What is the meaning of co-propagating beam?

[cks]

I want to ask, is counter propagating beam written as co-propagating beam?

which means two beams that are traveling opposite to each other.

 

[Andy Resnick]

counter propagating and co-propagating beams generally mean they have the same wavevector: for counterpropagating beams the wavevector has opposite sign, for copropagating, the same sign.