bluuebunny/crossref_metadata_2025 huggingface dataset:
Quadrant Pupil Detection for Optical Data Storage
Authors: Milster T. D. , Bletscher W. L. , Walker E. P. , Gage E. C.
Published: February 2023

We describe a technique that can be used to increase mark density by
reducing track spacing. The technique can be understood by observing
that, as track spacing is reduced, data signal zs contains an
intertrack interference term Δi in addition to the
ideal signal i0, where
is is given by Δi is
commonly referred to as crosstalk. We generate a signal that is
proportional to the derivative of Δi by a technique
we call quadrant pupil detection (QPD). The QPD signal
i
ϵ
can be subtracted from
the derivative of the data signal to yield which can be used for data
detection. Alternatively,
i
ϵ
can be integrated and
subtracted from is directly.
Volumetric Magneto-Optic Storage on Multiple Recording Surfaces
Authors: Rubin Kurt A. , Rosen Hal J. , McDaniel Terry , Tang Wade
Published: February 2023

We demonstrate experimentally, for the first time, erasable magneto-optic recording on an optical disk containing multiple data layers. This technology is based on the use of multiple, partially transmissive data layers separated by spacer regions. It takes advantage of the narrow depth of focus provided by the objective lens to allow selective access to data on each layer by moving the focal position of the objective lens.
Output Beam Quality of Variable Groove Depth Grating Waveguide Couplers
Authors: Bates A. Keith , Erwin J. Kevin , Li Lifeng , Burke James J.
Published: February 2023

Integrated optics technology offers the potential to reduce the size and cost of optical disk read/write heads. Fig. 1 shows how integrated optics technology can be used to generate short wavelength laser light in waveguides using second harmonic generation techniques. Most integrated optical devices depend on optical waveguides to transport laser light between the individual optical components comprising the integrated optical device. For practical use, a method to efficiently couple laser light into and out of the waveguide is necessary to interface the integrated optical device to an external application.
Highly Field Sensitive (150Oe) Quadri-Valued MO Media for High Speed Overwriting
Authors: Takao H. , Shimazaki K. , Ohta N. , Yoshihiro M. , Nagai N. , Imai S.
Published: February 2023

Aiming at the high density MO media, a new scheme of Magnetic Multi-Valued (MMV) recording was introduced[1]. A quadri-valued MO media has been realized using a magnetic field modulation method. For actual application of the media, it is necessary to increase the data transfer rate and recording density. The purpose of this study is producing a quadri-valued MO media which can record with a very small switching field less than 200 Oe, which is similar field strength with an conventional MO drive. On such a media, the quadri-valued recording is available without a drastic change of the drive design. The media has twice a large data transfer rate and linear bit density than those of a conventional MO media.
A Study of Recording Codes for High Density Optical Disks
Authors: Tazaki Saburo
Published: February 2023

This paper surveys several technologies for constructing revolutional types of recording codes based on entirely different ideas from the conventional binary (d, k)RLL codes.
A Partial-Response Maximum-Likelihood Detection Method for MO Recording
Authors: Narahara T. , Aratani K. , Fukumoto A. , Masuhara S.
Published: February 2023

Magnetic field modulation recording (MFM) on a magneto-optical (MO) disk has the advantage of being able to write shorter marks corresponding to higher linear recording density. We reported on an approach to increasing the recording density in an MO disk by improving the signal to noise-ratio (SNR) and optimizing the conventional media structure[1]. The conventional edge detection method combined with a run-length limited (RLL) code has the limitation of detecting recorded bits at linear densities where the minimum carrier level is small because of increasing intersymbol interference (ISI). The partial-response maximum-likelihood (PRML) detection method is well known for being efficient especially for channels that suffers severe ISI but has good linearity.
Dual Wavelength Optical Head for 0.6mm and 1.2mm Substrate Thickness
Authors: Katayama Ryuichi , Komatsu Yuichi , Ono Yuzo
Published: February 2023

Recently, high density optical disk systems employing 0.6mm substrate thickness, such as Digital Versatile Disk (DVD), have been standardized. In these systems, compatibility with conventional optical disk systems employing 1.2mm substrate thickness, such as Compact Disc (CD), is strongly required. In case of reading a 0.6mm disk and a 1.2mm disk using the same optical head, it is necessary to compensate for the spherical aberration due to different substrate thickness. Several kinds of optical heads have been reported for this purpose, such as a dual focus type1), a twin lens type2), and a variable aperture type3).
DVD/CD compatible pickup head
Authors: Takahashi N. , Sato H. , Osawa H. , Nagai K , Isobe H. , Kasuga I.
Published: February 2023

Recently a high density optical disk system: DVD (having about 7 times higher recording capacity than that of the conventional CD disk) has been announced to be marketed within this year. The DVD has designed to have a sufficient capacity enough to store full length movies, and is also expected to be used as a large capacity memory for the personal computer memory application. This DVD disk has a same diameter to that of the CD disk, but its substrate thickness is halved to realize the high recording density, the DVD disks are made by bonding two 0.6 mm thickness substrates back to back and we can read data from each/single side. As a DVD being a kind of optical disks, the DVD drive is assumed to have a compatibility to be able to read conventional CD disks besides DVDs, though the used optical parameters are definitely different We studied several compatible pickup head designs, and we successfully realized a truly compatible optical pickup head which overcame 2 times different substrate thickness and different recording density. We report the structure of our DVD/CD compatible pickup.
A Prototype Optical Tape Recorder
Authors: Put P.L.M. , van Rosmalen G.E. , Kahlman J.A.H.
Published: February 2023

