Approaches are demonstrated that enable mobile devices, such as smartphones, to function as spectrophotometers with equivalent performance to laboratory instruments for measuring any diagnostic test that generates a colored liquid, fluorescent liquid, or colored solid surface. We envision mobile health diagnostic applications in which smartphone-integrated measurement of point-of-care assays enables smart service systems for efficiently connecting patients with health care providers and other health services. A key to this capability is to offer valid tests that are equivalent to those performed in the laboratory by utilizing the same reagents, experimental controls, and calibration standards as conventional assays.

We have been developing and characterizing microplasma-optical emission spectrometry systems for chemical analysis on-site (i.e., in the field). For introduction of micro- and nano-samples into a microplasma, we used our sample introduction system in which small amount of sample (e.g., 3 µL) is first dried and it is then rapidly vaporized into the microplasma, thus generating a transient signal. Typically, sharper signals result in improved Signal-to-Noise Ratios (SNRs) and as a consequence, improved detection limits. For such transient signals, we initially developed FFTs using a desk top computer. We are now porting the desktop FFT-based signal processing to a smartphone. In this presentation, software development will be described, the effect of FFT filtering on SNR will be discussed and progress toward using a smartphone for FFT-based signal processing will be described.

For the past 15 years the development of portable Raman systems have gone from a benchtop Raman system with a lap top computer to a smart phone based sensor. We will discuss the transition from the first handled system to the newly developed smart phone based Raman sensor and present data from this mini sensor. Combining a Raman senor with a smartphone opens up a large number of capabilities due to the advanced processors and cloud computing. We will discuss the application of a smartphone senor ranging from process to security.

The internet of things (IoT) has been defined as a network of physical devices (e.g., bridges, vehicles, sensors, actuators) with connectivity that enables them to exchange data. In this case, a portable spectrometer is used. There are two basic ways of placing a portable spectrometer on the internet of things. One, is by designing the spectrometer from the ground up for IoT connectivity. The other, is by using a commercially available spectrometer. However, portable spectrometer vendors do not provide software source code. To by-pass this, a Windows-10, light-weight, single board computer is used to run the vendor-provided software. A VPN (Virtual Private Network) is then set up (either using WiFi or Ethernet), and the “screen” of the controlling computer is captured by the smartphone (used as a user interface device). In this presentation, developments toward putting a portable optical spectrometer on IoT using a smartphone will be described in detail.

Portable spectrometers designed for users with little technical training must be more robust than spectrometers designed for professionals. Such instruments require software-driven operation using inexpensive components whose limitations are compensated algorithmically. We describe progress towards a hand-held grating spectrometer providing absorption, diffuse reflectance, and luminescence measurements. Low camera dynamic range is compensated by observing orders with a wide range of throughputs. This requires significant effort for wavelength calibration and inter-order intensity normalization. The paper discusses progress in automatic calibration algorithms, software modularization, and method development for quantifying nitrate and phosphate in agricultural runoff.

High resolution gas spectroscopy in the mid-infrared in a transportable device is a big challenge allowing to address numerous applications: air quality or industrial process monitoring, defense and security, medical diagnostics... We use and compactness and robustness OPO with high tunability in the mid-infrared (>1µm) allowing to obtain spectral purity and narrow bandwidth. We use fan-out configuration to increase tunability performances of our source. Experiment and theory are compared. This lead to fine wavelength control on the overall emission spectrum (over 1 µm) without using crystal temperature tuning that slow down tuning speed.

OPOs are a well-known solution when a wide tunability in the mid-infrared is needed. A specific design called NesCOPO (Nested Cavity doubly resonant OPO) is currently integrated in the X-FLR8 portable gas analyzer from Blue Industry and Science. Commercial wavelength meter do not meet the price and compactness that were required in the context of an affordable and portable gas analyzer. We now present an enhanced wavelength meter that meets the need for our application. The first results are displayed and new ways of improving the current device are discussed.

Silicon integration of mid-infrared (MIR) photonic devices promises to enable low-cost, compact sensing systems that are compatible with existing silicon photonic and silicon electronic technologies. Here we report here the first heterogeneous integration of 7-stage interband cascade lasers (ICLs) with silicon waveguides formed on a silicon-on-insulator platform. For pulsed operation the devices display threshold currents as low as 394 mA and output powers up to 560 µW centered at a wavelength near 3.6 µm. The maximum pulsed operating temperature is at least 36 ºC. It should be possible to dramatically improve the efficiency and achieve continuous-wave operation.

