Freeform optics, due to the more general surface geometry that offers high degrees of design freedom to control light propagation, has already been widely used in both nonimaging optics and imaging optics. With the recent advances in design and fabrication of freeform optics, one of the remaining challenges is how to accurately measure freeform optical surfaces, especially those included in freeform refractive optics. To meet this imperative need, for the first time, we believe, present an effective simultaneous multisurface measurement method for freeform refractive optics. Instead of using a reflected optical field to reconstruct tested optical surfaces, we develop a surface reconstruction method based on a transmitted field to tackle the challenges caused by the low reflectivity and compound effect of multiple reflection of refractive surfaces. The transmitted fields from refractive elements are measured by computer-aided deflectometry in order to achieve a large measurement dynamic range and high accuracy. Using the transmitted fields, a multisurface reconstruction model based on iterative optimization is then employed to achieve the accurate multisurface measurement simultaneously. The proposed method is demonstrated to be very effective and robust in testing freeform refractive optics, with a future potential for in situ metrology.

Simultaneous multisurface measurement of freeform refractive optics based on computer-aided deflectometry

Off-axis deflectometry is widely applied in the measurement of specular surfaces. However, the measuring accuracy depends on the reliability of geometrical calibration. Existing methods are inconvenient to be utilized due to their disadvantages of low efficiency and operational complexity. A simple geometrical calibration method is proposed by applying a flat mirror with markers, and only one image needs to be captured. A compensation process is introduced to correct the form error of the mirror. Experimental results show that the re-projection errors decrease from 0.319 pixels down to 0.12 pixels; thus the measuring efficiency and accuracy of optical surfaces can be greatly improved.

Flexible one-shot geometric calibration for off-axis deflectometry.

Compact snapshot dual-mode interferometric system for on-machine measurement

The invention provides a detection method for surface shapes of multiple surfaces of a transmission component and relates to the technical field of measurement. The detection method comprises the steps of: on the premise of measuring a wave aberration of a to-be-detected component by use of a reverse hartmann light path detection device, adding multiple groups of different surface shape errors tothe surface shape of each surface of the to-be-detected component in a light ray tracing model by use of a modeled detection system established by a computer to obtain the corresponding wave aberration; solving a minimum difference value between the wave aberration and an actually measured wave aberration in the modeled detection system; and finally obtaining an actual surface shape error of the to-be-detected transmission component. With the detection method for the surface shapes of multiple surfaces of the transmission component, the technical problems in the prior art that detection for multiple surfaces of the transmission component does not possess high precision and universality. The invention has the beneficial effect that the detection method with high precision and large dynamicrange is provided for detection of the surface shapes of multiple surfaces of the transmission component.

Detection method for surface shape of multiple surfaces of transmission component

The invention provides a free-form surface detecting method based on reverse Hartmann detection and relates to the technical field of measurement. Structure position parameters of an optical path system are calibrated; an ideal optical path system model using a detected object as an ideal surface is established; according to the ideal optical path system model, an experiment is performed to obtainwave front aberrations including surface errors and structure errors; parameters of the ideal optical path system model are adjusted to conduct two-step structure error correction based on high-orderand low-order aberration separation and optimization is conducted on the detected data to obtain a standard optical path system model; ray tracing is conducted on the standard optical path system model, wave front aberrations caused by surface errors of the detected surface are detected, and the surface errors of the detected surface are calculated. The technical problem is solved that in the prior art, high-precision free-form surface detection does not have universality. The free-form surface detecting method has the advantages that two-step optimization based on Zernike fitting is conducted on structure errors, structure position errors of the system are effectively eliminated, the detection precision of the system is improved, and detection is universalized.

Free-form surface detecting method based on reverse Hartmann detection

The deflectometry provides a powerful metrological technique enabling the high-precision testing of reflective surfaces with high dynamic range, such as aspheric and freeform surfaces. In the fringe-illumination deflectometry based on reverse-Hartmann-test configuration, the calibration of system geometry is required to achieve “null” testing. However, the system miscalibration can introduce a significant systematic error in the testing results. A general double-step calibration method, which is based on the low-order Zernike aberration optimization and high-order aberration separation, is proposed to separate and eliminate the geometrical error due to system miscalibration. Both the numerical simulation and experiments have been performed to validate the feasibility of the proposed calibration method. The proposed method provides a general way for the accurate calibration of system geometrical error, avoids the over-correction and is feasible for the testing of various complex freeform surfaces.

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Accurate calibration of geometrical error in reflective surface testing based on reverse Hartmann test

Snapshot phase-shifting lateral shearing interferometer

The invention discloses a free-form surface detection method which includes the following steps: using three-coordinate measuring equipment to measure and calibrate the structural position parameter Sof a reverse Hartmann test optical path including a to-be-detected reflective spherical surface, a projection screen and a CCD camera; determining surface shape error data W0 of the to-be-detected reflective spherical surface according to the measured and calibrated structural position parameter S; determining the surface shape deviation optimization objective of the to-be-detected reflective spherical surface through Zernike fitting according to the measured and calibrated structural position parameter S and the surface shape error data W0; and determining the deviations of the initial measured and calibrated structural position parameter S according to the determined surface shape deviation optimization objective, and determining the actual surface shape error Delta(W) of the to-be-detected reflective spherical surface according to the deviations. By using the method, the surface shape measurement error of the free-form surface is reduced.

Free-form surface detection method and system

The measuring probe integrated with multiple fiber point-diffraction sources can be applied to measure both the three-dimensional coordinates and highly accurate point-diffraction wavefront. The probe determines the achievable measurement accuracy of fiber point-diffraction interferometer (PDI), in which the fiber exit end plane is required to be parallel with the detector plane. The probe misalignment due to fabrication error could introduce significant measurement error. A high-precision method is proposed to calibrate the probe misalignment in fiber PDI, including the central positioning based on phase difference and tilt adjustment based on Zernike polynomials fitting. Both numerical simulation and experiments have been carried out to demonstrate the feasibility and accuracy of the proposed probe misalignment calibration method. The proposed method provides a feasible way to address the processing uncertainty on measuring probe in fiber PDI, and enables high-precision geometry alignment and misalignment calibration in the interferometric testing systems with case of no imaging lens.

Probe misalignment calibration in fiber point-diffraction interferometer

Zhejiang Provincial Natural Science Foundation of China [LY17E050014]; National Natural Science Foundation of China (NSFC) [51375467, 11404312, 51476154, 51404223]; Zhejiang Key Discipline of Instrument Science and Technology [JL150508]

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Chao Wang

Papers

Accurate calibration of geometrical error in reflective surface testing based on reverse Hartmann test

Snapshot phase-shifting lateral shearing interferometer

Free-form surface detection method and system

Probe misalignment calibration in fiber point-diffraction interferometer

Geometrical error calibration in reflective surface testing based on reverse Hartmann test