Hi Veluru, 

What you can do is call a nanoflow with a custom JavaScript snippet that has 1 input parameter called url.

Then put this code snippet in your custom JavaScript action:

window.open(url, '_blank').focus();

Make sure that the url in the code snippet is your input parameter.

After that do a close page action in your nanoflow call. 

The resulting nanoflow would look like this:

And the JavaScript code looking like this:

Set the action of the link button to call a nanoflow

Create a new nanoflow which has

1. Action open url
2. Action close page

Your nanoflow will require a input parameter with object of you popup page, so that you can use url value of object attribute

In Link button ,on click event >call microflow in that microflow first use close page activity  and then continue your flow.