Cost effective multi-wavelength light sources are key enablers for spectroscopic applications at Mid-IR. Utilizing a novel Mid-IR Si-based photonic integrated circuit filter and wide-band Mid-IR SLEDs, we show the concept of a light source that covers 2.7…3.5 μm wavelength range with a resolution <1nm. The spectral bands are switchable and tunable and they can be modulated. The PIC is based on the use of thick-SOI technology, SLED based on AlGaInAsSb materials and the hot-embossed lenses are based on tailored single crystal, non-oxide glass and heavy metal oxide glasses. The packaging concept utilizing automated assembly tools are depicted.

Recent advances in the deposition of patterned thin film spectral filters have enabled a new class of radically miniaturized spectral sensors. This new technology enables numerically large arrays of spectral bandpass filters with unprecedented manufacturing economy. For example, a 64-channel array occupying 1 square millimeter and covering the spectral range from 400 – 900 nm can be deposited with as few as eight coating steps. By mating this filter array to a photodiode array or imager chip, a tiny multispectral sensor is realized with diverse applications including health, fitness, food, pharma, agriculture, and chemical detection.

A Fabry-Pérot interferometer platform for the visible spectral rang is presented. Application in miniaturized spectral sensors, spectrometers, tunable solar background filters for high precision LIDAR and in highly integrated spectral cameras are discussed. The interferometers size is 7.5 mm x 7.5 mm x 0.6 mm. The optical resonator is built in between two quarter-wavelength stack dielectric reflectors of 2 mm diameter, which are deposited on movable membranes of 5 mm diameter. Alternative reflector concepts of periodic structured, subwavelength sized surfaces, as well as algorithms for extending the usable spectral rang and enhancing the wavelength resolution of Fabry-Pérot interferometers are reviewed.

In-plane linear variable optical filter (LVOF) was fabricated on Si wafer. The high Bragg contrast Si-air LVOF comprises of [HLH]-taper-[HLH] configuration. The fine taper angle was determined by electron beam lithography which in turn, dry etched via deep reactive ion etching. 90o pillars were vertically etched into Si with scallop depth <30nm. The fabricated LVOF was characterized using benchtop FTIR. It has a free space working range of 3.1-3.8µm. FWHM of 95nm is observed at 3.3µm.

Wedge or staircase micro-optics have become important components for building miniature optical spectrometers. These devices create spectral discrimination through interference between beams resulting from reflections at the surfaces of the optic. We present a mathematical description of the signal model for such spectrometers. We show that in the case of spectrally uniform reflectance, the signal has a specific relationship to the spectrum’s Fourier transform. We cast the spectral recovery problem as a matrix inversion, and derive formulas for calculating the solution matrix. The solution matrix is shown to yield the exact spectrum when applied to modeled wedge spectrometer signals.

Due to the growth of miniature Unmanned Aerial Vehicles (UAVs) and small spacecraft (SmallSats) in recent years, there has been a push for the development of miniaturized spectral imagers to be incorporated with them. An efficient, compact hyperspectral imager integrated with these vehicles provides a cost effective platform for environmental sensing applications. We present here the development and integration of a snapshot hyperspectral imaging system called the Image Mapping Spectrometer (SNAP-IMS). The benefits to size, weight, and power reduction this system offers enables its potential future integration into a variety of small, unmanned vehicles.

Computational Fluid Dynamics (CFDs) are widely used by multi-billion dollar industries to simulate fluid flow around objects (e.g., ranging from an aircraft wing to an entire automobile). Subsequently, a prototype is produced and it is tested using a wind-tunnel and smoke experiments (to show fluid flow around the object being tested). We have using an empirical design for a vaporization chamber we used for sample introduction into our battery-operated microplasmas. To provide an initial starting point toward a design of an optimized vaporization chamber, we started by 3D printing candidate designs. In this presentation, 3D printing of vaporization chambers will be described and the results of smoke visualization-experiments will be shown. Toward the end of the presentation, progress toward CFD simulations will be reported.

