Perturbed Talbot patterns for the measurement of low particle concentrations in fluids

• Meike Hofmann, Ronald Kampmann, and Stefan Sinzinger
• received 11/02/2011; accepted 02/02/2012; posted 02/02/2012; Doc. ID 153002
• [full text: PDF (1676) KB)]
• Abstract: Behind periodic amplitude or phase objects the object transmittance is repeated at the so called Talbot distances. In these planes perpendicular to the propagation direction Talbot self-images are formed. In the case of plane wave illumination the distances between the self-images are equally spaced and a periodic pattern called optical carpet or Talbot carpet is formed along propagation direction. We show theoretically how the presence of spherical particles (10 to 100 µm in diameter) behind the grating affects the formation of Talbot carpets as well as of Talbot self-images. The scattering of the particles is modeled by the Fresnel diffraction of its geometrical shadow. We analytically calculate the interference of the particle disturbed diffraction orders of rectangular and sinusoidal amplitude gratings. To verify our model we present measurements of Talbot carpets pertubed with both opaque disks and transparent spheres and discuss the effects for different size parameters. We present an approach to simulate a real time movement of particles within the Talbot pattern. We simulate and measure axial and lateral particle movements within a probe volume and evaluate the effect on the signal formation in a Talbot interferometric set-up. We evaluate the best system parameters in terms of grating period and particle-detector-distance for a prospective measuring set-up to determine characteristics of flowing suspensions such as particle volume concentration or particle size distribution.

Keywords (OCIS):

• (050.1940) Diffraction and gratings : Diffraction
• (110.6760) Imaging systems : Talbot and self-imaging effects
• (120.3180) Instrumentation, measurement, and metrology : Interferometry
• (290.2558) Scattering : Forward scattering
• (280.4788) Remote sensing and sensors : Optical sensing and sensors

(CO) WAVELET ANALYSIS OF FOURIER POLARIZED IMAGES OF THE HUMAN BILE

• Yuriy Ushenko, Olexander Dubolazov, Artem Karachevtsev, Mykhaylo Gorsky, and Yuriy Marchuk
• received 12/12/2011; accepted 02/02/2012; posted 02/02/2012; Doc. ID 159308
• [full text: PDF (457) KB)]
• Abstract: A model of generalized optical anisotropy of human bile is suggested and a method of polarimetric of the module and phase Fourier of the image of the field of laser radiation is analytically substantiated, that is generated by the mechanisms of linear and circular birefringence of polycrystalline networks with a wavelet-diagnosis and differentiation of cholelithiasis against a background of chronic cholecystitis.

Keywords (OCIS):

• (030.0030) Coherence and statistical optics : Coherence and statistical optics
• (070.0070) Fourier optics and signal processing : Fourier optics and signal processing

Modeling of end-pumped Yb:YAG thin disk lasers with non-uniform temperature distribution

• Guangzhi Zhu, Xiao Zhu, Changhong Zhu, Jianli Shang, Hailin Wan, and Fei Guo
• received 11/22/2011; accepted 02/01/2012; posted 02/02/2012; Doc. ID 158648
• [full text: PDF (1045) KB)]
• Abstract: A plane wave model with non-uniform temperature distribution in the thin disk crystal is developed to describe the dynamic behavior of end-pumped Yb:YAG thin disk laser. A set of couple rate equations and 2D stationary heat conduction equations are derived. The stable temperature distribution in the disk crystal is calculated using numerical iterative method. The analytic expressions is capable of dealing with more practical laser systems than previous works on this subject as it allows for non-uniform temperature distribution in the disk crystal. Based on these results, we examined laser output intensity as a function of pump intensity, dopant concentration, resonator coupler reflectivity, crystal thickness and temperature of cooing liquid.

