Xe Laser Research Articles

Optimization of conditions for excitation of Xe laser plasma in an extreme ultraviolet radiation source for nanolithography in order to increase its efficiency

Subject of study. The study focuses on laser plasma excited by a Xe gas-jet target. Aim of study. The aim of this study is to increase the output of extreme ultraviolet radiation from such a plasma to a level that meets the requirements of industrial production, specifically for use as a radiation source in a new branch of lithography with a wavelength near 11.2 nm. Method. The primary method used involves changing the diameter of the laser beam by moving a Xe gas-jet target along its axis. This adjustment leads to a change in the interaction area between the beam and the target, which in turn alters the size of the laser spark. The intensity of plasma radiation at wavelengths of 11.2 nm and 13.5 nm was measured using a surface-barrier Si photosensor and a Bragg mirror. Additionally, the energy of the laser radiation absorbed by the plasma was measured. Main results. The results show that, when the diameter of the laser beam illuminating the target increases from 46 µm to 344 µm, the energy emitted in the extreme ultraviolet range increases by approximately 5 times. In the identified irradiation mode, the efficiency of converting laser radiation into radiation with a wavelength of 11.2 nm was 3.9%. Recent measurements of the plasma lifetime have shown that it depends on the size of the plasma and, in several experiments, is significantly shorter than the laser pulse duration. This finding suggests that the plasma lifetime can be used as an optimization parameter when selecting the laser pulse duration. Practical significance. A record-high efficiency is obtained for the conversion of laser pulse energy into extreme ultraviolet radiation by a laser-plasma radiation source with a gas target. This achievement opens up the prospect of using such sources in the industrial production of microcircuits.

Further development of the Xe laser plasma 11-nm radiation source – new data on laser energy absorption and spectroscopy

Absorption of the laser pulse energy in the plasma has been shown to change from 8.5% at irradiation of a gas-puff target with a beam narrow-focused onto a near-central area of the jet up to 65% at the wide defocused irradiation. An analysis of this phenomenon is based on a hypothesis that plasma density decays significantly during the 10ns laser pulse due to hydrodynamic expansion of the hot plasma. A similarity of the EUV (Extreme UltraViolet) intensity and the laser light absorption as functions of the laser beam diameter suggests a revision of the conventional idea of a strong EUV radiation self-absorption in a cold peripheral shell of the laser plasma whereas the high absorptivity of the laser radiation by the plasma looks like a major feature to gain high efficiency of an EUV source.

An IR Inductive Xe Laser Pumped by Pulsed Longitudinal Induction Discharges

IR laser radiation of XeI atoms in the range of 1700–2050 nm is obtained for the first time upon the pumping of xenon and mixtures of it with helium and argon by a pulsed longitudinal induction discharge. The spectrum of generation consists of two lines with wavelengths of 1733 nm and 2026 nm. The half-amplitude duration of the optical radiation is 60 ± 2 ns (FWHM).

Planar multifrequency mid-IR microwave-pumped lasers

The characteristics of planar repetitively pulsed diffusion-cooled HF, DF, HF – DF, Xe, and HF – DF – Xe(Kr) lasers pumped by a microwave discharge (2.45 GHz) are studied depending on the pump pulse duration (10 – 40 μs) and repletion rate (50 – 400 Hz), as well as on the composition and pressure of the working gas mixture (30 – 200 Torr) at low (to 0.6 L s−1) gas flow rates. It is demonstrated for the first time that a HF – DF – Xe gas-discharge laser may simultaneously operate as a HF – DF chemical molecular laser and a recombination laser based on xenon atom transitions and generate broadband (octave) radiation in the range 2.0 – 4.2 μm with an average output power of 43 mW and an efficiency of 0.9 %. With substitution of xenon for krypton, lasing in a HF – DF – Kr laser is obtained at wavelengths of 2.52 – 4.15 μm. Lasing in a HF – DF laser was achieved simultaneously in two spectral regions (2.7 – 2.9 and 3.6 – 4.2 μm) with an output power of ∼50 mW. It is found that a decrease in the pump pulse duration with a simultaneous increase in the pulse repletion rate for retaining the average energy deposition leads to an increase in the average output power and efficiency of the laser. At low pulse repetition rates (50 – 100 Hz) and a low gas mixture flow rate, helium buffer gas can be effectively substituted for neon. Operation of the Xe laser was achieved in the spectral range 2.03 – 3.65 μm with an average output power of 580 Mw at a pump pulse duration of 20 μs, a pulse repetition rate to 10 kHz, and a maximum efficiency of 55 %. The obtained experimental results demonstrate the possibility of creating broadband HF – DF – Xe lasers emitting in the frequency range 2 – 4 μm with a desired ratio of intensities in different spectral ranges.