Separation and concentration of rare earth elements (REEs) from coal and coal (mining and combustion) byproducts is a growing technology. To achieve industrial scale and reliability, process control and process development need analytical tools that can provide rapid and accurate feedback on elemental concentrations at various process stages. Analytical chemistry methods such as ICP-MS, while sensitive and accurate, are time consuming and expensive. We present the designs and results from the development of a laser-induced breakdown spectroscopy (LIBS) instrument intended to monitor REE recovery processes “at line”, from the very high concentration product to the very low concentration feedstock.

A developed modular, compact Raman spectrometer, utilizing a green laser pointer, or a hand-held green laser for excitation, was tested for short distance detection and imaging of explosives. The ensuing signals were employed for sensitive and selective detection of different liquids and individual particles, placed on a variety of substrates. Synchronization of sample movement with detector readout, allowed obtaining not only characteristic Raman signals but also Raman images of the traces via point-mapping (PM) and photo-guided sampling/PM and line-mapping, which led to considerably reduced sampling times. It is anticipated that realization of these operation modes can lead to improved performance.

A new technique to enhance spontaneous Raman scattering utilizing a highly reflective integrating cavity is presented. Elastically scattered light circulates within the cavity volume continuously interacting with the sample, whether a bulk sample or gas, resulting in significant Raman enhancement. In addition, the Raman scattered light is collected from all directions before being coupled out of the cavity. Enhancements of 10^7 have been realized with the use of inexpensive low power diode lasers and a modest CCD based spectrometer. Application of the iCERS technique to near real-time detection and measurement of trace gases, chemicals, and biological compounds is discussed.

Portable hyperspectral imagers enable real time decision-making in application areas such as threat detection, forensics, environmental and agricultural monitoring and biomedical screening. High spectral and spatial resolution provide far more actionable information than obtainable by multispectral imagers. High-resolution VNIR reflectance imagers characterize photosynthetic productivity via solar-induced fluorescence (SIF) monitoring, representing a substantial improvement over earlier multispectral analytics such as normalized difference vegetation index (NDVI). Handheld Raman instruments enable high speed screening for explosives, narcotics and hazardous materials. A line scan/area imaging approach detects trace quantities of target materials, such as small particles of explosives or narcotics, within a bulk sample.

We have developed a novel technique to collect infrared hyperspectral images below the IR diffraction limit. Optically Sensed photothermal InfraRed Imaging micro-Spectroscopy (OSIRIS) permits the construction of infrared images at a resolution limited by the wavelength of the probe beam. In this technique, an infrared laser is used to excite the sample, while a short wavelength probe beam senses the resultant change in temperature. With this technique, hyperspectral images can be acquired orders of magnitude faster than with the competing scanning probe techniques. Furthermore, a confocal setup permits tomography, which scanning probe techniques cannot achieve due to their surface nature.

Hyperbolic metamaterials (HMM), a class of artificially engineered materials with a highly anisotropic permittivity response originating from opposite signs of the principal components of the electric tensor, have attracted significant interest in recent years due to their ability to manipulate the propagation light in exotic ways. Here we exploit the hyperbolic iso-frequency characteristic of a planar type-II HMM (composed of alternating, sputtered films of Ag and SiO2) to achieve high-sensitivity proximity detection of metallic and dielectric nanoparticles in a transmission dark-field configuration. Due to its high sensitivity to nanoparticles in deep-subwavelength proximity to a surface, achieved without the use of cumbersome dark-field optics, this HMM-based device hints at promising applications in bio-chemical sensing, particle tracking and contamination analysis.

We present a hyperspectral imaging system in the 1100-1700 nm wavelength range based on a novel, miniaturized and highly robust optical MEMS-based tunable Fabry-Pérot interferometer, which has been developed at SINTEF. The system consists of a 128 by 128 pixels InGaAs camera, the Fabry-Pérot interferometer and software for acquisition and processing of hyperspectral images. Hyper-spectral data from relevant applications are presented and discussed.

The advancement of modern camera technology has enabled the encoding of additional information into an image by utilizing the increased spatial resolution in detector arrays. We present a hyperspectral imaging technique employing multiple scattering and compressive sensing for use as a compact, high spectral resolution imaging spectrometer. We show that the amount of data collected at the acquisition stage can be significantly reduced, well below the Nyquist-Shannon limit in order to decrease the computational demands required to recover spatial and spectral information. We reconstruct both noisy and sparse signals over a broad wavelength range.

