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Special Issue "Laser Spectroscopy and Sensing"

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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 January 2010)

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

The special issue on "Laser Spectroscopy and Sensing" addresses following topics, but is not limited by:
  • Laser-based sensors for gases, liquids, and solid
  • Requirements: sensitivity, specificity, temporal resolution, in situ, remote, etc.
  • Mathematical analysis of multi-component spectra
  • UV vis. IR spectroscopy
  • Laser sources: tunable diode lasers, VCSELs and VECSELS, interband cascade lasers (ICLs), quantum cascade lasers (QCLs), lead salt diode lasers, nonlinear optical sources (difference frequency generation (DFG), optical parametric oscillators (OPOs), tuning performance, linewidth, etc.
  • Interaction of radiation with matter: absorption, scattering, fluorescence Measurements schemes: Multipass and intracavity absorption, photoacoustics, cavity ringdown, etc.
  • Application areas:
    • Isotope ratio determination
    • Environment: temporal and spatial distribution of trace gases and particulate matter, urban and rural areas
    • Agriculture and food science: dynamic control of atmosphere in green- and storage houses, surveillance of ripening, wilting and fermentation processes, toxic compounds like melamine, acrylamide, etc.
    • Industry: emission control, workplace safety, process monitoring, etc.

Published Papers (33 papers)

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Research

Jump to: Review

Open AccessArticle A Microring Resonator Sensor for Sensitive Detection of 1,3,5-Trinitrotoluene (TNT)
Sensors 2010, 10(7), 6788-6795; doi:10.3390/s100706788
Received: 6 April 2010 / Revised: 8 June 2010 / Accepted: 24 June 2010 / Published: 13 July 2010
Cited by 49 | PDF Full-text (378 KB) | HTML Full-text | XML Full-text
Abstract A microring resonator sensor device for sensitive detection of the explosive 1,3,5-trinitrotoluene (TNT) is presented. It is based on the combination of a silicon microring resonator and tailored receptor molecules. Full article
(This article belongs to the Special Issue Laser Spectroscopy and Sensing)
Open AccessArticle An Efficient and Compact Difference-Frequency-Generation Spectrometer and Its Application to 12CH3D/12CH4 Isotope Ratio Measurements
Sensors 2010, 10(7), 6612-6622; doi:10.3390/s100706612
Received: 4 February 2010 / Revised: 28 April 2010 / Accepted: 7 June 2010 / Published: 9 July 2010
Cited by 4 | PDF Full-text (314 KB) | HTML Full-text | XML Full-text
Abstract
We have developed an efficient and compact 3.4 μm difference-frequency-generation spectrometer using a 1.55 μm distributed feedback (DFB) laser diode, a 1.06 μm DFB laser diode, and a ridge-waveguide periodically poled lithium niobate. It is continuously tunable in the 30 cm–1 [...] Read more.
We have developed an efficient and compact 3.4 μm difference-frequency-generation spectrometer using a 1.55 μm distributed feedback (DFB) laser diode, a 1.06 μm DFB laser diode, and a ridge-waveguide periodically poled lithium niobate. It is continuously tunable in the 30 cm–1 span and is applied to 12CH3D/12CH4 isotope ratio measurements. The suitable pair of 12CH3D n4 pP(7,6) and 12CH4 ν24 R(6) F1(1) lines enabled us to determine their isotope ratio with a precision repeatability of 0.8‰ using a sample and a working standard of pure methane with an effective signal averaging time of 100 ms. Full article
(This article belongs to the Special Issue Laser Spectroscopy and Sensing)
Open AccessArticle Transversely Excited Multipass Photoacoustic Cell Using Electromechanical Film as Microphone
Sensors 2010, 10(6), 5294-5307; doi:10.3390/s100605294
Received: 19 April 2010 / Revised: 21 May 2010 / Accepted: 24 May 2010 / Published: 26 May 2010
Cited by 6 | PDF Full-text (262 KB) | HTML Full-text | XML Full-text
Abstract
A novel multipass photoacoustic cell with five stacked electromechanical films as a microphone has been constructed, tested and characterized. The photoacoustic cell is an open rectangular structure with two steel plates facing each other. The longitudinal acoustic resonances are excited transversely in [...] Read more.
A novel multipass photoacoustic cell with five stacked electromechanical films as a microphone has been constructed, tested and characterized. The photoacoustic cell is an open rectangular structure with two steel plates facing each other. The longitudinal acoustic resonances are excited transversely in an optical multipass configuration. A detection limit of 22 ppb (10−9) was achieved for flowing NO2 in N2 at normal pressure by using the maximum of 70 laser beams between the resonator plates. The corresponding minimum detectable absorption and the normalized noise-equivalent absorption coefficients were 2:2 × 10−7 cm−1 and 3:2 × 10−9 cm−1WHz−1/2, respectively. Full article
(This article belongs to the Special Issue Laser Spectroscopy and Sensing)
Open AccessArticle Comparative Laser Spectroscopy Diagnostics for Ancient Metallic Artefacts Exposed to Environmental Pollution
Sensors 2010, 10(5), 4926-4949; doi:10.3390/s100504926
Received: 3 February 2010 / Revised: 29 April 2010 / Accepted: 4 May 2010 / Published: 14 May 2010
Cited by 13 | PDF Full-text (2048 KB) | HTML Full-text | XML Full-text
Abstract
Metal artworks are subjected to corrosion and oxidation processes due to reactive agents present in the air, water and in the ground that these objects have been in contact with for hundreds of years. This is the case for archaeological metals that [...] Read more.
