Telecentric Objective Research Articles

Fully refractive telecentric f-theta microscope based on adaptive elements for 3D raster scanning of biological tissues.

Various techniques in microscopy are based on point-wise acquisition, which provides advantages in acquiring sectioned images, for example in confocal or two-photon microscopy. The advantages come along with the need to perform three-dimensional scanning, which is often realized by mechanical movement achieved by stage-scanning or piezo-based scanning in the axial direction. Lateral scanning often employs galvo-mirrors, leading to a reflective setup and hence to a folded beam path. In this paper, we introduce a fully refractive microscope capable of three-dimensional scanning, which employs the combination of an adaptive lens, an adaptive prism, and a tailored telecentric f-theta objective. Our results show that this microscope is capable to perform flexible three-dimensional scanning, with low scan-induced aberrations, at a uniform resolution over a large tuning range of X=Y=6300 μ m and Z=480 μ m with only transmissive components. We demonstrate the capabilities at the example of volumetric measurements on the transgenic fluorescence of the thyroid of a zebrafish embryo and mixed pollen grains. This is the first step towards flexible aberration-free volumetric smart microscopy of three-dimensional samples like embryos and organoids, which could be exploited for the demands in both lateral and axial dimensions in biomedical samples without compromising image quality.

Droplet sizing in atomizing sprays using polarization ratio with structured laser illumination planar imaging.

Previous research has shown that the polarization ratio technique allows the characterization of the surface mean diameter, D21, of droplets forming dilute sprays. However, its application to optically dense sprays has posed significant challenges due to the presence of multiple light scattering. Additionally, errors in measurement can arise from the angular dependence of the signal. In this Letter, we present a novel, to the best of our knowledge, method that addresses these challenges. Our approach combines the use of a telecentric objective with structured laser illumination, to both optimize light detection and suppress the unwanted intensity from multiple scattering. This approach enables the utilization of the polarization ratio technique for measuring the droplet size of challenging atomizing sprays. The method offers a promising solution for accurate and comprehensive spray characterization. It is applied, here, to a hollow-cone water spray running at 30, 50, and 70 bar injection pressure, reaching an optical depth up to three.

Use of Image Correlation to Measure Macroscopic Strains by Hygric Swelling in Sandstone Rocks

Some materials undergo hygric expansion when soaked. In porous rocks, this effect is enhanced by the pore space, because it allows water to reach every part of its volume and to hydrate most swelling parts. In the vicinity, this enlargement has negative structural consequences as adjacent elements support some compressions or displacements. In this work, we propose a normalized cross-correlation between rock surface texture images to determine the hygric expansion of such materials. We used small porous sandstone samples (11 × 11 × 30 mm3) to measure hygric swelling. The experimental setup comprised an industrial digital camera and a telecentric objective. We took one image every 5 min for 3 h to characterize the whole swelling process. An error analysis of both the mathematical and experimental methods was performed. The results showed that the proposed methodology provided, despite some limitations, reliable hygric swelling information by a non-contact methodology with an accuracy of 1 micron and permitted the deformation in both the vertical and horizontal directions to be explored, which is an advantage over traditional linear variable displacement transformers.

A Simply Equipped Fourier Ptychography Platform Based on an Industrial Camera and Telecentric Objective.

Fourier ptychography microscopy (FPM) is a recently emerged computational imaging method, which combines the advantages of synthetic aperture and phase retrieval to achieve super-resolution microscopic imaging. FPM can bypass the diffraction limit of the numerical aperture (NA) system and achieve complex images with wide field of view and high resolution (HR) on the basis of the existing microscopic platform, which has low resolution and wide field of view. Conventional FPM platforms are constructed based on basic microscopic platform and a scientific complementary metal–oxide–semiconductor (sCMOS) camera, which has ultrahigh dynamic range. However, sCMOS, or even the microscopic platform, is too expensive to afford for some researchers. Furthermore, the fixed microscopic platform limits the space for function expansion and system modification. In this work, we present a simply equipped FPM platform based on an industrial camera and telecentric objective, which is much cheaper than sCMOS camera and microscopic platform and has accurate optical calibration. A corresponding algorithm was embedded into a conventional FP framework to overcome the low dynamic range of industrial cameras. Simulation and experimental results showed the feasibility and good performance of the designed FPM platform and algorithms.

