Open-Path Cavity Ring-Down Spectroscopy for Simultaneous Detection of Hydrogen Chloride and Particles in Cleanroom Environment.

The present study addresses advanced monitoring techniques for particles and airborne molecular contaminants (AMCs) in cleanroom environments, which are crucial for ensuring the integrity of semiconductor manufacturing processes. We focus on quantifying particle levels and a representative AMC, hydrogen chloride (HCl), having known detrimental effects on equipment longevity, product yield, and human health. We have developed a compact laser sensor based on open-path cavity ring-down spectroscopy (CRDS) using a 1742 nm near-infrared diode laser source.

Open-Path Laser Absorption Sensor for Mobile Measurements of Atmospheric Ammonia.

Anthropogenic emissions of ammonia to the atmosphere, particularly those from agricultural sources, can be damaging to the environment and human health and can drive a need for sensor technologies that can be used to detect and quantify the emissions. Mobile sensing approaches that can be deployed on ground-based or aerial vehicles can provide scalable solutions for high throughput measurements but require relatively compact and low-power sensor systems. This contribution presents an ammonia sensor based on wavelength modulation spectroscopy (WMS) integrated with a Herriott multi-pass cell and a quantum cascade laser (QCL) at 10.

Ozone Detection via Deep-Ultraviolet Cavity-Enhanced Absorption Spectroscopy with a Laser Driven Light Source.

We present a novel sensing approach for ambient ozone detection based on deep-ultraviolet (DUV) cavity-enhanced absorption spectroscopy (CEAS) using a laser driven light source (LDLS). The LDLS has broadband spectral output which, with filtering, provides illumination between ~230-280 nm. The lamp light is coupled to an optical cavity formed from a pair of high-reflectivity (R~0.

In-Situ Elemental Composition Analysis of Large Inhalable Aerosol Using Laser Induced Breakdown Spectroscopy.

The ability to obtain information on the composition of airborne particles is a necessary part of identifying and controlling risks from exposure to potentially toxic materials, especially in the workplace. However, very few aerosol sampling instruments can characterize elemental composition in real time or measure large inhalable particles with aerodynamic diameter exceeding 20 µm. Here, we present the development and validation of a method for real time elemental composition analysis of large inhalable particles using laser-induced breakdown spectroscopy (LIBS).

Mobile Measurement System for the Rapid and Cost-Effective Surveillance of Methane and Volatile Organic Compound Emissions from Oil and Gas Production Sites.

In this study, a ground-based mobile measurement system was developed to provide rapid and cost-effective emission surveillance of both methane (CH) and volatile organic compounds (VOCs) from oil and gas (O&G) production sites. After testing in several controlled release experiments, the system was deployed in a field campaign in the Eagle Ford basin, TX. We found fat-tail distributions for both methane and total VOC (C4-C12) emissions (e.

Resonant dual-pulse laser ignition technique based on oxygen REMPI pre-ionization.

This contribution investigates a novel laser ignition method based on a dual-pulse resonant pre-ionization scheme. The first laser pulse efficiently creates initial gas ionization (seed electrons) through a 2 + 1 resonantly-enhanced multiphoton ionization (REMPI) scheme targeting molecular oxygen (λ ~ 287.6 nm).

Gas dynamics and vorticity generation in laser-induced breakdown of air.

Research has shown that the ignition characteristics of laser-induced plasmas in fuel-air mixtures are influenced by the gas dynamics effects induced during the gas breakdown stage. Here, we present the numerical modeling of the fluid mechanics induced by breakdown (plasma formation) from a nanosecond near-infrared (NIR) laser pulse in air. The simulations focus on the post-discharge kernel dynamics with the goal of developing a better understanding of how vorticity is generated during the kernel cooling phase.

Cavity Ring-Down Methane Sensor for Small Unmanned Aerial Systems.