Absolutely calibrated EUV spectra of Xe laser plasma radiation for lithography needs

Spectra of Xe laser plasma radiation were measured using Si/Mo and Mo/Be interference mirrors. The intensity within the 11.0-11.8 nm wavelength band has been shown to be 6-7 times as high than that in the 12.5-14 nm range. The spectra obtained by means of the mirrors are compared with those measured earlier using a spectrometer.

Absolutely Calibrated Spectrally Resolved Measurements of Xe Laser Plasma Radiation Intensity in the EUV Range

With the aid of Mo/Be and Si/Mo interference mirrors, measurements of radiation intensity from laser plasma with Xe gas-jet target have been realized within a wavelength interval of 11–14 nm with a spectral resolution of 3–6 A. The results are compared with the spectrum formerly measured with the aid of a spectrograph. The ratio of intensities at wavelengths of 11.2 and 13.5 nm has been found to be about 10 under experimental conditions studied.

Kinetic analysis of rare gas metastable production and optically pumped Xe lasers

Optically pumped all-rare-gas lasers use metastable rare gas atoms as the lasing species in mixtures with He or Ar buffer gas. The metastables are generated in a glow discharge, and we report model calculations for the optimal production of Ne*, Ar*, Kr* and Xe*. Discharge efficiency was estimated by solving the Boltzmann equation.Laser efficiency, gain and output power of the CW optically pumped Xe laser were assessed as functions of heavier rare gas content, pressure, optical pump intensity and the optical path length. It was found that, for efficient operation the heavier rare gas content has to be of the order of one percent or less, and the total pressure—in the range 0.3–1.5 atm. Output power and specific discharge power increase approximately linearly with pump intensity over the output range from 300–500 W cm−2. Ternary mixtures Xe:Ar:He were found to be the most promising. Total laser efficiency was found to be nearly the same for pumping the 2p8 or 2p9 state, reaching 61%–70% for a pump intensity of ~720 W cm−2 when the Xe fraction was in the range 0.001 ÷ 0.01 and Ar fraction—0.1 ÷ 0.5. However, when the 2p8 state was pumped, the maximum total efficiency occurred at larger pressures than for pumping of the 2p9 state. The discharge power density required to sustain a sufficient Xe* number density was in the range of tens of watts per cubic centimeter for 50% Ar in the mixture.

Submersible Spectrofluorometer for Real-Time Sensing of Water Quality.

In this work, we present a newly developed submersible spectrofluorometer (patent pending) applied to real-time sensing of water quality, suitable for monitoring some important indicators of the ecological status of natural waters such as chlorophyll-a, oil and protein-like material. For the optomechanical realization of the apparatus, a novel conceptual design has been adopted in order to avoid filters and pumps while maintaining a high signal-to-noise ratio. The elimination of filters and pumps has the advantage of greater system simplicity and especially of avoiding the risk of sample degradation. The use of light-emitting diodes as an excitation source instead of Xe lamps or laser diodes helped save on size, weight, power consumption and costs. For sensor calibration we performed measurements on water samples with added chlorophyll prepared in the laboratory. The sensor functionality was tested during field campaigns conducted at Albano Lake in Latium Region of Italy as well as in the Herzliya Harbor, a few kilometers North East of Tel Aviv in Israel. The obtained results are reported in the paper. The sensitivity achieved for chlorophyll-a detection was found to be at least 0.2 µg/L.

Characterization, Photoluminescence and Magnetic Properties of SiC Nanowires Synthesized with Nickel Catalyst via Microwave Heating

Large scale SiC nanowires were synthesized through a rapid and low-cost microwave heating method. Silicon, silica, graphite and nickel powders were used as raw materials and catalyst, respectively, and no inert protective gas was employed during the preparation. The microstructures of the products were comprehensively characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrum (EDS), and transmission electron microscopy (TEM). Results showed that the nanowires have lengths of several dozens of micrometers and diameters of 50nm approximately. The growth of them was governed by vapor-liquid-solid (VLS) growth mechanism. In addition, the photoluminescence (PL) and magnetic properties of the products were subsequently investigated by fluorescent photometer and vibrating sample magnetometer (VSM). The PL spectrum, employing a Xe laser (240 nm) as an excitation source, shows an emission band centered at about 390 nm, indicating that the obtained SiC nanowires possess excellent optical property. The hysteresis loop shows big magnetic saturation (Ms) of 0.96 emu/g and small coercivity (Hc) of 37.92 Oe. So, the obtained SiC nanowires can be characterized as typical soft magnetic material, and the improvement of magnetic properties may be attributed to the existence of Ni2Si phase in the SiC nanowires.

