Google's spider looks at the structure and content of the website (basically the source files). It doesn't automate human interaction with the site to get the popup.
While this assertion is generally (99%) true, there are some cases—up to you to create the good conditions—in which popup pages can be crawled by Google and any other search engine (SE). I'll tell you the reason why in few seconds but let remind you how it works before. Popup pages are triggered by an event being fired by the web client—usually regardless of the user interacting with the page—, e.g., page loading, page unloading, click, programmed timeout, living the site. This event is usually programmed by the web page developer within what is called a scripting section. The example below present the code for a popup that is triggered when the page unloads, i.e., when the user exits the page (code is simplified for better readability): <script type="javascript"> function DoPop(PageToPop){ window.open(PageToPop); } </script> <body onunload="DoPop("popup.html");"> (...page content here...) Here is the reason why... —1. Google CANNOT crawl popup pages. As shown in the example above, the link to the popup page is embedded within the script section and, as is, it's considered as a mere piece of text by any search engine—SE's being reportedly not able to interpret such logic, yet. Therefore, SE's are not aware of a page existing at that address, hence, they will never visit and reference it in their catalog, period. Here's now the reason why... —2. Google CAN crawl popup pages. Should you want to make SE's aware of your popup page—and you can still embed it within your script section, don't change anything—you just need to insert a link, called an anchor, within your page as a regular link, as follows: <a href="popup.html"> Usually, the best place to embed it is at the bottom of the page, as part of a dedicated section you may want to create specifically for these pages, not to give them too much prominence. Nevertheless, some may say that their page is not in fact a real popup but a real page—i.e., full of valuable content for the user—they want at the same time to have it pop as a standard popup page (for any reason) and to still expose to SE's as part of the visible content of the page, or even make it more prominent within the content. Is it feasible, really? YES. The trick is to mix the safe part of the 2 worlds, as follows: <a href="PageToPop.html" onclick="DoPop("PageToPop.html"); return false;">text here</a> Here is how and why it works... When SE's crawl the page, they see the link as a real link and not mere text as with the script section. When a user visits the page and click on the link, the "onclick" parameter of an anchor is executed first, then the page referenced in the "href" parameter. By adding "return false;" within the "onclick" parameter, we instruct the web browser to stop the execution flow right after having executed the function "DoPop", hampering the web client to visit the page referenced in the "href" parameter, simple. This way you can benefit from both the flexibility of displaying a page as you like (e.g., popup), and its crawlability and inclusion in SE's catalog.