Buffer gas

About: Buffer gas is a research topic. Over the lifetime, 3565 publications have been published within this topic receiving 47283 citations.

Radiation trapping of the Hg 185 nm resonance line

Abstract: The decay rate of the Hg 61P1 level was measured as a function of cold spot temperature (Hg density) and buffer gas pressure in cylindrical, sealed fused silica cells. The decay rates were obtained using a time-resolved laser-induced 185 nm fluorescence experiment with multi-step excitation. Cold spot temperatures from 25 to 100 °C were studied. The Hg densities for this temperature range and with no buffer gas yield the lowest possible decay rates due to radiation trapping with partial frequency redistribution. Decay rates with argon buffer gas pressures of 3 and 30 Torr were also studied. The results are in agreement with published data from a discharge afterglow experiment. Monte Carlo simulations of radiation transport in the cells, including the effects of hyperfine and isotope structure, the effects of foreign gas broadening, and partial frequency redistribution are compared to the experimental data. Reasonably good agreement is obtained, however there is evidence of quenching of Hg 61P1 atoms in co...

A parametric study of single-wall carbon nanotube growth by laser ablation

Abstract: Results of a parametric study of carbon nanotube production by the double-pulse laser oven process are presented. The effect of various operating parameters on the production of single-wall carbon nanotubes (SWCNTs) is estimated by characterizing the nanotube material using analytical techniques, including scanning electron microscopy, transmission electron microscopy, thermo gravimetric analysis and Raman spectroscopy. The study included changing the sequence of the laser pulses, laser energy, pulse separation, type of buffer gas used, operating pressure, flow rate, inner tube diameter, as well as its material, and oven temperature. It was found that the material quality and quantity improve with deviation from normal operation parameters such as laser energy density higher than 1.5 J/cm2, pressure lower than 67 kPa, and flow rates higher than 100 sccm. Use of helium produced mainly small diameter tubes and a lower yield. The diameter of SWCNTs decreases with decreasing oven temperature and lower flow rates.

Design and performance of a 20 watt copper vapour laser

Abstract: The design of a simple discharge-heated copper vapour laser (DHCVL) is presented and its output characteristics studied. An auxiliary power supply is used to precondition the discharge tube so as to eliminate the possibility of thyratron damage. The laser gives an average power of 20 W at a repetition rate of 5 kHz. Helium was used as the buffer gas.

Purification of laser gases

Abstract: Purification of the gas mixture used in an excimer laser is carried out by cooling such mixture in a cryogenic trap to a temperature that is low enough that the lasting gas or gases (e.g. krypton, xenon, fluorine, hydrogen chloride) and the impurities are all substantially fully condensed. This temperature is nevertheless sufficiently high that the buffer gas (neon or helium or a mixture thereof) remains substantially all in gaseous form. The trap is then isolated from the laser vessel and the condensed gases therein are treated to remove at least the condensed impurities from the system. In a xenon chloride laser the condensed impurities can be effectively separated from the condensed laser gases by heating, i.e. differential distillation. After this has been done, the laser gases are returned to the laser vessel. In those instances in which such separation by differential distillation is not practicable, e.g. a krypton fluoride laser, some or all of the condensed lasing gas or gases is removed from the system together with the condensed impurities. Fresh charges of these lasing gases are then supplied to the laser vessel as required. The procedure is characterized by the fact that the buffer gas is retained and reused indefinitely. The method avoids the expense of having to periodically recharge the laser vessel with an entire fill of fresh buffer and lasing gases.

Cold Collisions of O 2 with Helium

Abstract: Collision cross sections between oxygen molecules and helium atoms are computed at translational energies between 0.1 K and 10.0 K, motivated by the recently demonstrated cooling of molecules by a helium buffer gas. Detailed calculations based on a rigid-rotor model demonstrate the differences among various isotopic combinations of oxygen atoms and also serve to illustrate resonant features unique to cold molecules. Comparisons of elastic versus spin-changing inelastic collision rates suggest that buffer-gas cooling is likely to be a widely applicable tool for producing cold molecular samples.