Optical alignment method for linear astigmatism-free system based on coordinate measuring machine (CMM)

We present an off-axis design of three freeform mirrors satisfying the linear astigmatism-free (LAF) condition for remote sensing. Sensitivity analysis and Monte Carlo simulations reveal that the alignment is highly sensitive to mirror positioning, with tolerances of < ±20μm in decenter and < ±0.175mrad in tilt, based on a 10% Modulation Transfer Function (MTF) criterion at the Nyquist frequency. To achieve this tolerance, we developed an optomechanical design with monolithic measurement cubes and a precise alignment method using a coordinate measuring machine (CMM). We calculate misalignments for each degree of freedom relative to the design. Misalignments are corrected using 10μm and 50μm ring shims, as well as 10μm shim tapes. The alignment is validated by comparing the point spread function and MTF measurements with the Nyquist criterion. Since the CMM method finally aligns the LAF system in the tolerance range of < ±50µm, additional wavefront-based alignment is required.