The PDF file contains the front matter associated with SPIE Proceedings Volume 11899, including the Title Page, Copyright information, and Table of Contents.

This paper proposed a frequency-domain-decomposition denoising algorithm for nano-scale measurement in white light interferometry (WLI). In this work, the captured correlogram is firstly divided into a series of short-time stationary signals, the phase distribution can then be derived as the sum of the corresponding phase components after Fourier transform. By applying windowed threshold filtering, the noises existed in phase map can be eliminated, and a denoised correlogram is precisely reconstructed. Afterwards, the surface height is retrieved through phase-frequency least-square fitting. In simulations, the phase noises with different levels are investigated. By comparing the noise deviations in the reconstructed phase map with the original one, the effectiveness on noise suppression of the proposed method is properly verified. In the experiments, a height step standard with calibrated values 182±2.0nm are tested, where the height deviations below 3nm and the repeatability of 0.5% has proved the robustness of our proposed method.

Digital interferometer is widely used for evaluating optical surfaces due to its outstanding sub-nanometer accuracy and precision. In this paper, we will summarize its advantages and then describe its applications in industry, especially in both absolute flat and cylindrical surface and measurements. Transmission flat has normally 1/20 wavelength PV. However, when a flat surface under test is better or much better than the transmission flat, we need the absolute flat measurement. We developed a method to be easily able to achieve the accuracy of 1/100 wavelength PV. Two different measurement methods are proposed for the surface shape measurement of the inner surface and the outer surface of the cylinder, and the circular data is converted into rectangular data. For off-axis aspheric surfaces, we also propose a new measurement method. We have dedicated our efforts to do so. The theoretical analysis and experimental validation are presented in the paper.

Aspheric surfaces are widely used in advanced optical instrument. Measuring aspheric surface parameter errors (SPEs) in high accuracy is of vital importance in manufacturing and aligning optical aspheric surfaces. A simulation to prove the effectiveness and accuracy of an interferometric measurement method for high-order aspheric SPEs is carried out based on the ideal situation that there is no error of the BCD. The relative accuracy of vertex radius of curvature error, conic constant error and fourth order aspheric coefficient error can reach 5.58×10^-8 %, 1.36×10^-4 % and 0.02%. The influence of the BCD error is analyzed to prove the feasibility of this method and provide a theoretical guidance for real measurement configurations. This method can measure all kinds of aspheric surface parameter errors mentioned above simultaneously in high accuracy.

Phase measuring deflectometry (PMD) has been widely used to measure three-dimensional (3D) shape of specular objects because of its advantages of non-contact, large dynamic range, high-precision and fast-acquisition. However, due to the limited depth of field (DOF) of a camera lens, a liquid crystal display (LCD) screen and a tested specular object cannot be clearly imaged together, which affects the measurement accuracy. To tackle this issue, this paper proposes a novel PMD method of auxiliary imaging LCD screen by using a concave mirror. The LCD screen and a reference are in the same plane via the center of the concave mirror, and are perpendicular to the optical axis of the mirror. Both the LCD screen and the reference are symmetric each other through the optical axis, so that the imaging of one is the location of the other. Based on the imaging principle of concave mirror, the LCD screen is reflected and an inverted real image of the equal size is formed at the reference, and then reflected into the camera by the reference mirror during calibration. During the measuring procedure, a tested specular object is placed at the position of the reference. The displayed fringe patterns on the LCD screen are modulated by the tested specular object and the deformed fringes are captured by the camera. After phase calculation from the captured fringe patterns, 3D shape of the tested specular object can be obtained. The proposed PMD method can avoid the limited DOF of the camera lens, because fringe patterns displayed on the LCD screen and the tested specular surface can be clearly imaged together at the same position. Some simulated experiments on measuring specular objects have been carried out and the results demonstrate that the proposed PMD method can effectively and accurately measure 3D shape of specular surfaces.

A high resolution spectrum analyzer is required to measure a large thickness of a glass plate with a spectral resolved interferometer. In order to solve this requirement, two positions of a reference surface are used to produce short optical differences in the interference signals. Moreover, in order to reduce the dispersion effect a compensation glass is used for the measurement of the rear surface of a glass plate. Linear and nonlinear components of spectral phase distribution of the interference signal are utilized to obtain position of a reflecting surface and thickness of a dispersive medium, respectively. Experimental results show that the measurement error is less than 800 nm and 2 μm for 1 mm and 5mm-thickness glass plates, respectively.

