Showing papers by "Dong Liu published in 2015"

Practical phase unwrapping of interferometric fringes based on unscented Kalman filter technique

Abstract: A phase unwrapping algorithm for interferometric fringes based on the unscented Kalman filter (UKF) technique is proposed. The algorithm can bring about accurate phase unwrapping and good noise suppression simultaneously by incorporating the true phase and its derivative in the state vector estimation through the UKF process. Simulations indicate that the proposed algorithm has better accuracy than some widely employed phase unwrapping approaches in the same noise condition. Also, the time consumption of the algorithm is reasonably acceptable. Applications of the algorithm in our different optical interferometer systems are provided to demonstrate its practicability with good performance. We hope this algorithm can be a practical approach that can help to reduce the systematic errors significantly induced by phase unwrapping process for interferometric measurements such as wavefront distortion testing, surface figure testing of optics, etc.

Flow Boiling Heat Transfer and Two-Phase Flow Instability of Nanofluids in a Minichannel

Abstract: Single-phase convective heat transfer of nanofluids has been studied extensively, and different degrees of enhancement were observed over the base fluids, whereas there is still debate on the improvement in overall thermal performance when both heat transfer and hydrodynamic characteristics are considered. Meanwhile, very few studies have been devoted to investigating two-phase heat transfer of nanofluids, and it remains inconclusive whether the same pessimistic outlook should be expected. In this work, an experimental study of forced convective flow boiling and two-phase flow was conducted for Al2O3–water nanofluids through a minichannel. General flow boiling heat transfer characteristics were measured, and the effects of nanofluids on the onset of nucleate boiling (ONB) were studied. Two-phase flow instabilities were also explored with an emphasis on the transition boundaries of onset of flow instabilities (OFI). It was found that the presence of nanoparticles delays ONB and suppresses OFI, and the extent is correlated to the nanoparticle volume concentration. These effects were attributed to the changes in available nucleation sites and surface wettability as well as thinning of thermal boundary layers in nanofluid flow. Additionally, it was observed that the pressure-drop type flow instability prevails in two-phase flow of nanofluids, but with reduced amplitude in pressure, temperature, and mass flux oscillations. [DOI: 10.1115/1.4029647]

Aspheric subaperture stitching based on system modeling.

Abstract: Instead of various mathematical stitching algorithms, an aspheric subaperture stitching interferometric method relying on modern computer modeling technique is presented. Based on our previously reported non-null annular subaperture stitching interferometry (NASSI), a simultaneous reverse optimizing reconstruction (SROR) method based on system modeling is proposed for full aperture figure error reconstruction. All the subaperture measurements are simulated simultaneously with a multi-configuration model in a ray tracing program. With the multi-configuration model, full aperture figure error would be extracted in form of Zernike polynomials from subapertures wavefront data by the SROR method. This method concurrently accomplishes subaperture retrace error and misalignment correction, requiring neither complex mathematical algorithms nor subaperture overlaps. Experiment results showing the validity of SROR method are presented.

Chemical Effects of Carbon Dioxide Addition on Dimethyl Ether and Ethanol Flames: A Comparative Study

Abstract: The chemical effects of CO2 addition on premixed laminar low-pressure dimethyl ether and ethanol flames were studied by comprehensive numerical analysis from fuel-lean to fuel-rich conditions. Added CO2 is assumed as normal reactive CO2 and fictitious inert CO2 to assess the chemical effects of CO2. The dilution and thermal effects of CO2 addition decrease C2H2 mole fractions in ethanol flames instead of DME flames, but the chemical effects can reduce C2H2 mole fractions in both DME and ethanol flames at all equivalence ratios, which reveals that C2H2 formation can be suppressed chemically by CO2 addition. The chemical effects have a weak influence on formaldehyde formation in both DME and ethanol flames. The CO2 chemical effects only result in a slight decrease of acetaldehyde peak mole fractions in DME flames but not in ethanol flames at all equivalence ratios. Mole fractions of the H radical decrease because of the chemical effects of CO2 addition by shifting the equilibrium of CO + OH = CO2 + H in bot...

