A near-infrared laser dispersion spectrometer with phase modulation for open-path methane sensing.

A laser-based open-path dispersion spectrometer for measuring atmospheric methane has been developed with the goal of achieving a very simple architecture, yet enabling molecular dispersion measurements immune to optical power variation. Well-mature, near-infrared photonics components were retained to demonstrate a compact, cost-effective, and low-power consumption dispersion spectrometer. In particular, measurements immune to received optical power variations are demonstrated despite the use of only phase modulation and are supported by the development of the corresponding physical model.

Locating and Quantifying Methane Emissions by Inverse Analysis of Path-Integrated Concentration Data Using a Markov-Chain Monte Carlo Approach.

The action to reduce anthropogenic greenhouse gas emissions is severely constrained by the difficulty of locating sources and quantifying their emission rates. Methane emissions by the energy sector are of particular concern. We report results achieved with a new area monitoring approach using laser dispersion spectroscopy to measure path-averaged concentrations along multiple beams.

Broadband gas phase absorber detection and quantification by chirped laser dispersion spectroscopy at 1.55 µm.

The demonstration and first evaluation of chirped laser dispersion spectroscopy (CLaDS) for quantitative measurements of gas molecules with broad spectral features is reported. The demonstration is conducted on propyne (methyl acetylene) gas, using a widely tunable external cavity near infrared laser, λ ≈ 1.55 µm, whose frequency can be swept at 2.

Hollow waveguide-miniaturized quantum cascade laser heterodyne spectro-radiometer.

A miniature thermal infrared laser heterodyne spectro-radiometer based on hybrid optical integration is demonstrated. A quantum cascade laser emitting at 953 cm (10.5 μm) is used as the local oscillator.

Hollow waveguide integrated laser spectrometer for CO/CO analysis.

Using hollow waveguide hybrid optical integration, a miniaturized mid-infrared laser absorption spectrometer for CO/CO isotopologue ratio analysis is presented. The laser analyzer described focuses on applications where samples contain a few percent of CO, such as breath analysis and characterization of geo-carbon fluxes, where miniaturization facilitates deployment. As part of the spectrometer design, hollow waveguide mode coupling and propagation is analyzed to inform the arrangement of the integrated optical system.

Spectrally resolved thermal emission of atmospheric gases measured by laser heterodyne spectrometry.

The demonstration of thermal infrared quantum cascade laser heterodyne spectrometry to resolve local thermodynamic equilibrium molecular emission lines from earth's atmospheric constituents is presented. The instrument is described, as well as the early steps towards radiometric calibration. Room temperature ethylene emission line measurements carried out in the laboratory are used to validate the instrument.

Broadband standoff detection of large molecules by mid-infrared active coherent laser spectrometry.

A widely tunable active coherent laser spectrometer (ACLaS) has been demonstrated for standoff detection of broadband absorbers in the 1280 to 1318 cm spectral region using an external cavity quantum cascade laser as a mid-infrared source. The broad tuning range allows detection and quantification of vapor phase molecules, such as dichloroethane, ethylene glycol dinitrate, and tetrafluoroethane. The level of confidence in molecular mixing ratios retrieved from interfering spectral measurements is assessed in a quantitative manner.

Middle infrared active coherent laser spectrometer for standoff detection of chemicals.

Using a quantum cascade laser emitting at 7.85 μm, a middle infrared active coherent laser spectrometer has been developed for the standoff detection of vapor phase chemicals. The first prototype has been tested using diffuse target backscattering at ranges up to ~30 m.

Hollow waveguide photomixing for quantum cascade laser heterodyne spectro-radiometry.

An integrated optic approach, using hollow waveguides, has been evaluated for a compact, rugged, high efficiency heterodyne optical mixing circuit in the middle infrared. The approach has involved the creation of hollow waveguides and alignment features for a beam combiner component in a glass-ceramic substrate. The performance of the integrated beam combiner was tested as part of a full laser heterodyne spectro-radiometer in which a quantum cascade laser local oscillator emitting at 9.

Atmospheric observations of multiple molecular species using ultra-high-resolution external cavity quantum cascade laser heterodyne radiometry.

We demonstrate a widely tunable laser heterodyne radiometer operating in the thermal IR during an atmospheric observation campaign in the solar occultation viewing mode. An external cavity quantum cascade laser tunable within a range of 1120 to 1238 cm(-1) is used as the local oscillator (LO) of the instrument. Ultra-high-resolution (60 MHz or 0.

Characterisation of transmission Raman spectroscopy for rapid quantitative analysis of intact multi-component pharmaceutical capsules.