It is very challenging to characterize surface/sub-surface defects for large-aperture optics. The first challenge is the conflict between high resolution and large field of view, namely how to reach a good balance between high resolution and high efficiency for detecting various defects with sub-micronover the meter-size surface of optics. The second challenge is how to classify defects accurately, which is very important for determining origin of defects and improving optics quality.In this paper, a multimodal inspection technique for surface/sub-surface defects of large-aperture optics is reported, in which a high speed laser scattering imaging with a sensitivity at 200-nm scale is used for defect discovery of large-aperture optics. The defect discovery provides a statistical result of defects of the optics. After that, a multifunctional microscopic method is used for local defect review. A photo thermal scanning microscopy is used for specific characterization of absorption defects, and a confocal microscopy is used for characterization of sub-surface defects. The defect review provides information for defect classification. Based on this multimodal technique, an inspection system is also developed and used for defect characterization of large optics.

The signal processing of the grating encoder has a great impact on its accuracy and resolution. We proposed a new type of signal processing method for a grating encoder using a two-phase differential algorithm based on the two-phase physical structure. The interference signal could be divided into two phases with 90 degrees phase delay, capable of effectively reducing the number of optical devices and the space occupied by the reading head. Owing to the rapid elimination of the DC component in the measurement signal, the measurement displacement was solved swiftly by the two-phase signal using the algorithm. In the experiment, a 660 nm laser and a 1 µm-period grating were used, and the scale grating was actuated at a speed of 1 µm/s by a linear stage. With a sampling rate of 20 kHz, the system resolution of the grating encoder was enabled to reach 50 pm. Simultaneously, there was a measurement error of ±1 µm at a stroke of 4 mm, and the error within a single cycle was 2 nm. Compared with the four-phase algorithm, our proposed two-phase differential algorithm exhibits a compact physical structure and fast solution without reducing the accuracy and resolution, which will be of great significance to the real-time measurement and miniaturization of grating encoders.

Nowadays most commercial measurement software only indirectly evaluates the accuracy of the cooperative measurement and lacks intuitiveness. Therefore an accuracy evaluation method of the cooperative measurement is studied so that the transformation parameters’ error and the final results’ error in the cooperative measurement are directly quantified. And customized software is developed which is used to quickly and easily evaluate and visually display the accuracy of the cooperative measurement in the industrial field. Finally an experiment with two laser trackers is conducted to prove the accuracy evaluation method and the software of cooperative measurement. It is obvious that the accuracy evaluation method is feasible and the accuracy evaluation software is user-friendly

This contribution presents simulation and measurement results considering the identification and preclusion of aliasing effects in Modulation Transfer Function (MTF) measurements of unknown specimens. An adaptation of the commonly applied slanted edge algorithm is employed to retrieve the MTF from tilted Line Spread Function (LSF) images, which are recorded for different microscope objective magnifications and tilt angles. Measurement results demonstrate the capability of the slanted slit oversampling technique to detect and resolve aliasing issues. The variation of magnification objectives, tilt angle, binning value, camera detector and evaluation algorithm reveals systematic MTF error contributions due to these parameters.

Frequency-swept interferometry (FSI) is a well-established technique for static ranging or clearance measurement. However, when measuring the dynamic clearance in turbines, both the FSI-Doppler effect induced by target drift and the sweeping nonlinearity of the light source restricts the measurement accuracy significantly. These are two inevitable problems and must be solved. Therefore, an improved FSI-based system is proposed to realize the dynamic clearance measurement. The system consists of two sensing arms and one reference arm. Two sensing arms refer to an FSI and a frequency-fixed interferometer (FFI) with an acoustic optical modulator (AOM), while the reference arm contains a determined Machzender interferometry. The Machzender interferometry is adopted to correct the nonlinear error of the FSI signal, and the FFI with the AOM is used to suppress the Doppler error. An optimized fusion algorithm will be used combining the information of three arms. And the dynamic clearance can be reconstructed at each sampling point with the algorithm suppressing the Doppler effect and the sweeping nonlinearity problems. The system with its algorithm was verified theoretically by measurement simulations for targets in multiple forms of motion. Further experiments will be carried out in the near future.

