Independent Component Analysis Applied to Raman Spectra for Classification of In Vitro Human Coronary Arteries

Abstract

Optical diagnostic methods, such as near‐infrared Raman spectroscopy allow quantification and evaluation of human affecting diseases, which could be useful in identifying and diagnosing atherosclerosis in coronary arteries. The goal of the present work is to apply Independent Component Analysis (ICA) for data reduction and feature extraction of Raman spectra and to perform the Mahalanobis distance for group classification according to histopathology, obtaining feasible diagnostic information to detect atheromatous plaque. An 830 nm Ti:sapphire laser pumped by an argon laser provides near‐infrared excitation. A spectrograph disperses light scattered from arterial tissues over a liquid‐nitrogen cooled CCD to detect the Raman spectra. A total of 111 spectra from arterial fragments were utilized.     

Forensic Analysis of Color Toners by Raman Spectroscopy

Abstract

Raman spectroscopy has recently become more popular for the chemical analysis of several types of materials of forensic interest. The Raman technique allows the measurement of the inelastic scattering of light due to the vibrational modes of a molecule when irradiated by an intense monochromatic source such as a laser. Forensic laboratories must often work with small samples in order to determine the type of material and its possible manufacturer for investigatory and evidence purposes. This paper describes the analysis of a color photocopied document for the identification of the particular type of toner used in the generation of the document.     

Some New Types of Sample Cells for Raman Spectroscopy with Laser Excitation in Molten Salts

SUMMARY

The introduction of the laser as an excitation source in Raman spectroscopy offers numerous new possibilities of investigations but demands the design of new types of sample cells specially suited for laser application. Two cells for work with molten salts corrosive to glass and quartz and a simple cell for melts noncorrosive to glass are described. The best results are obtained with a cell which provides total utilization of the laser energy for excitation by multiple reflection of the laser beam. In addition, some necessary accessories for molten salt work, i.e., a gas heater and filtration equipment to free the melt of suspended impurities which might cause an undesirable level of Tyndall and Rayleigh scattering, are mentioned.     

Electro-Optical Multichannel Spectrometer Directly Interfaced to a PDP 11/20 Computer. Application in Fast Raman Spectroscopy.

ABSTRACT

This paper describes the hardware and software required to interface the TV camera tube of a CODERG UF 11 fast multichannel spectrophotometer with a PDP 11 minicomputer. Up to 21 lines of the video signal are sampled, each at 96 points, then stored in the computer memory. Each line is displayed separately for examination, afterwards significant ones are summed in order to enhance the signal/noise ratio of the spectra. A set of software modules facilitates spectral data processing. The capabilities of the system are illustrated by recording fast Raman and emission spectra, excited. by a 30 ns laser pulse.     

Laser-Based Fluorescence Eem Instrument for In-Situ Groundwater Monitoring

I. ABSTRACT

A fluorescence excitation-emission matrix (EEM) instrument is described which employs laser excitation and optical fiber light delivery for remote sensing applications. Ultraviolet laser light is generated at a variety of discrete wavelengths by pumping a Raman shifter with the third or fourth harmonic of a Nd:YAG laser, and this Raman-shifted light is used for fluorescence excitation to generate EEM spectra. Seven-meter optical fibers are used for laser beam delivery and fluorescence light collection, and a diode array detector is used to detect fluorescence emission spectra. As a test of the capability of this instrument, the composition of a two-component mixture of the groundwater pollutants carbazole and p-cresol is determined quantitatively by least-squares analysis of the mixture's fluorescence EEM. Detection limits were in the ppb range and the linear dynamic range was better than 3 orders of magnitude.     

Near Infrared Raman Spectroscopy System for Real Time Monitoring of Fast Processes: A Resin Composite Photopolymerization Application

Abstract

This work describes the implementation of a technique for data monitoring using dispersive near‐infrared Raman spectroscopy that presents the advantage of non‐invasively being capable to make real time fast measurements. The degree of conversion of an odontological resin composite (A3, Z100^®, 3 M), photopolymerized by an LED (450 nm, 230 mW), was measured as an application of the technique. The Raman system consisted of a 785 nm Ti:Sapphire laser, a Chromex spectrograph with an entrance slit of 200 µm, and a liquid nitrogen cooled CCD detector. The system allowed acquisition of Raman spectra at times as short as 6 s. The progress of the photopolymerization was followed by obtaining Raman spectra every 6 s during 84 s. The intensity of the 1640 cm^?1 Raman peak, attributed to the aliphatic carbon double bonds, was chosen to calculate the conversion degree of the resin photopolymerization. Results showed that the degree of conversion presented an exponential growth, reaching a maximum of 50% after 60 s. Findings seem to confirm the trustworthiness of the system.     

