In order to effectively and efficiently couple NPRO light into the Corning PM980 fibers, the beam needs to be focused from its beam size (on the order of hundreds to thousands of micrometers) down to 3.3um, the size of the optical core of the fibers.
In order to do so, we must design a telescope, comprised of two lenses and a collimator. We will use "a la mode" and other mode matching techniques to design this telescope by first measuring and locating the NPRO beam waist, through use of either a razor blade, or beam profiler. After doing so, however, there are other considerations we must make:
Photodiode Power Constraints
The photodiode that will eventually be measuring the beat note, and creating the analog input signal to our system, will have a limited range of power that it may accept as its own input, before it either becomes saturated (that is to say, responds only to a certain level) or destroyed by high powered laser light. So naturally, we must attenuate the light that we pick off from both each of the AUX lasers, and the PSL before it enters our system. This plays into the next section, Space constraints.
Space Constraints
As our setup will be taking up some space on both optical tables at the ends of the arms, and at the vertex, we need to consider the space available to us. The types of lenses we are able to use in the telescope designs for both X and Y AUX lasers will be appreciably affected by the amount of space available to us on the tables.
X arm and Y arm
We need to measure the characteristics of all the lasers that we will be coupling using the telescopes, and design a new telescope for each of them, so as to couple each of them as efficiently as possible.