General measurement of optical system aberrations with a continuously variable lateral shear ratio by a randomly encoded hybrid grating.

Abstract: A general lateral shearing interferometry method to measure the wavefront aberrations with a continuously variable shear ratio by the randomly encoded hybrid grating (REHG) is proposed. The REHG consists of a randomly encoded binary amplitude grating and a phase chessboard. Its Fraunhofer diffractions contain only four orders which are the ±1 orders in two orthogonal directions due to the combined modulation of the amplitude and phase. As a result, no orders selection mask is needed for the REHG and the shear ratio is continuously variable, which is beneficial to the variation of sensitivity and testing range for different requirements. To determine the fabrication tolerance of this hybrid grating, the analysis of the effects of different errors on the diffraction intensity distributions is carried out. Experiments have shown that the testing method can achieve a continuously variable shear ratio with the same REHG, and the comparison with a ZYGO GPI interferometer exhibits that the aberration testing method by the REHG is highly precise and also has a good repeatability. This testing method by the REHG is available for general use in testing the aberrations of different optical systems in situ.

Pattern recognition model for aerosol classification with atmospheric backscatter lidars: principles and simulations

Abstract: A pattern recognition model for aerosol classification with atmospheric backscatter lidars is proposed and studied in detail. The theoretical framework and the implementation process of the proposed model are presented. Computer simulations have been carried out to verify the practicability and robustness of this model. The k-fold cross-validation method is employed in the process of classifier designing to choose the proper decision rule, which is mainly based on statistical pattern recognition theory. At the same time, the validity of the model is evaluated. The generalized self-validation is also carried out in the computer simulations to verify the stability of the model. The analysis of the performances in reduced status, especially the instance of application to Cloud-Aerosol Lidar with Orthogonal Polarization, demonstrates the generalization ability and performance of this model.

Coal Char Gasification on a Circulating Fluidized Bed for Hydrogen Generation: Experiments and Simulation

Abstract: Char is the solid product of coal pyrolysis and its utilization is closely related to the scale of coal pyrolysis and tar processing. Char gasification is a promising choice for char utilization as it can provide hydrogen, which is needed for tar hydrogenation and chemical synthesis. However, reliable and mature coal char gasification technology has not yet been developed. The fluidized bed has been adopted as a gasifier in many studies, and its gasification temperature is relatively low. In this work, the feasibility of char gasification using a fluidized bed has been studied. A pyrolyzed bituminous coal char was gasified in a mixture of O2 and steam using a circulating fluidized bed. The height of the fluidized bed is 2360 mm and the inner diameter is 66 mm. The reactor is made of Ni-Cd alloy steel, and a loopseal was used for solid circulation. In the experiments, the gasification temperature was varied between 870 and 900 °C, and the effects of O2/char and steam/char mass ratios on the gasification results were analyzed. The volume fraction of combustible gas, dry gas yield, carbon conversion, and lower heating value of the best case were 43.92 %, 1.64 Nm3 kg−1, 0.85, and 5.17 MJ N m−3, respectively. In addition, a simple model and a complex model were established by using Aspen Plus software. The two models were used to simulate char gasification, and the simulation results were validated with the experimental results. The results indicated that the complex model is more accurate than the simple model and is more suitable to simulate char gasification in a circulating fluidized bed.

Dynamics of ferromagnetic nanowires in a rotating magnetic field

Abstract: Manipulating nanowires with external magnetic fields has emerged as a powerful tool in various engineering applications, which prompts an urgent need to better understand the dynamics of nanowire r...

A New Route for Unburned Carbon Concentration Measurements Eliminating Mineral Content and Coal Rank Effects

Abstract: 500 million tons of coal fly ash are produced worldwide every year with only 16% of the total amount utilized. Therefore, potential applications using fly ash have both environmental and industrial interests. Unburned carbon concentration measurements are fundamental to effective fly ash applications. Current on-line measurement accuracies are strongly affected by the mineral content and coal rank. This paper describes a char/ash particle cluster spectral emittance method for unburned carbon concentration measurements. The char/ash particle cluster spectral emittance is predicted theoretically here for various unburned carbon concentrations to show that the measurements are sensitive to unburned carbon concentration but insensitive to the mineral content and coal rank at short wavelengths. The results show that the char/ash particle cluster spectral emittance method is a novel and promising route for unburned carbon concentration on-line measurements without being influenced by mineral content or coal rank effects.

