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Applied Optics

APPLICATIONS-CENTERED RESEARCH IN OPTICS

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April


The Derivative Matrices of a Skew-Ray for Spherical Boundary Surfaces and Their Applications in System Analysis and Design

  • Psang Dain Lin
  • received 01/22/2014; accepted 04/08/2014; posted 04/09/2014; Doc. ID 205161
  • [full text: PDF (2103) KB)]
  • Abstract: In a previous paper [P. D. Lin, Appl. Opt. 52, 4151 (2013)], we presented the first- and second-order derivatives of a ray for a flat boundary surface to design prisms. In this paper, that scheme is extended to determine the Jacobian and Hessian matrices of a skew-ray as it is reflected / refracted at a spherical boundary surface. The validity of the proposed approach as an analysis and design tool is demonstrated using an axis-symmetrical system for illustration purpose. It is found that these two matrices can provide the search direction used by existing gradient-based schemes to minimize the merit function during the optimization stage of the optical system design process. It is also possible to make the optical system designs more automatic, if the image defects can be extracted from the Jacobian and Hessian matrices of a skew-ray.

Keywords (OCIS):

  • (080.0080) Geometric optics : Geometric optics
  • (080.2740) Geometric optics : Geometric optical design
  • (080.3620) Geometric optics : Lens system design
  • (080.1753) Geometric optics : Computation methods

Three-dimensional inline inspection for substrate warpage and ball grid array coplanarity using stereo vision

  • Takeshi Nakazawa and Ayman Samara
  • received 01/30/2014; accepted 04/08/2014; posted 04/09/2014; Doc. ID 205491
  • [full text: PDF (2634) KB)]
  • Abstract: We present a method for full field 3D measurement of substrate warpage and ball grid array coplanarity, which is suitable for inline back-end inspection and process monitoring. For evaluating the performance of the proposed system, the linearity between our system and a reference confocal microscope is studied by measuring a particular substrate sample with an area of 38 mm x 28.5 mm. The correlation coefficient is 0.965 and the 2 sigma difference in the two methods is 26.9 um for the warpage measurement. 1 sigma repeatability is 4.2 um based on 35 measurements. For BGA coplanarity inspection the correlation coefficient is 0.952 and the 2 sigma difference is 31.2 um. 1 sigma repeatability is 3.7um. Data acquisition takes about 0.2 seconds for full field measurements.

Keywords (OCIS):

  • (120.4630) Instrumentation, measurement, and metrology : Optical inspection
  • (150.0150) Machine vision : Machine vision
  • (150.6910) Machine vision : Three-dimensional sensing
  • (150.3045) Machine vision : Industrial optical metrology
  • (150.5495) Machine vision : Process monitoring and control

Frequency doubling of a passively mode-locked monolithic distributed Bragg reflector diode laser

  • D. Jedrzejczyk, T. Prziwarka, A. Klehr, O. Brox, H. Wenzel, K. Paschke, and G. Erbert
  • received 11/12/2013; accepted 04/08/2014; posted 04/17/2014; Doc. ID 201265
  • [full text: PDF (441) KB)]
  • Abstract: In this work frequency doubling of a passively mode-locked 3.5 mm long monolithic distributed Bragg reflector diode laser is investigated experimentally. At 1064 nm optical pulses with a duration of 12.4 ps are generated at a repetition rate of 13 GHz and a peak power of 825 mW resulting in an average power of 133 mW. Second-harmonic generation (SHG) is carried-out in a periodically poled MgO doped LiNbO3 ridge waveguide at a normalized nonlinear conversion efficiency of 930 %/W. A max. average second-harmonic power of 40.9 mW corresponding to a pulse energy of 3.15 pJ is reached in the experiment at an opto-optical conversion efficiency of 30.8 %. The normalized nonlinear conversion efficiency in mode-locked operation is more than two times larger compared to continuous-wave operation.