Planar Xe laser with cw radio-frequency pumping

The characteristics of the radiation of a planar Xe laser excited by transverse RF discharge at a frequency of 40.68 MHz with diffusive cooling of the active medium and a nonselective optical cavity have been investigated. The spectral and power characteristics of the Xe laser have been experimentally studied as functions of the interelectrode-gap width (1.4 — 2.5 mm), composition and pressure (30 — 100 Torr) of working gas mixture, input power density (0.4 — 34 W cm-3), and the electrode temperature. The output laser power was found to decrease at an interelectrode gap above 1.6 mm. The threshold pump power was 12 W (power density 0.4 W cm-3). Addition of butane to the working mixture increases the output power by approximately 50 % at interelectrode gaps of 2.0 — 2.5 mm. A cw lasing power of 4 W and a maximum efficiency of ∼0.7 % are obtained. Good prospects of the Xe laser operatingat wavelengths of 2.03, 2.65, and 3.51 μm are shown.

Using Zn as target to fabricate ZnO coating by thermal oxidation in air on quartz substrate

In this work, ZnO coatings were fabricated by the RF-sputtering method on quartz substrates in an inert gas ambient of Ar followed by a thermal oxidation process in air at different temperatures. The effect of thermal oxidation temperatures on the structures and photoluminescence (PL) properties of the coatings were studied. The structural characteristics of the samples were analyzed by X-ray diffraction (XRD) and atomic force microscope (AFM). The PL spectra were obtained by using a Xe laser as a light source with an excitation wavelength of 325nm at room temperature. The force-curves were obtained by AFM. The results show that all the prepared ZnO coatings have a compact hexagonal wurtzite structure. With the increasing annealing temperature from 400°C to 600°C, the particle size, surface RMS roughness, photoluminescence intensity and adhesion force of the prepared ZnO coatings were increased as well.

Synthesis, characterization, and photoluminescence properties of bulk-quantity β-SiC/SiOx coaxial nanowires

The bulk-quantity synthesis of coaxial nanowires consisting of a β-phase silicon carbide (β-SiC) core and a silicon oxide (SiOx) shell has been achieved through a rapid and low-cost microwave heating method. In the preparation process, only silicon, silica, and graphite powders were used, without any metal catalysts or inert protective gas. The microstructures and optical properties of β-SiC/SiOx nanowires have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrum (EDS), transmission electron microscopy (TEM), and photoluminescence (PL) measurements at room temperature. The nanowires have lengths of several dozens of micrometers and diameters of 20–30 nm, with SiOx shells exhibiting approximately 30 nm in thickness. They have a growth direction along the <111> planes, with the vapor solid (VS) growth mechanism. The PL spectra, employing a Xe laser (325 nm) as an excitation source, show two emission bands centered at about 444 and 470 nm. The blue-shift phenomenon can be explained by the interface defects and oxygen vacancy defects in the coaxial nanowires.

Oxygen mediated and wavelength tunable cationic photopolymerization reactions under air and low intensity: A new concept

A new concept which allows efficient cationic photopolymerization reactions under air, at any excitation wavelength in the UV–visible range and under low light intensities (conventional Xe lamp and/or laser diodes) is presented. It is based on the use of a versatile free radical promoted cationic process for the photoinitiation step which only requires a radical source, a silane and an usual iodonium salt and takes advantage of the presence of oxygen. The tunable character of the absorption is connected with the choice of the radical source. The oxygen enhancement is due to the particular role played by the silane. In every case, the silylium cation is the most efficient structure for the cationic ring opening reaction. Examples of the performance achieved (e.g. a conversion close to 100%) with such systems over the 390–580nm range using various irradiation devices is shown and discussed.

Electron beam generation in open hollow-cathode discharge and the characteristics of He—Xe laser on the Xe line at λ = 2.026 μm

An open hollow-cathode discharge, generating an electron beam, is implemented in a cell with an active volume of 6.2 L. An electron-beam current of 3.4 A at an average power of 2.5 kW is obtained in helium in the quasi-cw regime at an anode voltage of 1.5 kV. Lasing in a He—Xe mixture on the 5d[3/2]01—6p[3/2]1 transition in xenon at the wavelength λ = 2.026 μm under electron-beam excitation is investigated. The optimal component ratio in the He : Xe mixture is 99.5 : 0.5 (pHe = 4–8 Torr). The lasing power linearly increases with increasing the electron-beam power. It is shown that the discharge of this type can be used as an electron-beam source for exciting gaseous active media.

Optimizing the Ar–Xe infrared laser on the Naval Research Laboratory’s Electra generator

The Ar–Xe infrared laser has been investigated in several series of experiments carried out on the Naval Research Laboratory’s Electra generator. Our primary goals were to optimize the efficiency of the laser (within Electra’s capabilities) and to gain understanding of the main physical processes underlying the laser’s output as a function of controllable parameters such as Xe fraction, power deposition, and gas pressure. We find that the intrinsic efficiency maximizes at ∼3% at a total pressure of 2.5 atm, Xe fraction of 1%, and electron beam power deposition density of 50–100 kW cm−3. We deployed an interferometer to measure the electron density during lasing; the ionization fractions of 10−5–10−4 that it detected well exceed previous theoretical estimates. Some trends in the data as a function of beam power and xenon fraction are not fully understood. The as-yet incomplete picture of Ar–Xe laser physics is likely traceable in large part to significant uncertainties still present in many important rates influencing the atomic and molecular kinetics.

