A review of the KMOS IFU component metrology programme

The K-Band Multi-Object Spectrometer Integral Field Unit (KMOS IFU) is a complex optical instrument with over a thousand diamond machined optical surfaces. Many of these surfaces are highly unorthodox and extremely difficult to characterise accurately. In this paper, we summarise the analysis of form and surface texture measurements made on these complex surfaces. In particular we focus on a general analysis of all the form measurement results. The measurement of such a large number of surfaces offers an unprecedented opportunity for the general analysis of form errors in complex diamond machined surfaces. The wealth of statistical information is of exceptional value in the refinement of the manufacturing process. In particular, we analyse in some detail the variation of form error contributions with spatial frequency. In general, there is a substantial reduction in form error contribution with spatial frequency. This form error variation with spatial frequency may also be modelled using Zernike polynomials This approach is particularly suited to optical modelling of systems incorporating such perturbed components. As such, this knowledge can be applied directly to the modelling of form errors in new optical designs. Application to tolerance modelling of future instrument designs is discussed.