388 research outputs found
Bond-Selective Intensity Diffraction Tomography
Recovering molecular information remains a grand challenge in the widely used
holographic and computational imaging technologies. To address this challenge,
we developed a computational mid-infrared photothermal microscope, termed
Bond-selective Intensity Diffraction Tomography (BS-IDT). Based on a low-cost
brightfield microscope with an add-on pulsed light source, BS-IDT recovers both
infrared spectra and bond-selective 3D refractive index maps from
intensity-only measurements. High-fidelity infrared fingerprint spectra
extraction is validated. Volumetric chemical imaging of biological cells is
demonstrated at a speed of ~20 seconds per volume, with a lateral and axial
resolution of ~350 nm and ~1.1 micron, respectively. BS-IDT's application
potential is investigated by chemically quantifying lipids stored in cancer
cells and volumetric chemical imaging on Caenorhabditis elegans with a large
field of view (~100 micron X 100 micron)
Characterisation of the topography of metal additive surface features with different measurement technologies
The challenges of measuring the surface topography of metallic surfaces produced by additive manufacturing are investigated. The differences between measurements made using various optical and non-optical technologies, including confocal and focus-variation microscopy, coherence scanning interferometry and x-ray computed tomography, are examined. As opposed to concentrating on differences which may arise through computing surface texture parameters from measured topography datasets, a comparative analysis is performed focussing on investigation of the quality of the topographic reconstruction of a series of surface features. The investigation is carried out by considering the typical surface features of a metal powder-bed fusion process: weld tracks, weld ripples, attached particles and surface recesses. Results show that no single measurement technology provides a completely reliable rendition of the topographic features that characterise the metal powder-bed fusion process. However, through analysis of measurement discrepancies, light can be shed on where instruments are more susceptible to error, and why differences between measurements occur. The results presented in this work increase the understanding of the behaviour and performance of areal topography measurement, and thus promote the development of improved surface characterisation pipelines
3-D IR imaging with uncooled GaN photodiodes using nondegenerate two-photon absorption
We utilize the recently demonstrated orders of magnitude enhancement of
extremely nondegenerate two-photon absorption in direct-gap semiconductor
photodiodes to perform scanned imaging of 3D structures using IR femtosecond
illumination pulses (1.6 um and 4.93 um) gated on the GaN detector by sub-gap,
femtosecond pulses. While transverse resolution is limited by the usual imaging
criteria, the longitudinal or depth resolution can be less than a wavelength,
dependent on the pulsewidths in this nonlinear interaction within the detector
element. The imaging system can accommodate a wide range of wavelengths in the
mid-IR and near-IR without the need to modify the detection and imaging
systems.Comment: 9 pages, 6 figure
Polymer powder bed fusion surface texture measurement
Polymer laser powder bed fusion (LPBF) surfaces can be challenging to measure. These surfaces comprise complex features including undercuts, deep recesses, step-like transitions, a large range of measurement scales and unfavourable optically materials properties. While recent research has begun to examine the nature of these surfaces, there has not yet been significant effort in understanding how different measurement instruments interact with them. In this paper, we compare the results of LPBF surface topography measurements using a series of different instrument technologies, including contact stylus, focus variation microscopy, coherence scanning interferometry, laser scanning confocal microscopy and X-ray computed tomography. Measurements are made on both side and top surfaces of a cubic polyamide-12 LPBF sample. Different instrument behaviours are highlighted through qualitative visual inspection of surface reconstructions. Further comparisons are then performed through evaluation of profile and areal surface texture parameters and statistical modelling of surface topographies. These analyses allow for the identification both of discrepancies between texture parameters and discrepancies between local topographies reconstructed from measurements. Instrument repeatability metrics are also presented for each measurement of the test surfaces. Results show that discrepancies in measurements made on the acquired datasets are often similar in magnitude to the size of the features present on the surfaces. Conclusions are drawn regarding the suitability of various surface measurement instruments for polymer LPBF surfaces
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