[AnotherCat]

If you just want to get a list of authors, and not their books as well you can do that in Windows itself. One can just open the Calibre library folder in Windows Explorer (aka File Explorer in Win 8.x) and as books are placed in a folder under that for each author you will have a screen "list" of authors.

One can then send this list of author folders to a text file; how to do so may differ according to the version of Windows you are using. Google will find how but for Win 7 and 8 just hold Shift while Right clicking with the mouse in a clear area of the Explorer window, select "Open command window here.." and type DIR > authors.txt.

The file authors.txt will appear in your Calibre library folder and will contain a list of the author folders i.e. a list of the authors in your Calibre database. It will also include the date and size of each folder but if you just want a list of authors for checking purposes then I assume that will not matter.