This PDF file contains the front matter associated with SPIE Proceedings Volume 11390, including the Title Page, Copyright information, and Table of Contents.

Carcinogenesis involves DNA methylation, a primary alteration in DNA, in the development of cancer before genetic mutation. Because abnormal DNA methylation is found in most cancer cells, the assessment and manipulation of DNA methylation using terahertz radiation can be a novel optical method to detect and control cancer. By directly observing the methylation via terahertz spectroscopy at approximately 1.65 THz, this epigenetic chemical change can be manipulated to the state of demethylation using high-power terahertz radiation. Demethylation of cancer DNA is a key issue in epigenetic cancer therapy, and our results may lead to the treatment of cancer using electromagnetic waves.

We discuss the unique possibilities stemming from exploiting the exotic properties of artificial metasurfaces designed for operation in the THz regime. We mainly focus on graphene based metasurfaces acting as modulators for the THz regime. Graphene exhibits unique optical properties particularly in the THz spectrum, where it predominantly exhibits a Drude-like response. Here we present that ultrafast modulation response in a graphene thin film absorber which can be assessed with use of a broadband THz time-domain-spectroscopic system (THz-TDS) in an IR pump-THz probe configuration. The simple scheme of the absorber can be used as a platform for ultrafast flat optics and metasurfaces.

We present our systematic experimental study on the responsivity to THz wave and the noise in the photoconductive antennas made on low-temperature-grown (LTG) GaAs. In particular, we show that both depend on the properties of the LTG GaAs and the type of the metallization. On the basis of the results, we will discuss a device model in a manner independent of the details of the device fabrication to facilitate the standardized description.

Terahertz (THz) band (0.1-10 THz) communication is envisioned as a key wireless technology to support faster and denser wireless networks. However, absorption by water vapor molecules splits the THz band into multiple transmission windows, each tens to hundreds of Gigahertz (GHz) wide. Because of the broadening of the absorption lines, the available bandwidth within each transmission window changes drastically with distance. As a result, a large portion of the bandwidth close to the absorption lines is considered not practical for communications or, in the best case, practical only for short-range applications. In this paper, chirp spread spectrum communication is proposed as a way to enable ultra-broadband communication links spanning across absorption lines in the THz band. More specifically, first, the performance of Chirp-Spread Binary Phase Shift Keying (CS-BPSK) is analytically derived and compared to that of Binary Chirp Spread Spectrum (BCSS) as well as non-spread Binary Phase Shift Keying (BPSK). Extensive numerical results based on an analytical channel model of the THz band are provided to illustrate the performance of the proposed scheme. Finally, experimental results above conducted in the first absorption-defined window above 1 THz are provided, validating the original hypothesis and highlighting the opportunities and challenges in communication across absorption lines at THz frequencies.

Extreme nonlinear interactions of THz electromagnetic fields with matter are the next frontier in nonlinear optics. However, reaching this frontier in free space is limited by the existing lack of appropriate powerful THz sources. Here we demonstrate both theoretically and experimentally the realization of a novel THz source with high peak power performance based on two-color filamentation of femtosecond mid-infrared laser pulses at 3.9 μm. Our theory predicts that under this scheme sub-cycle THz pulses with multi-millijoule energies and record conversion efficiencies can be produced. Besides, we elucidate the origin of this high efficiency, which is made up of several factors, including a novel mechanism where the harmonics produced by the mid-infrared pulses strongly contribute to the field symmetry breaking and enhance the THz generation. In our experiments we verify the theoretical predictions by demonstrating ultrashort sub-cycle THz pulses with sub-millijoule energy and THz conversion efficiency of 2.36%, resulting in THz field amplitudes above 100 MV cm^-1. Moreover, we show that these intense THz fields can drive nonlinear effects in bulk semiconductors (ZnSe and ZnTe) in free space and at room temperature. Our numerical simulations indicate that the observed THz yield can be significantly upscaled by further optimizing the experimental setup leading to even higher field strengths. Such intense THz pulses enable extreme field science, including into other, relativistic phenomena.

