Grating-Stabilized External Cavity Diode Lasers for Raman Spectroscopy—A Review

Abstract: Conventional Raman techniques require a continuous-wave laser with stabilized wavelength, narrow line width, and sufficient output power. Due to their miniature size and low cost, diode lasers are good choice as light sources for Raman spectroscopy, especially when compact and portable instruments are needed. However, a solitary multimode diode laser has certain drawbacks that limit its use for Raman application. To circumvent these drawbacks, an external cavity can be coupled to the active gain medium of the diode to enhance the laser performance. A grating-based external cavity allows the laser to operate in a single longitudinal mode with greatly reduced line width and stabilized wavelength. This article examines the fundamentals of semiconductor lasers to show the necessity of operating diode lasers in an external cavity for Raman applications. Two feedback grating-based external cavity diode laser (ECDL) designs, viz. Littrow and Littman-Metcalf configurations, are explained. Historic and recent progress in the development of ECDL devices is reported. An updated summary of ECDL-equipped Raman systems applied to fields such as in vivo biomedical studies and in situ process/quality control is provided. Topics on mode-hop-free continuous scanning, wavelength stabilization, and dealing with ambient conditions are discussed.     

RECENT DEVELOPMENTS IN INSTRUMENTATION FOR LASER INDUCED BREAKDOWN SPECTROSCOPY

ABSTRACT

This review describes, in detail, the most recent developments in instrumentation for laser induced breakdown spectroscopy (LIBS). The paper focuses on various laser systems, including excimer, CO₂, and Nd: YAG and their performance in LIBS. The coupling of fiber-optics to LIBS and development of portable LIBS systems and their performance is presented. New approaches such as dual pulse operation, multi-fiber, resonant ablation, and combination with laser induced fluorescence are further described. Finally the use of the Echelle spectrometer in which it has been combined with various charge coupled devices.     

Applications of Terahertz Spectroscopy in the Field of Construction and Building Materials

Abstract: In last two decades, rapid development in the field of terahertz (THz) technology has opened new possibilities for creating innovative imaging and sensing systems. Although the applications of THz technology in different sectors constantly increase, the construction industry lags behind them. The aim of this article is to review the current applications of THz spectroscopy in research and industry related to construction and building materials, along with the key drawbacks of technology and recommendations for future use. The review concludes that THz spectroscopy and imaging have promising potential and provide many opportunities for applications in construction and building materials characterization.     

Pulsed Laser Ablation for Tin Dioxide: Nucleation,Growth, and Microstructures

Pulsed-laser ablation approaches are being developed for the growth of oxide thin films as versatile platform for advanced applications. Semiconducting SnO ₂ thin film is of fundamental importance in the advancement of microdevices. In this review, SnO ₂ thin films of various microstructures have been made using the pulsed-laser deposition method. The microstructural aspects include tetragonal, porous, and orthorhombic structure characteristics. The quantum-dots and dynamic simulations of SnO ₂ nanocrystals have blossomed into a submonolayer regime devoted to the nucleation and growth for these functional films. SnO ₂ thin films with some of the microstructural features may have great implications for the development of novel prototype gas sensors and transparent conduction electrodes.     

External-field-induced formation of stabilized F 2 + centers in colored LiF crystals

The production of complexes, which are thermally stable at room temperature, with F ₂ ⁺ centers in radiation-colored LiF crystals by the combined action of different fields is investigated. The half-life of these laser centers produced by, specifically, hard UV radiation and a shock wave increased by almost two orders of magnitude. Fiz. Tverd. Tela (St. Petersburg) 40, 2044–2050 (November 1998)     

Lasers as Light Sources for Analytical Atomic Spectrometry

Abstract

Lasers have advantages compared to conventional light sources, which include high power, a monochromatic emission profile, stability, and rapid tuning across an atomic line. These advantages have resulted in superior analytical figures of merit and methods of background correction compared to conventional light sources. The most widely used lasers for atomic spectrometry include dye laser systems, optical parametric oscillator systems, and diode lasers. Three principal techniques employ lasers as light sources. Laser‐excited atomic fluorescence spectrometry (LEAFS) involves the use of laser light to excite atoms that emit fluorescence and serves as the analytical signal. Laser‐enhanced ionization (LEI) involves laser excitation of atoms to an excited state energy level at which collisional ionization occurs at a higher rate than from the ground state. Diode laser atomic absorption spectrometry (DLAAS) employs a DL as a source to excite atoms in an atom cell from the ground state to an excited state. The analytical signal is involves the ratio of the incident and transmitted beams. Recent applications of these techniques are discussed, including practical applications, hyphenated techniques employing laser‐induced plasmas, and work to characterize fundamental spectroscopic parameters.     

