Optical frequency references in acetylene-filled hollow-core optical fiber and photonic microcells

Doctor of PhilosophyDepartment of PhysicsKristan L. CorwinOptical frequency references have been widely used in applications such as navigation, remote sensing, and telecommunication industry. For stable frequency references in the near-infrared (NIR), lasers can be locked to narrow absorption features in gases such as acetylene. Currently, most Near NIR references are realized in free space setups. In this thesis, a low-loss hollow-core optical fiber with a diameter of sub millimeters is integrated into the reference setup to provide long interaction lengths between the filling gas and the laser field, also facilitate the optical interaction with low power levels. To make portable NIR reference, gas can be sealed inside the hollow-core fiber, by creating a photonic microcell. This work has demonstrated all-fiber optical frequency references in the Near IR by fabricating and integrating gas sealed photonic microcells in the reference setup. Also, a thoughtful study regarding the lineshape of the fiber-based reference has been accomplished. According the proper modeling of a shift due to lineshape, a correction was applied to our previous absolute frequency measurement of an NIR optical frequency reference. Furthermore, effects of the hollow-core fibers, including mode-dependence frequency shift related to surface modes are explored. In addition, angle splicing techniques, which will improve the performance of the fiber-based frequency reference have been created. Low transmission and return loss angle splices of photonic bandgap fiber, single mode PCF, and large core kagome to SMF-28 are developed and those fibers are demonstrated to be promising for photonic microcell based optical frequency references. Finally, a potentially portable optical metrology system is demonstrated by stabilizing a fiber-laser based frequency comb to an acetylene-filled optical fiber frequency reference. Further work is necessary to fabricate an all-fiber portable optical metrology system with high optical transmission and low molecular contamination

The HITRAN2016 Molecular Spectroscopic Database

This paper describes the contents of the 2016 edition of the HITRAN molecular spectroscopic compilation. The new edition replaces the previous HITRAN edition of 2012 and its updates during the intervening years. The HITRAN molecular absorption compilation is composed of five major components: the traditional line-by-line spectroscopic parameters required for high-resolution radiative-transfer codes, infrared absorption cross-sections for molecules not yet amenable to representation in a line-by-line form, collision-induced absorption data, aerosol indices of refraction, and general tables such as partition sums that apply globally to the data. The new HITRAN is greatly extended in terms of accuracy, spectral coverage, additional absorption phenomena, added line-shape formalisms, and validity. Moreover, molecules, isotopologues, and perturbing gases have been added that address the issues of atmospheres beyond the Earth. Of considerable note, experimental IR cross-sections for almost 300 additional molecules important in different areas of atmospheric science have been added to the database. The compilation can be accessed through www.hitran.org. Most of the HITRAN data have now been cast into an underlying relational database structure that offers many advantages over the long-standing sequential text-based structure. The new structure empowers the user in many ways. It enables the incorporation of an extended set of fundamental parameters per transition, sophisticated line-shape formalisms, easy user-defined output formats, and very convenient searching, filtering, and plotting of data. A powerful application programming interface making use of structured query language (SQL) features for higher-level applications of HITRAN is also provided

The HITRAN2020 Molecular Spectroscopic Database

The HITRAN database is a compilation of molecular spectroscopic parameters. It was established in the early 1970s and is used by various computer codes to predict and simulate the transmission and emission of light in gaseous media (with an emphasis on terrestrial and planetary atmospheres). The HITRAN compilation is composed of five major components: the line-by-line spectroscopic parameters required for high-resolution radiative-transfer codes, experimental infrared absorption cross-sections (for molecules where it is not yet feasible for representation in a line-by-line form), collision-induced absorption data, aerosol indices of refraction, and general tables (including partition sums) that apply globally to the data. This paper describes the contents of the 2020 quadrennial edition of HITRAN. The HITRAN2020 edition takes advantage of recent experimental and theoretical data that were meticulously validated, in particular, against laboratory and atmospheric spectra. The new edition replaces the previous HITRAN edition of 2016 (including its updates during the intervening years). All five components of HITRAN have undergone major updates. In particular, the extent of the updates in the HITRAN2020 edition range from updating a few lines of specific molecules to complete replacements of the lists, and also the introduction of additional isotopologues and new (to HITRAN) molecules: SO, CH3F, GeH4, CS2, CH3I and NF3. Many new vibrational bands were added, extending the spectral coverage and completeness of the line lists. Also, the accuracy of the parameters for major atmospheric absorbers has been increased substantially, often featuring sub-percent uncertainties. Broadening parameters associated with the ambient pressure of water vapor were introduced to HITRAN for the first time and are now available for several molecules. The HITRAN2020 edition continues to take advantage of the relational structure and efficient interface available at www.hitran.org and the HITRAN Application Programming Interface (HAPI). The functionality of both tools has been extended for the new edition

