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Special Issue "Laser Sensing and Imaging"

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A special issue of Sensors (ISSN 1424-8220). This special issue belongs to the section "Physical Sensors".

Deadline for manuscript submissions: closed (31 December 2012)

Special Issue Editor

Guest Editor
Prof. Dr. Markus W. Sigrist (Website)

ETH Zürich, Institute for Quantum Electronics, HPF D 19, Schafmattstrasse 16, CH-8093 Zürich, Switzerland
Phone: +41-44-633 2289
Fax: +41 44 633 12 30
Interests: widely tunable infrared laser sources; sensitive and selective monitoring methods such as multipass absorption, photoacoustics and cavity ringdown; algorithms for spectral analyses of multi-component mixtures; low-cost photoacoustic gas sensors; application of laser-spectroscopic schemes

Special Issue Information

Dear Colleagues,

Sensing applications are of ever growing importance in very diverse fields. This trend is also illustrated by special conferences and symposia devoted to certain aspects of sensing. New laser sources, spectroscopic approaches and imaging techniques play an increasing role as they enable non-contact sensing without or with only minimum sample pretreatment and/or sample preparation. Furthermore, hyperspectral approaches and improved data retrieval techniques have a great impact on the development of such techniques.

This special issue on Laser Sensing and Imaging addresses the following topics, but is not limited to:

  • Laser-based sensors for gases, liquids, and solids
  • Spectroscopy from UV to THz range
  • Laser sources (with emphasis on tunability): diode lasers, VCSELs and VECSELS, interband cascade lasers (ICLs), quantum cascade lasers (QCLs), lead salt diode lasers, fiber lasers, nonlinear optical sources (difference frequency generation (DFG), optical parametric oscillators (OPOs)), frequency combs, etc.
  • Measurement principles: absorption, fluorescence, reflection, scattering, photoacoustic and photothermal, Raman, Coherent Anti-Stokes Raman (CARS), dispersion, microring resonators, microfluidics, lab-on-a-chip, etc.
  • Imaging techniques for spatially and temporally resolved information, e.g., for stand-off detection of explosives
  • Mathematical algorithms for multi-component spectral analysis
  • Application areas such as air monitoring, combustion, waste water, industrial process monitoring, workplace safety, agriculture and food science, security (particularly explosive detection), biological, medical such as breath analysis, non-invasive glucose monitoring, drug detection, etc.

We solicit review articles and original research papers on systems with emphasis on laser-based devices; and applications of such systems in areas as mentioned above. New sensing concepts, which are especially suited for multi-component or multi-parameter monitoring, novel approaches which allow measuring or controlling of so far inaccessible parameters or new application areas of such systems are also welcome.

Prof. Dr. Markus W. Sigrist
Guest Editor

Keywords

  • tunable lasers
  • UV- to IR- to THz-spectroscopy and imaging
  • laser-analytical principles
  • sensing applications
  • data retrieval algorithms

Published Papers (24 papers)

