White Light Diffraction Research Articles

ВЛИЯНИЕ МОДИФИЦИРОВАННЫХ МИКРОПРИЗМ ФРЕНЕЛЯ НА КОНТРАСТНУЮ ЧУВСТВИТЕЛЬНОСТЬ ОРГАНА ЗРЕНИЯ

Исследовано влияние модифицированных микропризм Френеля на контрастную чувствительность и остроту зрения. Определены условия снижения контраста тестовых оптотипив вследствие дифракции и хроматизма белого света при использовании призм различного призматического действия. Получены данные о снижении контраста, которые необходимо учитывать при проведении исследований дефектов зрения методами визоконтрастометрии.

White-light diffraction phase microscopy at doubled space-bandwidth product.

White light diffraction microscopy (wDPM) is a quantitative phase imaging method that benefits from both temporal and spatial phase sensitivity, granted, respectively, by the common-path geometry and white light illumination. However, like all off-axis quantitative phase imaging methods, wDPM is characterized by a reduced space-bandwidth product compared to phase shifting approaches. This happens essentially because the ultimate resolution of the image is governed by the period of the interferogram and not just the diffraction limit. As a result, off-axis techniques generates single-shot, i.e., high time-bandwidth, phase measurements, at the expense of either spatial resolution or field of view. Here, we show that combining phase-shifting and off-axis, the original space-bandwidth is preserved. Specifically, we developed phase-shifting diffraction phase microscopy with white light, in which we measure and combine two phase shifted interferograms. Due to the white light illumination, the phase images are characterized by low spatial noise, i.e., <1nm pathlength. We illustrate the operation of the instrument with test samples, blood cells, and unlabeled prostate tissue biopsy.

WHITE LIGHT DIFFRACTION PHASE MICROSCOPY

Quantitative phase imaging (QPI) techniques are very advantageous compared to the qualitative phase imaging techniques like bright field microscopy, phase contrast microscopy, differential interference contrast microscopy due to measurement of phase information quantitatively. In QPI techniques, there is no need of exogenous contrast agents to stain or tag the specimen. White light diffraction phase microscopy (wDPM) is one of the QPI techniques which is used to quantify the phase information from the samples. The phase information retrieved is dependent on the local refractive index and thickness of the biological cells. So, by measuring the phase one can find the refractive index and/or thickness of the specimen in nanometer scales. In this technique, the acquisition speed is only limited by the sensing device due to its single shot feature, it is better compared to other quantitative phase imaging techniques as its common path geometry provides better temporal phase sensitivity by cancelling out the most mechanisms responsible for noise and with the use of white light source the images are speckle-free. So we achieve better spatial phase sensitivity compared to other techniques. This method has attractive applications in biomedicine. We have developed wDPM set up for extracting phase information from the live yeast cells and sperm cells. The phase is reconstructed from the recorded interferograms by using a fast phase reconstruction algorithm. This algorithm avoids the unwrapping step which is needed in conventional phase reconstruction by Hilbert’s transform method. We have calculated the thickness of the yeast cells and sperm cells and demonstrate a video for visualizing the dynamics of yeast cells.

Linear halogen bulb as a powerful light source for physics experiments

The paper describes the usage of a conventional lamp equipped with a linear halogen bulb for physics experiments. The irradiance gain and limitation of spectral resolution are treated in detail theoretically and verified experimentally. The analysis shows that, in comparison with a standard bulb and slit arrangement, the linear bulb can increase irradiance of the spectrum image by an order of magnitude without a significant loss of spectral resolution in comparable experimental arrangements. Some concrete examples of experiments with a white light spectrum and diffraction are presented.

Inverse scattering solutions using low-coherence light.

We present a new wave-vector-space approach for solving inverse scattering problems. In our formulation, the theories for diffraction tomography and coherence gating are combined to explain 3D reconstruction with low-coherence light. Specifically, we apply this method to solve the scattering problem with broadband fields for transmission and reflection measurements. Our results can be applied to any interferometric measurements with low-coherence light, including optical coherence tomography, angle-resolved low-coherence interferometry, and white-light diffraction tomography.

White light diffraction phase microscopy as profilometry tool

A reflection type white light diffraction phase microscope for full field surface profiling of opaque samples is proposed. The system can extract surface profile from one recorded interferogram without any mechanical movement and the use of white light makes it free from speckle noise. We validated the performance of our system by measuring a known step sample and a high-quality plane sample. The step height of the step sample is found to be 88.5 nm with a standard deviation of 1.4 nm, and the surface peak to valley value of the plane sample is found to be 28.6 nm with a standard deviation of 3 nm.