We present the development, integration, and testing of an open-path cavity ring-down spectroscopy (CRDS) methane sensor for deployment on small unmanned aerial systems (sUAS). The open-path configuration used here (without pump or flow-cell) enables a low mass (4 kg) and low power (12 W) instrument that can be readily integrated to sUAS, defined here as having all-up mass of <25 kg. The instrument uses a compact telecom style laser at 1651 nm (near-infrared) and a linear 2-mirror high-finesse cavity.

Open-path cavity ring-down methane sensor for mobile monitoring of natural gas emissions.

We present the design, development, and testing results of a novel laser-based cavity ring-down spectroscopy (CRDS) sensor for methane detection. The sensor is specifically oriented for mobile (i.e.

Cavity-enhanced Thomson scattering measurements of electron density and temperature in a hollow cathode discharge.

A cavity-enhanced Thomson scattering (CETS) diagnostic has been developed to perform electron density and temperature measurements in low-density weakly ionized discharges. The diagnostic approach is based on generating a high-power beam in an optical build-up cavity and using the beam as a light source for Thomson scattering from plasma housed within the cavity. In our setup, a high-power (∼5  W) fiber laser at 1064 nm allows an intra-cavity power of 11.

Control of Early Flame Kernel Growth by Multi-Wavelength Laser Pulses for Enhanced Ignition.

The present contribution examines the impact of plasma dynamics and plasma-driven fluid dynamics on the flame growth of laser ignited mixtures and shows that a new dual-pulse scheme can be used to control the kernel formation process in ways that extend the lean ignition limit. We perform a comparative study between (conventional) single-pulse laser ignition (λ = 1064 nm) and a novel dual-pulse method based on combining an ultraviolet (UV) pre-ionization pulse (λ = 266 nm) with an overlapped near-infrared (NIR) energy addition pulse (λ = 1064 nm). We employ OH* chemiluminescence to visualize the evolution of the early flame kernel.

Fabrication of Nanostructured Omniphobic and Superomniphobic Surfaces with Inexpensive CO Laser Engraver.

Superomniphobic surfaces (i.e., surfaces that are extremely repellent to both high surface tension liquids like water and low surface tension liquid like oils) can be fabricated through a combination of surface chemistry that imparts low solid surface energy with a re-entrant surface texture.

Water Plume Temperature Measurements by an Unmanned Aerial System (UAS).

We report on the development and testing of a proof of principle water temperature measurement system deployed on an unmanned aerial system (UAS), for field measurements of thermal discharges into water. The primary elements of the system include a quad-copter UAS to which has been integrated, for the first time, both a thermal imaging infrared (IR) camera and an immersible probe that can be dipped below the water surface to obtain vertical water temperature profiles. The IR camera is used to take images of the overall water surface to geo-locate the plume, while the immersible probe provides quantitative temperature depth profiles at specific locations.

Cavity-enhanced rotational Raman scattering in gases using a 20 mW near-infrared fiber laser.

A novel cavity-enhanced laser diagnostic has been developed to perform point measurements of spontaneous rotational Raman scattering. A narrow linewidth fiber laser source (1064 nm) is frequency locked to a high-finesse cavity containing the sample gas. Intracavity powers of 22 W are generated from 3.

Open-path cavity ring-down spectroscopy for trace gas measurements in ambient air.

The present work used a near-infrared methane cavity ring-down spectroscopy (CRDS) sensor to examine performance and limitations of open-path CRDS for atmospheric measurements. A simple purge-enclosure was developed to maintain high mirror reflectivity and allowed >100 hours of operation with mirror reflectivity above 0.99996.

High Power Spark Delivery System Using Hollow Core Kagome Lattice Fibers.

This study examines the use of the recently developed hollow core kagome lattice fibers for delivery of high power laser pulses. Compared to other photonic crystal fibers (PCFs), the hollow core kagome fibers have larger core diameter (~50 µm), which allows for higher energy coupling in the fiber while also maintaining high beam quality at the output (² = 1.25).

A high-finesse broadband optical cavity using calcium fluoride prism retroreflectors.