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Open AccessArticle Novel RF Interrogation of a Fiber Bragg Grating Sensor Using Bidirectional Modulation of a Mach-Zehnder Electro-Optical Modulator
Sensors 2013, 13(7), 8403-8411; doi:10.3390/s130708403
Received: 10 April 2013 / Revised: 20 June 2013 / Accepted: 28 June 2013 / Published: 2 July 2013
Cited by 7 | PDF Full-text (540 KB) | HTML Full-text | XML Full-text
Abstract
We propose and experimentally demonstrate the novel radio-frequency (RF) interrogation of a fiber Bragg grating (FBG) sensor using bidirectional modulation of a Mach-Zehnder electro-optical modulator (MZ-EOM). Based on the microwave photonic technique and active detection, the transfer function of the proposed system [...] Read more.
We propose and experimentally demonstrate the novel radio-frequency (RF) interrogation of a fiber Bragg grating (FBG) sensor using bidirectional modulation of a Mach-Zehnder electro-optical modulator (MZ-EOM). Based on the microwave photonic technique and active detection, the transfer function of the proposed system was obtained, and the time delay was calculated from the change in the free spectral range (FSR) at different wavelengths over the optimal measuring range. The results show that the time delay and the wavelength variation have a good linear relationship, with a gradient of 9.31 ps/nm. An actual measurement taken with a sensing FBG for temperature variation shows the relationship with a gradient of 0.93 ps/10 °C. The developed system could be used for FBG temperature or strain sensing and other multiplexed sensor applications. Full article
(This article belongs to the Special Issue Laser Sensing and Imaging)
Open AccessArticle Wireless Laser Range Finder System for Vertical Displacement Monitoring of Mega-Trusses during Construction
Sensors 2013, 13(5), 5796-5813; doi:10.3390/s130505796
Received: 7 March 2013 / Revised: 18 April 2013 / Accepted: 27 April 2013 / Published: 6 May 2013
Cited by 7 | PDF Full-text (1448 KB) | HTML Full-text | XML Full-text
Abstract
As buildings become increasingly complex, construction monitoring using various sensors is urgently needed for both more systematic and accurate safety management and high-quality productivity in construction. In this study, a monitoring system that is composed of a laser displacement sensor (LDS) and [...] Read more.
As buildings become increasingly complex, construction monitoring using various sensors is urgently needed for both more systematic and accurate safety management and high-quality productivity in construction. In this study, a monitoring system that is composed of a laser displacement sensor (LDS) and a wireless sensor node was proposed and applied to an irregular building under construction. The subject building consists of large cross-sectional members, such as mega-columns, mega-trusses, and edge truss, which secured the large spaces. The mega-trusses and edge truss that support this large space are of the cantilever type. The vertical displacement occurring at the free end of these members was directly measured using an LDS. To validate the accuracy and reliability of the deflection data measured from the LDS, a total station was also employed as a sensor for comparison with the LDS. In addition, the numerical simulation result was compared with the deflection obtained from the LDS and total station. Based on these investigations, the proposed wireless displacement monitoring system was able to improve the construction quality by monitoring the real-time behavior of the structure, and the applicability of the proposed system to buildings under construction for the evaluation of structural safety was confirmed. Full article
(This article belongs to the Special Issue Laser Sensing and Imaging)
Open AccessArticle Garment Counting in a Textile Warehouse by Means of a Laser Imaging System
Sensors 2013, 13(5), 5630-5648; doi:10.3390/s130505630
Received: 4 April 2013 / Revised: 25 April 2013 / Accepted: 25 April 2013 / Published: 29 April 2013
PDF Full-text (3864 KB) | HTML Full-text | XML Full-text
Abstract
Textile logistic warehouses are highly automated mechanized places where control points are needed to count and validate the number of garments in each batch. This paper proposes and describes a low cost and small size automated system designed to count the number [...] Read more.
Textile logistic warehouses are highly automated mechanized places where control points are needed to count and validate the number of garments in each batch. This paper proposes and describes a low cost and small size automated system designed to count the number of garments by processing an image of the corresponding hanger hooks generated using an array of phototransistors sensors and a linear laser beam. The generated image is processed using computer vision techniques to infer the number of garment units. The system has been tested on two logistic warehouses with a mean error in the estimated number of hangers of 0.13%. Full article
(This article belongs to the Special Issue Laser Sensing and Imaging)
Open AccessArticle Validation of Noninvasive MOEMS-Assisted Measurement System Based on CCD Sensor for Radial Pulse Analysis
Sensors 2013, 13(4), 5368-5380; doi:10.3390/s130405368
Received: 30 January 2013 / Revised: 22 March 2013 / Accepted: 25 March 2013 / Published: 22 April 2013
Cited by 3 | PDF Full-text (1020 KB) | HTML Full-text | XML Full-text
Abstract
Examination of wrist radial pulse is a noninvasive diagnostic method, which occupies a very important position in Traditional Chinese Medicine. It is based on manual palpation and therefore relies largely on the practitioner’s subjective technical skills and judgment. Consequently, it lacks reliability [...] Read more.
Examination of wrist radial pulse is a noninvasive diagnostic method, which occupies a very important position in Traditional Chinese Medicine. It is based on manual palpation and therefore relies largely on the practitioner’s subjective technical skills and judgment. Consequently, it lacks reliability and consistency, which limits practical applications in clinical medicine. Thus, quantifiable characterization of the wrist pulse diagnosis method is a prerequisite for its further development and widespread use. This paper reports application of a noninvasive CCD sensor-based hybrid measurement system for radial pulse signal analysis. First, artery wall deformations caused by the blood flow are calibrated with a laser triangulation displacement sensor, following by the measurement of the deformations with projection moiré method. Different input pressures and fluids of various viscosities are used in the assembled artificial blood flow system in order to test the performance of laser triangulation technique with detection sensitivity enhancement through microfabricated retroreflective optical element placed on a synthetic vascular graft. Subsequently, the applicability of double-exposure whole-field projection moiré technique for registration of blood flow pulses is considered: a computational model and representative example are provided, followed by in vitro experiment performed on a vascular graft with artificial skin atop, which validates the suitability of the technique for characterization of skin surface deformations caused by the radial pulsation. Full article
