Experimental and numerical study of self-induced transparency in a neon absorber

Self-induced transparency on the neon transition 2s ₂(J=1)–2p ₄(J=2) is studied both experimentally by investigating the propagation of 3-nsec laser pulses at 1.15 µm in an absorber discharge and theoretically by a numerical integration of Bloch's equations and the wave equation.—The application of linearly and circularly polarized light corresponds to the interaction with a quasi-nondegenerate and degenerate transition, respectively. Pulse shapes, delays, and transmittancevs. input peak intensity are found in quantitative agreement with the calculated data. While with linear light polarization all SIT characteristics clearly appear, with circular polarization the pulse break-up and the oscillation of transmittance due to optical nutations are washed out.—The homogeneous linewidth derived from pulse delay data agrees with the value from conventional measurements. The results prove SIT useful as a quantitative spectroscopic method.Work supported by the Deutsche Forschungsgemeinschaft     

Experimental and numerical study of self-induced transparency in a neon absorber

Self-induced transparency on the neon transition 2s ₂(J=1)–2p ₄(J=2) is studied both experimentally by investigating the propagation of 3-nsec laser pulses at 1.15 µm in an absorber discharge and theoretically by a numerical integration of Bloch's equations and the wave equation.—The application of linearly and circularly polarized light corresponds to the interaction with a quasi-nondegenerate and degenerate transition, respectively. Pulse shapes, delays, and transmittancevs. input peak intensity are found in quantitative agreement with the calculated data. While with linear light polarization all SIT characteristics clearly appear, with circular polarization the pulse break-up and the oscillation of transmittance due to optical nutations are washed out.—The homogeneous linewidth derived from pulse delay data agrees with the value from conventional measurements. The results prove SIT useful as a quantitative spectroscopic method.     

Atom lithography with a cold, metastable neon beam

We study different aspects of atom lithography with metastable neon atoms. Proximity printing of stencil masks is used to test suitable resists that are sensitive to the internal energy of the atoms, including dodecanethiols on gold and octadecyltrichlorosilanes grown on a SiO₂ surface. As an example of patterning the atomic beam with laser light, we create parallel line structures on the surface with a periodicity of half the laser wavelength by locally de-exciting the atoms in a standing quenching wave. Received: 29 June 1999 / Revised version: 30 August 1999 / Published online: 10 November 1999     

The shape of saturated-absorption polarimetric resonances caused by transitions between degenerate states of the neon atom

We have studied experimentally and theoretically the shapes of spectropolarimetric resonances of a linearly polarized probe wave for the transitions 1s ₅-2p ₂ and 1s ₅-2p ₄ in the neon atom in the presence of a strong counterpropagating circularly polarized wave of the same frequency. Physical processes that lead to a change in the shape of polarimetric resonances under the action of a longitudinal magnetic field have been determined.     

Neon ion irradiation studies on MgB2 superconductor

160 MeV of neon ion irradiation has been carried out on MgB₂ polycrystalline pellets at various doses. There has not been any significant change in T_c except at the highest dose of 1×10¹⁵ ions/cm². Increase in resistivity has been noticed. Resistivity data have been fitted with Bloch-Grüneisen function to extract the values of Debye temperature, residual resistivity and temperature coefficient of resistivity for irradiated as well as unirradiated samples. There has not been any significant effect on electron-phonon coupling due to irradiation as evident from Debye temperature and the electron-phonon coupling constant.     

Penning neon laser excited by background-electron multiplication wave

The Penning neon laser was studied in a Ne-H₂ mixture excited by a transverse discharge. Theoretical modeling allowed the conclusion that the laser active medium was excited due to the background-electron multiplication wave passed through the discharge gap.     

Penning neon laser with excitation by background-electron multiplication wave

The Penning neon laser was studied in a Ne-H₂ mixture excited by a transverse discharge. Theoretical modeling allowed the conclusion that the laser active medium was excited due to the background-electron multiplication wave passed through the discharge gap.     

