| 1. |
- Arwin, Hans, 1950-, et al.
(author)
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Total internal reflection ellipsometry : principles and applications
- 2004
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In: Applied Optics. - 0003-6935 .- 1539-4522. ; 43:15, s. 3028-3036
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Journal article (peer-reviewed)abstract
- A concept for a measurement technique based on ellipsometry in conditions of total internal reflection is presented. When combined with surface plasmon resonance (SPR) effects, this technique becomes powerful for monitoring and analyzing adsorption and desorption on thin semitransparent metal films as well as for analyzing the semitransparent films themselves. We call this technique total internal reflection ellipsometry (TIRE). The theory of ellipsometry under total internal reflection combined with SPR is discussed for some simple cases. For more advanced cases and to prove the concept, simulations are performed with the Fresnel formalism. The use of TIRE is exemplified by applications in protein adsorption, corrosion monitoring, and adsorption from opaque liquids on metal surfaces. Simulations and experiments show greatly enhanced thin-film sensitivity compared with ordinary ellipsometry.
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| 2. |
- Askebjer, P., et al.
(author)
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Optical properties of deep ice at the South Pole : Absorption
- 1997
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In: Applied Optics. - : Optical Society of America. - 0003-6935 .- 1539-4522. ; 36:18, s. 4168-4180
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Journal article (peer-reviewed)abstract
- We discuss recent measurements of the wavelength-dependent absorption coefficients in deep South Pole ice. The method uses transit-time distributions of pulses from a variable-frequency laser sent between emitters and receivers embedded in the ice. At depths of 800-1000 m scattering is dominated by residual air bubbles, whereas absorption occurs both in ice itself and in insoluble impurities. The absorption coefficient increases approximately exponentially with wavelength in the measured interval 410-610 nm. At the shortest wavelength our value is approximately a factor 20 below previous values obtained for laboratory ice and lake ice; with increasing wavelength the discrepancy with previous measurements decreases. At ∼415 to ∼500 nm the experimental uncertainties are small enough for us to resolve an extrinsic contribution to absorption in ice: submicrometer dust particles contribute by an amount that increases with depth and corresponds well with the expected increase seen near the Last Glacial Maximum in Vostok and Dome C ice cores. The laser pulse method allows remote mapping of gross structure in dust concentration as a function of depth in glacial ice.
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| 3. |
- Bennett, J. M., et al.
(author)
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Test of Opticlean strip coating material for removing surface contamination
- 2000
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In: Applied Optics. - 0003-6935 .- 1539-4522. ; 39:16, s. 2737-2739
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Journal article (peer-reviewed)abstract
- The strip coating material, Opticlean, which has been reformulated, has been shown to remove 1-5-mu m-diameter particles as well as contamination remaining from previous drag wipe cleaning on a used silicon wafer. In addition, no residue that produced scattering was found on a fresh silicon wafer when Opticlean was applied and then stripped off. The total integrated scattering technique used for the measurements could measure scattering levels of He-Ne laser light as low as a few ppm (parts in 106), corresponding to a surface roughness of <1 Angstrom rms.
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| 4. |
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| 5. |
- Bergström, Per, et al.
(author)
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Dual-wavelength digital holography : single-shot shape evaluation using speckle displacements and regularization
- 2014
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In: Applied Optics. - : Optical Society of America. - 1559-128X .- 2155-3165 .- 0003-6935 .- 1539-4522. ; 53:1, s. 123-131
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Journal article (peer-reviewed)abstract
- This paper discusses the possibility of evaluating the shape of a free-form object in comparison with its shape prescribed by a CAD model. Measurements are made based on a single-shot recording using dual-wavelength holography with a synthetic wavelength of 1.4 mm. Each hologram is numerically propagated to different focus planes and correlated. The result is a vector field of speckle displacements that is linearly dependent on the local distance between the measured surface and the focus plane. From these speckle displacements, a gradient field of the measured surface is extracted through a proportional relationship. The gradient field obtained from the measurement is then aligned to the shape of the CAD model using the iterative closest point (ICP) algorithm and regularization. Deviations between the measured shape and the CAD model are found from the phase difference field, giving a high precision shape evaluation. The phase differences and the CAD model are also used to find a representation of the measured shape. The standard deviation of the measured shape relative the CAD model varies between 7 and 19 μm, depending on the slope.
