Excluding characters from a wildcard query

[Ben]

Passing in a RegularExpression like "[^_]*_[^_]*" (e.g. matching 
anything with an underscore in the string) using some code like :

...
parameters.add("fq", "vector:[^_]*_[^_]*");
...
seems to cause problems for SOLR, I assume because of the [ or ^ character.

Can somebody please advise how to handle character exclusion in such 
searches?

Any help or pointers are much appreciated!

Thanks

Ben