(This article belongs to the Special Issue Laser Sensing and Imaging)
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Open AccessArticle A Two-Dimensional Laser Scanning Mirror Using Motion-Decoupling Electromagnetic Actuators
Sensors 2013, 13(4), 4146-4156; doi:10.3390/s130404146
Received: 21 January 2013 / Revised: 28 January 2013 / Accepted: 18 March 2013 / Published: 27 March 2013
Cited by 4 | PDF Full-text (878 KB) | HTML Full-text | XML Full-text
Abstract
This work proposes a two-dimensional (2-D) laser scanning mirror with a novel actuating structure composed of one magnet and two coils. The mirror-actuating device generates decoupled scanning motions about two orthogonal axes by combining two electromagnetic actuators of the conventional moving-coil and [...] Read more.
This work proposes a two-dimensional (2-D) laser scanning mirror with a novel actuating structure composed of one magnet and two coils. The mirror-actuating device generates decoupled scanning motions about two orthogonal axes by combining two electromagnetic actuators of the conventional moving-coil and the moving-magnet types. We implement a finite element analysis to calculate magnetic flux in the electromagnetic system and experiments using a prototype with the overall size of 22 mm (W) × 20 mm (D) × 15 mm (H) for the mirror size of 8 mm × 8 mm. The upper moving-coil type actuator to rotate only the mirror part has the optical reflection angle of 15.7° at 10 Hz, 90° at the resonance frequency of 60 Hz at ±3 V (±70 mA) and the bandwidth of 91 Hz. The lower moving-magnet type actuator has the optical reflection angle of 16.20° at 10 Hz and 50° at the resonance frequency of 60 Hz at ±5 V (±34 mA) and the bandwidth of 88 Hz. The proposed compact and simple 2-D scanning mirror has advantages of large 2-D angular deflections, wide frequency bandwidth and low manufacturing cost. Full article
(This article belongs to the Special Issue Laser Sensing and Imaging)
Open AccessArticle THz QCL-Based Cryogen-Free Spectrometer for in Situ Trace Gas Sensing
Sensors 2013, 13(3), 3331-3340; doi:10.3390/s130303331
Received: 3 January 2013 / Revised: 2 March 2013 / Accepted: 8 March 2013 / Published: 11 March 2013
Cited by 20 | PDF Full-text (391 KB) | HTML Full-text | XML Full-text
Abstract
We report on a set of high-sensitivity terahertz spectroscopy experiments making use of QCLs to detect rotational molecular transitions in the far-infrared. We demonstrate that using a compact and transportable cryogen-free setup, based on a quantum cascade laser in a closed-cycle Stirling [...] Read more.
We report on a set of high-sensitivity terahertz spectroscopy experiments making use of QCLs to detect rotational molecular transitions in the far-infrared. We demonstrate that using a compact and transportable cryogen-free setup, based on a quantum cascade laser in a closed-cycle Stirling cryostat, and pyroelectric detectors, a considerable improvement in sensitivity can be obtained by implementing a wavelength modulation spectroscopy technique. Indeed, we show that the sensitivity of methanol vapour detection can be improved by a factor ≈ 4 with respect to standard direct absorption approaches, offering perspectives for high sensitivity detection of a number of chemical compounds across the far-infrared spectral range. Full article
(This article belongs to the Special Issue Laser Sensing and Imaging)
Open AccessArticle High Temperature Optical Fiber Sensor Based on Compact Fattened Long-Period Fiber Gratings
Sensors 2013, 13(3), 3028-3038; doi:10.3390/s130303028
Received: 5 January 2013 / Revised: 15 February 2013 / Accepted: 22 February 2013 / Published: 4 March 2013
Cited by 5 | PDF Full-text (310 KB) | HTML Full-text | XML Full-text
Abstract
A compact high temperature fiber sensor where the sensor head consists of a short fattened long period fiber grating (F-LPFG) of at least 2 mm in length and background loss of −5 dBm is reported. On purpose two different F-LPFGs were used [...] Read more.
A compact high temperature fiber sensor where the sensor head consists of a short fattened long period fiber grating (F-LPFG) of at least 2 mm in length and background loss of −5 dBm is reported. On purpose two different F-LPFGs were used to measure temperature variations, taking advantage of their broad spectrum and the slope characteristics of the erbium light source. This approach affected the spectrum gain as the linear band shifting took place. The measured sensitivity of the long period fiber gratings were about 72 pm/°C in a range from 25 to 500 °C. Here, the temperature rate of the experiment was 0.17 °C/s and the temperature response time was within 3 s. Moreover, temperature changes were detected with an InGaAs photodetector, where a sensitivity of 0.05 mV/°C was achieved. Full article
(This article belongs to the Special Issue Laser Sensing and Imaging)
Open AccessArticle Trapping and Propelling Microparticles at Long Range by Using an Entirely Stripped and Slightly Tapered No-Core Optical Fiber
Sensors 2013, 13(3), 2884-2894; doi:10.3390/s130302884
Received: 3 December 2012 / Revised: 28 January 2013 / Accepted: 25 February 2013 / Published: 28 February 2013
Cited by 2 | PDF Full-text (631 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
A stripped no-core optical fiber with a 125 µm diameter was transformed into a symmetric and unbroken optical fiber that tapers slightly to a 45-µm-diameter waist. The laser light can be easily launched into the no-core optical fiber. The enhanced evanescent wave [...] Read more.
A stripped no-core optical fiber with a 125 µm diameter was transformed into a symmetric and unbroken optical fiber that tapers slightly to a 45-µm-diameter waist. The laser light can be easily launched into the no-core optical fiber. The enhanced evanescent wave of the slightly tapered no-core optical fiber can attract nearby 5-µm-diameter polystyrene microparticles onto the surface of the tapered multimode optical fiber within fast flowing fluid and propel the trapped particles in the direction of the light propagation to longer delivery range than is possible using a slightly tapered telecom single-mode optical fiber. Full article
(This article belongs to the Special Issue Laser Sensing and Imaging)
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Open AccessArticle On the Effects of the Lateral Strains on the Fiber Bragg Grating Response