In 1994 [1] a new concept for an optical tape recorder, based on a very fast spinning polygon was presented. Since then, a prototype tape recorder was developed on the basis of this technology. In order to reduce the complexity of the system, the optical configuration was redesigned. Also a new polygon with 10 facets was developed. Finally, the tape transport mechanism was modified in order to further decrease the access time. The result is a smaller recorder consisting of fewer components and with better performance.
Distributed Digital Servo
Authors: Monen Marinus J.
Published: February 2023

The characteristics of a DDS tracking system for optical discs, which supports challenging track eccentricities, recording densities and read/write performance, are discussed.
Ultramicrotoming of Phase-Change Optical Disks for Cross-Sectional Transmission Electron Microscopy
Authors: Kim Myong R. , Park Jeong W. , Lee Jeong S.
Published: February 2023

Ultramicrotomy for the preparation of cross-sectional TEM thin foils of phase-change optical disks and analytical electron microscopy were carried out to examine detailed microstructural features.
3-D Optical Data Storage in Transparent Materials
Authors: Glezer E.N. , Milosavljevic M. , Huang L. , Finlay R.J. , Her T.-H. , Callan J.P. , Mazur E.
Published: February 2023

Three-dimensional optical data storage offers the potential for very large recording capacity and has the possibility of parallel read-out. In addition to research in volume holographic data storage, work has been done in point-like binary 3-D optical storage. Optical recording at a density of 1.6×1012 bits/cm3 has been demonstrated in a photopolymer using two-photon absorption [1]. The stored information consisted of less than 1% changes in the local index of refraction, and was read out serially with a differential interference contrast (DIC) laser microscope.
The Resolution Limit of Optical Disc Mastering
Authors: Put P.L.M. , Morton R.D. , Rusch J.J. , Urbach H.P.
Published: February 2023

With the increase of the information density on optical discs, it becomes increasingly necessary to improve the quality and the resolution of the optical disc mastering process. One possible approach is to reduce the size of recorded structures by a reduction of the λ/NA ratio of the recorder. Indeed, mastering at UV wavelengths has been put into practice by several companies. This paper deals with another possible route towards higher resolution. It is shown that the combination of improved photoresist processes and better exposure techniques can lead to a clear reduction of the smallest achievable pit size. Combining such techniques with UV mastering, pit lengths below 200nm should be well within reach of classical optical disc mastering.
Co/Pt Disks with a Simplified Structure
Authors: Tyan Y.-S. , Hatwar T.K. , Farruggia G. , Victora R. H. , Culver M. W. , Brucker C. F.
Published: February 2023

MO technology is now widely used for erasable optical storage. Almost all MO media products to date are based on rare-earth/transition metal alloys (RE-TM), such as TbFeCo. Although these alloys provide excellent recording performance, their intrinsic corrosion sensitivity necessitates the use of protective layers, typically thin nitride films, on both sides of the recording layer, to protect them from the environment. Frequently, to further enhance the recording performance, an additional reflector layer is used to form an optically tuned quadri-layer structure. The nitride type protective layers are slow and difficult to fabricate. The multilayer, optically tuned structure necessitates tight manufacturing tolerance. The compatibility between layers in terms of adhesion and stress often is difficult to control. These factors, and the fact that the RE-TM alloys are sensitive to oxidation and need to be coated in an excellent vacuum environment, all contribute to the cost of the media.
Image Segmentation with Detection of Highlights and Inter-reflections Using Color
Authors: Bajcsy Ruzena , Lee Sang Wook , Leonardis Aleš
Published: February 2023

There have been some approaches to the image segmentation by manipulating color in red (R), green (G) and blue (B) or in transformed values from RGB [5]. Further, color in RGB has also been used for detecting highlights based on the dichromatic model [1].
Estimation of Surface Spectral Reflectance on the Standard Model
Authors: Tominaga Shoji , Wandell Brian A.
Published: February 2023

The standard reflectance model for inhomogeneous materials suggests that to a good approximation the reflectance function can be described as the weighted sum of two functions1,2. One function represents the interface (specular) reflection, and the second function represents the subsurface (diffuse) reflection. Let S
I
(λ) and S
S
(λ) be the surface spectral reflectances for the two components of interface and subsurface reflections, and let E(λ) be the spectral power distribution of the incident light. Then reflected light is where c
I
(θ) and c
S
(θ) are the geometric scale factors. The parameters θ vary with the viewing geometry. In a previous paper2 we have evaluated this model and shown how to use light reflected from pairs of surfaces to estimate the spectral power distribution of the illuminant.
Direct Estimation of Displacement Histograms
Authors: Girod Bernd , Kuo David
Published: February 2023

