Qian Liu

China Academy of Engineering Physics · Institute of Machinery Manufacturing Technology

Precise three-dimensional (3D) inspection of surface and subsurface defects for optical components has become more and more urgent in high-power laser systems. In this paper, a dark-field structured illumination microscopy (DSIM) is proposed for 3D defect detection method in optical components. This method improves the axial resolution by structure...

Axicon lenses are critical in the beam transforming, such as the Bessel beam and hollow beam generation, and its manufacturing accuracy directly affects the quality of the output beam. Aiming at the versatility and high accuracy, we propose a two-dimensional differential null interferometry for measuring transmission wavefront of axicon lens. The m...

To deal with the light intensity crosstalk between R, G and B channels of colour camera in multi-colour interferometry, we present a fast and in-situ correction method based on Fourier transform of carrier fringes. The crosstalk coefficients of camera channels are obtained in the Fourier frequency domain of captured colour carrier fringes, and the...

As the primary error source in white-light interferometry (WLI), the error of scanning steps directly affects coherence peak sensing and greatly lowers the measurement accuracy. Based on the least-squares iterative algorithm, we present an algorithm to detect and compensate for scanning error in WLI. The actual scanning step is calculated from the...

The interference microscope is a powerful tool for surface topography measurement, but its high sensitivity to vibration hinders its application to on-machine measurement. To measure surface roughness on a machine for the ultra-precision machining, a vibration-resistant interference microscope (VRIM) with an assistant focusing function is developed...

High-performance optics puts stringent requirements on the defect control of transparent optical components (TOCs). In order to accurately and reliably detect the surface and internal defects of TOCs, this paper proposes a three-dimensional (3D) defect distribution detection method based on coaxial transmission dark-field (CTDF) microscopy. The ill...

To deal with vibration disturbance in interferometric measurement of surface topography, we present a simultaneous dual-wavelength phase-shifting interferometry (SDWPSI). SDWPSI collects phase-shifting interferograms of two wavelengths simultaneously with two cameras to accelerate data collection. The optical phases are retrieved from dual-waveleng...

Sinusoidal phase-shifting interferometry (SinPSI) suffered from modulation error. To cope with this problem, an arbitrary sinusoidal modulation SinPSI (ASM-SinPSI) method was proposed, which extracted wavefront phase from Fourier spectrum of the interferometric signal. In ASM-SinPSI, firstly the modulation amplitude was determined from the strength...

In the interferometric subaperture stitching, the subaperture-overlapped regions are often inaccurately positioned due to positioning error. To achieve better stitching effect, we propose a robust subaperture stitching method based on three-dimensional surface data matching. Speeded up robust features algorithm is used to calculate the relative dis...

Iterative algorithms are useful for retrieving wavefront phase from vibration disturbed interferograms for phase-shifting interferometry (PSI). But the dependence of convergence on the initial value deviation from the exact value impairs their application in severe vibration. In this paper, performance investigation of a representative iterative al...

Phase-shifting interferometry (PSI) is sensitive to many disturbances, including the environmental vibration, laser instability, phase-shifting error and camera nonlinearity. A robust PSI (RPSI) based on the temporal spectrum analysis is proposed to suppress the effects of these common disturbances. RPSI retrieves wavefront phase from the temporal...

The sensitivity of phase-shifting interferometers (PSIs) to vibration impairs their application in unsteady environment. Iterative algorithms were developed to desensitise the effect of vibration on PSIs, but their desensitising capability is restricted by the estimated initial value. In this paper, a spatial carrier-assisted method is proposed, in...

Absolute phase information is required when multiple separated objects are being measured. The recent proposed phase-coding method can effectively achieve absolute phase retrieval by embedding the fringe order information in phase domain. However, it suffers from the limitation of codewords and the requirement of more coding patterns. To overcome t...

Instrument transfer function (ITF) of white light interferometer (WLI) influences the measurement accuracy of power spectral density (PSD) for optical surfaces. To understand the nature of ITF, WLI was treated as an incoherent optical system and a sinusoidal surface was the input signal. Studying the Bessel function expansion of interference intens...

Vibration hinders the application of phase-shifting interferometry (PSI) to on-machine test and large-aperture mirror measurement. The investigation of PSI fringe disturbed by vibration indicates that, besides tilt-shifting error, inter- and intra-frame contrast variation is significant. The contrast variation is another dominant error source in ph...

