The international society of optics and photonics SPIE has a webpage where they post links to the most downloaded papers each month. These papers are from the Proceedings of the SPIE and the various SPIE journals. Some of these papers are open access, meaning that you can download them for free during the month they are posted, but not all. Waldo Library does not subscribe to the SPIE journals nor do we have most of the Proceedings of the SPIE (you can see the ones we have here). So if you want copies of the articles that are not open access, please order them through Interlibrary Loan.