Xe Laser Research Articles

Laser patterning of metallic films via buffer layer

A novel method is presented for a single pulse laser-patterning of variable width conducting lines on solid surfaces. Employing laser induced thermal desorption (LITD), potassium coverage grating on top of multilayer Xe is formed on Ru(0 0 1) at 20 K. Optical second harmonic-diffraction measurements were performed to characterize the grating as a function of Xe layer thickness and laser power density. Upon annealing to 80 K, the Xe layer desorbs and the metallic pattern softly lands on the substrate. The potential application of this procedure for the parallel writing of conducting wires millimeters long and less than 50 nm wide is discussed.

Complete optimisation of an electron-beam-pumped Xe laser emitting at 1.73, 2.03, 2.65, 2.63, 3.37, and 3.51 μm

The results of complete numerical optimisation of an electron-beam-pumped Xe laser emitting at 1.73, 2.03, 2.65, 2.63, 3.37, and 3.51 μm are presented. At all these wavelengths, the best output parameters are achieved in the Ar—Xe mixture. The maximum lasing efficiency (4.5 %) and the highest specific energy output (19 J L-1) are obtained at a wavelength of 1.73 μm. For wavelengths 2.03, 2.65, 2.63, 3.37, and 3.51 μm, the maximum efficiencies were 2 %, 1.7 %, 1.2 %, 0.6 % and 0.48 %, respectively. These maximum values of output characteristics in the Ar—Xe mixture can be obtained in a certain range of operating parameters.

Output power limitation in a Xe laser pumped by a periodic-pulsed electric beam

We report the experimental and theoretical characteristics of generation at 1.73 μm for a Xe laser pumped with an electron beam of a pulsed electron accelerator operating at a repetition rate of up to 100 Hz. A decrease in the average output power with time is caused by electron-beam heating of the active medium.

Formation of microscopic coloured oxide dots on the titanium foil surface irradiated by a laser

Experiments are performed on the formation of coloured dots of a submillimetre size on the titanium foil surface irradiated by pulsed IR lasers. It is shown that the parameters of laser pulses can be selected so that the dots produced on the titanium foil surface will change their colour from yellow to blue with increasing exposure time. The threshold laser power densities required for the formation of contrast coloured dots on the titanium foil surface irradiated by laser pulses with low repetition rates are estimated as ~1.5 × 103 J cm-2 for a 1.73-μm Xe laser and ~2.3 × 103 J cm-2 for a 10.6-μm CO2 laser.

Spontaneous coherent pulsations in 339-m He–Ne standing-wave laser oscillators

Spontaneous pulsations similar to the type discovered in 3.51-μm Xe laser oscillators were reported several years ago in 3.39-μm He–Ne lasers, but no numerical interpretation of the He–Ne data has been given. The model for the Xe laser instability is adapted here to the He–Ne system, and the results include direct comparisons between theoretical calculations and published experimental data. Good agreement is obtained for the instability threshold, the pulsation frequencies, and many other features; and unmeasured but potentially useful pulsation characteristics are also readily obtained from the model.

UV and IR laser radiation's interaction with metal film and teflon surfaces

The interaction of Xe (λ ∼ 1.73 μm) and XeCl (0.308 μm) laser radiation with surfaces of metal and TiN-ceramic coatings on glass and steel substrates has been studied. Correlation between parameters of surface erosion versus laser-specific energy was investigated. Monitoring of laser-induced erosion on smooth polished surfaces was performed using optical microscopy. The correlation has been revealed between characteristic zones of thin coatings damaged by irradiation and energy distribution over the laser beam cross section allowing evaluation of defects and adhesion of coatings. The interaction of pulsed periodical CO2 (λ ∼ 10.6 μm), and Xe (λ ∼ 1.73 μm) laser radiation with surfaces of teflon (polytetrafluoroethylene—PTFE) has been studied. Monitoring of erosion track on surfaces was performed through optical microscopy. It has been shown that at pulsed periodical CO2-radiation interaction with teflon the sputtering of polymer with formation of submicron-size particles occurs. Dependencies of particle sizes, form, and sputtering velocity on laser pulse duration and target temperature have been obtained.

Xe laser pumped by fast electrons generated in a barrier discharge

A compact pulsed generator of a kiloelectronvolt electron beam based on an open barrier discharge in a dense gas is proposed and developed. A stable discharge was observed in the experimental setup in a broad range of pressures up to the atmospheric pressure. At moderate pressures of the gas (~ 5 — 20 Torr), the efficient generation of an electron beam was observed with a current density of ~ 1 A cm-2 and the discharge area of ~ 100 cm2. The electron energy was ~ 2 — 10 keV. The pulse repetition rate could be varied from 10 Hz to 10 kHz without changing the electron-beam parameters. By injecting an electron beam into a neutral gas, lasing was obtained at the transitions of a Xe atom in the 2-μm region with an output power of ~ 0.22 mW kHz-1.