The HITRAN2016 molecular spectroscopic database

This paper describes the contents of the 2016 edition of the HITRAN molecular spectroscopic compilation. The new edition replaces the previous HITRAN edition of 2012 and its updates during the intervening years. The HITRAN molecular absorption compilation is composed of five major components: the traditional line-by-line spectroscopic parameters required for high-resolution radiative-transfer codes, infrared absorption cross-sections for molecules not yet amenable to representation in a line-by-line form, collision-induced absorption data, aerosol indices of refraction, and general tables such as partition sums that apply globally to the data. The new HITRAN is greatly extended in terms of accuracy, spectral coverage, additional absorption phenomena, added line-shape formalisms, and validity. Moreover, molecules, isotopologues, and perturbing gases have been added that address the issues of atmospheres beyond the Earth. Of considerable note, experimental IR cross-sections for almost 300 additional molecules important in different areas of atmospheric science have been added to the database. The compilation can be accessed through www.hitran.org. Most of the HITRAN data have now been cast into an underlying relational database structure that offers many advantages over the long-standing sequential text-based structure. The new structure empowers the user in many, ways. It enables the incorporation of an extended set of fundamental parameters per transition, sophisticated line-shape formalisms, easy user-defined output formats, and very convenient searching, filtering, and plotting of data. A powerful application programming interface making use of structured query language (SQL) features for higher-level applications of HITRAN is also provided. Published by Elsevier Ltd

The HITRAN2020 molecular spectroscopic database

The HITRAN database is a compilation of molecular spectroscopic parameters. It was established in the early 1970s and is used by various computer codes to predict and simulate the transmission and emission of light in gaseous media (with an emphasis on terrestrial and planetary atmospheres). The HITRAN compilation is composed of five major components: the line-by-line spectroscopic parameters required for high-resolution radiative-transfer codes, experimental infrared absorption cross-sections (for molecules where it is not yet feasible for representation in a line-by-line form), collision-induced absorption data, aerosol indices of refraction, and general tables (including partition sums) that apply globally to the data. This paper describes the contents of the 2020 quadrennial edition of HITRAN. The HITRAN2020 edition takes advantage of recent experimental and theoretical data that were meticulously validated, in particular, against laboratory and atmospheric spectra. The new edition replaces the previous HITRAN edition of 2016 (including its updates during the intervening years). All five components of HITRAN have undergone major updates. In particular, the extent of the updates in the HITRAN2020 edition range from updating a few lines of specific molecules to complete replacements of the lists, and also the introduction of additional isotopologues and new (to HITRAN) molecules: SO, CH3F, GeH4, CS2, CH3I and NF3. Many new vibrational bands were added, extending the spectral coverage and completeness of the line lists. Also, the accuracy of the parameters for major atmospheric absorbers has been increased substantially, often featuring sub-percent uncertainties. Broadening parameters associated with the ambient pressure of water vapor were introduced to HITRAN for the first time and are now available for several molecules. The HITRAN2020 edition continues to take advantage of the relational structure and efficient interface available at www.hitran.org and the HITRAN Application Programming Interface (HAPI). The functionality of both tools has been extended for the new edition

Laboratory spectroscopic study of acetylene and carbon dioxide for atmospheric remote sensing purposes

This thesis presents line-shape studies of carbon dioxide and acetylene, found as trace constituents in planetary atmospheres. The v1+v3 band of acetylene broadened by CO2 was recorded using a tunable diode laser spectrometer at different pressures (50-750 Torr) and temperatures (216-333 K) to retrieve pressure induced line-shape parameters as well as their temperature dependences. A second study was carried out to analyze line shapes of the Q-branch transitions of three weak bands (12201-03301, 11101-10002 and 12201-11102) of pure CO2 recorded at room temperature and different pressures (0.2-140 Torr) using a Fourier transform spectrometer. For both of these studies a non-linear least squares fitting software was used. A constraint analysis was performed in the CO2 study in order to reduce correlations between the retrieved line-shape parameters. Furthermore, theoretical calculation of line mixing parameters corresponding to the three bands of CO2 was performed using Exponential Power Gap (EPG) law.Amethyst, School of Graduate Studie

