Synthetic wavelength to increase the snapshot optical sensor's elevated vertical measurement ranges.

Screening manufactured products that are conducted faster to enhance the contemporary manufacture processes and quality is possible by implementing enhanced quality control. Such quality control of manufactured products has increased the market for process-focused precision metrology that can execute evaluations faster while providing significant feedback for the manufacturing system. This investigation examines spatial dispersive interferometry's potential for producing accurate surface profile measurements by emphasizing vertical range measurements and identifying a system that can enable them to increase incrementally while maintaining the results' quality. Thus, this investigation selected Fourier transform profilometry (FTP) to assess surface profile measurements, as it provides the most reliable and fastest outcome data regarding this sensor. Exploring new surface scanning methods is important, as crucial weaknesses hinder several common approaches. As optical metrology sensors are bulky, difficult to establish, and expensive, the investigation will prove that FTP can resolve these restrictions. The investigation uses the synthetic wavelength approach for addressing vertical measurement limitation concerning optical systems for extending surface step height's vertical measurement range. Though it was observed that the FTP technique surmounts the vertical height limitations, certain limitations were also noted, with all outcomes considering key variables, including the scanning objective lens, system resolution, the spectrometer resolution, and diffraction grating. Future examinations must examine a wider vertical range to expand the snapshot spatial dispersive interferometry process's scope. Further, the step-height repeatability is enhanced, showing a good outcome range from 22 to 20 nm.

Improvement of the fringe analysis algorithm for wavelength scanning interferometry based on filter parameter optimization.

The phase slope method which estimates height through fringe pattern frequency and the algorithm which estimates height through the fringe phase are the fringe analysis algorithms widely used in interferometry. Generally they both extract the phase information by filtering the signal in frequency domain after Fourier transform. Among the numerous papers in the literature about these algorithms, it is found that the design of the filter, which plays an important role, has never been discussed in detail. This paper focuses on the filter design in these algorithms for wavelength scanning interferometry (WSI), trying to optimize the parameters to acquire the optimal results. The spectral characteristics of the interference signal are analyzed first. The effective signal is found to be narrow-band (near single frequency), and the central frequency is calculated theoretically. Therefore, the position of the filter pass-band is determined. The width of the filter window is optimized with the simulation to balance the elimination of the noise and the ringing of the filter. Experimental validation of the approach is provided, and the results agree very well with the simulation. The experiment shows that accuracy can be improved by optimizing the filter design, especially when the signal quality, i.e., the signal noise ratio (SNR), is low. The proposed method also shows the potential of improving the immunity to the environmental noise by adapting the signal to acquire the optimal results through designing an adaptive filter once the signal SNR can be estimated accurately.

Development of a spatially dispersed short-coherence interferometry sensor using diffraction grating orders: publisher's note.

This publisher's note amends the author listing and the funding and acknowledgment sections in Appl. Opt.57, 6391 (2017)APOPAI0003-693510.1364/AO.56.006391.

Development of an optical system for the non-invasive tracking of stem cell growth on microcarriers.

The emergence of medicinal indications for stem cell therapies has seen a need to develop the manufacturing capacity for adherent cells such as mesenchymal stem cells (MSCs). One such development is in the use of microcarriers, which facilitate enhanced cell densities for adherent stem cell cultures when compared with 2D culture platforms. Given the variety of stem cell expansion systems commercially available, novel methods of non-invasive and automated monitoring of cell number, confluence, and aggregation, within disparate environments, will become imperative to process control, ensuring reliable and consistent performance. The in situ epi-illumination of mouse embryonic fibroblasts and human mesenchymal stem cells attached to Cytodex 1 and 3 microcarriers was achieved using a bespoke microscope. Robust image processing techniques were developed to provide quantitative measurements of confluence, aggregate recognition, and cell number, without the need for fluorescent labeling or cell detachment. Large datasets of cells counted on individual microcarriers were statistically analyzed and compared with NucleoCounter measurements, with an average difference of less than 7% observed from days 0 to 6 of a 12-day culture noted, prior to the onset of aggregation. The developed image acquisition system and post-processing methodologies were successfully applied to dynamically moving colonized microcarriers. The proposed system offers a novel method of cell identification at the individual level, to consistently and accurately assess viable cell number, confluence, and cell distribution, while also minimizing the variability inherent in the current invasive means by which cells adhered to microcarriers are analyzed. Biotechnol. Bioeng. 2017;114: 2032-2042. © 2017 The Authors. Biotechnology and Bioengineering Published by Wiley Periodicals, Inc.

High resolution position measurement from dispersed reference interferometry using template matching.

This paper describes a method to extract high resolution position data from a dispersed reference interferometry (DRI) by applying a template matching technique to the acquired spectral interferograms. Calculation of the correlation coefficient between windowed spectral interferograms acquired from the DRI apparatus and a set of numerically calculated template interferograms allows the absolute determination of position with nanometer resolution. Both the operating principle of the DRI apparatus and implementation of the template matching method is presented. Experimental validation of the method is provided through the demonstration of position tracking and an assessment of linearity, repeatability and noise performance.

Actively stabilized optical fiber interferometry technique for online/in-process surface measurement.

In this paper, we report the recent progress in optical-beam scanning fiber interferometry for potential online nanoscale surface measurement based on the previous research. It attempts to generate a robust and miniature measurement device for future development into a multiprobe array measurement system. In this research, both fiber-optic-interferometry and the wavelength-division-multiplexing techniques have been used, so that the optical probe and the optical interferometer are well spaced and fast surface scanning can be carried out, allowing flexibility for online measurement. In addition, this system provides a self-reference signal to stabilize the optical detection with high common-mode noise suppression by adopting an active phase tracking and stabilization technique. Low-frequency noise was significantly reduced compared with unstabilized result. The measurement of a sample surface shows an attained repeatability of 3.3 nm.

Vibration compensating beam scanning interferometer for surface measurement.

Light beam scanning using a dispersive element and wavelength tuning is coupled with fiber-optic interferometry to realize a new surface measurement instrument. The instrument is capable of measuring nanoscale surface structures and form deviations. It features active vibration compensation and a small optical probe size that may be placed remotely from the main apparatus. Active vibration compensation is provided by the multiplexing of two interferometers with near common paths. Closed loop control of a mirror mounted on a piezoelectric transducer is used to keep the path length stable. Experiments were carried out to deduce the effectiveness of the vibration compensation and the ability to carry out a real measurement in the face of large environmental disturbance.

Near common-path optical fiber interferometer for potentially fast on-line microscale-nanoscale surface measurement.

We introduce a new surface measurement method for potential online application. Compared with our previous research, the new design is a significant improvement. It also features high stability because it uses a near common-path configuration. The method should be of great benefit to advanced manufacturing, especially for quality and process control in ultraprecision manufacturing and on the production line. Proof-of-concept experiments have been successfully conducted by measuring the system repeatability and the displacements of a mirror surface.