Send a Jquery AJAX POST request with the data that is to be used to generate excel report, and store that data in a session variable. Return an arbitrary string like 'success' as the response.
If the output of the above AJAX call is 'success', then do a GET request to another URL in your application, that reads the data from session (stored in the first step, else throw an error), prepares an excel file out of that data, and forces the download of that excel file to the browser.