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Hadamard-transform multiplexing has recently been applied to increasingly complex spectroscopic techniques. It had been shown that the data acquisition time for fluorescence Excitation-Emission-Matrix spectroscopy can be reduced by one or two orders of magnitude using Hadamard-Transform multiplexing of the excitation light using a programmable lightsource. In these previous studies, the data acquisition rate had been limited by the time it took to record an EEM, i.e. to complete one cycle of multiplexed excitation spectra. The extraction of chemical information, such as concentration and chemical identity, is then obtained from parallel factor (PARAFAC) analysis of the sequence of EEM spectra. In this contribution we increase the data acquisition rate by another order of magnitude, i.e. to the time it takes to record a single excitation spectrum. Our algorithm is entirely based on improved data processing, i.e. it can be applied to previously recorded Hadamard-Transform multiplexed data sets. The algorithm is based on three previously unexplored approaches: (1) we perform a PARAFAC multivariate analysis on the raw (multiplexed) data set (2) the PARAFAC loading vectors are obtained prior to obtaining the score vectors, (3) when loading vectors are difficult to obtain from the stack of EEM spectra, we instead use a rolling-average approach to considerably increase the number of spectra and the stability of the fit. Analysis of experimental data shows that fluorescence EEM spectra with 7 excitation wavelengths and over 1000 emission wavelengths can be obtained in less than 20 ms.

We present a new rapid-acquisition HPLC detector based on a Hadamard-transform (HT) excitation-emission-matrix (EEM) fluorescence spectrometer allowing the acquisition of two-dimensional spectra at a rate faster than 6 spectra per second (

We present a one-step fabrication method for a new multiplexed electrospray emitter with nine parallel micronozzles. The nozzles were formed by wet chemical etching of the end of a microstructured silica fiber containing nine 10 μm flow channels. By carefully adjusting the water flow through the channels while etching, we controlled the shape of the conical micronozzles and were able to obtain conditions under which the micronozzles, together with the flow channels, formed optical micro-axicon lenses. When 1064 nm light was guided through the flow channels and focused by the micro-axicon lenses into the Taylor cones, we were able to increase the desolvation of a model analyte and thereby increased the spray current produced by the emitter. This work paves the way towards a rapidly modulated mass-spectrometry source having a greatly enhanced throughput.

Compact interferometers based on waveguiding structures have found countless applications in refractive index measurements, chemical sensing, as well as temperature and pressure measurements. The most common fiber devices are based on Mach–Zehnder interferometry and Michelson interferometry—two design concepts that can readily be implemented using simple fiber optic components, such as mode splitters and combiners, fiber optic gratings, and fiber tapers, among others. Fiber interferometry can also be conducted based on the Sagnac effect and the Young (double-slit) interferometer. In this review, we examine and compare over 400 fiber optic interferometers as well as more than 60 fiber optic refractive sensors based on fiber optic cavities. Even though many of the devices show temperature-, strain-, and pressure-sensitivity, we focus our review on refractive index measurements, as these are the most common applications. Many devices were characterized by their inventors using their sensitivity to refractive index changes. While the sensitivity is an important characteristic of the device, it does not easily relate to the smallest resolvable refractive index change or the limit of detection when applied to chemical measurements. Instead, we propose here that one should use the figure of merit, which is defined through the refractive index sensitivity and the width of an interferometer fringe. Using simple assumptions, we were able to mathematically relate the sensitivity and the figure of merit to common design parameters, such as the length of the interferometer arms, the operating wavelength, refractive indices of the fiber and the sample, as well as an overlap parameter, which describes the fraction of the guided wave in the sensing arm that interacts with the sample. We determined this overlap parameter for each reviewed device from the reported interferograms. Our meta-analysis provides for the first time simple and easily applicable guidance to increase the figure of merit of fiber optic interferometers and fiber optic cavities with regard to their ability to detect small refractive index changes. A high figure of merit allows measuring very small refractive index changes such as those of gases at different pressures or of very dilute solutions.

We present a strain sensing system capable of measuring strain over 75 km using a diode laser locked to a π-shifted grating. The system has applications in remote sensing of ocean turbulence and seismic activity.