Impact of the vectorial degrees of freedom on the nonlinear behavior of class B lasers

A model of a weakly anisotropic (vector) class B single-mode laser operating on the j=1→ j ′=0 ( j is an angular momentum quantum number) homogeneously broadened transition has been presented. It takes into account dynamics of the intersublevel coherence of the upper laser level. The model is suitable for modeling of He–Ne, He–Xe, CO 2, and solid-state lasers. Nonlinear anisotropy of the gain medium in such an isotropic-cavity system favors either linearly or circularly polarized emission, that distinguishes two qualitatively different types of lasers. We have studied in detail, both analytically and numerically, impact of the vectorial degrees of freedom on selection of the polarization states, their stability, mechanisms of their destabilization, and symmetry properties of both types of weakly anisotropic lasers. Dominant role of the vector degrees of freedom in the development of laser instabilities is revealed. Two basic mechanisms of destabilization of the laser states, which are polarization amplitude and polarization phase mechanisms, are analytically distinguished. Among other phenomena our model predicts phenomena of polarization multistability, amplitude polarization chaos, quasiperiodic dynamics with scalar and vector incommensurate relaxation frequencies. Analytical treatment of the problem allowed us to generalize the polarization bad cavity limits to the case of anisotropic-cavity lasers.

Measurements of Laser Absorption and Ion Energy inFemtosecond Laser-Cluster Interaction

Laser absorption is measured in Xe, Ar and He clusters irradiated by5 mJ laser pulses in 150 fs. The measurements show that the absorptionefficiency strongly depends on the backing pressure of the gas jets, thelaser pulse duration and the atomic number Z of the working gas. The laserabsorption for Xe clusters is found to be as high as 45% at a backingpressure of 20 atm and a laser intensity of 1×1015 W/cm2.Significant numbers of ions with energies up to 100 keV are detectedfrom Xe cluster explosion. The variation trend of the average ion energyat different backing pressures is consistent with that of the laserenergy absorption.

Prediction of the thermal properties of CO 2, CO, and Xe laser media

Approximation functions describing the experimental data of thermal conductivity and viscosity of chosen gases ( CO 2, N 2, He, Xe, CO, O 2, Ar) are given in the paper. Introduced formulas allow to predict thermal conductivity and temperature distribution of typical high-power laser gas mixture. Examples of temperature distribution in RF excited CO 2, CO, and Xe laser media are shown. Knowledge of the temperature distribution in the laser cavity can be useful for predicting the general properties of laser.

Asymmetric output profile of Xe laser

A new set of asymmetric modes was recently revealed in a Xe slab laser with pronounced lens effects originating from gas heating in the discharge. The appearance of these modes is a threshold effect. Their domain of existence in the Xe laser is discussed. It is shown that mode competition can result in output radiation asymmetry. Theoretical results are compared with experimental data.

Evidence of orbital mixing for KrXe and ArXe excited states in the vacuum ultraviolet

The dissociation limits for two KrXe Rydberg states near 80000 cm−1 have been reassigned using single-photon vacuum ultraviolet (VUV) laser resonance enhanced multiphoton ionization (REMPI)/time-of-flight (TOF) mass spectrometry. These new assignments follow from spectral intensity changes that occur when the excited states are populated by single-photon excitation instead of a two-photon transition. The observations can be rationalized on the basis of strong 6p–5d orbital mixing on the Xe center induced by ground state Kr in the excited state of the dimer. ArXe transitions in this region have also been found by (1 + 1′) REMPI. There is also strong intensity evidence here for strong p–d mixing. Isotopic transition wavenumbers for the newly observed ArXe bands are provided, but molecular constants have not been derived due to severe interstate perturbations. Where possible the relationship between these results and our current understanding of the rare gas kinetics leading to gain in the infrared Xe laser is discussed.

A slab Xe laser excited by a non-self-sustained discharge

Repetitively pulsed lasing with a high repetition rate of 10 — 20 kHz is obtained for the first time in the near-IR region from Xe atoms excited by a non-self-sustained dc discharge with preionisation by high-voltage pulses. For an active medium with dimensions 190 mm×20 mm×20 mm, the average output power was ~100 mW and the peak power was ~5 W. The relative intensity of lasing transitions can be controlled by varying the dc discharge input power and selecting the composition and pressure of a gas mixture.

Temperature and electron density gradient in Xe laser produced plasmas, by spectral analysis

We have performed a spectroscopic analysis on laser produced plasmas in Xe at intermediates pressures (less than 1 atm), resolved both spectrally and temporally, also discriminating different regions of the plasma. This is produced by tightly focusing the radiation of a Q-switched Nd : YAG laser on a cell equipped with an observation window at right angles with respect to the laser. Our results confirm that there is a gradient in electron density in the plasma ball formed by the laser. This gradient almost defines at least two regions, an outer layer of higher electron number density, and an inner core of lower electron number density. The electron temperature gradient has the same sign. These conclusions are supported by evidence taken using the spectral results mentioned above.