Detailed influences of ethanol as fuel additive on combustion chemistry of premixed fuel-rich ethylene flames

Abstract: To better understand potential pollutant formations during combustion of conventional hydrocarbon fuels blended with oxygenated fuels, detailed influences of ethanol as fuel additive on small polycyclic aromatic hydrocarbons (PAHs) precursors, aldehydes, ketene and other important intermediate species in premixed fuel-rich low-pressure ethylene flames are distinguished among dilution, thermal and chemical effects of additives. Dominant effects of ethanol addition on each species are underlined respectively. Ethylene oxidation process is delayed when ethylene is substituted by ethanol. The influence of ethanol dilution and thermal effects on ethylene consumption are larger than chemical effects. CO mole fractions slightly decrease mainly as a result of dilution and thermal effects of added ethanol. The reductions in small PAHs precursors (acetylene and propargyl) are attributed to dilution and thermal effects of ethanol addition instead of chemical effects. The ethanol chemical effects promote formations of hazardous pollutants formaldehyde and acetaldehyde, and especially are responsible for the significant increase of acetaldehyde. C2H6, C4H2 and C4H4 mole fractions decrease in a similar way with acetylene and propargyl as ethanol is added. Ethanol used here only serves as a prototype of oxygenated additive, and identification method in this work is more universal which can be easily extended for analyzing other fuel blends of hydrocarbon and oxygenated fuels.

Partial compensation lens and detected surface alignment device and alignment method in non-null detection

Abstract: The invention discloses a partial compensation lens and detected surface alignment device and alignment method in non-null detection. The partial compensation lens and detected surface alignment device of the invention comprises a laser, a collimating and beam expanding system, a beam splitter, an alignment plate, an imaging system, a detector, a reference plane reflector, a shading plate, a partial compensating lens and a detected surface; the detected surface can move along a linear guide rail parallel to the optical axis of an interferometer; the tilt of the partial compensating lens is adjusted, so that light spots reflected by the front surface and the rear surface of the partial compensating lens are concentric with each other and are concentric with interference fringes; the deviation of the partial compensating lens is adjusted, so that the centers of the light spots and the interference fringes can be aligned with the image center of the alignment plate; the detected surface is clamped, and the detected surface is moved along the guide rail so as to approach and go away from the partial compensating lens; and the attitude of the detected surface is adjusted, so that the centers of the light spots returned by the detected surface can be constantly aligned with the image center of the alignment plate. The partial compensation lens and detected surface alignment device and alignment method in non-null detection of the invention have the advantages of simplicity, quickness and no need for extra design and machining of optical machine elements. With the partial compensation lens and detected surface alignment device and alignment method in non-null detection adopted, alignment efficiency can be effectively improved, and cost can be decreased, and high precision and universal alignment of the partial compensation lens and the detected surface can be realized.

Ultrathin planar hematite film for solar photoelectrochemical water splitting.

Abstract: Hematite holds promise for photoelectrochemical (PEC) water splitting due to its stability, low-cost, abundance and appropriate bandgap. However, it suffers from a mismatch between the hole diffusion length and light penetration length. We have theoretically designed and characterized an ultrathin planar hematite/silver nanohole array/silver substrate photoanode. Due to the supported destructive interference and surface plasmon resonance, photons are efficiently absorbed in an ultrathin hematite film. Compared with ultrathin hematite photoanodes with nanophotonic structures, this photoanode has comparable photon absorption but with intrinsically lower recombination losses due to its planar structure and promises to exceed the state-of-the-art photocurrent of hematite photoanodes.

