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Energy and temporal radiation characteristics of the pulsed inductive CO2 gas laser with RF excitation as the function of RF pump-pulse duration τ with xenon additions to a gas mixture of the laser have been experimentally investigated. This made it possible to develop an efficient pulsed inductive CO2 laser with an output energy E > 1.2 J (the efficiency η ~ 17%), using a He:N2:CO2:Xe gas mixture [the (Xe) = 4%]. In this case, the lasing pulse duration tpuls (a full width at half-maximum) was 3.5 ms at a τ = 10 ms. For the pulsed inductive CO2 laser with RF excitation, it was shown for the first time a xenon addition to a gas mixture made it possible to achieve an efficiency η ~ 27% at the output energy E more 600 mJ. Pulses of RF current propagated along the solenoid, and the inductive discharge was formed to create population inversion by IR transitions of CO2 molecules. [ABSTRACT FROM AUTHOR]

The historical aspect, present status, and future prospects of diode-pumped alkali lasers (DPAL) are discussed. DPAL is a relatively new laser, first reported in 2003. It is characterized by extremely high scalability, good beam quality by virtue of its gaseous laser medium, and intrinsically high efficiency because it is a three-level laser with a small Stokes defect. Because of these features, DPAL is being studied as a directed energy weapon and is also expected to find applications in industry and space. We propose the use of DPAL for space debris removal. Some of the research results of our group are also introduced. [ABSTRACT FROM AUTHOR]

The characteristics of x-ray radiation of a target that is bombarded by a beam of accelerated electrons ejected by a low-power vacuum discharge with laser ignition are studied. It is shown that the maximum radiation energy exceeds the applied potential difference across the discharge gap by almost an order of magnitude and is inversely proportional to the mass of the cathode material ablated by laser radiation. The energy spectrum of x-ray radiation reconstructed from the radiation attenuation curve by filters-absorbers of various thicknesses showed that in the maximum acceleration mode the average energy of the main part of the spectrum is more than four times higher than the voltage across the discharge gap at the moment of beam emission. Possible mechanisms providing anomalous acceleration of electrons in the discharge are considered. [ABSTRACT FROM AUTHOR]

A novel near-infrared light-induced thermoelastic spectroscopy (LITES) based on a multilayer surface-coated quartz tuning fork (QTF) is proposed for gas detection. Thin-film of reduced graphene oxide (rGO) and polydimethylsiloxane (PDMS) is successively coated on the surface of QTF to improve the laser absorption and thermoelastic conversion efficiency, respectively. NH3 is selected as the target analyte for the measurements. The experimental results indicate that introducing a thin layer of PDMS-rGO composite allows a maximum gain factor of 8.64 and 5.53 for the signal amplitude and signal-to-noise ratio (SNR), respectively, compared to a commercial standard QTF. A minimum detectable concentration of 8.98 ppmv was obtained, improved by 5.12 times than that of a bare QTF, and a normalized noise equivalent absorption coefficient (NNEA) of ${1.53}\times {10}^{-{9}}\,\text {cm}^{-{1}} \cdot \text {W} \cdot \text {Hz}^{-\text {1/2}}$ was achieved. The results of Allan deviation analysis show that the detection sensitivity reaches 2.63 ppmv when the averaging time is 555 s. The research work and related results have laid a good foundation for trace gas detection by the cost-effective and easy-to-operate infrared sensor. [ABSTRACT FROM AUTHOR]

The systems of active Brownian grains can be considered as open systems, in which there is an exchange of energy and matter with the environment. The collective phenomena of active Brownian grains can demonstrate analogies with ordinary phase transitions. We study the active Brownian motion of light-absorbing and strongly interacting grains far from equilibrium suspended in gas discharge under laser irradiation when the nature and intensity of the active motion depend on the effect of radiation. Active Brownian motion is caused by photophoresis, i.e., absorption of laser radiation at the metal-coated surface of the grain creates radiometric force, which in turn drives the grains. We experimentally observed the active Brownian motion of charged grains in the transition of the grain monolayer from the solid to liquid state. An analysis of the character of motion, including the mean-square and linear displacement and persistence length at various values of the randomization (coupling parameter) of the grain structure, was presented. [ABSTRACT FROM AUTHOR]

