Optical Multichannel Analyzer System Research Articles

Radiative parameters for some transitions in the spectrum of Ag ii

Radiative parameters for transitions depopulating the levels belonging to the 4d85s2, 4d96s and 4d95d configurations of Ag ii have been obtained from a combination of theoretical lifetimes and experimental branching fractions. On the experimental side, a laser-produced plasma was used as a source of Ag+ ions. The light emitted by the plasma was analysed by a grating monochromator coupled with a time-resolved optical multichannel analyser system. Spectral response calibration of the experimental system was performed using a deuterium lamp in the wavelength range from 200 to 400 nm, and a standard tungsten lamp in the range from 350 to 600 nm. The transition probabilities were obtained from measured branching ratios and theoretical radiative lifetimes of the corresponding states calculated with a relativistic Hartree-Fock approach including core-polarization effects and configuration interaction in an extensive way. Theoretical and experimental data have been compared and the new data have also been compared with the few previous results available in the literature.

Fungus Covered Insulator Materials Studied with Laser-Induced Fluorescence and Principal Component Analysis

A method combining laser-induced fluorescence and principal component analysis to detect and discriminate between algal and fungal growth on insulator materials has been studied. Eight fungal cultures and four insulator materials have been analyzed. Multivariate classifications were utilized to characterize the insulator material, and fungal growth could readily be distinguished from a clean surface. The results of the principal component analyses make it possible to distinguish between algae infected, fungi infected, and clean silicone rubber materials. The experiments were performed in the laboratory using a fiber-optic fluorosensor that consisted of a nitrogen laser and an optical multi-channel analyzer system.

Radiative parameters for some transitions in Cu(II) and Ag(II) spectrum

Radiative parameters for transitions depopulating the levels belonging to the 3 d 8 4 s 2 configuration of Cu(II) and 4 d 9 6 s and 4 d 9 5 d configurations of Ag(II) have been obtained both theoretically and experimentally. On the experimental side, a laser-produced plasma was used as a source of Cu(II) and Ag(II) spectra. The light emitted by the plasma was focused on the input slit of a grating monochromator coupled with a time-resolved optical multichannel analyzer system. Spectral response calibration of the experimental system was made using a deuterium lamp in the wavelength range extending from 200 to 400 nm, and a standard tungsten lamp in the range from 350 to 600 nm. The transition probabilities were obtained using measured branching fractions and available radiative lifetimes of the corresponding states. On the theoretical side, a relativistic Hartree-Fock (HFR) approach, including core-polarization effects, has been used for the calculations. A reasonable agreement theory–experiment has been observed.

Fluorescence lidar imaging of fungal growth on high-voltage outdoor composite insulators

Remote fluorescence imaging of fungal growth on polymeric high-voltage insulators was performed using a mobile lidar system with a laser wavelength of 355 nm. Insulator areas contaminated by fungal growth could be distinguished from clean surfaces and readily be imaged. The experiments were supported by detailed spectral studies performed in laboratory using a fibre-optic fluorosensor incorporating an optical multi-channel analyser system (OMA) and a nitrogen laser emitting radiation at 337 nm.

Spectrochemical Analysis Using Low-Background Laser Plasma Induced by Nd-YAG Laser at Low Pressure

It was demonstrated that the atomic emission lines emitted from a low-background plasma which is produced when a Q-switched Nd-YAG laser (28 mJ, 1064 nm, 8 ns) is focused on a sample at a reduced pressure of 0.5 Torr, can be successfully applied to microarea analysis of samples such as stone. In this regard, it was stressed that analytical equipment can be constructed at low cost using low-background plasma spectroscopy because the gated optical multichannel analyzer (OMA) which is normally used in laser plasma spectroscopy can be replaced by a much simpler OMA system without gating. By comparing the results obtained by low-background plasma spectroscopy and those obtained using an electron-probe microanalyzer (EPMA), it was shown that by using this laser method, a much more sensitive analysis can be achieved. By attaching a small chamber directly to the sample surface with the aid of an o-ring, and applying this laser method, we can construct an in-situ mobile analytical system for use in fields such as geology and archeology.

