We report on the development of mid-infrared spectroscopy-based sensors for inline water and wastewater analysis. Midinfrared spectroscopy is a powerful tool for chemical identification and quantification. To overcome the limitations of the technique imposed by rapid extinction of the infrared signal in water, we have developed pre-concentration techniques that achieve beyond four orders of magnitude enhancement of measurement sensitivity, along with enhanced selectivity, for analytes. Applications include monitoring of nutrients and metabolites in bioreactor systems for wastewater treatment and industrial processes (e.g. biofuel production), in-line process control in chemical manufacturing, and rapid on-site screening of contaminants in environmental samples for assessment and remediation of environmental contamination sites.
We report on development of a novel type of sensor for in-line analysis of nitrogen-based molecules, such as nitrate, nitrite and ammonia, in municipal wastewater. The sensor utilizes pre-concentration of analytes with ion-selective materials and subsequent optical detection in the mid-infrared spectral range. Advantages of this sensor include in-line autonomous measurements, self-calibration mechanisms and high selectivity to different nitrogen species. The sensor targets implementation at wastewater treatment plants (WWTPs) to enable control and optimization of the aeration process, thereby reducing energy consumption and cost. We will discuss challenges encountered during the transition of the technology from the lab bench to WWTPs, including operational efficiency of the optical sources, such as quantum cascade lasers (QCLs) vs. thermal sources. Extension of the sensor capabilities for sensing of additional contaminants and for bioreactor systems control will be discussed.
Infrared technology can provide a wealth of information related to biological and chemical hazards in the environment. However, this technology mostly exists in the form of bulky instrumentation on optical benches in academic laboratories. We discuss the transition of IR sensing to various points-of-need applications, including food and water safety, bioreactor process control and chemical analysis of drinking water. In particular, in remote locations the access to clean drinking water is critical to soldiers’ health. Mid-infrared spectroscopy is a powerful tool for identification and quantification of a wide range of common organic and inorganic compounds. In this contribution we present data demonstrating proof-of-concept of a quantum cascade laser (QCL)-based infrared sensor for evaluation of toxic industrial chemicals (TICs) and toxic industrial materials (TIMs) and discuss the path for development of miniaturized, point-of-need IR photonic integrated circuits (IR-PIC).
There is a growing demand for hand-held and/or field-grade sensors for biochemical analysis of fluids. These systems have applications in monitoring of nitrogen-based compounds (such as nitrate and ammonia) in the wastewater treatment industry; bacterial detection in drinking water; analysis of biofluids, such as urine or blood; and in many other areas. Mid-infrared (midIR) spectroscopy is a powerful tool for identification and quantification of a wide range of common organic and inorganic compounds. Although IR radiation is strongly absorbed in water, this technology can be adapted for analysis of fluids by utilizing the principles of attenuated total reflection (ATR). In this contribution we highlight the application of IR spectroscopy in wastewater analysis as well as for metabolomic analysis in bioreactors. We discuss the requirements for IR signal stability that are necessary for biochemical analysis of fluids and provide examples of challenges encountered during transition from FTIR to a QCL-based platform. Overall, our stepwise efforts target eventual integration of a QCL light source, waveguide sensor, and IR detector onto a single photonic integrated circuit (PIC) for applications in the defense sector as well as for a broad consumer market.
Monitoring water quality by detecting chemical and biological contaminants is critical to ensuring the provision and discharge of clean water, hence protecting human health and the ecosystem. Among the available analytical techniques, infrared (IR) spectroscopy provides sensitive and selective detection of multiple water contaminants. In this work, we present an application of IR spectroscopy for qualitative and quantitative assessment of chemical and biological water contaminants. We focus on in-line detection of nitrogen pollutants in the form of nitrate and ammonium for wastewater treatment process control and automation. We discuss the effects of water quality parameters such as salinity, pH, and temperature on the IR spectra of nitrogen pollutants. We then focus on application of the sensor for detection of contaminants of emerging concern, such as arsenic and Per- and polyfluoroalkyl substances (PFAS) in drinking water. We demonstrate the use of multivariate statistical analysis for automated data processing in complex fluids. Finally, we discuss application of IR spectroscopy for detecting biological water contaminants. We use the metabolomic signature of E. coli bacteria to determine its presence in water as well as distinguish between different strains of bacteria. Overall, this work shows that IR spectroscopy is a promising technique for monitoring both chemical and biological contaminants in water and has the potential for real-time, inline water quality monitoring.