Due to complexity and bulkiness of instrumentation, it has been difficult to make hyperspectral measurements on the sample locations. Demanding data processing has prevented obtaining immediate results for decisions and actions on the measurement spot. To solve these issues Specim Ltd has introduced a mobile hyperspectral camera for 400-1000nm spectral range. In addition to the portability, the camera has integrated data processing capability and easy user interface. Paper illustrates the design targets, and the features of the mobile hyperspectral imager. In addition to the technological description, the results from the pilot phase field and laboratory tests are shown.

CISS has developed a wide-field, near real-time, portable shortwave infrared hyperspectral imaging (SWIR HSI) sensor capable of detecting threat materials (i.e. explosives, narcotics) at standoff distances. The sensor is configured to operate at standoff distances from 1-20+ meters and has a custom developed software package that provides the operator the ability to adapt its spectral library to incorporate new threat materials or change the type of target of interest. This paper will provide an overview of the SWIR HSI technology as well as a discussion on how it may be effectively applied to room clearing applications.

A novel, adaptable, shortwave infrared hyperspectral imaging (SWIR HSI) system has been developed for real-time standoff detection of hazardous materials. At the heart of this system is the Conformal Filter (CF), which is a liquid crystal based tunable filter that transmits multi-band waveforms that mimic the functionality of a discriminant vector for classification of target threats amongst background clutter. Real-time detection is achieved by operating two CFs in tandem within a dual polarization (DP) system allowing for simultaneous acquisition of the compressed HSI data. This paper will discuss the development, characterization, and test results of the DP-CF sensor.

We used a tunable quantum cascade laser to characterize a novel nano-engineered tunable spectral filter based on the grating mode resonance (GMR) phenomenon operating in the longwave infrared from 8 to 12 micron. The filter is designed to reflect the incident broadband light at one (or more) narrow spectral band while fully transmitting in the rest of the spectral range. Tuning of the reflection wavelength is achieved by changing the angle of incidence of light by mechanically tilting the filter. We will present the design, detailed characterization experiment and comparison of the theoretical and experimental results for a 1-d filter.

Terahertz wireless systems are a promising means of supporting the massive data produced by the numerous distributed spectroscopic systems coming online. Yet relatively little work has focused on the nature of terahertz propagation through real-world atmospheres. We present new measurements and studies on terahertz propagation and wireless data movement through atmospheres of various conditions. These are compared to previous data and international standards in the framework of underpinning system-level engineering of terahertz wireless systems. We also explore how such wireless systems might simultaneously serve as in-situ spectroscopy tools, providing another avenue of ubiquitous sensing.

In our research, we have studied symmetric and asymmetric SRRs based metamaterials to improve Q factors hence leading to a high figure of merit (FoM). The first problem we have primarily focused on a comprehensive study of sensing capabilities of different orders of resonances in single split gap (relatively simple geometry) terahertz metamaterials and have reported the usefulness of sensing performances of the odd and even resonance orders based THz metamaterials. In another work, we have discussed sensing capabilities of dark modes in asymmetric SRR based metamaterials. The metamaterial unit cell consists of an asymmetric SRR with identical split gaps at opposite ends, but the terminal ends of one side plate of the split gap are not the same as the other side.

By revitalizing an age old, little known, and unconventional material-design technology called artificial dielectrics, here we demonstrate how to fabricate several key fundamental device components that can control and manipulate THz radiation. In particular, we demonstrate a lens that can focus THz radiation, a polarizing-beamsplitter that can split an arbitrarily polarized beam into two linearly polarized orthogonal components, a quarter-waveplate that can change a linearly polarized beam into a circularly polarized one, and an isolator that can minimize back-reflections. These artificial-dielectric devices exhibit remarkable performance characteristics. Indeed, our device specifications rival those of similar devices commercially available for optical wavelengths.

Dipole induced quadrupole resonance leads to transmission peak within the broad dipole absorption as shown in plasmonic metamaterials. We show quadrupolar interactions as a new paradigm to control this classical analogue of electromagnetically induced transparency (i.e. plasmon induced transparency, PIT) in metamaterials. While the asymmetry factor of the resultant Fano line shape of a EIT spectrum limits the quality factor (Q) of the resonance and thus the sensing application, we show that quadrupolar interactions give a handle on the Q factor. A Q as high as 600 is seen in simulations at about 1 THz. Limited by the experimental resolution, a Q of about 100 is experimentally observed. Further plasmonic structures can be designed to make use of the quadrupolar interactions for high sensitive devices at THz frequencies.

