193nm Wavelength Research Articles

Mass-selected ion-molecule cluster beam apparatus for ultrafast photofragmentation studies.

We describe an apparatus for investigating the excited-state dissociation dynamics of mass-selected ion-molecule clusters by mass-resolving and detecting photofragment-ions and neutrals, in coincidence, using an ultrafast laser operating at high repetition rates. The apparatus comprises a source that generates ion-molecule clusters, a time-of-flight spectrometer, and a mass filter that selects the desired anions, and a linear-plus-quadratic reflectron mass spectrometer that discriminates the fragment anions after the femtosecond laser excites the clusters. The fragment neutrals and anions are then captured by two channeltron detectors. The apparatus performance is tested by measuring the photofragments: I-, CF3I-, and neutrals from photoexcitation of the ion-molecule cluster CF3I·I- using femtosecond UV laser pulses with a wavelength of 266nm. The experimental results are compared with our ground state and excited state electronic structure calculations as well as the existing results and calculations, with particular attention to the generation mechanism of the anion fragments and dissociation channels of the ion-molecule cluster CF3I·I- in the charge-transfer excited state.

Wave theory-based fourth harmonic generation of Bessel–Gauss beam by total internal reflection-quasi phase matching in a rectangular slab of beta barium borate

This work presents a theoretical approach to a highly multimode-guided wave-based fourth harmonic (FH) generation method by exploiting a zero-order Bessel–Gauss beam through the total internal reflection quasi phase-matching technique. An anisotropic crystal featuring a rectangular structure of beta barium borate has been used to carry out this analysis. In contrast to the conventional frequency conversion scheme using a Gaussian beam, the projected scheme yields a maximum six times superior efficiency of 6.9547% in a crystal length of nearly 6.3 mm, corresponding to a 266-nm FH wavelength. The analysis has also taken into account optical losses, such as absorption, Goos–Hänchen-shift, surface roughness, and the effect of the nonlinear law of reflection. Finally, a systematic study has been performed to describe the influence of parametric modification, such as variations in slab length and thickness, to provide a more comprehensive picture of the overall analysis.

Innovative Observation of a 266-nm Laser Inhibiting Egg Laying in Caenorhabditis elegans

Infrared laser as a heat source could induce gene expression by activating heat promoter genes in Caenorhabditis elegans, as previously reported. In this study, we innovatively used a 266-nm laser to irradiate C. elegans for only one second and observed a significant inhibition of the overall number of eggs laid (P < 0.0001) and the first day egg laying (P=0.005). This is the first study to establish how light with a wavelength of 266-nm can influence a life activity such as laying eggs in C. elegans.

RP-HPLC Method development and Validation for Rapid estimation of Diazepam in Bulk and Pharmaceutical Dosage Form

The main objective of the study is to establish simple, precise and rapid RP-HPLC method for determination of diazepam and its decomposition products present in bulk and pharmaceutical dosage form. Various parameters that can potentially affect the analytical method were investigated and optimized. The compounds were well resolved in an isocratic method using the mobile phase composition of potassium dihydrogen phosphate buffer(0.05M) along with diluted o-phosphoric acid adjusted to pH 4.5: methanol (40:60v/v) at a flow rate of 1 ml/min using C18 (25cm x 0.46 cm) Hypersil BDS column. The detection was carried out at wavelength of 248nm.The retention time of diazepam was 3.3 min. The developed method was validated by evaluating various parameters such as linearity, precision, accuracy, robustness, specificity, limit of detection, and limit of quantification according to the international council for harmonization guidelines. The standard calibration curve was obtained in the concentration range of 20µg/ml for diazepam. The % of label claim was found out to be 93.66 for diazepam. Observation of all these parameters leads to the point that developed RP-HPLC method is accurate, precise, linear, specific and robust. It can be successfully adopted for routine quality control analysis of Diazepam in bulk and pharmaceutical dosage form without any interference.