This work addresses the need to spectrally analyze of the absorption of middle-infrared (mid-IR) radiation in single living cells, with subwavelength spatial resolution, to identify molecular groups in them. The challenge is considerable, no lens can be used, so to realize such a device, a near-field probe was developed, from an optical fiber that is transparent in the mid-IR, non soluble in water, non-toxic and mechanically suitable. Incorporation of this probe in a scanning microscope, and use on a specially contained single living cell in water, allowed to achieve subwavelength imaging. Our fiber-material of choice is silver halides, i.e. AgClxBr1-x, made in the Applied Phyics Group of Tel-Aviv University. In spite of being bulky they were mechanically adapted to scanning microscopy. Theoretical and experimental investigations into the dampening of the motion of the probe in water were performed. A grid-like holder for containing living-cells for near-field microscopy has been introduced. The operating principle of this grid is based on sinking the cells inside the holes of the grid and letting them only negligibly protrude out of the holes (compared to the height-range of motion of the tip), in air and water. The result is a demonstration of the operation of the SNIM on different types of objects, including yeast cells, in water.
In this work, we present the development of an infrared scanning near-field optical microscope (IR-SNOM) for thermal imaging. As an example, we explore thermal imaging of quantum cascade lasers (QCLs). QCLs are attractive infrared (IR) sources for chemical detection due to their tunability and wide emission range spanning from mid-wavelength to longwavelength infrared radiation (MWIR and LWIR). However, they require high performance cooling systems and have limited use at low power in continuous wave (CW) operation due to the potential for thermal failure of the device. Thermal imaging can help identify mechanisms and points of failure during laser operation. Because the size of the features of QCLs (~1 μm) are much smaller than the wavelength of the emitted thermal radiation, IR-SNOM is an ideal technique to image the spatial thermal profile of QCLs during operation to guide design improvement.
We report on the development of infrared sensor for monitoring of nitrogen as nitrate, nitrite and ammonia in municipal wastewater. To overcome the challenge of strong absorption of the infrared radiation in water, the radiation is transmitted through a waveguide in contact with water rather than through water itself, implementing an attenuated total reflection (ATR) mechanism. Infrared spectroscopy is a powerful tool for identification and quantification of functional molecular groups. Introduction of QCLs reduces the reliance on bulky Fourier Transform Infrared (FT-IR) spectrometers that are sensitive to vibrations and enables development of versatile, portable instrumentation. Efficient nitrogen removal is one of the key objectives of any municipal wastewater treatment operation, yet today, nitrogen is monitored through grab-sampling and sending samples to laboratories for analysis. The sensor will enable reliable, real-time, unsupervised sensing in harsh environment.
KEYWORDS: Thermography, Quantum cascade lasers, Near field scanning optical microscopy, Spatial resolution, Temperature metrology, Infrared imaging, Infrared radiation, Modulation, Near field
The fundamental optical diffraction in infrared microscopes limits their spatial resolution to about ~5μm and hinders the detailed observation of heat generation and dissipation behaviors in micrometer-sized optoelectronic and semiconductor devices, thus impeding the understanding of basic material properties, electrical shorts and structural defects at a micron and sub-micron scale. We report the recent development of a scanning near-field optical microscopy (SNOM) method for thermal imaging with subwavelength spatial resolution. The system implements infrared fiber-optic probes with subwavelength apertures at the apex of a tip for coupling to thermal radiation. Topographic imaging and tip-to-sample distance control are enabled by the implementation of a macroscopic aluminum tuning fork of centimeter size to support IR thermal macro-probes. The SNOM-on-a-fork system is developed as a capability primarily for the thermal profiling of MWIR quantum cascade lasers (QCLs) during pulsed and continuous wave (CW) operation, targeting QCL design optimization. Time-resolved thermal measurements with high spatial resolution will enable better understanding of thermal effects that can have a significant impact on a laser's optical performance and reliability, and furthermore, will serve as a tool to diagnose failure mechanisms.
