Optical Interferometric Microscopy Research Articles

Label-free optical interferometric microscopy to characterize morphodynamics in living plants.

During the last century, fluorescence microscopy has played a pivotal role in a range of scientific discoveries. The success of fluorescence microscopy has prevailed despite several shortcomings like measurement time, photobleaching, temporal resolution, and specific sample preparation. To bypass these obstacles, label-free interferometric methods have been developed. Interferometry exploits the full wavefront information of laser light after interaction with biological material to yield interference patterns that contain information about structure and activity. Here, we review recent studies in interferometric imaging of plant cells and tissues, using techniques such as biospeckle imaging, optical coherence tomography, and digital holography. These methods enable quantification of cell morphology and dynamic intracellular measurements over extended periods of time. Recent investigations have showcased the potential of interferometric techniques for precise identification of seed viability and germination, plant diseases, plant growth and cell texture, intracellular activity and cytoplasmic transport. We envision that further developments of these label-free approaches, will allow for high-resolution, dynamic imaging of plants and their organelles, ranging in scales from sub-cellular to tissue and from milliseconds to hours.

Ice thickness monitoring for cryo-EM grids by interferometry imaging

While recent technological developments contributed to breakthrough advances in single particle cryo-electron microscopy (cryo-EM), sample preparation remains a significant bottleneck for the structure determination of macromolecular complexes. A critical time factor is sample optimization that requires the use of an electron microscope to screen grids prepared under different conditions to achieve the ideal vitreous ice thickness containing the particles. Evaluating sample quality requires access to cryo-electron microscopes and a strong expertise in EM. To facilitate and accelerate the selection procedure of probes suitable for high-resolution cryo-EM, we devised a method to assess the vitreous ice layer thickness of sample coated grids. The experimental setup comprises an optical interferometric microscope equipped with a cryogenic stage and image analysis software based on artificial neural networks (ANN) for an unbiased sample selection. We present and validate this approach for different protein complexes and grid types, and demonstrate its performance for the assessment of ice quality. This technique is moderate in cost and can be easily performed on a laboratory bench. We expect that its throughput and its versatility will contribute to facilitate the sample optimization process for structural biologists.

Femtosecond laser-ablation of gel and water.

We study the expansion dynamics of super-heated material during ultra-fast laser ablation of water and gel, using transient-reflectivity microscopy. We find that the expansion dynamics of water and gel, as observed during the first few nanoseconds, are extremely similar over a large range of ablation energies. We measure the crater topography of the gel after irradiation with a single laser shot, using optical interferometric microscopy, and estimate the mass that is ejected during the ablation. We calculate the laser energy deposited during irradiation by simulating the precise spatial distribution of the electron plasma density and temperature. We link the amount of removed mass obtained experimentally with the simulations of the deposited laser energy.

Correlation of surface features with corrosion behaviors of interstitial free steel processed by temper rolling

Temper rolling, as a final manufacturing procedure, brings the change of surface features and hence affects the corrosion behaviors of interstitial-free (IF) steel. This study investigates changes in residual stress, microstructure, and surface topography of IF steel using X-ray diffraction, electron backscatter diffraction, and optical interferometric microscopy. And the synthetic influence of surface features on the corrosion process of the steel was evaluated by damp heat tests and electrochemical measurements. Results showed that low tensile and compressive residual stresses are introduced to the surface of the IF steel. Some grains had a grain orientation spread (GOS) value greater than 0.5° after temper rolling. Moreover, temper rolling caused a slight change in the surface profile of the IF steel. The compressive residual stress had an overwhelming role at the macroscopic level, in retarding the corrosion evolution process of IF steel, as well as in decreasing the average corrosion rate. And corrosion was more likely to initiate and propagate in matrices with a high GOS value, which played the determinant role at the microscopic level. Moreover, the depth of valley in the surface profile could affect the diffusion process involved in the electrode reactions, which was more likely to exert an extra influence on the corrosion rate of IF steel.

Phase-induced amplitude apodization complex mask coronagraph mask fabrication, characterization, and modeling for WFIRST-AFTA

This work describes the fabrication, characterization, and modeling of a second-generation occulting mask for a phase-induced amplitude apodization complex mask coronagraph, designed for use on the WFIRST-AFTA mission. The mask has many small features (∼micron lateral scales) and was fabricated at the Jet Propulsion Laboratory Microdevices Laboratory, then characterized using a scanning electron microscope, atomic force microscope, and optical interferometric microscope. The measured fabrication errors were then fed to a wavefront control model which predicts the contrast performance of a full coronagraph. The expected coronagraphic performance using this mask is consistent with observing ∼15 planetary targets with WFIRST-AFTA in a reasonable time (<1 day/target).

