Condenser Lens Research Articles

Blanking characteristics of a miniature electron beam column

A commercial field emission scanning electron microscopy (SEM) based around a miniature electron beam column includes an integrated electrostatic blanker, making the system well-suited for lithography. A previous version of the miniature column design demonstrated direct-write lithography with 70 nm lines and spaces written into resist. That column also demonstrated an 85 MHz blanking speed and a 6 nA beam current using a condenser lens. This article presents a study of the field emission SEM’s integrated blanking system, including measurements and simulations of the electron beam optics. Rise and settle times are discussed, as well as beam extinction ratios under various operating conditions. The column’s conjugate blanking optics are described, and measurements are presented, which suggest that the column may be used in a conjugate blanking mode for lithography. Finally, this article discusses how these results will feedback into the system design in order to improve the SEM’s existing lithography capabilities.

Phase-Shifting Gabor Holographic Microscopy

A new lensless microscopy method able to recover the complex wavefront diffracted by a sample from a set of inline recorded holograms is presented. It is based on a modified Gabor-like setup where a condenser lens and a spatial light modulator (SLM) are inserted in a classical Gabor configuration. The condenser lens provides the sample's spectrum at the system Fourier plane while the SLM allows phase shifting modulation of the central spot (DC term) of the sample's spectrum. As consequence, the proposed imaging system recovers the complex amplitude distribution of the diffracted sample wavefront without an additional reference beam. Experimental results validate the proposed method and expand the Gabor method applicability beyond cases of weak diffraction assumption.

N-body Monte Carlo Simulation on High Contrast Biology Transmission Electron Microscope

Inner and outer diameters of the phase plate limit the number of electrons passing and can affect the high-resolution information in the phase contrast image. A more practical column model including the First Condenser Lens CL1, Second Condenser Lens CL2, Mini-condenser Lens CM and Objective Lens(OL) was first built to obtain the beam performance at the upper surface of the phase plate. N -body Monte Carlo simulation was used to avoid error caused by big defocus from the Guassian image plane where a lens field exists. In building the motion equation in a practical field, second order finite element method and Hermite function interpolation were applied to get the axial field and its arbitrary order derivative. N motion equations were then solved by fifth-order Runge-Kutta algorithm and the performance of un-scattered and scattered electrons was given for a 200kV TEM. Results show that the beam spots are 2.7µm and 39µm for un-scattered and scattered electrons respectively. N -body Monte Carlo simulation can obtain both positions and velocities of un-scattered and scattered electrons at the arbitrary plane with aberrations being considered, which effectively avoids error from the defocus distance in classic aberration integrated methods.

Condenser‐Based Instant Reflectometry

AbstractWe present a technique for rapid capture of high quality bidirectional reflection distribution functions(BRDFs) of surface points. Our method represents the BRDF at each point by a generalized microfacet model with tabulated normal distribution function (NDF) and assumes that the BRDF is symmetrical. A compact and light‐weight reflectometry apparatus is developed for capturing reflectance data from each surface point within one second. The device consists of a pair of condenser lenses, a video camera, and six LED light sources. During capture, the reflected rays from a surface point lit by a LED lighting are refracted by a condenser lenses and efficiently collected by the camera CCD. Taking advantage of BRDF symmetry, our reflectometry apparatus provides an efficient optical design to improve the measurement quality. We also propose a model fitting algorithm for reconstructing the generalized microfacet model from the sparse BRDF slices captured from a material surface point. Our new algorithm addresses the measurement errors and generates more accurate results than previous work. Our technique provides a practical and efficient solution for BRDF acquisition, especially for materials with anisotropic reflectance. We test the accuracy of our approach by comparing our results with ground truth. We demonstrate the efficiency of our reflectometry by measuring materials with different degrees of specularity, values of Fresnel factor, and angular variation.

Solving the accelerator-condenser coupling problem in a nanosecond dynamic transmission electron microscope

We describe a modification to a transmission electron microscope (TEM) that allows it to briefly (using a pulsed-laser-driven photocathode) operate at currents in excess of 10 mA while keeping the effects of condenser lens aberrations to a minimum. This modification allows real-space imaging of material microstructure with a resolution of order 10 nm over regions several microm across with an exposure time of 15 ns. This is more than six orders of magnitude faster than typical video-rate TEM imaging. The key is the addition of a weak magnetic lens to couple the large-diameter high-current beam exiting the accelerator into the acceptance aperture of a conventional TEM condenser lens system. We show that the performance of the system is essentially consistent with models derived from ray tracing and finite element simulations. The instrument can also be operated as a conventional TEM by using the electron gun in a thermionic mode. The modification enables very high electron current densities in microm-sized areas and could also be used in a nonpulsed system for high-throughput imaging and analytical TEM.