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| 6. |
- Carlsson, Torgny E., et al.
(author)
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Method for fringe enhancement in holographic interferometry for measurement of in-plane displacements
- 1998
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In: Applied Optics. - : Optical Society of America. - 0003-6935 .- 1539-4522. ; 37:10, s. 1845-1848
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Journal article (peer-reviewed)abstract
- Theoretical background along with experimental results are given for a simple method for in-plane fringe enhancement in dual-beam illumination holographic interferometry. In this method, the fringes representing in-plane displacements arise as a moirépattern between two interferograms. To distinguish the in-plane displacement, a sequence of images is recorded while the reference mirror is continuously tilted at random. The in-plane fringes arethen found as the maximum contrast of the out-of-plane fringes in the image sequence. The resulting fringe quality is close to the quality of the out-of-plane fringes.
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| 7. |
- Enejder, Annika, 1969, et al.
(author)
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Influence of cell shape and aggregate formation on the optical properties of flowing whole blood
- 2003
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In: Applied Optics. - : The Optical Society. - 2155-3165 .- 0003-6935 .- 1539-4522. ; 42:7, s. 1384-1394
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Journal article (peer-reviewed)abstract
- We studied the influence of shape and secondary, or intercellular, organization on the absorption and scattering properties of red blood cells to determine whether these properties are of any practical significance for optical evaluation of whole blood and its constituents. A series of measurements of transmittance and reflectance of light from bovine blood in a flow cuvette was conducted with a 650-900-nm integrating sphere at shear rates of 0-1600 s(-1), from which the influence of cell orientation, elongation, and aggregate formation on the absorption (mu(a)) and the reduced scattering coefficients could be quantified. Aggregation was accompanied by a decrease of 4% in mu(s)' compared with the value in randomly oriented single cells. Increasing the degree of cell alignment and elongation as a result of increasing shear rate reduced mu(s)' by 6% and mu(a) by 3%, evaluated at a shear rate of 1600 s(-1). Comparison with T-matrix computations for oblate- and prolate-shaped cells with corresponding elongation and orientation indicates that the optical properties of whole blood are determined by those of its individual cells, though influenced by a collective scattering factor that depends on the cell-to-cell organization. We demonstrate that cell morphological changes must be taken into consideration when one is conducting whole blood spectroscopy. (C) 2003 Optical Society of America.
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| 8. |
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| 9. |
- Fällman, Erik, et al.
(author)
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Design for fully steerable dual-trap optical tweezers
- 1997
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In: Applied Optics. - : Optical Society of America. - 0003-6935 .- 1539-4522. ; 36:10, s. 2107-2113
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Journal article (peer-reviewed)abstract
- A design for complete beam steering (in three dimensions) of one or two optical tweezers traps is presented. The two most important requirements for efficient and stable movement of an optical trap are identified. A detailed recipe for the construction of a movable optical tweezers trap that fulfills these requirements is given (exemplified with an inverted microscope). The system has been found to allow for precise and free movements of both traps in all three dimensions in a dual-trap optical tweezers configuration and to be robust and reliable, as well as forgiving of small misalignments in the optical system.
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| 10. |
- Fällman, Erik, et al.
(author)
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Influence of a glass-water interface on the on-axis trapping of micrometer-sized spherical objects by optical tweezers
- 2003
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In: Applied Optics. - : Optical Society of America. - 0003-6935 .- 1539-4522. ; 42:19, s. 3915-3926
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Journal article (peer-reviewed)abstract
- A systematic study of the influence of a glass-water interface on the on-axis trapping of micrometer-sized spherical objects by optical tweezers is presented. The ways in which the escape force and the trapping position, as well as the stiffness of the trap, depend on the focusing depth, the numerical aperture, and the degree of overfilling of the objective entrance pupil are investigated. It is concluded, among other things, that objectives with the highest numerical aperture and the use of large degrees of overfilling do not always provide the optimum trapping conditions at finite depths.