A high-finesse broadband optical cavity has been developed for use in the ultraviolet and visible region using Brewster-angle calcium fluoride (CaF₂) prism retroreflectors. Prior to prism construction, optical loss measurements of CaF₂ windows were performed using cavity ring-down spectroscopy at 250 nm. Total optical loss showed high spatial correlation with crystal birefringence, which was partially mitigated by orienting the <111> crystal axis with the laser beam.

High power fiber delivery for laser ignition applications.

The present contribution provides a concise review of high power fiber delivery research for laser ignition applications. The fiber delivery requirements are discussed in terms of exit energy, intensity, and beam quality. Past research using hollow core fibers, solid step-index fibers, and photonic crystal and bandgap fibers is summarized.

Fiber-coupled ultraviolet planar laser-induced fluorescence for combustion diagnostics.

Multimode silica step-index optical fibers are examined for use in planar laser-induced fluorescence (PLIF) for combustion diagnostics using ultraviolet (UV) laser sources. The multimode step-index fibers are characterized at UV wavelengths by examining their energy damage thresholds and solarization performance. The beam quality achievable with large clad step-index multimode fibers is also studied.

Mode coupling and output beam quality of 100-400 μm core silica fibers.

Propagation and mode coupling within relatively short (∼1-10 m) large core, nominally multimode, fibers are of interest in a number of applications. In this research, we have studied the output beam quality and mode coupling in various fibers with core diameters of 100-400 μm and lengths of 2 m. Output beam quality (M2) and mode-coupling coefficients (D) have been studied for different clad dimensions, numerical apertures, and wavelengths.

Laser-induced breakdown spectroscopy for in-cylinder equivalence ratio measurements in laser-ignited natural gas engines.

In this contribution we present the first demonstration of simultaneous use of laser sparks for engine ignition and laser-induced breakdown spectroscopy (LIBS) measurements of in-cylinder equivalence ratios. A 1064 nm neodynium yttrium aluminum garnet (Nd:YAG) laser beam is used with an optical spark plug to ignite a single cylinder natural gas engine. The optical emission from the combustion initiating laser spark is collected through the optical spark plug and cycle-by-cycle spectra are analyzed for H(alpha)(656 nm), O(777 nm), and N(742 nm, 744 nm, and 746 nm) neutral atomic lines.

Fiber-optic spark delivery for gas-phase laser-induced breakdown spectroscopy.

This article reports what are to the authors' knowledge the first gas-phase laser-induced breakdown spectroscopy (LIBS) measurements using a fiber-optically delivered spark. A silver- and polymer-coated hollow fiber delivered high-energy nanosecond 1064 nm Nd:YAG laser pulses, which were focused to generate high-energy-density plasmas in ultra-lean methane-air mixtures. Emissions from these plasmas were collected and spectroscopically analyzed to quantify relative fuel-to-air ratio.

Use of hollow core fibers, fiber lasers, and photonic crystal fibers for spark delivery and laser ignition in gases.

The fiber-optic delivery of sparks in gases is challenging as the output beam must be refocused to high intensity (approximately 200 GW/cm(2) for nanosecond pulses). Analysis suggests the use of coated hollow core fibers, fiber lasers, and photonic crystal fibers (PCFs). We study the effects of launch conditions and bending for 2 m long coated hollow fibers and find an optimum launch f# of approximately 55 allowing spark formation with approximately 98% reliability for bends up to a radius of curvature of 1.

Differential sputter yield measurements using cavity ringdown spectroscopy.

The first use of cavity ringdown spectroscopy (CRDS) to measure differential (angular) sputter yield profiles of sputtered particles is reported. Owing to the path-integrated nature of CRDS, inversion techniques are required. Our approach is to scan the optical axis relative to the source of sputtered particles and to measure the spatial profile of the CRDS signals.

Gas temperature measurements in weakly ionized glow discharges with filtered Rayleigh scattering.

We report the first gas temperature measurements in plasmas to our knowledge obtained by filtered Rayleigh scattering (FRS). A narrow-linewidth Ti:sapphire laser is used as the illumination source, and a mercury filter provides strong suppression of elastic background. We perform measurements in weakly ionized glow discharges in pure argon and in an argon-plus-1%-nitrogen mixture.