Microcalorimetry of dust particles in a radio-frequency plasma

The internal temperature of rhodamine B-dyed dust particles (2rp=1.2 μm) immersed in radio-frequency (rf) plasmas has been measured for various plasma conditions. For this purpose, the dye has been excited with an argon-ion laser and the fluorescent emission of the particles has been recorded with an optical multichannel analyzer system. The temperature has been determined after comparison with calibration curves. In argon, the particle temperature increases with rf power and is independent of pressure. In oxygen, an increase with rf power is observed, too. However, the energy flux towards the particles includes also heating by atom recombination (association) and exothermic combustion reactions. These temperature measurements have been compared with calculations based on the thermal balance, where measurements of gas temperature, electron density, and electron temperature have been used. A good agreement between theory and experiment has been found.

System for Fast Measurements of in Vivo Fluorescence Spectra of the Gastrointestinal Tract at Multiple Excitation Wavelengths

We describe a nitrogen dye laser—optical multichannel analyzer (OMA) system capable of quickly measuring tissue autofluorescence spectra in vivo at multiple excitation wavelengths. Sample spectra were acquired successfully from patients undergoing gastrointestinal (GI) endoscopic examination.

Neutral and Ionic Emission in Q-Switched Nd:YAG Laser-Induced Shock Wave Plasma

Excitation mechanisms for copper and zinc atoms as well as their ionic species in the Q-switched (Q-sw) Nd:YAG laser-induced shock wave plasma have been investigated with a time-gated optical multichannel analyzer (OMA) system for various experimental conditions. It is demonstrated that the shock excitation process is the main mechanism responsible for the emission spectra for laser energy ranging from 8 to 86 mJ and surrounding air pressure from 2 to 50 Torr. At air pressure below 2 Torr, collision-induced excitation appears to take over and becomes the operative mechanism. In all cases, the neutral emission dominates over the ionic emission, leading to a high signal-to-background ratio, which tends to decrease, however, at higher laser energy and air pressure.

AUTOFLUORESCENCE GUIDED BIOPSY FOR THE EARLY DIAGNOSIS OF BLADDER CARCINOMA

Purpose We validate the usefulness of laser-induced autofluorescence for the detection of bladder carcinoma. Materials and Methods We obtained and analyzed fluorescence spectra from 75 patients in whom bladder cancer was suspected. Tissue fluorescence was excited by a nitrogen laser using a quartz optical fiber placed in gentle contact with the area of interest. The laser-induced autofluorescence spectrum was recorded using an intensified optical multichannel analyzer system. Spectra were corrected for the spectral response of the optical system, and the ratios of laser-induced autofluorescence intensities (I) at 385 and 455 nm. (I 385/I 455) were determined. We had previously established this ratio as a diagnostic algorithm. We included only suspicious bladder lesions (erythematous, edematous, raised and so forth) that were difficult to diagnose by cystoscopy as well as areas from which random biopsies were obtained. The fluorescence ratio algorithm was applied to 130 bladder areas. Results Of the 130 biopsies obtained during routine cystoscopy 107 (82%) were nonmalignant by histological classification. In contrast, because laser-induced autofluorescence effectively guides biopsies towards malignant lesions, only 30 biopsies (72% fewer) would have been obtained from nonmalignant tissue if the fluorescence ratio that identifies 95% of malignant lesions (95th percentile) had been selected as the decision criterion during standard cystoscopy. Conclusions By guiding the surgeon to suspicious lesions that are most likely to be malignant, laser-induced autofluorescence substantially decreases the number of biopsies obtained from nonmalignant tissue during cystoscopy to diagnose bladder carcinoma.

Spectroscopic measurement of diffuse reflectance for enhanced detection of bladder carcinoma

