Update progress not working with PostBackTrigger

In my web page, I have a gridview and link button to export gridview data to excel.I want to show a progress bar while exporting to excel.

But my button works as:

 <Triggers>
     <asp:PostBackTrigger ControlID="exportButton" />
</Triggers>
</asp:UpdatePanel>

Because of this my ajax update progress is not showing.

 I tried to show it by using javascript. But its not disappears after export is completed.

Is there any way to show progress using ajax update progress or jquery or javascript? pls help.