how to passing the backslash in crystal report

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VB

ASP.NET

database

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Purchase Order Number have some backslash so that way not passing the parameter in Crystal report .. how to slove this problem

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
    If rdbPO.Checked = True And ddl_PO_Cod.SelectedValue.ToString <> -1 Then
        btnPrint.Attributes.Add("onclick", "window.open('Reports.aspx?rptid=11&val=" & ddl_PO_Cod.SelectedValue.ToString & "','','location=0,resizable=0,ScrollBars=1,statusbar=1,width=980,height=800,left=20,top=10,moveable=0') ;return false")
    End If
End Sub

Reports.aspx code

iam using multiple reports so iam using Case

Dim rptid As Integer = Request.QueryString("rptid")
Select Case (rptid)
    Case "11"
        report.Load(Server.MapPath("Reports/RepOPODevice.rpt"))
        report.RecordSelectionFormula = "{TBL_DEVMASTER.PONO}=" & Request.QueryString("val").ToString
        Page.Title = "PODevice Reports"
        Exit Select
End Select
CRptViewer.ReportSource = report