The spacecraft need to do vacuum thermal tests in a vacuum chamber before they lunched. The solar simulator can simulate the collimation, uniformity and spectrum of the sunlight accurately, which provides higher precision space thermal external flux in the vacuum thermal tests of spacecraft. These solar simulators usually are installed on the vacuum chambers. Its light source is outside the vacuum chamber, the light incidents into the chamber by the optical vacuum sealed window. In order to get uniformity irradiation testing volume, the off-axis collimating solar simulator is selected which installed on the KM6 large vacuum chamber. The main chamber is vertical to place the test-articles, which has the overall height of 22000mm, the diameter of 16000mm. The auxiliary chamber is horizontally to place the collimating reflector of the solar simulator, which has the overall height of 13000mm, the diameter of 7500mm. Thesolar simulator is included optical system, cooling system and control system. The optical system consists of the collector mirrors, the collimating reflector and the optical integrator. This solar simulator is developed successful, and it has finished a vacuum thermal test of the camera. In the test the irradiance of the solar simulator is 1420W/m² , it worked more than 100 hours. The test is successful, and gets more valuable experimental data.

A coherent random modulation LiDAR based on phase-coded subcarrier modulation is proposed to mitigate the impact of Doppler-frequency-shift (DFS) from the pseudo-random (PR) pattern. DFS is firstly obtained from the beat signal of the reflected optical carrier and the local optical signal. Then digital DFS compensation is used to mitigate the impact of the DFS from the PR-coded subcarrier. In the demonstration experiment, a 1.25-GHz RF signal is used as the subcarrier which is phase-coded with a 500-Mbit/s M-sequence. The DFS is simulated by an acousto-optic modulator (AOM). The length of fiber is measured, which demonstrate the feasibility of the proposed DFS mitigation method.

In this paper, we present a wide-spectrum plug-and-play Fizeau interferometric system, which can complete precision interferometric measurement at any wavelength in the range of 600-1600 nm with a maximum measurement aperture of 150 mm. The system can be designed with multiple optical fiber input terminals, different wavelengths share only one set of interferometric system, and no components need to be adjusted when switching the working wavelength. The development of the system is helpful to accurately measure the surface profile error of coated optical elements at a specified wavelength.

The laser beam is considered as an important technique tool for 3D measurement. For precise 3D measurement, the spatial pose of a laser beam must be calibrated before measurement. To make the spatial pose of a laser beam more precise, an optimization method of a laser beam is proposed in this paper. Utilizing the points measured by a laser tracker as benchmark, the more precise parameters of the laser beams can be obtained through Levenberg-Marquarelt algorithm. Comparing improved results with initial ones, the effect of the method can be shown obviously. The method is considered to be a feasible way to optimize the laser beam through experiment verification.

In this paper, a new encoding method for single-track absolute shaft encoder is introduced based on the analysis of the characteristics of the code. This code using the new method has the characteristics of customizable code length and good code balance, which solves the problem that the traditional code length can only be some discrete value and the problem of poor code balance. The new code has abundant redundant information, based on which, it is easy to distinguish whether there is fault in the code recognition.

In order to meet high quality measurement requirements with less cost and lesser time consumption, the sampling strategy has to be planned before the measuring device is already available. In this paper, a common 3D geometric measuring system based on laser scanning technique is presented. An measurement cost model is established by consider of several cost sources in 3D geometric measurement process. In terms of view angle of laser scanner, an optimal inspection strategy planning is developed on a circular feature too. Finally, a series of experiments on typical circular of workpieces are performed based on coordinate measuring system equipped with a laser line scanner. In case of desired measurement accuracy for the measured feature, the minimum inspection cost can be obtained by the iterative optimization algorithm, thus generating a reliable and an efficient sampling path planning. Those results are most promising for on-machine applications in optimal inspection strategy of 3D geometric of workpiece.