Photonic Crystal Negative Refractive Optics

Photonic crystals (PCs) are multi-dimensional periodic gratings, in which the light propagation is dominated by Bragg diffraction that appears to be refraction at the flat surfaces of the PC. The refraction angle from positive to negative, perfectly or only partially obeying Snell's law, can be tailored using photonic band theory. The negative refraction enables novel prism, collimation, and lens effects. Because PCs usually consist of two transparent media, these effects occur at absorption-free frequencies, affording significant design flexibility for free-space optics. The PC slab, a high-index membrane with a two-dimensional airhole array, must be carefully designed to avoid reflection and diffraction losses. Light focusing based on negative refraction forms a parallel image of a light source, facilitating optical couplers and condenser lenses for wavelength demultiplexing. A compact wavelength demultiplexer can be designed by combining the prism and lens effects. The collimation effect is obtainable not only inside but also outside of the PC by optimizing negative refractive condition.

Evaluation of erythrocyte dysmorphism by light microscopy with lowering of the condenser lens: A simple and efficient method

To demonstrate that the evaluation of erythrocyte dysmorphism by light microscopy with lowering of the condenser lens (LMLC) is useful to identify patients with a haematuria of glomerular or non-glomerular origin. A comparative double-blind study between phase contrast microscopy (PCM) and LMLC is reported to evaluate the efficacy of these techniques. Urine samples of 39 patients followed up for 9 months were analyzed, and classified as glomerular and non-glomerular haematuria. The different microscopic techniques were compared using receiver-operator curve (ROC) analysis and area under curve (AUC). Reproducibility was assessed by coefficient of variation (CV). Specific cut-offs were set for each method according to their best rate of specificity and sensitivity as follows: 30% for phase contrast microscopy and 40% for standard LMLC, reaching in the first method the rate of 95% and 100% of sensitivity and specificity, respectively, and in the second method the rate of 90% and 100% of sensitivity and specificity, respectively. In ROC analysis, AUC for PCM was 0.99 and AUC for LMLC was 0.96. The CV was very similar in glomerular haematuria group for PCM (35%) and LMLC (35.3%). LMLC proved to be effective in contributing to the direction of investigation of haematuria, toward the nephrological or urological side. This method can substitute PCM when this equipment is not available.

Optical Trap for Manipulating Plural Particles by Using a Liquid Crystal Device

We propose an optical manipulation system for simultaneously trapping and controlling the positions of microscopic multiple particles by using a liquid crystal (LC) optical device and a condenser lens. The positions of the multiple particles trapped at the bright region of the linear interference fringe patterns can easily be shifted along the fringe patterns by controlling the applied voltage to the LC optical device.

Practical integrated design of a condenser-objective lens for transmission electron microscope

A condenser-objective lens is designed through combination of separating and integrating to consider the effect of the front condenser field on its objective performance. A practical lens model including magnetic pole piece, magnetic circuit and coil windings is built to optimize its rear field. The front field can be integrated into the rear one by simply adjusting the position of the specimen and the excitation on the condenser-objective lens. Optical performance of the integrated lens is researched as both a condenser lens and an imaging one. The total aberrations at the specimen plane are 0.01nm under STEM operation mode and its spherical aberration coefficient is 1.5mm when being an imaging objective lens, which can meet for high resolution microanalysis and TEM imaging.

Optical Design of LCOS Optical Engine and Optimization With Genetic Algorithm

This paper demonstrates an optical design of miniature of LCOS optical engine and optics with white light-emitting diode (LED) and the most importantly, proposes a new optimization method for non-image optics via Genetic Algorithm (GA) written in Optical Software ASAP, in order to achieve best performance for light efficiency and uniformity. Thanks to the development of modern digital equipment, optimization work for non-image optics plays a role in modern optical engineering. So far Least Damping Square, Taguchi Fuzzy, and simulation annealing methods have been introduced and some of them has been applied to many items of commercial simulation software. However, GA is first introduced in this paper for non-image optical design and optimization, although it has been for many years been used as effective optimization method in image optics; In this paper, GAs are written in the form of macro language from ASAP. During the design process, we used one OPTEK Technology OVS3WBCR44 LED as the light source of the general projection display. Because of the extensiveness of the LEDs, the collection efficiency within the desired acceptance angle was not expected to be high. Due to the particular acceptance angle (cone), we needed a condenser lens system, which satisfied the light small angle incident to 0.59-in liquid-crystal-on-silicon (LCOS) pixels. The optical engine in this paper is designed for a compact LCOS projector with a white LED light source and the employment of an LCOS panel has been reduced to one piece in order to get the best volumetric size. Optical design specification is mainly for an 11 projected screen, whose objective distance is close to 420 mm with fixed focal lens. GA methods are applied in this research in order to achieve maximum brightness and uniformity. Compared to traditional optimization methods, such as Least Damping Square, the GA used in this research gives reasonably good results.

