RESUMEN
Significant advancements in waveguide technology in the mid-infrared (MIR) regime during recent decades have assisted in establishing MIR spectroscopic and sensing technologies as a routine tool among nondestructive analytical methods. In this review, the evolution of MIR waveguides along with state-of-the-art technologies facilitating next-generation MIR chem/bio sensors will be discussed introducing a classification scheme defining three "generations" of MIR waveguides: (1) conventional internal reflection elements as "first generation" waveguides; (2) MIR-transparent optical fibers as "second generation" waveguides; and most recently introduced(3) thin-film structures as "third generation" waveguides. Selected application examples for these each waveguide category along with future trends will highlight utility and perspectives for waveguide-based MIR spectroscopy and sensing systems.
RESUMEN
The analytical performance of four commercially available infrared attenuated total reflection (IR-ATR) accessories with various ATR waveguide materials has been analyzed and evaluated using acetate, CO2, and CO3 (2-) solutions. Calibration functions have been established to determine and compare analytically relevant parameters such as sensitivity, signal-to-noise ratio (SNR), and efficiency. The obtained parameters were further analyzed to support conclusions on the differences in performance of the individual IR-ATR accessories.
RESUMEN
An infrared attenuated total reflection (IR-ATR) method for detecting, differentiating, and quantifying hydrocarbons dissolved in water relevant for oil spills by evaluating the "fingerprint" of the volatile organic compounds (VOCs) associated with individual oil types in the mid-infrared spectral range (i.e., 800-600 cm(-1)) is presented. In this spectral regime, these hydrocarbons provide distinctive absorption features, which may be used to identify specific hydrocarbon patterns that are characteristic for different crude and refined oils. For analyzing the "VOC fingerprint" resulting from various oil samples, aqueous solutions containing the dissolved hydrocarbons from different crude oils (i.e., types "Barrow", "Goodwyn", and "Saladin") and refined oils (i.e., "Petrol" and "Diesel") were analyzed using a ZnSe ATR waveguide as the optical sensing element. To minimize interferences from the surrounding water matrix and for amplifying the VOC signatures by enrichment, a thin layer of poly(ethylene-co-propylene) was coated onto the ATR waveguide surface, thereby enabling the establishment of suitable calibration functions for the quantification of characteristic concentration patterns of the detected VOCs. Multivariate data analysis was then used for a prelininary classification of various oil-types via their VOC patterns.
RESUMEN
Grating couplers for planar silver halide waveguides were designed and fabricated by using focused ion beam (FIB) milling technology, facilitating coupling of mid-infrared radiation from quantum cascade lasers into thin-film waveguide structures. An optimized rectangular grating structure for an emitted wavelength of 10.4 µm, with a grating constant of 16.4 µm was integrated into a silver halide waveguide substrate via an optimized FIB fabrication procedure. Efficient incoupling and radiation propagation through the waveguide was confirmed by analyzing droplets of acetic acid at different concentrations, deposited at the waveguide surface via evanescent field absorption spectroscopy.