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| 11. |
- Jason, Johan, et al.
(author)
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Temperature characteristics of the birefringence properties of filled side-hole fibers
- 2013
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In: Applied Optics. - : Optical Society of America. - 0003-6935 .- 1539-4522 .- 1559-128X .- 2155-3165. ; 52:21, s. 5208-5215
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Journal article (peer-reviewed)abstract
- The temperature characteristics of the birefringence of side-hole fibers filled with liquids or metal are investigated, aiming at providing a basis for on/off temperature sensing. Short pieces of fiber are filled and the change in birefringence is registered using measurements in reflective mode of the transmitted power through a linear polarizer at 1550 nm. The rapid change in the birefringence behavior of the fiber at the temperature of the phase transition of the filler substance is shown, and from the measurement data the phase transition temperatures can be determined as well as an estimation of the birefringence change with temperature. The experimental results are supported by numerical simulations.
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| 12. |
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| 13. |
- Khodadad, Davood, 1985-, et al.
(author)
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Fast and robust automatic calibration for single-shot dual-wavelength digital holography based on speckle displacements
- 2015
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In: Applied Optics. - : Optical Society of America. - 1559-128X .- 2155-3165 .- 0003-6935 .- 1539-4522. ; 54:16, s. 5003-5010
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Journal article (peer-reviewed)abstract
- The objective of this paper is to describe a fast and robust automatic single-shot dual-wavelength holographic calibration method that can be used for online shape measurement applications. We present a model of the correction in two terms for each lobe, one to compensate the systematic errors caused by off-axis angles and the other for the curvature of the reference waves, respectively. Each hologram is calibrated independently without a need for an iterative procedure or information of the experimental set-up. The calibration parameters are extracted directly from speckle displacements between different reconstruction planes. The parameters can be defined as any fraction of a pixel to avoid the effect of quantization. Using the speckle displacements, problems associated with phase wrapping is avoided. The procedure is shown to give a shape accuracy of 34 μm using a synthetic wavelength of 1.1 mm for a measurement on a cylindrical test object with a trace over a field of view of 18 mm×18 mm.
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| 14. |
- Khodadad, Davood, et al.
(author)
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Full-field 3D deformation measurement : Comparison between speckle phase and displacement evaluation
- 2016
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In: Applied Optics. - : Optical Society of America. - 1559-128X .- 2155-3165 .- 0003-6935 .- 1539-4522. ; 55:27, s. 7735-7743
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Journal article (peer-reviewed)abstract
- The objective of this paper is to describe a full-field deformation measurement method based on 3D speckle displacements. The deformation is evaluated from the slope of the speckle displacement function that connects the different reconstruction planes. For our experiment, a symmetrical arrangement with four illuminations parallel to the planes (x,z) and (y,z) was used. Four sets of speckle patterns were sequentially recorded by illuminating an object from the four directions, respectively. A single camera is used to record the holograms before and after deformations. Digital speckle photography is then used to calculate relative speckle displacements in each direction between two numerically propagated planes. The 3D speckle displacements vector is calculated as a combination of the speckle displacements from the holograms recorded in each illumination direction. Using the speckle displacements, problems associated with rigid body movements and phase wrapping are avoided. In our experiment, the procedure is shown to give the theoretical accuracy of 0.17 pixels yielding the accuracy of 2 × 10-3 in the measurement of deformation gradients
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| 15. |
- Khodadad, Davood, 1985-
(author)
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Phase-derivative-based estimation of a digital reference wave from a single off-axis digital hologram
- 2016
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In: Applied Optics. - : Optical Society of America. - 1559-128X .- 2155-3165 .- 0003-6935 .- 1539-4522. ; 55:7, s. 1663-1669
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Journal article (peer-reviewed)abstract
- This paper describes a method to obtain an estimated digital reference wave from a single off-axis digital hologram that matches the actual experimental reference wave as closely as possible. The proposed method is independent of a reference flat plate and speckles. The digital reference wave parameters are estimated directly from the recorded phase information. The parameters include both the off-axis tilt angle and the curvature of the reference wave. Phase derivatives are used to extract the digital reference wave parameters without the need for a phase unwrapping process. Thus, problems associated with phase wrapping are avoided. Experimental results for the proposed method are provided. The simulated effect of the digital reference wave parameters on the reconstructed image phase distribution is shown. The pseudo phase gradient originating from incorrect estimation of the digital reference wave parameters and its effect on object reconstruction are discussed.
