11 research outputs found
Hyperspectral interferometry for single-shot profilometry and depth-resolved displacement field measurement
A new approach to the absolute measurement of two-dimensional optical path differences
is presented in this thesis. The method, which incorporates a white light interferometer and
a hyperspectral imaging system, is referred to as Hyperspectral Interferometry. A prototype
of the Hyperspectral Interferometry (HSI) system has been designed, constructed and
tested for two types of measurement: for surface profilometry and for depth-resolved
displacement measurement, both of which have been implemented so as to achieve single
shot data acquisition.
The prototype has been shown to be capable of performing a single-shot 3-D shape
measurement of an optically-flat step-height sample, with less than 5% difference from the
result obtained by a standard optical (microscope) based method. The HSI prototype has
been demonstrated to be able to perform single-shot measurement with an unambiguous
352 (m depth range and a rms measurement error of around 80 nm. The prototype has also
been tested to perform measurements on optically rough surfaces. The rms error of these
measurements was found to increase to around 4Ă— that of the smooth surface.
For the depth-resolved displacement field measurements, an experimental setup was
designed and constructed in which a weakly-scattering sample underwent simple
compression with a PZT actuator. Depth-resolved displacement fields were reconstructed
from pairs of hyperspectral interferograms. However, the experimental results did not
show the expected result of linear phase variation with depth. Analysis of several possible
causes has been carried out with the most plausible reasons being excessive scattering
particle density inside the sample and the possibility of insignificant deformation of the
sample due to insufficient physical contact between the transducer and the sample
Single-shot profilometry of rough surfaces using hyperspectral interferometry
The combination of white light interferometry with hyperspectral imaging (“hyperspectral interferometry”) is a recently proposed technique for single-shot measurement of 3D surface profiles. We consider for the first time its application to speckled wavefronts from optically rough surfaces. The intensity versus wavenumber signal at each pixel provides unambiguous range information despite the speckle-induced random phase shifts. Experimental results with samples undergoing controlled rigid body translation demonstrate a measurement repeatability of 460 nm for a bandwidth of approximately 30 nm. Potential applications include roughness measurement and coordinate measurement machine probes where rapid data acquisition in noncooperative environments is essential
Multi-view fringe projection system for surface topography measurement during metal powder bed fusion
Metal powder bed fusion (PBF) methods need in-process measurement methods to increase user confidence and encourage further adoption in high-value manufacturing sectors. In this paper, a novel measurement method for PBF systems is proposed that uses multi-view fringe projection to acquire high-resolution surface topography information of the powder bed. Measurements were made using a mock-up of a commercial PBF system to assess the system’s accuracy and precision in comparison to conventional single-view fringe projection techniques for the same application. Results show that the multi-view system is more accurate, but less precise, than single view fringe projection on a point-by-point basis. The multi-view system also achieves a high degree of surface coverage by using alternate views to access areas not measured by a single camera
Soliton and Breather Splitting on Star Graphs from Tricrystal Josephson Junctions
We consider the interactions of traveling localized wave solutions with a vertex in a star graph domain that describes multiple Josephson junctions with a common/branch point (i.e., tricrystal junctions). The system is modeled by the sine-Gordon equation. The vertex is represented by boundary conditions that are determined by the continuity of the magnetic field and vanishing total fluxes. When one considers small-amplitude breather solutions, the system can be reduced into the nonlinear Schrödinger equation posed on a star graph. Using the equation, we show that a high-velocity incoming soliton is split into a transmitted component and a reflected one. The transmission is shown to be in good agreement with the transmission rate of plane waves in the linear Schrödinger equation on the same graph (i.e., a quantum graph). In the context of the sine-Gordon equation, small-amplitude breathers show similar qualitative behaviors, while large-amplitude ones produce complex dynamics
Taufiq Widjanarko's Quick Files
The Quick Files feature was discontinued and it’s files were migrated into this Project on March 11, 2022. The file URL’s will still resolve properly, and the Quick Files logs are available in the Project’s Recent Activity
A Post-processing Technique for Extending Depth of Focus in Conventional Optical Microscopy
In this paper, we propose a post-processing technique to obtain optical microscope images with extended depth of focus using a conventional microscope. With the proposed technique, we collect a sequence of images focused at different depths. We then combine the in-focus regions of each acquired frame to compose a single all-in-focus image. That is, a new image with extended depth of focus is obtained. The key to such an algorithm is in selecting the “in-focus” regions from each frame. In this paper, we describe the technique used to identify the in-focus region on every depth slice. Quantitative simulation results are presented where mean absolute error is used as a metric to assess the algorithm performance. Results using real imagery are also presented for subjective evaluation. Based on subjective evaluation and the quantitative simulation results, we believe that the proposed algorithm provides useful depth of focus extension
Hyperspectral interferometry for single-shot absolute measurement of two-dimensional optical path distributions
We propose a method that we call hyperspectral interferometry (HSI) to resolve the 2Ď€ phase
unwrapping problem in the analysis of interferograms recorded with a narrow-band light
source. By using a broadband light source and a hyperspectral imaging system, a set of
interferograms at different wave numbers are recorded simultaneously on a high resolution
image sensor. These are then assembled to form a three-dimensional intensity distribution. By
Fourier transformation along the wave number axis, an absolute optical path difference is
obtained for each pixel independently of the other pixels in the field of view. As a result,
interferograms with spatially distinct regions are analysed as easily as continuous ones. The
approach is illustrated with a HSI system to measure 3D profiles of optically smooth or rough
surfaces. Compared to existing profilometers able to measure absolute path differences, the
single-shot nature of the approach provides greater immunity from environmental disturbance