Models of asparagine‐containing dipeptides specifically designed to favor intrinsic folding into an Asx turn were characterized both theoretically, by using quantum chemistry, and experimentally, by using laser spectroscopy in the gas phase. Both approaches provided evidence for the spontaneous folding of both the Asn‐Ala and Asn‐Gly dipeptide models into the most stable Asx turn, a conformation stabilized by a C10 H‐bond that was very similar to a type II' β‐turn. In parallel, analysis of Asx turns implicating asparagine in crystallized protein structures in the Protein Data Bank revealed a sequence‐dependent behavior. In Asn‐Ala sequences, the Asx turn was found in conjunction with a type I β‐turn for which the first of the four defining residues was Asn. The observation that the Asx turn in these structures is mostly of type II' (i. e. its most stable innate structure) suggests that this motif might foster the formation and/or enhance the stability of the backbone β‐turn. In contrast, the Asx turns observed in Asn‐Gly sequences extensively adopted a type II Asx‐turn structure, thus suggesting that their formation should be ascribed to other factors, such as hydration. The fact that the Asx turn in a Asn‐Gly sequence is also often found in combination with a hydrated β‐bulge supports the premise that a Asn‐Gly sequence might efficiently promote the formation of the β‐bulge secondary structure. [ABSTRACT FROM AUTHOR]

In this paper, a new electronic system is designed for methane gas laser analyzers using the tunable diode laser absorption spectroscopy (TDLAS) technique. This electronic system is presented in such a way that, based on this technique, optical wavelength and stability confirm the power of the laser light source. The proposed design includes current and temperature control circuits, amplifier circuits, and laser sensor circuits. This system leads to the control of laser light power. Due to the high cost of a laser sensor distributed feedback diode (DFB) and the impossibility of purchasing it for the actual implementation of the proposed electronic system, the design and simulation stage of this system was performed in the proteus simulator environment at normal atmospheric temperature and constant control flow conditions. The simulation results show that the proposed new electronic system based on the TDLAS technique detected the amount of leaking methane gas by generating a wavelength of 1653.72 nm related to the DFB laser sensor and displaying it on display during calculation. The test of optical wavelength stability, optical power, and methane gas wavelength generation by the laser sensor in the proteus simulator environment at different distances is excellent and remarkable. These results show that if we buy a laser sensor and build a gas analyzer device, we can achieve perfect results by using the device with the provided technique. [ABSTRACT FROM AUTHOR]

Soft-glass fiber lasers have attracted lots of attentions as they are most likely to achieve compact, stable, and highly efficient mid-infrared emission, which has unique applications in many fields. However, due to the immature manufacturing technique of soft glass fibers and the limited types of doped rear-earth, laser power enhancing and wavelength expansion beyond 4 μm are greatly restricted. Gas-filled hollow-core fibers (HCFs) have been proved to be an effective way to generate mid-infrared emission. We previously demonstrated a continuous-wave 4.3 μm fiber source with power of 82 mW in CO2-filled HCFs. Here, the maximum output power is increased to 557 mW, and laser wavelengths densely step-tunable from 4276 to 4428 nm including 46 lines have been demonstrated. The output spectrum and power properties with gas pressure and pump power are investigated in detail. In addition, the influence of buffer gases on laser characteristics is studied experimentally for the first time. This work provides significant guidance for the development of high-power tunable mid-infrared fiber gas lasers. [ABSTRACT FROM AUTHOR]

To explore the method of low-damage gas-assisted laser processing of carbon fiber reinforced plastics, using QCW450 quasi-continuous fiber laser cutting machine (maximum peak power 4500 W), and laser scribing carbon fiber reinforced plastics with three gas-assisted methods: coaxial nitrogen, coaxial oxygen, and coaxial oxygen paraxial nitrogen compound gas-assisted, and study the influence of the three on cutting quality. At the same time, the single factor experiment method is used to study the impact of laser peak power, scanning speed, and gas pressure on processing quality, mainly analyzing the size of the heat-affected zone of the cutting section, the cutting depth, and the width of the upper slit, and analyze the action mechanism of gas-assisted laser processing of carbon fiber reinforced plastics. The experimental results show that nitrogen can bring a certain cooling effect during high-power and high-speed processing. Oxidation exothermic effect of oxygen can promote the removal of thermal melting of materials, and high-pressure airflow can take away a part of the excess heat and erosion of the residual kerf. Meanwhile, the nitrogen and oxygen mixed gas assists comprehensively in reducing thermal damage and improving the feasibility of etching. The greater the laser peak power, the deeper the etching depth, and the greater the width of the heat-affected zone, the higher the cutting speed, the width of the heat-affected zone, and the cutting depth will decrease. Too much or too little gas pressure is not conducive to improving quality. This research provides a reference for low-damage gas laser processing carbon fiber reinforced plastics. [ABSTRACT FROM AUTHOR]

