def make_file_name(data_path,shot_num,freq):
    """construct the output file name based on the shot number and frequency

    Arguments:
        shot_num: string,
        freq: double, in GHz
    return:
        string, 
    """

    return '{0}{1}_{2:4.3}GHz.h5'.format(data_path,shot_num,float(freq))