Shack–Hartmann centroid detection method based on high dynamic range imaging and normalization techniques

Abstract

In the optical quality measuring process of an optical system, including diamond-turning components, the use of a laser light source can produce an undesirable speckle effect in a Shack-Hartmann (SH) CCD sensor. This speckle noise can deteriorate the precision and accuracy of the wavefront sensor measurement. Here we present a SH centroid detection method founded on computer-based techniques and capable of measurement in the presence of strong speckle noise. The method extends the dynamic range imaging capabilities of the SH sensor through the use of a set of different CCD integration times. The resultant extended range spot map is normalized to accurately obtain the spot centroids. The proposed method has been applied to measure the optical quality of the main optical system (MOS) of the mid-infrared instrument telescope smulator. The wavefront at the exit of this optical system is affected by speckle noise when it is illuminated by a laser source and by air turbulence because it has a long back focal length (3017 mm). Using the proposed technique, the MOS wavefront error was measured and satisfactory results were obtained.

Local computational methods to improve the interpretability and analysis of cryo-EM maps

“…The common link between all these approaches is the use of the spiral phase transform, which is used to factorise cryo-EM maps into amplitude and phase terms in real space for different resolutions. The spiral phase transform has been extensively used in optics for phase extraction in interferometry 35 – 39 or by Shack-Hartmann sensors 40 , 41 . This transformation is not new in cryo-EM as it has been proposed previously to facilitate particle screening 42 , CTF estimation 43 and local and directional resolution determination 34 , 44 .…”

Local computational methods to improve the interpretability and analysis of cryo-EM maps

“…The common link between all these approaches is the use of the spiral phase transform, which is used to factorize cryo-EM maps into amplitude and phase terms in real space for different resolutions. The spiral phase transform has been extensively used in optics for phase extraction in interferometry (Larkin, Bone et al 2001, Antonio Quiroga and Servin 2003, Vargas, Restrepo et al 2011, Vargas, Quiroga et al 2012 or by Shack-Hartmann sensors (Vargas, González-Fernandez et al 2010, Vargas, Restrepo et al 2012). This transformation is not new in cryo-EM as it has been proposed previously to facilitate particle screening (Vargas, Abrishami et al 2013), CTF estimation (Vargas, Oton et al 2013) and local and directional resolution determination (Vilas, Gomez-Blanco et al 2018, Vilas, Tagare et al 2020.…”

Shack-Hartmann spot dislocation map determination using an optical flow method

“…In order to assure the brightness constancy assumption shown in Eq. (1), we preprocess the Hartmann diagrams by a fast pattern normalization using the spiral phase transform [7] [14], and then, we compute the optical flow approach over this normalized patterns. This normalization performs background suppression and modulation equalization processes.…”