Acoustic resonances of an opto-acoustic detector (OAD) with differential cylindrical Helmholtz resonators are studied numerically upon variation of their main parameters. Dependences of quality factor of the acoustic resonance and the resonance frequency on geometric parameters of the OAD are obtained and analyzed. The results are of interest for development of opto-acoustic gas analyzers. [ABSTRACT FROM AUTHOR]

In this paper, a theoretical method is presented to calculate Brillouin linewidth (BLW) in gas mixtures. The presented model is based on Newton's viscosity law and the kinetic theory of gases. From a combination of Chapman–Enskog theory and Navier–Stokes mathematical model, we recovered the appropriate terms of the viscosity tensor for gas mixtures. We demonstrated that viscosity is not necessarily the dominant mechanism in the enhancement or suppression of the BLW in a gas mixture, and other parameters, such as density, can be dominant instead. It was found that the contribution of thermodynamics quantities was negligible compared to other parameters. The numerical results were also compared to those obtained from the molar refraction-mixing method and confirmed that these results were completely coherent. [ABSTRACT FROM AUTHOR]

In order to realize real-time capnographic monitoring, a compact carbon dioxide sensor based on tunable diode laser spectroscopy technology was developed by means of a 2004 nm distributed feedback laser and a circular gas cell. The toroidal cell can achieve an optical path length of 3.49 m in a volume of 38 ml, which enables the tunable diode laser spectroscopy carbon dioxide sensor to achieve a detection limit of 175 ppm at a measurement rate of 12.5 Hz. The actual exhaled carbon dioxide gas detection experiments were implemented, including the breath analysis of a normal subject under different conditions and another subject with pneumothorax. It indicates that the sensor has good effectiveness and practicability for carbon dioxide metabolic monitoring and related disease diagnosis. [ABSTRACT FROM AUTHOR]

We report the results of experimental and numerical investigations of a discharge KrF laser with specific pump power of 3.5 and 7 MW/cm3; generation is obtained with specific radiation pulse energy of about 6 and 9.5 J/L for an internal energy efficiency of about 4%. Time dependences of the formation of charged and excited particles in a dense excimer plasma with an electron concentration of ~1016 cm–3 are obtained. The conditions for effective operation of the laser are proposed, which will ensure a further increase in the specific radiation energy by more than two times with preserved high internal laser efficiency relative to the energy input into the discharge. [ABSTRACT FROM AUTHOR]

This study demonstrates the enhancement effect of spark discharge on laser-induced breakdown spectroscopy detection of Fe particles in transformer oil. To obtain a better discharge enhancement effect and improve the quantitative analysis ability, the discharge characteristics of a circuit with different parameters and the corresponding spectral enhancement effect were studied. The results show that the discharge lag time increases with the increase of capacitance, the increase of the electrode gap and the decrease of discharge capacity. At the same time, the increase of capacitance and its charging quantity leads to the increase of the discharge power in the discharge half cycle. The circuit with a 6 mm electrode gap, 8.7 nF capacitor and 500 ns 3 pulse charging ensures that the plasma has good stability and the enhanced background spectrum does not interfere with the analysis lines, increasing the limit of quantitation from 0.048 μg g−1 to 0.016 μg g−1. This work is beneficial to understand the synergistic relationship between discharge characteristics and laser ablated plasma enhancement, and promotes the application of laser-induced breakdown spectroscopy technology in the detection of particulate matter in oil. [ABSTRACT FROM AUTHOR]

A scheme for second-harmonic generation (SHG) of a short-laser pulse from a gas jet immersed in a magnetic field has been investigated. A laser pulse with sufficient intensity interacting with gas produces free electrons by tunnel ionization. The electrons accelerated by the laser pulse generate nonlinear currents at the second-harmonic (SH) frequency of the fundamental laser pulse. The ambient magnetic field provides an additional resonance to enhance the SH field amplitude. Based on the plasma current model, we estimate the SH field and provide various scaling laws for optimization and controlling the SHG process. This study might provide a new way to optimize the SH field from the laser interactions with a gas jet immersed in a magnetic field. [ABSTRACT FROM AUTHOR]

