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Applied Optics

APPLICATIONS-CENTERED RESEARCH IN OPTICS

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April


Microscopy mineral image enhancement through center operator construction

  • Xiangzhi Bai
  • received 01/08/2015; accepted 04/17/2015; posted 04/17/2015; Doc. ID 231764
  • [full text: PDF (8530) KB)]
  • Abstract: Enhancing microscopy mineral image to produce clear mineral image with rich details is important for mineral analysis. To effectively enhance the microscopy mineral images, an algorithm through utilizing the constructed center operator from the opening and closing based toggle operator is proposed in this paper. Firstly, the center operator is constructed from the opening and closing based toggle operator. Secondly, the mineral image features are extracted by using the constructed center operator for mineral image enhancement. Thirdly, the multi-scale mineral image features are extracted through multi-scale morphological theory using multi-scale structuring elements. Fourthly, the final features for mineral image enhancement are constructed from the extracted multi-scale features. Finally, the mineral image is effectively enhanced through importing the final features into the original mineral image. Experimental results on various microscopy mineral images verified that the proposed algorithm performed well for mineral image enhancement and had competing performance comparing with some existed algorithms.

Keywords (OCIS):

  • (100.0100) Image processing : Image processing
  • (100.2000) Image processing : Digital image processing
  • (110.0180) Imaging systems : Microscopy
  • (180.0180) Microscopy : Microscopy

Subnanometer absolute displacement measurement using a frequency comb referenced dual resonance tracking Fabry-Perot interferometer

  • Minhao Zhu, Haoyun Wei, Shijie Zhao, Xuejian Wu, and Yan Li
  • received 01/26/2015; accepted 04/17/2015; posted 04/17/2015; Doc. ID 233108
  • [full text: PDF (568) KB)]
  • Abstract: Fabry-Perot (F-P) interferometry is a traceable high resolution method for displacement metrology that has no nonlinearity. Compared with the single resonance tracking (SRT) F-P interferometry, the dual resonance tracking (DRT) F-P interferometer system is able to realize tens of millimeter measurement range while maintaining the intrinsic high resolution. A DRT F-P system is thus developed for absolute displacement measurement in metrology applications. Two external cavity diode lasers (ECDL) are simultaneously locked to two resonances of a high finesse F-P cavity using the Pound-Drever-Hall locking scheme. The absolute optical frequencies of the locked ECDLs are measured using a reference diode laser, with the frequency stabilized and controlled by an optical frequency comb. The absolute cavity resonance order numbers are investigated. The measurement range is experimentally tested to achieve 20 mm, while the resolution reaches ∼10 pm level, mainly limited by the mechanical stability of the F-P cavity. Compared with the measurement results from a self-developed displacement-angle heterodyne interferometer, the displacement residuals are within 10 nm in the range of 20 mm.

Keywords (OCIS):

  • (120.0120) Instrumentation, measurement, and metrology : Instrumentation, measurement, and metrology
  • (120.2230) Instrumentation, measurement, and metrology : Fabry-Perot
  • (120.3180) Instrumentation, measurement, and metrology : Interferometry
  • (140.7090) Lasers and laser optics : Ultrafast lasers
  • (140.3325) Lasers and laser optics : Laser coupling

Strain field measurements around notches using SIFT features and meshless methods

  • Giancarlo Gonzales and Marco Antonio Meggiolaro
  • received 02/09/2015; accepted 04/17/2015; posted 04/17/2015; Doc. ID 234230
  • [full text: PDF (2997) KB)]
  • Abstract: This work proposes a hybrid experimental-numerical technique with the aim to improve the strain measurements at stress concentration regions. The novel technique is performed employing the computer vision SIFT algorithm and meshless methods, here termed SIFT-Meshless. The SIFT is applied to perform the feature points matching in two images of the specimen surface at different stages of mechanical deformation. The output data are provided as a set of displacement measurements by tracking matched feature points. This information is then used to model both displacement and strain field on the surface by means of a meshless formulation based on the moving least squares (MLS) approximation. By applying the proposed SIFT-Meshless method, the strain distribution around a semicircular notch in a plate under bending load was investigated. The experimental results were compared to those obtained by Digital Image Correlation technique based on a subset approach and to simulations from Finite Element (FE) analysis software. The experimental results demonstrated that the present method is capable of performing reliable strain measurements at distances close to the notch where the peak strain value is expected, even in the presence of high strain gradients.

