http://www.mdpi.com/journal/sensors/special_issues/laser_sensing/ 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. {snippet name="submission_info"} http://www.mdpi.com/1424-8220/10/7/6861/ 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. http://www.mdpi.com/1424-8220/10/7/6861/ Fri, 16 Jul 2010 00:00:00 CEST Sensors 2010-07-16 10 7 Review 6861 6900 1424-8220 Quantum Cascade Laser Absorption Spectroscopy as a Plasma Diagnostic Tool: An Overview 2010-07-16 doi: 10.3390/s100706861 Stefan Welzel Frank Hempel Marko Hübner Norbert Lang Paul B. Davies Jürgen Röpcke http://www.mdpi.com/1424-8220/10/7/6788/ 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. http://www.mdpi.com/1424-8220/10/7/6788/ Tue, 13 Jul 2010 00:00:00 CEST Sensors 2010-07-13 10 7 Article 6788 6795 1424-8220 A Microring Resonator Sensor for Sensitive Detection of 1,3,5-Trinitrotoluene (TNT) 2010-07-13 doi: 10.3390/s100706788 Orghici Lützow Burgmeier Koch Heidrich Schade Welschoff Waldvogel http://www.mdpi.com/1424-8220/10/7/6612/ 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 ν2+ν4 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. http://www.mdpi.com/1424-8220/10/7/6612/ Fri, 09 Jul 2010 00:00:00 CEST Sensors 2010-07-09 10 7 Article 6612 6622 1424-8220 An Efficient and Compact Difference-Frequency-Generation Spectrometer and Its Application to 12CH3D/12CH4 Isotope Ratio Measurements 2010-07-09 doi: 10.3390/s100706612 Tsuji Teshima Sasada Yoshida http://www.mdpi.com/1424-8220/10/6/5927/ 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. http://www.mdpi.com/1424-8220/10/6/5927/ Thu, 10 Jun 2010 00:00:00 CEST Sensors 2010-06-10 10 6 Review 5927 5948 1424-8220 Recent Applications of Fluorescence Recovery after Photobleaching (FRAP) to Membrane Bio-Macromolecules 2010-06-10 doi: 10.3390/s100605927 Rayan Guet Taulier Pincet Urbach http://www.mdpi.com/1424-8220/10/6/5642/ 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. http://www.mdpi.com/1424-8220/10/6/5642/ Thu, 03 Jun 2010 00:00:00 CEST Sensors 2010-06-03 10 6 Review 5642 5667 1424-8220 Methodology of Pulsed Photoacoustics and Its Application to Probe Photosystems and Receptors 2010-06-03 doi: 10.3390/s100605642 Hou Sakmar http://www.mdpi.com/1424-8220/10/6/5294/ 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. http://www.mdpi.com/1424-8220/10/6/5294/ Wed, 26 May 2010 00:00:00 CEST Sensors 2010-05-26 10 6 Article 5294 5307 1424-8220 Transversely Excited Multipass Photoacoustic Cell Using Electromechanical Film as Microphone 2010-05-26 doi: 10.3390/s100605294 Saarela Sand Sorvajärvi Manninen Toivonen http://www.mdpi.com/1424-8220/10/5/4926/ 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. http://www.mdpi.com/1424-8220/10/5/4926/ Fri, 14 May 2010 00:00:00 CEST Sensors 2010-05-14 10 5 Article 4926 4949 1424-8220 Comparative Laser Spectroscopy Diagnostics for Ancient Metallic Artefacts Exposed to Environmental Pollution 2010-05-14 doi: 10.3390/s100504926 Ciupiński Fortuna-Zaleśna Garbacz Koss Kurzydłowski Marczak Mróz Onyszczuk Rycyk Sarzyński Skrzeczanowski Strzelec Zatorska Żukowska http://www.mdpi.com/1424-8220/10/5/4907/ 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. http://www.mdpi.com/1424-8220/10/5/4907/ Fri, 14 May 2010 00:00:00 CEST Sensors 2010-05-14 10 5 Review 4907 4925 1424-8220 