Sensors 2013, 13(2), 2631-2644; doi:10.3390/s130202631
Received: 6 December 2012 / Revised: 6 February 2013 / Accepted: 13 February 2013 / Published: 21 February 2013
Cited by 9 | PDF Full-text (822 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, a combined experimental-numerical based work was undertaken to investigate the Bragg wavelength shift response of an embedded FBG sensor when subjected to different conditions of multi-axial loading (deformation). The following cases are examined: (a) when an isotropic host material [...] Read more.
In this paper, a combined experimental-numerical based work was undertaken to investigate the Bragg wavelength shift response of an embedded FBG sensor when subjected to different conditions of multi-axial loading (deformation). The following cases are examined: (a) when an isotropic host material with no constrains on planes normal to the embedded sensor’s axis is biaxially loaded, (b) when the same isotropic host material is subjected to hydrostatic pressure and (c) when the hydrostatically loaded host material is an anisotropic one, as in the case of a composite material, where the optical fiber is embedded along the reinforcing fibers. The comparison of the experimental results and the finite element simulations shows that, when the axial strain on the FBG sensor is the dominant component, the standard wavelength-shift strain relation can be used even if large lateral strains apply on the sensor. However when this is not the case, large errors may be introduced in the conversion of the wavelength to axial strains on the fiber. This situation arises when the FBG is placed parallel to high modulus reinforcing fibers of a polymer composite. Full article
(This article belongs to the Special Issue Laser Sensing and Imaging)
Open AccessArticle Wedge-Filtering of Geomorphologic Terrestrial Laser Scan Data
Sensors 2013, 13(2), 2579-2594; doi:10.3390/s130202579
Received: 4 January 2013 / Revised: 4 February 2013 / Accepted: 8 February 2013 / Published: 20 February 2013
Cited by 3 | PDF Full-text (1559 KB) | HTML Full-text | XML Full-text
Abstract
Terrestrial laser scanning is of increasing importance for surveying and hazard assessments. Digital terrain models are generated using the resultant data to analyze surface processes. In order to determine the terrain surface as precisely as possible, it is often necessary to filter [...] Read more.
Terrestrial laser scanning is of increasing importance for surveying and hazard assessments. Digital terrain models are generated using the resultant data to analyze surface processes. In order to determine the terrain surface as precisely as possible, it is often necessary to filter out points that do not represent the terrain surface. Examples are vegetation, vehicles, and animals. Filtering in mountainous terrain is more difficult than in other topography types. Here, existing automatic filtering solutions are not acceptable, because they are usually designed for airborne scan data. The present article describes a method specifically suitable for filtering terrestrial laser scanning data. This method is based on the direct line of sight between the scanner and the measured point and the assumption that no other surface point can be located in the area above this connection line. This assumption is only true for terrestrial laser data, but not for airborne data. We present a comparison of the wedge filtering to a modified inverse distance filtering method (IDWMO) filtered point cloud data. Both methods use manually filtered surfaces as reference. The comparison shows that the mean error and root–mean-square-error (RSME) between the results and the manually filtered surface of the two methods are similar. A significantly higher number of points of the terrain surface could be preserved, however, using the wedge-filtering approach. Therefore, we suggest that wedge-filtering should be integrated as a further parameter into already existing filtering processes, but is not suited as a standalone solution so far. Full article
(This article belongs to the Special Issue Laser Sensing and Imaging)
Open AccessArticle Frequency Noise Properties of Lasers for Interferometry in Nanometrology
Sensors 2013, 13(2), 2206-2219; doi:10.3390/s130202206
Received: 26 November 2012 / Revised: 31 January 2013 / Accepted: 4 February 2013 / Published: 7 February 2013
Cited by 20 | PDF Full-text (886 KB) | HTML Full-text | XML Full-text
Abstract
In this contribution we focus on laser frequency noise properties and their influence on the interferometric displacement measurements. A setup for measurement of laser frequency noise is proposed and tested together with simultaneous measurement of fluctuations in displacement in the Michelson interferometer. [...] Read more.
In this contribution we focus on laser frequency noise properties and their influence on the interferometric displacement measurements. A setup for measurement of laser frequency noise is proposed and tested together with simultaneous measurement of fluctuations in displacement in the Michelson interferometer. Several laser sources, including traditional He-Ne and solid-state lasers, and their noise properties are evaluated and compared. The contribution of the laser frequency noise to the displacement measurement is discussed in the context of other sources of uncertainty associated with the interferometric setup, such as, mechanics, resolution of analog-to-digital conversion, frequency bandwidth of the detection chain, and variations of the refractive index of air. Full article
(This article belongs to the Special Issue Laser Sensing and Imaging)
Open AccessArticle Monolithically Integrated Mid-Infrared Quantum Cascade Laser and Detector
Sensors 2013, 13(2), 2196-2205; doi:10.3390/s130202196
Received: 4 January 2013 / Revised: 30 January 2013 / Accepted: 1 February 2013 / Published: 6 February 2013
Cited by 13 | PDF Full-text (356 KB) | HTML Full-text | XML Full-text
Abstract
We demonstrate the monolithic integration of a mid-infrared laser and detector utilizing a bi-functional quantum cascade active region. When biased, this active region provides optical gain, while it can be used as a detector at zero bias. With our novel approach we [...] Read more.