This paper reports development of a real time flow control system for precise, controlled and uniform gas feed to a flowing medium Chemical Oxygen Iodine Laser (COIL). The optimal operation of this prominent laser depends upon the desired supply of gas constituents such as nitrogen (N2), chlorine (Cl2) and iodine (I2) to achieve adequately mixed laser gas. The laser also demands real time variation of flow rates during gas constituent transitions in order to maintain stabilised pressures in critical subsystems. Diluent nitrogen utilised for singlet oxygen transport is termed as primary buffer gas and that for iodine transport is termed as secondary buffer gas (with main and bypass components). Also, nitrogen in precise flows is used for mirror blowing, nozzle curtain, cavity bleed and diffuser startup. A compact hybrid data acquisition system (Hybrid DAS) for precise flow control using LabVIEW 2014 platform has been developed. The supported flow ranges may vary from few mmole.s-1 to few hundred mmole.s-1. The estimated relative uncertainty in the largest gas component i.e. primary buffer gas feed is nearly 0.7%. The implementation of in-operation variation using flow ramp enables swift stabilisation of singlet oxygen generator pressures critical for successful COIL operation. The performance of Hybrid DAS is at par with fully wired DAS providing the crucial benefit of remote field operation at distances of nearly 80m in line of sight and 35m with obstacles. [ABSTRACT FROM AUTHOR]

Photothermal interferometry (PTI) with hollow core fibers (HCFs) have enabled highly sensitive spectroscopic gas sensors in an all-fiber format. Here we report remarkable improvement in the limit of detection of HCF-PTI, in terms of noise equivalent concentration (NEC), by exploiting the optical-phase-modulation amplifying (OPMA) effect of an HCF resonating cavity. By locking the wavelength of a 1550 nm probe laser to the resonance of a 10-cm-long HCF Fabry-Pérot cavity with a finesse of ∼700, OPMA of more than two orders of magnitude is achieved, which enables ultra-sensitive gas detection with large dynamic range. With 1654 nm, 1532 nm, and 761 nm pump lasers, we demonstrate detection of methane, acetylene, and oxygen with noise-equivalent-concentration of 15 parts-per-trillion (ppt), 2.7 ppt, and 0.56 parts-per-million (ppm), respectively. Further improvement in NEC is possible by use of a higher finesse cavity with a longer length of HCF. Extension of the technique to other gases, other types of phase or dispersion modulation-based sensors, and other optical resonating cavities is straightforward. [ABSTRACT FROM AUTHOR]

Terahertz (THz) radiation has a wide range of applications including use in medicine. However, effects of high‐power THz radiation have not been clearly elucidated. We used a 2.52 THz self‐made optically pumped gas THz laser, the low‐ and high‐energy group, to irradiate the backs of Hartley guinea pigs. RNA‐sequencing was done to explore global transcriptional responses in the irradiated skin. Gene Ontology analysis revealed that differentially expressed genes (DEGs) between the unexposed and low‐energy exposed groups were associated with skin development, skin barrier establishment, and multicellular organismal water homeostasis or water loss regulation via the skin. On the other hand, comparison between the unexposed and high‐energy exposed groups showed that the DEGs mediated monocarboxylic acid metabolism, blood vessel morphogenesis, establishment of skin barrier, blood vessel development, or angiogenesis. Our analyses demonstrate the potential effects of high‐power THz source on the skin and sets the basis for further studies on the safety and application of the high‐power THz in dermatology. [ABSTRACT FROM AUTHOR]

We present a high-resolution and large dynamic range π-phase-shifted fiber Bragg grating (π-PSFBG) temperature sensor. A current modulated laser diode with a linearized optical frequency sweep is used to interrogate the sensor. The sensor is comprised of a π-PSFBG sensing head and an HCN gas cell. The gas cell functions as an absolute frequency reference to compensate for the laser frequency drift. The reflection spectrum is sent to a lock-in amplifier to generate the error signal, proportional to the first order derivative of the spectrum. The center frequency difference that carries sensing information between the π-PSFBG and HCN gas cell is calculated by cross-correlation of their error signals. A sinusoidal modulation enables to move the data processing from low-frequency stage to high-frequency stage, by phase-sensitive detection and low-pass filtering, the interferences caused by laser intensity noises and electronic devices’ noises are significantly reduced. In the experiment, a frequency resolution of 3.696 MHz with a 55 GHz mode-hop-free tuning range, is achieved, corresponding to a temperature resolution of 2.6 mK with a dynamic range from 5 to 40 °C. [ABSTRACT FROM AUTHOR]