Thickness measurement for the optical thin films is very important for the industries of mechanics, printing, battery and so on. Infrared transmittance method is a very useful method to achieve the physical response, which is related to the film thickness according to the Lambert-Beer law. A detail measurement system is designed with two light paths of reflectance and transmittance, consisting of the light source, filter motor, beam splitter, paraboloid mirror, PbSe detector, and so on. An experimental setup is also established with two different infrared wavelengths by two different bandpass optical filters. The stability of the measurement system is tested to be only about 0.3% in 10 min. The experiments show the feasibility of the proposed double-wavelength infrared transmittance method for film thickness measurement.

The traditional methods of measuring refractive index have their unique value and advantages. In order to study the properties of materials and the application of multi-wavelength laser interferometer, a new method of measuring refractive index and dispersion of materials is proposed. The multi-wavelength laser interferometer is designed and built based on the principle of the Fizeau interferometer. It integrates five kinds of laser bands with a wide coverage range through a splitting prism, and can quickly change the measurement wavelength during remeasurement and improve the detection efficiency. In order to further verify the refractive index measurement method, a parallel plate is taken as an example to measure the refractive index. The multi-wavelength laser interferometer combined with variable wavelength standard spherical mirror is used to measure the displacement of ray focus in the case of parallel plate or not, and the refractive index of parallel plate is calculated by geometric optics. The refractive index corresponding to each wavelength is measured, and the refractive index curve of the parallel plate material is calculated by Conrady formula and ACF formula by fitting polynomial method using the measured data, and then the dispersion coefficient of the material can be calculated. The comparison results show that the ACF formula can be used to calculate the refractive index of materials accurately in a larger band range. The experimental results also show that the multi-wavelength laser interferometer has the advantage of measuring multi-wavelength transmission wavefront and can also play a role in more measurement applications.

Accurate measurement of the aperture area has always been the focus of optics and optical radiation measurement. The metrology institutes around the world have established absolute aperture area measurement facilities. In this paper, a measuring system of the aperture area based on optical flux comparison method is designed and implemented., which can transfer absolute values efficiently and accurately. The results show that the deviation between the area measured by optical flux comparison method and the area measured by effective area method is about 5×10^-4 . The influences of the light source stability, irradiation field uniformity and aperture positioning difference on the measurement results are analyzed emphatically. The uncertainty of the measurement results is also evaluated, the relative expanded uncertainty is 9.9×10^{- 4} (k=2).

The measurement of large aperture optical components becomes much more critical as they are increasingly being used in high power systems and astronomical systems. Large aperture transmissive optical elements always suffer from stressinduced birefringence, which leads to the difference of profiles for linearly polarized beams with different orientations. A spatially varying optical path difference is introduced into the measurement result as wavefront aberration in a dynamic interferometer based on the polarization phase-shifting method. This paper proposed a method to measure and correct the birefringence effect for a 600mm aperture dynamic interferometer based on the rotation of the incident polarized beam, needing no more additional elements. The interferometer includes a Kepler beam expander system consisting of two collimators with 100mm and 600mm aperture. The 600mm aperture collimator is viewed as a transmitting element between the interference cavity of a 100mm TF and a 600mm RF. The polarization state of the incident beam can be switched between P light and S light, where a phase difference can be obtained between two measurements. The difference between the two distributions can be viewed as the birefringence effect on the dynamic interferometer. Besides, the system error can be removed during the data subtraction. Experiments are conducted on a 600mm dynamic interferometer and the correction result is compared with a wavelength tuning method which is free of polarization errors brought by the stress-induced birefringence stress. A comparison is also conducted with the correction result realized via a wave plate model proposed before.

Based on the research on the on-line construction of dynamic control system in intelligent manufacturing, the theory, function and model of intelligent design and intelligent manufacturing （IDIM）are established. Explore and improve in engineering practice have been corrected. And many effective solutions have been achieved.

Null interferometric microscope (NIM) is an effective method for detecting the isolated defects on the ICF capsule’s surfaces thanks to its null interference and high-resolution imaging ability. However, the limited depth-of-focus (DOF) caused by the large numerical aperture is the main drawback that prevents measuring defects in the full field of view (FOV) on the curved surface. In this work, a depth-of-focus (DOF) extension method based on numerical propagation is proposed to expand the field of view (FOV) of the NIM. The capability of the proposed DOF extension method is proved by the measurement of a 1-mm diameter ICF capsule. Experiment results indicate that the FOV of NIM is expanded from 140 μm to 320 μm.