Non-null annular subaperture stitching interferometry for aspheric test

Abstract: A non-null annular subaperture stitching interferometry (NASSI), combining the subaperture stitching idea and non-null test method, is proposed for steep aspheric testing. Compared with standard annular subaperture stitching interferometry (ASSI), a partial null lens (PNL) is employed as an alternative to the transmission sphere, to generate different aspherical wavefronts as the references. The coverage subaperture number would thus be reduced greatly for the better performance of aspherical wavefronts in matching the local slope of aspheric surfaces. Instead of various mathematical stitching algorithms, a simultaneous reverse optimizing reconstruction (SROR) method based on system modeling and ray tracing is proposed for full aperture figure error reconstruction. All the subaperture measurements are simulated simultaneously with a multi-configuration model in a ray-tracing program, including the interferometric system modeling and subaperture misalignments modeling. With the multi-configuration model, full aperture figure error would be extracted in form of Zernike polynomials from subapertures wavefront data by the SROR method. This method concurrently accomplishes subaperture retrace error and misalignment correction, requiring neither complex mathematical algorithms nor subaperture overlaps. A numerical simulation exhibits the comparison of the performance of the NASSI and standard ASSI, which demonstrates the high accuracy of the NASSI in testing steep aspheric. Experimental results of NASSI are shown to be in good agreement with that of Zygo® Verifire TM Asphere interferometer.

A high-resolution detecting system based on machine vision for defects on large aperture and super-smooth surface

Abstract: The high-resolution detecting system based on machine vision for defects on large aperture and super-smooth surface uses a novel ring telecentric lighting optical system detecting the defects on the sample all round and without blind spots. The scattering light induced by surface defects enters the adaptive and highly zoom microscopic scattering dark-field imaging system for defect detecting and then forms digital images. Sub-aperture microscopic scanning sampling and fast stitching on the surface is realized by using precise multi-axis shifting guided scanning system and a standard comparison board based upon binary optics is used to implement fast calibration of micron-dimension defects detected actually. The pattern recognition technology of digital image processing which can automatically output digitalized surface defects statements after scaling is established to comprehensively evaluate defects. This system which can reach micron-dimension defect resolution can achieve detections of large aperture components of 850 mm × 500 mm, solve the durable problem of subjective uncertainty brought in by human visual detection of defects and achieve quantitative detection of defects with machine vision.

Retrieval of phase distributions from the quadriwave lateral shearing interferogram obtained by randomly encoded hybrid grating

Abstract: A wavefront retrieval method for the quadriwave lateral shearing interferogram obtained by randomly encoded hybrid grating (REHG) is proposed. The REHG consists of a binary amplitude grating and a phase chessboard, and the Faunhofer diffractions of this grating only contain the ±1 orders in two orthogonal directions. As a result, no order selection mask is ever needed by the REHG for quadriwave lateral shearing interference. To retrieve the phase distributions from the REHG interferograms, fast Fourier transform (FFT) technique is employed at first to get the frequency spectrum. By performing inverse fast Fourier transform (IFFT) of the +1 order spectrum in the x and y directions, it is possible to extract shearing wavefronts from the interferogram in both two orthogonal directions. Using the translation property of Fourier transform, the relationship between the Fourier spectrum of the shearing wavefronts and the Fourier spectrum of the wavefront under test is deduced. The wavefront under test is retrieved by establishing an evaluation function firstly and finding the minimum value with least-square-solution. Analysis and compensations are made to reduce the errors in the testing results. Simulation experiments have shown that this method can retrieve different phase distributions without losing high-frequency information.

Model-based phase-shifting interferometer

Abstract: A model-based phase-shifting interferometer (MPI) is developed, in which a novel calculation technique is proposed instead of the traditional complicated system structure, to achieve versatile, high precision and quantitative surface tests. In the MPI, the partial null lens (PNL) is employed to implement the non-null test. With some alternative PNLs, similar as the transmission spheres in ZYGO interferometers, the MPI provides a flexible test for general spherical and aspherical surfaces. Based on modern computer modeling technique, a reverse iterative optimizing construction (ROR) method is employed for the retrace error correction of non-null test, as well as figure error reconstruction. A self-compiled ray-tracing program is set up for the accurate system modeling and reverse ray tracing. The surface figure error then can be easily extracted from the wavefront data in forms of Zernike polynomials by the ROR method. Experiments of the spherical and aspherical tests are presented to validate the flexibility and accuracy. The test results are compared with those of Zygo interferometer (null tests), which demonstrates the high accuracy of the MPI. With such accuracy and flexibility, the MPI would possess large potential in modern optical shop testing.