Optimization of optical lens-controlled scanning electron microscopic resolution using generalized regression neural network and genetic algorithm

A scanning electron microscope (SEM) is a sophisticated equipment employed for fine imaging of a variety of surfaces. In this study, prediction models of SEM were constructed by using a generalized regression neural network (GRNN) and genetic algorithm (GA). The SEM components examined include condenser lens 1 and 2 and objective lens (coarse and fine) referred to as CL1, CL2, OL-Coarse, and OL-Fine. For a systematic modeling of SEM resolution ( R), a face-centered Box–Wilson experiment was conducted. Two sets of data were collected with or without the adjustment of magnification. Root-mean-squared prediction error of optimized GRNN models are GA 0.481 and 1.96 × 10 - 12 for non-adjusted and adjusted data, respectively. The optimized models demonstrated a much improved prediction over statistical regression models. The optimized models were used to optimize parameters particularly under best tuned SEM environment. For the variations in CL2 and OL-Coarse, the highest R could be achieved at all conditions except a larger CL2 either at smaller or larger OL-Coarse. For the variations in CL1 and CL2, the highest R was obtained at all conditions but larger CL2 and smaller CL1.

Phase-shifting Gabor holography

We present a modified Gabor-like setup able to recover the complex amplitude distribution of the object wavefront from a set of inline recorded holograms. The proposed configuration is characterized by the insertion of a condenser lens and a spatial light modulator (SLM) into the classical Gabor configuration. The phase shift is introduced by the SLM that modulates the central spot (dc term) in an intermediate plane, without an additional reference beam. Experimental results validate the proposed method and produce superior results to the Gabor method.

High performance diffuse reflectance circular dichroism spectrophotometer

A new dual-purpose transmittance circular dichroism (CD) and diffuse reflectance CD (DRCD) universal chiroptical spectrophotometer (UCS-3, J-800KCMFII) was successfully developed to have the capability of measuring DRCD spectra down to 190 nm with high efficiency, based on UCS-2: J-800KCMF. Optical components newly used in UCS-3 are the integrating sphere of optimum size and material to achieve high performance particularly in the shorter wavelength region, a baffle installed to reduce the first specular reflection signals, and a condenser lens to increase light intensity per area for small samples. As a result, UCS-3 has become a very powerful instrument to measure DRCD spectra of powdered samples in situ, with approximately 20 times sensitivity of existing UCS-2. We could show that to achieve similar quality DRCD spectra, only 50 mug of (S)-(+)-1,1(')-binaphthyl-2,2(')-diyl hydrogen phosphate is required on UCS-3, as compared with 1.12 mg for UCS-2.

Integrated three-dimensional optical MEMS for chip-based fluorescence detection

This paper presents a novel fluorescence sensing chip for parallel protein microarray detection in the context of a 3-in-1 protein chip system. This portable microchip consists of a monolithic integration of CMOS-based avalanche photo diodes (APDs) combined with a polymer micro-lens, a set of three-dimensional (3D) inclined mirrors for separating adjacent light signals and a low-noise transformer-free dc–dc boost mini-circuit to power the APDs (ripple below 1.28 mV, 0–5 V input, 142 V and 12 mA output). We fabricated our APDs using the planar CMOS process so as to facilitate the post-CMOS integration of optical MEMS components such as the lenses. The APD arrays were arranged in unique circular patterns appropriate for detecting the specific fluorescently labelled protein spots in our study. The array-type APDs were designed so as to compensate for any alignment error as detected by a positional error signal algorithm. The condenser lens was used as a structure for light collection to enhance the fluorescent signals by about 25%. This element also helped to reduce the light loss due to surface absorption. We fabricated an inclined mirror to separate two adjacent fluorescent signals from different specimens. Excitation using evanescent waves helped reduce the interference of the excitation light source. This approach also reduced the number of required optical lenses and minimized the complexity of the structural design. We achieved detection floors for anti-rabbit IgG and Cy5 fluorescent dye as low as 0.5 ng/µl (∼3.268 nM). We argue that the intrinsic nature of point-to-point and batch-detection methods as showcased in our chip offers advantages over the serial-scanning approach used in traditional scanner systems. In addition, our system is low cost and lightweight.

A rapid method to correct objective lens astigmatism in a TEM

This work describes a rapid method to correct the two-fold astigmatism of transmission electron microscope (TEM) objective lens employing caustic curve when no objective aperture is inserted. The method makes use of rounding the caustic curve via the objective lens stigmators after the condenser lens astigmatism has been corrected. It has many advantages over other methods, it is fast, straightforward, and does not need holes or an amorphous material.