红外D2喇曼激光器的实验研究

用高功率TEA CO₂激光TEM₀₀模泵浦低温多程池中的D₂,利用其受激转动Raman散射(SRRS),我们获得了11～14μm光谱范围内可调谐Raman激光输出。典型的TEA CO₂ 10R(20)线30MW输入泵浦可获得大约7.93MW的12.5μm红外激光输出。     

温度对仲氢受激拉曼散射的影响

研究了仲氢气体温度对受激拉曼散射的影响.导出一个简明的粒子数密度差与温度的关系式.利用该式计算的结果表明,仲氢拉曼激光器最适宜的工作温度为液氮温度.温度更低时,拉曼增益出现饱和.借助该式,讨论了激光在拉曼多程池中的最佳传输次数与温度的关系.降低温度对提高拉曼增益和减少最佳传输次数是一条有效的途径.     

Computer-Controlled Liquid Chromatographic System that Includes a UV-Visible Scanning Spectrophotometer and a Coherent Anti-Stokes Raman Spectrometer

ABSTRACT

Resonance enhanced coherent anti-Stokes Raman spectrometry (CARS) has been demonstrated as a specific identification system for liquid chromatography. To achieve this work in the areas of CARS. liquid chromatographic preconcentration and separation, and computer control of the liquid chromatograph/ultraviolet-visible/CARS experiments were undertaken. Column selection, flow rate, and solvent composition were monitored and controlled. The ultraviolet-visible spectrometer was used at a fixed wavelength until a species was detected. The flow was stopped, the absorption spectrum was scanned, and flow was resumed. After calculation of the optimum excitation frequency, the Raman spectrum was scanned under control of the computer with on-line signal averaging and data smoothing.     

Timing Circuitry for Pulsed Laser Desorption on a Scanning Mass Spectrometer

ABSTRACT

A laser desorption chemical ionization mass spectrometer configuration has been previously reported (1). The system uses a short pulsed (40 nS) CO₂ laser interfaced to a mass spectrometer (Dupont 491) which normally acquires spectra by continuous scanning of the magnetic field. In this article, the details of the timing circuitry which enables coordination of the laser pulse, mass scanning, and data acquisition are described.     

A Raman Spectroscopic Study of MoS<Subscript>2</Subscript> and MoO<Subscript>3</Subscript>: Applications to Tribological Systems

Molybdenum disulfide (MoS₂) and molybdenum trioxide are investigated using Raman spectroscopy with emphasis on the application to tribological systems. The Raman vibrational modes were investigated for excitation wavelengths at 632.8 and 488 nm using both micro-crystalline MoS₂ powder and natural MoS₂ crystals. Differences are noted in the Raman spectra for these two different wavelengths, which are attributed to resonance effects due to overlap of the 632.8 nm source with electronic absorption bands. In addition, significant laser intensity effects are found that result in laser-induced transformation of MoS₂ to MoO₃. Finally, the transformation to molybdenum trioxide is explored as a function of temperature and atmosphere, revealing an apparent transformation at 375 K in the presence of oxygen. Overall, Raman spectroscopy is an useful tool for tribological study of MoS₂ coatings, including the role of molybdenum trioxide transformations, although careful attention must be given to the laser excitation parameters (both wavelength and intensity) when interpreting Raman spectra.     

Picosecond Fluorescence Spectroscopy By Time-Correlated Single-Photon Counting

Abstract:

We describe the recent progress made in our laboratory on the time-resolved fluorescence spectroscopy by the combination of stable short-duration pulses from a CW mode-locked laser and a time-correlated single-photon counting method. Particular emphasis is placed on the achievement of high time resolution with side-on and microchannel-plate photomultipliers. We also discuss the limitation of using this method in the picosecond time range. Several applications of this spectroscopy such as the measurements of fluorescence decay characteristics and time behavior of fluorescence depolarization are reported. It is also shown that the high sensitivity of this method with pico-second time resolution is very suitable for the temporal rejection of cumbersome background-fluorescence in Raman spectroscopy. Finally, we present a novel method of photon time-of-flight fluorescence spectroscopy, in which an optical fiber is employed as a dispersive element.     