Objectives. To assess the diagnostic potential of diffuse reflectance spectroscopy for the detection of bladder carcinoma during cystoscopy. Our hypothesis is that neovasculature in neoplastic (dysplastic and malignant) regions will lead to a blood absorption “signature” that is different from that of normal tissue. Methods. Diffuse reflectance measurements have been performed in 14 patients undergoing mucosal biopsies or transurethral resection of a bladder tumor. A quartz optical fiber was advanced through the working channel of a cystoscope and placed in gentle contact with the bladder surface. A standard cystoscopy xenon light source was used for illumination and the reflectance spectra were recorded using an optical multichannel analyzer (OMA) system. From the spectra, the relative concentrations of hemoglobin (Hb), oxyhemoglobin (HbO 2), oxygen saturation (HbO 2%), and the total amount of blood (arbitrary units) were calculated to assess their usefulness in differentiating between neoplastic and benign bladder areas. Results. The spectra of 26 bladder areas (9 malignant areas including 4 carcinomata in situ, 2 dysplastic lesions, and 15 benign areas) have been analyzed. Only the total amount of blood was a useful parameter for the differentiation between neoplastic and benign bladder areas. The sensitivity, specificity, and positive and negative predictive values of this method for neoplastic tissue were found to be 91%, 60%, 63%, and 90%, respectively. Conclusions. The measurement of diffuse reflectance is a fast, simple, and noninvasive method which allows in vivo determination of bladder blood perfusion. The total blood concentration was increased in neoplastic bladder tissue, making it a tool for tissue diagnosis. The relatively low specificity is a result of inflammatory areas also exhibiting an increased total blood concentration. This pilot study encourages further studies to assess the usefulness of reflectance measurements for enhanced detection of bladder cancer.

Correlated electrical and optical measurements of firing semiconductor bridges

Description is given of a high-resolved optical multichannel analyzer (OMA) system and of a firing set whereby OMA records and electrical measurements from a single discharge of a semiconductor bridge (SCB) may be accurately correlated in time. Such a correlation obtained by the novel experimental system is used in order to explain the dynamic discharge behaviors, especially the plasma formation, of the bridges. From the results of the experiments, the minimum electric field to generate a plasma from the W-land SCB is about 0.77×103 V/cm and the time required to evolve the plasma from the bridge is about 1.5 μs, for the SCB 47 μm long and 140 μm wide.

Laser-induced excitation and dispersed fluorescence spectra of the ethoxy radical

Extensive laser excitation and dispersed fluorescence spectra of the ethoxy radical have been recorded in a supersonic jet expansion. Neon transitions have been used to calibrate both the wavelength of the excitation dye laser and the optical multichannel analyser system used to record the wavelength-resolved emission spectra. Both the excitation and dispersed spectra are characterized by prominent progressions involving the C - O stretch vibrational mode. Seven vibrational frequencies for the excited electronic state and eight for the ground state have been assigned. To the best of our knowledge, 10 of these 15 assigned frequencies are reported here for the first time. Vibrational and anharmonic constants for the C - O stretch mode have been determined via least-squares fits for the X state and the B state .

Laser Induced Autofluorescence Diagnosis of Bladder Cancer

Purpose We assessed the ability of laser induced autofluorescence to differentiate malignant from nonmalignant bladder lesions. Materials and Methods We studied 53 patients with bladder cancer undergoing mucosal biopsies or transurethral resection of a bladder tumor. A quartz optical fiber was advanced through the working channel of a cystoscope and placed in gentle contact with the bladder. Tissue fluorescence was excited by 337 nm. light pulses (nitrogen laser). One fiber was used for transmission of the excitation and emission (fluorescence) light. An optical multichannel analyzer system was used to record fluorescence spectra of the sites of interest. Results We analyzed the fluorescence spectra of 114 bladder areas (1 carcinoma in situ as well as 28 malignant, 35 inflammatory, 7 dysplastic, 1 squamous metaplastic and 42 normal areas). These lesions included 44 difficult to diagnose suspicious tumors (11 malignant and 33 nonmalignant). We developed an algorithm that used the I385:I455 nm. fluorescence ratio to distinguish malignant from nonmalignant lesions, including inflammatory areas. By analyzing the data on all 114 lesions, we noted the sensitivity, specificity, and positive and negative predictive values of this method for differentiating malignant from nonmalignant bladder lesions to be 97, 98, 93 and 99 percent, respectively. Conclusions Under excitation with 337 nm. light a clear differentiation between malignant and nonmalignant bladder tissues can be made using the I385:I455 nm. autofluorescence ratio.