Using a multiplexing technique, we have built an instrument that captures excitation emission matrices (EEM) for every pixel in an image, gaining information over four dimensions (x,y,λex,λem) and reduces acquisition time 500-fold from conventional designs. Comments and questions should be directed to the Optica Conference Papers staff (tel: +1 202.416.6191, e-mail: cstech@optica.org).

A novel Hadamard-transform excitation-emission matrix (EEM) spectrometer generates two-dimensional (2D) fluorescence matrices at a data acquisition rate of over 6 EEMs per minute and with a spectral resolution of 5.3 nm. Using Fresnel reflections from the sample cell, we could record optical transmission spectra synchronously with the 2D EEMs. The spectrometer was integrated into a custom-designed stopped-flow injection device to collect visible absorption and fluorescence EEM spectra of reacting solutions. Two different kinetic studies on two rapidly evolving chemical reactions with multiple overlapping spectral components were conducted by collecting over 8400 absorption spectra and EEMs. The third-order rate constant for the demetalation of chlorophyll

A pi(π)-shifted grating has been used as a passive strain sensor to achieve a resolution of 50 nanostrain (nε). The Pound-Drever-Hall frequency locking technique was used to obtain a stable signal at a distance of 50 km, paving the way for remote detection of sound, temperature and pressure at a long distance from sources of electricity.

A new UV-LED based Hadamard excitation-emission-matrix fluorescence spectrometer was designed and utilized to study the degradation of antioxidants additives to lubricant samples with acquisition times within 2 to 10 seconds.

Microcontact printed patterns of N-heterocyclic carbenes (NHCs) and thiols were prepared on gold substrates and utilized as templates for the creation of metallic Cu structures using electroplating. The presence of the NHC in the pattern is essential to enable the transfer of the resulting copper microstructures to a second substrate.

Objective: A fiber optic vibration sensor is developed and characterized with an ultrawide dynamic sensing range, from less than 1 Hz to clinical ultrasound frequencies near 6 MHz. The vibration sensor consists of a matched pair of fiber Bragg gratings coupled to a custom-built signal processing circuit. The wavelength of a laser diode is locked to one of the many cavity resonances using the Pound–Drever–Hall scheme. Methods: A calibrated piezoelectric vibration element was used to characterize the sensor's strain, temperature, and noise responses. To demonstrate its sensing capability, an ultrasound phantom with built-in low frequency vibration actuation was constructed. Results: The fiber optic senor was shown to simultaneously capture the low frequency vibration and the clinical ultrasound transmission waveforms with nanostrain sensitivity. Conclusion: This miniaturized and sensitive vibration sensor can provide comprehensive information regarding strain response and the resultant ultrasound waveforms.

The response of polysiloxane materials to volatile organic compounds (VOCs) including benzene, toluene, ethylbenzene, and toluene (BTEX), as well as cyclohexane, acetone, methanol and isopropanol is studied using thin film large-angle refractometry. Refractive index and thickness changes are measured to quantify the diffusion rate and partition coefficients associated with the absorption and desorption of VOC vapours into polydimethylsiloxane (PDMS) and polydiphenylsiloxane (PDPS) - PDMS copolymer films. Absorption of volatile solvent vapours into siloxane polymers is found to follow two distinct mechanisms with different absorption rates. These mechanisms are also associated with different excess volumes of mixing and may be accompanied by a polymer restructuring step.

The thermal, oxidative and photochemical stability of the scintillator liquid proposed for the SNO+ experiment has been tested experimentally using accelerated aging methods. The stability of the scintillator constituents was determined through fluorescence excitation emission matrix (EEM) spectroscopy and absorption spectroscopy, using parallel factor analysis (PARAFAC) as an multivariate analysis tool. By exposing the scintillator liquid to a well-known photon flux at 365 nm and by measuring the decay rate of the fluorescence shifters and the formation rate of their photochemical degradation products, we can place an upper limit on the acceptable photon flux as 1.38 ± 0.09 × 10-11 photon mol L-1. Similarly, the oxidative stability of the scintillator liquid was determined by exposure to air at several elevated temperatures. Through measurement of the corresponding activation energy it was determined that the average oxygen concentration would have to be kept below 4.3-7.1 ppbw (headspace partial pressure below 24 ppmv). On the other hand, the thermal stability of the scintillator cocktail in the absence of light and oxygen was remarkable and poses no concern to the SNO+ experiment.