Keywords (OCIS):

  • (140.2020) Lasers and laser optics : Diode lasers
  • (140.3490) Lasers and laser optics : Lasers, distributed-feedback
  • (140.4050) Lasers and laser optics : Mode-locked lasers
  • (140.7300) Lasers and laser optics : Visible lasers
  • (190.2620) Nonlinear optics : Harmonic generation and mixing
  • (190.4390) Nonlinear optics : Nonlinear optics, integrated optics

Probing micro-structural information of anisotropic scattering media using rotation independent polarization parameters

  • Minghao Sun, Honghui He, Nan Zeng, E Du, Yihong Guo, Cheng Peng, Yonghong He, and Hui Ma
  • received 01/07/2014; accepted 04/07/2014; posted 04/08/2014; Doc. ID 204267
  • [full text: PDF (1644) KB)]
  • Abstract: Polarization parameters contain rich information on the micro- and macro-structure of scattering media. However, many of these parameters are sensitive to the spatial orientation of anisotropic media, and may not effectively reveal the micro-structural information. In this paper, we take polarization images of different textile samples at different azimuth angles. The results demonstrate that the rotation insensitive polarization parameters from rotating linear polarization imaging and Mueller matrix transformation methods can be used to distinguish the characteristic features of different textile samples. Further examinations using both experiments and Monte Carlo simulations reveal that the residue rotation dependence in these polarization parameters are due to the oblique incidence illumination. This study shows that such rotation independent parameters are potentially capable of quantitative classification of anisotropic samples such as textiles or biological tissues.

Keywords (OCIS):

  • (160.2290) Materials : Fiber materials
  • (290.4210) Scattering : Multiple scattering
  • (290.5855) Scattering : Scattering, polarization

Analysis of the relationship between fringe angle and three-dimensional profilometry system sensitivity

  • Ping Zhou, Xinran Liu, and Tongjing Zhu
  • received 12/06/2013; accepted 04/06/2014; posted 04/07/2014; Doc. ID 202594
  • [full text: PDF (2380) KB)]
  • Abstract: The relationship between projector-camera baseline and the phase variation direction of fringe patterns is one of essential characteristics in three-dimensional profilometry system, although it has been ignored. This paper indicates that the three-dimensional profilometry system will be most sensitive to the object depth change when the phase variation direction of fringe patterns is parallel to the baseline, which is analyzed in the systems based on both triangulation and stereovision principles. An efficient method is proposed to achieve the most sensitivity by projecting a set of fringe patterns of different phase variation directions. Experimental results demonstrate our analysis and the proposed determination method.

Keywords (OCIS):

  • (100.5070) Image processing : Phase retrieval
  • (120.0120) Instrumentation, measurement, and metrology : Instrumentation, measurement, and metrology
  • (120.2650) Instrumentation, measurement, and metrology : Fringe analysis

Advanced birefringence measurements in standard terahertz time-domain spectroscopy

  • Michael Pfleger, Harald Pühringer, Karin Wiesauer, Hubert Grün, Stefan Katletz, and Heinz Roitner
  • received 03/17/2014; accepted 04/06/2014; posted 04/17/2014; Doc. ID 208439
  • [full text: PDF (563) KB)]
  • Abstract: Polarization-sensitive (PS) terahertz (THz) technology can be used for investigating anisotropic materials that are opaque for visible light. A full characterization of an anisotropic material requires the extraction of the birefringence as well as the orientation of the optical axis from the measurement data. We present an approach based on THz time-domain spectroscopy (TDS) that exploits the spectral content of the THz signal for determining these two parameters from only two measurements. In contrast to an earlier approach with a more sophisticated PS-THz system and quasi-circularly polarized THz radiation, now a simple standard THz-TDS system can be employed. After a description of the mathematical model for data analysis we demonstrate the applicability of our method for a lithium niobate crystal and furthermore for a glass-fiber reinforced polymer sample, for which the orientation of the optical axis and birefringence are obtained in a spatially resolved way, showing the potential of the method also for PS-THz imaging. As no specialized setup or components are required, our approach can be easily and extensively applied for the analysis of anisotropic samples at THz frequencies.

