Optimization of laser-based therapeutic devices in dermatology requires a knowledge of the distribution of laser fluence at different depths in skin. This distribution is particularly difficult to estimate or measure when the laser is focused into skin, due to high scattering and strong aberrations. An inaccurate estimation of the fluence at the target depth may result in adverse events or a lack of the desired therapeutic outcome. Estimates of fluence distribution in tissue from Monte Carlo simulations are only as good as the assumed geometrical model of skin and the choice of scattering and absorption coefficients, which vary widely in literature. Here we present a novel technique for directly measuring the spatial distribution of fluence in skin under a focused laser beam. A commercial grade CMOS camera was modified to allow tissue to be placed in direct contact with its sensor. Fluence distribution was measured from captured images followed by simple post processing. The thickness of skin samples was measured using OCT before mounting on the sensor. With a 0.5NA lens and a pulsed 1064nm laser focused through murine skin samples of different thickness, the fluence distribution was mapped as a function of thickness. The spread of energy was substantially larger than the diffraction limited spot that would be expected in the absence of scattering and aberrations. The measurements agree well with transmitted energy measured through tissue using a pinhole mounted on an integrating sphere. The experimental results are compared with Monte Carlo simulations and limitations of the simulation are also discussed.
We have developed a compact dual-view endoscopic probe without field obscuration to address the need of simultaneously observing forward and backward fields of view (FOVs) in the colon. The objective is compact with the forward-view and rear-view optical paths sharing the same optical elements. The compact objective is new in that no FOV is blocked. The illumination for forward-view imaging is provided by the cylindrical light guide and backward illumination is achieved with a reflector. We have designed, prototyped, and tested the endoscope by comparing it to a standard clinical colonoscope. We will discuss the system concept, objective design, fabrication of the freeform lens, and test results.