Metal artworks are subjected to corrosion and oxidation processes due to reactive agents present in the air, water and in the ground that these objects have been in contact with for hundreds of years. This is the case for archaeological metals that are recovered from excavation sites, as well as artefacts exposed to polluted air. Stabilization of the conservation state of these objects needs precise diagnostics of the accrued surface layers and identification of original, historical materials before further protective treatments, including safe laser cleaning of unwanted layers. This paper presents analyses of the chemical composition and stratigraphy of corrosion products with the use of laser induced breakdown spectroscopy (LIBS) and Raman spectroscopy. The discussion of the results is supported by material studies (SEM-EDS, XRF, ion-analyses). The tests were performed on several samples taken from original objects, including copper roofing from Wilanów Palace in Warsaw and Karol Poznański Palace in Łódź, bronze decorative figures from the Wilanów Palace gardens, and four archaeological examples of old jewellery (different copper alloys). Work has been performed as a part of the MATLAS project in the frames of EEA and Norway Grants (www.matlas.eu) and the results enable the comparison of the methodology and to elaborate the joint diagnostic procedures of the three project partner independent laboratories. Full article
(This article belongs to the Special Issue Laser Spectroscopy and Sensing)
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Open AccessArticle Diode Laser Detection of Greenhouse Gases in the Near-Infrared Region by Wavelength Modulation Spectroscopy: Pressure Dependence of the Detection Sensitivity
Sensors 2010, 10(5), 4686-4699; doi:10.3390/s100504686
Received: 27 January 2010 / Revised: 13 April 2010 / Accepted: 16 April 2010 / Published: 6 May 2010
Cited by 14 | PDF Full-text (502 KB) | HTML Full-text | XML Full-text
Abstract
We have investigated the pressure dependence of the detection sensitivity of CO2, N2O and CH4 using wavelength modulation spectroscopy (WMS) with distributed feed-back diode lasers in the near infrared region. The spectral line shapes and the background [...] Read more.
We have investigated the pressure dependence of the detection sensitivity of CO2, N2O and CH4 using wavelength modulation spectroscopy (WMS) with distributed feed-back diode lasers in the near infrared region. The spectral line shapes and the background noise of the second harmonics (2f) detection of the WMS were analyzed theoretically. We determined the optimum pressure conditions in the detection of CO2, N2O and CH4, by taking into consideration the background noise in the WMS. At the optimum total pressure for the detection of CO2, N2O and CH4, the limits of detection in the present system were determined. Full article
(This article belongs to the Special Issue Laser Spectroscopy and Sensing)
Open AccessArticle Spectroscopic Interpretation of PAH-Spectra in Minerals and Its Possible Application to Soil Monitoring
Sensors 2010, 10(4), 3868-3881; doi:10.3390/s100403868
Received: 3 February 2010 / Revised: 6 April 2010 / Accepted: 7 April 2010 / Published: 15 April 2010
Cited by 2 | PDF Full-text (597 KB) | HTML Full-text | XML Full-text
Abstract
In order to properly assess the feasibility of using Laser-Induced Fluorescence (LIF) spectroscopy for soil monitoring, the variation of fluorescence intensity due to the heterogeneity and complexity of soil media was investigated. Different soil minerals showed fluorescence spectral structures distinguishable from the [...] Read more.
In order to properly assess the feasibility of using Laser-Induced Fluorescence (LIF) spectroscopy for soil monitoring, the variation of fluorescence intensity due to the heterogeneity and complexity of soil media was investigated. Different soil minerals showed fluorescence spectral structures distinguishable from the contaminants, implying dissimilar interactions or the binding of contaminants on mineral surfaces. More interestingly, solvent and water addition showed different responses in the fluorescence spectral structure showing their effect on the interactions between contaminants and minerals. These results support the claim that the spectral structure contains information on contaminant-mineral interactions; therefore contaminants can be used as a fluorescence probe for these interactions. Full article
(This article belongs to the Special Issue Laser Spectroscopy and Sensing)
Open AccessArticle Optical Sensor for Characterizing the Phase Transition in Salted Solutions
Sensors 2010, 10(4), 3815-3823; doi:10.3390/s100403815
Received: 11 February 2010 / Revised: 27 February 2010 / Accepted: 17 March 2010 / Published: 14 April 2010
Cited by 8 | PDF Full-text (1779 KB) | HTML Full-text | XML Full-text
Abstract
We propose a new optical sensor to characterize the solid-liquid phase transition in salted solutions. The probe mainly consists of a Raman spectrometer that extracts the vibrational properties from the light scattered by the salty medium. The spectrum of the O-H stretching [...] Read more.
We propose a new optical sensor to characterize the solid-liquid phase transition in salted solutions. The probe mainly consists of a Raman spectrometer that extracts the vibrational properties from the light scattered by the salty medium. The spectrum of the O-H stretching band was shown to be strongly affected by the introduction of NaCl and the temperature change as well. A parameter SD defined as the ratio of the integrated intensities of two parts of this band allows to study the temperature and concentration dependences of the phase transition. Then, an easy and efficient signal processing and the exploitation of a modified Boltzmann equation give information on the phase transition. Validations were done on solutions with varying concentration of NaCl. Full article
(This article belongs to the Special Issue Laser Spectroscopy and Sensing)
Open AccessCommunication Laser Photoacoustic Detection of CO2 in Old Disc Tree-Rings
Sensors 2010, 10(4), 3305-3313; doi:10.3390/s100403305
Received: 29 December 2009 / Revised: 16 February 2010 / Accepted: 6 March 2010 / Published: 4 April 2010
Cited by 7 | PDF Full-text (315 KB) | HTML Full-text | XML Full-text
Abstract
A homemade CO2–laser photoacoustic spectrometer has been used for monitoring CO2 in gas samples extracted under vacuum from the wood of old spruce disc tree-rings for a ~60 year series. The experimental results show that (1) the CO2 [...] Read more.
