A Photomultiplier Tube (PMT) based optical fiber Raman sensor was developed for online
monitoring of nitrogen/oxygen concentration ratios in gaseous mixtures. The sensor employed a frequency
doubled 532 nm continuous wave (CW) Nd:YAG laser and a modified In-Photonics fiber optic state-of-art
miniaturized Raman Probe. The gaseous mixture was enclosed in a high pressure cell and subjected to
varying degrees of pressure. Raman signal of gaseous nitrogen and oxygen were first analyzed with a
miniature spectrometer. The detection system was then replacing by a Labview interfaced PMT module for
fast data acquisition and real time monitoring of relative Raman signals of nitrogen and oxygen.
Instrumentation features and sensor performances with different detection systems (i.e. spectrometer and
PMT) is presented in the paper.
Raman and Laser Induced Fluorescence (LIF) spectroscopic techniques were used for studying Azotobacter vinelandii- a genus of free-living diazotrophic soil bacteria. Azotobacter has generated a great deal of interest owing to their unique mode of metabolism. It is a large, obligately aerobic soil bacterium, which has one of the highest respiratory rates known among living organisms and is able to grow on a wide variety of carbohydrates, alcohols and organic acids. The Raman Scattering of Azotobacter, incubated with gold nanoparticles, was examined with 532-nm as an excitation laser wavelength. The basic instrumentation for characterizing the bacteria by Raman spectroscopy employed a continuous wave (CW) frequency doubled Nd: YAG laser (532-nm) and a modified In-Photonics fiber optic state-of-art miniaturized Raman Probe. The surface enhancement effects allowed the observation of Raman spectra of such bacterial cells, and were excited in the visible region of wavelength at low incident power for minimum sample degradation. LIF spectra of Azotobacter were measured with a 410-nm CW diode laser as an excitation source, and a reflection probe to deliver laser beam on the sample and collect the LIF signal from the sample. Spectral contrast observed in gold particles conjugated bacteria, from nitrogen fixing and non-nitrogen fixing condition was analyzed for characterizing the bacteria cells, and the results are presented in the paper.
A novel fiber optic prototype sensor based on Raman spectroscopy for qualitative and quantitative monitoring of various chemicals in the sample was developed. The sensor employs a high power 670nm laser diode as an excitation light source and a specially designed fiber optic Raman probe with launching and collecting fibers. Raman signal was collected by six optical fibers; filtered, and then fed to the spectrometer through another optical fiber bundle. The uniqueness of the sensor lies in its compact and stable design configuration, that includes carefully aligned optical components, viz. laser diode, filter holder, and miniature spectrometer. Developed sensor is immune to ambient light fluctuation and offers a cost effective solution for probing several species in harsh environment. Various issues like system fabrication, optimization, functional stability, signal/noise ratio, repeatibility etc are well addressed and presented in this paper.
An optical fiber sensor is being developed for diagnosis of human breast cancer cell lines. The sensor exploits laser-induced fluorescence spectroscopy in conjugation with fiber optics. The main advantage of fluorescence detection compared to absorption measurements is the greater achievable sensitivity due to the fact that the fluorescence signal has a very low background. However, an accurate and sensitive method for the diagnosis of cancer cell lines is quit challenging. The sensitivity and accuracy of LIF technique can be improved by optimizing the sensor configuration. In this work, the spectral characteristics of the fluorescence, which was induced by frequency tripled Nd:YAG laser operating at 355nm are recorded from two different type of human breast cancer cell line. Effects of various influential experimental parameters and configuration were investigated in order to optimize the sensor performance. The sensor with optimum configuration enables to differentiate two types of cancerous cell lines with a maximum achievable fluorescence spectral contrast. A unique data processing technique has been developed to analyze the recorded data for cell lines identification and differentiation.
A comprehensive experimental study of a fiber optic relative humidity (RH) sensor is carried out in terms of characterization and performance optimization against various parameters that affect the sensor response and sensitivity e.g., film composition, film thickness, fiber core diameter, and the sensor geometry. The sensor is based on evanescent wave absorption spectroscopy and utilizes a specific reagent immobilized permeable polymer membrane cladding on a declad U-bend optical fiber. An optimum film thickness and an optimum film composition exist. In addition, a fiber with a smaller core diameter was observed to be more sensitive, unlike the previously reported results. The sensitivity further increases with a decrease in the bending radius. The sensor is found to be sensitive to RH ranging from ~1.6 to ~92%, exhibiting a very fast response time, an extremely good degree of reversibility, repeatability, and a large dynamic range.
Auto fluorescence of tissue depends not only on the concentration of fluoro-phores present in tissues but also on the configuration of optical fiber sensor. In this paper, feasibility of using laser induced fluorescence spectroscopy as a diagnostic tool for distinguishing malignant animal tissue from its normal counterpart under various design configurations is explored. Three different design configurations are tested for the performance optimization. The optimized Y-shaped optical reflection fiber probe gives the best laser induced fluorescence signal comparing to other probes. This instrument incorporated a continuous wave (CW) Nd:YAG laser operating at 532 nm.
