I using examine for searching with a single character.Means I have a property named Firstname in my node and I have more than 100 nodes in my umbraco ,I trying to search all first name start with A and disply,so I using examine to impliment this.But it dosn''t return the values.here is my code.Can anyone help?.

 var contentSearcher = ExamineManager.Instance.SearchProviderCollection["WebsiteSearcher"];
    var searchCriteria = contentSearcher.CreateSearchCriteria(UmbracoExamine.IndexTypes.Content, BooleanOperation.And);

    List<SearchResult> contentResults = new List<SearchResult>();
    string keyword = "";

     string[] contentSearchFields = {"firstName"};
           keyword = "A";

    var luceneString = "";

    if ((!string.IsNullOrEmpty(Request.QueryString["keyword"])))
    {

        if (!string.IsNullOrEmpty(keyword))
        {
            var keyWordQuery = "";
            string finalKeywordQuery = " +({0})";
            keyWordQuery += "lastName:" + keyword + "~0.3 ";


            luceneString += string.Format(finalKeywordQuery, keyWordQuery);
            luceneString += "+umbracoNaviHide:0";
        }

    var fquery = searchCriteria.RawQuery(luceneString);
    contentResults = contentSearcher.Search(fquery).ToList();
    var results = contentResults;