A homemade CO2–laser photoacoustic spectrometer has been used for monitoring CO2 in gas samples extracted under vacuum from the wood of old spruce disc tree-rings for a ~60 year series. The experimental results show that (1) the CO2 concentration exhibits annual trends correlated with an increase in atmospheric CO2 in a number of cases; (2) at the time when the annual CO2 trend changes from positive to negative, the annual tree-ring stable carbon isotope ratios (δ13C) of CO2 change as well; (3) the disc tree-ring widths are observed to decrease in most cases where the annual CO2 increased; (4) simultaneously with the annual CO2 variation, annual H2O distribution was detected in gas samples of the wood tree-rings of one spruce disc. The observed patterns of the annual CO2 distribution in the disc tree-rings are assumed to be the evidence of the impact of the atmospheric CO2 increase. In other words, a change in the concentration gradient between the stem and the atmospheric CO2 may lead to a gradual CO2 accumulation in the stem because of a decrease in the diffusion rate and to a change in the tree parameters. Full article
(This article belongs to the Special Issue Laser Spectroscopy and Sensing)
Open AccessArticle Discriminant Analysis of Raman Spectra for Body Fluid Identification for Forensic Purposes
Sensors 2010, 10(4), 2869-2884; doi:10.3390/s100402869
Received: 11 February 2010 / Revised: 13 March 2010 / Accepted: 23 March 2010 / Published: 29 March 2010
Cited by 40 | PDF Full-text (880 KB) | HTML Full-text | XML Full-text
Abstract
Detection and identification of blood, semen and saliva stains, the most common body fluids encountered at a crime scene, are very important aspects of forensic science today. This study targets the development of a nondestructive, confirmatory method for body fluid identification based [...] Read more.
Detection and identification of blood, semen and saliva stains, the most common body fluids encountered at a crime scene, are very important aspects of forensic science today. This study targets the development of a nondestructive, confirmatory method for body fluid identification based on Raman spectroscopy coupled with advanced statistical analysis. Dry traces of blood, semen and saliva obtained from multiple donors were probed using a confocal Raman microscope with a 785-nm excitation wavelength under controlled laboratory conditions. Results demonstrated the capability of Raman spectroscopy to identify an unknown substance to be semen, blood or saliva with high confidence. Full article
(This article belongs to the Special Issue Laser Spectroscopy and Sensing)
Open AccessArticle Infrared Spectroscopy on Smoke Produced by Cauterization of Animal Tissue
Sensors 2010, 10(4), 2694-2708; doi:10.3390/s100402694
Received: 24 January 2010 / Revised: 20 February 2010 / Accepted: 19 March 2010 / Published: 26 March 2010
Cited by 10 | PDF Full-text (7238 KB) | HTML Full-text | XML Full-text
Abstract
In view of in vivo surgical smoke studies a difference-frequency-generation (DFG) laser spectrometer (spectral range 2900–3144 cm-1) and a Fourier-transform infrared (FTIR) spectrometer were employed for infrared absorption spectroscopy. The chemical composition of smoke produced in vitro with an electroknife [...] Read more.
In view of in vivo surgical smoke studies a difference-frequency-generation (DFG) laser spectrometer (spectral range 2900–3144 cm-1) and a Fourier-transform infrared (FTIR) spectrometer were employed for infrared absorption spectroscopy. The chemical composition of smoke produced in vitro with an electroknife by cauterization of different animal tissues in different atmospheres was investigated. Average concentrations derived are: water vapor (0.87%), methane (20 ppm), ethane (4.8 ppm), ethene (17 ppm), carbon monoxide (190 ppm), nitric oxide (25 ppm), nitrous oxide (40 ppm), ethyne (50 ppm) and hydrogen cyanide (25 ppm). No correlation between smoke composition and the atmosphere or the kind of cauterized tissue was found. Full article
(This article belongs to the Special Issue Laser Spectroscopy and Sensing)
Open AccessArticle Following Enzyme Activity with Infrared Spectroscopy
Sensors 2010, 10(4), 2626-2637; doi:10.3390/s100402626
Received: 24 January 2010 / Revised: 20 February 2010 / Accepted: 6 March 2010 / Published: 25 March 2010
Cited by 19 | PDF Full-text (175 KB) | HTML Full-text | XML Full-text
Abstract
Fourier transform infrared (FTIR) spectroscopy provides a direct, "on-line" monitor of enzymatic reactions. Measurement of enzymatic activity is based on the fact that the infrared spectra of reactants and products of an enzymatic reaction are usually different. Several examples are given using [...] Read more.
Fourier transform infrared (FTIR) spectroscopy provides a direct, "on-line" monitor of enzymatic reactions. Measurement of enzymatic activity is based on the fact that the infrared spectra of reactants and products of an enzymatic reaction are usually different. Several examples are given using the enzymes pyruvate kinase, fumarase and alcohol dehydrogenase. The main advantage of the infrared method is that it observes the reaction of interest directly, i.e.,no activity assay is required to convert the progress of the reaction into an observable quantity. Full article
(This article belongs to the Special Issue Laser Spectroscopy and Sensing)
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Open AccessArticle Estimation of Biological Oxygen Demand and Chemical Oxygen Demand for Combined Sewer Systems Using Synchronous Fluorescence Spectra
Sensors 2010, 10(4), 2460-2471; doi:10.3390/s100402460
Received: 21 January 2010 / Revised: 1 March 2010 / Accepted: 6 March 2010 / Published: 24 March 2010
Cited by 20 | PDF Full-text (222 KB) | HTML Full-text | XML Full-text
Abstract
Real-time monitoring of water quality for sewer system is required for efficient sewer network design because it provides information on the precise loading of pollutant to wastewater treatment facilities and the impact of loading on receiving water. In this study, synchronous fluorescence [...] Read more.
Real-time monitoring of water quality for sewer system is required for efficient sewer network design because it provides information on the precise loading of pollutant to wastewater treatment facilities and the impact of loading on receiving water. In this study, synchronous fluorescence spectra and its first derivatives were investigated using a number of wastewater samples collected in sewer systems in urban and non-urban areas, and the optimum fluorescence feature was explored for the estimation of biochemical oxygen demand (BOD) and chemical oxygen demand (COD) concentrations of sewer samples. The temporal variations in BOD and COD showed a regular pattern for urban areas whereas they were relatively irregular for non-urban areas. Irrespective of the sewer pipes and the types of the areas, two distinct peaks were identified from the synchronous fluorescence spectra, which correspond to protein-like fluorescence (PLF) and humic-like fluorescence (HLF), respectively. HLF in sewer samples appears to be associated with fluorescent whitening agents. Five fluorescence characteristics were selected from the synchronous spectra and the first-derivatives. Among the selected fluorescence indices, a peak in the PLF region (i.e., Index I) showed the highest correlation coefficient with both BOD and COD. A multiple regression approach based on suspended solid (SS) and Index I used to compensate for the contribution of SS to BOD and COD revealed an improvement in the estimation capability, showing good correlation coefficients of 0.92 and 0.94 for BOD and COD, respectively. Full article
(This article belongs to the Special Issue Laser Spectroscopy and Sensing)
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Open AccessArticle Trapped Ion Oscillation Frequencies as Sensors for Spectroscopy
Sensors 2010, 10(3), 2169-2187; doi:10.3390/s100302169
Received: 18 January 2010 / Revised: 2 March 2010 / Accepted: 10 March 2010 / Published: 16 March 2010
Cited by 7 | PDF Full-text (338 KB) | HTML Full-text | XML Full-text
Abstract
The oscillation frequencies of charged particles in a Penning trap can serve as sensors for spectroscopy when additional field components are introduced to the magnetic and electric fields used for confinement. The presence of so-called “magnetic bottles” and specific electric anharmonicities creates [...] Read more.