To overcome the shortcomings of conventional displacement estimation techniques we propose to estimate the displacement probability density function (pdf) rather than a single displacement vector. The displacement pdf is related to the cross spectrum between successive frames and the signal power spectrum. We derive techniques to calculate the displacement pdf using either a forward image model, a backward image model, or a combination of both models. In an application example the displacement pdf is estimated for a real image pair, and the result is used for motion-based image segmentation.
A Closer Look at the Contribution of a Third Camera Towards Accuracy in Stereo Correspondence2
Authors: Dhond Umesh R. , Aggarwal J. K.
Published: February 2023

In the recent past, trinocular matching [1]-[3] has been proposed as a new technique for achieving local matching in stereo analysis. However, the use of a third image for stereo analysis requires additional computations like preprocessing an extra image (which usually involves expensive 2-D convolutions). Understanding the trade-off between the contribution of a third camera in stereo correspondence and the additional computations needed for the third image is of paramount importance for the design of a real-time stereo-based vision system. Contemporary literature does not contain detailed analysis of the gain in local matching performance of trinocular stereo vis-a-vis binocular stereo. Comparing the two systems based upon accurate ground truth verification of computed disparity has also not been presented. This paper analyzes quantitatively the improvement in local matches when a third image is used.
Needles: A Stereo Algorithm for Texture
Authors: McLauchlan Philip , Mayhew John
Published: February 2023

This paper describes Needles, an edge based stereo algorithm designed to take advantage of the smoothness of many textured surfaces. The correspondence problem is not addressed explicitly. Rather, a simple two stage process extracts surface position and orientation directly. Firstly local disparity histograms over a large range are constructed. Maxima in the histograms correspond to the possible surface depths. A Hough transform is used to fit a plane to the ambiguous disparity points close to the histogram maxima. This confirms and makes more precise the estimates of disparity obtained from the histograms. Local surface disparity and orientation are calculated from the best planar fit after all the histogram maxima (above a threshold) have been tried. This is an extension of an algorithm described in (Pollard 1985) which uses a Hough transform to find local surface orientation without explicit matching. In his algorithm pairs of possible matches vote for the disparity gradient between them. When all pairs have voted the winning disparity gradient (and hence, surface orientation) has the highest Hough accumulator value.
Robust Image Recovery by a Least Median Square Technique
Authors: Kim Dong Yoon , Meer Peter , Mintz Doron , Rosenfeld Azriel
Published: February 2023

To compensate for the inherent limitations of least square based surface fitting (regression) methods, in recent years robust statistical techniques have been developed, the results of which remain trustworthy even if the contaminating noise has a non-Gaussian distribution and/or part of the data is missing (for reviews see the books of Huber, 1981; Rousseeuw and Leroy, 1987)
Steerable Filters
Authors: Freeman William T. , Adelson Edward H.
Published: February 2023

Many early vision tasks require the use of oriented filters; examples are texture analysis [6], noise removal [3], image compression [2], and motion estimation [1]. It is often useful to adaptively control the orientation and phase of the filtering process, in a time-variant or space-variant manner. In this paper we discuss an efficient architecture for such processing and develop flexible design methods for filters used in such a system.
From Depth Map to Wire Frame
Authors: Muck Kin , Porrill John , Pollard Stephen , Mayhew John , Frisby John
Published: February 2023

This paper describes the recovery of wireframe object models from the edge data delivered by stereo vision systems. Edges are typically broken into segments, vertices are often absent, and the recovered geometry may be inaccurate, in addition data associated with surface texture and shadows is not distinguished from the objects edges. The work reported here is addressed at the problem of deriving from such data accurate object models representing geometrical and topological properties explicitly in the form of a Surface/Edge Vertex (SEV) graph. Such viewpoint invariant models will form the basis for automatic model acquisition, model matching, and geometric reasoning for motion planning, grasping etc.
Optical Mammography with Intensity-Modulated Light
Authors: Fantini Sergio , Heffer Erica L. , Franceschini Maria Angela , Götz Linda , Heinig Anke , Heywang-Köbrunner Sylvia , Schütz Oliver , Siebold Horst
Published: February 2023

We report the results of our initial analysis of the frequency-domain optical mammograms collected on a clinical population of 131 patients. The instrument for optical mammography employs four intensity-modulated (at 70 MHz) laser diodes emitting at 690, 750, 788, and 856 nm. The amplitude and phase images of the breast are combined to produce edge-corrected optical images at each of the four wavelengths. The one-wavelength (690 nm) edge-corrected images have been examined according to two different criteria for the assignment of positive optical mammograms. Criterion 1 requires both views of the breast to be positive, while criterion 2 requires at least one view to be positive. The resulting (sensitivity; specificity) was (72%; 52%) (criterion 1) and (88%; 30%) (criterion 2). We show how adding spectral information can improve on these results.
Spatio-Temporal Imaging of Vascular Reactivity by Optical Tomography
Authors: Barbour Randall L. , Graber Harry L. , Schmitz Christoph H. , Pei Yaling , Zhong Sheng , Barbour San-Lian S. , Blattman Seth , Panetta Thomas
Published: February 2023