Keywords (OCIS):

• (140.3430) Lasers and laser optics : Laser theory
• (140.3480) Lasers and laser optics : Lasers, diode-pumped
• (140.6810) Lasers and laser optics : Thermal effects

Influence of water environment on holmium laser ablation performance for hard tissues

• Tao Lü, Qing Xiao, Zheng Li, and Ling Fu
• received 11/21/2011; accepted 01/31/2012; posted 01/31/2012; Doc. ID 158524
• [full text: PDF (2481) KB)]
• Abstract: The objective of this study is to clarify the ablation difference for hard biological tissues in air and in water, which are irradiated by fiber-guided long pulsed holmium lasers. High-speed photography is used to record the dynamic characteristics of ablation plumes and vaporization bubbles induced by IR long pulsed lasers. The ablation morphologies and depths of hard tissues are quantitatively measured by using optical coherence microscopy. Multi-times of explosive vaporization effect happening in water play a positive role in contact ablation process, which are directly responsible for significant ablation enhancement. Furthermore, the deeper water layer can also contribute to ablation performance. Under the same laser parameters, for fiber-tissue contact ablation in air and in water, ablation performances are comparable for a single laser pulse, but for more laser pulses the ablation performance in water is better than that in air. Comprehensive knowledge of ablation difference under various environments is important, especially in some medical procedures which are performed in a liquid environment.

Keywords (OCIS):

• (140.3070) Lasers and laser optics : Infrared and far-infrared lasers
• (170.1020) Medical optics and biotechnology : Ablation of tissue
• (170.4580) Medical optics and biotechnology : Optical diagnostics for medicine

(CO) Limitations of adaptive control efficiency due to singular points in the wave-front of a laser beam

• Vladimir Lukin
• received 12/13/2011; accepted 01/31/2012; posted 01/31/2012; Doc. ID 159897
• [full text: PDF (331) KB)]
• Abstract: The optical vortices occur at light propagation in the inhomogeneous medium, disturbing the op-eration of adaptive optical systems assuring a priori continuity of the phase fluctuation function. The occurrence of vortices is also undesirable at light propagation in optical fibers, because in this case a noise modulation of light occur. Nevertheless the opportunity of the using of optical vortices arise and disappear not one by one, but in pairs, where they have opposite screws. The appearance of zeros indicates the transition of phenomenon in a new condition. It is clear that the physical process of the light wave propagation has a threshold of complexity relative to the description and measurement of this process, after which the light wave contains points with zero intensity and there is no continuos wave front. The results of the analysis show that an essential component of the estimation of the efficiency of operation of adaptive optical systems using phase conjugation to correct atmospheric distortions is a knowledge of the peculiarities of the statistics of the phase fluctuations of optical waves being corrected. In fact, the analysis of the efficiency of operation of adaptive optical systems and of the corresponding correction algorithms together with the ongoing development of the basic compo-nents of optical amplitude-phase meters and controllable adaptive mirror elements have formed a new field of scientific endeavor - the study of the propagation of optical waves in the atmosphere under conditions of adaptive control. The results of numerous studies of phase fluctuations of optical waves in the atmosphere provide a basis, first of all, for estimating the efficiency of operation of adaptive optical systems and, sec-ondly, make it possible to determine the requirements on the wavefront sensors and adaptive mir-rors, and finally, to determine the structure and properties of phase-conjugated adaptive optical systems.

Keywords (OCIS):

• (010.1300) Atmospheric and oceanic optics : Atmospheric propagation
• (010.1330) Atmospheric and oceanic optics : Atmospheric turbulence
• (030.7060) Coherence and statistical optics : Turbulence

Segment side-pumped Q-switched Nd:YAG laser

• Wei Wang, Chen Fu, Zhengyue Hu, Qin Zhao, and Mali Gong
• received 10/17/2011; accepted 01/31/2012; posted 01/31/2012; Doc. ID 156240
• [full text: PDF (2077) KB)]
• Abstract: Side-pumped configuration design of lasers focuses on how to solve the space conflict between pump and heat-removal device due to the demands for larger lateral surface of a laser rod. The conflict can be balanced better by a segment side-pumped geometry in a periodical arrangement between circular LD arrays and holders. This design has great potential to be used in compact and miniature laser systems. Design optimization and simulation on thermal affects have been performed. A segment side-pumped Q-switched Nd:YAG laser has been demonstrated and the experiment carried out. A maximum pulse out of 190mJ (recorded by an EPM2000 energy detector with frosted glass) was obtained at the pump pulse energy of 823mJ, the corresponding optical-optical conversion efficiency (calculated by 190mJ) of 23.1%, and the pulse width of 10.4ns.