The oscillation frequencies of charged particles in a Penning trap can serve as sensors for spectroscopy when additional field components are introduced to the magnetic and electric fields used for confinement. The presence of so-called “magnetic bottles” and specific electric anharmonicities creates calculable energy-dependences of the oscillation frequencies in the radiofrequency domain which may be used to detect the absorption or emission of photons both in the microwave and optical frequency domains. The precise electronic measurement of these oscillation frequencies therefore represents an optical sensor for spectroscopy. We discuss possible applications for precision laser and microwave spectroscopy and their role in the determination of magnetic moments and excited state lifetimes. Also, the trap-assisted measurement of radiative nuclear de-excitations in the X-ray domain is discussed. This way, the different applications range over more than 12 orders of magnitude in the detectable photon energies, from below μeV in the microwave domain to beyond MeV in the X-ray domain. Full article
(This article belongs to the Special Issue Laser Spectroscopy and Sensing)
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Open AccessArticle Quantum Cascade Laser-Based Photoacoustic Spectroscopy for Trace Vapor Detection and Molecular Discrimination
Sensors 2010, 10(3), 1986-2002; doi:10.3390/s100301986
Received: 1 February 2010 / Revised: 12 February 2010 / Accepted: 28 February 2010 / Published: 11 March 2010
Cited by 35 | PDF Full-text (290 KB) | HTML Full-text | XML Full-text
Abstract
We report on the development of a microelectromechanical systems (MEMS)-scale photoacoustic sensor for the detection of trace gases. A mid-infrared quantum cascade laser (QCL) was used to determine detection limits for acetic acid, acetone, 1,4-dioxane, and vinyl acetate. The source was continuously [...] Read more.
We report on the development of a microelectromechanical systems (MEMS)-scale photoacoustic sensor for the detection of trace gases. A mid-infrared quantum cascade laser (QCL) was used to determine detection limits for acetic acid, acetone, 1,4-dioxane, and vinyl acetate. The source was continuously tunable from 1015 cm-1 to 1240 cm-1, allowing for the collection of photoacoustic vibrational spectra for these gases. Exceptional agreement between the measured photoacoustic spectra and the infrared spectra for acetic acid, acetone, 1,4-dioxane, and vinyl acetate was observed. Partial least-squares (PLS) regression was used to develop an algorithm for classification of these compounds based solely on photoacoustic spectra. Full article
(This article belongs to the Special Issue Laser Spectroscopy and Sensing)
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Open AccessArticle Semiconductor Laser Multi-Spectral Sensing and Imaging
Sensors 2010, 10(1), 544-583; doi:10.3390/s100100544
Received: 23 November 2009 / Revised: 14 December 2009 / Accepted: 5 January 2010 / Published: 13 January 2010
Cited by 3 | PDF Full-text (2239 KB) | HTML Full-text | XML Full-text
Abstract
Multi-spectral laser imaging is a technique that can offer a combination of the laser capability of accurate spectral sensing with the desirable features of passive multispectral imaging. The technique can be used for detection, discrimination, and identification of objects by their spectral [...] Read more.
Multi-spectral laser imaging is a technique that can offer a combination of the laser capability of accurate spectral sensing with the desirable features of passive multispectral imaging. The technique can be used for detection, discrimination, and identification of objects by their spectral signature. This article describes and reviews the development and evaluation of semiconductor multi-spectral laser imaging systems. Although the method is certainly not specific to any laser technology, the use of semiconductor lasers is significant with respect to practicality and affordability. More relevantly, semiconductor lasers have their own characteristics; they offer excellent wavelength diversity but usually with modest power. Thus, system design and engineering issues are analyzed for approaches and trade-offs that can make the best use of semiconductor laser capabilities in multispectral imaging. A few systems were developed and the technique was tested and evaluated on a variety of natural and man-made objects. It was shown capable of high spectral resolution imaging which, unlike non-imaging point sensing, allows detecting and discriminating objects of interest even without a priori spectroscopic knowledge of the targets. Examples include material and chemical discrimination. It was also shown capable of dealing with the complexity of interpreting diffuse scattered spectral images and produced results that could otherwise be ambiguous with conventional imaging. Examples with glucose and spectral imaging of drug pills were discussed. Lastly, the technique was shown with conventional laser spectroscopy such as wavelength modulation spectroscopy to image a gas (CO). These results suggest the versatility and power of multi-spectral laser imaging, which can be practical with the use of semiconductor lasers. Full article
(This article belongs to the Special Issue Laser Spectroscopy and Sensing)
Open AccessArticle Perfluorinated Plastic Optical Fiber Tapers for Evanescent Wave Sensing
Sensors 2009, 9(12), 10423-10433; doi:10.3390/s91210423
Received: 26 October 2009 / Revised: 27 November 2009 / Accepted: 11 December 2009 / Published: 22 December 2009
Cited by 27 | PDF Full-text (259 KB) | HTML Full-text | XML Full-text
Abstract
In this work we describe the fabrication and the characterization of perfluorinated plastic-cladded optical fiber tapers. The heat-and-pull procedure has been used to fabricate symmetric tapers. Devices with different taper ratio have been produced and the repeatability of the process has been [...] Read more.