Representative results from simulated, laboratory and physiological studies are presented, demonstrating the ability to extract important features of dynamic behavior from dense scattering media. These results were obtained by analyzing time series of reconstructed images. Investigations on the human forearm clearly reveal the ability to identify and correctly locate principal features of the vasculature. Characterization of these features using linear and nonlinear time-series analysis methods can produce a wealth of information regarding the spatio-temporal features of the dynamics of vascular reactivity.
Performance of a Multi-channel Time-Resolved Optical Tomographic Imaging System and Tomographic Images
Authors: Yamada Y. , Tamura M. , Eda H. , Oda I. , Ito Y. , Wada Y. , Oikawa Y. , Tsunazawa Y. , Takada M. , Tsuchiya Y. , Yamashita Y. , Oda M. , Sassaroli A.
Published: February 2023

A time-resolved optical imaging system using near-infrared light has been developed and its performance is demonstrated. The system had three pulsed light sources and total 64 channels of detection, working simultaneously for acquisition of the time-resolved data of the pulsed light transmitted through scattering media like biological tissues. The light sources were provided by high power picosecond pulsed diode lasers, and optical switches directed one of the light sources to the object through an optical fiber. The light signals re-emitted from the surface of the object were collected by optical fibers, and transmitted to a time-resolved detecting system. Each of the detecting channels consisted of an optical attenuator, a fast photomultiplier, and a time-correlated single photon counting circuit which contained a miniaturized constant fraction discriminator / time-to-amplitude converter module, and a signal acquisition unit with an A/D converter. The performance and potentiality of the imaging system have been examined by the image reconstruction from the measured data using solid phantoms containing absorbing rods and blood flow.
New Method for the Calculation of Cerebral Blood Flow in Near-infrared Spectroscopy
Authors: Lee Ting-Yim , Gora Felix , Elwell Clare , Smith Martin , Springett Roger , Gharavi Jafar , Goldstone John , Delpy David
Published: February 2023

The method uses linear systems techniques to model the tissue concentration of a near-infrared chromophore following an abrupt change in the arterial concentration. A robust deconvolution algorithm was developed to derive the impulse residue function (IRF) of the cerebral circulation from the arterial and tissue concentration vs time data measured with near-infrared spectroscopy. The height of the derived IRF is cerebral blood flow (CBF) in absolute physiological units. Experimental studies in human volunteers shows that the precision of CBF measurements with the method is about 12%. Cerebrovascular reactivity towards arterial carbon dioxide tension was also demonstrated in piglets.
High Speed Imaging of Scattered Light Signals that Track the Neural Electrical Response
Authors: Rector David M. , Rogers Robert F. , George John S.
Published: February 2023

A number of studies have utilized bright field illumination of neural tissue to image intrinsic absorbance changes associated with slow hemodynamic responses. These methods produce high-resolution but static spatial activation maps from the cortical surface. In order to capture dynamic spatio-temporal patterns, other investigators have employed voltage sensitive dyes. We imaged and investigated fast intrinsic optical responses to vagal nerve stimulation within the nucleus tractus solitarius (NTS) of the rat dorsal brainstem using a novel variable-focus imaging probe without dyes. Dark field illumination enhanced the contrast of light scattering changes, that track electrical dynamics of neuronal activation.
Recent Advances for OCT Imaging of Vascular Tissue
Authors: Saunders Kathleen , Li Xingde , Jesser Christine , Fujimoto James , Brezinski Mark
Published: February 2023

A feasibility for OCT in the identification of vulnerable plaque, the plaques which lead to most heart attacks, has been previously demonstrated (Circulation 93,1206-1213, 1996, Heart 77:397-404, 1997, Heart 82:128-133, 1999). However, poor imaging through blood remains the most significant disadvantage for OCT for vascular imaging. Since blood scatters primarily due to a mismatch in the refractive index between the cytoplasm and the serum, the refractive index of the serum was raised to increase the transparency of blood. Dextran and IV contrast were the test compounds used, which significantly increased penetration. The effect was not due to changes in the red cell concentration or red cell size, at least in the case of dextran, because changes were not significantly different then the saline control. Therefore, this study suggests a feasibility of index matching for increasing OCT imaging through blood.
Localization effects from local phase shifts in the modulation of waveguide arrays
Authors: Tschernig Konrad , Perez-Leija Armando , Busch Kurt
Published: February 2023

Artificial gauge fields enable the intriguing possibility to manipulate the propagation of light as if it were under the influence of a magnetic field even though photons possess no intrinsic electric charge. Typically, such fields are engineered via periodic modulations of photonic lattices such that the effective coupling coefficients after one period become complex-valued. In this work, we investigate the possibility of introducing randomness into artificial gauge fields by applying local random phase shifts in the modulation of lattices of optical waveguides. We first study the elemental unit consisting of two coupled single-mode waveguides and determine the effective complex-valued coupling coefficient after one period of modulation as a function of the phase shift, modulation amplitude, and modulation frequency. Thereby we identify the regime where varying the modulation phase yields sufficiently large changes of the effective coupling coefficient to induce Anderson localization. Using these results, we demonstrate numerically the onset of Anderson localization in 1D and 2D lattices of x- and helically modulated waveguides via randomly choosing the modulation phases of individual waveguides. Besides further fundamental investigations of wave propagation in the presence of random gauge fields, our findings enable the engineering of coupling coefficients without changing the footprint of the overall lattice. As a proof of concept, we demonstrate how to engineer out-of-phase modulated lattices that exhibit dynamic localization and defect-free surface states. Therefore, we anticipate that the modulation phase will play an important role in the judicious design of functional waveguide lattices.
New Fluorescence Techniques for Detecting Noble Gases(*)
Authors: Whitaker Tom J. , Cannon Bret D. , Bushaw Bruce A.
Published: February 2023