Keywords (OCIS):

• (140.3480) Lasers and laser optics : Lasers, diode-pumped
• (140.3540) Lasers and laser optics : Lasers, Q-switched

Nd:Li6Y(BO3)3 crystal waveguide properties at wavelengths of 633 and 1539 nm produced by oxygen or silicon ion implantation

• Peng Liu, Qing Huang, Tao Liu, Sha-Sha Guo, Lian Zhang, and Xue-Lin Wang
• received 11/21/2011; accepted 01/30/2012; posted 01/31/2012; Doc. ID 158574
• [full text: PDF (1597) KB)]
• Abstract: In this work, we report on waveguide formation in Nd:Li6Y(BO3)3 laser crystal by O- or Si-ion implantation, respectively, and Nd:Li6Y(BO3)3 waveguide can support effectively fundamental mode in visible and near-infrared telecommunication band. Compared with Si-ion, the waveguide produced by O-ion has a larger effective refractive index of fundamental mode and lower propagation loss, which shows that peak position of implanted ion nuclear energy loss has a significant impact on waveguide features. The research of photoluminescence and Raman spectra demonstrates that Nd3+ luminescence feature and crystal structure of waveguide active region don’t change obviously and gain good preservation after ion implantation.

Keywords (OCIS):

• (160.3380) Materials : Laser materials
• (230.7390) Optical devices : Waveguides, planar
• (300.2530) Spectroscopy : Fluorescence, laser-induced

S-band Multi-Wavelength Ring Brillouin/Raman Fiber Laser with 20 GHz Channels Spacing

• Harith Ahmad, Mohd Zulkifli, Noor Hassan, and Sulaiman Harun
• received 10/03/2011; accepted 01/28/2012; posted 01/31/2012; Doc. ID 155619
• [full text: PDF (2043) KB)]
• Abstract: In this paper, we propose and demonstrate a tunable S-band Multiwavelength Brillouin–Raman Fiber Laser (MBRFL) with a tuning range of between 1490 to 1530 nm. The proposed MBRFL is designed around a 7.7 km long Dispersion Compensating Fiber in a simple ring configuration, acting as a non-linear medium for the generation of multiple wavelengths from Stimulated Brillouin Scattering (SBS) and also as a non-linear gain medium for Stimulated Raman Scattering (SRS) amplification. A laser source, with a maximum power of 12 dBm acts as the Brillouin Pump (BP), whilst two 1420nm laser diodes with a total power of 371 mW act as the Raman Pumps (RPs). The MBRFL can generate a multiwavelength comb consisting of Even and Odd Stokes at an average power of -12 dBm and – 14 dBm respectively, and by separating the Even and Odd Stokes outputs, a 20 GHz channel spacing is obtained between two consecutive wavelengths. Due to the Four-Wave-Mixing (FWM) effect, Anti-Stokes lines are also observed. The multiwavelength comb generated is not dependent on the BP, thus providing high stability and repeatability and making it a highly potential source for many real-world applications. This is the first time, to the knowledge of the authors, that a tunable MBRFL has been developed using to SRS to obtain gain in the S-band region.

Keywords (OCIS):

• (060.2380) Fiber optics and optical communications : Fiber optics sources and detectors
• (060.4370) Fiber optics and optical communications : Nonlinear optics, fibers

Visible and infrared optical properties of stacked cone graphitic microtubes

• Charles Bruce and Sharhabeel Alyones
• received 11/30/2011; accepted 01/27/2012; posted 01/27/2012; Doc. ID 159072
• [full text: PDF (806) KB)]
• Abstract: The absorptive and scattering optical properties of heat treated, vapor grown graphite microtubes consisting of nanotubes in a "stacked cone” configuration were investigated through the visible and infrared wavelengths using photoacoustical and other spectrometric techniques. However, computations of these properties involved uncertainties that were not easily resolved; the appropriate dielectric coefficients were presumed to be a combination of the published values for the distinct orientations of graphite but the correct proportions are not evident and none of the reasonable choices produced satisfactory agreement (within the measurement limits of error). Since both of the primary components of the extinction were measured, the appropriate computational codes were employed in reverse to compute the dielectric coefficients for the graphite microtubes. Differences, primarily for the imaginary index, are most distinct for visible and near infrared wavelengths; in this wavelength region the imaginary index falls progressively to less than half that for the computed mixture.

