This PDF file contains the front matter associated with SPIE Proceedings Volume 8718, including the Title Page, Copyright Information, Table of Contents, and the Conference Committee listing.

Optical sensors based on Raman spectroscopy are suitable for a rapid identification and quantification of pollutants such as Polycyclic Aromatic Hydrocarbons (PAHs). Additionally, Surface enhanced Raman spectroscopy (SERS) has gained increasing attention as a powerful technique for in-situ monitoring of these substances in seawater to achieve limits of detection (LODs) in the sub-nmol/l range. A low-cost method based on electroless plating solution of chloroauric acid (HAuCl₄) and hydrogen peroxide (H₂O₂) was developed in our group to construct a gold island film as SERS substrate to achieve a well reproducible, high sensitive and seawater resistant SERS sensor. The substrates show good resistance against seawater determined by long-term stability tests carried out over 12 weeks of storage of the substrates in artificial seawater. The investigations show that the substrates still have about 50 % of their initial activity after 4 weeks of storage and about 15 % after two months. This type of substrate is reproducible with variability in the SERS intensities of about 8 %. Shifted excitation Raman difference spectroscopy (SERDS) was applied by using a microsystem diode laser emitting at 784.3 nm and 784.8 nm to remove the fluorescence interference and to improve the Raman signals. This combination of SERS and SERDS yields a limit of detection of 1 nmol/l for pyrene which was selected as representative PAH. These quantitative results show that the designed SERS substrates are suitable for the in-situ monitoring of PAHs in the marine environment.

Monitoring of water contaminants implies a need for determining their dielectric response properties with re- spect to electromagnetic wave excitation at various frequencies. Iron is a naturally occurring water contaminant resulting from decaying vegetation, which is at much higher concentrations than any other metal contaminant. The present study uses density functional theory (DFT) for the calculation of ground state resonance struc- ture and molecular stability analysis for Fe water complexes. The calculations presented are for excitation by electromagnetic waves at frequencies within the THz range. Dielectric response functions calculated by DFT can be used for the analysis of water contaminants. These functions provide quantitative initial estimates of spectral response features for subsequent adjustment with respect to additional information such as laboratory measurements and other types of theory based calculations. In addition, with respect to qualitative analysis, DFT calculated absorption spectra provide for molecular level interpretation of response structure. The DFT software GAUSSIAN was used for the calculations of ground state resonance structure presented here.

Surface enhanced Raman spectroscopy (SERS) is a highly sensitive sensing technique, offering sensitivity comparable to that of fluorescence while providing structure-dependent analyte information. In recent years, we have developed an innovative optofluidic SERS substrate by inkjet printing metal nanoparticles onto paper. By virtue of generating a SERS substrate on cellulose, we gain a flexible SERS sensing device, as well as the ability to harness the intrinsic wicking properties of paper to enable both separation and concentration of analytes. Here we demonstrate the application of paper-chromatographic separation to allow on-substrate separation, concentration and discrimination. By using inexpensive single-labeled DNA probes in a typical PCR amplification, we obtain a mixture containing whole probes (negative result) and probes which have been hydrolyzed by the Taq polymerase (positive result). Leveraging the solubility differences between the whole and hydrolyzed probes and the cellulose separation matrix, we are able to perform a multiplexed interrogation of the targets. Notably, this does not require the use of dual labeled DNA probes (expensive) or multiple excitation sources and filter sets needed for a multiplexed fluorescence measurement (expensive and bulky). All SERS measurements are performed using a portable spectrometer and diode laser; in combination with a portable low-power DNA amplification system, this technique has the potential to be used for rapid on-site multiplexed genetic detection, without requiring complex optical equipment.

A dual-wavelength laser diode source suitable for shifted excitation Raman difference spectroscopy (SERDS) is presented. This monolithic device contains two ridge waveguide (RW) sections with wavelengths adjusted distributed Bragg reflection (DBR) gratings as rear side mirrors. An integrated Y-branch coupler guides the emission into a common output aperture. The two wavelengths are centered at 671 nm with a well-defined spectral spacing of about 0.5 nm, i.e. 10 cm^-1. Separate RW sections can be individually addressed by injection current. An output power up to 110 mW was achieved. Raman experiments demonstrate the suitability of these devices for SERDS.