On practical aspects of Laser Guide Stars

The Gemini Observatory has developed an extensive Adaptive Optics (AO) program, including Classical AO, Laser Guide Star (LGS) AO, Multi-Conjugate AO (MCAO), extreme AO (eXAO) and Ground Layer AO (GLAO). Most of these instruments use one or several LGSs. A laser has been in operation at Gemini since May 2005. Most of the laser related systems (beam transport, launch, safety systems) have been developed in house. These are major components, requiring a development effort not to be underestimated. In this article, we propose to share the Gemini experience in terms of practical issues and calibration requirements associated with the use of lasers in AO. To cite this article: F. Rigaut, C. d'Orgeville, C. R. Physique 6 (2005).     

Laser Ablation Inductively Coupled Plasma Mass Spectrometry: Principles and Applications

Abstract

The application of laser ablation inductively plasma mass spectrometry (LA‐ICP‐MS) to the determination of major, minor, and trace elements as well as isotope‐ratio measurements offers superior technology for direct solid sampling in analytical chemistry. The advantages of LA‐ICP‐MS include direct analysis of solids; no chemical dissolution is necessary, reduced risk of contamination, analysis of small sample mass, and determination of spatial distributions of elemental compositions. This review aims to summarize recent research to apply LA‐ICP‐MS, primarily in the field of environmental chemistry. Experimental systems, fractionation, calibration procedures, figures of merit, and new applications are discussed. Selected applications highlighting LA‐ICP‐MS are presented.     

Microplasma-Based Detectors for Gas Chromatography: Current Status and Future Trends

Abstract: Microplasma is a useful detector for analyzing the effluent of gas chromato-graphy due to its remarkable capacity for portability, high sensitivity, and excellent multielement selectivity. Compared to classical detectors, microplasma detectors have the advantages of small size, low cost, and low energy consumption in design and operation. We aim to provide an overview of microplasma detectors and show their applications in various chemical analyses. The operational characteristics and analytical performance of different microplasma detectors, such as capacitively coupled microplasma, glow discharge microplasma, and microhollow-cathode microplasma, are presented in detail to reveal the current status of microplasma detectors for gas chromatography. In addition, several approaches for the design of microplasma are discussed and the future trends in the development of microplasma detectors are highlighted at the end of this review. Various applications of microplasma detectors for gas chromatography systems are also presented in this review.     

A Pressure Sensor Using Fiber Bragg Grating

In the present investigation, a Q-switched Nd:YAG laser is used to study the various aspects of diamond processing for fabricating integrated optic and UV optoelectronic devices. Diamond is a better choice of substrate compared to silicon and gallium arsenide for the fabrication of waveguides to perform operations such as modulation, switching, multiplexing, and filtering, particularly in the ultraviolet spectrum. The experimental setup of the present investigation consists of two Q-Switched Nd:YAG lasers capable of operating at wavelengths of 1064 nm and 532 nm. The diamond cutting is performed using these two wavelengths by making the “V”-shaped groove with various opening angle. The variation of material loss of diamond during cutting is noted for the two wavelengths. The cut surface morphology and elemental and structural analysis of graphite formed during processing in both cases are compared using scanning electron microscopy (SEM) and laser Raman spectroscopy. Both the Q-Switched Nd:YAG laser systems (at 1064 nm and 532 nm) show very good performance in terms of peak-to-peak output stability, minimal spot diameter, smaller divergence angle, higher peak power in Q-switched mode, and good fundamental TEM ₀₀ mode quality for processing natural diamond stones. Less material loss and minimal micro cracks are achieved with wavelength 532 nm whereas a better diamond cut surface is achieved with processing at 1064 nm with minimum roughness.     