Keywords (OCIS):

• (300.6340) Spectroscopy : Spectroscopy, infrared
• (300.6550) Spectroscopy : Spectroscopy, visible

In-plane effects on segmented mirror control

• Douglas MacMynowski, Lewis Roberts, J. Shelton, Gary Chanan, and Henri Bonnet
• received 12/14/2011; accepted 01/27/2012; posted 01/27/2012; Doc. ID 159097
• [full text: PDF (1372) KB)]
• Abstract: Extremely large optical telescopes are being designed with primary mirrors composed of hundreds of segments. The “out-of-plane” piston, tip and tilt degrees of freedom of each segment are actively controlled using feedback from relative height measurements between neighboring segments. The “in-plane” segment translations and clocking (rotation) are not actively controlled; however, in-plane motions affect the active control problem in several ways, and thus need to be considered. We extend earlier analyses by constructing the “full” interaction matrix that relates the height, gap, and shear motion at sensor locations to all six degrees of freedom of segment motion, and use this to consider three effects. First, in-plane segment clocking results in height discontinuities between neighboring segments that can lead to a global control system response. Second, knowledge of the in-plane motion is required both to compensate for this effect and to compensate for sensor installation errors, and thus we next consider the estimation of in-plane motion and the associated noise propagation characteristics. In-plane motion can be accurately estimated using measurements of the gap between segments, but with one unobservable mode in which every segment clocks by an equal amount. Finally, we examine whether in-plane measurements (gap and/or shear) can be used to estimate out-of-plane segment motion; this is relevant for controlling the “focus-mode” of the segmented mirror array, which involves pure dihedral angle changes between segments and is not observable with only height measurements.

Keywords (OCIS):

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

Spectral optimized asymmetric segmented phase-only correlation filter

• Isabelle Léonard, Ayman Alfalou, and Christian Brosseau
• received 09/26/2011; accepted 01/27/2012; posted 02/02/2012; Doc. ID 155301
• [full text: PDF (2858) KB)]
• Abstract: We suggest a new type of optimized composite filter, i.e. the asymmetric segmented phase-only filter (ASPOF), for improving the effectiveness of a VanderLugt correlator (VLC) when used for face identification. Basically, it consists in merging several reference images after application of a specific spectral optimization method. After segmentation of the spectral filter plane to several areas, each area is assigned to a single winner reference according to a new optimized criterion. The point of the paper is to show that this method offers a significant performance improvement on standard composite filters for face identification. We first briefly revisit composite filters (adapted, phase-only, inverse, compromise optimal, segmented, minimum average correlation energy, optimal trade-off maximum average correlation, and amplitude modulated phase-only) which are tools of choice for face recognition based on correlation techniques and scrutinize their correlation performance which has not yet been discussed. We illustrate some of the drawbacks of current filters for several binary and gray scale images identifications. Next, we describe the optimization steps and introduce the ASPOF that can overcome these technical issues to improve the quality and the reliability of the correlation based decision. We derive performance measures, i.e. peak-to-correlation energy values and receiver operating characteristic curves, to confirm consistency of the results. We numerically find that this filter increases the recognition rate and decrease the false alarm rate. In addition, the ASPOF is robust against rotation and various types of noise sources. Our method has several features that make it amenable to experimental implementation using a VLC.

Keywords (OCIS):

• (100.5010) Image processing : Pattern recognition
• (100.3008) Image processing : Image recognition, algorithms and filters

Tungsten wire grid polarizer for applications in the DUV spectral range

• Thomas Weber, Thomas Käsebier, Michael Helgert, Ernst-Bernhard Kley, and Andreas Tünnermann
• received 01/23/2012; accepted 01/26/2012; posted 01/31/2012; Doc. ID 162020
• [full text: PDF (421) KB)]
• Abstract: In this paper, we present a broadband wire grid polarizer with a spectral working range down to a wavelength of 193 nm. Tungsten is chosen as grating material because it provides a high extinction ratio and transmission compared with other common grating materials. The fabrication of the grating with 100 nm period was accomplished using a spatial frequency doubling approach based on ultra fast electron beam lithography and a sophisticated deposition technique. At a wavelength of 193 nm a transmission of about 44% and an extinction ratio of 20 was measured.

