How to use your Mac display as an extension to your Macbook Air with Windows 8.1 as an operating system?

My Macbook Air has both iOS and Windows 8.1. When the iMac and the Macbook Air are connected via the Thunderbolt cable, I can use my iMac display as an extension. This is only possible when I press command+F2. When I'm using Windows OS on my Macbook Air, I am no longer able to use the iMac display as an extension. I have a mid-2011 Mac and a 13-inch mid-2013 Macbook Air. Any suggestions?