Transversely Excited Atmospheric-pressure CO2 Laser Research Articles

Design of a New Diffractive Optical Element for Flattening the Gaussian High-Repetition-Rate Transversely Excited Atmospheric-Pressure CO2 Laser Beam Using an Iterative Angular Spectrum Algorithm through MATLAB

The editorial board announced this article has been retracted on December 21, 2012. If you have any further question, please contact us at: mas@ccsenet.org Article Title: Design of a New Diffractive Optical Element for Flattening the Gaussian High-Repetition-Rate Transversely Excited Atmospheric-Pressure CO2 Laser Beam Using an Iterative Angular Spectrum Algorithm through MATLAB Author/s: Alireza Heidari, Mehrnoosh Zeinalkhani, Abolhasan Nabatchian, Mohammad Amin Zare Soltani, Tahere Godarzvand Chegini, Mohammadreza Seifi Aghdam Malakabad & Mohammadali Ghorbani Journal Title: Modern Applied Science ISSN 1913-1844 (Print) E-ISSN 1913-1852 Volume and Number: Vol. 6, No. 5, 2012 Pages: 82-90 DOI: 10.5539/mas.v6n5p82 Mr. Mohammadali Ghorbani (Corresponding Author) formally apologizes to his dear and respected colleagues and journal editorial board. He gave deceiving them and got abuse their names, brilliant academic records, and reputations. His dear and respected colleagues have no knowledge or fault. He is a legal and moral responsibility to get this problem.

Excitation Mechanism of H, He, C, and F Atoms in Metal-Assisted Atmospheric Helium Gas Plasma Induced by Transversely Excited Atmospheric-Pressure CO2Laser Bombardment

To clarify the excitation mechanism of hydrogen in transversely excited atmospheric-pressure (TEA) CO2 laser-induced helium gas plasma, atomic emission characteristics of H, C, F, and He were studied using a Teflon sheet (thickness of 2 mm) attached to a metal subtarget. The TEA CO2 laser (750 mJ, 200 ns) was focused on the Teflon sheet in the surrounding He gas at 1 atm. Atomic emissions of H, C, F, and He occurred with a long lifetime, a narrow spectrum width, and a low-background spectrum. The correlation emission intensity curves of H–He and F–He indicated a parabolic functions. To explain the emission characteristics, we offered a model in which helium metastable atoms (He*) play an important role in the excitation processes; namely, atoms collide with helium metastable atoms (He*) to be ionized by the Penning effect, and then recombine with electrons to produce excited states, from which atomic emissions occur.

Excitation Mechanism of H, He, C, and F Atoms in Metal-Assisted Atmospheric Helium Gas Plasma Induced by Transversely Excited Atmospheric-Pressure CO2 Laser Bombardment

To clarify the excitation mechanism of hydrogen in transversely excited atmospheric-pressure (TEA) CO2 laser-induced helium gas plasma, atomic emission characteristics of H, C, F, and He were studied using a Teflon sheet (thickness of 2 mm) attached to a metal subtarget. The TEA CO2 laser (750 mJ, 200 ns) was focused on the Teflon sheet in the surrounding He gas at 1 atm. Atomic emissions of H, C, F, and He occurred with a long lifetime, a narrow spectrum width, and a low-background spectrum. The correlation emission intensity curves of H–He and F–He indicated a parabolic functions. To explain the emission characteristics, we offered a model in which helium metastable atoms (He*) play an important role in the excitation processes; namely, atoms collide with helium metastable atoms (He*) to be ionized by the Penning effect, and then recombine with electrons to produce excited states, from which atomic emissions occur.

Detecting excess ionizing radiation by electromagnetic breakdown of air

A scheme is proposed for detecting a concealed source of ionizing radiation by observing the occurrence of breakdown in atmospheric air by an electromagnetic wave whose electric field surpasses the breakdown field in a limited volume. The volume is chosen to be smaller than the reciprocal of the naturally occurring concentration of free electrons. The pulse duration of the electromagnetic wave must exceed the avalanche breakdown time (10–200 ns) and could profitably be as long as the statistical lag time in ambient air (typically, microseconds). Candidate pulsed electromagnetic sources over a wavelength range, 3 mm>λ>10.6 μm, are evaluated. Suitable candidate sources are found to be a 670 GHz gyrotron oscillator with 200 kW, 10 μs output pulses and a Transversely Excited Atmospheric-Pressure (TEA) CO2 laser with 30 MW, 100 ns output pulses. A system based on 670 GHz gyrotron would have superior sensitivity. A system based on the TEA CO2 laser could have a longer range >100 m.

A novel double-pulse laser plasma spectroscopic technique for H analysis in metal samples utilizing transversely excited atmospheric-pressure CO2 laser-induced metastable He atoms

The analysis of hydrogen in a metal sample (zircaloy-4), which is usually difficult to perform using conventional laser-induced breakdown spectroscopy (LIBS) techniques, has been achieved using a double-pulse technique under He gas at atmospheric pressure. In this technique, a transversely excited atmospheric-pressure (TEA) CO2 laser (1.5 J, 200 ns) was focused onto the metal surface to induce a strong He gas plasma whilst simultaneously focussing a Nd-doped yttrium aluminum garnet (Nd:YAG) laser (120 mJ, 8 ns), synchronized with the TEA CO2 laser, onto the metal to ablate atoms into the resulting He gas plasma. The emission spectrum obtained shows a narrow H linewidth with low background intensity and long lifetime emission, thereby indicating that excitation takes place via metastable He atoms. The H emission from H2O can be suppressed by a careful pretreatment involving heating the sample in a vacuum chamber.

New Method of Laser Plasma Spectroscopy for Metal Samples Using Metastable He Atoms Induced by Transversely Excited Atmospheric-Pressure CO2 Laser in He Gas at 1 atm

A high-power transversely excited atmospheric-pressure (TEA) CO2 laser (600–1500 mJ) was focused on a metal target in surrounding He gas at 1 atm to produce strong He gas breakdown plasma, while leaving the metal surface undamaged, and a Q-switched Nd:YAG laser (60–90 mJ) was also simultaneously focused on the metal surface to be ablated at a slightly shifted spot position with various delay times (0–150 µs) relative to the TEA CO2 laser. It was concluded that the ablated atoms from the metal sample enter the He gas plasma region and are excited by metastable He atoms, which are produced in very large quantities in the He gas plasma region. Due to the fact that He gas plasma works as an exciting source with a very long lifetime (about 100 µs), the detected atomic emission lines are very narrow in spectral width with a very low background spectrum, and also the atomic emission spectrum profile does not follow the Boltzmann distribution during the long emission life. We call this new method LIPS-He*. This new method has high potential for realizing in situ high-sensitivity analysis.

Reflection and Diffraction of Laser Plasma Induced by Bombardment of TEA CO2 Laser at Low Pressures

A transversely excited atmospheric-pressure (TEA) CO2 laser beam has been focused on a Zn plate at reduced ambient gas pressure. It is demonstrated that reflection and diffraction phenomena take place in the laser plasma when the free expansion of the laser plasma is limited by an obstructing material placed in front of the target. These findings strongly support the shock wave model for explaining the mechanism in forming a laser plasma.