Effect of Atmospheric Conditions on LIBS Spectra 2010-05-14 doi: 10.3390/s100504907 Effenberger Scott http://www.mdpi.com/1424-8220/10/5/4686/ 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. http://www.mdpi.com/1424-8220/10/5/4686/ Thu, 06 May 2010 00:00:00 CEST Sensors 2010-05-06 10 5 Article 4686 4699 1424-8220 Diode Laser Detection of Greenhouse Gases in the Near-Infrared Region by Wavelength Modulation Spectroscopy: Pressure Dependence of the Detection Sensitivity 2010-05-06 doi: 10.3390/s100504686 Asakawa Kanno Tonokura http://www.mdpi.com/1424-8220/10/5/4342/ 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. http://www.mdpi.com/1424-8220/10/5/4342/ Thu, 29 Apr 2010 00:00:00 CEST Sensors 2010-04-29 10 5 Review 4342 4372 1424-8220 Ultrafast Laser-Based Spectroscopy and Sensing: Applications in LIBS, CARS, and THz Spectroscopy 2010-04-29 doi: 10.3390/s100504342 Leahy-Hoppa Miragliotta Osiander Burnett Dikmelik McEnnis Spicer http://www.mdpi.com/1424-8220/10/5/4296/ 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. http://www.mdpi.com/1424-8220/10/5/4296/ Thu, 29 Apr 2010 00:00:00 CEST Sensors 2010-04-29 10 5 Review 4296 4341 1424-8220 Generation and Amplification of Tunable Multicolored Femtosecond Laser Pulses by Using Cascaded Four-Wave Mixing in Transparent Bulk Media 2010-04-29 doi: 10.3390/s100504296 Liu Kobayashi http://www.mdpi.com/1424-8220/10/5/4253/ 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. http://www.mdpi.com/1424-8220/10/5/4253/ Wed, 28 Apr 2010 00:00:00 CEST Sensors 2010-04-28 10 5 Review 4253 4269 1424-8220 Real-Time Time-Frequency Two-Dimensional Imaging of Ultrafast Transient Signals in Solid-State Organic Materials 2010-04-28 doi: 10.3390/s100504253 Takeda Ishida Makishima Katayama http://www.mdpi.com/1424-8220/10/4/3868/ 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. http://www.mdpi.com/1424-8220/10/4/3868/ Thu, 15 Apr 2010 00:00:00 CEST Sensors 2010-04-15 10 4 Article 3868 3881 1424-8220 Spectroscopic Interpretation of PAH-Spectra in Minerals and Its Possible Application to Soil Monitoring 2010-04-15 doi: 10.3390/s100403868 Ko Kim Park Kim Kim Hamm Lee Wachsmuth http://www.mdpi.com/1424-8220/10/4/3815/ 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. http://www.mdpi.com/1424-8220/10/4/3815/ Wed, 14 Apr 2010 00:00:00 CEST Sensors 2010-04-14 10 4 Article 3815 3823 1424-8220 Optical Sensor for Characterizing the Phase Transition in Salted Solutions 2010-04-14 doi: 10.3390/s100403815 Claverie Fontana Duričković Bourson Marchetti Chassot http://www.mdpi.com/1424-8220/10/4/3519/ 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. http://www.mdpi.com/1424-8220/10/4/3519/ Thu, 08 Apr 2010 00:00:00 CEST Sensors 2010-04-08 10 4 Review 3519 3548 1424-8220 Structures and Encapsulation Motifs of Functional Molecules Probed by Laser Spectroscopic and Theoretical Methods 2010-04-08 doi: 10.3390/s100403519 Kusaka Inokuchi Xantheas Ebata http://www.mdpi.com/1424-8220/10/4/3305/ 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. http://www.mdpi.com/1424-8220/10/4/3305/ Sun, 04 Apr 2010 00:00:00 CEST Sensors 2010-04-04 10 4 Communication 3305 3313 1424-8220 Laser Photoacoustic Detection of CO2 in Old Disc Tree-Rings 2010-04-04 doi: 10.3390/s100403305 Ageev Ponomarev Sapozhnikova