Reading the data from Excel sheet and holding on the variable in C# and I have created the class that read from Excel but I am not sure If my code is optimized meaning I will be reading heavy from excel

Is there a room to optimized this code more?, I will be using this class heavy in my code and thought get some opinion/feedback -

I will be calling something like this...:

     ExcelReader xl = new ExcelReader();
     string sss = xl.ExcelOpenSpreadsheets("mysheet");
     .....
     ......


    public class ExcelReader  
    {             
        Application _excelApp;

        public ExcelReader()
        {
            _excelApp = new Application();
        }

        public string ExcelOpenSpreadsheets(string sheetName)
        {
            string _txt = string.Empty;
            try
            {
                Workbook workBook = _excelApp.Workbooks.Open("filename_here",....);
                _txt = ExcelScanIntenal(workBook, sheetName);
            }
           
            catch
            {
                //
                // Deal with exceptions.
                //
            }
            return _txt;
        }

        private string ExcelScanIntenal(Workbook workBookIn, string sheetName)
        {
            Worksheet sheet = workBookIn.Sheets[sheetName] as Worksheet;

            Range a1 = sheet.get_Range("A1", "B2");
            if (a1 != null)
            {
              string formattedText = r.Text;                   
            }

            return formattedText; 
        }