The optical response of nickel is studied in a wide range of laser fluence, below and above the ablation threshold, by self-reflectivity measurements of ultrashort 800 nm single laser pulses. At the ablation threshold, the reflectivity remains unchanged with respect to its unperturbed value irrespective of the pulse duration, from 15 to 100 fs, consistently with the steadiness of the laser-induced ablation threshold fluence Fth for all pulse durations tested. Until the ablation threshold (F ⩽ Fth) and whatever the pulse duration, the disturbances caused to the initial structure of the electron gas distribution by the laser energy deposition are limited, having no significant impact on the transient optical response of nickel and on its ablation threshold. At higher laser fluences (F > Fth), the reflectivity becomes rapidly dominated by the contribution to the optical response of the fast-thermalized free electrons (4s-band) with energy largely above the Fermi energy level. In these conditions, the reflectivity decreases for all pulse durations enhancing laser energy coupling and larger optical absorption at the surface of nickel. The optical response of nickel under ultrashort (15–100 fs) irradiation is thus fully elucidated on a wide range of fluence (0.3 Fth–30 Fth) and for pulse duration down to few-optical-cycle pulse duration. As a key parameter for benchmarking laser-matter interaction in poorly known conditions yet, the evolution of the effective electron collision rate is determined as a function of fluence and pulse duration in very good consistency with experiments. [ABSTRACT FROM AUTHOR]

Cylindrical structure of micro-swelling silicone rubber of approximately 1 µm diameter and 1.5 to 2 µm height was fabricated by the 193-nm ArF excimer laserinduced photodissociation of Si-O bonds of silicone rubber. To be periodically, single layer of silica glass microspheres was aligned on aluminum-coated silicone rubber during laser irradiation. The silicone rubber underneath each microsphere photochemically swelled, after laser-ablating aluminum to limit a diameter of the swelling. The aluminum also adjusted a focal point to the surface of silicone rubber to form a hole approximately 0.5 µm diameter centered at each the swelled silicone rubber. A purging O2 molecules in the laser beam path by N2 gas and lowering the laser pulse repetition rate were effective for fabricating the regular cylindrical structure. The regular cylindrical structure of micro-swelling silicone rubber showed superhydrophobicity. [ABSTRACT FROM AUTHOR]

Long pulse gas lasers utilizing double-discharge circuits are different from the single-short pulse gas lasers in that they do not require all of the desired energy to be deposited into the peaking capacitors prior to ignition of the main gap. Instead, the majority of the energy is held in another capacitor that is then discharged in the form of a longer duration discharge pulse output compared with that of single-short pulse lasers. Extended stability of the discharge is typically achieved by igniting the main gap discharge at higher ignition voltages. Several double-discharge circuit topologies exist in the literature. However, each topology has its own disadvantages primarily centered around the components needed and the resulting complexity. In this article we introduce the application of the new hybrid circuit pulsed power topology as a double-discharge circuit with high ignition voltages. The hybrid circuit pulsed power topology was originally published by the authors of this article in their previous publication titled “A New Hybrid Pulsed Power Circuit Topology for Gas Laser Applications.” The advantage of the hybrid circuit as a double-discharge circuit is that it does not require any special device [e.g., semiconductor opening switch (SOS) diode] and can use commonly available components. [ABSTRACT FROM AUTHOR]

We have demonstrated a low noise superconducting MgB2 hot electron bolometer (HEB) mixer working at the frequency of 5.3 terahertz (THz) with 20 K operation temperature. The bolometer consists of a 7 nm thick MgB2 submicrometer bridge contacted with a spiral antenna to couple THz radiation through a high resistive Si lens, and it has a superconducting critical temperature of 38 K. By using hot/cold blackbody loads and a Mylar beam splitter all in vacuum and applying a 5.25 THz far-infrared gas laser as a local oscillator, we measured a minimal double sideband receiver noise temperature of 3960 K at the LO power of 9.5 μW. This can be further reduced to 2920 K if a Si lens with an antireflection coating optimized at this frequency and a 3 μm beam splitter are used. The measured intermediate frequency (IF) noise bandwidth is 9.5 GHz. The low noise, wide IF bandwidth mixers, which can be operated in a compact, low dissipation Stirling cooler, are more suitable for space applications than the existing HEB mixers. Furthermore, we likely observed a signature of the double-gap in MgB2 by comparing current–voltage curves pumped at 5.3 and 1.6 THz. [ABSTRACT FROM AUTHOR]

