Calibrated Spatial Profile Measurements of Extended Light Sources

The purpose of SAM is to image individual atoms that fluoresce upon excitation with a light source that we choose based upon the properties of those atoms. In the past, we’ve made the simplifying assumption that the spatial profile of a light source is uniform, but, for real extended light sources, this is not true. As a consequence, the excitation rate will be spatially dependent. In order to calibrate the fluorescence yield of atoms embedded in solid neon, we’ll have to account for this effect by first measuring the spatial profile of our light sources. The picture below depicts a typical beam spot from a UV LED, which is readily seen to be nonuniform:


Last week I completed the development of a method to measure the spatial profile of our LED light sources. A key component is a computer program to quickly analyze and report the shape of the beam. Once the data is recorded, a plot is returned with minimal effort, only taking a minute or two to change parameters depending on the specific light source. Below is an example of such a plot which shows the calibrated number of photons per unit time per unit area as a function of position. Note that not only is this LED nonuniform, but it is also not cylindrically symmetric, which was another simplifying assumption that we had made earlier. -DF