MXenes are 2D transition metal carbides and nitrides with electronic properties that can be tuned by their chemistry and structure. Three members of MXene family, Ti3C2Tz , Mo2Ti2C3Tz and Mo2TiC2Tz are all intrinsically metallic, with high free carrier densities and high carrier mobility within individual nanosheets. However, they respond to photoexcitation in dramatically different ways: while photoexcitation suppresses conductivity in Ti3C2Tz, it results in a long-lived positive photoconductivity in both Mo2Ti2C3Tz and Mo2TiC2Tz. Those responses suggest applications of MXenes in a variety of electro-optical and THz devices.

CMOS (Complementary Metal Oxide Semiconductor) transmitter and receiver circuits for rotational spectroscopy are demonstrated. The IC’s implemented in 65-nm CMOS consist of a 208-252 GHz transmitter and a 225-280 GHz receiver. Use of CMOS electronics can reduce the cost of electronics for rotational spectrometer application from over $50k to less than $1k. The receiver (RX) includes an on-chip antenna for air-to-chip interface, a 2nd order sub-harmonic down-conversion mixer, a low noise IF amplifier and an amplitude detector. The transmitter (TX) includes an on-chip antenna for chip-to-air interface, Fractional-N synthesizer with a frequency step less than 1 kHz with a built-in frequency shift keying circuit as well as a frequency up-converter to generate the signal at the RF. The integrated circuits were assembled into a rotational spectrometer and utilized to detect numerous gases including Ethanol and Acetone in human breath. It is the first ever demonstration of spectroscopy on pure gases as well as breath using CMOS circuits, and this work paves the way toward a more compact, affordable and efficient rotational spectroscopy system.

Recent progress in the development of resonant-tunneling diodes (RTDs) and THz RTD oscillators is described. Strategies and concepts to increase their operating frequencies are pointed out, different types of fundamental RTD oscillators and novel oscillator concepts are outlined.

We developed a novel InGaAs-channel high-electron-mobility transistor (HEMT) integrated with a uni-traveling-carrier photodiode (UTC-PD) structure for the optical-to-wireless carrier frequency down-conversion. We experimentally demonstrated that the output intensity of the down-converted signal is significantly enhanced by 34 dB compared with a standard HEMT, owning to the integration of the UTC-PD structure. We also verified the feasibility of the UTC-PDintegrated HEMT for practical use in the future full coherent network systems.

In ultra-wideband or impulse radio terahertz wireless communication, the atmosphere reshapes terahertz pulses via group velocity dispersion, a result of the frequency-dependent refractivity of air. Without correction, this can significantly degrade the achievable data transmission rate. We present realistic studies of the effects of dispersion over various wireless terahertz links, illustrating how future ultra-wideband links may be limited not by loss, but by inter-symbol interference, stemming from group velocity dispersion. These results show how typical dispersion management approaches are not valid in this case. We also present a novel method for reversing atmospheric group velocity dispersion in terahertz links in the 0.2-0.3 THz atmospheric window using a cohort of stratified media reflectors. To our knowledge, this effort is the first of its kind. Analytical and numerical simulations predict this entirely passive approach can achieve up to 99% of the theoretically possible compensation, while maintaining a power efficiency of greater than 98% across a 100 GHz bandwidth. Finally, we present a prototype reflector that was constructed and experimentally validated our simulations.

The Intelligence Advanced Research Projects Activity (IARPA) SILMARILS program aims to develop a portable system for real-time standoff detection and identification of trace chemical residues on surfaces using active infrared spectroscopy at a 30-50 meter range. Program goals include compact size, rapid scan rate, high chemical sensitivity and specificity across a broad range of target classes, effective operation in a real-world environment including background clutter, uncontrolled substrates, and temperature, humidity and background light variations, and a system that is Class 1M eye safe with a visually unobservable illumination beam. Towards these goals, a number of advances have been demonstrated in infrared illumination sources and novel spectroscopic approaches that are both enablers for the program and have wider utility to the next-generation spectroscopic community. This paper describes three key program developments from both a technical capability and a future use perspective: 1) high-sensitivity QCL-based hyperspectral imaging that has demonstrated the ability to detect nanogram quantities of target chemicals as well as identify targets at >25m standoff; 2) an extremely broadband (1.5 - 11.5 micron) supercontinuum laser source utilizing a novel cascade of three nonlinear optical fibers coupled to a high-speed rotating-prism Fourier Transform Infrared (FTIR) spectrometer; and 3) a compact, tri-band (Short Wave Infrared (SWIR)/Mid-Wave Infrared (MWIR)/Long Wave Infrared (LWIR) hyperspectral imaging (HSI) sensor employing a spatial interferometric element mounted inside the camera Dewar with a final package size no larger than a conventional panchromatic infrared camera.