Acaricidal efficacy of ultraviolet-C irradiation of Tetranychus urticae adults and eggs using a pulsed krypton fluoride excimer laser

BackgroundPulsed ultraviolet (UV)-C light sources, such as excimer lasers, are used in emerging non-thermal food-decontamination methods and also have high potential for use in a wide range of microbial decontamination applications. The acaricidal effect of an experimental UV-C irradiation device was assessed using female adults and eggs of a model organism, the two-spotted spider mite Tetranychus urticae.MethodsUV-C light was generated by a pulsed krypton fluoride excimer laser operating at 248-nm emission wavelength. The pulse energy and pulse repetition rate were 5 mJ and up to 100 Hz, respectively. The distance from the light source to the target was 150 mm; the target surface area was 2.16 cm2. The exposure time for the mites and fresh eggs varied from 1 to 4 min at 5–300 mW, which corresponded to UV doses of 5–80 kJ/m2. Post-irradiation acaricidal effects (mite mortality) were assessed immediately and also measured at 24 h. The effects of UV-C irradiation on the hatchability of eggs were observed daily for up to 12 days post-irradiation.ResultsThe mortality of mites at 5 and 40 kJ/m2 was 26% and 92%, respectively. Mite mortality reached 98% at 80 kJ/m2. The effect of exposure duration on mortality was minimal. The effect of irradiation on egg hatchability was even more significant than that on adult mite mortality, i.e. about 100% egg mortality at an accumulated dose of as little as 5 kJ/m2 for each exposure time.ConclusionsA high rate of mite mortality and lethal egg damage were observed after less than 1 min of exposure to 5 mJ UV-C pulsed irradiation at 60 Hz. Pending further developments (such as beam steering, beam shaping and miniaturisation) and feasibility studies (such as testing with mites in real-life situations), the reported results and characteristics of the UV-C generator (modulation of energy output and adaptability to varying spot sizes) open up the use of this technology for a vast field of acaricidal applications that require long-range radiation.Graphical

Surface characterization of laser-induced molten area in micro-grooving of silicon by ultraviolet (UV) laser

The objective of this research is to understand the fundamental mechanisms that govern the formation of laser-induced molten area during the micro-grooved fabrication on silicon material. In this research work, micro grooves were fabricated on silicon wafer by using ultraviolet (UV) laser of 248nm wavelength. Influence of lasing parameters such as pulse duration, laser pulse energy and scanning speed on the surface of micro-grooved was characterized. It is found that, the width of the micro grooves become wider with increasing laser pulse energy when ultraviolet laser was irradiated on silicon material. On the other hand, heat affected zone (HAZ) can be found at the surface of micro groove line at high pulse energy, high pulse repetition rate and lower scanning speed irradiation condition. This is considered due to the excessive heat input of the laser irradiation condition. It is concluded that proper selection of laser processing parameters of pulse energy, E, pulse repetition rate, R p , and scanning speed is necessary to achieve high quality micro-grooves.

Understanding the Exposure Process in the Extreme Ultra Violet Lithography.

Although being the optical lithography, the extreme ultraviolet (EUV) lithography with 13.5-nm wavelength is very different from the deep ultraviolet (DUV) lithography with 193-nm wavelength. Hence, the understanding of the complex detailed EUV mechanisms to cause a chemical reaction in chemically amplified resists (CARs) is required to develop EUV resists and exposure process. In this paper, for organic, metal-organic and metal-oxide resists, the electron-scattering model of exposure mechanisms needs to include the elastic and inelastic mean free paths. On top of that, Dill's parameters of DUV and EUV resisters from the photo-generated reaction are discussed to indicate the physical and chemical characteristics. For CAR and EUV resists, Dill B parameter is large than Dill A and B parameters.

Second Harmonic Generation of 266 nm Laser Beam Using BBO Nonlinear Crystal

Second harmonic generation (SHG) is a phenomenon observed in nonlinear optics that leads to frequency duplication for a high intensity laser incident on nonlinear crystal using BBO crystal. The SHG yield is achieved when the photons interact with a nonlinear optical material and effectively combine to form new photons with double frequency, and therefore double energy and half wavelength. This paper is concerned with the establishment of an SHG experiment to govern the process of producing half-wavelength laser beam from the input one. The theoretical effort was extended to compute the efficiency by using MATLAB software based on mathematical relationships. The values of the conversion maximum efficiencies, which were computed as a function of the input and output powers of the theoretical computations, were 15.6% and 16% at input and output power values of 0.6 and 0.1, respectively. The experimental results of the laser source of 532nm wavelength (fundamental frequency was 0.563x1015s-1) gave a half wavelength of 266nm (double frequency was 1.126x1015s-1). The conversion efficiencies, computed as a function of the input and output powers of the experimental measurements, were 14.32% and 12.97%, respectively.