Keywords (OCIS):

  • (100.2000) Image processing : Digital image processing
  • (120.6650) Instrumentation, measurement, and metrology : Surface measurements, figure

One-way regular electromagnetic mode immune to backscattering

  • Linfang Shen, Xiaohua Deng, Lujun Hong, and Xiaodong Zheng
  • received 02/17/2015; accepted 04/16/2015; posted 04/17/2015; Doc. ID 234834
  • [full text: PDF (856) KB)]
  • Abstract: In this paper, we present a basic model of robust one-way electromagnetic (EM) modes at microwave frequencies, which is formed by a semi-infinite gyromagnetic yttrium-iron-garnet (YIG) with dielectric cladding terminated by a metal plate. It is shown that this system supports not only one-way surface magnetoplasmons (SMPs) but also one-way regular mode, which is guided by the mechanism of the total internal reflection. Like one-way SMPs, the one-way regular mode can be immune to backscattering, and two types of one-way modes together comprise a complete dispersion band for the system.

Keywords (OCIS):

  • (230.3810) Optical devices : Magneto-optic systems
  • (230.7380) Optical devices : Waveguides, channeled
  • (240.6680) Optics at surfaces : Surface plasmons
  • (350.4010) Other areas of optics : Microwaves

Polarized Reflectance and Transmittance Properties of Wind-blown Sea Surfaces

  • Curtis Mobley
  • received 01/28/2015; accepted 04/16/2015; posted 04/17/2015; Doc. ID 233427
  • [full text: PDF (4200) KB)]
  • Abstract: Generation of random sea surfaces using wave variance spectra and Fourier transforms is formulated so that wave energy is conserved and both wave height and slope variance are fully resolved. Monte Carlo polarized ray tracing that accounts for multiple scattering between light rays and wave facets is used to compute effective Mueller matrices for reflection and transmission of air- or water-incident polarized radiance. Irradiance reflectances computed using a Rayleigh sky radiance distribution, sea surfaces generated with Cox-Munk statistics, and unpolarized ray tracing are in error by 10-18% compared to values computed using elevation- and slope-resolving surfaces and polarized ray tracing. Radiance reflectance factors as used to estimate water-leaving radiance from measured upwelling and sky radiances are shown to depend on sky polarization, and improved values are given.

Keywords (OCIS):

  • (010.4450) Atmospheric and oceanic optics : Oceanic optics
  • (290.5855) Scattering : Scattering, polarization
  • (010.5620) Atmospheric and oceanic optics : Radiative transfer
  • (010.0280) Atmospheric and oceanic optics : Remote sensing and sensors

Optimized Actuators for Ultra-Thin Deformable Primary Mirrors

  • Sergio Pellegrino, Marie Laslandes, and Keith Patterson
  • received 01/07/2015; accepted 04/16/2015; posted 04/17/2015; Doc. ID 231885
  • [full text: PDF (813) KB)]
  • Abstract: A novel design and selection scheme for surface-parallel actuators for ultra-thin, lightweight mirrors is presented. The actuation system consists of electrodes printed on a continuous layer of piezoelectric material bonded to an optical-quality substrate. The electrodes provide almost full coverage of the piezoelectric layer, in order to maximize the amount of active material that is available for actuation, and their shape is optimized to maximize the correctability and stroke of the mirror for a chosen number of independent actuators and for a dominant imperfection mode. The starting point for the design of the electrodes is the observation that the correction of a figure error that has at least two planes of mirror symmetry is optimally done with twin actuators that have the same optimized shape but are rotated through a suitable angle. Additional sets of optimized twin actuators are defined by considering the intersection between the twin actuators, and hence an arbitrarily fine actuation pattern can be generated. It is shown that this approach leads to actuator systems with better performance than simple, geometrically-based actuators. Several actuator patterns to correct third-order astigmatism aberrations are presented, and an experimental demonstration of a 41-actuator mirror is also presented.

Keywords (OCIS):

  • (110.1220) Imaging systems : Apertures
  • (110.6770) Imaging systems : Telescopes
  • (110.1080) Imaging systems : Active or adaptive optics

High efficiency quantum dot remote phosphor film

  • Shin-Tson Wu, Qi Hong, Kuo-Chang Lee, and Zhenyue Luo
  • received 01/13/2015; accepted 04/16/2015; posted 04/17/2015; Doc. ID 232339
  • [full text: PDF (433) KB)]
  • Abstract: We report a high efficiency quantum dot film for high color gamut edge-lit LCD backlight. On the film’s input surface, an array of asymmetric micro-prisms is used to preserve the large off-axis angle of the incident blue light. On the exit surface, the retroreflective micro-prisms retain blue light inside the film. The extended optical path effectively enhances the blue light’s probability to hit quantum dots and generate down-converted wavelengths. Without using any volume scattering particle, fewer quantum dots are needed to re-emit higher power green and red lights, which helps to lower the material cost.