Fast-field-cycling NMR: Applications and instrumentation

Magnetic field cycling in nuclear magnetic resonance (NMR) experiments has been used since the early days of NMR. Originally such time-dependent magnetic field experiments were motivated to study cross relaxation, spin system thermodynamics and indirect detection of quadrupolar resonance. The first apparatus used mechanical or pneumatic systems to shoot the sample between two magnets, the typical “flying time” being a few hundreds of milliseconds. As a natural evolution of the experimental technique and the need to extend its application to samples with higher relaxation rates, faster magnetic field switching devices were developed during the last years. Special electric networks combined with sophisticated air core magnets allowed one to switch magnetic fields between zero and fields of the order of 0.5 T in a few milliseconds. Today we refer to this new generation of instruments as “fast-field-cycling” devices. The technique has been successfully used during the last years to obtain information on the molecular dynamics and order in different materials, ranging from organic solids, metals, polymers, liquid crystals, porous media to biological systems. At present it is also turning to be an important tool for the design of contrast agents for magnetic resonance imaging. Fast field cycling was mainly oriented toT ₁ relaxometry as a unique technique offering a dynamic window of several decades, ranging from few kilohertz to several megahertz. However, there exist less conventional applications of the technique that can also provide relevant information concerning molecular dynamics, structure and molecular order. In this article we will briefly deal with basic aspects of the technique, its evolution, present-day relevant applications and the last improvements concerning specialized instrumentation.     

Use of Infrared Spectroscopy for In-Field Measurement and Phenotyping of Plant Properties: Instrumentation,Data Analysis,and Examples

Abstract: Recent developments in agricultural technology have led to a demand for a new era of nondestructive methods of plant analysis in the field rather than in the laboratory. The combination of fundamental science (e.g., plant physiology, biochemistry, and other disciplines), multivariate data analysis, and spectroscopy will enable the development of technologies for reliable and rapid on-farm or in-field low-cost testing. This will enable both farmers and scientist to maximize sales in existing markets and to target new markets with differentiated products or select new varieties, better soil management, among other issues. Infrared (IR) spectroscopy has been successfully applied for the determination of composition analysis in several fields (e.g., agriculture, pharmaceutical, etc.) and in product quality assessment and production control. The IR spectrum can give a global signature of composition (fingerprint), which, with the application of chemometric techniques, can be used to elucidate particular compositional characteristics not easily detected by traditional targeted chemical analyses. This article highlights the principles of IR spectroscopy, commercially available instruments and software, and calibration issues including calibration development, networking, and transfer. In addition, recent and potential applications of IR spectroscopy in grains, fruits, and other plant tissues are presented and discussed.     

Recent advances in lead-chalcogenide diode lasers

The fundamental material properties of Pb_1−xSn_xTe, PbS_1−xSe_x and Pb_1−xSn_xSe are reviewed. Expressions for the temperature and compositional dependences of the band parameters and dielectric constants based on recently published data are presented. As far as device technology is concerned, crystal growth techniques and diode fabrication procedures which are in use today are reviewed and compared. A comprehensive summary of laser properties like threshold current density, output power, efficiency, maximum operating temperature and tuning range of different diode structures are presented. Application related aspects such as long term stability are treated. Recent progress in laser theory is applied to explain experimentali _th vs.T curves. The various laser applications are reviewed briefly. A new technique for monitoring gas concentrations using pulsed lasers and an integral method for signal processing is discussed and compared with the differential absorption, derivative spectroscopy. A long-path trace-gas monitoring system incorporating this new technique is presented.     

Recent Advances in Near-Infrared Reflectance Spectroscopy

Abstract

A proliferation of applications for near-infrared reflectance spectroscopy has been driven by recent advances in instrumentation and chemometrics. These include the development of smaller, portable instruments with no moving parts, suitable for process environments, and new data treatments and calibration algorithms to model nonlinear relationships between spectra and chemical constituents. The intent of this review is to focus on recent developments in near-infrared reflectance spectroscopy, including chemometrics and new applications of NIR reflectance in several diverse fields, rather than to address indepth the historical development of NIR. Certain topics, such as chemometrics, deserve a comprehensive review by themselves, and the reader is urged to consult the original sources for greater depth. As a newcomer to the field, I have attempted to present those topics which may be of greater interest to the novice.     