We demonstrate the monolithic integration of a mid-infrared laser and detector utilizing a bi-functional quantum cascade active region. When biased, this active region provides optical gain, while it can be used as a detector at zero bias. With our novel approach we can measure the light intensity of the laser on the same chip without the need of external lenses or detectors. Based on a bound-to-continuum design, the bi-functional active region has an inherent broad electro-luminescence spectrum of 200 cm-1, which indicates its use for single mode laser arrays. We have measured a peak signal of 191.5 mV at the on-chip detector, without any amplification. The room-temperature pulsed emission with an averaged power consumption of 4 mW and the high-speed detection makes these devices ideal for low-power sensors. The combination of the on-chip detection functionality, the broad emission spectrum and the low average power consumption indicates the potential of our bi-functional quantum cascade structures to build a mid-infrared lab-on-a-chip based on quantum cascade laser technology. Full article
(This article belongs to the Special Issue Laser Sensing and Imaging)
Open AccessArticle Low-Loss Hollow Waveguide Fibers for Mid-Infrared Quantum Cascade Laser Sensing Applications
Sensors 2013, 13(1), 1329-1340; doi:10.3390/s130101329
Received: 19 November 2012 / Revised: 8 January 2013 / Accepted: 9 January 2013 / Published: 21 January 2013
Cited by 16 | PDF Full-text (2594 KB) | HTML Full-text | XML Full-text
Abstract
We report on single mode optical transmission of hollow core glass waveguides (HWG) coupled with an external cavity mid-IR quantum cascade lasers (QCLs). The QCL mode results perfectly matched to the hybrid HE11 waveguide mode and the higher losses TE-like modes [...] Read more.
We report on single mode optical transmission of hollow core glass waveguides (HWG) coupled with an external cavity mid-IR quantum cascade lasers (QCLs). The QCL mode results perfectly matched to the hybrid HE11 waveguide mode and the higher losses TE-like modes have efficiently suppressed by the deposited inner dielectric coating. Optical losses down to 0.44 dB/m and output beam divergence of ~5 mrad were measured. Using a HGW fiber with internal core size of 300 µm we obtained single mode laser transmission at 10.54 µm and successful employed it in a quartz enhanced photoacoustic gas sensor setup. Full article
(This article belongs to the Special Issue Laser Sensing and Imaging)
Open AccessArticle A Homodyne Quadrature Laser Interferometer for Micro-Asperity Deformation Analysis
Sensors 2013, 13(1), 703-720; doi:10.3390/s130100703
Received: 31 October 2012 / Revised: 18 December 2012 / Accepted: 24 December 2012 / Published: 7 January 2013
Cited by 1 | PDF Full-text (490 KB) | HTML Full-text | XML Full-text
Abstract
We report on the successful realization of a contactless, non-perturbing, displacement-measuring system for characterizing the surface roughness of polymer materials used in tribological applications. A single, time-dependent, scalar value, dubbed the collective micro-asperity deformation, is extracted from the normal-displacement measurements of normally [...] Read more.
We report on the successful realization of a contactless, non-perturbing, displacement-measuring system for characterizing the surface roughness of polymer materials used in tribological applications. A single, time-dependent, scalar value, dubbed the collective micro-asperity deformation, is extracted from the normal-displacement measurements of normally loaded polymer samples. The displacement measurements with a sub-nanometer resolution are obtained with a homodyne quadrature laser interferometer. The measured collective micro-asperity deformation is critical for a determination of the real contact area and thus for the realistic contact conditions in tribological applications. The designed measuring system senses both the bulk creep as well as the micro-asperity creep occurring at the roughness peaks. The final results of our experimental measurements are three time-dependent values of the collective micro-asperity deformation for the three selected surface roughnesses. These values can be directly compared to theoretical deformation curves, which can be derived using existing real-contact-area models. Full article
(This article belongs to the Special Issue Laser Sensing and Imaging)
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Open AccessArticle Absorption Measurements of Periodically Poled Potassium Titanyl Phosphate (PPKTP) at 775 nm and 1550 nm
Sensors 2013, 13(1), 565-573; doi:10.3390/s130100565
Received: 1 November 2012 / Revised: 6 December 2012 / Accepted: 19 December 2012 / Published: 4 January 2013
Cited by 2 | PDF Full-text (285 KB) | HTML Full-text | XML Full-text
Abstract
The efficient generation of second-harmonic light and squeezed light requires non-linear crystals that have low absorption at the fundamental and harmonic wavelengths. In this work the photo-thermal self-phase modulation technique is exploited to measure the absorption coefficient of periodically poled potassium titanyl [...] Read more.
The efficient generation of second-harmonic light and squeezed light requires non-linear crystals that have low absorption at the fundamental and harmonic wavelengths. In this work the photo-thermal self-phase modulation technique is exploited to measure the absorption coefficient of periodically poled potassium titanyl phosphate (PPKTP) at 1,550 nm and 775 nm. Themeasurement results are (84±40) ppm/cmand (127±24) ppm/cm, respectively. We conclude that the performance of state-of-the-art frequency doubling and squeezed light generation in PPKTP is not limited by absorption. Full article
(This article belongs to the Special Issue Laser Sensing and Imaging)
Open AccessArticle Mid-Infrared Fiber-Coupled Photoacoustic Sensor for Biomedical Applications
Sensors 2013, 13(1), 535-549; doi:10.3390/s130100535
Received: 29 October 2012 / Revised: 20 December 2012 / Accepted: 22 December 2012 / Published: 2 January 2013
Cited by 13 | PDF Full-text (1829 KB) | HTML Full-text | XML Full-text
Abstract
Biomedical devices employed in therapy, diagnostics and for self-monitoring often require a high degree of flexibility and compactness. Many near infrared (NIR) optical fiber-coupled systems meet these requirements and are employed on a daily basis. However, mid-infrared (MIR) fibers-based systems have not [...] Read more.
Biomedical devices employed in therapy, diagnostics and for self-monitoring often require a high degree of flexibility and compactness. Many near infrared (NIR) optical fiber-coupled systems meet these requirements and are employed on a daily basis. However, mid-infrared (MIR) fibers-based systems have not yet found their way to routine application in medicine. In this work we present the implementation of the first MIR fiber-coupled photoacoustic sensor for the investigation of condensed samples in the MIR fingerprint region. The light of an external-cavity quantum-cascade laser (1010–1095 cm-1) is delivered by a silver halide fiber, which is attached to the PA cell. The PA chamber is conically shaped to perfectly match the beam escaping the fiber and to minimize the cell volume. This results in a compact and handy sensor for investigations of biological samples and the monitoring of constituents both in vitro and in vivo. The performance of the fiber-coupled PA sensor is demonstrated by sensing glucose in aqueous solutions. These measurements yield a detection limit of 57 mg/dL (SNR = 1). Furthermore, the fiber-coupled sensor has been applied to record human skin spectra at different body sites to illustrate its flexibility. Full article
