Evaluation and control of performance of in-house achromatic triplet collimator assembly by infinite conjugate lens test using a Fizeau interferometer

The laboratory measurement and evaluation of the performance of an apo-achromatic collimator is presented in this work. This customized collimator was optimized to utilize with a high-resolution spectrograph located at Thai National Telescope (TNT). The Center for Optics and Photonics (COP) under the National Astronomical Research Institute of Thailand (NARIT) aims to evaluate and control the performance of the achromatic triplet collimator with a Fizeau interferometer to ensure that the correspondence with optical and opto-mechanical tolerances. The parameters controlled include the Root-Mean-Square (RMS) and Peak-To-Valley (PTV) wavefront errors and the Modulation Transfer Function (MTF). The result suggests the performance of the assembled achromatic triplet lens conforms with Zemax optical design below 0.1 NA. The RMS and PTV wavefront errors and MTF measured with the interferometer appear comparable to the Zemax optical design of the collimator within this range. Therefore, we conclude that our in-house manufacturing, assembly, and control are acceptable for astronomy applications.