Ethanol and methanol form the essential components in the hydrocarbon-based fuels, serving as transportation fuels also; and will likely play an increasingly important role in the future as crucial fuel components. The motivation of the present work is to differentiate such hydrocarbons from their mixture sample on the basis of their spectrum analysis for various ratios of their composition. A fiber optic Spontaneous Raman sensor is developed as a probe indicator for component detection of such hydrocarbon mixtures. The sensor employs a frequency doubled 532 nm continuous ND:YAG laser and a specially designed fiber optic Raman probe. Raman signal was collected by six optical fibers; filtered, and then fed to the spectrometer through another optical fiber bundle. Attractiveness of our scheme lies in the online determination of sample constituents without employing specially designed IR fiber with much-complicated and expensive IR spectroscopy and, with no alteration in sample physico-chemical structure. Spectral analysis techniques based on spectral shape band intensities and areas and some multi-component analysis are being tested to find the most effective tool for measuring ethanol and methanol from the mixture. The analysis results from these tests will be presented in the paper.
Laser-induced fluorescence (LIF) is an accurate, sensitive and rapid method for the diagnosis of a normal and malignant tissue. In this paper, an optical fiber sensor was developed to enhance spectral difference between the normal and malignant tissue with sensor optimization to improve the accuracy of cancer diagnosis. This instrument incorporated a pulsed laser operating at 355 nm (frequency triple Nd:YAG and Q-switched Nd:YAG pump dye laser) with bifurcated optical fiber to allow illumination of tissue and collection of fluorescence with a single fiber. Using the laser excitation, the detection of the fluorescence signal from the tissue was performed almost instantaneously. A sufficient fluorescence contrast (of the order of more than 22.22 times) for malignant versus normal tissue was obtained. The results of our approach were compared with histopathology results and indicated excellent agreement in the classification of normal and malignant tissue.
The paper describes an optical fiber based sensor (FOS) for the detection of the pollutant gas, NO2, in a mixture of gases.
The design comprises of a fiber optic transflection probe with a sensor element placed at one end. In the present FOS, the transducing component is prepared by sol-gel process. An equal quantity of a diazotizing reagent together with a coupling reagent is immobilized in the sol-gel matrix, which forms an azo dye in the presence of NO2. The sensor relies on the coloration reaction occurring at the micropores of this sol-gel film in the NO2 environment and offers a consequent variation in the optical absorption at a specific wavelength. The current sensor design gives more than 85% of variation in the output intensity at a NO2 concentration of few parts per million in air sample.
We report a novel fiber optic relative humidity sensor based on the evanescent wave absorption spectroscopy. A comprehensive study of the sensor was made in terms of performance optimization against various parameters, which affects the sensor response and sensitivity e.g. film composition, film thickness, fiber core diameter and the sensor geometry. The sensor was compared against a commercially available relative humidity sensor and was found to be sensitive to relative humidity ranging from ~1.6 % to ~92%. We found that the sensor was having a very fast response to the relative humidity, and was fully reversible, repeatable with an extremely large dynamical range.
The motivation of this work is to monitor the real time concentration of nitrates in the radioactive wastes, as they are the key molecules in the solution. The effect of different optical configurations of the probes on the Raman signal was studied using acetone as the test sample. We found that InPhotonicsTM Raman probe give best signal-to-noise data comparing to the other two probes evaluated. The Raman spectra of 10% NaNO3 solution were then successfully recorded with this probe. The Raman signal of Nitrate at 1054 cm-1 is very strong with 500 ms sampling time. The initial study shows that the Raman sensor is capable to monitor the nitrate in the nuclear waste tank.
We present here a very fast, responsive fiber optic relative humidity (RH) sensor. The sensor was obtained by coating a thin PVA/CoCl2 film on the core of a plastic cladding fiber; the film was deposited after removing the cladding of the fiber. The sensor response is very fast even to a slight change in relative humidity and has a good dynamical range. The sensor is quite repeatable and fully reversible. The performance of the sensor was compared against a commercially available relative humidity sensor and was found to be sensitive to RH ranging from 3 to 90%. The sensor developed was found to be faster than the commercially available sensor in the higher humidity range. The time stability of the sensor has also been checked and was found suitable for a long term monitoring application. The sensor should be quite useful for monitoring RH in harsh industrial environments.
Optical fiber has been used to develop various sensors such as temperature, pressure, magnetic field, stress, moisture, etc. A recent development in optical fiber technology due to fiber communication has drawn lot of interests in developing new optical fiber sensor. It has several advantages over conventional sensors. This paper will describe some of our works on the application of optical fiber sensors for the measurement of strain and moisture.