How to Close Child Page when Parent is Closed

I have two pages page1.aspx and page2.aspx.

Say Page1.aspx as parent page and Page2.aspx as Child page.

In Parent page , i have one button, button name is Show.

if i click Show button it opens Child Page(page2.aspx) as pop window.

My requirement is that, when i closed Parent Page(Page1.aspx) it should automatically close the Child Page(Page2.aspx) page.

Please Help Me,

Thanks.