I wanted to know if it is possible to use subscript in axis description. I have the following code
XYItemRenderer lineYY = new StandardXYItemRenderer();
I am not sure about jFreeChart, but a pure java string could bear that, please try:
final NumberAxis yaxY = new NumberAxis("a\u2093 [m/s²]");
see: http://www.fileformat.info/info/unicode/char/2093/index.htm