For calibration of the phase shifter in a phase-shifting interferometer, an iterative algorithm was proposed to extract phase shift from a set of interference patterns. In each iteration cycle, the wavefront phase and phase shifts were calculated in two individual steps. Firsly, the phase shifts were assumed knowns and the calibration wavefront pha...

To apply phase-shifting interferometry (PSI) to in-situ measurement, we have proposed an algorithm to detect and suppress phase-shifting error and contrast fluctuation. The phase shift and contrast are analyzed in spatial-frequency domain. The strength of baseband and sideband implies the pattern contrast. The position and phase angle of the sideba...

To suppress the sensitivity of phase-shifting interferometry to mechanical vibration, a modified three-step iteration algorithm (MTIA) is proposed. The wavefront phase, x - and y -directional phase shifts are calculated in three individual steps in an iteration cycle. MTIA solves the tilt factors of phase shift through orthogonal decomposition and...

The fluctuations of background and contrast cause measurement errors in the phase-shifting technique. To extract the phase shifts from interferograms with background and contrast fluctuations, an iterative algorithm is represented. The phase shifts and wavefront phase are calculated in two individual steps with the least-squares method. The fluctua...

An algorithm was proposed to deal with the phase-shifting error and contrast variation in a Phase-shifting Interferometry (PSI) under vibration. The algorithm detected phase shifts and contrast variation by analyzing the spectra of spatial-carrier interferograms firstly. Then the phase shifts were used as priori information to retrieve the wavefron...

Phase shift error and contrast variation caused by vibration lead to a large measurement error in temporal phase-shifting interferometry (PSI). To suppress the error, a sideband correlation algorithm is proposed to detect phase shift and contrast variation. The tilt factors and translational values of phase shift are determined by analyzing the cor...

An algorithm is proposed to deal with tilt-shift errors in temporal phase-shift interferometry (PSI). In the algorithm, the tilt shifts are detected with the spatial-carrier phase-shift (SCPS) method and then the tilt shifts are applied as priori information to the least-squares fittings of phase retrieval. The algorithm combines the best features...

We built a chromatic confocal microscope for micro metrology. Based on dispersive aberration principle and optimization of lens glasses, a dispersive objective was designed, of which the dispersive aberration was linear to wavelength. The linear dispersive aberration could help to balance the sensitivity of chromatic confocal microscope. Designed d...

An iterative method based on least-squares fittings is proposed to retrieve wavefront phase from tilt phase-shift interferograms. In each iteration cycle, proposed method calculates wavefront phase and tilt phase shifts in x- and y-directions in three individual least-squares fitting steps. In tilt phase shifts extracting steps, phase shifts of int...

A spatial frequency domain method is presented to deal with tilt-shift errors and random phase shift in temporal phase-shift interferometry. The proposed method determines tilt shift and phase shift by analyzing positions and phase variances of sidebands in spatial frequency domain. The method is computationally fast for it is noniterative and need...

As the nonlinearity between the Axial Chromatic Aberration (ACA) and the wavelength of a dispersive objective would lower the overall performance of a chromatic confocal microscope, the dependence of the ACA of an optical system on the lens assembly was studied and the transfer principle of ACA was derived. Based on ACA transfer principle, a disper...

With the minimization of optical devices, the size of lens becomes much smaller. As a crucial parameter of spherical lens, the measurement of curvature radius is valuable in small lens manufacturing. In this paper, confocal microscope method is proposed to measure curvature radius of spherical lens, especially small spherical lens. The setup of thi...

Dispersive objective is the key component of Chromatic Confocal Microscope (CCM). The measuring range of CCM depends on the chromatic aberration of dispersive objective, and the nonlinear axial chromatic aberration of dispersive objective would lower the sensitivity of CCM. To achieve large axial chromatic aberration, optimization method of selecti...

Chromatic Confocal Displacement Sensor (CCDS) is now used widely for its high precise and robust property. As the key component, the objective is used to achieve longitudinal focus vibration with wavelength. The theory of CCDS is analyzed and formulae for calculating the parameters of objective are presented. With the formulae guiding, a dispersive...

Dynamic concentricity measurement of small holes distributed in large room is valuable in assembling some big and complex optical facility. It's not feasible for the conventional measurement with portable CMM or laser tracker. A solution of dynamic concentricity measurement is put forward in this article, in which low power laser was selected as re...

Machine vision now is widely used as non-contact metrology which is a trend of measurement. In this article, a 3D machine vision probe for engineering is designed. The XY axial measurement is done by 2D vision metrology, while the Z axial height is measured by microscope through auto-focus (AF). As the critical part of probe, a long work distance (...