(This article belongs to the Special Issue Laser Sensing and Imaging)
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Open AccessFeature PaperArticle Chirped Laser Dispersion Spectroscopy for Remote Open-Path Trace-Gas Sensing
Sensors 2012, 12(12), 16466-16481; doi:10.3390/s121216466
Received: 29 August 2012 / Revised: 26 October 2012 / Accepted: 21 November 2012 / Published: 28 November 2012
Cited by 29 | PDF Full-text (1338 KB) | HTML Full-text | XML Full-text
Abstract
In this paper we present a prototype instrument for remote open-path detection of nitrous oxide. The sensor is based on a 4.53 μm quantum cascade laser and uses the chirped laser dispersion spectroscopy (CLaDS) technique for molecular concentration measurements. To the best [...] Read more.
In this paper we present a prototype instrument for remote open-path detection of nitrous oxide. The sensor is based on a 4.53 μm quantum cascade laser and uses the chirped laser dispersion spectroscopy (CLaDS) technique for molecular concentration measurements. To the best of our knowledge this is the first demonstration of open-path laser-based trace-gas detection using a molecular dispersion measurement. The prototype sensor achieves a detection limit down to the single-ppbv level and exhibits excellent stability and robustness. The instrument characterization, field deployment performance, and the advantages of applying dispersion sensing to sensitive trace-gas detection in a remote open-path configuration are presented. Full article
(This article belongs to the Special Issue Laser Sensing and Imaging)
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Open AccessArticle Two-Dimensional Radial Laser Scanning for Circular Marker Detection and External Mobile Robot Tracking
Sensors 2012, 12(12), 16482-16497; doi:10.3390/s121216482
Received: 19 October 2012 / Revised: 22 November 2012 / Accepted: 23 November 2012 / Published: 28 November 2012
Cited by 6 | PDF Full-text (522 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents the use of an external fixed two-dimensional laser scanner to detect cylindrical targets attached to moving devices, such as a mobile robot. This proposal is based on the detection of circular markers in the raw data provided by the [...] Read more.
This paper presents the use of an external fixed two-dimensional laser scanner to detect cylindrical targets attached to moving devices, such as a mobile robot. This proposal is based on the detection of circular markers in the raw data provided by the laser scanner by applying an algorithm for outlier avoidance and a least-squares circular fitting. Some experiments have been developed to empirically validate the proposal with different cylindrical targets in order to estimate the location and tracking errors achieved, which are generally less than 20 mm in the area covered by the laser sensor. As a result of the validation experiments, several error maps have been obtained in order to give an estimate of the uncertainty of any location computed. This proposal has been validated with a medium-sized mobile robot with an attached cylindrical target (diameter 200 mm). The trajectory of the mobile robot was estimated with an average location error of less than 15 mm, and the real location error in each individual circular fitting was similar to the error estimated with the obtained error maps. The radial area covered in this validation experiment was up to 10 m, a value that depends on the radius of the cylindrical target and the radial density of the distance range points provided by the laser scanner but this area can be increased by combining the information of additional external laser scanners. Full article
(This article belongs to the Special Issue Laser Sensing and Imaging)
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Open AccessArticle Automatic Method for Building Indoor Boundary Models from Dense Point Clouds Collected by Laser Scanners
Sensors 2012, 12(12), 16099-16115; doi:10.3390/s121216099
Received: 31 August 2012 / Revised: 30 October 2012 / Accepted: 8 November 2012 / Published: 22 November 2012
Cited by 19 | PDF Full-text (1425 KB) | HTML Full-text | XML Full-text
Abstract
In this paper we present a method that automatically yields Boundary Representation Models (B-rep) for indoors after processing dense point clouds collected by laser scanners from key locations through an existing facility. Our objective is particularly focused on providing single models which [...] Read more.
In this paper we present a method that automatically yields Boundary Representation Models (B-rep) for indoors after processing dense point clouds collected by laser scanners from key locations through an existing facility. Our objective is particularly focused on providing single models which contain the shape, location and relationship of primitive structural elements of inhabited scenarios such as walls, ceilings and floors. We propose a discretization of the space in order to accurately segment the 3D data and generate complete B-rep models of indoors in which faces, edges and vertices are coherently connected. The approach has been tested in real scenarios with data coming from laser scanners yielding promising results. We have deeply evaluated the results by analyzing how reliably these elements can be detected and how accurately they are modeled. Full article
(This article belongs to the Special Issue Laser Sensing and Imaging)
Open AccessArticle Detection of Interference Phase by Digital Computation of Quadrature Signals in Homodyne Laser Interferometry
Sensors 2012, 12(10), 14095-14112; doi:10.3390/s121014095
Received: 31 August 2012 / Revised: 10 October 2012 / Accepted: 12 October 2012 / Published: 19 October 2012
Cited by 16 | PDF Full-text (480 KB) | HTML Full-text | XML Full-text
Abstract
We have proposed an approach to the interference phase extraction in the homodyne laser interferometry. The method employs a series of computational steps to reconstruct the signals for quadrature detection from an interference signal from a non-polarising interferometer sampled by a simple [...] Read more.
