export file through webservice jquery

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jQuery

webservice

Hi,
I am trying to export file using Web Method and JQuery AJAX. Web method of file downloading individually working fine but when I am consuming service method in AJAX it is not working
code----

[WebMethod]
    public  String ExportToExcel()
    {
        try
        {
            // DataSet ds;
            HttpResponse response = HttpContext.Current.Response;
            // first let's clean up the response.object
            response.Clear();
            response.Charset = "";
            response.ContentEncoding = System.Text.Encoding.Default;

            // set the response mime type for excel
            response.ContentType = "application/vnd.ms-excel";
            response.AddHeader("Content-Disposition", "attachment;filename=\"ExportTest.xls\"");

            // create a string writer
            using (StringWriter sw = new StringWriter())
            {
                using (HtmlTextWriter htw = new HtmlTextWriter(sw))
                {
                    response.Write(sw.ToString());
                    response.End();
                }
            }
            return "Exported";
        }
        catch (Exception ex) {
            return ex.Message;
        }
    }

Javascript calling:

$.ajax({
              url:"WebService.asmx?op=ExportToExcel"
          , type: "GET"
          ,contentType: "application/vnd.ms-excel"
          , data: {}
          , success: function (res) {
              alert("Success");
          }
          , error: function (res) {
              alert("Error");
          }
      });