Keywords (OCIS):

• (050.2770) Diffraction and gratings : Gratings
• (230.5440) Optical devices : Polarization-selective devices
• (220.4241) Optical design and fabrication : Nanostructure fabrication

Generation of doubly charged vortex beam by concentrated loading of glass disks along their diameter

• Ihor Skab, Yuriy Vasylkiv, Oleh Krupych, Viktoriya Savaryn, and Rostyslav Vlokh
• received 01/03/2012; accepted 01/26/2012; posted 02/02/2012; Doc. ID 160564
• [full text: PDF (626) KB)]
• Abstract: We show that a system of glass disks compressed along their diameters enables one to induce a doubly charged vortex beam in the emergent light when the incident light is circularly polarized. Using such a disk system, one can control the efficiency of conversion of the spin angular momentum to the orbital angular momentum by a loading force. The consideration presented here can be extended for the case of crys-talline materials with high optical damage thresholds, in order to induce high-power vortex beams.

Keywords (OCIS):

• (260.1180) Physical optics : Crystal optics
• (260.1440) Physical optics : Birefringence
• (260.6042) Physical optics : Singular optics
• (260.2710) Physical optics : Inhomogeneous optical media

Thermo-optic coefficients study in KGd(WO4)2 and KY(WO4)2 by a modified minimum deviation method

• Pavel Loiko, Valery Filippov, Konstantin Yumashev, Nikolai Kuleshov, and Anatoly Pavlyuk
• received 12/05/2011; accepted 01/26/2012; posted 01/27/2012; Doc. ID 159350
• [full text: PDF (1100) KB)]
• Abstract: Thermo-optic coefficients anisotropy was characterized in monoclinic potassium (rare-earth) double tungstates KGd(WO4)2 and KY(WO4)2 in the spectral range of 0.44–0.63 μm by a modified minimum deviation method. This approach takes into account the changes in the shape and dimensions of the prismatic sample caused by anisotropic thermal expansion effect under uniform heating together with the conventional measurements of minimum deviation angle. At room temperature at the wavelength of 633 nm, principal refractive indices for KGdW are np=2.0135, nm=2.0458, ng=2.0860 and for KYW they are np=1.9979, nm=2.0396, ng=2.0869. Opt-ical axes position for KGdW (KYW) crystals is Ng±42.6° (Ng±44.1°) in the Np-Ng plane. For both crystals, all the thermo-optic coefficients are negative and equal dnp/dT = –10.6, dnm/dT = –8.4, dng/dT = –15.2 for KGdW; dnp/dT = –10.1, dnm/dT = –7.3, dng/dT = –8.4 for KYW [10-6 K-1] (at 633 nm).

Keywords (OCIS):

• (140.6810) Lasers and laser optics : Thermal effects
• (160.1190) Materials : Anisotropic optical materials
• (160.4760) Materials : Optical properties
• (260.1180) Physical optics : Crystal optics

(LIBS)Comparative Study of Nd:YAG Laser-Induced Breakdown Spectroscopy (LIBS) and Transversely Excited Atmospheric CO2 Laser-Induced Gas Plasma Spectroscopy on CCA Preservative-Treated Wood

• Ali khumaeni, Zener Sukra Lie, Hideaki Niki, Yong Lee, Kazuyoshi Kurihara, Motoomi Wakasugi, Touru Takahashi, and Kiichiro Kagawa
• received 10/05/2011; accepted 01/26/2012; posted 01/27/2012; Doc. ID 155502
• [full text: PDF (731) KB)]
• Abstract: Taking advantages of the specific characteristics of a TEA CO2 laser, a sophisticated technique for the analysis of chromated copper arsenate (CCA) in wood sample has been developed. In this study, a CCA-treated wood sample with a dimension of 20 mm x 20 mm and a thickness of 2 mm was attached in contact onto a nickel plate (20 mm x 20 mm x 0.15 mm), which functions as a subtarget. When a TEA CO2 laser was successfully irradiated onto a wood surface, a hole with a diameter of around 2.5 mm was produced inside the sample and the laser beam was directly impinged onto the metal subtarget. A strong and stable gas plasma was induced with very big diameter of around 10 mm once the laser beam had directly struck the metal subtarget. This gas plasma then interacted with the fine particles of the sample inside the hole and finally the particles were effectively dissociated and excited in the gas plasma region. By using this technique, high precision and sensitive analysis of CCA-treated wood sample was realized. A linear calibration curve of Cr was successfully made using the CCA-treated wood sample. The detection limits of Cr, Cu, and As were estimated to be about 1, 2 and 15 mg/kg. In case of standard LIBS using the Nd:YAG laser, the analytical intensities fluctuate and the detection limit was much lower of around one tenth compared to that of TEA CO2 laser.

