Bessel beams

[GoogleCodeExporter]

It should be easy to implement Bessel beams in ADDA. They are becoming more and 
more popular, so applications should come by.

Original issue reported on code.google.com by yurkin on 2 Jul 2015 at 8:59

[myurkin]

/cc @stefaniagl

[myurkin]

Proof-of-principle is available at https://github.com/stefaniagl/adda

[stefaniagl]

6 Bessel beam types have been implemented - LE - linear electric field, LM - linear magnetic field, CS - circularly symmetric energy density, TEC, TMC - polarizations generating TE and TM Bessel beams, and M - generalized type.

[myurkin]

After the pull request (#304) will be merged we still need the following to finalize this issue (to be submitted as the new pull request):

• new tests in tests/2exec (new command lines in suites, and potentially ignores for comparison with previous versions).
• new tests in tests/2equiv (specification of M matrix vs. simple types).
• description of new beams in the manual (maybe even mention some formulae, but in a concise manner)

[myurkin]

Non-trivial application of Bessel beams for imitating circular polarization of a plane wave are discussed at https://groups.google.com/g/adda-discuss/c/k-ClVwvwQQk . In particular, interesting combinations are used in tests/equiv/ext_CD.py. One of them highlights the lack of robustness for M matrices corresponding to TE and TM beams for very small half-cone angles.