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| 16. |
- Kluczynski, Pawel, et al.
(author)
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Background signals in wavelength-modulation spectrometry by use of frequency-doubled diode-laser light : II Experiment
- 2001
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In: Applied Optics. - : Optical Society of America. - 0003-6935 .- 1539-4522. ; 40:6, s. 794-805
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Journal article (peer-reviewed)abstract
- In an accompanying paper [Appl. Opt. 40, 783-193 (2001)], we predict the existence of background signals from a frequency-doubled wavelength-modulated diode-laser system. We now demonstrate and characterize various nf harmonics of such background signals from a system producing light in the 422-nm region by use of a single-pass KNbO3 crystal with respect to the modulation amplitude, the laser center frequency, and the crystal temperature. It is demonstrated that 2f detection is plagued by considerably larger amounts of background signal than is detection at other higher, even harmonics. This result implies that 4f or 6f detection is often to be preferred in comparison with 2f detection when frequency-doubled wavelength-modulation spectrometry (WMS) is to be used. This preference is illustrated by the detection of Ca in an acetylene-air flame. It is also shown that the background signals have a much stronger dependence on the modulation amplitude than do the analytical signals. This difference implies that the optimum detectability for frequency-doubled WMS is often reached for modulation amplitudes lower than those normally used. An analysis of the effect of a finite temperature stability of the doubling crystal on the drift of the background signals as well as on the detectability is included. The results verify the theoretical description given in our accompanying paper.
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| 17. |
- Kluczynski, Pawel, et al.
(author)
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Background signals in wavelength-modulation spectrometry with frequency-doubled diode-laser light : I Theory
- 2001
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In: Applied Optics. - : Optical Society of America. - 0003-6935 .- 1539-4522. ; 40:6, s. 783-793
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Journal article (peer-reviewed)abstract
- Various types of background signals appear when wavelength-modulated (WM) diode-laser light is frequency doubled. We present a theoretical analysis of such background signals in terms of a previously derived formalism for WM spectrometry that is based on a Fourier series. Explicit expressions for various nf harmonics of the background signals are derived. The analysis shows that 2f detection will be plagued by significant background signals when frequency-doubled WM diode-laser light is used. It also demonstrates that 4f and 6f detection will experience background signals but not, however, to the same extent as 2f detection. The analysis illustrates clearly how the various nf harmonics of the background signals depend on entities such as modulation amplitude, associated intensity modulation, dispersion of the frequency-doubling material, laser power, and detuning. The background signals can take both positive and negative values, depending on the relation between these entities. Guidelines for how to minimize these background signals are given.
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| 18. |
- Kluczynski, Pawel, et al.
(author)
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Characterization of background signals in wavelength-modulation spectrometry in terms of a Fourier based theoretical formalism
- 2001
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In: Applied Optics. - : Optical Society of America. - 0003-6935 .- 1539-4522. ; 40:6, s. 770-782
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Journal article (peer-reviewed)abstract
- The detectability of wavelength-modulation (WM) diode-laser spectrometric techniques is frequently limited by various background signals. A new theoretical formalism for WM spectrometry, based on Fourier analysis and therefore capable of handling a variety of phenomena including the characterization and the analysis of analytical as well as background WM signals, was recently presented [Appl. Opt. 38, 5803 (1999)]. We report a detailed characterization of WM background signals from multiple reflections between pairs of surfaces in the optical system that act as etalons and from the associated intensity modulation in terms of this new formalism. The agreement between the background signals from a thin glass plate and those predicted by the formalism is good, which verifies the new Fourier analysis-based formalism.
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| 19. |
- Kluczynski, Pawel, et al.