Dynamic fluorescence changes during photodynamic therapy in vivo and in vitro of hydrophilic A1 (III) phthalocyanine tetrasulphonate and lipophilic ZN(II) phthalocyanine administered in liposomes

The fluorescence emission of hydrophilic tetrasulphonated aluminium phthalocyanine (AlPcS 4) and hydrophobic zinc phthalocyanine (ZnPc), bound to the membrane of liposomes, was investigated in vivo in an appropriate tumour model of the rat bladder and in RR 1022 epithelial cells of the rat. The sensitizers were administered systemically to the rats and photodynamic therapy (PDT) was performed 24 h later. During PDT treatment, the fluorescence was measured every 30 s. The fluorescence was excited with 633 nm light from an HeNe laser and the fluorescence spectra were detected with an optical multichannel analyser system. PDT was performed for both sensitizers using 672 nm light from an Ar + dye laser. The fluorescence changes during PDT were significantly different for the two phthalocyanines. For AlPcS 4, an initial fluorescence intensity increase, followed by subsequent photobleaching, was observed. In contrast, ZnPc fluorescence showed an exponential decrease and no increase at the start of treatment. Tumour necrosis 24 h after PDT was significant only for ZnPc. RR 1022 cells incubated for 24 h with AlPcS 4 revealed a granular fluorescence pattern, whereas ZnPc was localized diffusely in the cytoplasm of the cells. In agreement with the in vivo measurements, subcellular relocalization and a fluorescence intensity increase were detected exclusively in the case of AlPcS 4. Morphological changes at this time were significant only for ZnPc. The subcellular localization and fluorescence kinetics were obtained using a confocal laser scanning microscope.

OPTICAL SPECTROSCOPY STUDY OF PULSED EXCIMER LASER GENERATED PLASMA FROM CuO

Optical emissions from pulsed excimer laser induced plasma emanating from CuO target are studied by an Optical Multichannel Analyzer system in the context of its implications for thin film growth by Pulsed Laser Deposition. The plasma is generated in four different ambients viz. hydrogen, helium, oxygen (pressure of 100 mTorr in each case) and vacuum (2 × 10−5 Torr ) at different energy densities from 1 to 3.5 J/cm 2. The plasma constituents and their evolution in the growth space (i.e. at a distance of 1.5cm from the target) has been studied. Various transitions corresponding to Cu(I), H(I), Cu(II) and O(II) are observed. The observation of strong transitions due to O(II) in the plasma formed in vacuum, hydrogen and helium suggests significant degree of ionization of atoms via molecular splitting and inverse Bremsstrahlung process during early plasma formation. The persistence of ionicity in the plasma can be attributed to long recombination lifetimes for the specific conditions used. In the case of ablation in oxygen ambient a very significant and remarkably selective enhancement of the copper vapor lasing transition at 510.5 nm is observed which brings out the role of oxygen molecules in sustaining the radiation trapping condition. The changes in the concentrations of neutrals and ions as a function of the laser energy density are also examined. It is argued that impingement of ions/atoms in an excited state on the growing surface can potentially lead to localized energy deposition via non-radiative deexcitation resulting into enhancement of film quality and density.

ANALYSIS OF LASER‐INDUCED FLUORESCENCE LINE SHAPE OF INTACT LEAVES: APPLICATION TO UV STRESS DETECTION

Abstract— In vivo laser‐induced fluorescence spectra of intact leaves of healthy and UV‐irradiated Salvia splendens plants excited at 337 nm by a nitrogen laser were recorded using an optical multichannel analyzer system. The spectra showed the typical fluorescence bands centered around 450, 530, 685 and 730 nm. Exposure to UV radiation changed the relative intensity values of these bands and their peak positions. The analysis of the acquired spectra in terms of a linear combination of Gaussian bands was carried out to determine accurately the peak positions and the relative intensity contribution of the various bands to the laser‐induced fluorescence spectra on healthy and UV‐treated plants of different age.The results indicate that a curve‐fitting analysis of the measured fluorescence spectra is a useful and sensitive method to discriminate the various band contribution to the whole leaf fluorescence spectrum. The comparison among blue‐green and red‐far‐red fluorescence of leaves was also confirmed as an effective indicator of UV stress in plants.

New transients in the electron-transfer dynamics of photolyzed mixed-valence CO-cytochrome c oxidase.