Linear and nonlinear spectroscopic techniques applied to study of transient molecular species

Carbon chain radicals and ions have long been known to exist in the interstellar medium, and considered as potential carriers for diffuse interstellar bands. Measurements on these molecules are difficult because they are short-lived species generated in small number densities. Discharge and laser vaporization sources coupled to a supersonic jet expansion are, so far, the most effective techniques used to generate sufficiently large densities suitable for spectroscopic studies of these transients. The present work describes the combination of these molecular sources with high resolution cavity ring down (CRDS) and four wave mixing (FWM) spectroscopic techniques applied to detection of radicals and ions of astrophysical significance. CRDS offers high sensitivity because of the large absorption path lengths achieved inside the cavity and its immunity towards shot-to-shot laser fluctuations. Four-wave mixing, on the other hand, offers selectivity of the species studied by the application of very short discharge pulse lengths, in the nanosecond time scale. As a consequence, the molecules are separated out in the plasma discharge based on their masses. The 3Π-3Π electronic transition of C6H+ has been measured using CRDS; this is the first gas phase detection of the cation. Partially resolved P lines and observation of band heads permitted a rotational contour fit. Spectroscopic constants in the ground and excited-state were determined. Broadening of the spectral lines indicates the excited-state lifetime to be around 100 ps. The potential of degenerate and two-color FWM applied to selectivity of transient species has been studied extensively in this work using various molecular systems like C3/C4H, C3/HC2S and C2/HC4H+, only by varying the timings between the experimental components (laser/valve/discharge) while applying extremely short (<1µs) discharge pulses. The two color variant is exceptionally powerful in disentangling overlapping features even within the same spectroscopic system. This is demonstrated in the case of HC4H+ where P lines of the Ω=3/2 spin orbit component are effectively separated out from the overlapping Ω=1/2 component in the A←X electronic transition. The first ever detections of ions (HC4H+, C2-) by FWM are also reported. The results suggest convincingly that nonlinear four-wave mixing spectroscopy is applicable to study numerous neutral, cationic and anionic radicals that are produced in plasma environments in low particle densities by applying a discharged free-jet expansion. Both CRDS and FWM have been employed as tools for spectroscopic investigation of non-adiabatic effects in linear polyatomic molecules. The excitation of the ν3 (C-C stretch) and the 2ν7 (C≡C-C bend) levels in the A2Π electronic state of diacetylene cations results in Renner-Teller (R-T) and Fermi interactions. The ν3 and 2ν7 vibronic bands in the A←X transition of HC4H+ have been measured with rotational resolution using CRDS in a supersonic slit jet discharge. A vibronic analysis has been carried out taking into consideration the R-T, spin-orbit, and Fermi resonance interactions between the ν3 and ν7 modes. The spectroscopic constants for the excited electronic state are compared with the ground state. The double resonance four wave mixing approach was used to unambiguously identify the vibronic R-T manifold in the A2Π state up to 700 cm-1 above v=0 of C4H by pumping on the origin B←X electronic transition. On the basis of the experimental linelist, several of the energy levels are assigned to vibrations in the electronic X2Σ+ ground state. An assignment of the levels was carried out by R-T analysis, leading to a relatively large ε6 in the ground state for the second lowest bending mode as previously found in the upper state. This study results in the detection of levels located below the A2Π state because of high R-T interaction. CRDS has also been employed to detect broad absorption features of the B←X transition of H2CCC (l-C3H2). The observations provide evidence that the broad, diffuse interstellar bands (DIBs) at 4881 and 5450 Å are caused by the B←X transition of H2CCC (l-C3H2). The large widths of the bands are due to the short lifetime of the B 1B1 electronic state. The bands in the gas phase show exact matches to the profiles and wavelengths of the two broad DIBs. This makes l-C3H2 a carrier of the DIBs, which have remained a long standing mystery in astronomy. The present work provides an insight to understanding not only the fundamental spectroscopic properties of these transient species but also their astrophysical significance. Moreover, it also demonstrates the highly sensitive and selective capabilities of the employed experimental techniques, which could be of use in other fields like combustion, trace gas analysis, to name a few