Keywords (OCIS):

  • (160.4760) Materials : Optical properties
  • (160.5470) Materials : Polymers
  • (260.1440) Physical optics : Birefringence
  • (260.5430) Physical optics : Polarization
  • (300.6495) Spectroscopy : Spectroscopy, teraherz
  • (110.6795) Imaging systems : Terahertz imaging

Fabrication and Characterization of a Deep Ultraviolet Wire Grid Polarizer with a Chromium Oxide Sub-Wavelength Grating

  • Kosuke Asano, Satoshi Yokoyama, Atsushi Kemmochi, and Toyohiko Yatagai
  • received 12/05/2013; accepted 04/04/2014; posted 04/07/2014; Doc. ID 202477
  • [full text: PDF (954) KB)]
  • Abstract: A wire grid polarizer comprised of chromium oxide is designed for a micro-lithography system using an ArF excimer laser. Optical properties for some material candidates were calculated using a rigorous coupled-wave analysis (RCWA). The chromium oxide wire grid polarizer with a 90-nm period was fabricated by a double patterning technique using KrF lithography and dry etching. The extinction ratio of the grating was greater than 20 dB (100:1) at a wavelength of 193 nm. Differences between the calculated and experimental results are discussed.

Keywords (OCIS):

  • (050.2770) Diffraction and gratings : Gratings
  • (230.5440) Optical devices : Polarization-selective devices
  • (260.5430) Physical optics : Polarization
  • (220.4241) Optical design and fabrication : Nanostructure fabrication
  • (050.6624) Diffraction and gratings : Subwavelength structures

Mode-locked fiber lasers based on doped fiber arrays

  • Xiao Zhang and Yanrong Song
  • received 12/18/2013; accepted 04/04/2014; posted 04/07/2014; Doc. ID 202894
  • [full text: PDF (607) KB)]
  • Abstract: We design a new kind of fiber arrays, which central core is doped. A theoretical model is given of the all-fiber self-starting mode-locked laser based on this kind of doped fiber arrays. Two different kinds of all-fiber lasers with negative dispersion and positive dispersion are discussed in the simulation. The stable passive mode-locked pulses are generated from noise initial condition by the realistic parameters. The process of self-starting mode-locking, multi-pulsing transition and the relationship between the energies of the central core and the distance are discussed. Then we study difference between the averaged mode-locked laser and the discrete mode-locked laser.

Keywords (OCIS):

  • (140.4050) Lasers and laser optics : Mode-locked lasers
  • (140.7090) Lasers and laser optics : Ultrafast lasers

The Role of Dynamic Effects in the Characterization of Multilayers by Means of the Power Spectral Density

  • Anton Haase, Victor Soltwisch, Christian Laubis, and Frank Scholze
  • received 01/06/2014; accepted 04/04/2014; posted 04/08/2014; Doc. ID 203389
  • [full text: PDF (514) KB)]
  • Abstract: In this paper, we present measurements of angle and wavelength resolved diffuse scattering of EUV light on a Mo/Si multilayer. Our sample is optimized for high reflectivity at 13.5 nm wavelength near-normal incidence. We present a rigorous theoretical analysis of the off-specular EUV scattering on the basis of the distorted-wave Born approximation. We prove that the determination of the interface roughness power spectral density is only possible considering geometry-dependent and dynamic contributions. The scattering from multilayer mirrors leads to an intrinsic enhancement in off-specular intensity independent of roughness properties. The thickness oscillations in the scattering intensity (Kiessig fringes) are found to cause additional dynamic enhancement in analogy to Bragg-like peaks for grazing incidence geometry. Considering these effects, the interface power spectral density is consistently determined.

