How to convert string to base64 byte array, would this be valid?

I'm trying to write a function that converts a string to a base64 byte array. I've tried with this approach:

public byte[] stringToBase64ByteArray(String input)
{
    byte[] ret = System.Text.Encoding.Unicode.GetBytes(input);
    string s = Convert.ToBase64String(input);
    ret = System.Text.Encoding.Unicode.GetBytes(s);
    return ret;
}

Would this function produce a valid result (provided that the string is in unicode)? Thanks!