Improved performance of an optically pumped mid-infrared acetylene-filled hollow-core fiber laser

Doctor of PhilosophyDepartment of PhysicsKristan L. CorwinThe focus of this research is improving the pulse output energy of a mid-IR pulsed acetylene-filled Hollow-core Optical Fiber Gas LASer (HOFGLAS) system. Pump pulses and acetylene molecules interact with each other inside hollow-core photonic crystal fiber that effectively confines light and allows for strong gain. This results in lasing at 3.11 μm and 3.17 μm lines based on population inversion of acetylene molecules, which are optically pumped at rotational-vibrational overtones near 1.5 μm using 1 ns pulse duration from an optical parametric amplifier (OPA). This acetylene laser operates with no cavity mirrors because of a high gain in a single pass configuration. There are few laser sources in the mid-IR region while there are many applications for having a laser source in this range such as remote sensing, hazardous chemical detection, and breath analysis. This adds to the importance of the acetylene-filled HOFGLAS system. Some of the applications like remote sensing require high power. So, we moved toward power scaling this laser system by optimizing the laser operation through maximizing the OPA alignment to improve its modal content using longer length of fiber to increase the interaction length and improving the beam quality of the mid-IR emissions. The highest pulse energy ever obtained in the 3 µm mid-IR region from the acetylene-filled HOFGLAS after applying the improvements is reported here (1.4 μJ). Higher mid-IR pulse energies can be achieved by improving the pulse energy achievable from the OPA pump source and working with longer pulse duration to decrease the bandwidth of the OPA. This operation demonstrates many novel properties of acetylene-filled pulsed mid-IR hollow-core fiber lasers. The excellent spatial beam quality at highest power and phenomenological scaling of saturation power and efficiency with pressure that we observe point to the promise of power scaling and motivate further development of numerical models of the laser for deeper insight into these effects. M² measurement method was used to examine spatial beam quality and it was found to be fiber-dependent. For the improved setup, M² was investigated at several input pump powers in addition to the reproducibility checks. M² of 1.14 at the maximum output power motivates for beam combining to scale to higher power. The independence of efficiency on pressure is an evidence for reaching higher mid-IR power at a pressure where saturation behavior does not exist. achieving the highest mid-IR power to date, 1.4 μJ, encourages for building higher power OPA to produce high power mid-IR emissions. Taken as a whole, this laser exhibits novel behavior that motivates both numerical/theoretical investigation and further efforts to scale to higher powers

Mid-infrared absorption sensor for CO concentration and temperature measurements for pyrolysis and oxidation behind reflected shock waves