Keywords (OCIS):

  • (290.5820) Scattering : Scattering measurements
  • (290.5880) Scattering : Scattering, rough surfaces
  • (340.7470) X-ray optics : X-ray mirrors
  • (340.7480) X-ray optics : X-rays, soft x-rays, extreme ultraviolet (EUV)
  • (290.2648) Scattering : Stray light

Thermal-dynamical analysis of blister formation in chirped mirror irradiated by single femtosecond lasers

  • Shunli Chen, Pengpeng Gao, Yuanan Zhao, Yanzhi Wang, Zhou Fang, Yuxin Leng, and Jianda Shao
  • received 12/23/2013; accepted 04/04/2014; posted 04/08/2014; Doc. ID 203574
  • [full text: PDF (1478) KB)]
  • Abstract: Laser-induced damage behaviors of the chirped mirrors (CMs) are studied by single 800nm-38fs lasers. The CMs provide group delay dispersion (GDD) of around -60fs2 and average reflectivity of about 99.4% with bandwidth range of 200nm~300nm at a central wavelength of 800nm. Interestingly, a circular blister feature appears in the CMs at a wide range of laser fluence. Optical Microscope, Atomic Force Microscope, Scanning Electron Microscope and Surface Profiler, are applied to describe the blister characteristics. An adiabatic expansion model of ideal gas is adopted to illustrate the formation dynamics of blisters. The evolution of blisters can be explained by partial evaporation of the film and a subsequent gas expansion, driving the bulging of the film stack up to the stress limit, where the blister fractures. According to this model, the energy absorption ratio of blisters increases monotonously with increasing laser fluence before the occurrence of focal spot confinement effect.

Keywords (OCIS):

  • (140.3330) Lasers and laser optics : Laser damage
  • (310.1620) Thin films : Interference coatings
  • (320.2250) Ultrafast optics : Femtosecond phenomena

Encrypted imaging based on algebraic implementation of double random phase encoding

  • Kazuya Nakano, Masafumi Takeda, Hiroyuki Suzuki, and Masahiro Yamaguchi
  • received 01/09/2014; accepted 04/04/2014; posted 04/08/2014; Doc. ID 204270
  • [full text: PDF (1419) KB)]
  • Abstract: The security of important information captured by sensors and cameras is currently a growing concern as information theft via techniques such as side channel attacks become increasingly more prevalent. Double random phase encoding (DRPE) is an optical encryption method based on optical Fourier transform that is currently being used to implement secure coherent optical systems. In this paper, we propose a new DRPE implementation for incoherent optical systems based on integral photography that can be applied to “encrypted imaging (EI)” to optically encrypt an image before it is captured by an image sensor. Because the proposed incoherent DRPE is constituted from conventional DRPE by rewriting the optical encryption via discretization and Euler’s formula, its security level is the same as that of conventional DRPE. The results of an experiment in which we encrypted a plaintext image optically and then decrypted it numerically demonstrate that our proposed incoherent optical security system is feasible.

Keywords (OCIS):

  • (070.4560) Fourier optics and signal processing : Data processing by optical means
  • (110.1758) Imaging systems : Computational imaging
  • (060.4785) Fiber optics and optical communications : Optical security and encryption

Bistability and all-optical flip-flop with active microring-resonator

  • Qiliang Li, Hongliang Yuan, and Xianghong Tang
  • received 02/27/2014; accepted 04/04/2014; posted 04/08/2014; Doc. ID 207331
  • [full text: PDF (713) KB)]
  • Abstract: In this paper, we study the bistability of an active nonlinear microring resonator and design the flip-flop based on the active micro-ring resonator. In the presence of nonlinear loss and linear loss, we use the erbium-doped gain medium in micro-ring to obtain gain to compensate the loss of the resonator. Both analytical and numerical methods are used to solve the propagation in the microring with double couplers, and we obtain the hysteresis loops of the microring. These results obtained by two methods all reveal that in the presence of nonlinearity in micro-ring resonators, the system exhibits the bistability, and the gain in microring leads to a decrease of the bias power when the active microring is taken as a bistable switcher. Basing on the bistability of the microring, we realize the set-reset flip-flop through adding a positive or negative feedback onto the bias. We also find that the duration of the set and reset pulses must exceed the field build up time of microring if we want to achieve the switching of the bias signal. In our design the duration time is about 2 ps.