Deep Learning-Driven Simultaneous Layout Decomposition and Mask Optimization

Combining multiple patterning lithography (MPL) and optical proximity correction (OPC) pushes the limit of 193nm wavelength lithography to go further. Considering that layout decomposition may generate plenty of solutions with diverse printabilities, relying on conventional mask optimization process to select the best candidate for manufacturing is computationally expensive. Therefore, an accurate and efficient printability estimation is crucial and can significantly accelerate the layout decomposition and mask optimization (LDMO) flow. In this paper, we propose a convolutional neural network (CNN)-based prediction and integrate it into our new high-performance LDMO framework. The optimization process can be considerably improved as the decomposition quality has been inferred in the early phase. To facilitate the network training and ensure better estimation accuracy, we develop sampling strategies for both layout and decomposition. Moreover, we enhance the layout sampling approach by adopting auto-encoder to distance evaluation that promises superior sampling results. The experimental results demonstrate the effectiveness and the efficiency of the proposed algorithms.

In vivo combined virtual histology and vascular imaging with dual-wavelength photoacoustic remote sensing microscopy

Histological evaluation of tissues is currently a lengthy process that typically precludes intraoperative margin assessment. While numerous approaches have aimed to address the need for intraoperative virtual histology, none have yet proved sufficiently efficacious. We demonstrate the use of a new all-optical imaging modality, photoacoustic remote sensing (PARS), capable of virtual histopathological imaging, while simultaneously providing visualization of microvasculature in both freshly resected tissues and live animal subjects. We demonstrate high resolutions of 0.44µm and 1.2µm for 266-nm and 532-nm excitation wavelengths, respectively, as well as the characterization of maximum permissible exposure limits for both excitation wavelengths.

Electro-Optical Performance Study of 4H-SiC/Pd Schottky UV Photodetector Array for Space Applications

4H-SiC Schottky photodetector array was fabricated by pulsed dc sputter deposition of palladium thin film as UV semitransparent Schottky contact on active pixel. Results of electro-optical characterization of these devices as a function of temperature varying from 33 to 393 K are presented. A peak spectral responsivity of 122 mAW−1 at 280 nm is observed. Further, spatial response uniformity for a 4 mm $\times4$ mm detector, scanned by UV spot of $100~\mu \text{m}$ diameter, is within ±5%, whereas the crosstalk between the pixels in $4\times 2$ detector array with a pixel size of $850\,\,\mu \text{m}\,\,\times 850\,\,\mu \text{m}$ is within 1.3%. Capacitance at near zero bias is around 11 pF and 4.79 pF at a reverse bias of 30 V. From the ${I}$ – ${V}$ characteristics, the calculated Schottky barrier height is 1.37 eV for 70 A thick palladium metal film on 4H-SiC as against the theoretical value of 1.96 eV. Operating temperature studies on detector UV response at 300 nm have shown that the photo-current response at 113 K falls to half of its peak value at ambient. The responsivity of the detectors at 248-nm wavelength is almost constant over a wide temperature range of 33 to 393 K.

Effects of Pulse Duration and Heat on Laser-Induced Periodic Surface Structures

Compared with traditional nanotexturing methods, an ultrashort-pulsed laser is an efficient technology of fabricating nanostructures called laser-induced periodic surface structures (LIPSS) on material surfaces. LIPSS are easily fabricated when the pulse duration is shorter than collisional relaxation time (CRT). Accordingly, ultrashort-pulsed lasers have been mainly used to study LIPSS, but they unstably irradiate while requiring high costs. Although long-pulsed lasers have low cost and high stability, the phenomena (such as the effect of pulse duration, laser wavelength, and heat) of the LIPSS fabricated using short-pulsed lasers with the pulse duration close to the maximum CRT, which is greater than femtosecond, have not been clarified. However, the nanosecond pulse laser has been reported to produce LIPSS, but those were unclear and ununiform. In this study, the short-pulsed laser with the pulse duration of 20 ps, which is close to the maximum CRT, was employed to clarify the effects of pulse duration and heat on the fabrication of LIPSS and to solve problems associated with ultrashort-pulsed lasers. First, a finite-difference time-domain simulation was developed at 20-ps pulse duration to investigate the effects of irradiation conditions on the electric-field-intensity distribution. Subsequently, experiments were conducted using the 20-ps pulse laser by varying conditions. The aspect ratio of the LIPSS obtained was greater than that of the LIPSS fabricated using ultrashort-pulsed lasers, but LIPSS were not fabricated at 355- and 266-nm laser wavelength. In addition, the short-pulsed laser experienced thermal influences and a cooling material was effective for the fabrication of LIPSS with high-aspect-ratio. This demonstrates the effects of pulse duration close to the CRT and heat on the fabrication of LIPSS.