Due to the increasing energy demand and the related environmental issues, combustion effi-ciency and reduction of pollutants emission have become a major concern for combustion ap-plications. In combustion, pollutant formation and fuel ignition are controlled by chemical kinetics, therefore, the design and optimization of combustion systems heavily relies on an accurate understanding of the underlying chemical processes. While combustion processes are governed by an interaction of chemical kinetics and transport processes, for gaining funda-mental understanding it is beneficial to separate both processes. To this end, shock tubes are frequently applied to generate a uniform gas phase environment for a wide range of tempera-tures and pressures that is suited for initiating reactions with subsequent time-resolved detec-tion. The combination of shock tube technique and laser absorption spectroscopy provides the platform for accurate chemical kinetic studies. Infrared laser absorption diagnostics have been widely applied in combustion research for example for in situ, fast, and sensitive measure-ments of temperature, pressure, and species concentrations. In the present study, laser absorption spectroscopy of carbon monoxide (CO) near 4.7 µm has been developed for the sensing of temperature and CO concentration behind the reflected shock wave. The sensor was further developed to enable fiber-based thermometry for more flexible applications in harsh environments. The oxidation of fuel-rich CH4/O2 mixtures, the thermal decomposition of anisole (C6H5OCH3), and the pyrolysis of acetylene (C2H2) and benzene (C6H6) were investigated by monitoring the CO concentration and temperature based on two-line absorption thermometry. The experimental data were applied for validation of reaction mechanisms covering different kinetics conditions such as single elementary reaction, partial oxidation, and soot formation. The oxidation of fuel-rich CH4/O2 mixtures was investigated to validate reaction mechanisms for reaction conditions that are important for polygeneration processes where partial oxidation allows to convert natural gas to higher-value chemicals. With the presences of dimethyl ether (DME) and n-heptane, the initial reaction temperature is significantly reduced because they promote the production of additional OH radicals. Anisole has recently been identified as fluorescence tracer for fuel/air mixing studies, but its decomposition kinetics were not yet fully understood. In the investigation of thermal decom-position of anisole at elevated temperatures, the literature model was found to strongly under-estimate the CO formation. As main reaction path for CO formation, the unimolecular decom-position of phenoxy radical (C6H5O) was investigated independently and new rate constants were determined. Soot formation from combustion is of high scientific interest. The temperature dependence as well as the influence of H2, O2, and CH4 on soot formation in the pyrolysis of C2H2 and C6H6 were investigated. The temperature dependence of the soot yield and the particle formation induction time were found to be in a good agreement with literature data. The presence of H2 led to a depletion of the particle formation in both systems whereas the opposite trend yield was observed in the presence of CH4 and O2.Aufgrund des steigenden Energiebedarfs durch die industrielle Entwicklung ist der Schutz der Atmosphäre die wichtigste Aufgabe unserer Zeit. Das Interesse in modernen, umwelt-freundlichen Verbrennungssystemen hat zu Verbesserung der Verbrennungseffizienz und zur Verringerung der Schadstoffemissionen geführt. Das Design und die Optimierung von Ver-brennungssystemen beruht auf einer genauen Modellierung elementarer, chemischer Prozesse. Infrarot-Laserabsorptionsdiagnostik ist eine hochentwickelte Diagnostik in der Verbrennungs-forschung für schnelle, hochsensitive in-situ Messungen von Temperatur, Druck, und Spezies-konzentrationen. Stoßwellenrohre sind einfache und robuste Instrumente, die eine homogene Gasphasenumgebung in einem großen Temperatur- und Druckbereich erzeugen. Die Kombina-tion aus Stoßwellentechnik und Laserabsorptionsspektroskopie bietet eine Plattform für akku-rate, chemische kinetische Untersuchungen. In der vorliegenden Arbeit wurde die Laserabsorptionsspektroskopie von Kohlenmonoxid (CO) nahe 4.7 μm für die Erfassung von Temperatur und CO-Konzentration hinter den reflek-tierten Stoßwellen entwickelt. Des Weiteren wurde der Sensor als faserbasiertes Thermometer für flexible und robuste Anwendungen weiterentwickelt. Die Oxidation von fetten Methan (CH4)/Sauerstoff (O2) Gemischen, der thermische Zerfall von Anisol (C6H5OCH3) sowie die Pyrolyse von Acetylen (C2H2) und Benzol (C6H6) wurden in der Gasphase im Stoßwellenrohr in Kombination mit der CO-Thermometrie untersucht. Die experimentellen Daten wurden mit Simulationen auf der Basis ausgewählter Reaktions-mechanismen verglichen. Bei der Oxidation von fetten CH4/O2 Mischungen senkten die Addi-tive Dimethylether (DME) und n-Heptan die anfängliche Reaktionstemperatur signifikant, indem sie zusätzliche OH-Radikale erzeugen. Keiner der Mechanismen ist für chemische Umwandlungsreaktionen optimiert. Die CO-Bildung wird beim thermischen Zerfall von Anisol nur schlecht vom Modell wiedergegeben. Die Reaktionsgeschwindigkeit des unimole-kularen Zerfalls des Phenoxyradikals (C6H5O) wurde experimentell bestimmt. Bei der Pyrolyse von C2H2 und C6H6 wurde die Temperaturabhängigkeit der Rußbildung und deren Induktionszeit mittels Laserlicht-Extinktion gemessen und eine gute Übereinstimmung mit der Literatur gefunden. Die Anwesenheit von Wasserstoff (H2) führte zu einer Reduktion der Partikelbildung in beiden Systemen, wohingegen ein entgegengesetztes Verhalten bei der Rußbildung in Anwesenheit von CH4 und O2 bei C2H2 und C6H6 beobachtet wurde