Breakthroughs in Photonics 2013: Quantitative Phase Imaging: Metrology Meets Biology

Quantitative phase imaging (QPI) is an emerging optical approach that measures the optical path length of a transparent specimen noninvasively. Therefore, it is suitable for studying unstained biological tissues and cells with high sensitivity and resolution. This capability of QPI has fueled itself to grow rapidly as an active field of study for the past two decades. With this trend, QPI has experienced some breakthroughs in methods and applications in the past year. We briefly review some of these breakthroughs in method, including QPI through silicon marker-free phase nanoscopy and white-light diffraction tomography. Furthermore, some of the applications, such as quantitative phase measurement of cell growth and real-time blood testing, are introduced to show the importance and applicability of the field.

White-light diffraction tomography

A clever extension to a classic phase-contrast microscope allows speckle-free three-dimensional quantitative phase imaging of living cells in a tomographic imaging mode.

Effects of spatial coherence in diffraction phase microscopy

Quantitative phase imaging systems using white light illumination can exhibit lower noise figures than laser-based systems. However, they can also suffer from object-dependent artifacts, such as halos, which prevent accurate reconstruction of the surface topography. In this work, we show that white light diffraction phase microscopy using a standard halogen lamp can produce accurate height maps of even the most challenging structures provided that there is proper spatial filtering at: 1) the condenser to ensure adequate spatial coherence and 2) the output Fourier plane to produce a uniform reference beam. We explain that these object-dependent artifacts are a high-pass filtering phenomenon, establish design guidelines to reduce the artifacts, and then apply these guidelines to eliminate the halo effect. Since a spatially incoherent source requires significant spatial filtering, the irradiance is lower and proportionally longer exposure times are needed. To circumvent this tradeoff, we demonstrate that a supercontinuum laser, due to its high radiance, can provide accurate measurements with reduced exposure times, allowing for fast dynamic measurements.

White-light diffraction tomography of unlabelled live cells

We present a technique called white-light diffraction tomography (WDT) for imaging microscopic transparent objects such as live unlabelled cells. The approach extends diffraction tomography to white-light illumination and imaging rather than scattering plane measurements. Our experiments were performed using a conventional phase contrast microscope upgraded with a module to measure quantitative phase images. The axial dimension of the object was reconstructed by scanning the focus through the object and acquiring a stack of phase-resolved images. We reconstructed the three-dimensional structures of live, unlabelled, red blood cells and compared the results with confocal and scanning electron microscopy images. The 350 nm transverse and 900 nm axial resolution achieved reveals subcellular structures at high resolution in Escherichia coli cells. The results establish WDT as a means for measuring three-dimensional subcellular structures in a non-invasive and label-free manner. The three-dimensional structures of transparent objects, such as living cells, are captured by an imaging technique that uses white-light illumination and diffraction tomography to collect a stack of phase-based images.

Fast phase reconstruction in white light diffraction phase microscopy

In off-axis interferometry, we usually have to deal with the unwrapping process, which is very computationally intensive and prevents us from real time phase reconstruction. The wrapping problem usually occurs when imaging thick objects, which introduce phase shifts of more than 2π radians. However, in off-axis interferometry, the nonzero angle of interference of the two beams creates a ramp in the phase across the image that can produce phase wrapping errors. In this paper, we propose a simple technique that avoids the need for the unwrapping step in reconstructing quantitative phase images in white light diffraction phase microscopy of thin samples. We show that this approach can improve significantly the phase reconstruction speed and allow high impact applications, such as real-time blood testing.

Detection of a cylindrical boundary diffraction wave emanating from a straight edge by light interaction

The paper shows that the boundary diffraction wave originating at an edge is an omnidirectional cylindrical wave. The experimental set-up used to demonstrate this property employs a He–Ne laser beam. The beam is split into three beams using a glass plate. One of the beams passes straight through, the second beam passes through the glass plate and the third beam is the reflected beam. It is shown that the interference patterns are observed in all three beams. Analysis of these patterns shows that the boundary diffraction wave originating from the edge is an omnidirectional cylindrical wave. This analysis also provides strong evidence that the boundary diffraction wave travels not only within the beam where it originates but also to the neighboring coherent beam. The energy re-distribution was also shown to be dependent on the wavelength of the incident light beam and hence provides further evidence as to why longer wave lengths disperse more compared to shorter wavelengths in white light diffraction by an edge.

Diffraction phase microscopy with white light

We present white light diffraction phase microscopy (wDPM) as a quantitative phase imaging method that combines the single shot measurement benefit associated with off-axis methods, high temporal phase stability associated with common path geometries, and high spatial phase sensitivity due to the white light illumination. We propose a spatiotemporal filtering method that pushes the limit of the pathlength sensitivity to the subangstrom level at practical spatial and temporal bandwidths. We illustrate the utility of wDPM with measurements on red blood cell morphology and HeLa cell growth over 18 hours.

