How to refresh parent page after close of showModalDialog using Javascript

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C#

Javascript

In one of mine web application, i have one parent page, there is one button on parent page, on click this button i am calling javascript function for show Modal Dialog.

<script type="text/javascript">
    function getUrlVars() {
        var vars = {};
        var parts = window.location.href.replace(/[?&]+([^=&]+)=([^&]*)/gi, function (m, key, value) {
            vars[key] = value;
        });
        return vars;
    }

    function OpenDialog() {
        var _payrollId = getUrlVars()["payrollId"];
        if (_payrollId != "") {
            Options = "dialogWidth:900px;dialogHeight:500px;help:no;scroll:yes;status:no:";
            OpenReportJS = window.showModalDialog("/PickList/PayrollHead.aspx?payrollId=" + _payrollId, "_blank", Options);
        }
    }

</script>

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Now in the child page i have one button and when i click this button want to close the show modal dialog and want to refresh the parent page.
How can i do this, please give me some hints...