Deep-ultraviolet laser ablation electrospray ionization mass spectrometry.

A 193-nm wavelength deep ultraviolet laser was used for ambient laser ablation electrospray ionization mass spectrometry of biological samples. A pulsed ArF excimer laser was used to ablate solid samples, and the resulting plume of the desorbed material merged with charged electrospray droplets to form ions that were detected with a quadrupole time-of-flight mass spectrometer. Solutions containing peptide and protein standards up to 66-kDa molecular weight were deposited on a metal target, dried, and analyzed. No fragmentation was observed from peptides and proteins as well as from the more easily fragmented vitamin B12 molecule. The mass spectra contained peaks from multiply charged ions that were identical to conventional electrospray. Deep UV laser ablation of tissue allowed detection of lipids from untreated tissue. The mechanism of ionization is postulated to involve absorption of laser energy by a fraction of the analyte molecules that act as a sacrificial matrix or by residual water in the sample.

Impact of Plasmonic Parameters on 7-nm Patterning in Plasmonic Computational Lithography.

For the wavelength reduction to overcome the diffraction limit of the optical lithography, the surface plasmon lithography (SPL) has lower cost and simpler system configuration than the extreme ultraviolet (EUV) lithography. In this paper, for the below 10-nm critical dimension (CD) as one of critical challenges in the lithography technology, SPL based on the SP interference and metamaterial in bowtie and hexahedron structures is proposed and demonstrated by using computer simulations such as the rigorous coupled-wave analysis (RCWA) method and the finite difference time domain (FDTD) method. For 193-nm wavelength, the minimum FWHM (the full width at half maximum) of the transverse magnetic (TM) intensity in xz plane (and yz plane) is 10-nm (and 7-nm) in a bowtie plasmonic structure. For hexahedron structures, the minimum 30-nm FWHM of TM intensity with 193-nm wavelength is improved to the minimum 16-nm FWHM by using metamaterial and SP interference.

Preliminary measurements of fluorescent aerosol number concentrations using a laser-induced fluorescence lidar.

A laser-induced fluorescence lidar has been developed for detecting the concentration of fluorescent aerosols in the air. The fluorescence lidar was constructed with a pulsed fourth-harmonic Nd:YAG laser at the ultraviolet wavelength of 266nm with a repetition rate of 10Hz. A 250mm diameter custom telescope was used to collect optical spectra ranging from 260 to 560nm. Fluorescence signals with wavelengths ranging from 310-440nm were extracted, exploring a filter with a bandwidth of 130nm. The preliminary experiments were conducted at the campus of Xi'an University of Technology, in which the fluorescence signals of atmospheric fluorescent aerosols were continuously collected from 20:00 to 23:00 CST on 13 December 2017. Based on the fluorescence lidar equation, the density of fluorescence signals was calibrated using Rayleigh-Mie scattering signals and ozone (O3) concentration data at the ground level. Measured ranges show a strong dependence with the O3 concentrations due to its absorption characteristics at ultraviolet 266nm. Moreover, the concentration of the biogenic particles was also calculated based on the raw data of the fluorescence channel. Obtained results show that the concentration of biogenic particles in the Xi'an area varied greatly, ranging from 3456 particles · m-3 to 8835 particles · m-3 during winter.

Bragg Grating Inscription With Low Pulse Energy in Doped Microstructured Polymer Optical Fibers

We demonstrate that fiber Bragg gratings (FBGs) can be written in a doped polymer optical fiber (POF) in a low ultraviolet (UV) pulse energy regime (60Jpulse) using a 248-nm krypton fluoride excimer laser system. The total energy density per inscription necessary to obtain Bragg gratings is between 493.6 and 3825mJcm 2, depending on the number of pulses and the pulse energy. The impact of the pulse energy on the growth of the Bragg grating is investigated, and it is shown that the 248-nm light induces a positive refractive index change. This article demonstrates that the FBGs can be obtained in the POFs without high pulse energy (mJ level) at 248-nm wavelength, which reduces maintenance costs. Furthermore, we can consider it as a solution to increase the lifetime of the laser system without high energy still allowing fast and efficient production of the FBGs for sensing applications.