Microplasmas have been defined (somewhat arbitrarily) as those with one critical dimension (e.g., depth, height or radius) in the micrometer range. Although lab-scale plasmas consume ~20 Lit/min of costly inert gas and require 1-2 kW of electrical power, microplasmas consume only 0.250 mL/min of gas and can be operated from a rechargeable battery. Over time, we developed, evaluated and characterized numerous microplasmas (including those we developed on polymeric substrates). Their detection limits gradually improved after each design cycle. To demonstrate analytical applicability and utility, we show that a microplasma coupled to a fiber-optic spectrometer has the potential to be used for the determination of Cr (Chromim). We also compare optical emission background spectra obtained using different inert gases.

A fieldable sensor or system can be defined as a portable one that can be used in the field. Current needs for fieldable system development are driven by demands imposed from the Internet of Things (IoT), from Industry 4.0, and to a lesser degree from the requirement of “bringing part of the lab to the sample” (e.g., for measurements in the field). To operate in the field, fieldable sensors or systems must be operated from a battery. It would be ideal if field-operation did not require a battery, instead energy was harvested from the ambient environment, using for instance Tribo Electric Nano Generators (TENGs), as will be described here.

Optically Super-resolved InfraRed Imaging micro-Spectroscopy (OSIRIS) permits the collection of fully broadband hyperspectral images at the maximum optical spatial resolution. Modulated long wavelength light is directed onto the sample, while a short wavelength probe beam senses the resultant modulation in local temperature. Thus, OSIRIS constitutes the full generalization of color vision to full spectral bandwidth with spatial resolutions up to the maximum achievable with far-field optics (λprobe/4NA). The non-contact nature of OSIRIS permits deep tomography and real-time imaging, while preserving the versatility and ease of use of optical microscopy.

Raman spectroscopy has become an increasingly common analytical method for real-time, on-line, in-line, and off-line in situ monitoring of product quality in a variety of pharmaceutical, chemical, and biological manufacturing environments, including wastewater quality [1]. The major shortcomings of Raman spectroscopy conducted in the near UV, visible, and IR are that: 1) highly efficient fluorescence emissions from targeted and surrounding materials within the excitation volume of a complex sample often obscures or alters the Raman signature of the materials of interest [2,3,4]; 2) essential and informative fluorescence features of many organic and biological materials are not excited when excitation occurs at wavelengths longer than 250 nm [5]; and 3) Raman signal strength is diminished due to Rayleigh Law and lack of resonance effects. This is especially true of simple organic compounds and biological materials such as amino acids, proteins, peptides, and whole microbial organisms as well as a wide range of active pharmaceutical ingredients as well as their presence in other manufacturing environments and environmentally in wastewater. Unless excitation occurs at wavelength less than about 250 nm, there is significant overlap between Raman and native fluorescence spectral regions from a wide array of organic and biological materials including active pharmaceutical ingredients (APIs) and excipients. This overlap obscures weak Raman emissions and alters the emission spectra of fluorescence emissions due to strong CH and OH Raman bands, both of which reduce the fidelity of spectral classification. This overlap is considerably worse for excitation above 260 nm. Raman emissions provide information about the chemical bonds within the mixtures present in the excitation volume of detection. Fluorescence emissions provide complementary information about the overall electronic configuration of the targeted material. Together, Raman and fluorescence information more fully describe the chemical compounds of interest. Simultaneous acquisition of both forms of emissions coupled with chemometric analysis enables detection and characterization of a wide range of organic and biological material not possible when excitation occurs in the near UV, visible, or IR. We will describe two, new, compact, low cost, instruments employing deep UV excitation to address these growing applications: the DUV Raman PL 200, and the TraC-X. The DUV Raman PL 200 is a portable, 7”x 8”x 25”, 22 lb instrument, which is fully self-contained including a 248 nm laser and controller, a spectrometer with two, computer controlled, holographic gratings, and a multi-stage thermo-electrically cooled 2048x122 element, back thinned, back illuminated, high quantum efficiency detector. And we will also describe the TraC-X sensor, a 3”x 3.5”x 7.5”, < 2 lb, fully self-contained, deep UV excited autofluorescence-only instrument, with built-in deep UV source, low spectral resolution spectrometer, detectors, and microprocessor for analyzing spectral results and providing processed information. As examples, we will discuss applications for real-time in situ monitoring of APIs during continuous liquid and powder manufacturing in the pharmaceutical industry and measurement of nitrates and nitrites in wastewater treatment plants.