[Display omitted] The effect of the process gas during laser powder bed fusion (L-PBF) was investigated using high-speed shadowgraphy while melting Ti-6Al-4V powder under high purity argon, helium, and a mixture of both, on a laboratory-scale machine. These recordings reveal that the generation of incandescent spatters can be reduced by at least 60% using pure helium and by ∼30% using addition of helium to argon in comparison to the use of traditional argon. The quantity of colder spatters appeared unaffected by the change of process gas. Different configurations of gas flow versus laser scanning direction were investigated and revealed that fumes and spatters are less accumulated at the laser spot with helium addition. Furthermore, the use of the argon–helium mixture proved to be as efficient as pure argon in the dragging and extraction of the fumes. Shadowgraphs revealed the more rapid expansion of fumes in helium-rich atmospheres, limiting the accumulation of scattering objects close to the laser spot and thus melt pool instability. These results were correlated to process snapshots on an industrial-scale system, confirming the reduction of hot spatter generation. Finally, the findings put in evidence the more rapid cooling of spatters with helium addition to the process gas – a promising aspect to limit powder bed degradation during L-PBF. In addition, the use of mixtures of helium and argon would be economically interesting compared to pure helium, typically more expensive than the traditionally used argon. [ABSTRACT FROM AUTHOR]

The study has focused on determining the laser plug effects on engine characteristics and the laser plug usage results have compared with spark plug usage. The laser ignition technique is a type of new ignition technique and an important solution that can make combustion systems more efficient. The testing of an engine with a laser plug is the novelty of the study and the tests were carried out with reference to equivalence ratio and plug power ranges. The behaviors of the engine at full load were examined so experimentally for both ignition techniques at hydrogen enriched CNG and iso-octane mixture usage. The tests were carried out for variations of 0.4–2.0 equivalence ratio and 20–120 W plug power. A mixture that 90% iso-octane and 10% HCNG in mass was used at two ignition modes in tests for 3300 rpm maximum engine torque speed. Also, the flame formation and propagation for both ignition techniques were detected via a high-speed camera. The tests have shown the laser ignition leads to more energy consumption in the rich mixture conditions and also, less energy is required in the lean conditions. The laser ignition discharge has extended the engine's lean combustion limits via a small energy input at the tests. The high-speed camera images have shown that the laser ignition reduces the Kernel flame formation and propagation time. The laser ignition technique was produced less NO x than the conventional spark ignition method. • Laser ignition effects on engine performance characteristics and emissions. • The tests were carried out for iso-octane - HCNG mixture at maximum torque speed. • Comparison of laser ignition effects with spark ignition for the flame formation. • The laser ignition has lead to less energy is required in the lean conditions. • The laser ignition technique has produced less NO x than the spark plug. [ABSTRACT FROM AUTHOR]

Versatile and flexible gas analysis for compositional identification and quantification is a demand found in a variety of diverse sectors. As such, a compact, deployable instrument exhibiting both high specificity and sensitivity is a highly attractive proposition for a wide range of applications. In this paper, we describe a gas phase Raman spectroscopy‐based device using state‐of‐the‐art anti‐resonant (tubular) hollow core micro‐structured optical fibre (HC‐MOF). This fibre architecture allows the use of lengths that are typically longer than have been demonstrated previously, allowing substantially enhanced interaction lengths between the pump laser and the gas sample to be achieved, addressing the sensitivity challenges typically observed in gas‐phase Raman measurements and enabling application for remote sensing in hazardous environments. We describe the successful development of a compact, fibre‐integrated instrument and present results obtained during a test campaign at an industrial laboratory; marking a milestone in gas‐phase Raman spectroscopy. The unique properties of the MOF used allowed a 20‐m length to be utilised, representing a new record length for gas phase Raman measurements. The identification and quantification of a variety of gas species, ranging from simple homonuclear diatomic gases to heteronuclear organic gas species were achieved, and, building on previous studies, the instruments stability, gas concentration linearity response, and the hollow core fibre filling and purging characteristics were investigated. [ABSTRACT FROM AUTHOR]

