PHP is server-side.
A new pop-up window is client-side.
Usually this is done with either the target="_blank" attribute in a link, or with javascript using window()
I suppose you could set your php redirect with a get parameter, and use this condition to trigger a script
<?php
if (isset($_GET['popup'] )) { ?>
<script>
window.open("page name", $other_attributes_here );
</script>
<?php } ?>