This PDF file contains the front matter associated with SPIE Proceedings Volume 9110, including the Title Page, Copyright information, Table of Contents, Invited Panel Discussion, and Conference Committee listing.

This paper presents our comparing study on active and passive methods for compensating the phase error induced by the projector nonlinear gamma effect. The active method modifies the fringe patterns before their projection; and the passive method, in contrast, compensates for the phase error after capturing fringe patterns. Our study finds that the active method tends to provides more consistent high-quality fringe patterns regardless the amount of projector’s defocusing; yet the effectiveness of the passive method is sensitive to the measurement conditions, albeit the passive method could provide equally good quality phase under the optimal calibration condition. Experimental results will be presented to compare these two different methods.

This paper presents a thorough comparison between the digital-light-processing (DLP) technology and liquid-crystal-onsilicon (LCoS) technology on high-quality 3D shape measurement. Specifically, we will study not only each individual color, but also the combination of different color (i.e., white light). The binary defocusing and focused sinusoidal fringe projection methods will be evaluated under all these scenarios. Experimental data demonstrated that for slow speed measurements, DLP has better fringe contrast and thus higher signal to noise ratio (SNR) for better quality 3D shape measurement when the binary defocusing method is employed, or when proper synchronization is present when the focus sinusoidal method is used; and LCoS provides more flexibility for system development when the focus sinusoidal method is employed.

Point triangulation probes have been in use in industry for half a century. In that time, there has not been any big changes in the mechanism by which they operate A point laser triangulation gage bought today has about the same ratio of standard deviation to measurement range, or measurement dynamic range, as one bought 30+ years ago. A significant limiting factor of the measurement dynamic range of such sensors is the noise seen by the sensor, which consists of both classic speckle noise, but also the effects of surface texture on the reflected beam. This paper will discuss four different methods, based upon advances applied in other optical metrology systems that improve the standard deviation to measurement range ratio for point laser triangulation gages by a factor of 20 on average. We will present the theory of how each of these methods provide this improved measurement dynamic range as well as the results of laboratory tests made on breadboard systems.

Due to the high temperatures and stresses present in the high-pressure section of a gas turbine, the airfoils experience creep or radial stretching. Nowadays manufacturers are putting in place condition-based maintenance programs in which the condition of individual components is assessed to determine their remaining lives. To accurately track this creep effect and predict the impact on part life, the ability to accurately assess creep has become an important engineering challenge. One approach for measuring creep is using moiré imaging. Using pad-print technology, a grating pattern can be directly printed on a turbine bucket, and it compares against a reference pattern built in the creep measurement system to create moiré interference pattern. The authors assembled a creep measurement prototype for this application. By measuring the frequency change of the moiré fringes, it is then possible to determine the local creep distribution. However, since the sensitivity requirement for the creep measurement is very stringent (0.1 micron), the measurement result can be easily offset due to optical system aberrations, tilts and magnification. In this paper, a mechanical specimen subjected to a tensile test to induce plastic deformation up to 4% in the gage was used to evaluate the system. The results show some offset compared to the readings from a strain gage and an extensometer. By using a new grating pattern with two subset patterns, it was possible to correct these offset errors.

The deformation measurement method by using only two speckle patterns has been proposed in ESPI by using Fourier transform. In this paper, a new optical system which can measure precisely an in-plane and out-of-plane deformation of the object with rough surfaces is developed by using the proposed deformation measurement method. The in-plane deformation can be generally detected by using the two-beam speckle interferometer. Then, the measurement method for improving measuring accuracy using the new optical system has been discussed. The proposed optical system can also measure simultaneously the in-plane and out-of-plane deformations using two cameras and one beam. The analyzing algorithm, which can separate each component of the in-plane and out-of-plane deformations, is also proposed. Speckle patterns from each camera before and after the deformation are analyzed in order to detect the phase maps as the deformation information. Then, the optical path distance distribution before and after deformation in each camera is detected. Finally, the in-plane and out-of-plane deformations can be measured independently by using a pair of the optical path distance results based on the geometry of two cameras. From experimental results, it is confirmed that the new method can analyze a pair of in-plane and out-of-plane deformation simultaneously and independently in a high resolution power.