A 3d-printed, solar-powered, battery-operated, atmospheric-pressure, self-igniting microplasma the size of a sugar-cube has been used as light source to document the Ultra Violet (UV) and visible transmission characteristics of differentthickness polycarbonate chips that are often used for microfluidic applications. The hybrid microplasma chip was fitted with a quartz plate because quartz is transparent to UV.

Weak Raman bands are often covered by pronounced background signals due to fluorescence or Rayleigh scattering. Several techniques to separate Raman lines from the background are known. In this paper, diode laser based light sources will be presented suitable for shifted excitation Raman difference spectroscopy (SERDS). The two wavelengths are realized by varying the injection current, by addressing two micro-integrated ECLs or by temperature tuning. Due to the freedom of choice in the wavelengths using diode lasers, the emission wavelength can be selected with respect to the addressed application (e.g. the required penetration depth) or the plasmonic resonances of the substrates for surface enhanced Raman spectroscopy. Devices were developed for the wavelengths 488 nm, 671 nm, and 785 nm. The two emission wavelengths each were selected to have a spectral distance of 10 cm^-1 according to the typical width of Raman lines of solid or liquid samples. Output powers between 20 mW for the shorter wavelength devices and 200 mW for the red emitting lasers were achieved at electrical power consumptions below 1 W. With a footprint of only 25 x 25 mm² including all collimation and filter elements, these devices are well suited for portable applications. The diode lasers were implemented into Raman measurement systems. The SERDS signal-to-background ratio was improved by several orders of magnitude.

A compact light detection and ranging (LiDAR) system is used for the purpose of aerosols profile measurements by identifying the aerosol scattering ratio as function of the altitude. These color plots can be treated as images with high intensities referring to high scattering ratios and low intensities referring to low scattering ratios. In this paper, we explore the clustering of these plots into homogeneous regions via unsupervised clustering techniques such as fuzzy techniques and evaluate their performance on this type of data. We introduce a new clustering technique to work efficiently on this type of images and compare its results against the regular techniques. By capturing different aerosols profiles at different times, we are able to describe the aerosol existence structure in the area of our interest.

Quantum Cascade Lasers (QCL’s) have been successfully used to monitor atmospheric pollutants in the mid-infrared (mid-IR) region. However, their use for multiple gases in ambient conditions is less familiar. This paper explores the performance of a novel field deployable open path system based on a chirped single distributed-feedback QCL. In particular, we report both laboratory and open path measurements for simultaneous detection of two greenhouse gases (GHG) methane (CH₄) and nitrous oxide. (N₂O). We focused on CH₄ and N₂O because they are long-lived greenhouse gases in the atmosphere with significant global warming effects. Gas spectra were recorded by tuning the QC laser wavelength using a thermal down chirp technique over 1297–1300 cm^-1 optimal spectral window with 0.008 cm^-1 spectral resolution. Based on careful optimization of the spectral window for absorption features of CH₄ and N₂O, a dual-species, cost-effective, robust and rapid response open-path laser based monitor has been developed for ambient trace gas monitoring. Theoretical signal to noise ratio (SNR) analysis of the system based on an ideal system is briefly discussed in the paper but our main focus is on actual system performance, long term stability and systemic errors. Finally, preliminary results of the open path system are reported.