In this work we describe the fabrication and the characterization of perfluorinated plastic-cladded optical fiber tapers. The heat-and-pull procedure has been used to fabricate symmetric tapers. Devices with different taper ratio have been produced and the repeatability of the process has been verified. The very low refractive indexes of the core-cladding perfluorinated polymers (n = 1.35–1.34) permit a strong enhancement of the evanescent wave power fraction in aqueous environments (n = 1.33), making them very attractive for evanescent wave sensing. The tapers have been characterized carrying out evanescent field absorbance measurements with different concentrations of methylene blue in water and fluorescence collection measurements in an aqueous solution containing Cy5 dye. A good sensitivity, tightly related to the low refractive index of the core-cladding materials and the geometrical profile, has been shown. Full article
(This article belongs to the Special Issue Laser Spectroscopy and Sensing)
Open AccessArticle Recent Developments of an Opto-Electronic THz Spectrometer for High-Resolution Spectroscopy
Sensors 2009, 9(11), 9039-9057; doi:10.3390/s91109039
Received: 21 September 2009 / Revised: 13 October 2009 / Accepted: 29 October 2009 / Published: 13 November 2009
Cited by 16 | PDF Full-text (1016 KB) | HTML Full-text | XML Full-text
Abstract
A review is provided of sources and detectors that can be employed in the THz range before the description of an opto-electronic source of monochromatic THz radiation. The realized spectrometer has been applied to gas phase spectroscopy. Air-broadening coefficients of HCN are [...] Read more.
A review is provided of sources and detectors that can be employed in the THz range before the description of an opto-electronic source of monochromatic THz radiation. The realized spectrometer has been applied to gas phase spectroscopy. Air-broadening coefficients of HCN are determined and the insensitivity of this technique to aerosols is demonstrated by the analysis of cigarette smoke. A multiple pass sample cell has been used to obtain a sensitivity improvement allowing transitions of the volatile organic compounds to be observed. A solution to the frequency metrology is presented and promises to yield accurate molecular line center measurements. Full article
(This article belongs to the Special Issue Laser Spectroscopy and Sensing)
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Open AccessArticle Material Limitations on the Detection Limit in Refractometry
Sensors 2009, 9(11), 8382-8390; doi:10.3390/s91108382
Received: 3 July 2009 / Revised: 22 September 2009 / Accepted: 29 September 2009 / Published: 26 October 2009
Cited by 5 | PDF Full-text (342 KB) | HTML Full-text | XML Full-text
Abstract
We discuss the detection limit for refractometric sensors relying on high-Q optical cavities and show that the ultimate classical detection limit is given by min {Δn} ≳ η with n + iη being the complex refractive index of [...] Read more.
We discuss the detection limit for refractometric sensors relying on high-Q optical cavities and show that the ultimate classical detection limit is given by min {Δn} ≳ η with n + iη being the complex refractive index of the material under refractometric investigation. Taking finite Q factors and filling fractions into account, the detection limit declines. As an example we discuss the fundamental limits of silicon-based high-Q resonators, such as photonic crystal resonators, for sensing in a bio-liquid environment, such as a water buffer. In the transparency window (λ ≳ 1100 nm) of silicon the detection limit becomes almost independent on the filling fraction, while in the visible, the detection limit depends strongly on the filling fraction because the silicon absorbs strongly. Full article
(This article belongs to the Special Issue Laser Spectroscopy and Sensing)
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Review

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Open AccessReview Quantum Cascade Laser Absorption Spectroscopy as a Plasma Diagnostic Tool: An Overview
Sensors 2010, 10(7), 6861-6900; doi:10.3390/s100706861
Received: 8 June 2010 / Revised: 25 June 2010 / Accepted: 10 July 2010 / Published: 16 July 2010
Cited by 33 | PDF Full-text (1025 KB) | HTML Full-text | XML Full-text
Abstract
The recent availability of thermoelectrically cooled pulsed and continuous wave quantum and inter-band cascade lasers in the mid-infrared spectral region has led to significant improvements and new developments in chemical sensing techniques using in-situ laser absorption spectroscopy for plasma diagnostic purposes. The [...] Read more.
The recent availability of thermoelectrically cooled pulsed and continuous wave quantum and inter-band cascade lasers in the mid-infrared spectral region has led to significant improvements and new developments in chemical sensing techniques using in-situ laser absorption spectroscopy for plasma diagnostic purposes. The aim of this article is therefore two-fold: (i) to summarize the challenges which arise in the application of quantum cascade lasers in such environments, and, (ii) to provide an overview of recent spectroscopic results (encompassing cavity enhanced methods) obtained in different kinds of plasma used in both research and industry. Full article
(This article belongs to the Special Issue Laser Spectroscopy and Sensing)
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Open AccessReview Recent Applications of Fluorescence Recovery after Photobleaching (FRAP) to Membrane Bio-Macromolecules
Sensors 2010, 10(6), 5927-5948; doi:10.3390/s100605927
Received: 20 April 2010 / Revised: 10 May 2010 / Accepted: 28 May 2010 / Published: 10 June 2010
Cited by 18 | PDF Full-text (425 KB) | HTML Full-text | XML Full-text
Abstract
This review examines some recent applications of fluorescence recovery after photobleaching (FRAP) to biopolymers, while mainly focusing on membrane protein studies. Initially, we discuss the lateral diffusion of membrane proteins, as measured by FRAP. Then, we talk about the use of FRAP [...] Read more.
This review examines some recent applications of fluorescence recovery after photobleaching (FRAP) to biopolymers, while mainly focusing on membrane protein studies. Initially, we discuss the lateral diffusion of membrane proteins, as measured by FRAP. Then, we talk about the use of FRAP to probe interactions between membrane proteins by obtaining fundamental information such as geometry and stoichiometry of the interacting complex. Afterwards, we discuss some applications of FRAP at the cellular level as well as the level of organisms. We conclude by comparing diffusion coefficients obtained by FRAP and several other alternative methods. Full article
(This article belongs to the Special Issue Laser Spectroscopy and Sensing)
Open AccessReview Methodology of Pulsed Photoacoustics and Its Application to Probe Photosystems and Receptors
Sensors 2010, 10(6), 5642-5667; doi:10.3390/s100605642
Received: 23 February 2010 / Revised: 27 May 2010 / Accepted: 27 May 2010 / Published: 3 June 2010
Cited by 6 | PDF Full-text (802 KB) | HTML Full-text | XML Full-text
Abstract
We review recent advances in the methodology of pulsed time-resolved photoacoustics and its application to studies of photosynthetic reaction centers and membrane receptors such as the G protein-coupled receptor rhodopsin. The experimental parameters accessible to photoacoustics include molecular volume change and photoreaction [...] Read more.