A self-pulsation laser diode interferometer based on spectral-domain optical coherence tomography is proposed. A visible multimode laser diode allows easy optical alignment and an economical, configurable system. A cylindrical lens and acousto-optic deflector used in our system enable rapid and stable scanning. Experimental results confirm that full-field measurement is possible without mechanical scanning devices.

We present the design, modeling, construction, and results of a three-dimensional imager based upon multiplewavelength speckle interferometry. Speckle imaging used in non-destructive evaluation is well-known but requires a precisely acquired reference image and can measure excursions only within the 2π ambiguity range determined by the illumination wavelength. Our approach is based upon earlier efforts pioneered by Takeda, but with updated illumination, imaging, and processing tools, in which a surface under test is illuminated with tunable laser light in a Michelson interferometer configuration. A speckled image is acquired at each laser frequency step creating a data hypercube. Interference between the reference wavefront and light from the object causes the amplitude of the speckles to cycle with laser tuning. Fourier transforming the hypercube in the laser frequency dimension reveals periods that map heights of surface features. Height resolution is determined by the maximum tuning range of the laser, which for our 16-nm tuning range provides approximately 18 micron resolution without any efforts at interpolation. The largest height without wraparound depends on the smallest tuning steps, which for our laser is 15 cm for 0.002 nm (1 GHz) tuning steps. In this way, objects with large discontinuous steps or holes can be imaged without confusion. Also, due to the illumination beam being normal to the surface under test, shadowing is eliminated. To inform our design and better understand our system’s limitations, we have developed extensive numerical models based upon Monte Carlo ray tracing in which speckle patterns are produced after scattering from model surfaces by coherent summing of rays at the detector plane. Data acquired by the system as well as modeling results will be shown.

In this paper, we present a new approach for the 3D measurement using digital fringe projection. Instead of sinusoidal fringe patterns and the traditional phase shift detection, the proposed technique makes use of triangular patterns and the spatial shift estimation for extract the 3D shape. The proposed technique is advantageous not only by improved immunization to nonlinear distortion associated with digital projections, but also reduced computational burden for its implementation. Theoretical analysis and experimental results are also presented to confirm the effectiveness of the proposed technique.

In recent years, the demands on three-dimensional (3-D) measurement systems have been getting higher, es- pecially concerning their speed. The use of a 3-D array projector enables measurement frame rates of up to the 100-kHz range. Our contribution introduces a new purpose-built setup that projects aperiodic sinusoidal fringes. We explain the 3-D measurement principle and the basic design of a 3-D array projector and describe the method how the desired aperiodic sinusoidal fringes are generated. We verify the consistency between specified and projected patterns and point out the results of the setups’s characterization, e.g., of its high-speed capability. Furthermore, first 3-D shape measurements at a projection frame rate of 3 kHz resulting in a 3-D frame rate of <330 Hz are presented and evaluated.

A new optical sensor based on fringe projection technique for the accurate and fast measurement of the surface of objects mainly for industrial inspection tasks is introduced. High-speed fringe projection and image recording with 180 Hz allows 3D rates up to 60 Hz. The high measurement velocity was achieved by consequent fringe code reduction and parallel data processing. Reduction of the image sequence length was obtained by omission of the Gray-code sequence by using the geometric restrictions of the measurement objects. The sensor realizes three different measurement fields between 20 x 20 mm² and 40 x 40 mm² with lateral spatial solutions between 10 μm and 20 μm with the same working distance. Measurement object height extension is between ± 0.5 mm and ± 2 mm. Height resolution between 1 μm and 5 μm can be achieved depending on the properties of the measurement objects. The sensor may be used e.g. for quality inspection of conductor boards or plugs in real-time industrial applications.

A sinusoidal wavelength scanning interferometer is proposed for 3-D profile measurement. The interference phase-shift signal generated by the sinusoidal wavelength scanning contains information of optical path difference (OPD) covering nm-mm scale structure. The interference phase-shift signal was obtained by the four-step phase shifting method. The sinusoidal wavelength shifting bandwidth of 5.7 nm with a frequency of approximately 180 Hz was performed by the Littman-Metcalf external resonator-type tunable laser with a center of 772.1 nm. The full-field step-height surface profile measurement and 3-D surface measurement were conducted by a CCD image sensor with an accuracy of few tens nm. The surface profile of gauge blocks with a step-height of up to 10 μm was successfully measured.

