The detection and measurement of gas concentrations using the characteristic optical absorption of the gas species is important for both understanding and monitoring a variety of phenomena from industrial processes to environmental change. This study reviews the field, covering several individual gas detection techniques including non-dispersive infrared, spectrophotometry, tunable diode laser spectroscopy and photoacoustic spectroscopy. We present the basis for each technique, recent developments in methods and performance limitations. The technology available to support this field, in terms of key components such as light sources and gas cells, has advanced rapidly in recent years and we discuss these new developments. Finally, we present a performance comparison of different techniques, taking data reported over the preceding decade, and draw conclusions from this benchmarking.

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Optical gas sensing: a review

Recent research on fibre optic long-period gratings (LPGs) is reviewed with emphasis placed upon the characteristics of LPGs that make them attractive for applications in sensing strain, temperature, bend radius and external index of refraction. The prospect of the development of multi-parameter sensors, capable of simultaneously monitoring a number of these measurands will be discussed.

https://iopscience.iop.org/article/10.1088/0957-0233/14/5/201/pdf

Optical fibre long-period grating sensors: characteristics and application

Organic carbon (OC) accounts for a large fraction of atmospheric aerosol and has profound effects on air quality, atmospheric chemistry and climate forcing. Molecular composition of the OC and its evolution during common processes of atmospheric aging have been a subject of extensive research over the last decade (see reviews of Ervens et al.,1 Hallquist et al.,2 Herckes et al.,3 Carlton et al.,4 Kroll and Seinfeld,5 Rudich et al.,6 and Kanakidou et al.7). Even though many fundamental advances have been reported in these studies, our understanding of the climate-related properties of atmospheric OC is still incomplete and the specific ways in which OC impacts atmospheric environment and climate forcing are just beginning to be understood. This review covers one topic of particular interest in this area –environmental chemistry of light-absorbing aerosol OC and its impact on radiative forcing.

Chemistry of atmospheric brown carbon.

Driven by functionality and purity demand for applications of inorganic nanoparticle colloids in optics, biology, and energy, their surface chemistry has become a topic of intensive research interest. Consequently, ligand-free colloids are ideal reference materials for evaluating the effects of surface adsorbates from the initial state for application-oriented nanointegration purposes. After two decades of development, laser synthesis and processing of colloids (LSPC) has emerged as a convenient and scalable technique for the synthesis of ligand-free nanomaterials in sealed environments. In addition to the high-purity surface of LSPC-generated nanoparticles, other strengths of LSPC include its high throughput, convenience for preparing alloys or series of doped nanomaterials, and its continuous operation mode, suitable for downstream processing. Unscreened surface charge of LSPC-synthesized colloids is the key to achieving colloidal stability and high affinity to biomolecules as well as support materials,...

Laser Synthesis and Processing of Colloids: Fundamentals and Applications

Reactive species in non-equilibrium atmospheric-pressure plasmas: Generation, transport, and biological effects

Erratum: “Incoherent broad-band cavity-enhanced absorption spectroscopy of liquids” [Rev. Sci. Instrum.76, 023107 (2005)]

The S0→S3 transition in 1, 2-benzanthracene. Experimental evidence for the statistical limit of vibronic coupling of S3 with S2

The validity of Smoluchowski's theory is demonstrated by its application to the bimolecular triplet–triplet annihilation (TTA) T1 + T1 → S0 + S1 in viscous solution. For that purpose the delayed S1 → S0 fluorescence of anthracene in cis-1,3-dimethylcyclohexane/trans-1,4-dimethylcyclohexane (1∶1) was measured after UV excitation with long laser pulses (∼30 μs) in a temperature range where TTA is completely diffusion controlled. Through the adequate treatment of the kinetics of TTA upon spatially homogeneous and spatially periodic excitation (which is partially based on the results of previous publications)
				absolute values for the diffusion coefficients D of triplet molecules, for the effective annihilation distance RA and for the Forster radius RST of heterogeneous annihilation S1 + T1 → S0 + Tn were determined. The temperature dependence of all three parameters (D, RA and RST) is discussed. From the decrease of RA with increasing temperature, the parameters A and L can be determined, which define the exponential distance dependence of the annihilation of a triplet pair in the kinetic model of Butler and Pilling (1977). Differences of the two models and applicability criteria are discussed.

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Application of Smoluchowski's generalized theory to the kinetics of triplet–triplet annihilation of anthracene in viscous solution after long-pulse excitation

The phosphorescence excitation spectrum of isolated 4-H-1-benzopyrane-4-thione molecules (BPT) in a pulsed supersonic jet was investigated by direct excitation of the first excited triplet state, S 0 → T 1 . The electronic origin at 15828 cm −1 is assigned to the transition S 0,0 → T 1z,0 , the transition S 0,0 ⇌ T 1(xy),0 is too weak to be detected with this method. The triplet lifetime τ T 1z,0 ≈ 11 μ s is compatible with extrapolated values for BPT in dilute solutions. Vibronic transitions S 0,0 → T 1z,v were measured up to ∼ 1940 cm −1 above the origin; the vibrational structure of T 1 was compared with the vibrational structure of S 2 . S 0,0 → S 1,v absorptions were not observed in the laser-induced phosphorescence experiment. Hot bands were observed under specific experimental conditions.

The phosphorescence excitation spectrum of jet-cooled 4-H-1-benzopyrane-4-thione

The solvent spectral shifts of the S0 f T1 origin bands of jet-cooled 4H-pyran-4-thione (PT) and 4H-1benzopyran-4-thione (BPT) were observed in phosphorescence excitation spectra. Van der Waals complexes (1:1) of seed molecules with the carrier gas were observed in several rare gases. In all cases, the combination of a dispersive red-shift and a dipole-induced dipole blue-shift produced a total red-shift, up to a maximum of δν ) -21 cm-1 for PT-Xe and δν ) -30 cm-1 for BPT-Xe. Complexes of 1:n (n > 1) were not observable owing to the weakness of the direct S0 f T1 transition. The inductive contributions to the shifts were calculated using values of excited-state dipole moments estimated from solution Stokes shifts; the dipole moments of both molecules in T1 were found to be close to zero, significantly smaller than their ground-state dipole moments. The phosphorescence excitation spectrum of isolated PT is discussed in some detail. The electronic origin of T1 at 16 844 cm-1 is assigned to the transition S0,0 f T1z,0; the transitions S0,0 h T1(xy),0 are too weak to be detected with this method. Vibronic transitions S0,0 f T1z,V in PT were analyzed up to excess energies of ∼hc1450 cm-1.

Albert A. Ruth

Papers

Erratum: “Incoherent broad-band cavity-enhanced absorption spectroscopy of liquids” [Rev. Sci. Instrum.76, 023107 (2005)]

The S0→S3 transition in 1, 2-benzanthracene. Experimental evidence for the statistical limit of vibronic coupling of S3 with S2

Application of Smoluchowski's generalized theory to the kinetics of triplet–triplet annihilation of anthracene in viscous solution after long-pulse excitation

The phosphorescence excitation spectrum of jet-cooled 4-H-1-benzopyrane-4-thione

Van der Waals complexes of jet-cooled aromatic thiones with noble gases: The phosphorescence excitation spectrum of 4H-pyran-4-thione