CARS and Fluorescent study of ignition of H2/O2 mixtures upon photodissociation of O2 molecular

The research is devoted to gas mixtures ignition by UV laser radiation. The dissociation of O2 molecules by a pulse of excimer ArF laser radiation at 193-nm wavelength with formation of the chemically active oxygen atoms initiating chain reactions which cause ignition of H2/O2 mixture was employed. The experimental test bench was created with CARS and fluorescent techniques for experimental investigation of some peculiarities of mixture ignition and combustion caused by such photo-dissociation, at conditions typical for combustion chamber. Two-dimensional numerical modeling of combustion process in model combustion chamber, based on kinetic mechanism of H2 oxidation including atom O(1P) and radicals OH(A2Σ+), was performed.

UV-laser cleaning and surface characterization of an aerospace carbon fibre reinforced polymer

In the recent aerospace generations, composite materials have shown that they can fulfil the increasing demand for structural efficiency. In this context adhesive bonding could be used to max out the material properties of carbon fibre reinforced polymers (CFRP). However, investigations have shown that residues of release agents on the CFRP surface can cause adhesion problems. Thus, a reliable surface cleaning procedure for removing residues prior to bonding is necessary.Analytical surface investigations of an Aerospace CFRP material revealed the thickness and morphology of the predominant adhesion-weakening contamination. The optical absorptions of the epoxy material and the release agent characterised by UV–vis measurements were considered to develop a cleaning model based on a ns-pulsed ultra-violet laser with 266nm wavelength. This removal mechanism leads to chipping and peeling of the release agent layer and could be supported with light microscopy, scanning electron microscopy (SEM) and x-ray photoelectron spectroscopy (XPS) investigations. Single lap shear tests of the CFRP samples in the pristine and contaminated state, pre-treated with UV-laser as well as with the reference process (grinding) show that the laser pre-treated samples lead to the highest joint strength in the study. The failure mode changed from adhesion failure in the pristine state to a failure in the fibre-resin interface after laser treatment. Comparing a laser parameter with the focus on a smooth cleaning process and a laser parameter that lead to a surface with exposed carbon fibres, the surfaces treated with the smooth laser parameter showed the higher joint strength. The measured joint strength was 100% higher than with grinding, which underlines the high potential of laser technology for CFRP surface pre-treatment.

Major pathway for multiphoton air ionization at 248 nm laser wavelength

Multiphoton ionization mechanisms and ionization rates of atmospheric air and constituent gases are studied at the 248-nm KrF laser wavelength within a laser pulse intensity range of 108–1013 W/cm2 using both long 25-ns and short 160-fs pulses. We have experimentally shown that it is the photoionization of water vapor naturally contained in atmospheric air that acts as the dominant process of air ionization. (2 + 1) Resonance-Enhanced Multiphoton Ionization (REMPI) occurs through 2-photon resonant excitation of water molecules, which results in a quadratic dependence of electron density on laser intensity at lower laser intensities of 108–1010 W/cm2 in the long pulse and in a cubic dependence at higher intensities of 1010–1013 W/cm2 in the short pulse. Direct 3-photon ionization and (3 + 1) REMPI take place in pure O2 and N2, respectively, and their contributions to air ionization are in the ratio of 5:3. The total ionization rate of O2 and N2 in atmospheric air is about an order of magnitude less than that of water vapor. Relevant ionization coefficients (effective multiphoton ionization cross sections) have been measured and that for the H2O molecule is more than 2–3 orders of magnitude larger than the others.

Multi-parametric modeling of solid sample heating by nanosecond laser pulses in application for nano-ablation

Multi-parametric theoretical studies to analyze the effect of both the matter properties (absorption coefficient, thermal conductivity and diffusivity) and the heating field parameters (spatial distribution and pulse duration) on the resulted temperature distribution are presented. For heating in sub-micrometric range (<1μm), a low dependence of heating temperature distribution on the sample thermal properties and heating source duration was observed. Nano-ablation thresholds are found to be increasing inversely with heating source dimensions. The simulation results demonstrated a good agreement with the nanometer-size craters (100nm diameters, 10nm depth) obtained experimentally with a tip-enhanced near-field ablation (4ns laser pulse duration, 266nm wavelength) of Si- and Au-samples.