Highly sensitive lateral deformable optical MEMS displacement sensor: anomalous diffraction studied by rigorous coupled-wave analysis

Abstract: This paper discusses the pulse signal of a highly sensitive lateral deformable optical microelectromechanical systems (MEMS) displacement sensor based on Wood's anomalies and its corresponding tolerance. The optical reflection amplitude of the device changes with the displacement of the nanostructured grating elements. Unexpectedly, the device's original sinusoidal signal develops into a new signal form (i.e., a pulse signal), when the air gap between the two layers of gratings decreases. Since the slope of the pulse signal, namely 2.5%/nm (i.e., 0.65 dB/nm), is eight times higher than that of the original signal form, namely 0.3%/nm (i.e., 0.03 dB/nm), the sensitivity of the structure improves by eight times. However, this device is very sensitive to parameters such as its wavelength, period, duty ratio, and air gap. In this paper we used rigorous coupled wavelength analysis (RCWA) to analyze and optimize the respective influence of each parameter on the device's performance. We have introduced two methods to search for the optimal setting and have demonstrated the optimal settings of different incident lights. The simulation results indicate that it is close to 85% possible to achieve an actual device with the highest slope superior to 0.5%/nm and it is 64% possible that the highest slope of an actual device falls in the interval ranging from 1.0%/nm to 2.0%/nm. All the simulated data helped us better understand the tolerance of the pulse signal and guide us toward the development of an actual device.

Bubble Ebullition on a Hydrophilic Surface

Abstract: Nucleate boiling heat transfer depends on various aspects of the bubble ebullition, such as the bubble nucleation, growth and departure. In this work, a synchronized high-speed optical imaging and infrared (IR) thermography approach was employed to study the ebullition process of a single bubble on a hydrophilic surface. The boiling experiments were conducted at saturated temperature and atmospheric pressure conditions. De-ionized (DI) water was used as the working fluid. The boiling device was made of a 385-um thick silicon wafer. A thin film heater was deposited on one side, and the other side was used as the boiling surface. The onset of nucleate boiling (ONB) occurs at a wall superheat of ΔTsup= 12 oC and an applied heat flux of q” = 35.9 kW/m2. The evolution of the wall heat flux distribution was obtained from the IR temperature measurements, which clearly depicts the existence of the microlayer near the three-phase contact line of the nucleate bubble. The results suggest that, during the bubble growth stage, the evaporation in the microlayer region contributes dominantly to the nucleate boiling heat transfer; however, once the bubble starts to depart from the boiling surface, the microlayer quickly vanishes, and the transient conduction and the microconvection become the prevailing heat transfer mechanisms. 6.027 mm 6.027 mm

Compact wavefront diagnosis system based on the randomly encoded hybrid grating

Abstract: A compact wavefront diagnosis system with nice repeatability based on the randomly encoded hybrid grating (REHG) is proposed. The REHG comes from the ideally calculated grating for quadriwave lateral shearing interference, and it consists of a binary amplitude grating and a phase chessboard. The phase chessboard simulates the phase modulation of the ideally calculated grating, while the binary amplitude grating is designed and fabricated based on the randomly encoding method. In this method, the amplitude distribution on the ideally calculated grating is firstly divided into discrete grids. And the radiant flux in each grid is quantized into several quantization levels. The binary amplitude grating is then generated by encoding the pixels in the grids with 1 and 0, which stands for whether the light can pass through or not, so that the total radiant flux in each grid on this grating approximate to the flux in the corresponding grid on the ideally calculated quadriwave grating. In addition, random pattern is employed in the encoding process to avoid introducing extra diffraction orders. The far-field diffractions of the REHG only contain the ±1 orders in two orthogonal directions, and no order selection mask is needed for quadriwave lateral shearing interference. Due to the common-path configuration, the wavefront testing results obtained by the REHG lateral shearing interferometer exhibits nice repeatability and good suppression over environmental noise and vibration.

