base64 string to byte array c#

string author = "Mahesh Chand";  
// Convert a C# string to a byte array  
byte[] bytes = Encoding.ASCII.GetBytes(author);  

// Convert a byte array to a C# string. 
string str = Encoding.ASCII.GetString(bytes);

// Convert a string to a C# byte[]
//change encoding depending on your data
string someText = "some data as text.";
byte[] bytes = Encoding.ASCII.GetBytes(author);

// Convert a byte array to a C# string    
string str = Encoding.ASCII.GetString(bytes);  
Console.WriteLine(str);

byte[] l_Data = Convert.FromBase64String(l_PlainText);