We have proposed an approach to the interference phase extraction in the homodyne laser interferometry. The method employs a series of computational steps to reconstruct the signals for quadrature detection from an interference signal from a non-polarising interferometer sampled by a simple photodetector. The complexity trade-off is the use of laser beam with frequency modulation capability. It is analytically derived and its validity and performance is experimentally verified. The method has proven to be a feasible alternative for the traditional homodyne detection since it performs with comparable accuracy, especially where the optical setup complexity is principal issue and the modulation of laser beam is not a heavy burden (e.g., in multi-axis sensor or laser diode based systems). Full article
(This article belongs to the Special Issue Laser Sensing and Imaging)
Open AccessArticle On-Site Sensor Recalibration of a Spinning Multi-Beam LiDAR System Using Automatically-Detected Planar Targets
Sensors 2012, 12(10), 13736-13752; doi:10.3390/s121013736
Received: 3 August 2012 / Revised: 27 September 2012 / Accepted: 8 October 2012 / Published: 12 October 2012
Cited by 7 | PDF Full-text (1112 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents a fully-automated method to establish a calibration dataset from on-site scans and recalibrate the intrinsic parameters of a spinning multi-beam 3-D scanner. The proposed method has been tested on a Velodyne HDL-64E S2 LiDAR system, which contains 64 rotating laser rangefinders. By time series analysis, we found that the collected range data have random measurement errors of around ±25 mm. In addition, the layered misalignment of scans among the rangefinders, which is identified as a systematic error, also increases the difficulty to accurately locate planar surfaces. We propose a temporal-spatial range data fusion algorithm, along with a robust RANSAC-based plane detection algorithm to address these issues. Furthermore, we formulate an alternative geometric interpretation of sensory data using linear parameters, which is advantageous for the calibration procedure. The linear representation allows the proposed method to be generalized to any LiDAR system that follows the rotating beam model. We also confirmed in this paper, that given effective calibration datasets, the pre-calibrated factory parameters can be further tuned to achieve significantly improved performance. After the optimization, the systematic error is noticeable lowered, and evaluation shows that the recalibrated parameters outperform the factory parameters with the RMS planar errors reduced by up to 49%. Full article
(This article belongs to the Special Issue Laser Sensing and Imaging)
Open AccessArticle Tree Height Growth Measurement with Single-Scan Airborne, Static Terrestrial and Mobile Laser Scanning
Sensors 2012, 12(9), 12798-12813; doi:10.3390/s120912798
Received: 16 July 2012 / Revised: 23 August 2012 / Accepted: 10 September 2012 / Published: 19 September 2012
Cited by 11 | PDF Full-text (804 KB) | HTML Full-text | XML Full-text
Abstract
This study explores the feasibility of applying single-scan airborne, static terrestrial and mobile laser scanning for improving the accuracy of tree height growth measurement. Specifically, compared to the traditional works on forest growth inventory with airborne laser scanning, two issues are regarded: [...] Read more.
This study explores the feasibility of applying single-scan airborne, static terrestrial and mobile laser scanning for improving the accuracy of tree height growth measurement. Specifically, compared to the traditional works on forest growth inventory with airborne laser scanning, two issues are regarded: “Can the new technique characterize the height growth for each individual tree?” and “Can this technique refine the minimum growth-discernable temporal interval further?” To solve these two puzzles, the sampling principles of the three laser scanning modes were first examined, and their error sources against the task of tree-top capturing were also analyzed. Next, the three-year growths of 58 Nordic maple trees (Crimson King) for test were intermittently surveyed with one type of laser scanning each time and then analyzed by statistics. The evaluations show that the height growth of each individual tree still cannot be reliably characterized even by single-scan terrestrial laser scanning, and statistical analysis is necessary in this scenario. After Gaussian regression, it is found that the minimum temporal interval with distinguishable tree height growths can be refined into one month based on terrestrial laser scanning, far better than the two years deduced in the previous works based on airborne laser scanning. The associated mean growth was detected to be about 0.12 m. Moreover, the parameter of tree height generally under-estimated by airborne and even mobile laser scanning can be relatively revised by means of introducing static terrestrial laser scanning data. Overall, the effectiveness of the proposed technique is primarily validated. Full article
(This article belongs to the Special Issue Laser Sensing and Imaging)
Open AccessArticle Laser Scanning Measurements on Trees for Logging Harvesting Operations
Sensors 2012, 12(7), 9273-9285; doi:10.3390/s120709273
Received: 18 May 2012 / Revised: 26 June 2012 / Accepted: 3 July 2012 / Published: 5 July 2012
Cited by 10 | PDF Full-text (494 KB) | HTML Full-text | XML Full-text
Abstract
Logging harvesters represent a set of high-performance modern forestry machinery, which can finish a series of continuous operations such as felling, delimbing, peeling, bucking and so forth with human intervention. It is found by experiment that during the process of the alignment [...] Read more.
Logging harvesters represent a set of high-performance modern forestry machinery, which can finish a series of continuous operations such as felling, delimbing, peeling, bucking and so forth with human intervention. It is found by experiment that during the process of the alignment of the harvesting head to capture the trunk, the operator needs a lot of observation, judgment and repeated operations, which lead to the time and fuel losses. In order to improve the operation efficiency and reduce the operating costs, the point clouds for standing trees are collected with a low-cost 2D laser scanner. A cluster extracting algorithm and filtering algorithm are used to classify each trunk from the point cloud. On the assumption that every cross section of the target trunk is approximate a standard circle and combining the information of an Attitude and Heading Reference System, the radii and center locations of the trunks in the scanning range are calculated by the Fletcher-Reeves conjugate gradient algorithm. The method is validated through experiments in an aspen forest, and the optimized calculation time consumption is compared with the previous work of other researchers. Moreover, the implementation of the calculation result for automotive capturing trunks by the harvesting head during the logging operation is discussed in particular. Full article
(This article belongs to the Special Issue Laser Sensing and Imaging)