Measurement of precision for developing automatic transmission electron microscope

AbstractTransmission electron microscope (TEM) is one of the most useful tools for atomic‐level characterization; however, it is not user‐friendly because the condition of the electron beam in TEM changes every time it is started, that is, the reproducibility of the condition is insufficient. One of the reasons for the insufficient reproducibility is the magnetic hysteresis of the magnetic lenses used in TEM. We have found that the dumping oscillation around the set value of the condenser lens current reduces the effect of the magnetic hysteresis, and have determined the reproducibilities of the size and position of the electron beam on a sample. The results show that the reproducibilities were markedly improved. Copyright © 2008 John Wiley & Sons, Ltd.

Image contrast in X-ray reflection interface microscopy: comparison of data with model calculations and simulations

The contrast mechanism for imaging molecular-scale features on solid surfaces is described for X-ray reflection interface microscopy (XRIM) through comparison of experimental images with model calculations and simulated measurements. Images of elementary steps show that image contrast is controlled by changes in the incident angle of the X-ray beam with respect to the sample surface. Systematic changes in the magnitude and sign of image contrast are asymmetric for angular deviations of the sample from the specular reflection condition. No changes in image contrast are observed when defocusing the condenser or objective lenses. These data are explained with model structure-factor calculations that reproduce all of the qualitative features observed in the experimental data. These results provide new insights into the image contrast mechanism, including contrast reversal as a function of incident angle, the sensitivity of image contrast to step direction (i.e. up versus down), and the ability to maximize image contrast at almost any scattering condition defined by the vertical momentum transfer, Q(z). The full surface topography can then, in principle, be recovered by a series of images as a function of incident angle at fixed momentum transfer. Inclusion of relevant experimental details shows that the image contrast magnitude is controlled by the intersection of the reciprocal-space resolution function (i.e. controlled by numerical aperture of the condenser and objective lenses) and the spatially resolved interfacial structure factor of the object being imaged. Together these factors reduce the nominal contrast for a step near the specular reflection condition to a value similar to that observed experimentally. This formalism demonstrates that the XRIM images derive from limited aperture contrast, and explains how non-zero image contrast can be obtained when imaging a pure phase object corresponding to the interfacial topography.

Negative Refraction in Photonic Crystals

AbstractPhotonic crystals are multidimensional periodic gratings, in which the light propagation is dominated by Bragg diffraction that appears to be refraction at the flat surfaces of the crystals. The refraction angle from positive to negative, perfectly or only partially obeying Snell's law, can be tailored based on photonic band theory. Negative refraction enables novel prism, collimation, and lens effects. Because photonic crystals usually consist of two transparent media, these effects occur at absorption-free frequencies, affording significant design flexibility for free-space optics. The photonic-crystal slab, a high-index membrane with a two-dimensional airhole array, must be carefully designed to avoid unwanted reflection and diffraction. Light focusing based on negative refraction forms a parallel image of a light source, facilitating optical couplers and condenser lenses for wavelength demultiplexing. A compact wavelength demultiplexer can be designed by combining the prism and lens effects.

STEM probe characteristics at large defoci for use in ptychographical imaging

A possible configuration for undertaking diffractive imaging microscopy in the conventional scanning transmission electron microscope (STEM) is to defocus the probe by a large distance in order to minimise the number of diffraction patterns required to reconstruct the ptychographical image. Although the characteristics of STEM probes have been well explored and measured near the beam crossover, they are rarely observed (or calculated) at very large defoci. In this paper we compare probes calculated under a variety of approximations with measured data from a JEOL 2010F in STEM mode. When the illumination aperture is narrow and the defocus is large (near parallel illumination useful for ptychographical imaging) the Ronchigram cannot be used easily to characterize aberration, We develop an alternative method of estimating the effective aperture size and condenser lens spherical aberration.

Approximating the ITS-90 between Zinc and Copper with an Infrared Thermometer at NIS-Egypt

This paper presents an approximation to the International Temperature Scale of 1990 (ITS-90) between the Zn (420 °C) and Cu (1085 °C) fixed points using a 900 nm narrow-band radiation thermometer. This thermometer has a 400 mm working distance and a 150 mm objective focal length. An image of the measured target is focused by the objective lens onto a 1 mm aperture (drilled mirror). The light passing through the aperture is conveyed by a condenser lens through an interference filter with a nominal central wavelength of 900 nm and a half-bandwidth of 10 nm before reaching a silicon photodiode working in the photovoltaic mode. The thermometer was calibrated at the Zn, Al, Ag, and Cu blackbody fixed points. The results of the calibration were used to determine the constants A, B, and C of the Sakuma-Hattori interpolation equation. The results showed that the ITS-90 can be approximated within ± 0.051 °C throughout the Zn-Cu interval when the thermometer is calibrated at the Zn, Al, Ag, and Cu fixed points.