A new scheme is proposed to improve the electron beam quality of ionization-induced injection by tailoring gas profile in laser wakefield acceleration. Two-dimensional particle-in-cell simulations show that the ionization-induced injection mainly occurs in high-density stage and automatically truncates in low-density stage due to the decrease of the wakefield potential difference. The beam loading can be compensated by the elongated beam resulting from the density transition stage. The beam quality can be improved by shorter injection distance and beam loading effect. A quasi-monoenergetic electron beam with a central energy of 258 MeV and an energy spread of 5.1% is obtained under certain laserâ€"plasma conditions. [ABSTRACT FROM AUTHOR]

A method for measuring multiphoton absorption cross sections of Gaussian laser pulses in gases by means of an optoacoustic detector exhibiting temporal resolution (spectrophone) is developed. The functionality of the technique is tested using one- and three-photon absorption of nanosecond pulses of quasi-monochromatic radiation with a wavelength of 266 nm by molecular oxygen. [ABSTRACT FROM AUTHOR]

A major decision surrounding the design of pulsed power circuits for gas lasers is the choice between a thyratron and solid-state switches. The thyratron is a mature device technology whose cost is increasing. The ratings of solid-state switches still do not match those of a thyratron. Pulse transformer and pulse compression circuits must be added to overcome the lower ratings of solid-state switches leading to a higher parts count and cost. This article proposes a new solid-state pulse power topology called the hybrid circuit topology to address the parts count and cost issue. The hybrid circuit makes use of a combination of capacitive and inductive energy storage to reduce the time required to transfer the energy from the transformer primary to the secondary side. This ultimately reduces the quantity of magnetic material used in the pulse compression circuit. [ABSTRACT FROM AUTHOR]

One of the key challenges in the design of gas lasers powered by pulsed power circuits pertains to reducing the flow of current through the electrodes during the filamentary discharge phase. This phase occurs after the lasing period (“volume glow”) is terminated due to discharge instabilities and the current flow during this period is referred to as late currents. Late currents contribute to electrode erosion. The ejected electrode material contaminates the gas, and lowering the service life of the laser. Snubber circuits are an economic solution to reducing late currents in pulsed power circuits that do not employ a magnetic switch. In a simple snubber, which is connected directly across the main storage/drive capacitor $C_{0}$ , it was found that the stray series inductances of both $C_{0}$ and the high voltage snubber diodes significantly reduced the magnitude of current flowing through the snubber. A new coaxial capacitor and snubber assembly was proposed to improve the effectiveness of the snubber in reducing the late currents. The design exploited the high degree of mutual coupling between the concentric coaxial cylinders to reduce the total inductance in the snubber loop. Experimental results showed an almost 40% reduction in the total charge that flows through the discharge in the late currents stage. Although the improvement was significant, it is expected that improvements to the construction quality of the prototype could potentially lower the late currents even further. [ABSTRACT FROM AUTHOR]

CO2 dissociation stimulated by vibrational excitation in non-equilibrium discharges has drawn lots of attention. Nanosecond (ns) discharges are known for their highly non-equilibrium conditions. It is therefore of interest to investigate the CO2 excitation in such discharges. In this paper, we demonstrate the ability for monitoring the time evolution of CO2 ro-vibrational excitation with a well-selected wavelength window around 2289.0 cm−1 and a single continuous-wave quantum cascade laser with both high accuracy and temporal resolution. The rotational and vibrational temperatures for both the symmetric and the asymmetric modes of CO2 in the afterglow of CO2 + He ns-discharge were measured with a temporal resolution of 1.5 μs. The non-thermal feature and the preferential excitation of the asymmetric stretch mode of CO2 were experimentally observed, with a peak temperature of Tv3, max = 966 ± 1.5 K, Tv1,2, max = 438.4 ± 1.2 K and Trot = 334.6 ± 0.6 K reached at 3 μs after the nanosecond pulse. In the following relaxation process, an exponential decay with a time constant of 69 μs was observed for the asymmetric stretch (001) state, consistent with the dominant deexcitation mechanism due to VT transfer with He and deexcitation on the wall. Furthermore, a synchronous oscillation of the gas temperature and the total pressure was also observed and can be explained by a two-line thermometry and an adiabatic process. The period of the oscillation and its dependence on the gas components is consistent with a standing acoustic wave excited by the ns-discharge. [ABSTRACT FROM AUTHOR]