Two new concepts for detecting noble gases are reported. Both techniques involve formation of the long-lived 1s5 metastable state of noble gases. The first technique utilizes the photon-burst method and should be capable of isotopically selective detection at extremely small relative abundances. The second concept incorporates a shelving technique that stores noble gas atoms in the metastable state and then pumps these atoms to a higher excited state that radiatively cascades to the ground state, emitting vacuum ultraviolet (VUV) photons. A significant advantage is that AlGaAs diode lasers can be used for the techniques rather than continuous wave cw dye lasers.
Non-linear Laser Spectroscopic Probes of Lamps and other Hostile Chemical Environments
Authors: Greenhalgh D.A. , England W.A. , Webb S. , Devonshire R. , Dring I.S. , Boyson H.F.
Published: February 2023

We have applied CARS spectroscopy to the probing of laboratory and full size chemical reactors and to very high temperature gas flows inside incandescent lamps. This talk will describe the use of CARS measurements in both applications. The talk will conclude with a short summary of some alternative non—linear techniques which we plan to use in future studies.
Photofragment Fluorescence as an Analytical Technique for Gas-Phase Alkali Compounds
Authors: Oldenborg Richard C. , Baughcum Steven L. , Hof Douglas E.
Published: February 2023

Sensitive techniques are needed for the detection of highly corrosive gas-phase alkali compounds in the combustion of coal gas to drive gas turbines. It has been suggested1 that photofragment fluorescence, i.e., the observation of electronically excited photofragments from the photodissociation of the parent compound at suitably short ultraviolet wavelengths, would be a practical diagnostic technique. A recent investigation2 of the photodissociation of gas-phase sodium and potassium chlorides to produce excited alkali atoms has shown that the photofragment fluorescence technique can measure these compounds at concentrations down to sub-part-per-billion levels and is linear over at least six orders of magnitude. The photodissociation of other gas-phase alkali compounds has not been previously investigated.
Ion Dip Spectroscopy and Multiresonant Processes in Aromatic Molecules by Supersonic Molecular Beam Mass Spectroscopy
Authors: Syage Jack A. , Wessel John E.
Published: February 2023

Two-color, mass-resolved ion dip spectroscopy involving multiresonant single vibronic level excitation is described as a selective detection technique as well as a novel spectroscopic tool.
A New Frequency-Scanning Fluorometer for the Determination of Picosecond Rotational-Correlation Times1
Authors: Bright Frank V. , Monnig Curtis A. , Hieftje Gary M.
Published: February 2023

A new frequency-domain instrument is described which allows the determination of picosecond rotation correlation times by monitoring fluorescence-anisotropy decay. In this instrument, a mode-locked argon-ion laser provides the high-frequency excitation source for the fluorophore (Figure 1). The resulting frequency-domain emission is measured with a radio-frequency spectrum analyzer. Calcite polarizers are used to selectively monitor the polarization of the emission radiation parallel and perpendicular to the plane of polarization of the excitation source. Data collection with the new instrument is very rapid. Furthermore, the signal-averaging makes this instrument applicable to weakly fluorescent species.
"Zeeman Electrothermal Atomizer Laser Excited Atomic Fluorescence Spectrometry"
Authors: Dougherty Joseph P. , Preli Francis R. , Michel Robert G.
Published: February 2023

The work of Bolshov et al. (1) demonstrated elemental limits of detection at the femtogram level (part-per-trillion in solution) using Laser Excited Atomic Fluorescence Spectrometry (LEAFS) in a graphite cup atomizer. We have now shown that these detection limits can be equaled by using a graphite tube atomizer. Detection limits for LEAFS of seven elements are reported in Table 1. In this work two different graphite tube atomizers were used. One atomizer was a Perkin Elmer HGA-500 furnace (approximately 28 mm in length). The other was a laboratory constructed furnace (approximately 8 mm in length). The excitation source used for this work was a dye laser pumped by an excimer laser (308 nm). The dye laser output was frequency doubled to excite atomic transitions below 350 nm. The detection system consisted of a monochromator, a photomultiplier tube (PMT), a boxcar integrator and a computer.
Automatic Optimization of Signal-to-Noise Ratios in Time-Filtered Detection
Authors: Seitzinger Newton K. , Lytle Fred E.
Published: February 2023

Although a laser is capable of delivering orders of magnitude more photons in a smaller volume to a sample than a typical arc lamp, there has not been a concomitant decrease in the fluorescence detection limit due to the increased photon density. The reason for this phenomenon is that fluorescence is a blank limited technique. Thus, any increase in excitation power will increase the emission from both the sample and the blank. Therefore, other properties of the laser, such as production of picosecond pulses combined with time-resolved detection techniques, have been utilized to decrease the detection limit.
IR Tunable Diode Laser Absorption Spectroscopy in an no Seeded Molecular Beam
Authors: Hojer S. , Ahlberg H. , Lundqvist S. , Davidsson J. , Holmlid L.
Published: February 2023