CO2激光在P-H2中的受激喇曼转换

本文修正了Byer的分析结果,推导出新的CO₂激光在多程P-H₂腔池中受激喇曼散射激光输出功率的表达式,并据此给出P-H₂池中泵浦激光最佳散射次数的公式,为喇曼激光器设计及共性能分析提供了可靠的依据。     

A Simple Driver for Dynamic Or Static Operation of a Laser Diode Intracavity Spectrophotometer

ABSTRACT

Modulated operation of the recently described method of laser diode intracavity absorption spectrometry is discussed. A simple driver circuit which can be used for cw or modulated operation of laser diodes is described. Development of a modulated near infrared laser diode intracavity spectrophotometer for absorption measurements is also provided. This modulated operation mode was compared to cw mode as to sensitivity, noise, ease of operation and detection limit. This modulated driver was implemented using an inexpensive 3 mW 750 nm laser diode and an IR3C02A driver circuit. Advantages of modulated laser diodes in spectroscopic applications are also presented.     

Flexible and stable optical parametric oscillator based laser system for coherent anti‐Stokes Raman scattering microscopy

The characteristics of a stable and flexible laser system based on a synchronously pumped optical parametric oscillator (OPO) is presented. This OPO can offer very stable operation with both ～1 ps and ～300 fs outputs over a broad wavelength range, i.e., 920–1200 nm. Combining the pump tuning with the OPO tuning, a total Raman range of 1900–5500 cm^?1 is accessible. For maximum spectral sensitivity, the CARS microsope based on the ps laser system is presented in detail. The lateral resolution of the microscope is diffraction limited to be about 390 nm. Fast wavelength switching (sub‐second) between two Raman vibrational frequencies, i.e., 2848 cm^?1 for C? H aliphatic vibrations and 3035 cm^?1 for C? H aromatic vibrations is presented as an example, although this also extends to other Raman frequencies. The possibility of obtaining a multimodal imaging system based on the fs laser system is also discussed. Microsc. Res. Tech., 2010. © 2009 Wiley‐Liss, Inc.     

A High-Resolution Time-of-Flight Mass Spectrometer With Laser Desorption and a Laser Ionization Source

ABSTRACT

Details of the novel method of laser desorption with a low powered IR-laser and resonance-enhanced multiphoton ionization (REMPI) combined with a high-resolution Reflectron-Time-of-Flight (RETOF) mass spectrometer are explained. Different features of the method are discussed. Some results of mass spectrometric investigations of biomolecules are shown.     

Near-field and confocal surface-enhanced resonance Raman spectroscopy at cryogenic temperatures

For laser spectroscopy at variable temperatures with high spatial resolution a combined scanning near‐field optical and confocal microscope was developed. Rhodamine 6G (R6G) dye molecules dispersed on silver nano‐particles or nano‐clusters were investigated. For optical excitation of the molecules, either an aperture probe or a focused laser spot in confocal arrangement were employed. Raman spectra in the wavenumber range between 300 cm^?1 and 3000 cm^?1 at room temperatures down to 8.5 K were recorded. Many of the observed Raman lines can be associated with the structure of the adsorbed molecule. Intensity fluctuations in spectral sequences were observed down to 77 K and are indicative of single molecule sensitivity.     

Postionization of Laser-Desorbed Organic and Inorganic Compounds in a Time of Flight Mass Spectrometer

ABSTRACT

A new time-of-flight mass spectrometer for UV-excimer-laser desorption of neutrals, followed by resonant - or nonresonant postionization with a second excimer laser or excimer-dye-laser combination is described. The advantages of the technique are discussed and the performance of the instrument is demonstrated for a number of nonvolatile organic compounds.     

Suppression of spurious background in low-frequency Raman spectroscopy

A monochromator capable of suppressing spurious laser radiation to a level required for low-frequency (<100 cm^?1) Raman spectroscopy is proposed. It has a high spectral resolution, contains a small number of optical elements, and can be easily included into the experimental optical scheme. The effect of using this monochromator in low-frequency Raman spectroscopy is illustrated by examples with test samples.     

Interpretation of the hardness of worn DLC particles using micro-Raman spectroscopy

Minute DLC particles may be generated during running of DLC-coated rolling elements and cause further damage on the subsequent running. Their hardness, which is a key parameter in wear is, however, impossible to measure by conventional means. Are they as hard as the original DLC coating or softened by frictional heat? This paper proposes to make use of the Raman intensity ratio (I_D/I_G) to infer hardness of the tiny DLC particles. The Raman spectroscopy ultilizing laser as the light source makes it suitable for measurements on micron-sized particles.