Nonlinear microscope objective using thin layer of organic dye for optical tweezers Quy Ho Quang, Thanh Thai Doan, Tuan Doan Quoc, Viet Do Thanh, Kien Bui Xuan, Le Ly Nguyen and Thang Nguyen Manh Eur. Phys. J. D, 74 3 (2020) 52 Published online: 17 March 2020 DOI: 10.1140/epjd/e2020-100520-7