We review recent advances in the methodology of pulsed time-resolved photoacoustics and its application to studies of photosynthetic reaction centers and membrane receptors such as the G protein-coupled receptor rhodopsin. The experimental parameters accessible to photoacoustics include molecular volume change and photoreaction enthalpy change. Light-driven volume change secondary to protein conformational changes or electrostriction is directly related to the photoreaction and thus can be a useful measurement of activity and function. The enthalpy changes of the photochemical reactions observed can be measured directly by photoacoustics. With the measurement of enthalpy change, the reaction entropy can also be calculated when free energy is known. Dissecting the free energy of a photoreaction into enthalpic and entropic components may provide critical information about photoactivation mechanisms of photosystems and photoreceptors. The potential limitations and future applications of time-resolved photoacoustics are also discussed. Full article
(This article belongs to the Special Issue Laser Spectroscopy and Sensing)
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Open AccessReview Effect of Atmospheric Conditions on LIBS Spectra
Sensors 2010, 10(5), 4907-4925; doi:10.3390/s100504907
Received: 30 March 2010 / Revised: 4 May 2010 / Accepted: 10 May 2010 / Published: 14 May 2010
Cited by 54 | PDF Full-text (1294 KB) | HTML Full-text | XML Full-text
Abstract
Laser-induced breakdown spectroscopy (LIBS) is typically performed at ambient Earth atmospheric conditions. However, interest in LIBS in other atmospheric conditions has increased in recent years, especially for use in space exploration (e.g., Mars and Lunar) or to improve resolution for isotopic signatures. [...] Read more.
Laser-induced breakdown spectroscopy (LIBS) is typically performed at ambient Earth atmospheric conditions. However, interest in LIBS in other atmospheric conditions has increased in recent years, especially for use in space exploration (e.g., Mars and Lunar) or to improve resolution for isotopic signatures. This review focuses on what has been reported about the performance of LIBS in reduced pressure environments as well as in various gases other than air. Full article
(This article belongs to the Special Issue Laser Spectroscopy and Sensing)
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Open AccessReview Generation and Amplification of Tunable Multicolored Femtosecond Laser Pulses by Using Cascaded Four-Wave Mixing in Transparent Bulk Media
Sensors 2010, 10(5), 4296-4341; doi:10.3390/s100504296
Received: 22 January 2010 / Revised: 11 April 2010 / Accepted: 16 April 2010 / Published: 29 April 2010
Cited by 13 | PDF Full-text (2995 KB) | HTML Full-text | XML Full-text
Abstract
We have reviewed the generation and amplification of wavelength-tunable multicolored femtosecond laser pulses using cascaded four-wave mixing (CFWM) in transparent bulk media, mainly concentrating on our recent work. Theoretical analysis and calculations based on the phase-matching condition could explain well the process [...] Read more.
We have reviewed the generation and amplification of wavelength-tunable multicolored femtosecond laser pulses using cascaded four-wave mixing (CFWM) in transparent bulk media, mainly concentrating on our recent work. Theoretical analysis and calculations based on the phase-matching condition could explain well the process semi-quantitatively. The experimental studies showed: (1) as many as fifteen spectral up-shifted and two spectral down-shifted sidebands were obtained simultaneously with spectral bandwidth broader than 1.8 octaves from near ultraviolet (360 nm) to near infrared (1.2 μm); (2) the obtained sidebands were spatially separated well and had extremely high beam quality with M2 factor better than 1.1; (3) the wavelengths of the generated multicolor sidebands could be conveniently tuned by changing the crossing angle or simply replacing with different media; (4) as short as 15-fs negatively chirped or nearly transform limited 20-fs multicolored femtosecond pulses were obtained when one of the two input beams was negatively chirped and the other was positively chirped; (5) the pulse energy of the sideband can reach a μJ level with power stability better than 1% RMS; (6) broadband two-dimensional (2-D) multicolored arrays with more than ten periodic columns and more than ten rows were generated in a sapphire plate; (7) the obtained sidebands could be simultaneously spectra broadened and power amplified in another bulk medium by using cross-phase modulation (XPM) in conjunction with four-wave optical parametric amplification (FOPA). The characterization showed that this is interesting and the CFWM sidebands generated by this novel method have good enough qualities in terms of power stability, beam quality, and temporal features suited to various experiments such as ultrafast multicolor time-resolved spectroscopy and multicolor-excitation nonlinear microscopy. Full article
(This article belongs to the Special Issue Laser Spectroscopy and Sensing)
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Open AccessReview Ultrafast Laser-Based Spectroscopy and Sensing: Applications in LIBS, CARS, and THz Spectroscopy
Sensors 2010, 10(5), 4342-4372; doi:10.3390/s100504342
Received: 1 March 2010 / Revised: 30 March 2010 / Accepted: 9 April 2010 / Published: 29 April 2010
Cited by 29 | PDF Full-text (1089 KB) | HTML Full-text | XML Full-text
Abstract
Ultrafast pulsed lasers find application in a range of spectroscopy and sensing techniques including laser induced breakdown spectroscopy (LIBS), coherent Raman spectroscopy, and terahertz (THz) spectroscopy. Whether based on absorption or emission processes, the characteristics of these techniques are heavily influenced by [...] Read more.