Optical virtual imaging at 50 nm lateral resolution with a white-light nanoscope

The imaging resolution of a conventional optical microscope is limited by diffraction to ~200 nm in the visible spectrum. Efforts to overcome such limits have stimulated the development of optical nanoscopes using metamaterial superlenses, nanoscale solid immersion lenses and molecular fluorescence microscopy. These techniques either require an illuminating laser beam to resolve to 70 nm in the visible spectrum or have limited imaging resolution above 100 nm for a white-light source. Here we report a new 50-nm-resolution nanoscope that uses optically transparent microspheres (for example, SiO₂, with 2 μm<diameter<9 μm) as far-field superlenses (FSL) to overcome the white-light diffraction limit. The microsphere nanoscope operates in both transmission and reflection modes, and generates magnified virtual images with a magnification up to ×8. It may provide new opportunities to image viruses and biomolecules in real time.

Visible iridescence from self-assembled periodic rippling in vertically aligned carbon nanotube forests

We observe iridescence in the form of spectrally dispersed white light reflected from the structured sidewalls of vertically aligned carbon nanotube forests. The iridescence is a result of diffraction from a self-assembled periodic rippling pattern on the forest sidewalls that acts as a reflection grating. We measure the grating spacing via white light and laser diffraction experiments and see good agreement with the spacing of the rippling pattern as measured via scanning electron microscopy. The periodic rippling pattern self-assembles during chemical vapor deposition growth of the forests.

Reverse color sequence in the diffraction of white light by the wing of the male butterflyPierella luna(Nymphalidae: Satyrinae)

The butterfly Pierella luna (Nymphalidae) shows an intriguing rainbow iridescence effect: the forewings of the male, when illuminated along the axis from the body to the wing tip, decompose a white light beam as a diffraction grating would do. Violet light, however, emerges along a grazing angle, near the wing surface, while the other colors, from blue to red, exit respectively at angles progressively closer to the direction perpendicular to the wing plane. This sequence is the reverse of the usual decomposition of light by a grating with a periodicity parallel to the wing surface. It is shown that this effect is produced by a macroscopic deformation of the entire scale, which curls in such a way that it forms a "vertical" grating, perpendicular to the wing surface, and functions in transmission instead of reflection.

White-light diffraction with a CD

No abstract

Rainbow-Like Spectra with a CD: An Active-Learning Exercise

Rainbow-like spectra, produced by reflexive diffraction of white light on a CD, offer a spectacular visual effect as well as an excellent classroom opportunity for students to learn how physics works. In this paper we show that building a coherent qualitative explanation can be a challenging task that requires students to combine gained knowledge with observations and explorations.

Pressure-dependent real-time investigations on the rapid thermal sulfurization of Cu–In thin films

Rapid thermal processing (RTP) under high sulfur partial pressure of copper rich Cu–In alloy thin films is investigated using in situ energy dispersive X-ray diffraction (EDXRD). Cu–In precursors are sulfurized at S vapor pressures in the 1 mbar range. Diffraction of white synchrotron light and recording of EDXRD spectra every 10 s at the EDDI beamline of the BESSY facility is used to monitor in situ the solid phases during the sulfurization and the subsequent cool-down. Ternary CuInS 2 forms via the binary InS and CuS and the ternary CuIn 5S 8 phases. The concentration of copper in the secondary Cu 2− x S phase, which segregates on the surface of the CuInS 2, shows a strong dependence on the maximum sulfur pressure during the RTP-like process.

Dynamic control of lattice spacing within colloidal crystals

In this study, we demonstrate reversible changes in lattice spacing within colloidal crystals controlled by an electric field. Crystals are assembled from negatively charged, monodisperse latex particles (945 nm) in an aqueous dispersion, by the application of an alternating electric field (1 kHz, ∼35 kV m−1). The lattice spacing within the colloidal crystals is determined by optical microscopy, laser and white light diffraction. Temporary dipoles induced by the electric field cause particles to aggregate into crystal structures; however, electrostatic repulsion prevents adjacent particles touching. One-dimensional (1D) and 2D crystals can be assembled, which act as diffraction gratings with electrically controllable diffraction properties. Two methods of tuning the lattice spacing are presented. In the first method, 1D crystal ‘strings’ are formed, where the effective lattice spacing is controlled by changing the orientation of the electric field and consequently the orientation of the strings. In the second method, a rotating electric field generates 2D crystals where lattice spacing is controlled by varying the field intensity.