Keywords (OCIS):

• (300.6210) Spectroscopy : Spectroscopy, atomic
• (300.6365) Spectroscopy : Spectroscopy, laser induced breakdown

(LIBS)Application of Laser induced breakdown spectroscopy for carbon quantification in soil samples

• Dustin McIntyre, Jinesh Jain, Jagdish Singh, Fang Yu-Yueh, and Krishna Ayyalasomayajula
• received 10/04/2011; accepted 01/25/2012; posted 01/27/2012; Doc. ID 155830
• [full text: PDF (554) KB)]
• Abstract: The increase of green house gas levels in the atmosphere (i.e. CO2) has caused noticeable climate change. CO2 is a dynamic molecule because it is capable of cycling between the atmosphere and vegetation and soils. It may be possible to sequester significant amounts of CO2 in soils to reduce green house gases in the atmosphere. A reliable measurement of carbon in soil samples is needed to determine the amount of carbon that can be sequestered in soils. In this study, we quantitatively determine the carbon concentration in soil by using laser induced breakdown spectroscopy. A soil sample from Starkville, MS, USA was mixed with different amounts of carbon powder which was used as a calibration for soil. A 5g soil sample was mixed with 0.4ml polyvinyl alcohol (PVA) binder and pressed into a pellet, for ease of handling. LIBS spectra of five pellet samples of different carbon concentrations were collected at various experimental parameters. The data were analyzed to obtain optimized conditions for the measurement of carbon in soil with LIBS. The carbon content in the samples was also measured by a carbon analyzer and the data were used as a reference concentration in developing the calibration curves. The calibration data were then used to determine the carbon concentration of an unknown sample.

Keywords (OCIS):

• (140.3440) Lasers and laser optics : Laser-induced breakdown
• (300.6210) Spectroscopy : Spectroscopy, atomic

(LIBS) Correlation of Limestone Beds using Laser-Induced Breakdown Spectroscopy and Chemometric Analysis

• Nancy McMillan, Carlos Montoya, and Warren Chesner
• received 10/05/2011; accepted 01/25/2012; posted 01/27/2012; Doc. ID 155835
• [full text: PDF (1799) KB)]
• Abstract: Correlation of limestone beds is commonly based on a variety of features, including the age of the bed, the fossil assemblage, internal sedimentary structures, and the relationship to other units in the stratigraphy. This study uses laser-induced breakdown spectroscopy (LIBS) to correlate sixteen limestone beds from Kansas, USA, using a matching algorithm that consists of a sequence of binary PLS-1 chemometric models (patent pending by Applied Research Associates). Each gravel-sized limestone particle was analyzed by one LIBS shot; ten spectra were averaged into a single spectrum for chemometric analysis. Half of the spectra were used to construct the model; the other half were used for test-set validation. The overall success rate for correct identification of average spectra in the test-set is 95-96%. However, 100% success can be accomplished by accepting the classification of the majority of spectra for a given bed as the correct classification. This study indicates that LIBS can be applied to complex geologic correlation problems and provide rapid, accurate results.