Ultrafast pulsed lasers find application in a range of spectroscopy and sensing techniques including laser induced breakdown spectroscopy (LIBS), coherent Raman spectroscopy, and terahertz (THz) spectroscopy. Whether based on absorption or emission processes, the characteristics of these techniques are heavily influenced by the use of ultrafast pulses in the signal generation process. Depending on the energy of the pulses used, the essential laser interaction process can primarily involve lattice vibrations, molecular rotations, or a combination of excited states produced by laser heating. While some of these techniques are currently confined to sensing at close ranges, others can be implemented for remote spectroscopic sensing owing principally to the laser pulse duration. We present a review of ultrafast laser-based spectroscopy techniques and discuss the use of these techniques to current and potential chemical and environmental sensing applications. Full article
(This article belongs to the Special Issue Laser Spectroscopy and Sensing)
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Open AccessReview Real-Time Time-Frequency Two-Dimensional Imaging of Ultrafast Transient Signals in Solid-State Organic Materials
Sensors 2010, 10(5), 4253-4269; doi:10.3390/s100504253
Received: 28 February 2010 / Revised: 18 March 2010 / Accepted: 5 April 2010 / Published: 28 April 2010
Cited by 5 | PDF Full-text (596 KB) | HTML Full-text | XML Full-text
Abstract
In this review, we demonstrate a real-time time-frequency two-dimensional (2D) pump-probe imaging spectroscopy implemented on a single shot basis applicable to excited-state dynamics in solid-state organic and biological materials. Using this technique, we could successfully map ultrafast time-frequency 2D transient absorption signals [...] Read more.
In this review, we demonstrate a real-time time-frequency two-dimensional (2D) pump-probe imaging spectroscopy implemented on a single shot basis applicable to excited-state dynamics in solid-state organic and biological materials. Using this technique, we could successfully map ultrafast time-frequency 2D transient absorption signals of β-carotene in solid films with wide temporal and spectral ranges having very short accumulation time of 20 ms per unit frame. The results obtained indicate the high potential of this technique as a powerful and unique spectroscopic tool to observe ultrafast excited-state dynamics of organic and biological materials in solid-state, which undergo rapid photodegradation. Full article
(This article belongs to the Special Issue Laser Spectroscopy and Sensing)
Open AccessReview Structures and Encapsulation Motifs of Functional Molecules Probed by Laser Spectroscopic and Theoretical Methods
Sensors 2010, 10(4), 3519-3548; doi:10.3390/s100403519
Received: 29 January 2010 / Revised: 20 February 2010 / Accepted: 8 March 2010 / Published: 8 April 2010
Cited by 13 | PDF Full-text (1845 KB) | HTML Full-text | XML Full-text
Abstract
We report laser spectroscopic and computational studies of host/guest hydration interactions between functional molecules (hosts) and water (guest) in supersonic jets. The examined hosts include dibenzo-18-crown-6-ether (DB18C6), benzo-18-crown-6-ether (B18C6) and calix[4]arene (C4A). The gaseous complexes between the functional molecular hosts and water [...] Read more.
We report laser spectroscopic and computational studies of host/guest hydration interactions between functional molecules (hosts) and water (guest) in supersonic jets. The examined hosts include dibenzo-18-crown-6-ether (DB18C6), benzo-18-crown-6-ether (B18C6) and calix[4]arene (C4A). The gaseous complexes between the functional molecular hosts and water are generated under jet-cooled conditions. Various laser spectroscopic methods are applied for these species: the electronic spectra are observed by laser-induced fluorescence (LIF), mass-selected resonance enhanced multiphoton ionization (REMPI) and ultraviolet-ultraviolet hole-burning (UV-UV HB) spectroscopy, whereas the vibrational spectra for each individual species are observed by infrared-ultraviolet double resonance (IR-UV DR) spectroscopy. The obained results are analyzed by first principles electronic structure calculations. We discuss the conformations of the host molecules, the structures of the complexes, and key interactions forming the specific complexes. Full article
(This article belongs to the Special Issue Laser Spectroscopy and Sensing)
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Open AccessReview DFB Lasers Between 760 nm and 16 µm for Sensing Applications
Sensors 2010, 10(4), 2492-2510; doi:10.3390/s100402492
Received: 20 January 2010 / Revised: 22 February 2010 / Accepted: 6 March 2010 / Published: 24 March 2010
Cited by 56 | PDF Full-text (764 KB) | HTML Full-text | XML Full-text
Abstract
Recent years have shown the importance of tunable semiconductor lasers in optical sensing. We describe the status quo concerning DFB laser diodes between 760 nm and 3,000 nm as well as new developments aiming for up to 80 nm tuning range in [...] Read more.
Recent years have shown the importance of tunable semiconductor lasers in optical sensing. We describe the status quo concerning DFB laser diodes between 760 nm and 3,000 nm as well as new developments aiming for up to 80 nm tuning range in this spectral region. Furthermore we report on QCL between 3 µm and 16 µm and present new developments. An overview of the most interesting applications using such devices is given at the end of this paper. Full article
(This article belongs to the Special Issue Laser Spectroscopy and Sensing)
Open AccessReview Raman Spectroscopy and Related Techniques in Biomedicine
Sensors 2010, 10(3), 1871-1889; doi:10.3390/s100301871
Received: 27 January 2010 / Revised: 21 February 2010 / Accepted: 1 March 2010 / Published: 9 March 2010
Cited by 42 | PDF Full-text (2920 KB) | HTML Full-text | XML Full-text
Abstract
In this review we describe label-free optical spectroscopy techniques which are able to non-invasively measure the (bio)chemistry in biological systems. Raman spectroscopy uses visible or near-infrared light to measure a spectrum of vibrational bonds in seconds. Coherent anti-Stokes Raman (CARS) microscopy and [...] Read more.
In this review we describe label-free optical spectroscopy techniques which are able to non-invasively measure the (bio)chemistry in biological systems. Raman spectroscopy uses visible or near-infrared light to measure a spectrum of vibrational bonds in seconds. Coherent anti-Stokes Raman (CARS) microscopy and stimulated Raman loss (SRL) microscopy are orders of magnitude more efficient than Raman spectroscopy, and are able to acquire high quality chemically-specific images in seconds. We discuss the benefits and limitations of all techniques, with particular emphasis on applications in biomedicine—both in vivo (using fiber endoscopes) and in vitro (in optical microscopes). Full article
(This article belongs to the Special Issue Laser Spectroscopy and Sensing)
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Open AccessReview Optical Fiber Sensing Based on Reflection Laser Spectroscopy
Sensors 2010, 10(3), 1823-1845; doi:10.3390/s100301823
Received: 5 January 2010 / Revised: 3 February 2010 / Accepted: 5 February 2010 / Published: 5 March 2010
Cited by 20 | PDF Full-text (2387 KB) | HTML Full-text | XML Full-text
Abstract
An overview on high-resolution and fast interrogation of optical-fiber sensors relying on laser reflection spectroscopy is given. Fiber Bragg-gratings (FBGs) and FBG resonators built in fibers of different types are used for strain, temperature and acceleration measurements using heterodyne-detection and optical frequency-locking [...] Read more.