Electron momentum distribution in multiply-ionized neon atoms

We present momentum-space properties of multiply ionized neon atoms as a function of the degree of ionization of the atom. In particular, we have calculated the Compton profiles of all possible ionized states of neon atoms with electronic configurations 1s^m2sⁿ2p^q, m=1-2, n=0-2, q=0-6. The radial single-electron radial wave functions, obtained from the Hartree-Fock atomic model, were converted into momentum space wave functions by applying appropriate Fourier transformation. The values of the Compton profiles from the present calculation can be used to interpret experimental cross sections of variously ionized neon atoms colliding with other atoms. Compton profiles of neutral neon atoms, available in the literature, are in excellent agreement with the present calculation.     

Dynamic stark effect of an optical line observed by cross-saturated absorption

Cross-saturated absorption at the neon line 2s ₂–2p ₄ caused by the saturating line 3s ₂–2p ₄ has been applied to the observation of the dynamic Stark effect by 1) power broadening, due to triple-quantum and higher multiple-quantum transitions, of the light shift contribution to the susceptibility, and 2) a direct splitting in the electronic Raman-Stokes contribution which occurs because of the partial compensation of the Doppler broadening. Work supported by the “Deutsche Forschungsgemeinschaft”.     

Collisional broadening of saturated absorption in neon

Saturation spectroscopy involving laser light fields of two different frequencies has been applied to the investigation of Ne*-Ne collisions in an absorptive neon discharge. The pressure broadening of the saturation signals is interpreted in terms of “weak” collisions. Half the signal width results from velocity shifts of 2p ₄ atoms rather than from oscillator dephasing. The mean velocity shift is considerably larger than in collisions with helium atoms.     

A simple extended cavity diode laser for spectroscopy around 640 nm

We report on an extended cavity diode laser for operation near 640 nm. The laser is continuously tunable in 10 GHz ranges with a maximum output power of 3 mW. The laser system has been constructed using off-the-shelf optoelectronic components and easily machinable mechanical parts. The constructed system has been used to study the saturated absorption of the closed 1s₅–2p₉ neon transition in a radio-frequency discharge that can be maintained at neon pressures down to 10⁻² Pa.     

Relaxation of the Ne(2p1) level and populations of Ne(1s2) and Ne(1s4) in an afterglow

Radiation trapping of the transition 2p₁-1s₂ of neon has been demonstrated during laser-induced fluorescence in a pulsed microwave discharge through neon. The population of Ne(1s₂) atoms is deduced. Selective excitation is useful for the determination of lifetimes and cross sections of collisions with neutral atoms. The results may be utilized in processes for the creation of metastable atoms.     

Investigations on Afterglows of Neon Gas Discharges

We report on the experimental and numerical investigations on afterglows of neon gas discharges, which are performed at the Eindhoven University of Technology. The studied gas pressure range extends from 1 to 100 torr, the discharge current from 1 to 100 mA. The densities of the 1s-levels are measured with the help of the selective excitation spectroscopy (fluorescence technique). In this way a great number of decay curves of the 1s-densities have been measured in the afterglow of neon gas discharges. From these curves the diffusion coefficient of the metastable 1s-atoms, the coefficients of atomic collisional transfer between the 1s₅- and 1s₄-level, as well as the three body collision coefficient between metastable 1s₅-atoms and neon ground state atoms have been determined. Besides these experiments a numerical model of the neon afterglows has been developed. With this model the afterglow phenomena can be simulated and the influence of the particular processes on the whole afterglow can be studied conveniently. Comparison is made between the experimentally and numerically obtained decay curves. For the application of the numerical model a number of starting conditions, such as radial density profiles, gas temperature, (relative) densities of the 1s-levels, have been measured. Results of these measurements are presented. Also with the help of the selective excitation spectroscopy the coefficients of atomic collisional transfer between the 2p-levels have been measured in the afterglow. From these results, together with the measured (relative) intensities of the neon spectral lines in the afterglow the partial recombination coefficients for the 2p-levels were calculated.     

Pulsed-periodic laser on RM helium and strontium transitions

Conditions of generation of a running excitation wave in the active medium of gas lasers and efficiency of the running wave application for pumping of the active medium are considered by the example of a strontium vapor laser. It is demonstrated that the running excitation wave is generated directly in the active laser medium and is supported by the energy stored in the capacitive component of the impedance of a gas-discharge tube. Generation on the self-limited (2¹P₁-2¹S₀) transition of the helium atom at λ = 2058 nm and simultaneous generation on RM transitions of the strontium ion and strontium and helium atoms and on a number of neon atom transitions is first excited. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 6–9, January, 2008.     