Fringe projection profilometry (FPP) is a commonly used tool in the three-dimensional (3D) measurement of diffuse objects in reverse engineering, products online detection, medical diagnosis, etc. However, due to the limited depth-of-field (DOF) of projection-imaging lenses, the contrast of captured sinusoidal fringes will decrease with the increase of defocus, which affects the high-precision acquisition of axial 3D topography. Although the lenses can be designed based on Scheimpflug principle or double-telecentric optical path to extend the DOF, some problems such as off-axis aberration, fixed magnification and limited field-of-view are still existing. To overcome the aforementioned drawbacks, FPP with phase-coded optics is proposed in this paper, where the captured sinusoidal fringe patterns are modulated effectively and the projection-imaging DOF of the system is greatly extended. Experimental results demonstrate the effectiveness of the proposed technique.

As a fundamental geometric indicator, high precision roundness measurement is the basis evaluation index of cylindrical or spherical parts. In most roundness measurements, the rotation platforms are used to bring certain rotation error to the measurement result. Two-probe method is a typical roundness measurement strategy with error separation technique, coming from three-probe method with low cost, online integration, flexible installation, etc. We developed a roundness measurement system with three chromatic confocal displacement sensors with flexibility and high axial-resolution. As the measurement start, two sets of displacement data are achieved to take part in the frequency calculation. A typical cylindrical workpiece was measured for its roundness, which was very close with the measurement result by an ultra-precision roundness meter. In a word, the chromatic confocal roundness measurement system is feasible to provide high precision roundness with two-probe method.

Three-dimensional (3D) measurement based on structured light, as a non-contact, active, and high-precision measurement technology, is widely applied in the diverse fields of industrial detection, face recognition, reverse engineering, and so on. We adopted an adjustable grating-stripe coding as the dynamic structured-light mode, which can continuously cover the entire measured surface to guarantee high accuracy. A one-axis resonant-mode MEMS mirror combined with a linear laser was used to project the desired adjustable grating stripes, leading to a miniaturized module size. To make the scanning angle of the MEMS mirror matching the intensity distribution of the linear laser, we further introduced a single-chip microcomputer (STM32) to receive the feed-back signals from MEMS mirror, and synchronously controlled the laser power with corresponding function relationship output. Here, the MEMS mirror could provide a resonant frequency of 1.15 kHz, a scanning optical angle of ±30°, a feed-back scanning-angle resolution of 0.05°, and a reflected mirror size of 3 mm-diameter circle, respectively. Also, the laser source could generate a line width of 70 μm at a 300 mm focused distance. To decrease the error in the energy amplitude of each cycle of the structured light stripes, the empirical mode decomposition (EMD) was used to perform principal component analysis and recombination of the structured light stripes. In addition, total harmonic distortion (THD) is used to evaluate the quality of structured light stripes. Finally, the structured light based on the scanning of the MEMS mirrors exhibits a good sinusoidal stripes and high refresh rate, implying high adaptivity for the 3D reconstruction.

NIM has developed LED filament standard lamps for total luminous flux with excellent long-term stability, uniform distribution of luminous intensity, and the E27 Edison screw base which is compatible with present incandescent standard lamps. The standard lamp consists of six high-power LED filaments which are sealed in a G150 glass bulb and filled with He gas. All the 12 lamps were aged for 500 hours before the 315 days’ long-term stability test. 9 lamps are lighted for 1 hour every day. One lamp is continuously operated for about 6000 hours, and 2 lamps are well stored on a shelf. The results show that the long-term stabilities of the 3 cases are better than 0.07%. This LED filament lamp could be promising as a transfer standard of total luminous flux.