For two decades, extraordinary optical transmission (EOT) has amplified exploration into subwavelength systems. Researchers have previously suggested exploiting the spectrally selective electromagnetic field confinement of subwavelength slits for multispectral detectors. Utilizing the finite-difference frequency domain (FDFD) method, we examine electromagnetic field confinement in both 2-dimensional and 3-dimensional scenarios from 2.5 to 6 microns, i.e. midwave infrared (MWIR). We explore the trade space of deep subwavelength slits and its impact on resonant enhancement of the electromagnetic field. This builds fundamental understanding of the coupling mechanisms allowing for prediction of resonant spectral behavior based on slit geometry and material properties.

In this work, we are developing a custom-built broadband laser source in the Mid-LWIR range by combining several high power FP-QCLs for a single snap shot application. To minimize temperature variation or reduce the thermal load while the FP-QCL emits at high currents, the FP-QCL was operated in pulsed mode with varying diode temperatures and applied currents. The spectral outputs in pulsed mode were temporally resolved using a step scan FTIR spectrometer. FP mode peaks typically broaden by driving higher currents. FP mode hopping, emerging, and disappearing were observed during the laser pulse length (3000 ns) at different applied current values. The ideal spectral characteristics for a single snap shot application are discussed, with respect to a broad spectral bandwidth, a flat-top power profile, and high spectral power density.

By exploiting the bi-functional operation capability of interband cascade laser (ICL) frequency combs, we have utilized the laser medium not only for comb generation, but also as a room-temperature photodetector with near-GHz bandwidth for multi-heterodyne beating of the comb lines. Our self-contained platform consuming less than 2 W of electrical power enables free-running room-temperature broadband dual-comb spectroscopy of 1,1 difluoroethane with ~3% standard deviation in 2 ms over 600 GHz of optical bandwidth around 3.6 µm. We will discuss progress toward the optimization of ICL combs for realizing compact, low-power chemical sensors operating in the MWIR.

The physical and chemical quality of lubricating engine oil in the IC engine must be tracked regularly to obtain optimum execution and maintain an engine life and carbon footprint. Routine condition monitoring of engine oil requires costly research testing facility by highly skilled investigators. Various methods can check the concentration of the impurities in engine oil, but some drawbacks exist in already existing methods. An optical fiber-based photon measurement method is utilized in this paper. Our work presents the implementation of optical fiber with white light (WL) based spectrophotometer for continuous monitoring of degradation in engine oil. The optical absorbance of photons in engine oil relating to impurities is estimated by utilizing a photodetector sensor. Experimental results show the designed device provides a trustworthy method of detecting the sludge level in engine oil. Therefore, developed spectrophotometer has potential value in engine oil quality monitoring.

Raman spectroscopy was used to estimate stress in the sidewalls of silicon chips and predict the chips' breaking stress. Silicon wafers were diced using four methods; the breaking stress of the resulting chips was measured mechanically and compared with stress measurements made using Raman spectroscopy. The stress measure- ments made by Raman spectroscopy were loosely correlated with the breaking stress. We conclude that Raman spectroscopy is a promising technique for predicting breaking stress, but requires further development before it can be applied commercially.

3D printing (ranging from technology to materials) for additive manufacturing are receiving increased attention in the scientific and technical literature. More specifically, 3D printers (getting progressively cheaper) and properties of the starting printing materials (e.g., mechanical strength, electrical insulation, resistance to chemical attack) are particularly important for many chemistry-related applications. In this paper, 3D printing technology and materials will be reviewed in some detail. Limited examples from the author’s laboratory will be reported. Chemistry and bio-related applications of 3D printing will be outlined and possible future directions will be suggested.