In many experiments involving molecular beams for fundamental studies of e.g. chemical reactions in crossed beams [1,2], so called seeded beams are used. In such a beam a few percent of the desired molecule is mixed in an excess of light driver gas. This accelerates the heavier seed molecules, and also cools the translational, rotational, and vibrational degrees of freedom of the molecules. The translational acceleration and simultaneous cooling in the beam can be studied by molecular beam techniques coupled to mass spectroscopy, like rapid mechanical chopping and molecular time-of-flight measurements. The rotational and vibrational temperatures are much harder to determined in an ordinary molecular apparatus, and some optical spectroscopic method is usually needed [3,4,5].
Laser Mass Spectrometry of Solids and Surfaces
Authors: Hercules David M.
Published: February 2023

During the last few years intense effort has been aimed at devising sources for obtaining mass spectra of solids directly. Such sources include field desorption, fission fragment desorption, secondary ion mass spectrometry, fast-atom bombardment, and laser mass spectrometry. A commercially available laser microprobe mass specrometer (LAMMA-1000) provides the possibility for routine use to obtain laser mass spectra (LMS) of solids in the middle mass range.
Analytical Laser Atomic Spectrometry
Authors: Smith B. , Omenetto N. , Winefordner J.D.
Published: February 2023

The uses of laser excitation in analytical spectrometry will be discussed and compared. The analytical techniques include atomic fluorescence spectrometry, atomic ionization spectrometry, and atomic photothermal spectrometry. The ultimate and practical detection limits for each of these methods based upon signal-to-noise ratios will be given and will be compared with experimental values obtained in our laboratory and in other laboratories. Factors limiting the linear range of response (signal vs concentration or amount) for each of the laser based methods will be given as well as magnitude for the linear ranges. The shape of growth curves in atomic fluorescence and atomic ionization will be discussed. Other figures of merit, including the relative standard deviation and the selectivity of measurement, will be discussed. The relative standard deviation involves measurements at concentrations or amounts at least 100 x above the detection limit. The selectivity of measurement is determined by both sample matrix interferences and spectral interferences. Sample matrix interferences are primarily related to the sample cell, flame, plasma, furnace, etc. Whereas spectral interferences are intimately related to the width of the spectral absorption lines, the presence of background atomic and molecular species, and the selectivity possible with dye laser excitation. Sequential excitation with 2 dye laser wavelengths can greatly increase the spectral selectivity and thus the system resolving power. Typical instrumental systems for each of these laser based analytical methods will be briefly mentioned and compared and analytical figures of merit for them will be given. Potential analytical applications for these approaches which require standard samples/solutions will also be considered. Dye laser excited fluorescence, ionization, and photothermal detection also have potential use for measurement of absolute concentrations of species, such as atomic (molecular) species in flames, hot gases, furnaces, and plasmas. The difficulties and requirements of such measurements will be considered.
A Prototype Beryllium Monitoring Instrument Based on the Laser-Induced Breakdown Spectroscopic Technique
Authors: Cremers D.A. , Archuleta F.L. , Romero D.J. , Basinger R.W. , Griggs E.
Published: February 2023

In previous work, Laser-Induced Breakdown Spectroscopy (LIBS)1 was evaluated in the laboratory for application to monitoring beryllium particles in air2 and particles collected on filters3. Based on this work, which showed the feasibility of using LIBS to monitor beryllium, a prototype instrument has been constructed for use in an industrial environment. The instrument was designed to a provide an immediate determination of airborne beryllium concentrations by monitoring contaminated air in real-time (less than 10 secs) and to provide a rapid determination of beryllium collected on air sampling filters (less than 5 min). In contrast, current methods of analyzing beryllium filters can require up to 8 hours, with the majority of time devoted to sample preparation.
Elemental Analysis of Metals at Distances up to 2.4 Meters Using Laser-Induced Breakdown Spectroscopy
Authors: Cremers D.A.
Published: February 2023

The laser spark has been used extensively in the laboratory to provide an elemental analysis of metals.1 This method, called Laser-Induced Breakdown Spectroscopy (LIBS)2, uses a laser spark to vaporize and excite a material. The spark light is then spectrally and temporally resolved, as in other methods of atomic emission spectroscopy, to determine the elemental composition. The method has many potential advantages over more common laboratory-based methods like atomic absorption spectroscopy and the inductively coupled plasma. These advantages include simplicity, minimal sample preparation, possibility of non-invasive and in-situ analysis, and rapid response. On the other hand, the accuracy and precision of LIBS measurements are generally inferior to the laboratory methods thereby cancelling somewhat the advantages of LIBS for routine analyses. In some field-based applications, however, a high degree of analytical performance may not be required. These include prospecting, industrial process control monitoring, and metal identification. The latter area, which includes alloy sorting and identification of stockpiled metals, offers the best chance for immediate application and so has been examined in detail.
Application of Position-Sensitive, Photon-Counting Detectors in Raman Spectroscopy
Authors: Veirs Kirk , Chia Victor K.F. , Rosenblatt Gerd M.
Published: February 2023