This work presents a novel method to simultaneously measure a quarter-wave plate's phase retardation and fast axis using radially polarized vector beams and spatial Fourier analysis. The light beam is converted into a radially polarized beam after passing through a polarizer and a vortex retarder. The tested quarter-wave plate and a polarizer are placed after the vortex retarder in sequence, and an hourglass intensity distribution image is recorded by a camera. Then the phase retardation and fast axis of a quarter-wave plate can be calculated by using Fourier analysis of the recorded intensity image with a snapshot. The theoretical model of the proposed method is built based on the Stokes-Mueller formalism. And both simulation calculation and experiments are carried out with different fast axis angles of a quarter-wave plate. The measurement errors of the phase retardation and fast axis are also analyzed to validate the proposed method. Both simulation calculation and experimental results show good agreement with the theoretical values. It is demonstrated that the proposed method is convenient, simple, and accurate to measure the phase retardation and fast axis of a quarter-wave plate.

The equal optical path interferometer is a modified type of measuring device, which is used to improve the quality of interferences between multiple surfaces. In some cases, this modified kind of interferometer can polish the quality of images by bettering the character of interferences between multiple surfaces, which can not be ignored in traditional interferometers, such as the Fizeau interferometer and the Twyman Green interferometer. This paper mainly introduces the basic principles of equal optical path interferometer, and we carry out a series of simulations and do some analyses of equal optical path interferometer, in order to get a better solution. The main characteristic of equal optical path interferometer is equal optical path, which is realized by the inclinations of the reference lens and the beam splitting lens. There is a certain relationship between the inclination of the reference lens and the beam splitting lens. We use MATLAB and C language to simulate the relationships between mechanisms of it, and find out the influence weights and boundary conditions of each mechanism on the overall structure. Then according to the relationships between various mechanisms, the relatively good relations and structures are obtained, which are convenient for the realization of the actual experimental verification. According to the calculated results, we use Zemax to simulate and optimize them, and get the theoretical results of the experiment. Based on the theory-based calculations and simulations, we confirm that the equal optical path interferometer has the possibility of practical implementation, and the theory has a certain guiding significance for the experimental verification.

Owing to its advantages of simple system structure, large dynamic range and high measurement accuracy, fringe reflection technique (FRT) is becoming a powerful tool for specular free-form surface testing in the fields of reverse engineering, defect inspection, optical manufacturing, etc. However, due to the optical transfer function (OTF) of the FRT optical system, high-frequency information on the surface of an element under test is easily lost, which affects the high-precision acquisition of three-dimensional (3D) topography especially in microscopic measurement. Although the above problem can be suppressed to some extent by using or designing high-performance optical systems, the significant increase in the complexity and cost of the measurement system is sometimes unacceptable. To overcome the afore mentioned issue, a resolution-enhanced phase retrieval algorithm based on structured illumination microscopy (SIM) for FRT with an ordinary optical system is proposed in this paper. The combination of FRT and SIM is realized by projecting conventional phase-shifting fringe patterns in multiple directions. In principle, resolution-enhanced phase retrieval with super-diffraction limitation (up to twice the pass band of OTF) can be realized through spectrum extraction, stitching and shifting. A low cost, compact, coaxial FRT setup based on open-source hardware is designed and built for experimental verification. Simulations and experimental results demonstrate the effectiveness of the proposed technique.

Flatness metrology is needed in the optical industry as well as for synchrotron mirrors, for precision engineering and for telescope mirrors. Calibrated optical flats are a key element for quality assurance in many fields and applications of science, research, and industry. The National Metrology Institute of Germany (Physikalisch-Technische Bundesanstalt, PTB) offers interferometric flatness calibrations for specimens up to 300 mm in diameter and deflectometric flatness calibrations up to 900 mm for elongated specimens. We are continuously developing our flatness metrology further to meet future requirements, e. g. to achieve uncertainties of a few nanometers as well as to offer measurements of large flats up to 1.5 meters. In this contribution we focus on three current activities. Firstly, we show our new large form measuring system for smooth curved specimen, which can also be used for flatness measurements of specimens with diameters up to 1.5 meters. Secondly, we demonstrate, how sub-millimeter lateral resolutions can be achieved with small angle deflectometry. Thirdly, we present an international round robin comparison of an optical flat. The flatness on an aperture of 300 mm is to be measured and the participants shall reach an expanded uncertainty of less than 15 nm (k=2). This will also ensure a reliable traceability also for subaperture measurements of optical flats with larger diameters.