Two-step polishing technique for single crystal diamond (100) substrate utilizing a chemical reaction with iron plate

A polishing technique for diamond substrates is described. It is a two-step process, consisting of (1) a rough processing step using carbon reaction with an iron plate at elevated friction temperatures, and (2) a finish processing step using hydroxyl (OH) radicals generated by a Fenton reaction between an iron plate and hydrogen peroxide solution. We analyzed the processing characteristics using optical interferometric microscopy, atomic force microscopy and transmission electron microscopy. Experimental results show that the surface roughness of a diamond substrate is markedly improved to an atomic-scale smoothness, and that a damage-free diamond surface can be fabricated with 5h of polishing. These results provide useful information for obtaining atomically smooth diamond substrates.

AlGaInAs MOVPE selective area growth for photonic integrated circuits

Abstract We developed a generic photonic integration platform based on selective area growth (SAG) by metal organic vapor-phase epitaxy (MOVPE) of AlGaInAs/InP multiple quantum well (MQW) material. For efficient and predictive band gap engineering of photonic integrated circuits, different SAG zones of active and passive function heterostructures are precisely modeled and characterized. With the vapor-phase diffusion model, using numerical simulations of finite volumes, we extracted the three effective diffusion lengths of Al, Ga, and In species. In our growth conditions, these lengths were 32, 65, and 14 μm, respectively. The Kardar-Parisi-Zhang (KPZ) equation, a classic approach to describe the growing interface profile, is used. AlGaInAs MQW properties are then simulated in terms of thickness, composition, band gap, and biaxial strain variations. Highly resolved μ-photoluminescence and optical interferometer microscopy measurements confirm the validity of the band gap and thickness variations for both bulk and MQW layers. A new diffractometer, with a submillimeter X-ray spot, was used to study the structural properties of the MQW in the center of the SAG area. As an application, we present the realization and operation of full-monolithic high-speed advanced modulation format transmitters based on novel prefixed optical phase switching by fast electro-absorption modulators.

Detecting 20 nm Wide Defects in Large Area Nanopatterns Using Optical Interferometric Microscopy

Due to the diffraction limited resolution and the presence of speckle noise, visible laser light is generally thought to be impractical for finding deep subwavelength defects in patterned semiconductor wafers. Here, we report on a nondestructive low-noise interferometric imaging method capable of detecting nanoscale defects within a wide field of view using visible light. The method uses a common-path laser interferometer and a combination of digital image processing techniques to produce 70 μm by 27 μm panoramic phase and amplitude images of the test nanopattern. Significant noise reduction and high sensitivity are achieved, which enables successful detection of several different types of sparse defects with sizes on the order of 20 nm wide by 100 nm long by 110 nm tall.

An automatic optical inspection system for measuring a microlens array with an optical interferometric microscope and genetic algorithm

PurposeThe purpose of this paper is to propose an automatic optical inspection system for measuring the surface profile of a microlens array.Design/methodology/approachThe system set‐up was constructed according to the principle of the Fizeau interferometer. After capturing the ring interference fringe images of the microlens with a camera, the diameter, profile information and optical properties were analyzed through a microlens surface profile algorithm using innovative image pre‐processing with a precision of less than 0.09 micron.FindingsBy integrating with the genetic algorithm, the XY‐Table shortest moving path of the system is calculated to achieve the purpose of high‐speed inspection and automatic microlens array surface profile measurement.Originality/valueThe measurement results of this system were also compared with other systems, including the atomic force microscope and stylus profiler, to verify the measurement precision and accuracy of this system.

Lens Sag Measurement of Microlens Array Using Optical Interferometric Microscope

This study attempted to develop a detection system for lens sag of the microlens array in real time using an optical automatic inspection framework to link with the computer through a camera. An image processing technique was applied to detect the spherical microlens array, and then, the results were compared. The system light source used laser light and applied CCD to collocate with the microscope array to form an automatic optical detection system for an optical interferometric microscope. It applied the principle of the Fizeau interferometer, illuminated the surface of microlens array, and formed the phase difference required by the interference of two lights through the laser light reflected by the reference plane and the surface of the microlens array, thus, forming an interference fringe. When the sag of the microlens was much longer than the wave length of the detection light source, the fringe would be densely distributed, thus, only a few central fringes were clear in the microscopic image. An image processing method was used to search the center of the interference fringe and a creative algorithm was utilized to obtain the lens sag of the microlens. As proved by the experiment, lens sag of 4 microlens arrays were detected in real time, with a minimum detection error of 0.08 μm, and a maximum detection error of 4 μm (error value 1 ~ 9%), according to different sample processes. This system featured a simple structure and is applicable to non-contact detection and detection of different-sized microlens arrays.

