Ixon ultra 897u

The UCL intensity from tissue phantoms was measured in optical transmission geometry at room temperature. In the optical setup, all phantoms were placed at a distance of 165 mm away from the fiber tip (core $400\mu \mathrm{m}$ , 0.39 NA) delivering light from continuous wave (CW) excitation laser source at 975 nm (QPhotonics, QSP-975-10, United States). The incident beam diameter illuminating the front circular surface of the phantom was thereby 70 mm at the phantom location. Images of the upconverting phantoms were captured using an electron-multiplying charged coupled device (EMCCD) (Andor, iXon Ultra 897U, United Kingdom). Image J software (U.S. National Institutes of Health, United States) was used for image analysis.
During all measurements, the camera acquisition time was set to 1 s, and the laser power density was calculated to be $\sim 46{\mathrm{mW}/\mathrm{cm}}^2$ on the phantom surface. Furthermore, three different optical filters were used in front of the detector to effectively block excitation light that strayed in different angles. Two of them, a 794/32 nm bandpass filter and a 842-nm shortpass filter (Semrock, Models, United States), were placed inside the imaging lens system (50 mm/f1.8, Edmund Optics, United Kingdom), and the other one, a 900-nm shortpass filter (Thorlabs, FESH0900, United States), was placed between the lens system and camera sensor.