Electron transfer following photolysis of CO from mixed-valence (cytochrome a3+ Cu2+A cytochrome a2+3-CO Cu+B) cytochrome oxidase (ferrocytochrome-c; oxygen oxidoreductase, EC 1.9.3.1) was studied on time scales of nanoseconds to milliseconds by multichannel time-resolved optical absorption spectroscopy. In this method, the optical absorption was measured at many wavelengths simultaneously by using an optical spectrometric multichannel analyzer system. The high-quality time-resolved difference spectra showed a large increase on a microsecond time scale in the visible region centered at approximately 520 nm and in the UV region centered at approximately 390 nm. These absorbance changes were not observed after photodissociation of CO from the fully reduced enzyme and therefore are attributed to intramolecular electron transfer. Simultaneously, there was a blue shift and a small increase in the alpha band, which is attributed to the reduction of cytochrome alpha. Approximately one-third of the absorbance change at 520 nm can be attributed to reduction of cytochrome a. The absorbance changes associated with the 520- and the 390-nm bands are on the same time scale (t1/2 approximately 2 microseconds) as the dissociation of CO from Cu+B reported previously by time-resolved infrared spectroscopy. The position and shape of these bands are reasonable for charge-transfer transitions involving copper(II). We suggest that the absorbance increase at 520 nm, which cannot be attributed to a reduction of cytochrome a, may represent a charge transfer involving Cu2+B accompanying the oxidation of Cu+B to Cu2+B. The absorbance increase at 390 nm is also partially attributed to this transition. These results suggest that Cu2+B may be observed spectrophotometrically in the electron-transfer dynamics of cytochrome oxidase.

The feasibility of blind fragmentation in laser lithotripsy

In laser lithotripsy, it has been found that calculi fragmentation is always accompanied with the formation of a plasma which has two characteristics, i.e. the acoustic signal or shock waves, and the optical signal or plasma emission. By monitoring the feedback signals of the shock waves, the temporal behaviour and the spectra of plasma emission, the feasibility of so-called blind fragmentation has been investigated. The shock wave feedback is found to be not as reliable as the plasma emission feedback and the use of an optical multichannel analyser system to detect, analyse and display the spectra of the feedback plasma emission has proved to be reliable and direct for blind fragmentation. The blind fragmentation technique has been found to be successful in ex vivo experiments in which stones were inserted into pigs' ureters and then fragmented without the use of a ureteroscope. It has also been investigated in vivo in studies from about one dozen patients, and for the first time a series of the plasma spectra have been obtained and analysed in vivo. These indicate promising prospects for the clinical application of the technique and, in addition, application to real-time stone composition analysis. The technique has also been tested for biliary stone fragmentation and for laser angioplasty, again the results have shown good prospects.

Fully-automated excited state measurements with enhanced dynamic range by interfacing a quantel laser YG501 and an optical multichannel analyzer PAR 1205B to an IBM PC/XT

Abstract Transient absorption measurements of photoexcited organic molecules were made with picosecond and nanosecond laser pulses. Detection of the spectroscopic light pulses is carried out with an optical multichannel analyzer (OMA) system. The dynamic range of the vidicon was increased by modifying the readout of the OMA system using a personal computer. The whole arrangement can be controlled for completely automatic measurements and evaluation and processing of the data.

Fluorescence guided excimer laser ablation of intervertebral discs in vitro

Laser induced fluorescence of intervertebral discs was investigated in this study for the first time in order to develop a fluorescence guided percutaneous excimer laser discectomy. For this purpose 35 human cadaveric intervetebral discs from level L1 to L5 were irradiated with a 308 nm XeCl excimer laser with a 60 nsec pulse width at 10, 20 and 30 mj/mm2. Laser light was transmitted over a 1000 microns core optical fiber. Fluorescence emitted from the irradiated tissue was transmitted back over the same fiber over a semireflective mirror to another optical fiber, coupled into a spectrograph and O-SMA optical simultaneous multichannel spectral analyzer system. The spectral lineshape of both the annulus fibrosus and the nucleus pulposus was characterized by a broadband emission between 320 nm and 616 nm with 3 peak emissions at 358, 423 and 457 nm. Relative intensities were calculated by forming two ratios of the peak intensities of the three peaks (R1 = I 423/I 358; R2 = I 423/I 457). Statistical analysis of both ratios revealed a highly significant discrimination between annulus fibrosus and nucleus pulposus (P less than 0.001). Under penetrating conditions multiple recorded spectra showed the spectral profile of subsequently ablated nucleus and annulus. The results of this study demonstrate that discrimination between annulus fibrosus and nucleus pulposus by excimer laser-induced fluorescence is feasible under laboratory conditions. Fluorescence spectroscopy could possibly be developed into a valuable guiding system for percutaneous laser discectomy.