Laser-Induced Breakdown Spectroscopy for Chemical Mapping of Materials

Abstract: Analytical techniques able to perform spatially resolved analysis are highly demanded in the surface analysis and material science fields. Compared to other analytical techniques usually employed, laser-induced breakdown spectroscopy (LIBS) offers several advantages, such as simplicity and robustness of instrumentation, which permit on-line and in situ measurements. No or minimal sample preparation is required, and the analysis of any sample without restrictions on the shape, size, or conductive nature can be performed under atmospheric conditions in a matter of seconds. In this work, a review of the different instrumental approaches employed in the generation of compositional maps as well as a detailed discussion of the different applications that involve the use of LIBS to obtain two-dimensional or even three-dimensional chemical maps is presented.     

Identification of the multicomponent nature of E 0 photoreflectance spectra from moderately doped GaAs substrates

The paper considers methods used to identify the multicomponent character of photoreflectance (PR) spectra in the vicinity of the E ₀ transition measured at room temperature from moderately doped GaAs substrates. It is shown that that if an E ₀ PR spectrum contains an excitonic component, its presence can be established from both a mathematical and phase analysis, as well as from measurements performed at different laser excitation densities. Fiz. Tverd. Tela (St. Petersburg) 39, 2123–2129 (December 1997)     

Use of Infrared Microspectroscopy in Plant Growth and Development

Abstract

Infrared microspectroscopy (IMS) has emerged as a key technique for the study of plant growth and development. The combination of IMS and synchrotron radiation has enabled researchers to analyze plant development at a cellular level. The spatial distribution of functional groups in plant tissue can be determined by the “chemical imaging” ability of IMS. Attenuated total reflectance (ATR) and polarized IR spectroscopies in combination with IMS makes sampling rapid and easy, providing direct analysis in situ. This review covers applications of IMS to study cell wall architecture and the major cell wall components: lignin, cellulose, and polysaccharides; applications for agricultural and feed products; and changes to plant structure due to biotic and abiotic stressors.     

Plant elemental composition and portable X‐ray fluorescence (pXRF) spectroscopy: quantification under different analytical parameters

Emergence of portable X‐ray fluorescence (pXRF) systems presents new opportunities for rapid, low‐cost plant analysis, both as a lab system and in situ system. Numerous studies have extolled the virtues of using pXRF for a wide range of plant applications, however, for many such applications, there is need for further assessment with regards to analytical parameters for plant analysis. While pXRF is a potential powerful research tool for elemental composition analysis, its successful use in plant analysis is made more likely by having an understanding of X‐ray physics, calibration process, and ability to test a variety of homogenous and well‐characterized materials for developing a matrix‐specific calibration. Because potential pXRF users may often underestimate the complexity of proper analysis, this study aims at providing a technical background for plant analysis using pXRF. The focus is on elemental quantification under different analytical parameters and different methods of sample presentation: direct surface contact under vacuum, placement in a sample cup with prolene as a seal, and without the aid of a vacuum. Direct analysis on the surface of a pXRF provided highest sensitivity and accuracy (R² > 0.90) for light elements (Mg to P). Sulfur, K, and Ca can be reliably measured without the aid of a vacuum (R² > 0.99, 0.97, and 0.93 respectively), although lower detection limits may be compromised. pXRF instruments provide plant data of sufficient accuracy for many applications and will reduce the overall time and budget compared with the use of conventional techniques. Sensitivity and accuracy are dependent on the instrument's settings, make, and model. © 2015 The Authors. X‐Ray Spectrometry published by John Wiley & Sons, Ltd.     

Analysis of Birefringence Compensation Using a Quarter-Wave Plate in Solid-State Lasers

Using Jones matrix formulation, the theoretical calculations of birefringence compensation technique for a quarter-wave plate scheme are presented. This scheme was proposed and experimentally demonstrated by W. A. Clarkson et al. (Opt. Lett. 24 (1999) 820). In the present paper we have theoretically confirmed that using this method, even in principle, complete compensation is not possible. However, it is shown quantitatively that this scheme does makes possible effective compensation for the birefringence in as few as several tens of watts of pumping power region, which is an attractive feature for laser-diode (LD) pumped solid-state laser systems. We also found good agreement between our theoretical calculations and experimental results obtained by W. A. Clarkson et al. For example, from the analysis we show that only < 0.1% loss will be generated by about 10 W of heat deposited in the rod. This corresponds to about 30 W of LD pump power, which may generate from 6 to 10 W output power depending upon the conversion efficiency of type lasers