Although Quantum cascade lasers (QCLs) are frequently used in sensing, spectroscopy, and free space communication applications, their poor thermal properties lead to high temperature gradients in the devices. To diagnose failure mechanisms of mid-wave infrared (MWIR) QCLs, it is critical to understand their thermal generation and transport characteristics. In this work, we use 3D anisotropic steady state heat transfer analysis to investigate the thermal behavior in lattice matched InP/InAlAs/InGaAs buried heterostructure (Bh) mounted epi-layer side down QCLs. We introduce anisotropic thermal conductivities in the in-plane and cross-plane directions in QCL’s superlattice active region, and study the temperature distribution inside the laser. We consider several configurations, including the overhanging of the laser chip on the submount by different amounts, the choice of front facet dielectric coating materials and their thicknesses, and the width of the active region. Combining these effects, we optimize QCL’s thermal performance. This work aims to provide guidelines for the design of durable QCLs as well as to help diagnose QCL failure mechanisms.
Nitrate is a frequent water pollutant that results from human activities such as fertilizer over-application and agricultural runoff and improper disposal of human and animals waste. Excess levels of nitrate in watersheds can trigger harmful algal blooms (HABs) and biodiversity loss with consequences that affect the economy and pose a threat to human health. Municipal drinking water and wastewater treatment plants are therefore required to control nitrogen levels to ensure the safety of drinking water and the proper discharge of effluent. Nitrate exhibits distinct absorption bands in the infrared spectral range. While infrared radiation is strongly attenuated in water, implementation of fiber optic evanescent wave spectroscopy (FEWS) enables monitoring of water contaminants in real-time with high sensitivity. This work outlines the development of a non-dispersive infrared (NDIR) detector for the real-time monitoring of nitrate, nitrite and ammonia concentrations targeting implementation at municipal wastewater treatment plants (WWTPs) and onsite wastewater treatment systems (OWTS).
Performance of quantum well infrared photodetector (QWIP) device parameters such as detector cutoff wavelength and the dark current density depend strongly on the quality and the control of the epitaxy material growth. In this work, we report on a methodology to precisely control these critical material parameters for long wavelength infrared (LWIR) GaAs/AlGaAs QWIP epi wafers grown by multi-wafer production Molecular beam epitaxy (MBE). Critical growth parameters such as quantum well (QW) thickness, AlGaAs composition and QW doping level are discussed.
Epi-ready GaSb wafers with low absorption coefficients are of a special interest as substrates for molecular beam epitaxy (MBE) growth of material for IR focal plane arrays that operate under back-side illumination configuration, when the substrate is not completely removed. While low absorption coefficient across a broad IR spectral range (~2um-20um) is achievable in GaSb crystals with low Te doping, the control of the doping distribution across the wafers is especially challenging in the mass-production of optically transparent, high-resistivity Te-doped GaSb wafers. In this work, we examine data from the n-type and p-type Te-doped GaSb samples with doping concentration below 1e18 cm-3. The carrier concentration measured by the Hall and the transmission data measured by FTIR spectroscopy are correlated. We perform a rigorous analysis of the absorption coefficient based on the free-carrier absorption mechanism that is dominant for the n-type GaSb and the inter-valence band absorption due to the transitions from the light-hole to the heavy-hole band that is the dominant absorption mechanism for the p-type GaSb. Based on the correlation between the Hall and the FTIR data, carrier concentration profile can be estimated from the non-destructive FTIR transmission mapping of the wafer.
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