Recent developments of interferometric wavefront sensing

Abstract: Recent trends of interferometric wavefront sensing tend to focus on high precision, anti-vibration, compact, along with much more involved of electric and computer technology. And the optical principles employed not only limit to interference but also include diffraction, scattering, polarization, etc. In this paper, some selected examples basing on the research works in our group will be given to illustrate the trends mentioned above. To achieve extra high accuracy, phase-shifting point diffraction interferometry (PS-PDI) is believed to be a good candidate as it employs a nearly perfect point diffraction spherical wavefront as the reference and also takes advantage of the high precision of phase-shifting algorithms. Cyclic radial shearing interferometry (C-RSI) successively demonstrate the anti-vibration characteristic and can diagnose transient wavefront with only one single shot by employing a three-mirror common-path configuration and a synchronizing system. In contrast sharply with those early interferometers, interferometers with very compact configuration are more suitable to develop portable wavefront sensing instruments. Cross-grating lateral shearing interferometer (CG-LSI) is a very compact interferometer that adopts a cross-grating of millimeters to produce lateral shearing of the diffraction wave of the test wavefront. Be aware that, computer technique has been used a lot in all of the above interferometers but the non-null annual sub-aperture stitching interferometer (NASSI) for general aspheric surface testing mostly relies on the computer model of the physical interferometer setup and iterative ray-tracing optimization. The principles of the above mentioned interferometric wavefront sensing methods would be given in detail.

Reverse optimization reconstruction method in non-null aspheric interferometry

Abstract: Aspheric non-null test achieves more flexible measurements than the null test. However, the precision calibration for retrace error has always been difficult. A reverse optimization reconstruction (ROR) method is proposed for the retrace error calibration as well as the aspheric figure error extraction based on system modeling. An optimization function is set up with system model, in which the wavefront data from experiment is inserted as the optimization objective while the figure error under test in the model as the optimization variable. The optimization is executed by the reverse ray tracing in the system model until the test wavefront in the model is consistent with the one in experiment. At this point, the surface figure error in the model is considered to be consistent with the one in experiment. With the Zernike fitting, the aspheric surface figure error is then reconstructed in the form of Zernike polynomials. Numerical simulations verifying the high accuracy of the ROR method are presented with error considerations. A set of experiments are carried out to demonstrate the validity and repeatability of ROR method. Compared with the results of Zygo interferometer (null test), the measurement error by the ROR method achieves better than 1/10λ.

Retrieval of high-spectral-resolution lidar for atmospheric aerosol optical properties profiling

Abstract: High-spectral-resolution lidars (HSRLs) are increasingly being developed for atmospheric aerosol remote sensing applications due to the straightforward and independent retrieval of aerosol optical properties without reliance on assumptions about lidar ratio. In HSRL technique, spectral discrimination between scattering from molecules and aerosol particles is one of the most critical processes, which needs to be accomplished by means of a narrowband spectroscopic filter. To ensure a high retrieval accuracy of an HSRL system, the high-quality design of its spectral discrimination filter should be made. This paper reviews the available algorithms that were proposed for HSRLs and makes a general accuracy analysis of the HSRL technique focused on the spectral discrimination, in order to provide heuristic guidelines for the reasonable design of the spectral discrimination filter. We introduce a theoretical model for retrieval error evaluation of an HSRL instrument with general three-channel configuration. Monte Carlo (MC) simulations are performed to validate the correctness of the theoretical model. Results from both the model and MC simulations agree very well, and they illustrate one important, although not well realized fact: a large molecular transmittance and a large spectral discrimination ratio (SDR, i.e., ratio of the molecular transmittance to the aerosol transmittance) are beneficial t o promote the retrieval accuracy. The application of the conclusions obtained in this paper in the designing of a new type of spectroscopic filter, that is, the field-widened Michelson interferometer, is illustrated in detail. These works are with certain universality and expected to be useful guidelines for HSRL community, especially when choosing or designing the spectral discrimination filter.