Fiber-strain sensors have found numerous applications from structural health monitoring for vibrations, to pressure and temperature sensing. Many of these sensors exploit the strain-sensitivity of the reflection wavelength of fiber-bragg gratings, π-shifted gratings or other waveguide devices. The strain is typically inferred from a change of reflected or transmitted light intensity. Light intensity measurements are not very robust and have an inherently limited accuracy. We propose that a frequency-based strain measurements using fiber Fabry-Perot (FFP) cavities provide not only superior sensitivity but also retain a very high measurement bandwidth.

Conventional B-mode ultrasound imaging lacks soft tissue contrast to differentiate various tissue types. Emerging ultrasound imaging technologies have therefore focused on extracting tissue parameters important for tissue differentiation such as scatterer size, tissue elasticity, and micro-vasculatures. Among these technologies, shear wave elastography (SWE) is an approach that measures tissue viscoelastic parameters. Our group has proposed Temporal Enhanced Ultrasound (TeUS) that differentiates tissue types without requiring any external stimuli. Through analytical derivations and simulations, we previously showed that the source of tissue typing information in TeUS is physiological micro-vibrations resulting mainly from perfusion. We further demonstrated that TeUS is sensitive to the size and distributions of scatterers in the tissue, as well as its visco-elasticity. In this paper, we designed ultrasound phantoms to mimic tissue with two different elasticities and two scatterer sizes. A exible microtube was embedded in the phantoms to generate local micro-vibrations. We experimentally demonstrate the relationship between TeUS and SWE and their sensitivity to tissue elasticity and scatterer size. This work indicated that while shear wave measurements are sensitive to the phantoms viscoelasticity, they are not sensitive to ultrasound scatterer size. On the contrary, the TeUS amplitude depends on both scatterer size and tissue viscoelasticity. This work could potentially inform clinicians of choosing imaging modalities and interventions based on each cancer's unique traits and properties.

A fiber-coupled pyrometer was used to monitor the temperature and brightness of the flame in an industrial copper smelter and in a lab-scale drop tower. Optical emission spectroscopy is used to analyze the light emitted from combusting ore particles in the furnace reaction shaft.

An all-fiber-optical method is presented to monitor densities, viscosities, and temperatures of Newtonian liquids. The actuation is performed by photothermally heating the base of a steel cantilever with an intensity-modulated 808 nm diode laser. The cantilever vibrations are measured with an in-fiber Fabry–Perot cavity sensor attached along the length of the cantilever. When immersed in a viscous fluid, the cantilever response can be related to the fluid properties: a shift in the resonance frequency corresponds to a change in fluid density, and the width of the resonance peak gives information on the dynamic viscosity after calibration of the system. Aqueous glycerol and sucrose samples in the density range of 0.997–1.17 g cm−3 and in the viscosity range of 0.89–8.49 mPa s were used to investigate the limits of the sensor. Representative beverage samples were also analyzed as unknowns.

Synthetic lubricant oils based on a polyol ester base stock and containing amine-based antioxidants are characterised by fluorescence excitation–emission-matrix (EEM) spectroscopy. The main spectral features are attributed to antioxidants and are quantified using Parallel Factor (PARAFAC) analysis. The resulting PARAFAC component scores are compared to the relative antioxidant concentrations that were independently obtained with linear sweep voltammetry (LSV). An excellent correlation between the total intensity of the fluorescence signatures and the integrated LSV signal indicates that fluorescence EEM has a potential in the real-time – online or at-line – measurements of antioxidant concentrations. A modified fibre probe is presented that allows such measurements in strongly absorbing samples. The fibre probe contains a bevelled window to reduce the effects of fluorescence reabsorption and other “inner filter” effects.

A wineglass has been used as an acoustic resonator to enhance the photoacoustic signal generated by laser excitation of absorbing dyes in solution. The amplitude of the acoustic signal was recorded using a fiber-optic transducer based on a Fabry-Pérot cavity attached to the rim of the wineglass. The optical and acoustic properties of the setup were characterized, and it was used to quantify the concentration of phosphomolybdenum blue and methyl red solutions. Detection limits of 1.2 ppm and 8 muM were obtained, respectively.

Fiber optic cavities based on either on fiber loops or two identical FBGs are used to detect the optical loss due to absorbers, or their photoacoustic response, respectively.