A detailed characterisation of the performance of transmission Raman spectroscopy was performed from the standpoint of rapid quantitative analysis of pharmaceutical capsules using production relevant formulations comprising of active pharmaceutical ingredient (API) and 3 common pharmaceutical excipients. This research builds on our earlier studies that identified the unique benefits of transmission Raman spectroscopy compared to conventional Raman spectroscopy. These include the ability to provide bulk information of the content of capsules, thus avoiding the sub-sampling problem, and the suppression of interference from the capsule shell.

Temporal and spatial resolution in transmission Raman spectroscopy.

Picosecond time-resolved transmission Raman data were acquired for 1 mm thick powder samples of trans-stilbene, and a Monte Carlo model was developed that can successfully model the laser and Raman pulse profiles. Photon migration broadened the incident (approximately 1 ps) probe pulse by two orders of magnitude. As expected from previous studies of Raman photon migration in backscattering mode, the transmitted Raman pulse was broader than the transmitted laser pulse and took longer to propagate through the sample.

Technique for enhancing signal in conventional backscattering fluorescence and Raman spectroscopy of turbid media.

We demonstrate experimentally, for the first time, the feasibility of passively enhancing fluorescence and Raman signals from diffusely scattering media in a conventional backscattering collection geometry. The method employs transmission of the collimated excitation laser beam through a "unidirectional" dielectric mirror placed directly in front of the sample. This permits laser light that escapes from the sample surface to be reflected back into the sample where it can be more usefully employed in generating Raman and fluorescence signals.

Emerging non-invasive Raman methods in process control and forensic applications.

This article reviews emerging Raman techniques (Spatially Offset and Transmission Raman Spectroscopy) for non-invasive, sub-surface probing in process control and forensic applications. New capabilities offered by these methods are discussed and several application examples are given including the non-invasive detection of counterfeit drugs through blister packs and opaque plastic bottles and the rapid quantitative analysis of the bulk content of pharmaceutical tablets and capsules without sub-sampling.

Non-invasive quantitative assessment of the content of pharmaceutical capsules using transmission Raman spectroscopy.

This study demonstrates how transmission Raman spectroscopy can be used in the quantitative, non-invasive probing of the bulk content of production line relevant pharmaceutical products contained within capsules with a strong interfering Raman signal (principally TiO(2)). This approach is particularly beneficial in situations where the conventional Raman backscattering method is hampered or fails due to excessive Raman or fluorescence signals emanating from surface layers (capsule or coating) that pollute the much weaker subsurface Raman signals. In these feasibility experiments the interfering surface Raman signal was effectively suppressed, relative to the Raman signal of the internal content, by a factor of 33, in the transmission geometry in comparison with the conventional backscattering Raman approach.

Characterization of genuine and fake artesunate anti-malarial tablets using Fourier transform infrared imaging and spatially offset Raman spectroscopy through blister packs.

In support of the efforts to combat the illegal sale and distribution of counterfeit anti-malarial drugs, we evaluated a new analytical approach for the characterization and fast screening of fake and genuine artesunate tablets using a combination of Raman spectroscopy, Spatially Offset Raman Spectroscopy (SORS) and Attenuated Total Reflection-Fourier Transform Infrared (ATR-FTIR) imaging. Vibrational spectroscopy provided chemically specific information on the composition of the tablets; the complementary nature of Raman scattering and FTIR imaging allowed the characterization of both the overall and surface composition of the tablets. The depth-resolving power of the SORS approach provided chemically specific information on the overall composition of the tablets, non-invasively, through a variety of packaging types.

Infrared spectroscopy and structure of photochemically protonated biomolecules in the gas phase: a noradrenaline analogue, lysine and alanyl alanine.

A novel photochemical technique combined with mass spectrometry and resonant infrared multiphoton dissociation spectroscopy (R-IRMPD) has been used to record infrared vibrational spectra of the free protonated noradrenaline analogue, 2-amino-1-phenylethanol (APE-H(+)), the amino acid, lysine (Lys-H(+)), and the dipeptide, alanyl alanine (Ala-Ala-H(+)) in the gas phase. Coupling their spectra, obtained in the OH, NH and CH stretch regions, with ab initio calculations has allowed assignment of their preferred protonation sites and conformations. This simple technique will have wide applicability in future investigations of protonated biomolecular structure and conformation.

Structure, electronic circular dichroism and Raman optical activity in the gas phase and in solution: a computational and experimental investigation.

A computational (ab initio and molecular dynamics) and experimental exploration of the relative importance of molecular conformation and explicit solvent effects on the electronic circular dichroism (ECD) of chiral molecules, is presented. The exploration includes an assessment of the validity of angular correlation (sector) rules linking ECD to molecular conformation. It is based upon studies of 1-(R) phenylethanol (including its Raman optical activity spectrum), the corresponding 'benchmark' base, 1-(R)-phenylethylamine and its protonated cation; their hydrated clusters in the gas phase; and their non-polar and aqueous solutions.