http://www.mdpi.com/1424-8220/10/4/2869/ 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. http://www.mdpi.com/1424-8220/10/4/2869/ Mon, 29 Mar 2010 00:00:00 CEST Sensors 2010-03-29 10 4 Article 2869 2884 1424-8220 Discriminant Analysis of Raman Spectra for Body Fluid Identification for Forensic Purposes 2010-03-29 doi: 10.3390/s100402869 Sikirzhytski Virkler Lednev http://www.mdpi.com/1424-8220/10/4/2694/ 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. http://www.mdpi.com/1424-8220/10/4/2694/ Fri, 26 Mar 2010 00:00:00 CET Sensors 2010-03-26 10 4 Article 2694 2708 1424-8220 Infrared Spectroscopy on Smoke Produced by Cauterization of Animal Tissue 2010-03-26 doi: 10.3390/s100402694 Gianella Sigrist http://www.mdpi.com/1424-8220/10/4/2626/ 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. http://www.mdpi.com/1424-8220/10/4/2626/ Thu, 25 Mar 2010 00:00:00 CET Sensors 2010-03-25 10 4 Article 2626 2637 1424-8220 Following Enzyme Activity with Infrared Spectroscopy 2010-03-25 doi: 10.3390/s100402626 Kumar Barth http://www.mdpi.com/1424-8220/10/4/2492/ 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. http://www.mdpi.com/1424-8220/10/4/2492/ Wed, 24 Mar 2010 00:00:00 CET Sensors 2010-03-24 10 4 Review 2492 2510 1424-8220 DFB Lasers Between 760 nm and 16 µm for Sensing Applications 2010-03-24 doi: 10.3390/s100402492 Zeller Naehle Fuchs Gerschuetz Hildebrandt Koeth http://www.mdpi.com/1424-8220/10/4/2460/ 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. http://www.mdpi.com/1424-8220/10/4/2460/ Wed, 24 Mar 2010 00:00:00 CET Sensors 2010-03-24 10 4 Article 2460 2471 1424-8220 Estimation of Biological Oxygen Demand and Chemical Oxygen Demand for Combined Sewer Systems Using Synchronous Fluorescence Spectra 2010-03-24 doi: 10.3390/s100402460 Hur Lee Lee Park http://www.mdpi.com/1424-8220/10/3/2169/ 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. http://www.mdpi.com/1424-8220/10/3/2169/ Tue, 16 Mar 2010 00:00:00 CET Sensors 2010-03-16 10 3 Article 2169 2187 1424-8220 Trapped Ion Oscillation Frequencies as Sensors for Spectroscopy 2010-03-16 doi: 10.3390/s100302169 Vogel Quint Nörtershäuser http://www.mdpi.com/1424-8220/10/3/1986/ 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. http://www.mdpi.com/1424-8220/10/3/1986/ Thu, 11 Mar 2010 00:00:00 CET Sensors 2010-03-11 10 3 Article 1986 2002 1424-8220 Quantum Cascade Laser-Based Photoacoustic Spectroscopy for Trace Vapor Detection and Molecular Discrimination 2010-03-11 doi: 10.3390/s100301986 Ellen Holthoff John Bender Paul Pellegrino Almon Fisher http://www.mdpi.com/1424-8220/10/3/1871/ 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). http://www.mdpi.com/1424-8220/10/3/1871/ Tue, 09 Mar 2010 00:00:00 CET Sensors 2010-03-09 10 3 Review 1871 1889 1424-8220 Raman Spectroscopy and Related Techniques in Biomedicine 2010-03-09 doi: 10.3390/s100301871 Andrew Downes Alistair Elfick http://www.mdpi.com/1424-8220/10/3/1823/ 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. http://www.mdpi.com/1424-8220/10/3/1823/ Fri, 05 Mar 2010 00:00:00 CET Sensors 2010-03-05 10 3 Review 1823 1845 1424-8220 Optical Fiber Sensing Based on Reflection Laser Spectroscopy 2010-03-05 doi: 10.3390/s100301823 Gianluca Gagliardi Mario Salza Pietro Ferraro Edmond Chehura Ralph P. Tatam Tarun K. Gangopadhyay Nicholas Ballard Daniel Paz-Soldan Jack A. Barnes Hans-Peter Loock Timothy T.