Keywords (OCIS):

  • (160.2540) Materials : Fluorescent and luminescent materials
  • (230.3720) Optical devices : Liquid-crystal devices
  • (230.5590) Optical devices : Quantum-well, -wire and -dot devices
  • (250.5230) Optoelectronics : Photoluminescence

Image Reconstruction Method Based on CCD Calibration in Frequency Domain

  • Ze Zhang, Yang He, Bin Xiangli, and Shengjun Xiong
  • received 01/28/2015; accepted 04/16/2015; posted 04/16/2015; Doc. ID 233433
  • [full text: PDF (749) KB)]
  • Abstract: We demonstrate a method to reconstruct CCD images by calculating out both inter- and intra- pixel response function accurately with laser interference patterns. This method is proved theoretically to have the ability of improving image quality greatly, and thus may find great applications in high-quality imaging fields.

Keywords (OCIS):

  • (040.1520) Detectors : CCD, charge-coupled device
  • (100.2000) Image processing : Digital image processing
  • (110.3010) Imaging systems : Image reconstruction techniques

Spot centroid sensitivity to angle of intensity on image detector with lenslet array

  • Mei Hui, ping zhou, Peng Su, and Zhu Zhao
  • received 02/05/2015; accepted 04/16/2015; posted 04/16/2015; Doc. ID 234092
  • [full text: PDF (1048) KB)]
  • Abstract: Lenslet array has been introduced to detector to compensate for the low sensitivity. These lenses deviate the light from different incident angles, and potentially introduce error when sub-pixel accuracy is needed. We investigated the spot centroid position as the angle of incidence changes on Kodak KAI-16000 image detector with lenslet array, and noticed that there is a cubic dependency on the incident angle. The experiment results show that the dependence on angle of incidence is related to lenslet array in the Kodak detector used for the pentaprism test. This caused an error in spherical aberration on test surface after integration. The magnitude of the cubic component at incident angle of 14 degrees (equivalent to F/2) is 11.6 µm. It corresponds to 48 nm rms spherical aberration for the test surface and brings the scanning pentaprism test closer the principal test while there is a 56 nm rms discrepancy in them. The discrepancy in spherical aberration between the two tests reduced to 8 nm after this calibration. It also shows the contrast measurement results for Kodak detector and PointGrey detector. Experiments with two different detectors are performed to quantify this effect.

Keywords (OCIS):

  • (040.1240) Detectors : Arrays
  • (040.1490) Detectors : Cameras
  • (120.3180) Instrumentation, measurement, and metrology : Interferometry

Terahertz spectroscopic identification of explosive and drug simulants concealed by various hiding techniques

  • Uroš Puc, Andreja Abina, Aleksander Zidanšek, Anton Jeglič, Gintaras Valušis, and Melita Rutar
  • received 03/17/2015; accepted 04/16/2015; posted 04/16/2015; Doc. ID 236286
  • [full text: PDF (14051) KB)]
  • Abstract: Terahertz time-domain spectroscopy and imaging is used to study the effects of various hiding techniques on spectral features of drug and explosive simulants in combination with different paper and textile barriers. Results show that rapid detection and identification of concealed simulants is possible in the frequency range from 1.5 THz to 4.0 THz by using organic crystal based terahertz time-domain system and spectral peak analysis method.

Keywords (OCIS):

  • (190.4710) Nonlinear optics : Optical nonlinearities in organic materials
  • (300.1030) Spectroscopy : Absorption
  • (300.6170) Spectroscopy : Spectra
  • (300.6495) Spectroscopy : Spectroscopy, teraherz
  • (110.6795) Imaging systems : Terahertz imaging

Efficient line-based lens distortion correction for complete distortion with vanishing point reprojection model

  • Shixiong Jiang, Danhua Cao, Yubin Wu, Song Zhu, and Pan Hu
  • received 03/09/2015; accepted 04/16/2015; posted 04/16/2015; Doc. ID 232234
  • [full text: PDF (1773) KB)]
  • Abstract: Line-based correction method has been heavily investigated to improve the performance of lens distortion correction. However, it is difficult to achieve high-accuracy correction under the complete lens distortion (including radial, decentering and prism distortion), due to the coupling of the complete distortion parameters and the inaccuracy of line equation estimation. Here, we present a method that utilizes two models to resolve these problems, respectively. The recursive individual optimization model uses Levenberg-Marquardt (LM) to optimize each of the distortion parameters individually. And the vanishing point reprojection model improves the line equation by the known vanishing points calculated by a proposed expectation minimization (EM) algorithm. As a result, the accurate complete distortion correction can be achieved only by the line information. The validity of the proposed method was tested by some synthetic data and real images experiments. The results show that the proposed method can correct the image with the complete and non-complete distortion effectively.