This paper discusses the design and performance of fiber optic distributed intrinsic sensors for dissolved carbon dioxide, based on the use optical fibers fabricated so that their entire lengths are chemically sensitive. These fibers use a polymer-clad, silica-core structure where the cladding undergoes a large, reversible, change in optical absorbance in the presence of CO₂. The local “cladding loss” induced by this change is thus a direct indication of the carbon dioxide concentration in any section of the fiber. To create these fibers, have developed a carbon dioxide-permeable polymer material that adheres well to glass, is physically robust, has a refractive index lower than fused silica, and acts as excellent hosts for a unique colorimetric indicator system that respond to CO₂. We have used this proprietary material to produce carbon-dioxide sensitive fibers up to 50 meters long, using commercial optical fiber fabrication techniques. The sensors have shown a measurement range of dissolved CO₂ of 0 to 1,450 mg/l (0 to 100% CO₂ saturation), limit of detection of 0.3 mg/l and precision of 1.0 mg/l in the 0 to 50 mg/l dissolved CO₂ range, when a 5 meter-long sensor fiber segment is used. Maximum fiber length, minimum detectable concentration, and spatial resolution can be adjusted by adjusting indicator concentration and fiber design.

We performed comparative studies to establish favorable spectral regions and measurement wavelength combinations in alternative bands of CO2 and O2, for the sensing of CO2 mixing ratios (XCO2) in missions such as ASCENDS. The analysis employed several simulation approaches including separate layers calculations based on pre-analyzed atmospheric data from the modern-era retrospective analysis for research and applications (MERRA), and the line-by-line radiative transfer model (LBLRTM) to obtain achievable accuracy estimates as a function of altitude and for the total path over an annual span of variations in atmospheric parameters. Separate layer error estimates also allowed investigation of the uncertainties in the weighting functions at varying altitudes and atmospheric conditions. The parameters influencing the measurement accuracy were analyzed independently and included temperature sensitivity, water vapor interferences, selection of favorable weighting functions, excitations wavelength stabilities and other factors. The results were used to identify favorable spectral regions and combinations of on / off line wavelengths leading to reductions in interferences and the improved total accuracy.

Recent studies on signal enhancement of spontaneous Raman scattering for developing of sensitive Raman gas detectors are reported. Raman scattering is a gas detecting method with high feasibility, but usually its signal is very low. To improve the level and the quality of the Raman signal, the effects of pumping laser source, sample cell, and optical arrangement are studied in detail. It is found that not only the wall of sample cell will give a wide Raman or fluorescence background which will decrease the sensitivity, but the dichroic beam splitter will also contribute considerable background if it is not aligned properly. The sample cell of hollow fiber is characterized by its high responsibility as well as its high background and low signal contrast. When the hollow fiber is replaced by a free-space sample cell consisted of metal-coated parabolic reflector, the wide background is largely suppressed. If there is no common optical elements between the pumping and collecting optical systems, the wide background will be cut down obviously, which is proved by the intracavity-enhanced Raman scattering in a He-Ne laser. These experimental results will be helpful for the research and developing of highly sensitive Raman gas detectors.

With the increase worldwide demand for hydrocarbon fuels and the vast development of new fuel production and delivery infrastructure installations around the world, there is a growing need for reliable fuel leak detection technologies to provide safety and reduce environmental risks. Hydrocarbon leaks (gas or liquid) pose an extreme danger and need to be detected very quickly to avoid potential disasters. Gas leaks have the greatest potential for causing damage due to the explosion risk from the dispersion of gas clouds. This paper describes progress towards the development of a fast response, high sensitivity, distributed fiber optic fuel leak detection (HySense^TM) system based on the use of an optical fiber that uses a hydrocarbon sensitive fluorescent coating to detect the presence of fuel leaks present in close proximity along the length of the sensor fiber. The HySense^TM system operates in two modes, leak detection and leak localization, and will trigger an alarm within seconds of exposure contact. The fast and accurate response of the sensor provides reliable fluid leak detection for pipelines, tanks, airports, pumps, and valves to detect and minimize any potential catastrophic damage.

The model of relaxation of photoconductivity of porous silicon, in which recombination of photocarriers is taken into account on the spherical surface of pores at the shutdown of illumination, is presented and numerically investigated. By the finite element method it is calculated time evolution of the photoconductivity of porous silicon and dependence of the relaxation time of photoconductivity on the surface recombination velocity, which is determined by a concentration and nature of adsorbed gas, as well as on the radius of pores and average distance between them