An automated subaperture stitching interferometer workstation for spherical and aspherical surfaces

Wavefront measurement techniques used in high power lasers

“…The original stitching method only detects low order components of the surface by fitting polynomials to non-overlapping subapertures [19,20] ; by contrast, the stitching method of overlapping subapertures and connecting interferograms minimizes the error of connection down to λ/20 [21] . The use of subaperture stitching interferometers significantly reduces cost and increases spatial resolution [22] and measurement accuracy [23] . However, the subaperture stitching method possesses inherent disadvantages.…”

Fast Sub-aperture Stitching Algorithm Using Partial Derivatives

“…sub-apertures have nonzero piston, tilt, and defocus errors that are relative to the reference sub-aperture. Thus, we compensate for relative piston, tilt and defocus errors [9] as follows: …”

“…Assuming that there are N sub-apertures and that the reference sub-aperture is number 1, current sub-aperture stitching algorithms use the least-squares method to directly calculate the necessary compensations [5][6][7][8][9]: (2) In our algorithm, we first calculate the second-order partial derivative of Equation 1 with respect to the independent variable x:…”

“…However, location errors are inevitable with this method. Thus, researchers use overlapping areas between the sub-apertures to compensate for location errors [5][6][7][8][9] such as piston, tilt, defocus, clocking, and position errors. In most cases, only piston, tilt, and defocus errors are corrected.…”

Nano-Accuracy Surface Figure Metrology of Precision Optics

“…This technique works by adjusting the distance to the test surface to match the wavefront curvature to the surface radius at each zonal region. Subaperture stitching interferometry (SSI), developed by QED, enables the testing of larger aperture optics with standard Fizeau reference optics, without the need for dedicated large null optics, by automatically combining multiple overlapping sub-aperture measurements to form a full-aperture measurement (Fleig et al, 2003;Murphy et al, 200;. The QED system simultaneously produces an error map of both the larger test surface and the smaller reference surface, correcting for rigid body alignment in each sub-aperture and for reference surface errors.…”