Open New Tab on Browser from child popup window.

I have a popout window which when somone clicks a button it opens a new tab in the parent window

Doing it in the HTML works fine as this.

<a id="btnNewWindow" runat="server" class="btn-primary btn-xs" Height="20px" href="show.aspx" style="text-align: center" target="_blank" visible="false">Open Review in New Tab</a>

Select allOpen in new window

but I need to do it in the code behind .  

Below is what I'm currently doing but it redirects the popup window not open a new tab on the parent window.

    Protected Sub btnFullRecord_Click(sender As Object, e As EventArgs)
        Dim TRAINEEID = Session("TRAINEEID")
        Dim POT = Session("POT")
        Response.Redirect([String].Format("candidategeneral.aspx?TraineeID={0}&POT={1}", TRAINEEID, POT))
    End Sub

Select allOpen in new window