Poly(amide imide)s containing functional nitrile groups for high performance materials

Novel poly(amide imide)s containing functional nitrile groups were prepared by one step polycondensation reaction of two new diacid chlorides having nitrile substituents with various aromatic diamines incorporating flexible ether bridges. The polymers were readily soluble in polar organic solvents such as N-methylpyrrolidinone, N,N-dimethylformamide, dimethylsulfoxide, and were processed into thin films from such solutions. Most of these polymers showed high thermal stability with decomposition temperature being above 390 °C and glass transition temperature in the domain of 190–220 °C. The molecular relaxations in polymer films were evidenced by dynamic mechanical analyses and dielectric spectroscopy. The electrostrictive nano-actuation of polymer films was determined using an experimental setup for linear measurements, based on a Michelson type interferometer. Also the film surface with specific profiles was investigated using an optical interferometric microscope.

An automatic evaluation method for the surface profile of a microlens array using an optical interferometric microscope

In this paper, an automatic evaluation method for the surface profile of a microlens array using an optical interferometric microscope is presented. For inspecting the microlens array, an XY-table is used to position it. With a He–Ne laser beam and optical fiber as a probing light, the measured image is sent to the computer to analyze the surface profile. By binary image slicing and area recognition, this study located the center of each ring and determined the substrate of the microlens array image through the background of the entire microlens array interference image. The maximum and minimum values of every segment brightness curve were determined corresponding to the change in the segment phase angle from 0° to 180°. According to the ratio of the actual ring area and the ideal ring area, the area ratio method was adopted to find the phase-angle variation of the interference ring. Based on the ratio of actual ring brightness and the ideal ring brightness, the brightness ratio method was used to determine the phase-angle variation of the interference ring fringe. The area ratio method and brightness ratio method are interchangeable in precisely determining the phase angles of the innermost and outermost rings of the interference fringe and obtaining different microlens surface altitudes of respective pixels in the segment, to greatly increase the microlens array surface profile inspection accuracy and quality.

Advanced Lapping and Polishing Methods for Planarizing a Single-Crystal 4H-Sic Utilizing Fe Abrasive Particles

We have developed advanced lapping and polishing methods for silicon carbide (SiC) substrates using an Fe abrasive particles and hydrogen peroxide (H2O2) solution. In this method, a SiC surface is oxidized by hydroxyl radicals (OH*), which was generated by Fe catalyst reactions, and the oxide layer on the SiC is mechanically and/or chemically removed by Fe abrasive particles and solution [1-4]. In this study, we applied this planarization method for lapping and polishing SiC surface, in which catalytically generated hydroxyl radicals were utilized to oxidize the surface of a SiC wafer. The processed surfaces were observed by optical interferometric microscope, Nomarski differential interference contrast. These observations showed that surface roughness and flatness of a SiC substrate were markedly improved and scratch-free SiC surface was obtained. These results provide useful information for preparing a high-efficiency and high-accuracy SiC substrate.

Demonstration of planar thick InP layers by selective MOVPE

We studied the selective metal-organic vapor-phase epitaxy of thick InP bulk layers. The work focused on the obtention of planar thick layers by an adjustment of the growth conditions. We showed that reduced pressure and temperature in the reactor allowed to decrease the sharpness of the thickness profiles in the vicinity of the mask. This approach is consistent with the vapor phase diffusion model and the kinetic theory. Thick InP layers generally show huge overgrowths at the edges of the dielectric stripes. These overgrowths were suppressed by reducing the growth rate. All samples’ thickness profiles were characterized by means of optical interferometer microscopy and surface profiler. Scanning electronic microscopy was used in the observation of the edge overgrowths and highlighted the complexity and anisotropy of the growth at these edges.

Mask pattern interference in AlGaInAs selective area metal-organic vapor-phase epitaxy: Experimental and modeling analysis

We studied selective area growth modeling and characterization of the AlGaInAs material system. We used a three-dimensional vapor phase diffusion model to extract the effective diffusion lengths of Al, Ga, and In species from measured thickness profiles of the three binaries AlAs, GaAs, and InP. Our growth conditions yield to 50, 85, and 10 μm for Al, Ga, and In, respectively. Based on these values, we achieved a precise prediction of AlGaInAs thickness, composition, band gap, and biaxial strain variations in different selective area growth conditions. Particular attention was paid to the influence of neighboring cells in the case of high mask density. This configuration occurs in practical component mask layout. High mask density leads to interferences between masked cells and enhances the effect of the long diffusion length of aluminum and gallium species. Then, the biaxial strain is tensile shifted and the band gap is blue shifted in the vicinity of a mask, compared to reference material features grown away from the mask. High-resolution micro-photoluminescence and optical interferometer microscopy measurements confirmed the validity of simulated band gap and thickness variations for both bulk and multi-quantum well layers.