Cost, weight, performance, and lifetime requirements for precision components used throughout the aerospace and defense industries are driving innovative mechanical designs, manufacturing processes and use of new materials. In turn, these advanced components typically require tighter dimensional and surface tolerances to function as designed. Scratch testers, microscope-based systems, and other traditional metrology systems are inadequate for roughness, small-scale geometry, and defect determination on many of these parts. This talk will examine the advantages and disadvantages of some of the new technologies developed to provide more robust, versatile, and sensitive measurements of precision components for advanced manufacturing environments.

Center alignment is important technique to tune up the spindle of various precision machines in manufacturing industry. Conventionally such a tool as a dial indicator has been used to adjust and to position the axis by manual operations of a technical worker. However, it is not easy to precisely control its axis. In this paper, we developed the optical center alignment technique based on inner profile measurement using a ring beam device. In this case, the center position of the cylinder hole can be determined from circular profile detected by optical sectioning method using a ring beam device. In our trials, the resolution of the center position is proved less than 10 micrometers in extreme cases. This technique is available for practical applications in machine tool industry.

Terahertz dynamic scanning reflectometry (TDSR) was used for measuring layered materials’ deformation kinetics spectra. Multi-layered materials are used for protective devices such as helmet and body armor. An in-situ measurement of deformation profile and other dynamic characteristics is important when such material is subjected to ballistic impacts. Current instrumentation is limited in their abilities to provide sub-surface information in a non-destructive fashion. A high sensitivity TDSR has been used to measure dynamic surface deformation characteristics in real-time (in-situ) and also at post deformation (ex-situ). Real-time ballistic deformation kinetics was captured with a high speed measurement system. The kinetics spectra was used to compute a number of crucial parameters such as deformation length and its propagation profile, the relaxation position, and the macroscopic vibration profile. In addition, the loss of mass due to impact was quantified for accurate determination of the trauma causing energy. For non-metallic substrates, a transmitted beam was used to calibrate mass loss, a priori, of the laminate layers due to impact. Deformation kinetics information may then be used to formulate trauma diagnosis conditions from blunt hit via the Sturdivan criterion [1]. The basic difference in the proposed approach is that here diagnostic criteria are inferred by measuring the helmet itself; no need to draw blood or any biopsy from the patient.

A non-contact ultra-broadband photoacoustic (PA) / photothermal (PT) microscopy system has been developed to characterize material properties of specimens using optical transduction techniques. PT microscopy exploits optical changes induced by heat to highlight the presence of inhomogeneities such as defects, contaminants, inclusions, and impurities in materials. A monochromatic light source (e.g., a pulsed and amplitude-modulated laser) typically is used to create the PA effect. Heating the material produces a stress distribution that launches broadband ultrasonic emissions. Measurement of the ultrasonic emissions can be used to compute material properties like density, elastic modulus, anisotropy, etc. Sub-surface features can be detected using time-reversal and back-propagation techniques. In this work, PT-induced refractive index changes as well as the PA effect are detected optically on a microscopic scale using a Michelson-interferometer configuration. The system has a spatial resolution of ~600 nm with a detection bandwidth of 1 GHz and a displacement sensitivity of 1 pm per root Hz. Experimental results from thin films, coatings, nanoelectromechanical systems (NEMS) and biological samples demonstrate the versatility of the system as a nondestructive tool for material characterization.

Specifications for confocal microscopes, optical interferometers and other methods of measuring areal surface topography can be confusing and misleading. The emerging ISO 25178 standards, together with the established international vocabulary of metrology, provide a foundation for improved specifications for 3D surface metrology instrumentation. The approach in this paper links instrument specifications to metrological characteristics that can influence a measurement, using consistent definitions of terms, and reference to verification procedures.

