Open an aspx file in a new window and also redirect existing page to another page in button event

Hello,
I would like to ask how can I Open an aspx file in a new window and also redirect existing page to another page in button event server codes.
I know how to open a new window in server codes, however, I wish server could redirect the first page to another page after open a new window.
Here is the senario: First, I am in the first window with page1.aspx. And I click a button in page1.aspx, server will open a new window for page2.aspx, then server will redirect the first window to the defalt.aspx. Eventually, I will have 2 windows, first window is defalt.aspx and second window is page2.aspx.
Does anyone have idea for this?
Thank you!
...