Keywords (OCIS):

  • (150.0155) Machine vision : Machine vision optics
  • (150.1135) Machine vision : Algorithms
  • (150.1488) Machine vision : Calibration

Design and properties of a massive Coherent Amplifying Network

  • REMI SOULARD, Mark Quinn, and Gérard Mourou
  • received 01/12/2015; accepted 04/15/2015; posted 04/16/2015; Doc. ID 232423
  • [full text: PDF (838) KB)]
  • Abstract: The Coherent Amplifying Network laser is based on an array of thousands of active laser fibers coherently combined to generate high peak power pulses at high repetition rate. To achieve such a massive network, new combination architectures are presented here. They are based on implementing a spherical array of amplifying fibers thus removing the need for transport fibers from the initial scheme. These designs present an advantage in term of scalability leading to significant reduction of the temporal fluctuations compared to those of a conventional high peak power laser. Noise evolution with fiber number is calculated using a pertubative analysis of each channel parameters (phase, signal intensity, beam profile).

Keywords (OCIS):

  • (140.3510) Lasers and laser optics : Lasers, fiber
  • (220.4830) Optical design and fabrication : Systems design
  • (140.3298) Lasers and laser optics : Laser beam combining
  • (140.3425) Lasers and laser optics : Laser stabilization

Image Registration under Translation and Rotation in two dimensional planes Using Fourier Slice Theorem

  • Mausumi Pohit and J. Sharma
  • received 01/05/2015; accepted 04/15/2015; posted 04/16/2015; Doc. ID 231649
  • [full text: PDF (800) KB)]
  • Abstract: Image recognition in presence of both rotation and translation is a long standing problem in correlation pattern recognition. Use of log-polar transform gives a solution to this problem, however, at a cost of losing the vital phase information from the image. The main objective of this paper is to develop an algorithm based on Fourier Slice theorem for measuring the simultaneous rotation and translation of an object in a 2D plane. The algorithm is applicable for any arbitrary object shift for full 180 ̊ rotation.

Keywords (OCIS):

  • (070.0070) Fourier optics and signal processing : Fourier optics and signal processing
  • (100.4550) Image processing : Correlators
  • (150.1135) Machine vision : Algorithms
  • (100.3008) Image processing : Image recognition, algorithms and filters
  • (100.4994) Image processing : Pattern recognition, image transforms
  • (100.4999) Image processing : Pattern recognition, target tracking

Wave transfer matrix for a spiral phase plate

  • Yisa Rumala
  • received 01/22/2015; accepted 04/15/2015; posted 04/16/2015; Doc. ID 233078
  • [full text: PDF (2357) KB)]
  • Abstract: The wave transfer matrix (WTM) is applied to calculating various characteristics of a spiral phase plate (SPP) for the first time. In particular, it predicts the optical wave characteristics on input and output plane of the device when the SPP is fabricated on a substrate of the same refractive index as well as on a substrate of different refractive index compared to the SPP. The dependence of the parameters on the input laser frequency is studied in detail for a low finesse SPP etalon device for both cases. The equations derived from the WTM is used to show that a variation in input laser frequency causes the optical intensity pattern on output plane to rotate, while preserving the topology of the optical vortex, i.e. the variation in laser frequency has a minimal effect on the parameter describing the azimuthal intensity modulation and orbital angular momentum (OAM) content of the beam.