Partial compensation lens system of non-null detection concave parabolic mirror and design method

Abstract: The invention discloses a partial compensation lens system of a non-null detection concave parabolic mirror and a design method of the partial compensation lens system. The partial compensation lens system is composed of a plurality of partial compensation lenses; and the overall compensation range of the partial compensation lens system covers parameters of commonly-used detected parabolic mirrors. The design method includes the following steps that: an initial structure of a partial compensation lens is calculated for a tested parabolic mirror of which the F number is smaller than 1.2; a constraint condition is set, and the parameters of the initial structure of the partial compensation lens are optimized in a detection path model; the parameters of the detected parabolic mirror are changed, the distance between the detected parabolic mirror and the partial compensation lens is adjusted, so that the parameter boundary of the detected parabolic mirror can be determined, and a compensation range D-R diagram is drawn; a new partial compensation lens is designed for a tested parabolic mirrors of which the F number is smaller than 1.2 in an uncompensable area until a plurality of partial compensation lenses cover the parameter range of the commonly-used detected parabolic mirrors; and the plurality of partial compensation lenses are screened, so that a compensation ability database can be constructed. With the partial compensation lens system of the non-null detection concave parabolic mirror and the design method of the partial compensation lens system of the invention adopted, problems existing in partial compensation lens compensation range analysis and system design can be solved, and general detection of parabolic mirrors can be realized.

Alignment methods for partial compensating lens of aspheric testing in a non-null interferometer

Abstract: Careful alignment of optical elements is essential in interferometric tests. Misalignments of the key element largely influence the testing accuracy. For aspheric figure error testing, non-null tests achieve more flexible and economical measurements than the null ones. However, retrace error is induced due to the violation of null configuration, making the alignment difficult. In aspheric partial compensation testing, the partial compensating lens (PCL) as the key component needs careful adjustment. The aplanat alignment method is effective for the PCL adjusting with high accuracy employing a removable lens, which combined with the PCL as an aplanat. But its structure is complex. After describing this method, a PCL computer-aided alignment (CAA) method is posed basing on system modeling in a ray tracing software. The structure is simplified with computer calculations. The PCL tilt and decentration are easily aligned with a plane and a standard spherical mirror respectively, according to linear relations with wavefront coma aberrations on the detector. Alignment of the PCL was implemented with these two methods in an aspheric partial compensation testing experimental apparatus. Adjustment and aspheric testing results were presented in order. The CAA method is a generalized approach with simpler structure, while the aplanat alignment method is easy to carry out and suitable for industrial application.

Precisely connected and calculated algorithm of punctate scratches in the super-smooth surface defects evaluation system

Abstract: In the inertial confinement fusion system (ICF), surface scratches of the large diameter optical surface appear as dot lines (punctate scratches). This kind of scratches is only detected under a high microscope magnification system. This can be caused by the blemishes on the optical processing technology and shallow scratches (< 25nm ). As a result, it can have an impact on the relevant calculation of the width and length of the scratches. Besides, this kind of scratches has a serious impact on the ICF, such as system damage. To solve this problem, this paper proposes the image pattern charter of punctate scratches based on the existing surface defects detection system (SDES). Finally, it proposes an algorithm of scratches based on the linearity differential detection and connectivity. That is, using coordinate transformation and direction differential-threshold discrimination, the scratches can be connected effectively and calculated exactly. Experimental results show that punctate scratches parts can be connected correctly, and the accuracy of the calculated length reaches 95%. Also, the improved algorithm applies to the arc-shaped scratches, which is based the block image processing. Currently, this algorithm can be applied to connect and calculate the shallow scratches accurately and precisely on large fine optics in the ICF system. Thus it can also decrease the misdetection rate of nonconforming super-smooth optics in the ICF system.