在特定文档上搜索lucene

I'm using Lucene with java to index some text documents. Now, after I get some top documents for a keyword search, I want to further refine my search and search only those top documents with some additional keywords, so each document once. Can somebody tell me on how I can search a specific document with a specific keyword, not the whole index, but lets say just 123.xml with keywords "bla blah".I'm using Lucene with java to index some text d