Keywords (OCIS):

  • (190.0190) Nonlinear optics : Nonlinear optics
  • (190.1450) Nonlinear optics : Bistability
  • (190.3270) Nonlinear optics : Kerr effect
  • (230.1150) Optical devices : All-optical devices
  • (230.3990) Optical devices : Micro-optical devices

Corrective finishing of EUV photomask blanks by precessed bonnet polisher

  • Anthony Beaucamp, Yoshiharu Namba, and Phillip Charlton
  • received 03/04/2014; accepted 04/04/2014; posted 04/08/2014; Doc. ID 207559
  • [full text: PDF (1371) KB)]
  • Abstract: The progressive transition from Excimer to EUV lithography is driving a need for flatter and smoother photomask blanks. It is however proving difficult to meet the next generation specification with the conventional chemical mechanical polishing technology commonly used for finishing photomask blanks. This paper reports on the application of sub-aperture CNC precessed bonnet polishing technology to the corrective finishing of photomask substrates for EUV lithography. Full-factorial analysis was used to identify process parameters capable of delivering micro-roughness below 0.5 nm rms, whilst retaining relatively high removal rates. Experimental results show that masks pre-polished to 300~600 nm P-V flatness by CMP can then be improved down to 50~100 nm P-V flatness using the automated technology described in this paper. A series of edge polishing experiments also hints at the possibility of increasing the quality area beyond the 142 mm square defined in the official EUV photomask specification.

Keywords (OCIS):

  • (220.3740) Optical design and fabrication : Lithography
  • (220.5450) Optical design and fabrication : Polishing
  • (340.7480) X-ray optics : X-rays, soft x-rays, extreme ultraviolet (EUV)

Integral image rendering procedure for aberration correction and size measurement

  • Holger Sommer, Melanie Ebenau, Dirk Flühs, Marion Eichmann, Andreas Ihrig, and Bernhard Spaan
  • received 02/12/2014; accepted 04/04/2014; posted 04/08/2014; Doc. ID 205779
  • [full text: PDF (2639) KB)]
  • Abstract: The challenge in rendering integral images is to use as much information preserved by the lightfield as possible to reconstruct a captured scene in a three-dimensional way. We propose a three-dimensional rendering algorithm based on the projection of rays through a detailed simulation of the optical path, considering all the physical properties and locations of the optical elements. The rendered images contain information about the correct size of imaged objects without the need to calibrate the imaging device. Additionally, aberrations of the optical system may be corrected, depending on the setup of the integral imaging device. We show simulation data that illustrates the aberration correction ability and experimental data from our plenoptic camera, which illustrates the capability of our proposed algorithm to measure size and distance. We believe this rendering procedure will be useful in the future for three-dimensional ophthalmic imaging of the human retina.

Keywords (OCIS):

  • (040.1240) Detectors : Arrays
  • (100.2000) Image processing : Digital image processing
  • (100.6890) Image processing : Three-dimensional image processing
  • (150.6910) Machine vision : Three-dimensional sensing
  • (230.0230) Optical devices : Optical devices
  • (330.4460) Vision, color, and visual optics : Ophthalmic optics and devices

Simultaneous measurement of phase and local orientation of linearly polarized light: implementation and measurement results