Raman spectroscopy has benefited from recent advances in the technology of lasers, optics, thin film interference filters and multichannel detectors. A new generation of imaging detectors based upon microchannel plates with position sensitive anodes may increase the sensitivity of Raman spectroscopy. Such detectors would be particularly useful to Raman spectroscopy without surface enhancement. A position-sensitive detector (PSD) with resolution of 70 microns in both the x and y axis on a 1 inch diameter photocathode with a dark count of 30 counts per second (cps) was used. The signal and signal to noise ratio (SNR) of this detector was compared to the standard intensified photodiode array (IPDA) detector using the Raman spectra of the fundamental vibration of O2 in air.
Detection and Differentiation of Neutral and Ionic Reaction Mechanisms in Molecular Clusters
Authors: Steadman J. , Fournier E. W. , Syage J. A.
Published: February 2023

A longstanding goal in the chemical analysis of reaction mechanisms is understanding the role of the solvent. We have been involved in work that addresses this issue on a single molecule basis by studying reactions in molecular clusters.1–3 In this report we describe a means for detecting and measuring rapid intermolecular cluster chemistry using mass-selective picosecond resonance-enhanced multiphoton ionization (REMPI). Molecular beam mass spectrometry offers a powerful means for identifying a variety of product species and distinguishing precursor cluster size. However, such investigations demand an independent means for differentiating neutral cluster reactions from ionic reactions. Our approach is to obtain direct measurements of the ion dissociation mechanisms by electron-impact (El) ionization and by mass-selective ion photodissociation.
Laser Desorption Jet-Cooling Spectroscopy of Organic Molecules
Authors: Meijer G. , de Vries M.S. , Wendt H.R. , Hunziker H.E.
Published: February 2023

Laser desorption coupled with mass selective detection enables a sensitive detection of molecules, desorbed from a surface without fragmentation. Additional selectivity is obtained when the desorption is performed in the expansion region of a supersonic free jet. In this approach the internal degrees of freedom of the desorbed species are cooled down by multiple collisions, the desorbed molecules are brought into the detection region with a high efficiency, and both mass selective and wavelength selective detection can be performed using a Resonance Enhanced Multi Photon Ionization (REMPI) detection scheme.
Single Molecule Detection in Flowing Sample Streams As An Approach to DNA Sequencing
Authors: Jett James H. , Davis Lloyd C. , Hahn Jong Hoon , Keller Richard A. , Krakowski Letitia , Marrone Babetta , Martin John C. , Ratliff Robert , Seitzinger Newton K. , Shera E. Brooks
Published: February 2023

We are exploring a technique which has the potential to sequence large fragments of DNA at a rate of hundreds of bases per second. Our technique is based upon a projected ability to detect single chromophores by laser-induced fluorescence in flowing sample streams.1 The technique involves: (1) labeling the nucleotides with base specific tags suitable for fluorescence detection, (2) selecting a desired fragment of DNA, (3) suspending the single DNA fragment in a flowing sample stream, (4) sequentially cleaving labeled bases from the free end of the DNA fragment using an exonuclease, and (5) detecting and identifying the cleaved, labeled bases as they flow through a focused laser beam.2
Measurements of Rotation and Fluorescence Lifetimes for Optimizing the Detection of Single Fluorescinated Bases
Authors: Davis Lloyd M. , Seitzinger Newton K. , Shera E. Brooks , Keller Richard A.
Published: February 2023

Time Correlated Single Photon Counting is an optimum technique for acquiring fluo­rescence decay profiles over a large dynamic range with accurately known errors. The data are fully utilized in a statistical sense when analyzed by weighted non-linear fitting to a decay function convolved with the experimentally measured prompt response function.1
Diagnosis of Disease in Human Tissue using Laser-Induced Fluorescence
Authors: Rava Richard P.
Published: February 2023

With the development of fiber optics, it is now possible to obtain fluorescence spectra from remote parts of the body. Thus, laser induced fluorescence (LIF) is becoming an important method for diagnosing pathology in human tissue [1-4]. In the short period of time since such studies have been undertaken, however, it is clear that consideration of the morphological and/or molecular species responsible for the fluorescence is necessary for developing accurate algorithms for diagnosing disease from tissue LIF [1-2].
Application of UV Laser-Produced Microplasmas as a Novel Detector for Gas Chromatography
Authors: Miziolek Andrzej W. , Morris Jeffrey B. , Forch Brad E.
Published: February 2023

Earlier work in our laboratory has demonstrated the unusual ability of UV lasers to produce microplasmas in gaseous flows using very low pulse energies (< 1 mJ). One of the reasons that this pulse energy requirement is so low is that there are strong resonance effects in the production of the seed electrons necessary for microplasma growth. One application of this phenomenon is to use microplasma formation in the effluent gases of a gas chromatograph (GC) as the basis for a new GC detector.
Waveguide Excimer Lasers: New Light Sources for Chemical Analysis
Authors: Christensen C. Paul , Cohn Sarah
Published: February 2023

Excimer laser wavelengths in the 353 - 193 nm portion of the spectrum
have many applications in chemical analysis. However, fully utilizing
the potential of the excimer laser has always been a challenging
problem. Waveguide excimer lasers combine excimer laser technology
with optical waveguiding concepts and microwave discharge excitation
to produce a family of lasers with novel operating parameters. These
unique lasers address the problems of size, cost, reliability,
lifetime and gas handling associated with conventional excimer lasers,
thus making them viable light sources for applications such as
fluorescence spectroscopy, electrophoresis, surface analysis,
combustion diagnostics.
Laser-Enhanced Ionization Spectroscopy and its Applications for Trace Element Analysis.
Authors: Rubinsztein-Dunlop Halina
Published: February 2023