Modification of spectral characteristics and optogalvanic response in neon hollow cathode under laser excitation

The changes in emission characteristics of a neon hollow cathode discharge by resonant laser excitation of 1s ₅→2p ₂ and 1s ₅→2p ₄ transition have been studied by simultaneously monitoring the optogalvanic effect and the laser induced fluorescence. It has been observed that resonant excitation causes substantial variation in the relative intensities of lines in the emission spectrum of neon discharge.     

Anomalous behavior of optogalvanic signal in a miniature neon discharge lamp

A strong optogalvanic effect has been observed in a negative glow of a miniature neon discharge lamp using tunable pulse dye laser pumped by a copper vapor laser. A comparative study on temporal evolution of optogalvanic signal in a positive and negative dynamic resistance region of the discharge is described. Dye laser beam was tuned to various neon transitions 1s_i → 2p_j (Paschen notations) within 570-617 nm wavelength range. Anomalous behavior of optogalvanic signal was observed at 588.2 nm for (1s₅ → 2p₂) neon transition at low discharge current (<220 μA). This anomalous behavior is the attributes of damped oscillations of optogalvanic signal that correlate with negative dynamic resistance (dV/di < 0) of the discharge. Penning ionization at low discharge current and small energy mismatch is assumed to be the main cause of the negative dynamic resistance. Penning ionization process has been explained by resonantly ionizing energy transfer via collisions between neon buffer gas atoms in the lowest metastable state (1s₅) and electrode sputtered atoms in ground state using their partial energy level diagram.     

Chromatic polarization in solid parahydrogen with an argon impurity at an extremely low concentration

The effect of chromatic polarization observed in samples prepared for studying thermal conductivity of weak solid solutions (p-H₂)_{1 − x} Ar _x has been described. Bulk cylindrical samples have been grown in a molybdenum glass ampule through desublimation followed by control of their quality in polarized light. In contrast to weak solid solutions (p-H₂)_{1 − x} Ne _x with a heavy quasi-isotopic neon impurity, the samples with argon at the same concentrations (several parts per million) exhibit inclined chromatic bands due to elastic mechanical stresses induced after cooling to liquid-helium temperature.     

Improved conversion efficiency of XeCl radiation to the first stokes at high pump energy

An XeCl laser beam has been used to investigate stimulated Raman scattering in H₂ and in various H₂-foreign gas mixtures. Helium, neon, argon, and nitrogen have been tested as foreign gases. In all the investigated mixtures with 50% of H₂, the energy conversion efficiency to the first Stokes (353 nm) was more than 70% higher than that obtained in H₂ at the same total pressure (40 bar) and pump energy (60 mJ). The dependence of the energy conversion efficiency on pump beam divergence has also been investigated.     

Field evaporation end forms of tungsten

The anomalous field ion images consisting of bright bands of variable width parallel to the 〈111〉 zones, previously reported for tungsten pulse evaporated in helium at 78 K, have also been observed with neon as imaging gas. For both gases the upper limit to the pulse lengths for production of the bands is about 1 ms. The influence of the ratio, R, of pulse height to the total evaporation voltage on the intensity distribution in field ion images of tungsten has been studied for helium and neon together with the effect of residual gases peculiar to ion pumped stainless steel UHV systems (H₂, CH₄ and CO). It is found that when R is raised to a certain level traces of residual gases if present in sufficient quantities, can produce, with tungsten, images with intensity distributions similar to those found with molybdenum after slow evaporation. These are attributed to preferential adsorption of the residual gases on different parts of the specimen and, depending on the nature of the adsorbate, leading to a promotion or a reduction of the ionization probability of the imaging gas. It is pointed out that before an image can be described as typical of a particulaelement or alloy, the conditions of prior evaporation should be carefully controlled.     

Optogalvanic signals generated in a neon positive column discharge by resonant chopped CW radiation at 588.2 nm

The optogalvanic line profile for the 1s₅?2p₂ transition (Paschen notation) in a neon positive column discharge has shown a change in sign as a function of dye laser power for a pressure of 1.5 Torr and small currents (2–20 mA). Rate equation analysis suggests this may be due to the increase in the 1s₃ metastable density.