548 lu2017 pdf cache all wpfb_file_category citations 1488874653 39b8947e3666c5737e7e8b5105dc69eb 93d8c8e7edcdc056b9f2ec0ae57726420e07a5f25fe73acb2ead840e9d07b9f0 high efficiency quantum cascade laser frequency comb 2017 03 07 09 17 33 0 123 125 71 32 2020 01 18 54 1528055060 pdf application num_pages analyze pdf_pages pdf_2text timings