Telecentric broadband objective lenses for optical coherence tomography (OCT) in the context of low uncertainty metrology of freeform optical components: from design to testing for wavefront and telecentricity.

Freeform optical components enable significant advances for optical systems. A major challenge for freeform optics is the current lack of metrology methods with measurement uncertainty on the order of tens of nanometers or less. Towards addressing this challenge, optical coherence tomography (OCT) is a viable technique. In the context of low uncertainty metrology, the design requirements pertaining to the sample arm of an OCT metrology system are explicitly addressed in this paper. Two telecentric, broadband, diffraction limited, custom objective lens designs are presented with their design strategies. One objective lens was fabricated and experimentally tested for wavefront performance and telecentricity. This lens demonstrates near diffraction limited performance and a maximum deviation from telecentricity of 8.7 arcseconds across the full field of view, correlating to measurement uncertainty of less than 12 nm in simulation. The telecentricity test method developed completes the loop with respect to the design requirements and strategies presented and provides further intuition for telecentric lens designs in general.

Spatial multiplexing and autofocus in holographic contouring for inspection of micro-parts.

We present a method for fast geometrical inspection of micro deep drawing parts. It is based on single-shot two-wavelength contouring digital holographic microscopy (DHM). Within the capturing process, spatial multiplexing is utilized in order to record the two required holograms in a single-shot. For fast evaluation, determining the locations where the object is in focus and stitching all focus object's areas together is achieved digitally without the need for any external intervention using an autofocus algorithm. Thus, the limited depth of focus of the microscope objective is improved. The autofocus algorithm is based on minimizing the total variation (TV) of phase difference residuals of the two-wavelength measurements. In contrast to standard DHM, an object side telecentric microscope objective is used for overcoming the image scaling distortions caused by a conventional microscope objective. The method is used to reconstruct the 3D geometrical shape of a cold drawing micro cup. Experimental results verify the improvement of DHM's depth of focus.

Single-shot low coherence pointwise measuring interferometer with potential for in-line inspection

Low-coherence-interferometry (LCI) is a well-known optical metrology technique which offers high resolution and a low measurement uncertainty. For the inspection of dynamic and fast processes, single-shot point sensors can show their full capability. Therefore, a new approach of an interferometer is presented, allowing an single-shot acquisition of a LCI signal. The presented concept is based on tilted wavefronts to generate a spatial modulated interferogram. Using a three faceted mirror (TFM) in the reference path, a virtual field point is generated leading to a tilted planar reference wavefront in the pupil plane of the telecentric objective lens. Three mirror surfaces, which are diamond milled out of a monolithic copper cube, are applied to guarantee a stable TFM geometry, resulting in an invariant reference field point position.

Snapshot, reconfigurable multispectral and multi-polarization telecentric imaging system.

A reconfigurable telecentric imaging system that can simultaneously capture multispectral and multi-polarization information in a single snapshot is demonstrated. The proposed design utilizes a telecentric imaging objective and a light pipe for image multiplexing. An array of filters is used to filter each of the multiplexed images at an intermediate image plane. In this paper, we will discuss the system configuration and present the experimental results.

Damage visualization and deformation measurement in glass laminates during projectile penetration

Abstract Transparent armor consists of glass-polymer laminates in most cases. The formation and propagation of damage in the different glass layers has a strong influence on the ballistic resistance of such laminates. In order to clarify the course of events during projectile penetration, an experimental technique was developed, which allows visualizing the onset and propagation of damage in each single layer of the laminate. A telecentric objective lens was used together with a microsecond video camera that allows recording 100 frames at a maximum rate of 1 MHz in a backlit photography set-up. With this technique, the damage evolution could be visualized in glass laminates consisting of four glass layers with lateral dimensions 500 mm × 500 mm. Damage evolution was recorded during penetration of 7.62 mm AP projectiles with tungsten carbide core and a total mass of 11.1 g in the impact velocity range from 800 to 880 m/s. In order to measure the deformation of single glass plates within the laminates, a piece of reflecting tape was attached to the corresponding glass plate, and photonic Doppler velocimetry (PDV) was applied. With the photonic Doppler velocimeter, an infrared laser is used to illuminate an object to be measured and the Doppler-shifted light is superimposed to a reference light beam at the detector. The simultaneous visualization and PDV measurement of the glass deformation allow determining the deformation at the time of the onset of fracture. The analysis of the experimental data was supported by numerical simulations, using the AUTODYN commercial hydro-code.