Keywords (OCIS):

  • (050.5080) Diffraction and gratings : Phase shift
  • (120.5700) Instrumentation, measurement, and metrology : Reflection
  • (120.7000) Instrumentation, measurement, and metrology : Transmission
  • (230.4170) Optical devices : Multilayers
  • (260.3160) Physical optics : Interference
  • (050.4865) Diffraction and gratings : Optical vortices

Surface profile measurement of a highly reflective silicon wafer by phase-shifting interferometry

  • YANGJIN KIM, Kenichi Hibino, Naohiko Sugita, and Mamoru Mitsuishi
  • received 03/05/2015; accepted 04/14/2015; posted 04/14/2015; Doc. ID 235738
  • [full text: PDF (2406) KB)]
  • Abstract: In phase-shifting Fizeau interferometers, the phase-shift error and multiple-beam interference are the most common sources of systematic error affecting high-precision phase measurements. The nonsinusoidal waveforms can be minimized by applying synchronous detection with more than 4-sample. However, when the phase-shift calibration is inaccurate, these algorithms cannot eliminate the effects of nonsinusoidal characteristics. Moreover, when measuring the surface profile of highly-reflective samples, the calculated phase is critically determined not only by the decrease in the fringe contrast but also by the coupling error between the harmonics and phase-shift error. In this paper, the phase errors calculated by conventional phase-shifting algorithms were estimated by considering the coupling error. We show that the 4N – 3 algorithm, comprising the polynomial window function and the DFT term, has the smallest phase error among the conventional phase-shifting algorithms. The surface profile of the highly-reflective silicon wafer was measured using a wavelength-tuning Fizeau interferometer and the 4N – 3 algorithm.

Keywords (OCIS):

  • (100.2650) Image processing : Fringe analysis
  • (120.3180) Instrumentation, measurement, and metrology : Interferometry
  • (120.3940) Instrumentation, measurement, and metrology : Metrology
  • (120.4290) Instrumentation, measurement, and metrology : Nondestructive testing

A texture orientation-based algorithm for detecting infrared maritime targets

  • Bin Wang, Lili Dong, Zhao Ming, Wu De, and Wenhai Xu
  • received 01/26/2015; accepted 04/14/2015; posted 04/15/2015; Doc. ID 233226
  • [full text: PDF (1147) KB)]
  • Abstract: In infrared maritime image (IMI) taken under strong wind waves, background interferences, such as ocean waves, usually has high intensity that can easily overwhelm the brightness of small dim target, which, however, is difficult for traditional target detection algorithms to overcome. To this problem, the paper proposes a novel target detection algorithm based on texture orientation (TO). The proposed algorithm firstly analyzes the inter-subband correlation between horizontal and vertical wavelet subbands, and then, thresholding and local singularity analysis are combined to suppress background interferences. The experiment shows that, compared with traditional algorithms, the proposed one can overcome the background interferences well. Besides, in order to realize accurate target extraction, pipeline-filtering algorithm is adopted to remove background interferences completely.

Keywords (OCIS):

  • (100.2000) Image processing : Digital image processing
  • (150.1135) Machine vision : Algorithms
  • (100.4999) Image processing : Pattern recognition, target tracking

A hybrid method of freeform lens design for arbitrary illumination target

  • Yufei Ma, Hang Zhang, Zeyu Su, Yu He, Liang Xu, Xu Liu, and Haifeng Li
  • received 02/11/2015; accepted 04/14/2015; posted 04/15/2015; Doc. ID 234465
  • [full text: PDF (4817) KB)]
  • Abstract: We propose a hybrid method of the freeform illumination design for arbitrary target form, imposing no restriction on the boundary of the irradiance distribution. Smooth continuous surfaces and continuous irradiance distributions are achieved with two independent steps. Initial solutions of the illumination problem are obtained with the method of Supporting Paraboloids, and final solutions are acquired by solving the elliptic Monge–Ampére equations numerically. Lenses which are able to produce complex irradiance distributions can be achieved with this method and fabricated in practice. The feasibility of this approach is demonstrated by some examples with experimental results. © 2015 Optical Society of America

Keywords (OCIS):

  • (080.2740) Geometric optics : Geometric optical design
  • (080.3630) Geometric optics : Lenses
  • (220.2945) Optical design and fabrication : Illumination design
  • (220.4298) Optical design and fabrication : Nonimaging optics

Quantitative photothermal phase imaging of red blood cells using digital holographic photothermal microscope

  • Srivathsan Vasudevan, George Chen, Zhiping Lin, and Beng Koon Ng
  • received 01/19/2015; accepted 04/14/2015; posted 04/14/2015; Doc. ID 231595
  • [full text: PDF (1817) KB)]
  • Abstract: Photothermal microscopy (PTM), a non-invasive pump-probe high resolution microscopy, has been applied as a bio-imaging tool in many biomedical studies. PTM utilizes conventional phase contrast microscope to obtain highly resolved photothermal images. However, phase information could not be extracted from these photothermal images as they are not quantitative. Moreover, the problem of halos inherent in conventional phase contrast microscopy need to be tackled. Hence digital holographic photothermal microscopy technique is proposed as a solution to obtain quantitative phase images. The proposed technique is demonstrated by extracting phase values of red blood cells from their photothermal images. These phase values can potentially be used to determine the temperature distribution of the photothermal images, a very important study in live cell monitoring applications.