-Y. Lam Jong H. Chow Paolo De Natale http://www.mdpi.com/1424-8220/10/3/1716/ 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. http://www.mdpi.com/1424-8220/10/3/1716/ Tue, 02 Mar 2010 00:00:00 CET Sensors 2010-03-02 10 3 Review 1716 1742 1424-8220 Chemical Sensing Using Fiber Cavity Ring-Down Spectroscopy 2010-03-02 doi: 10.3390/s100301716 Helen Waechter Jessica Litman Adrienne H. Cheung Jack A. Barnes Hans-Peter Loock http://www.mdpi.com/1424-8220/10/1/544/ 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. http://www.mdpi.com/1424-8220/10/1/544/ Wed, 13 Jan 2010 00:00:00 CET Sensors 2010-01-13 10 1 Article 544 583 1424-8220 Semiconductor Laser Multi-Spectral Sensing and Imaging 2010-01-13 doi: 10.3390/s100100544 Han Q. Le Yang Wang http://www.mdpi.com/1424-8220/9/12/10447/ 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). http://www.mdpi.com/1424-8220/9/12/10447/ Tue, 22 Dec 2009 00:00:00 CET Sensors 2009-12-22 9 12 Review 10447 10512 1424-8220 Laser Spectroscopy for Atmospheric and Environmental Sensing 2009-12-22 doi: 10.3390/s91210447 Marc N. Fiddler Israel Begashaw Matthew A. Mickens Michael S. Collingwood Zerihun Assefa Solomon Bililign http://www.mdpi.com/1424-8220/9/12/10423/ 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. http://www.mdpi.com/1424-8220/9/12/10423/ Tue, 22 Dec 2009 00:00:00 CET Sensors 2009-12-22 9 12 Article 10423 10433 1424-8220 Perfluorinated Plastic Optical Fiber Tapers for Evanescent Wave Sensing 2009-12-22 doi: 10.3390/s91210423 Roberto Gravina Genni Testa Romeo Bernini http://www.mdpi.com/1424-8220/9/12/9616/ 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. http://www.mdpi.com/1424-8220/9/12/9616/ Wed, 02 Dec 2009 00:00:00 CET Sensors 2009-12-02 9 12 Review 9616 9628 1424-8220 Photoacoustic Techniques for Trace Gas Sensing Based on Semiconductor Laser Sources 2009-12-02 doi: 10.3390/s91209616 Angela Elia Pietro Mario Lugarà Cinzia Di Franco Vincenzo Spagnolo http://www.mdpi.com/1424-8220/9/11/9039/ 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. http://www.mdpi.com/1424-8220/9/11/9039/ Fri, 13 Nov 2009 00:00:00 CET Sensors 2009-11-13 9 11 Article 9039 9057 1424-8220 Recent Developments of an Opto-Electronic THz Spectrometer for High-Resolution Spectroscopy 2009-11-13 doi: 10.3390/s91109039 Francis Hindle Chun Yang Gael Mouret Arnaud Cuisset Robin Bocquet Jean-François Lampin Karine Blary Emilien Peytavit Tahsin Akalin Guillaume Ducournau http://www.mdpi.com/1424-8220/9/11/8382/ 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. http://www.mdpi.com/1424-8220/9/11/8382/ Mon, 26 Oct 2009 00:00:00 CET Sensors 2009-10-26 9 11 Article 8382 8390 1424-8220 Material Limitations on the Detection Limit in Refractometry 2009-10-26 doi: 10.3390/s91108382 Peder Skafte-Pedersen Pedro S. Nunes Sanshui Xiao Niels Asger Mortensen http://www.mdpi.com/1424-8220/9/10/7595/ 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. http://www.mdpi.com/1424-8220/9/10/7595/ Mon, 28 Sep 2009 00:00:00 CEST Sensors 2009-09-28 9 10 Review 7595 7621 1424-8220 Fiber Loop Ringdown — a Time-Domain Sensing Technique for Multi-Function Fiber Optic Sensor Platforms: Current Status and Design Perspectives 2009-09-28 doi: 10.3390/s91007595 Chuji Wang