Laser-based methods have manifested themselves as powerful tools for ultra-sensitive trace element analysis. They can be conveniently divided into the methods which utilize light processes for detection and those which use the charges created in the optical processes for detection.
Characterization of III-V Materials by Resonance Ionization Mass Spectrometry.
Authors: Downey S.W. , Hozack R.S.
Published: February 2023

Layered, III-V compound semiconductors are important as both electrical and optical devices in communications technology. Often, these heterostructures have complicated elemental distributions that need quantitative characterization. Depth profiling by sputtering through these layered materials is one method of obtaining elemental distributions. Under optimum conditions, atoms are the predominantly sputtered product; the atom flux therefore provides information about the sample that is relatively free from chemical (matrix) interferences. Resonance Ionization Mass Spectrometry (RIMS) [1] is used to record elemental depth profiles by probing the atom flux from sputtered III-V heterostructures providing information that is quite representative of the sputtering sample.
Laser Applications at the Naval Weapons Center.
Authors: Geyer T. J. , Gruber J. B. , Hills M. E. , Johnson C. E. , Seltzer M. D. , Weimer W. A. , Green R. B.
Published: February 2023

Research in the Chemistry Division at the Naval Weapons Center (NWC) is primarily devoted to the design, synthesis, and characterization of new materials for a variety of Navy applications. The impact of lasers in the processing and characterization of materials is growing in significance.
Surface Plasmon Enhanced Raman Spectroscopy As A Generic Sensing Technology
Authors: Pester Paul D , Hopkins Andrew R
Published: February 2023

Raman Spectroscopy is one of the most versatile methods of molecular analysis. The Raman effect is seen when light interacts with an atomic or molecular species, in the solid, liquid or gas phase, to produce scattered light, the frequency of which is shifted from that of the incident light. The shift in frequency corresponds to electronic, vibrational or rotational energy transitions in the sample and, since these energies are species specific, the scattered Raman light can provide identification of the molecules irradiated.
Non-Contact Thermometry of Acoustically Levitated Water Drops
Authors: Seaver Mark , Peele J. R. , Manuccia T. J.
Published: February 2023

Evaporative cooling of volatile liquids is a well known phenomenon. In the case of liquid drops, however, the theoretically predicted temperature has never been observed. This discrepancy arises due to heat conduction along the thermocouple which is used to suspend the drops and measure their temperature[1,2]. As a remedy to this situation, we have developed a fluorescence based method that remotely measures the temperature of levitated water drops. Application of this method to individual drops of water provides drop temperatures which agree with those predicted by theory.
Near-Infrared Fluorescence Techniques in Analytical Chemistry
Authors: Patonay Gabor , Williams Richard J. , Shealy Dana
Published: February 2023

The near-infrared (NIR) region is advantageous due to lower interference since there are only a few groups of compounds that can fluoresce. Examples of analytical application of NIR fluorescence with emphasis on laser diode spectroscopy will be given.
Semiconductor Laser-Induced Fluorescence Spectroscopy in Pico-liter Volume Flow-Cells
Authors: Larson Anders P. , Ahlberg Henrik , Folestad Staffan
Published: February 2023

In this study the potential of using visible semiconductor lasers as the excitation source for laser-induced fluorescence spectroscopy (LIF) of nano-liter to pico-liter samples has been evaluated. The incentive to work with LIF in the upper visible and near infrared wavelength region is the possibility to design a system that is not limited by any background fluorescence, e.g. from a capillary flow-cell or the liquid eluent [1]. The system described here was mainly designed for applications to chemical ultra-trace analysis when combined with miniaturized separation techniques such as capillary liquid chromatography and capillary electrophoresis. A concentration limit of detection in the lower pico-molar range (6.3 - 58 · 10-12 mol/L) was obtained for a model fluorescent compound, HITCI (1,1’,3,3,3',3'-hexamethyl-indotricarbocyanine iodide). The smallest illuminated volume was 0.7·10-12 L using an 11 μm inner diameter fused silica capillary flow-cell. These figures compares well with the best obtained using conventional gas-lasers for LIF [2,3]. An important advantage with the semiconductor LIF system, except from that it is inexpensive, is that the compactness and the high performance of the components makes it highly suitable for portability.
SERS Fiber Optic Probes
Authors: Mullen Ken , Carron Keith
Published: February 2023

We are using Surface Enhanced Raman Scattering (SERS) to develop a fiber optic probe for monitoring groundwater contamination. Attaching a molecule to a SERS surface produces a million fold enhancement of the Raman signal. Our approach is to fabricate a SERS surface at the fiber tip and attach indicators to the silver SERS surface. The SERS surface is fabricated by roughening the end of the optical fiber with polishing paper and vacuum depositing silver over the roughened fiber tip. We irreversibly bind the indicators by modifying the acid group of the indicator with a thiol containing species. The thiol anchors the indicator to the silver surface and forms an inert, robust coating.