Review

Jump to: Research

Open AccessReview Aspects of the Application of Cavity Enhanced Spectroscopy to Nitrogen Oxides Detection
Sensors 2013, 13(6), 7570-7598; doi:10.3390/s130607570
Received: 10 April 2013 / Revised: 2 May 2013 / Accepted: 27 May 2013 / Published: 10 June 2013
Cited by 5 | PDF Full-text (1669 KB) | HTML Full-text | XML Full-text
Abstract
This article presents design issues of high-sensitive laser absorption spectroscopy systems for nitrogen oxides (NOx) detection. Examples of our systems and their investigation results are also described. The constructed systems use one of the most sensitive methods, cavity enhanced absorption [...] Read more.
This article presents design issues of high-sensitive laser absorption spectroscopy systems for nitrogen oxides (NOx) detection. Examples of our systems and their investigation results are also described. The constructed systems use one of the most sensitive methods, cavity enhanced absorption spectroscopy (CEAS). They operate at different wavelength ranges using a blue—violet laser diode (410 nm) as well as quantum cascade lasers (5.27 µm and 4.53 µm). Each of them is configured as a one or two channel measurement device using, e.g., time division multiplexing and averaging. During the testing procedure, the main performance features such as detection limits and measurements uncertainties have been determined. The obtained results are 1 ppb NO2, 75 ppb NO and 45 ppb N2O. For all systems, the uncertainty of concentration measurements does not exceed a value of 13%. Some experiments with explosives are also discussed. A setup equipped with a concentrator of explosives vapours was used. The detection method is based either on the reaction of the sensors to the nitrogen oxides directly emitted by the explosives or on the reaction to the nitrogen oxides produced during thermal decomposition of explosive vapours. For TNT, PETN, RDX and HMX a detection limit better than 1 ng has been achieved. Full article
(This article belongs to the Special Issue Laser Sensing and Imaging)
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