Incorporating plasmonic nanostructures inside the active area of photoconductive terahertz sources and detectors offers enhanced quantum efficiencies while maintaining ultrafast operation. This enhancement is due to the unique capability of plasmonic nanostructures to significantly increase the concentration of photo-induced carriers inside the device active area, where they interact with a bias/terahertz electric field to generate/detect terahertz radiation. By the use of this powerful technique, broadband terahertz spectroscopy with record-high signal-to-noise ratio levels exceeding 110 dB and broadband terahertz spectrometry with quantum-level sensitivities are demonstrated.

We present our work on terahertz optical diode effect in natural multiferroic and artificial plasmonic structures. Terahertz beam traveling in one direction in a crystal may experience different optical properties (absorption and dispersion) compared to the beam traveling in the exact opposite direction. This nonreciprocity can be extremely useful in the field of terahertz photonics. We discuss the physical origin of the effect in naturally occurring magnetoelectric multiferroic materials, and report the observation of the effect in multiferroic FeZnMn3O8 in its high-temperature paramagnetic state. We also explore the possible architectures for artificial nonreciprocal metamaterials based on terahertz surface plasmons.

The THz pulses are propagated through 186 m and 910 m distance which are approximately equal to 52 and 255 round-trips of the circulating 50 fs optical pulse within the mode-locked ring laser, respectively. When the humidity and temperature are continuously varied during the measurement, the THz pulses also continuously shifted with 2.36 and 15.53 ps/(g/m3) ratio for a 186- and 910-m propagation, respectively. Meanwhile, the characteristics of the N2O and CO gases are investigated 93 meters away from the THz transmitter using the THz pulse which propagates an outside environment of 79 m between two buildings. The natural resonances of the gases are detected in the 0.5 THz bandwidth except water vapor resonances.

Ammonium nitrate (AN), often used in improvised explosives, exhibits featureless reflection/transmission spectrum at THz frequencies at room temperature. However, the low frequency vibrational modes exhibit strong temperature dependence below room temperature (<240k) due to the polymorphic phase transitions. In this work, we study the effective dielectric properties of AN embedded in a polytetrafluoroethylene (PTFE) host medium using terahertz time domain spectroscopy in the temperature ranging from 5K to 300K. The dielectric properties of pure AN were extracted using three different effective medium theories (EMT): (i) the simple effective medium approach, (ii) the Maxwell-Garnett (MG) model, and (iii) the Bruggeman (BR) model. The dielectric properties obtained from theoretical approximations agree well with the experimental values. We identified six lattice vibrational modes between 0.2-3.0 THz that are associated with the polymorphic phase transitions at low temperature.

For detection of pulsed THz waves, EO sampling technique has been commonly used. In the conventional collinear EO sampling scheme, however, the efficiency is limited by the velocity mismatch between the optical sampling wave and THz wave in EO crystals. The intrinsic birefringence in the EO crystal is another problem. To solve these problems, a non-collinear and non-ellipsometric electro-optic sampling technique can be used. This technique is called as "Heterodyne EO sampling" and it is free from the velocity mismatch problem and the influence of the birefringence. It is possible to use metallic parallel plate waveguide structures for enhancement of EO sampling sensitivity.

In this talk I will show spin injection dynamics from a ferromagnet (FM) into a topological insulator (TI) in a FM/TI heterostructure --- Co/Bi2Se3, resulting in spin-to-charge conversion and consequently THz emission. By measuring the emitted THz pulses in the time and frequency domain, as a function of pump polarization, pump fluence, magnetic field direction, sample direction, BisSe3 thickness and Co thickness, both in the pure TI film and the FM/TI heterostructure, we demonstrate highly-efficient THz emission from Co/Bi2Se3, and conclude that the Bi2Se3 surface states play a dominant role in spin-to-charge conversion via the inverse Rashba-Edelstein effect. Compared to the instantaneous shift current THz emission mechanism in pure Bi2Se3, we observe a temporal delay of ~0.12 ps in the spin-current-related component, which characterizes the spin-to-charge conversion timescale in topological insulators.