An overview on high-resolution and fast interrogation of optical-fiber sensors relying on laser reflection spectroscopy is given. Fiber Bragg-gratings (FBGs) and FBG resonators built in fibers of different types are used for strain, temperature and acceleration measurements using heterodyne-detection and optical frequency-locking techniques. Silica fiber-ring cavities are used for chemical sensing based on evanescent-wave spectroscopy. Various arrangements for signal recovery and noise reduction, as an extension of most typical spectroscopic techniques, are illustrated and results on detection performances are presented. Full article
(This article belongs to the Special Issue Laser Spectroscopy and Sensing)
Open AccessReview Chemical Sensing Using Fiber Cavity Ring-Down Spectroscopy
Sensors 2010, 10(3), 1716-1742; doi:10.3390/s100301716
Received: 15 December 2009 / Revised: 23 January 2010 / Accepted: 6 February 2010 / Published: 2 March 2010
Cited by 48 | PDF Full-text (1705 KB) | HTML Full-text | XML Full-text
Abstract
Waveguide-based cavity ring-down spectroscopy (CRD) can be used for quantitative measurements of chemical concentrations in small amounts of liquid, in gases or in films. The change in ring-down time can be correlated to analyte concentration when using fiber optic sensing elements that [...] Read more.
Waveguide-based cavity ring-down spectroscopy (CRD) can be used for quantitative measurements of chemical concentrations in small amounts of liquid, in gases or in films. The change in ring-down time can be correlated to analyte concentration when using fiber optic sensing elements that change their attenuation in dependence of either sample absorption or refractive index. Two types of fiber cavities, i.e., fiber loops and fiber strands containing reflective elements, are distinguished. Both types of cavities were coupled to a variety of chemical sensor elements, which are discussed and compared. Full article
(This article belongs to the Special Issue Laser Spectroscopy and Sensing)
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Open AccessReview Laser Spectroscopy for Atmospheric and Environmental Sensing
Sensors 2009, 9(12), 10447-10512; doi:10.3390/s91210447
Received: 18 November 2009 / Accepted: 2 December 2009 / Published: 22 December 2009
Cited by 36 | PDF Full-text (1074 KB) | HTML Full-text | XML Full-text
Abstract
Lasers and laser spectroscopic techniques have been extensively used in several applications since their advent, and the subject has been reviewed extensively in the last several decades. This review is focused on three areas of laser spectroscopic applications in atmospheric and environmental [...] Read more.
Lasers and laser spectroscopic techniques have been extensively used in several applications since their advent, and the subject has been reviewed extensively in the last several decades. This review is focused on three areas of laser spectroscopic applications in atmospheric and environmental sensing; namely laser-induced fluorescence (LIF), cavity ring-down spectroscopy (CRDS), and photoluminescence (PL) techniques used in the detection of solids, liquids, aerosols, trace gases, and volatile organic compounds (VOCs). Full article
(This article belongs to the Special Issue Laser Spectroscopy and Sensing)
Open AccessReview Photoacoustic Techniques for Trace Gas Sensing Based on Semiconductor Laser Sources
Sensors 2009, 9(12), 9616-9628; doi:10.3390/s91209616
Received: 9 October 2009 / Revised: 19 November 2009 / Accepted: 23 November 2009 / Published: 2 December 2009
Cited by 62 | PDF Full-text (356 KB) | HTML Full-text | XML Full-text
Abstract The paper provides an overview on the use of photoacoustic sensors based on semiconductor laser sources for the detection of trace gases. We review the results obtained using standard, differential and quartz enhanced photoacoustic techniques. Full article
(This article belongs to the Special Issue Laser Spectroscopy and Sensing)
Open AccessReview Fiber Loop Ringdown — a Time-Domain Sensing Technique for Multi-Function Fiber Optic Sensor Platforms: Current Status and Design Perspectives
Sensors 2009, 9(10), 7595-7621; doi:10.3390/s91007595
Received: 31 July 2009 / Revised: 9 September 2009 / Accepted: 17 September 2009 / Published: 28 September 2009
Cited by 48 | PDF Full-text (810 KB) | HTML Full-text | XML Full-text
Abstract
Fiber loop ringdown (FLRD) utilizes an inexpensive telecommunications light source, a photodiode, and a section of single-mode fiber to form a uniform fiber optic sensor platform for sensing various quantities, such as pressure, temperature, strain, refractive index, chemical species, biological cells, and [...] Read more.
Fiber loop ringdown (FLRD) utilizes an inexpensive telecommunications light source, a photodiode, and a section of single-mode fiber to form a uniform fiber optic sensor platform for sensing various quantities, such as pressure, temperature, strain, refractive index, chemical species, biological cells, and small volume of fluids. In FLRD, optical losses of a light pulse in a fiber loop induced by changes in a quantity are measured by the light decay time constants. FLRD measures time to detect a quantity; thus, FLRD is referred to as a time-domain sensing technique. FLRD sensors have near real-time response, multi-pass enhanced high-sensitivity, and relatively low cost (i.e., without using an optical spectral analyzer). During the last eight years since the introduction of the original form of fiber ringdown spectroscopy, there has been increasing interest in the FLRD technique in fiber optic sensor developments, and new application potential is being explored. This paper first discusses the challenging issues in development of multi-function, fiber optic sensors or sensor networks using current fiber optic sensor sensing schemes, and then gives a review on current fiber optic sensor development using FLRD technique. Finally, design perspectives on new generation, multi-function, fiber optic sensor platforms using FLRD technique are particularly presented. Full article
(This article belongs to the Special Issue Laser Spectroscopy and Sensing)

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