(author)
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Theoretical description based on Fourier analysis of wavelength-modulation spectrometry in terms of analytical and background signals
- 1999
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In: Applied Optics. - : Optical Society of America. - 0003-6935 .- 1539-4522. ; 38:27, s. 5803-5815
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Journal article (peer-reviewed)abstract
- A theoretical description of the wavelength-modulation (WM) spectrometry technique is given. The formalism is based on Fourier analysis and can therefore correctly handle arbitrary large frequency-modulation amplitudes. It can also deal with associated intensity modulations as well as wavelength-dependent transmission effects. It elucidates clearly how various Fourier components of these entities combine with those of the line-shape function to yield separately the final analytical and background nf WM signals. Explicit expressions are given for the 2f and the 4f signals. It is shown, among other things, that the 4f technique in general gives rise to smaller background signals (and therefore larger signal-to-background ratios) than does the 2f technique when the background is dominated by etalon effects from short cavities and that a finite intensity modulation necessarily leads to an out-of-phase nf WM signal. The formalism is also able to elucidate clearly that a linear intensity modulation is not sufficient to cause any 2f background residual-amplitude-modulation signals (as was the general consensus until recently in the literature) but that 2f background signals instead can exist only in systems with either wavelength-dependent transmission or a laser with nonlinear intensity modulation.
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| 20. |
- Letalick, Dietmar, et al.
(author)
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Terrain Segmentation using Laser Radar Range Data
- 1992
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In: Applied Optics. - 0003-6935 .- 1539-4522. ; 31:15, s. 2883-2890
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Journal article (peer-reviewed)abstract
- A novel approach to segmentation of laser radar range images is presented. The approach is based on modeling horizontal and vertical scans of the terrain as piecewise-constant or piecewise-linear functions. The approach uses adaptive estimation based on Kalman filtering techniques. The performance of the segmentation algorithm is evaluated by application to laser range measurements. We also discuss how the output from the segmentation algorithm can be used for, e.g., object detection.
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| 21. |
- Li, Yu, et al.
(author)
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Optical emission enhancement of laser-produced copper plasma under a steady magnetic field
- 2009
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In: Applied Optics. - 1539-4522 .- 0003-6935. ; 48:4, s. 105-110
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Conference paper (peer-reviewed)abstract
- From a copper target, laser-ablated plasma was investigated by spectral- and temporal-resolved emission spectroscopy. With the presence of a 0.8T steady magnetic field, the emission of the expanding plasma showed significant enhancements of the spectral lines for all neutral, singly, and doubly ionized species. The relative enhancements for different species have been studied with temporal-resolved measurement by comparing the spectra obtained with and without the magnetic field. The enhanced emission from the plasma plume is attributed to an increase of the radiative recombination rate in the plasma due to magnetic confinement. The temporal evolution of the plasma parameters, including electron temperature and electron density, was deduced and discussed for the cases with and without a magnetic field. (C) 2008 Optical Society of America
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| 22. |
- Ljungberg, Peter, et al.
(author)
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Degenerate four-wave mixing from laser-populated excited states
- 1995
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In: Applied Optics. - : Optical Society of America. - 0003-6935 .- 1539-4522. ; 34:3, s. 527-536
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Journal article (peer-reviewed)abstract
- Degenerate four-wave mixing (DFWM) from laser-populated excited states, i.e., two-step DFWM (2S-DFWM), has been performed to investigate the possibility of increasing signal quality (i.e., strength or signal-to-noise ratio) when species with low transition probabilities or far-UV transitions are to be detected or when large beam areas are used. Gold atoms, aspirated into an air-acetylene flame, were chosen as a suitable species for this investigation. The 2S-DFWM signal strength was found to be comparable to the ordinary (one-step) DFWM signals for moderately high UV-light intensities but substantially better for low UV-light intensities. This finding implies that DFWM detection of species with lower transition probabilities in the first step as compared with gold (< 10-8 s-1) can benefit from the 2S-DFWM technique when moderate or low UV-light intensities are available. Additional possible advantages of using 2S-DFWM are also discussed.
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| 23. |
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| 24. |
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| 25. |
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