Increasing demand for high-brightness (HB) LEDs is prompting manufacturers to refine production methods and improve performance of LED light sources. Achieving either of these requires high precision metrology tools that are also fast and non-destructive. In particular, there is a need for the metrology for patterned sapphire substrates (PSS) used in LED manufacturing to enhance light-extraction efficiency. This article describes a gauge-capable metrology tool that is currently used for these purposes: the 3D optical microscope based on white-light interferometer (WLI) which with special algorithms for fringe analysis can specifically quantify the height, width and pitch for each individual PSS structure. We have measured a variety of structures and their dimensions and compared them to SEM or AFM results. The white-light interferometer (WLI) is a tool that better meets the needs of these applications because of the ease of its full field measurement and for faster defects detection. 3D optical microscopes also provide excellent repeatability, especially when employing the automated position calibration of the reference mirror position in the interferometric objective.

With the advent of smart devices, the semiconductor packaging process has been proposed to realize devices that have high performance devices and compact size. Several silicon wafers are stacked vertically to create 3 dimensional devices with a high degree of integration. In this process, we measured two important parameters: the thickness of the silicon wafers and the depth and diameter of the through-silicon vias, which are vertical electrical connection lines between the stacked silicon wafers. To avoid pattern distortion and failure during the optical lithography process, the absolute value of the thickness as well as the thickness uniformity needed to be measured. The proposed method directly extracts the geometrical thickness from optical thickness. Because short through-silicon vias lead to disconnection between the silicon wafers, and narrow though-silicon vias may cause voids, the depth and diameter of the through-silicon vias must also be measured accurately. For these purposes, we propose two high-speed optical interferometers based on spectrum-domain analysis. The light source was a femtosecond pulse laser which has the advantages of a wide-spectral bandwidth, high peak power and long coherence length. The measurement uncertainty of the thickness was estimated to be 100 nm (k=2) in the range of 100 mm. The depth and diameter of the through-silicon vias were measured at the same time with a measurement resolution of 10 nm and 100 nm, respectively. It is expected that the proposed interferometers will be used for on-line metrology and inspection as well as new metrological methods for dimensional standards.

Three-dimensional (3D) scanners are becoming increasingly common in many industries. However most of these scanning technologies have drawbacks for practical use due to size, weight, accessibility, and ease-of-use. Depending on the application, speed, flexibility and portability can often be deemed more important than accuracy. We have developed a solution to address this market requirement and overcome the aforementioned limitations. To counteract shortcomings such as heavy weight and large size, an optical sensor is used that consists of a laser projector, a camera system, and a multi-touch screen. Structured laser light is projected onto the measured object with a newly designed laser projector employing a single Micro Electro Mechanical Systems (MEMS) mirror. The optical system is optimized for the combination of a Laser Diode (LD), the MEMS mirror and the size of measurement area to secure the ideal contrast of structured light. Also, we developed a new calibration algorithm for this sensor with MEMS laser projector that uses an optical camera model for point cloud calculation. These technical advancements make the sensor compact, save power consumption, and reduce heat generation yet still allows for rapid calculation. Due to the principle of the measurement, structured light triangulation utilizing phase-shifting technology, resolution is improved. To meet requirements for practical applications, the optics, electronics, image processing, display and data management capabilities have been integrated into a single compact unit.

The line patterns obtained by the self-assembly of the block copolymer (BCP) polystyrene-b-polyethylene oxide (PS-b-PEO) was investigated. The hexagonal PS-b-PEO 42k-11.5k in a thin film was solvent annealed in a chlorophorm saturated atmosphere for three different annealing times. The microphase segregation of this BCP returned 18nm cylinders of PEO through the PS matrix, with an approximately 40 n periodicity, as expected. Under chlorophorm vapours, the PEO cylinders oriented perpendicular to the silicon substrate while increasing the annealing time. These cylinders formed linear patterns with different alignment. To achieve insights about the percentage of alignment, defect type pareto and density, and order quantification to compare the three annealing recipes, the samples were analysed with innovative image analysis software specifically developed in our laboratory to identify elements and defects of line arrays from block copolymer self-assembly. From this technique, it was extracted dimensional metrology estimating pitch size and placement error, and the line-width of the lines was estimated. Secondly, the methodology allows identification and quantification of typical defects observable in BCP systems, such as turning points, disclination or branching points, break or lone points and end points. The defect density and the quantification of the alignment were estimated using our technique. The methodology presented here represents a step forward in dimensional metrology and defect analysis of BCP DSA systems and can be readily used to analyze other lithographic or non-lithographic patterns.