A silicon-on-insulator (SOI) microresonator coated with amine functionalized silanes was used to detect the phosphate ions in aqueous solutions as an online real-time sensor. Trace level phosphates were detected to parts per million (ppm) levels.

We present a fluorescence excitation-emission-matrix spectrometer with superior data acquisition rates over previous instruments. Light from a white light emitting diode (LED) source is dispersed onto a digital micromirror array (DMA) and encoded using binary n-size Walsh functions ("barcodes"). The encoded excitation light is used to irradiate the liquid sample and its fluorescence is dispersed and detected using a conventional array spectrometer. After exposure to excitation light encoded in n different ways, the 2-dimensional excitation-emission-matrix (EEM) spectrum is obtained by inverse Hadamard transformation. Using this technique we examined the kinetics of the fluorescence of rhodamine B as a function of temperature and the acid-driven demetalation of chlorophyll-a into pheophytin-a. For these experiments, EEM spectra with 31 excitation channels and 2048 emission channels were recorded every 15 s. In total, data from over 3000 EEM spectra were included in this report. It is shown that the increase in data acquisition rate can be as high as [{n(n + 1)}/2]-fold over conventional EEM spectrometers. Spectral acquisition rates of more than two spectra per second were demonstrated.

Temporal-enhanced ultrasound (TeUS) imaging is a recently developed method based on the analysis of US time series. In this report, we show experimentally that the TeUS amplitude is sensitive to scatterer size and their density, as well as to the microvibration amplitude. Since the microvibration amplitude depends on the local elasticity of the medium, TeUS is able to differentiate tissues based on their elasticity, in addition to scatterer density and cross section. It is argued that interference effects, i.e., US speckle, are enhancing the TeUS effect. In this study, ultrasound phantoms were designed to mimic tissues with three different viscoelasticities and three different scatterer sizes. Into each of the nine phantoms, a flexible tubing was embedded and used to generate local microvibrations at 1 Hz and with an amplitude below 20 μm. Time series of raw ultrasound images were analyzed to extract the B-mode intensity, the scatterer displacement, and the shear modulus at a variety of different microvibration amplitudes.

Cavity ring-down spectroscopy is performed using a single-mode fibre loop as an optical cavity. The loop contains absorption cells for either liquids or gases, as well as an erbium-doped fibre amplifier. The fibre amplifier is gain-clamped using a second fibre-loop. Ring-down times can be tuned to permit several hundred roundtrips by adjusting the loss ratio between the two nested loops using a variable optical attenuator. Ring-down measurements were performed either in the time domain or using phase shift measurements. Acetylene gas was detected through a ro-vibrational absorption line of the ν1–ν3 combination band at 1532 nm at a limit of detection of 50 ppm. Liquid 1-octyne and 1-dodecyne were detected in a 1 pL volume at detection limits of ∼20% dilution in dodecane through their C–H stretch vibrational overtone transition.

a b s t r a c t We report a chemical vapor sensor in which polymer swelling, upon analyte absorption, is used to deform an on-chip silicon Fabry-Perot interferometer (FPI). The magnitude of the deformation, recorded through the resonance wavelength shift, is proportional to the analyte concentration in accordance with a simplified analytical model and with finite element simulations. Conventional and phenyl-doped poly- dimethylsiloxane (PDMS) polymers are used to functionalize different interferometers, which are tested for the detection of two volatile organic compounds, i.e. m-xylene and cyclohexane. The detection of m-xylene concentrations down to 34 ppm—limited by our flow-meter setup—is achieved experimen- tally. Based on the sensitivities and the noise characteristics of the devices, limits of detection (LODs) of 1.6 ppm m-xylene and 6.3 ppm cyclohexane are expected.

The limit of detection (LOD) and the sensitivity of a chemical sensor are defined using IUPAC guidelines. The LOD from simulated and experimental data is calculated from a calibration curve using a simple statistical model that was implemented into a spreadsheet program. This definition of the LOD is compared with the commonly used definition of the LOD, which is based on the product of sensitivity and the theoretical instrument resolution.