Drop swarm analysis in dispersions with incident-light and transmitted-light illumination

The new developed Optical Multimode Online Probe (OMOP) can process images from either incident-light illumination (also called epi-illumination) or transmitted-light illumination (also called trans-illumination). The probe has an outer diameter of 38mm and the illumination is achieved by high performance Light Emitting Diodes (LEDs) with specifications of 1.96mm² and 493lm (251.53lm/mm²) at an angular deviation of 0.37°. A camera probe is used with either an object-space telecentric (telecentricity <0.2°, 2437mm virtual pupil distance) or entocentric objective (Köhler based illumination, 6238mm virtual pupil distance). Using the telecentric mode, the particle distance independency is located within 20mm while the focal depth is approximately 5mm. The local resolution is between 20 and 30μm, according to the used optics, with a standard deviation less than 4.5%. Maximum particle diameter is up to 5mm while particles can reach up to 2m/s as function of exposure. The basic distance transform approach with watershed segmentation for analysis of transmitted-light images gives deviations less than 5% at high particle densities and less than 2% at low ones. The error of false positives typically is below 5% while the error of wrong radiuses is below 1% for up to 90% of all droplets and below 5% otherwise. Up to five images per core and second (trans-illumination) can be analyzed automatically and online at densities up to 25% (trans-illumination, gap width less than 5mm) 40% (object side telecentric epi-illumination, single probe) respectively.The advanced pre-segmentation approach based on the Random Forest Classifier (RFC) is used to perform the more complex image analysis with epi-illumination. As long as the quality of pre-segmentation is high enough, the classification results in images, which can be analyzed in the following distance transform approach. This is considerably depending on the quality of training the algorithm and recurring image features. Compared to the distance transform analysis at low densities the deviation increases. The RFC pre-segmented image gives an additional deviation of 1.1% (both in regard to the total amount of evaluated pixels) and a deviation of 12.9% in regard to the mean particle diameter. Below a particle size of 50 pixels the image analysis overestimates the actual number of particles due to the sensitivity of the Euclidian distance approach.

A new phase-shift microscope designed for high accuracy stitching interferometry

Characterizing nanofocusing X-ray mirrors for the soon coming nano-imaging beamlines of synchrotron light sources motivates the development of new instruments with improved performances. The sensitivity and accuracy goal is now fixed well under the nm level and, at the same time, the spatial frequency range of the measurement should be pushed toward 50mm−1. SOLEIL synchrotron facility has therefore undertaken to equip with an interferential microscope suitable for stitching interferometry at this performance level. In order to keep control on the whole metrology chain it was decided to build a custom instrument in partnership with two small optics companies EOTECH and MBO.The new instrument is a Michelson micro-interferometer equipped with a custom-designed telecentric objective. It achieves the large depth of focus suitable for performing reliable calibrations and measurements. The concept has been validated with a predevelopment set-up, delivered in July 2010, which showed a static repeatability below 1nm PV despite a non-thermally stabilized environment. The final instrument was delivered early this year and was installed inside SOLEIL's controlled environment facility, where thorough characterization tests are under way. Latest test results and first stitching measurements are presented.

A goniometric light scattering instrument with high-resolution imaging

This paper describes a new goniometric optical scattering instrument whose distinctive features include a mobile light source, a telecentric objective, and a fixed photodiode array. A scientific-grade CCD detector allows the instrument to reliably detect BRDF levels as low as 5 × 10 - 8 sr - 1 , while generating a high-resolution map of light scattered from the sample surface. These data reveal the position and size of localized defects, which can then be excised from the sample to give an unbiased determination of the surface’s intrinsic roughness. High-quality signature and calibration data are also obtained, as well as a practical characterization of a silicon wafer.