Numerical and experimental comparison of MEMS suspended plates dynamic behaviour under squeeze film damping effect

Dynamic behaviour of oscillating perforated microplates under the effect of squeeze film damping is analyzed. Two simplified finite element numerical approaches are adopted to predict damping and stiffness effects transferred from the surrounding ambient air to oscillating structures; the effects of holes cross section and plate dimension are observed. The applicability of the numerical models in terms of precision of results and mesh density is investigated. Results obtained by FE models are compared with experimental measurements conduced by an optical interferometric microscope.

Optical Interferometer Microscope for Monitoring and Control of Focused Ion Beam Processes

Extended abstract of a paper presented at Microscopy and Microanalysis 2006 in Chicago, Illinois, USA, July 30 – August 3, 2006

Laser microprobe (U–Th)/He geochronology

A new analytical method had been developed to enable high-spatial-resolution (U–Th)/He dating of accessory minerals. It involves the use of a focused ArF excimer to ablate pits in a polished grain surface, with the evolved gases spiked for isotope-dilution measurement of radiogenic 4He. These data are converted to concentrations by precise measurement of each pit using an optical interferometric microscope. U, Th, and Sm concentration measurements are made using one of several alternative microanalytical techniques (e.g., wavelength-dispersive electron microprobe analysis or laser-ablation, inductively coupled plasma mass spectrometry). By way of illustration, we present both conventional and laser microprobe (U–Th)/He dating results for a Brazilian monazite sample. Laser microprobe data (28 measurements on two crystal fragments) yield a weighted mean (U–Th)/He date of 455.3 ± 3.7 Ma (2SE). This result is statistically indistinguishable from the mean conventional (U–Th)/He date for three separate grain fragments: 449.6 ± 9.8 Ma (2SE). The agreement of conventional and laser ablation dates should encourage a wide variety of applications of the technique, including: (1) detrital mineral dating for provenance and unroofing studies; (2) the dating of broken, included, highly zoned, or irregular grains which are not easily corrected for α-ejection; and (3) measuring 4He loss profiles that can be inverted to determine cooling histories.

On the mechanism of popcorn blistering in copper clad laminates

Printed circuit boards are subject to increasingly hostile environment, for example, to a higher reflow temperature with the new lead-free solders. Consequently, thermal stability of copper clad laminates, a major component in printed circuit boards, is a critical issue in electronic packaging industries. In order to understand thermal degradation behavior, popcorn blister tests were performed at high temperatures for three different brands of copper clads laminated with FR-4 epoxy-saturated glass fabrics. Regardless of the brand, all the specimens became defective with blisters at about 250 °C. Detailed examination of fracture morphology with a scanning electron and an optical interferometric microscope revealed that popcorn blisters started not at the interface between copper foil and epoxy resin but at the interface between epoxy resin and glass yarns inside the FR-4 fabric. Sizing agent, an organic lubricant used for glass fibers, is suspected for the initial breakdown of the interface between glass yarns and epoxy resin. As epoxy resin degraded through decomposition of amino-alcohol portion or some other reaction, the gas products then diffused to the yarn-resin interface area. When the temperature reached about 250 °C, the pressure of such gas pockets became strong enough to rupture the laminate under both tension and shear stresses or to advance the fracture through the epoxy via cleavage fracture. Fracture patterns displayed both river and hackle markings, typical characteristics of epoxy fracture. The river markings seemed to indicate cleavage fracture of the epoxy (mode I) which was in close contact with glass yarns. The hackle markings, on the other hand, suggested rupturing of epoxy under both tension and shear stresses (modes I and II), which were most likely caused by a change in the maximum principal tensile stress direction due to interlocked copper nodules.

The Problem of Subrayleigh Resolution in Interference Microscopy

A method allowing subwavelength resolution within the framework of optical interferometric microscopy is proposed. It is shown that overcoming the diffraction limit is not a necessary requirement. Generally speaking, “subrayleigh resolution” and “overcoming the diffraction limit” are basically different concepts. The method developed uses the all-parameter modulation of the light source and separation of the phase shifts generated due to different reasons. In this method, a topological phase technique is used to separate the phases and therefore determine the corresponding characteristics of an object. The approach developed provides for a way to create a new type of optical devices. Within the framework of a uniform measuring procedure these devices make possible determining both geometrical and material parameters of the object under study.