Keywords (OCIS):

  • (190.4870) Nonlinear optics : Photothermal effects
  • (090.1995) Holography : Digital holography

Impact of plasma dynamics on equivalence ratio measurements by laser-induced breakdown spectroscopy

  • Johannes Kiefer, Bo Zhou, ZhongShan Li, and Marcus L.E. Alden
  • received 01/08/2015; accepted 04/14/2015; posted 04/14/2015; Doc. ID 232127
  • [full text: PDF (489) KB)]
  • Abstract: The systematic errors introduced by triggering a USB-spectrometer for LIBS equivalence ratio measurements are studied. We analyze the temporal behavior of laser-induced plasma in a non-reacting methane/air mixture and investigate the influence of the dynamics on equivalence ratio measurements with gated and ungated detection. For use of gated detectors optimal delay times were found to be between 500 and 2000 ns to allow effective suppression of interferences while maintaining sufficient signal-to-noise levels. Good precision was found for short and long exposure time intervals when an intensified CCD camera was employed. On the other hand, the jitter of an externally triggered ungated spectrometer leads to high uncertainties. Running the ungated spectrometer freely, the single-shot uncertainty can be reduced by more than one order of magnitude.

Keywords (OCIS):

  • (230.0040) Optical devices : Detectors
  • (280.1740) Remote sensing and sensors : Combustion diagnostics
  • (300.6365) Spectroscopy : Spectroscopy, laser induced breakdown

Schlieren-based temperature measurement inside the cylinder of an optical spark ignition and homogeneous charge compression ignition engine

  • Nikolaos Soulopoulos, Pavlos Aleiferis, Alexandros Charalambides, Yannis Hardalupas, Alex Taylor, and Yunichi Urata
  • received 01/20/2015; accepted 04/14/2015; posted 04/14/2015; Doc. ID 232294
  • [full text: PDF (2030) KB)]
  • Abstract: Schlieren is a non-intrusive technique that can be used to detect density variations in a medium, and thus, under constant pressure and mixture concentration conditions, measure whole field temperature distributions. The objective of the current work was to design a schlieren system to measure line-of-sight averaged temperature distribution with the final aim to determine the temperature distribution inside the cylinder of Internal Combustion engines. In a preliminary step, we assess theoretically the errors arising from the data reduction used to determine temperature from a schlieren measurement and find that the total error, random and systematic, is less than 3%, for typical conditions encountered in the present experiments. A Z-type, curved-mirror schlieren system was used to measure the temperature distribution from a hot air jet in an open air environment in order to evaluate the method. Using the Abel transform, the radial distribution of the temperature was reconstructed from the line of sight measurements. There was good agreement in the peak temperature between the reconstructed schlieren and thermocouple measurements. Experiments were then conducted in a four-stroke, single-cylinder, optical spark ignition engine with a four-valve, pentroof-type cylinder head to measure the temperature distribution of the reaction zone of an iso-octane-air mixture. The engine optical windows were designed to produce parallel rays and allow accurate application of the technique. The feasibility of the method to measure temperature distributions in IC engines was evaluated with simulations of the deflection angle combined with equilibrium chemistry calculations that estimated the temperature of the reaction zone at the position of maximum ray deflection as recorded in a schlieren image. Further simulations showed that the effects of exhaust gas recirculation and air-to-fuel ratio on the schlieren images were minimal under engine conditions compared to the temperature effect. At 20 crank angle degrees before top dead centre (i.e. 20 crank angle degrees after ignition timing), the measured temperature of the flame front was in agreement with the simulations (730–1320 K depending on the shape of the flame front). Furthermore, the schlieren images identified the presence of hot gases ahead of the reaction zone due to diffusion and showed that there were no hot spots in the unburned mixture.

Keywords (OCIS):

  • (080.2740) Geometric optics : Geometric optical design
  • (100.0100) Image processing : Image processing
  • (110.0110) Imaging systems : Imaging systems
  • (110.2960) Imaging systems : Image analysis
  • (120.1740) Instrumentation, measurement, and metrology : Combustion diagnostics
  • (120.6780) Instrumentation, measurement, and metrology : Temperature

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