Open new tab in asp.net code behind

//HTML

<asp:Button ID="Button1" runat="server" Text="Button" 

onclick="Button1_Click" 
OnClientClick ="document.forms[0].target = '_blank';" />

//Code Behind

protected void Button1_Click(object sender, EventArgs e)

    {

        string newtabl = @"~/FrmNewContent.aspx";

        Response.Redirect(newtabl);       

    }