Electron kinetics of the e-beam pumped Ar–Xe laser

Extensive electron collision data for Ar and Xe are assembled and employed to study the e-beam deposition in this noble gas mixture for application to the Ar–Xe laser. Nineteen states of Xe and thirteen of Ar are used for the atomic model. The electron energy distribution function is calculated from the Boltzmann equation using atomic cross sections for excitations from the ground states computed from atomic physics codes. The resulting electron distribution is then used to investigate the electron temperature, energy per electron–ion pair, ionization rates and excitation-to-ionization ratios for both species as a function of three parameters: the Xe mole fraction, the fractional ionization, and the power deposition per Ar atom. While the Ar ionization and excitation are fairly insensitive to these parameters, the rates for Xe, especially total excitation-to-ionization ratio, can vary with all three. Cross sections for excited to excited transitions among all the considered upper states in Xe are also calculated and transition rates, fitted to an Arrhenius form, are presented in tabular form. The assembled atomic data and calculated rates are useful for further detailed electron kinetics modelling of the Ar–Xe laser.

Abordaje de la enseñanza de aspectos importantes de la física moderna a traves del uso de un laser de xenon multi-ionico pulsado

Este trabajo tiene por finalidad presentar un láser de Xe multi-iónico pulsado, a partir del cual se pueden realizar demostraciones, prácticas de laboratorio o iniciar trabajos de investigación en temas de física moderna, espectroscopía atómica y láseres gaseosos, así como para ser utilizado en la enseñanza de grado y postgrado. Además, el empleo de todo el instrumental que compone el equipo, permite tomar contacto con fuentes de alta tensión, equipos de vacío, de óptica y con el uso de detectores y analizadores de radiación luminosa, instrumental que generalmente no se utiliza dentro de los esquemas de la enseñanza tradicional.

The breakdown stage in long laser tubes and plasma focus devices

The breakdown stage in a long Xe laser tube and a deuterium filled plasma focus device operating in the mbar pressure range is studied theoretically and experimentally. A simple model for describing the conditions to reach an electron plasma thermalized regime is given and its evolution in terms of the applied voltage is derived. The model is shown to be consistent with the experimental data, and enables determination of the plasma state at the breakdown time in both devices. It is also shown that the stage previous to electron thermalization is the main component of the breakdown time delay in the studied cases, and that the duration of this stage diminishes with the filling pressure, contrary to the expected inverse dependence on the reduced electric field.

Experimental evidence for the role of Xe2+ in pumping the Ar–Xe infrared laser

In a series of experiments on the Naval Research Laboratory's Electra generator, we have measured the dependence of the laser output in the principal (1.733μm) transition of the Ar–Xe laser upon both initial gas temperature and Xe concentration. The data show that the laser output is less sensitive to gas temperature when the laser gas contains more Xe. The destruction rate of the molecular ion ArXe+ increases rapidly with gas temperature, but that of Xe2+ does not. Interpreted with a kinetics model, these data indicate that both Xe2+ and ArXe+ contribute to the pumping of the ArXe laser.

Repetitively pulsed operating regime of a high-pressure atomic xenon transition laser

The repetitively pulsed regime of an atomic xenon transition laser pumped by an electron beam with various pulse durations and an electron-beam-initiated discharge is studied experimentally. An average radiation power of 2.5 W has been achieved in a quasi-stationary regime for a pulse repetition rate of 5 Hz in a laser pumped by a radially convergent electron beam of duration 100 μs without circulation of the Ar — Xe working mixture. The average output power for a laser pumped by a planar electron beam in quasi-stationary regime is 2 W. It is shown that for a specific energy contribution not exceeding 50 J L-1 and laser excitation by a train of electron-beam pulses at a repetition rate of 50 Hz, the amplitude and duration of the second lasing pulse virtually coincide with those of the first. For a laser pumped by a discharge initiated by a nanosecond electron beam, an average lasing power of 380 mW is achieved under steady-state conditions upon transverse circulation of the working mixture and a pump pulse repetition rate of 25 Hz. Pumping by an electron beam from two accelerators with a pulse duration of a few tens of microseconds under an Ar — Xe mixture pressure of about 1 atm and a specific pump power of 1 — 3 kW cm-3 per pulse is proposed for the development of 1.73-μm repetitively pulsed Xe lasers with a high average output power.