Sub-Nyquist sampling rate temporal correlation method for measuring the surface of the transparent planar element.

When deflectometry is applied to measure transparent planar elements, parasitic reflection from the back surface can introduce errors in the reconstruction result. Traditional frequency-domain methods typically require over thousands of fringe patterns to satisfy the Nyquist sampling law, which allows for the separation of parasitic reflection. Failure to meet the requirement of the sampling rate can lead to accuracy decrease of the screen coordinate extracted by the frequency-domain method, deteriorating the accuracy of surface reconstruction.

online deflectometry with synchronized calibration and measurement.

Delicate calibration is essential for high-accuracy deflectometric measurements of specular surfaces. However, traditional methods rely on assumptions that can introduce significant systematic errors, particularly regarding system stability throughout the calibration-measurement process. This Letter proposes a synchronized calibration and measurement method for deflectometry, effectively tackling the instability-induced systematic error.

In-situ high-accuracy figure measurement based on stereo deflectometry for the off-axis aspheric mirror.

The misalignment between the geometric and optical axes, combined with rotational asymmetry, poses significant challenges for achieving high-accuracy measurement of the off-axis aspheric mirror during the fabrication and polishing processes. To address this issue, this paper presents a method based on stereo deflectometry for measuring the figure of the off-axis aspheric mirror. In this method, point cloud of the off-axis aspheric mirror is first obtained using stereo deflectometry.

Frequency-domain searching algorithm in deflectometry for measuring the surface of a transparent planar element.

This Letter presents the frequency-domain searching algorithm in deflectometry (FSAD). By encoding specialized multi-frequency fringe patterns and employing a correlation searching algorithm, the limitations of existing frequency-domain methods can be overcome to some extent, thereby separating front and back surface reflections to obtain complete measurement data. The principles of FSAD are described in detail.

Refractive index measurement deflectometry for measuring gradient refractive index lens.

A method based on deflectometry to measure the refractive index distribution of radial gradient refractive index (GRIN) lens is proposed in this paper. The method establishes the relationship between the refractive index distribution and the direction of light ray by deriving the propagation equation of light in a non-uniform medium. By measuring the deflection angle using the principle of deflectometry and the assumption of central refraction, the refractive index distribution of the radial GRIN lens is determined.