Design of Catadioptric Lens with Servo Optical Mechanism in Holographic Recording System

In this paper, we present a catadioptric telecentric objective for a holographic recording system. The lens was made of Zeonex, whose aspherical surfaces were formed by diamond-turning machining. A least-squares method was used to solve a set of linear equations for the spot size of charge-coupled device (CCD). The data were obtained to generate an S curve, which was used in the pupil obscuration method, for the control of the system operated in a linear range of ±0.3 mm.

An optical shadowgraph microscope for a semiconductor wafer bump height measurement

We describe an optical micro shadowgraph for measuring the height of a micro solderball on a semiconductor wafer. The proposed optical system consists of a white-light microscopic inclination illumination and a telecentric objective. The solderball shadow image resulting from a slant illumination onto the protruded bump/solderball on the wafer is clearly captured. In terms of geometrical optics, a formula is derived to resolve the bump height from the length of the resulting shadow on the wafer surface. Experimental results demonstrate that the bump height measurement can be readily implemented.

Inspection of micro-solderballs on a semiconductor bumped wafer using optical shadowgraph

We describe a simple way to effectively measure the height of a micro-solderball of a micro-ball grid array (micro-BGA) on a bumped wafer. The proposed method derived using a white-light illumination source can perform a speedy whole field inspection of the micro-solderballs. The optical system consists of a white-light telecentric configuration and a long-working-distance microscope with a telecentric objective. The optical axes of the illuminating light and microscope are symmetrically arranged with respect to the normal of the test surface and hence the technique is applicable to optical measurement on a mirror-like test surface, such as a silicon wafer. The height of a solderball is computed from a simple formula based on the geometry of the specimen and the system configuration. Experimental results demonstrate that the height of a micro-solderball can be readily measured with accuracy in the order of micrometers.

Influence of the optical configuration on temperature measurements with fluid-dispersed TLCs

An accurate temperature calibration of fluid-dispersed thermochromic liquid crystal (TLC) particles is an important prerequisite for quantitative liquid crystal thermometry (LCT) measurements in flows. Encapsulated TLCs are subjected to uniform and linear temperature fields and are illuminated with a sheet of white light. A digital camera records the color distribution reflected by the particles. For the first time, a telecentric objective is used to eliminate the angular dependence of the color within the image plane.

Telecentric three-dimensional sensor with a liquid mirror for large-object inspection

We describe a device that applies the advantages of the space invariance of telecentric triangulation with the measurement of large objects (1 m(3)). Because the scan motion of the laser beam is decoupled from the physical transport of the sensor head, the fast scanning of large volumes becomes feasible. The device consists of a triangulation laser telemeter head that uses a large liquid primary mirror and an aspheric secondary mirror to realize the telecentric f-theta objective. We propose using liquid-mirror technology to make low-cost large objectives that have low f numbers, a diffraction-limited performance, and low scattering in the visible. This new optical system is useful for 3-D measurement. We discuss the optical configuration of the system and the performance of a laboratory prototype. The prototype has a standoff distance of 1.5 m, a telecentric scan as long as 1 m, a depth of view of 1 m, and a relative depth resolution of 0.5-1 mm.

Lens Systems with Frontal Aperture Stops

The requirements for the aberration correction in lenses with frontal aperture stops (FASs) are determined. The theory of distortion and field curvature correction is examined in such asymmetrical optical configurations. Computed results for an orthoscopic telecentric objective of the OR-3 type are given. A design for an f/1·6 photographic lens with field 65° is given. Some conclusions for the trends in FAS system development are drawn. The theoretical results of the synthesis and aberration correction for this type of lens system are given.

A Telecentric Camera Lens for Bubble Chamber Photography

A 127 mm, F/25, 54° telecentric objective has been designed and made for use with the 80 cm liquid helium bubble chamber of the Rutherford High Energy Laboratory.