Kinetics of the active medium of a multiwave IR xenon laser in hard-ioniser-pumped mixtures with He and Ar. I. Electron-beam pumping

A description is given of a detailed nonsteady-state multiwave kinetic model of a laser, based on xenon atom transitions with λ = 1.73, 7.03, 2.65, 2.63, 3.37, and 3.51 μm in an He — Ar — Xe mixture pumped by a hard ioniser. The proposed kinetic model is tested against the results of experiments on electron-beam pumping of an Xe laser containing pure xenon, as well as binary and ternary mixtures. Numerical modelling is used to identify the main mechanisms pumping the upper active levels: three-particle recombination of atomic Xe+ ions (He — Xe mixture), dissociative recombination of molecular Xe2+ ions (pure Xe), dissociative recombination of molecular ArXe+ ions and electron excitation from the 6s' xenon atom states in an (He) — Ar — Xe mixture. It is shown that the contribution of each of the mechanisms to pumping of the upper active level is determined by the composition and pressure of the mixture.

Mechanism of the operation of an rf-pumped cw Xe laser

Formation of specific structures of the radiation field of an rf-pumped cw Ar — He — Xe laser was observed experimentally. A model of the active medium was developed taking account of the spatial inhomogeneity of the gas-discharge parameters. It was found that under the conditions of a high input energy and gas heating the inhomogeneity of the refractive index led to the formation of optical field configurations differing significantly from the known hollow-waveguide modes. The effective mechanism of the recombination of electrons with molecular ArXe+ and Xe+2 ions in the regions near the walls with an enhanced electric field intensity, together with displacement of the field to the periphery of the active region, ensured conditions favouring energy extraction in such a laser.

Influence of the pump power and of the addition of helium on the energy parameters of an electron-beam-pumped Ar—Xe laser

An investigation was made of the influence of the addition of helium on the lasing and amplifying characteristics of an electron-beam-pumped Ar—Xe laser emitting in the near-IR part of the spectrum. The efficiency of this laser was far from maximal when the pressure of the two-component laser mixture was ~1 bar and the electron current density had the maximum (in the present investigation) value j~1.4 A cm-2. A major improvement in the energy parameters was obtained by reducing the electron current density or by adding helium to the active medium. The results obtained were interpreted by compensation of the excess pump power as a result of a reduction in the rates of the processes of mixing of laser-active levels by electron collisions on lowering the secondary-electron concentration in the former case or as a result of electron cooling in collisions with light helium atoms in the latter case. A record (for electron-beam-pumped lasers) efficiency of 4.5% was achieved with a mixture of the Ar : Xe=200:1 composition at a pressure of 1 bar for j=0.2 A cm-2.

Characteristic of a negative corona discharge in active media of Xe(6p−5d) and eximer lasers

The article contains results of a study of electric and optical characteristics of a negative corona discharge in a “needles-grid” electrode system in the mixtures He/Xe and He/Xe(Kr)/HCl, which are used in periodic pulsed electric-discharge Xe(6p−5d), XeCl, and KrCl lasers. The corona discharge was ignited in a multielectrode system whose length is commensurable with the length of the active medium of the lasers. Voltage-current characteristics, radiation spectra of the discharge plasma, and the dependences of the radiation intensity of atomic spectral lines and the band λ=308 nm of XeCl (B-X) on parameters of the corona discharge are studied. For the mixture He/Xe the corona discharge exists as a spatially homogeneous discharge that is intermediate between corona and glow discharges and is transformed into an anode streamer at higher charge voltages. Collisional purification of the 6p states of the Xe atom by helium was observed. In the mixture He/Xe/HCl the corona discharge is ignited in the form of individual generation zones and a dark external region and can be used in electric systems for pumping the active media of XeCl and KrCl lasers.

Collisional deactivation of the 6s' states of the Xe atom in the active medium of a high-pressure Ar — Xe laser

The method of absorption probing was used to investigate collisional deactivation of resonant (6s'[1/210]) and metastable (6s'[1/2]00) states of the Xe atom in high-pressure Ar—Xe mixtures with low Xe concentrations. The rate constants were determined for the following plasma-chemical reactions: Xe(6s') + Ar → Xe*+ Ar [(1–2) × 10-14 cm3 s-1], Xe(6s') + 2Ar → ArXe* + Ar (less than 10-35 cm6 s-1), and Xe( 6s') + Xe + Ar → Xe2* + Ar [(3–3) × 10-32 cm6 s-1].

Single line operation and line competition effects in RF discharge excited cw Xe lasers

We describe the first observation of single-line operation of cw atomic xenon lasers at Watt-level output powers. Single frequency output powers of 3.5 W on the 2.03 μm line and 780 mW on the 3.51 μm line have been observed. The single line performance of the laser is compared with observations made during multi-line operation. An explanation for the observed behaviour is proposed involving the suppression of line competition and the selective quenching and pumping of relevant transitions.