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This research developed a feedback control system of laser compensation for the rapid prototyping (RP) machine using layer-wise slurry deposition and selective laser sintering (SLS). The slurry was prepared by silica power and silica sol with 60 and 40 wt.% with suitable rheological properties for 0.1 mm layer deposition. Four ceramics for comparison of the formability of fabricated ceramic green parts with/without the feedback control system of laser energy density for models were designed With this laser feedback control, batter quality ceramic green parts can be manufactured and the rapid prototyping machine with steady laser energy radiated on slurry layer was achieved. Experimental results validate the well performance of the measuring laser power and feedback control system.

This article presents new white light interferometry with vibration–resistant capability achieved by in–situ optical detection and closed–loop feedback strategies. Scanning white light interferometry (SWLI) has become a popular measurement method due to its long measurement range and high measurement accuracy. However, the drawback of in–situ interferometry lies mainly in unacceptable measurement errors caused by environmental disturbance such as mechanical vibration and acoustic noise. This paper describes a method employing dual–sensing configuration and active fringe–locking strategy to overcome the issue. A specially designed band–pass filter is employed to generate a high–coherent light field for real–time detecting vibratory displacement. As proven by the experimental results, the maximum measurement error caused by vibration can be effectively reduced by more than six folds.

White light interferometry has become an important method for measuring micro surface profiles with a long vertical range and nano-scale resolution. However, environmental vibration encountered in in-field optical inspection is usually unavoidable and it affects measurement performance significantly. Isolating vibration sources from the measurement system sometimes is not completely effective, especially within complicated in-field fabrication environment. Therefore, in this research we aim to develop a novel method in achieving white-light fringe-locking condition during vertical scanning processes. The developed optical system consists of white light source, a Mirau objective, a PZT vertical scanner, an optical band-pass filter and two image sensing devices. The developed system generates a high and a low coherent interferograms, simultaneously captured by two charged coupled devices (CCDs). The high coherent interferogram is employed to detect high-speed nano-scale displacement and direction of the external vibration. An innovative real time fringe-locking operation is performed and a new vertical scanning technique is performed accordingly to isolate vertical scanning from environmental disturbances. The feasibility of the anti-vibration VSI system is verified by performing some of industrial in-field examples. Based on the experimental result, the fringe locking technique can improve the measurement result.

Although barcodes can be used to manage data conveniently, they cannot be applied to small areas. Therefore, pointcodes are used to overcome the issue in this article. A pointcode uses a pointcode pattern to encode data and uses a pointcode image to decode data. A pointcode pattern is composed of many grating dots with different specified grating pitches and grating orientations. Moreover, there are two grating-dot sizes generated. When a laser beam illuminates a pointcode pattern with correct illuminating conditions, a pointcode image corresponding to the hidden data is diffractively reconstructed. A pointcode image is composed of many bright points with different positions. There are two possible bright-point sizes generated. A bright point or two bright points at specified positions are used to denote a number. Small pointcode patterns are enough to diffractively form pointcode images.

A new type of diffusion pattern is proposed. The proposed patterns are composed of 2D diffusion dots. The diffusion dots are created on a photoresist plate by recording the image of a local area of a piece of ground glass dot by dot. An imaging lens covered by a mask with a slit aperture is used to form the image. By changing the orientation of the slit aperture on the mask plane, the diffusion dots can have different microintensity distributions for the same incident light beam. Therefore the diffusion dots created by the same slit aperture orientation show the same brightness, and the diffusion dots created by different slit orientations show different brightness for the same illuminating and viewing conditions. Thus a proposed diffusion pattern can show dynamic images by changing its illuminating or viewing directions. By applying the double-exposure technique to the diffusion dots of a pattern, the pattern not only can show dynamic effects but also can possess several hidden features for identifying the pattern. Therefore the proposed patterns are dynamic and anticounterfeiting.

The images on a dot-matrix hologram contain many two-dimensional (2D) dots with different grating orientations and different grating pitches. Because the zeroth-order light nondiffracted by different grating structures has the same progress direction, the nondiffracted light can be diffracted to a 2D spot spectrum by the 2D dot structure. The 2D spot spectrum depends on grating depths and dot sizes. Although ordinary noises are troublesome for 2D spots, noises caused by special dot arrangement defects or special grating moiré fringes are useful in checking holograms. Since the features of grating depths, dot sizes, dot arrangement defects, and grating moiré fringes can be randomly changed on a case by case basis, 2D spot spectra in different cases are different. The aforementioned random features are used to identify dot-matrix holograms.