The accurate measurement of surface roughness is essential in ensuring the desired quality of machined parts. Today the most common method to check roughness is to use a contact stylus profiler. There are many challenges for the application of a contact stylus for measuring the surface roughness of machined parts especially for the hard to access areas such as slots, deep holes and curved pockets. This study proposes a surface roughness measurement technique for these hard to access areas that are based on the measurement of the statistical analysis of the specular and scattered light intensity. In order to solve the accessibility issue, a miniaturized roughness measurement sensor with an Ø3mm diameter was designed using a dual laser emitting configuration. This dual laser approach makes the system more durable and reliable for different materials and machining processes such as polishing, lapping and precision grinding. This paper will present initial research results that demonstrate the applications of this approach to real industrial parts. Tests were performed to evaluate the sensitivity and feasibility of the proposed technique with various machined surfaces and materials.

3D structured light systems based upon phase shifting analysis are well described in the literature. One of the challenges to obtaining high quality data is the noise often associated with the mechanism to shift the projected pattern accurately. The common methods of realizing a phase shift is to either mechanically move a grating pattern that is then projected to the part, or to move the pattern electronically in a programmable projector such as an LCD, LCOS or other projector. These projectors, often made for office use, are limited by the pixel resolution and the stability of the projectors. Mechanical shifts can be very precise, but require time and the maintenance of a mechanical movement. Other systems using projected interference patterns that use piezo shifters are faster and more reliable, but then can suffer from coherent speckle noise. This paper will discuss a unique optical design using a lens made telecentric in image space and an electro-optical image shifting approach that provides very fast image shifts in a very repeatable and controlled manner.

Three-dimensional shape measurement is a subject that consistently produces high scientific interest and provides information for medical, industrial and investigative applications, among others. In this paper, it is proposed to implement a three-dimensional (3D) reconstruction system for applications in superficial inspection of non-metallic pipes for the hydrocarbons transport. The system is formed by a CCD camera, a video-projector and a laptop and it is based on fringe projection technique. System functionality is evidenced by evaluating the quality of three-dimensional reconstructions obtained, which allow observing the failures and defects on the study object surface.

The stitching interferometry for the surface profile measurement of a large aperture component is studied. To analyze the overlapping region interferogram of the adjacent subapertures with Scale Invariant Feature Transform(SIFT) algorithm, the stitching parameters of the adjacent subapertures and then overall surface information of the tested component can be obtained. SIFT algorithm of subaperture positioning, interferogram processing, phase unwrapping, Zernike polynomials wavefront fitting and subaperture wavefront stitching programs are written. A principle experiment has been carried out. Compared with the measurement results between the stitching interferometry and full caliber testing, the deviation of RMS is less than 2nm.

In order to get measures with a high accurate, three-dimensional reconstruction systems are implemented in industrial, medical, and investigative fields. To obtain high accurate is necessary to carry out an appropriate calibration procedure. In fringe projection profilometry, this procedure allows obtaining a relation between absolute phase and three-dimensional (3D) information of the object in study; however, to execute such procedure a precise movement stage is required. A fringe projection system is formed by a projector, a digital camera and a control unit, called like a projection-acquisition unit in this paper. The calibration of the projection-acquisition unit consists in to establish the parameters that are required to transform the phase of the projected fringes to metric coordinates of the object surface. These parameters are a function of the intrinsic and extrinsic parameters of both camera and projector, due to the projector is modeled as an inverse camera. For this purpose, in this paper a novel and flexible calibration method that allows calibrating any device that works with fringe projection profilometry is proposed. In this method is used a reference plane placed in random positions and the projection of an encoded pattern of control points. The camera parameters are computed using Zhang’s calibration method; and the projector parameters are computed from the camera parameters and the phase of the pattern of control points, which is determined by using Fourier analysis. Experimental results are presented to demonstrate the performance of the calibration method.