Several mathematical models exist in the literature to describe the properties of optical resonators. Here, coupled mode theory and coherent superposition theory are compared and their consistency is demonstrated as they are applied to phase-shift cavity ring-down measurements in optical (micro-)cavities. In the particular case of a whispering gallery mode in a microsphere cavity these models are applied to transmission measurements and backscattering measurements through the fiber taper that couples light into the microresonator. It is shown that both models produce identical relations when applied to these traveling wave cavities.

The photodissociation and photoionization dynamics of HBr via low-n Rydberg and ion-pair states was studied by using 2 + 1 REMPI spectroscopy and velocity map imaging of photoelectrons. Two-photon excitation at about 9.4-10 eV was used to prepare rotationally selected excited states. Following absorption of the third photon the unperturbed F (1)Delta(2) and i (3)Delta(2) states ionize directly into the ground vibrational state of the molecular ion according to the Franck-Condon principle and upon preservation of the ion core. In case of the V (1)Sigma(+)(0(+)) ion-pair state and the perturbed E (1)Sigma(+)(0(+)), g (3)Sigma(-)(0(+)), and H (1)Sigma(+)(0(+)) Rydberg states the absorption of the third photon additionally results in a long vibrational progression of HBr(+) in the X (2)Pi state as well as formation of electronically excited atomic photofragments. The vibrational excitation of the molecular ion is explained by autoionization of repulsive superexcited states into the ground state of the molecular ion. In contrast to HCl, the perturbed Rydberg states of HBr show strong participation of the direct ionization process, with ionic core preservation.

An acoustic transducer based on a fiber Bragg grating (FBG) is presented and characterized for use in time-resolved laser-induced photoacoustic spectroscopy (PAS) on solid samples. The photoacoustic wave was generated by pulsed laser excitation of immobilized carbon black or erbium oxide powder, and detected by recording either the transmission or reflection spectrum of a clamped fiber Bragg grating (FBG). The characterization of the FBGs photoacoustic response is based on the experimental comparison with a static lateral strain source and on theoretical analysis using the piecewise-uniform approach to photoelastic theory. The temporal resolution of the response is determined by the arrangement of the FBG with respect to the source of the acoustic wave and is better than 150 ns, as was verified in a deconvolution analysis. The method has not only a fast time response but also is simple, inexpensive, and accurate as indicated by the good agreement of the experimental photoacoustic spectrum with previous measurements.

Ring-down absorption spectroscopy is an emerging ‘‘label-free’’ detection method for analytical microdevices, such as micrototal analysis systems (l-TAS). Developed from the related gas-phase cavity ring-down absorption spectroscopy, fiber-optic-based ring-down techniques for liquid samples offer low detection limits, high sensitivity and fast response. ª 2006 Elsevier Ltd. All rights reserved.

An etched long-period grating was used as a refractive index sensor for vapours of four volatile organic compounds, i.e. m-xylene, cyclohexane, trichloroethylene and commercial gasoline. The sensitivity to the vapours was further increased by solid-phase microextraction into a coating made of polydimethylsiloxane (PDMS)/polymethyl-octylsiloxane (PMOS) co-polymer. By further amplification of the optical loss in an optical cavity made of two identical fiber-Bragg gratings and interrogation by phase-shift cavity ring-down spectroscopy we could detect and distinguish xylene (detection limit: 134 ppm) from trichloroethylene (3300 ppm), cyclohexane (1850 ppm) and gasoline (10,500 ppm).

The contour lithography method [1] is used to improve the fabrication yield of previously demonstrated [2] microfluidic Fabry-Perot (FP) refractive index (RI) sensors. The sensors are then coated with polydimethylsiloxane (PDMS) based polymers to detect vapor analytes by solid-phase microextraction (SPME). Preliminary characterization of devices coated with two different polymers and exposed to xylenes vapors yields a maximum sensitivity of 0.015 nm/ppm and a detection limit below 120 ppm.