We propose a new speckle method for enhancing the anticounterfeiting ability of holograms. The method adds light-diffusion marks on holograms. These marks are constituted with periodic speckle patterns. The size of element patterns is very small, so a microscope must be used to check the 2-D microstructure of a mark. When a laser beam illuminates a light-diffusion mark, the diffused light produces a special matrix intensity distribution. Because it is difficult to create an identical random speckle arrangement using different process setups, the matrix intensity distribution diffracted from a specially created light-diffusion mark is nearly impossible to counterfeit. Although holographic films possess birefringent phenomena, the diffraction efficiencies of marks that fit some confinement conditions can be kept stable for light with different polarizations. The proposed method is a good choice for enhancing hologram anticounterfeiting characteristics. © 2004 Society of Photo-Optical Instrumentation Engineers.

To enhance the security of a dot-matrix hologram (DMH), a method to hide an image inside the DMH is proposed. The hidden image, which does not depress the visibility and the dynamic-effect feature of the DMH, is invisible but can be reconstructed by illuminating the DMH with a specified laser beam. The reconstructed hidden image is invariable to the lateral shift between the laser beam and DMH. Two experiments are carried out to illustrate the applicability of the proposed method. © 2002 Society of Photo-Optical Instrumentation Engineers.

This work proposes an orthogonal polarization Mirau interferometry using a reflective-type waveplate to generate different polarization orientations for broadband white light interferometry. The reflective-type half-waveplate is employed as the reference arm of the Mirau interferometer to convert polarization and it generates a reference light with an orientation orthogonal to the object light. An advantage of the proposed interferometer is its ability to control the ratio of light intensity between the object and reference arms to maximize the interferometric fringe contrast. Better, more accurate calibration of standard step height has been achieved by the developed interferometer, which also can measure solder bumps that traditional Mirau interferometers usually cannot measure.

A shearing interferometer based on using broadband light source, Savart plate, and angular scanning technique is proposed for slope contour measurements in this Letter. Of which, the Savart plate divides the wavefront reflected from the detected surface into two laterally displaced ones, the interference pattern generated by the interference of the divided wavefronts is modulated by an envelope function, and the slope contour of the detected surface is determined by examining the shifting of the darkest fringe as the shear plate is angularly scanned. A setup for realizing the interferometer is constructed. The experimental results of using this setup agree the validity and feasibility of the proposed interferometer.

This Letter introduces a polarization phase-shifting Newton interferometer that can be utilized for plane optical surface measurements, a setup constructed to realize the interferometer, and the experimental results from the use of the setup. The results confirm not only the validity but also the feasibility of the interferometer.

An optical measurement method to get the in-plane and out-of-plane displacements of a local surface using a laser is proposed. The proposed method simultaneously derives the in-plane and out-of-plane displacements by measuring the shift of interference fringes formed by scattered beams. The average errors of the in-plane and out-of-plane displacement measurements are significantly smaller than 10 nm. Moreover, the proposed method uses only low-cost optical elements.

An interferometer based on using low-coherent light source, a square prism, and the angular-scanning technique is proposed for absolute angular-displacement determinations. An angular displacement of the square prism shifts the correlogram, which is modulated by an envelope function, of the interference signal of the beams passing through the prism. This angle can thus be discovered by detecting the shifting of the envelope peak. A setup constructed to validate the interferometer is used. The results of using this setup are then presented.

Bar arrangements used by conventional diffractive barcodes are usually similar to those used by diffusive barcodes. We, however, propose a modified diffractive barcode with bar arrangements different from those used by diffusive barcodes. A modified diffractive barcode pattern is composed of many parallel grating-dot lines. When the grating-dot lines are scanned by a laser beam in sequence, different bright bar arrangements corresponding to different codes appear in sequence.

A dot-matrix hologram contains many two-dimensional grating dots, which may have different features, e.g., two-dimensional positions, grating pitches, grating orientations, and dot sizes. In this paper, such features are used to encode binary data to hide a figure almost without changing the hologram appearance. Because many encoding methods are available, decoding the hidden figure without authorization can be very difficult. The encrypting scheme presented here possesses both feasible and confidential features.

Dot-matrix holograms created by two-beam writers usually contain two-dimensional grating dots. Although the dot positions may be accurate, the fringe positions of the dots are randomly determined. The random fringe positions are good tools to identify a hologram. A grating position-deviation coefficient derived from the fringe position difference of two grating dots with the same pitch and the same orientation is defined and it is used as data to identify a dot-matrix hologram. Experiments have proved the proposed method practical and feasible. Because the fringe position difference between the two grating dots with the same pitch and the same orientation is difficult to reproduce, it is excellent for anticounterfeiting.

Modified light-diffusion patterns created by contact-copy interference of diffused laser lights are proposed. A conventional light-diffusion pattern is created by means of a diffuser and a noncontact photosensitive plate (a noncontact or sandwich method). The proposed method uses a contact photosensitive plate and allows implementation of new applications such as surface-relief holograms, anticounterfeiting, and light-diffusion eyemarks.