[TYPO3] extra php-file in extension

[PEF]

Hi,

I'm working on an extension that I want to extend with an extra 
php-file. This extra php-file is called from a javascript: 
window.open("my_extra_php.php, ...)

For convenience I want have access to the Typo3 globals TSFE, TYPO3_DB 
and the tslib.pi_base.php

Anyone who can tell me the right way to do it?

Regards
Peter Falk