivities without blowing up.
This is not a property of Meep specifically. FDTD is unstable for non-
dispersive negative epsilon (which also violates the Kramers-Kronig
relations).
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