A low-noise transducer based on a fiber Fabry-Perot (FFP) cavity was used as a pickup for an acoustic guitar. A distributed feedback (DFB) laser was locked to a 25 MHz-wide resonance of the FFP cavity using the Pound-Drever-Hall method. The correction signal was used as the audio output and was preamplified and sampled at up to 96 kHz. The pickup system is largely immune against optical noise sources, exhibits a flat frequency response from the infrasound region to about 25 kHz, and has a distortion-free audio output range of about 50 dB. (C) 2011 Optical Society of America

We report a method for real-time monitoring of vapor uptake by simultaneous detection of the refractive index, 𝑛 , and thickness, 𝑑 , of thin transparent films with a precision of 𝛿𝑛=10 −4 and 𝛿𝑑

The fluorescence of antioxidant additives in lubricant oil was used as an indicator of oxidative stability of the oil. It was found that the decrease in fluorescence intensities of phenyl-α-napthylamine, its dimer, and another unidentified antioxidant coincide with the formation of decomposition products of the oil base stock. Simple kinetic models were developed that were capable of describing antioxidant reactions as a pseudo first-order processes. It is shown that fluorescence excitation emission matrix (EEM) spectroscopy coupled with an optical fiber probe can provide real-time assessment of the oxidative stability of the lubricant. Parallel factor (PARAFAC) analysis was used to correlate the component scores to the oil breakdown number.

Using a large-angle refractometer, the refractive indices of water, methanol, acetonitrile, acetone, ethanol, formaldehyde solution, 2-propanol, hexanes, 1-propanol, 2-butanol, tetrahydrofuran, dichloromethane, 1,4-dioxane, cyclohexane, N,N-dimethylformamide, ethylene glycol, N,N-dimethylacetamide, chloroform, glycerol, trichloroethylene, dimethylsulfoxide, p-xylene, ethylbenzene, toluene, m-xylene, benzene, and o-xylene were measured at 1550 nm and compared to literature values. In addition, the refractive indices of 48 aqueous sucrose solutions, 34 aqueous sodium chloride solutions, 40 DMSO-water, 40 ethylene glycol-water, and 40 glycerol-water mixtures were also measured at different concentrations and fit with third-order polynomial expressions. This study provides near-infrared refractive indices that were not previously available and may help with the calibration of refractive index sensors that operate at or near 1550 nm.

Trace level lead Pb(II) to parts per billion (ppb) in water was detected using silicon-on-insulator (SOI) microresonators. The SOI microchips were coated with tetrasulfide functionalized mesoporous silicates.

We describe a simple large-angle interferometer that permits the independent measurements of thickness and refractive index of films in the 20-200 micron thickness range at a 10Hz DAQ rate.

The uptake and release of sorbates into films and coatings is typically accompanied by changes of the films' refractive index and thickness. We provide a comprehensive model to calculate the concentration of the sorbate from the average refractive index and the film thickness, and validate the model experimentally. The mass fraction of the analyte partitioned into a film is described quantitatively by the Lorentz-Lorenz equation and the Clausius-Mosotti equation. To validate the model, the uptake kinetics of water and other solvents into SU-8 films (d = 40-45 μm) were explored. Large-angle interferometric refractometry measurements can be used to characterize films that are between 15 μm to 150 μm thick and, Fourier analysis, is used to determine independently the thickness, the average refractive index and the refractive index at the film-substrate interface at one-second time intervals. From these values the mass fraction of water in SU-8 was calculated. The kinetics were best described by two independent uptake processes having different rates. Each process followed one-dimensional Fickian diffusion kinetics with diffusion coefficients for water into SU-8 photoresist film of 5.67 × 10(-9) cm(2) s(-1) and 61.2 × 10(-9) cm(2) s(-1).

We demonstrate a method for measuring optical loss simultaneously at multiple wavelengths with cavity ring-down spectroscopy (CRD). Phase-shift CRD spectroscopy is used to obtain the absorption of a sample from the phase lag of intensity modulated light that is entering and exiting an optical cavity. We performed dual-wavelength detection by using two different laser light sources and frequency-division multiplexing. Each wavelength is modulated at a separate frequency, and a broadband detector records the total signal. This signal is then demodulated by lock-in amplifiers at the corresponding two frequencies allowing us to obtain the phase-shift and therefore the optical loss at several wavelengths simultaneously without the use of a dispersive element. In applying this method to fiber-loop cavity ring-down spectroscopy, we achieve detection at low micromolar concentrations in a 100 nL liquid volume. Measurements at two wavelengths (405 and 810 nm) were performed simultaneously on two dyes each absorbing at mainly one of the wavelengths. The respective concentrations could be quantified independently in pure samples as well as in mixtures. No crosstalk between the two channels was observed, and a minimal detectable absorbance of 0.02 cm(-1) was achieved at 405 nm.