  • Sergej Rothau, Christine Kellermann, Vanusch Nercissian, Andreas Berger, Klaus Mantel, and Norbert Lindlein
  • received 01/31/2014; accepted 04/04/2014; posted 04/08/2014; Doc. ID 205784
  • [full text: PDF (10091) KB)]
  • Abstract: Optical components manipulating both polarization and phase of wave fields find many applications in todays optical systems. With modern lithography methods it is possible to fabricate optical elements with nanostructured surfaces from dierent materials capable of generating spatially varying, locally linearly polarized light distributions, tailored to the application in question. Since such elements in general also aect the phase of the light field, the characterization of the function of such elements consists in measuring the phase and the polarization of the generated light, preferably at the same time. Here we will present first results of an interferometric approach for a simultaneous and spatially resolved measurement of both phase and polarization, as long as the local polarization at any point is linear (like e.g. for radially or azimuthally polarized light).

Keywords (OCIS):

  • (120.3180) Instrumentation, measurement, and metrology : Interferometry
  • (120.5050) Instrumentation, measurement, and metrology : Phase measurement
  • (160.1190) Materials : Anisotropic optical materials
  • (260.5430) Physical optics : Polarization

Observation of the waveguide resonance in a periodically patterned high refractive index broadband antireflection coating

  • O. Stenzel, S. Wilbrandt, X. Chen, R. Schlegel, L. Coriand, A. Duparré, U. Zeitner, T. Benkenstein, and C. Wächter
  • received 02/03/2014; accepted 04/04/2014; posted 04/08/2014; Doc. ID 205843
  • [full text: PDF (1759) KB)]
  • Abstract: Grating waveguide structures have been prepared by deposition of a high refractive index broadband antireflection coating onto a patterned fused silica substrate. Aluminum and hafnium oxide have been used as coating materials. Optical reflection measurements combined with atomic force microscopy have been used to characterize the structures. Upon illumination with a TE wave, the best structure shows a narrow reflection peak located at 633 nm at an incidence angle of about 17°. The nominal peak reflectance of that sample accounts to more than 90%. Off-resonance interference structures appear strongly suppressed in the spectrum between 450 nm and 800 nm because of the characteristics of the designed antireflection layer. The structure thus possesses a notch filter spectral characteristic in a broad spectral range.

Keywords (OCIS):

  • (050.1950) Diffraction and gratings : Diffraction gratings
  • (310.1210) Thin films : Antireflection coatings
  • (310.2785) Thin films : Guided wave applications
  • (310.6188) Thin films : Spectral properties
  • (310.6628) Thin films : Subwavelength structures, nanostructures

Comparative analysis on viewing angle change in Fresnel and Fourier holographic images reconstructed by tilted plane wave

  • Byung Gyu Chae
  • received 02/18/2014; accepted 04/04/2014; posted 04/08/2014; Doc. ID 206628
  • [full text: PDF (1208) KB)]
  • Abstract: We carry out the comparative analysis on the viewing angle change in the Fresnel and Fourier holographic images reconstructed by a tilted plane wave. The tilted plane wave illuminating to the on-axis hologram generates the diffractive wave carrying the holographic image with a new viewing zone. The reconstructed image in the Fresnel hologram is deformed along a new viewing direction, which is well described as Affine transformation. In the Fourier holographic image, the replica of the image is formed without its deformation when the hologram is placed in the front focal plane of the lens, whereas in case of the hologram located at a distance different from the focal length, it enables to retrieve the three-dimensional image with other perspective. This property is verified through the numerical simulation based on the Fresnel propagation between tilted planes. We discuss the possibility of varying the viewing angle in high-order diffraction images appeared in the sampled Fourier hologram with pixel structure.

