Optical systems are often athermalized over large temperature ranges through the proper choice of glasses and mounting materials. However, variations in the coefficients of thermal expansion (CTE) and thermo-optical coefficients that govern thermal behavior are seldom included in the tolerance analysis. Manufacturers rarely provide these material tolerances and we can only account for their effects through custom macros in lens design software. We demonstrate that a first-order sensitivity analysis on the change in focus position at each environmental condition accurately predicts the degradation of the system performance. We verified this correlation by creating a custom catalog of identical glasses with perturbed thermal parameters and evaluating the RMS wavefront error for each material substitution.
In the design of optical assemblies, emphasis is placed on tolerancing the surface irregularity, which is a driving factor in price and manufacturing prices and time during polishing. Quite often, the default irregularity tolerance in modeling software is assumed to be a 50:50 split between astigmatism and 3rd order spherical aberration (i.e. symmetric zonal errors). In this paper, we reviewed the irregularity of over 1,000 custom fabrication optical surfaces. We looked at the relationship between the spherical and astigmatism aberrations and found generally that a surface will be either astigmatic or spherical, but rarely a mixture of the two. We also looked at the PV and rms of the surfaces and how that compares to the model and the general knowledge. One striking result of our analysis came from a closer analysis of how the optical modeling software package handles ‘power’ errors in the irregularity tolerance. It is possible that there is a mismatch between the model and the optical manufacturer.
Optical cooling in an all fiber system using fiber laser pumps and cooling fibers doped with rare earth ions has been
investigated both theoretically and experimentally. A 2% Tm doped germanate glass was selected from glasses with
different Tm concentrations 0.5, 1, 2, 3, 4, 5, 6, 8 and 10% wt for fabrication of the cooling fiber. A high efficiency,
single mode Tm-doped fiber laser has been built to pump a Tm-doped fiber cooler. The cooling experiments done in a
vacuum chamber show indications that cooling has occurred in the fiber. A theoretical framework to understand the
nature of cooling in this laser cooling system has been developed which highlights the cooling power available as a
function of various material and fiber parameters including background loss and absorption saturation effects in the
cooling fiber. Cooling characteristics, with special emphasis on the fiber's saturation behavior, have been studied using
theoretical models of Tm3+-doped glass (4-level models) and Tm3+ doped KLa(WO4)2 crystals (20-level model).