Falsely accused & cleared of sexual harassment in the workplace, can I now file charges of slander, defamation of character, etc. against my accuser ?

Thank you so much for reading! My husband is a Federal government, law enforcement employee, in a prison setting. He does not work for the prison, he was assigned there by the government. A female, who is a contracted employee in the prison but employed by an outside contractor, falsely accused my husband of sexual harassment. He was removed from his job "for his protection" by the government and had to commute 2 hours daily for 4 mos to work at another facility. No criminal charges were ever filed against him nor disciplinary action taken. Of course this caused us great strain in our marriage though I knew my husband was not capable of what he was accused of. An internal government investigation was conducted, the allegations were deemed false and my husband was reinstated to his job. What legal recourse do we have against his accuser who suffered no reprimand / repercussions and we have learned has done this previously! Please point us in the right direction, thank you so much.