Twitter Authentication Popup are losing properties in Safari

I create a popup for twitter authentication in safari. After that, I want to check data on the popup continuously. But second time, properties are lost.

Code part is here:

     tempWindow = window.open(authToken.url,"Twitter","width=600, height=600");

     co = setInterval(function(){

          check(tempWindow);

     }, 1500);

Second time: tempWindow equals Window{}.

How i can access the window property? Is it possible?