Keywords (OCIS):

• (160.0160) Materials : Materials
• (300.6365) Spectroscopy : Spectroscopy, laser induced breakdown

(LIBS)Determination of elemental impurities in plastic calibration standards using laser induced breakdown spectroscopy

• Krishna Ayyalasomayajula, Dustin McIntyre, Jinesh Jain, Jagdish Singh, and Fang Yu-Yueh
• received 10/03/2011; accepted 01/25/2012; posted 01/27/2012; Doc. ID 155865
• [full text: PDF (289) KB)]
• Abstract: Dual energy CT-scanning is a rapidly emerging imaging technique employed in non-destructive evaluation of various materials. Although CT (Computerized Tomography) has been used for characterizing rocks and visualizing multiphase flow through rocks for over 25 years, most of the scanning is done at a voltage setting above 100kV taking advantage of the compton scattering (CS) effect, which responds to density changes. Below 100kV the photoelectric effect (PE) is dominant which responds to the effective atomic numbers (Zeff), which is directly related to the photoelectric factor. Using the combination of the two effects provides a better characterization of reservoir rocks. The most common technique for dual energy CT-scanning relies on homogeneous calibration standards with impurities increases the probability of error in the reconstructed data and results in poor rock characterization. The work combines ICP-AES (Inductively coupled plasma atomic emission spectroscopy) and LIBS (Laser induced breakdown spectroscopy) analytical techniques to quantify the type and level of impurities in a set of commerically purchased calibration standards used in dual energy scanning for material identification within coal samples. The precision and accuracy of each technique is compared and discussed.

Keywords (OCIS):

• (140.3440) Lasers and laser optics : Laser-induced breakdown
• (300.6210) Spectroscopy : Spectroscopy, atomic

Polarization resolved classification of winter road condition in the near infrared region

• Johan Casselgren and Mikael Sjödahl
• received 01/20/2012; accepted 01/24/2012; posted 01/27/2012; Doc. ID 161851
• [full text: PDF (1470) KB)]
• Abstract: Three different configurations utilizing polarized short-wave infrared light (SWIR) to classify winter road conditions have been investigated. In the first configuration polarized broadband light was detected in the specular and backward direction, respectively, and the quotient between the detected intensities was used as the classification parameter. Best results were obtained for the SS-configuration. This sensor was shown to be able to distinguish between the smooth road conditions water and ice from the diffuse road conditions snow and dry asphalt with a probability of wrong classification as low as 7 %. The second sensor configuration considered was a pure backward architecture utilizing polarized light with two distinct wavelengths. This configuration was shown effective for the important problem of distinguishing water from ice with a probability of wrong classification of only 1.5 %. The last architecture considered was a combination of the two previous configurations. This combined sensor utilizing bi-spectral illumination and bi-directional detection results in a probability of wrong classification as low as 2 % between all four surfaces.

Keywords (OCIS):

• (280.0280) Remote sensing and sensors : Remote sensing and sensors
• (300.6340) Spectroscopy : Spectroscopy, infrared
• (310.5448) Thin films : Polarization, other optical properties
• (280.1350) Remote sensing and sensors : Backscattering
• (130.5440) Integrated optics : Polarization-selective devices

Design and fabrication of a freeform microlens array for a compact large field-of-view compound eye camera

• Lei Li and Allen Yi
• received 09/23/2011; accepted 01/24/2012; posted 01/24/2012; Doc. ID 155149
• [full text: PDF (2191) KB)]
• Abstract: In this research a unique freeform microlens array was designed and fabricated for a compact compound eye camera to achieve a large field-of-view. The microlens array in this research has a field-of-view of 48º×48º and its thickness is only 1.6 mm. The freeform microlens array resides on a flat substrate allow it to be directly mounted to a commercial 2D image sensor. Freeform surfaces were used to design the microlens profiles thus allowing the microlenses to steer and focus incident rays simultaneously. The profiles of the freeform microlenses were represented using extended polynomials and the coefficients of these polynomials were optimized with an optical design software. The freeform microlens array was then fabricated using a combination of ultraprecision diamond broaching and microinjection molding process. This approach was aimed for high replication quality and low manufacturing cost. To reduce crosstalk among neighboring channels, a micro aperture array was machined using high-speed micromilling. The molded microlens array was assembled with the micro aperture array, an adjustable fixture, and a board level image sensor to form a compact compound eye camera. The imaging tests using the compound eye camera showed that the unique freeform microlens array installed were capable of forming images as designed. The measured field-of-view of ±23.5º also matches the initial design and is considerably larger compared to most similar camera designs using conventional microlens arrays.

Keywords (OCIS):

• (220.1920) Optical design and fabrication : Diamond machining
• (230.3990) Optical devices : Micro-optical devices