Keywords (OCIS):

  • (090.1970) Holography : Diffractive optics
  • (090.2870) Holography : Holographic display
  • (090.1995) Holography : Digital holography

Analytical description of interference between two misaligned and mismatched complete Gaussian beams

  • Gudrun Wanner and Gerhard Heinzel
  • received 02/27/2014; accepted 04/03/2014; posted 04/08/2014; Doc. ID 207293
  • [full text: PDF (440) KB)]
  • Abstract: A typical application for laser interferometers is a precision measurement of length changes that result in interferometric phase shifts. Such phase changes are typically predicted numerically, due to the complexity of the overlap integral that needs to be solved. In this paper we will derive analytical representations of the interferometric phase and contrast (aka. fringe visibility) for two beam interferometers, both homodyne and heterodyne. The fundamental Gaussian beams can be arbitrarily misaligned and mismatched to each other. A limitation of the analytical result is that both beams must be detected completely, which can experimentally be realized by a sufficiently large single-element photodetector.

Keywords (OCIS):

  • (000.3860) General : Mathematical methods in physics
  • (120.3180) Instrumentation, measurement, and metrology : Interferometry
  • (200.1130) Optics in computing : Algebraic optical processing

Standoff two-color quantum ghost imaging through turbulence

  • Yu-Lang Xue, Ren-Gang Wan, Fei Feng, and Tong-Yi Zhang
  • received 01/28/2014; accepted 04/03/2014; posted 04/08/2014; Doc. ID 205429
  • [full text: PDF (1704) KB)]
  • Abstract: Recently, a two-color quantum ghost imaging configuration appropriate for standoff sensing was proposed [S. Karmakar et al., Phys. Rev. A 81, 033845 (2010)]. In practice, the signal beam must propagate through atmosphere in the presence of serious turbulence. We analyzed theoretically the performance of this ghost imaging configuration through turbulence. Based on the Gaussian state source model and extended Huygens-Fresnel integral, a formula is derived to depict the ghost image formed through turbulence of a standoff reflective object. Numerical calculations are also given according to the formula. The results show that the image quality will be degraded by the turbulence. But the resolution can be improved by means of optimizing the wavelength of the reference and signal beams even when the turbulence is very serious.

Keywords (OCIS):

  • (100.2960) Image processing : Image analysis
  • (280.3640) Remote sensing and sensors : Lidar
  • (110.0115) Imaging systems : Imaging through turbulent media

Performance of line-scan Raman microscopy (LSRM) for high-throughput chemical imaging of cell population

  • Ji Qi and Wei-Chuan Shih
  • received 12/24/2013; accepted 04/03/2014; posted 04/03/2014; Doc. ID 203683
  • [full text: PDF (2974) KB)]
  • Abstract: We evaluate the performance of line-scan Raman microscopy (LSRM), a versatile label-free technique, for high-throughput chemical imaging of cell population. We provide detailed design and configuration of a home-built LSRM system developed in our laboratory. By exploiting parallel acquisition, the LSRM system achieves significant throughput advantage over conventional point-scan Raman microscopy by projecting a laser line onto the sample and imaging the Raman scattered light from the entire line using a grating spectrograph and a charge-coupled device (CCD) camera. Two-dimensional chemical maps can be generated by scanning the projected line in the transverse direction. The resolution in the x- and y-direction has been characterized to be ~600-800 nm for 785 nm laser excitation. Our system enables rapid classification of microparticles with similar shape, size and refractive index based on their chemical composition. An equivalent imaging throughput of 100 microparticles/sec for 1 μm polystyrene beads has been achieved. We demonstrate the application of LSRM to imaging bacterial spores by identifying endogenous calcium dipicolinate. We also demonstrate that LSRM enables the study of intact microalgal cells at the colonial level and the identification of intra and extracellular chemical constituents and metabolites such as chlorophyll, carotenoids, lipids, and hydrocarbons. We conclude that LSRM can be an effective and practical tool for obtaining endogenous microscopic chemical and molecular information from cell population.

Keywords (OCIS):

  • (110.0180) Imaging systems : Microscopy
  • (300.6450) Spectroscopy : Spectroscopy, Raman
  • (110.4234) Imaging systems : Multispectral and hyperspectral imaging

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