[Research on the dynamics of ion debris from Sn plasma by use of dual laser pulses].

Extreme ultraviolet lithography is one of the most promising technologies on the next generation of high-capacity integrated circuit manufacturing. However, techniques for ion debris mitigation have to be considered in the application of extreme ultraviolet source for lithography. In our paper the dynamics of ion debris from Sn plasma by using dual ns laser pulses were investigated. The results show that debris from plasma greatly depends on the energy of pre-pulse and the delay time between the two laser pulses. The energy of Sn ions debris was efficiently mitigated from 2. 47 to 0. 40 keV in the case of dual laser pulses, up to 6. 1 times lower than that by using single laser pulse. We also found that Sn ions debris can be mitigated at all angles by using the dual laser pulses method.

[The LIBS experiment condition optimization of alloy steel].

Laser induced plasma spectroscopy of alloy steel was produced by Nd : YAG pulsed laser at 1 064 nm, and the spectral signal was detected by high resolution and width controlled ICCD. Several Fe atomic spectral lines such as 404.581, 414.387, 427.176 and 438.355 nm were chosen for analysis, and the effects of different experimental parameters on LIBS spectral signal intensity were investigated. It is shown that the experimental parameters such as pulse energy, laser focus location and laser delay time have great influence on the LIBS signal. LIBS signals with high spectral intensity and signal-background ratio (SBR) as well as the optimum experiment conditions were obtained by optimizing these experiment parameters so as to make composition analysis of the alloy steel.

PCF-based cavity enhanced spectroscopic sensors for simultaneous multicomponent trace gas analysis.

A multiwavelength, multicomponent CRDS gas sensor operating on the basis of a compact photonic crystal fibre supercontinuum light source has been constructed. It features a simple design encompassing one radiation source, one cavity and one detection unit (a spectrograph with a fitted ICCD camera) that are common for all wavelengths. Multicomponent detection capability of the device is demonstrated by simultaneous measurements of the absorption spectra of molecular oxygen (spin-forbidden b-X branch) and water vapor (polyads 4v, 4v + δ) in ambient atmospheric air. Issues related to multimodal cavity excitation, as well as to obtaining the best signal-to-noise ratio are discussed together with methods for their practical resolution based on operating the cavity in a "quasi continuum" mode and setting long camera gate widths, respectively. A comprehensive review of multiwavelength CRDS techniques is also given.

Triggering and guiding HV discharge in air by filamentation of single and dual fs pulses.

The triggering and guiding of the stationary high voltage (HV) discharges at 5-40 kV are demonstrated by using plasma filaments generated by single and dual femtosecond(fs) laser pulses in air. A significant reduction of the breakdown voltage threshold due to the pre-ionization of the air gap by laser pulse filamentaion was observed. The amount of free electrons of filaments generated by different pulse configurations was compared by sonography method. The lifetime of filaments is measured by using time-resolved fluorescence spectrum, and the lifetime of filaments generated by dual fs laser pulses was doubled due to the re-ionization by the succeeding pulse. The triggering ability of dual fs laser pulses was demonstrated to be enhanced due to the longer lifetime of filaments.

Revival of femtosecond laser plasma filaments in air by a nanosecond laser.

Short lived plasma channels generated through filamentation of femtosecond laser pulses in air can be revived after several milliseconds by a delayed nanosecond pulse. Electrons initially ionized from oxygen molecules and subsequently captured by neutral oxygen molecules provide the long-lived reservoir of low affinity allowing this process. A Bessel-like nanosecond-duration laser beam can easily detach these weakly bound electrons and multiply them in an avalanche process. We have experimentally demonstrated such revivals over a channel length of 50 cm by focusing the nanosecond laser with an axicon.

Optimization of multiple filamentation of femtosecond laser pulses in air using a pinhole.

The robustness and prolongation of multiple filamentation (MF) for femtosecond laser propagation in air are investigated experimentally and numerically. It is shown that the number, pattern, propagation distance, and spatial stability of MF can be controlled by a variable-aperture on-axis pinhole. The random MF pattern can be optimized to a deterministic pattern. In our numerical simulations, we configured double filaments to principlly simulate the experimental MF interactions. It is experimentally and numerically demonstrated that the pinhole can reduce the modulational instability of MF and is favorable for a more stable MF evolution.

Spatial evolution of multiple filaments in air induced by femtosecond laser pulses.

The spatial evolution of plasma filaments in air induced by femtosecond laser pulses is investigated experimentally. Several major filaments and small scaled additional filaments are detected in the plasma channel. The complicated interaction process of filaments as splitting, fusion and spreading is observed. The major filaments propagate stably, and the small scaled additional filaments can be attracted to the major filaments and merged with them. The major filaments are formed due to the perturbation of initial beam profile and the small scaled filaments are mainly caused by the transverse modulational instability.

Paper airplane propelled by laser plasma channels generated by femtosecond laser pulses in air.

A long plasma channel, formed due to the dynamic balance between the nonlinear self-focusing and the plasma defocusing in the propagation of intense femtosecond laser pulses in air, is demonstrated to be able to continuously propel a paper airplane without complicated focusing optics. The maximum coupling coefficient generated by the plasma channel is found to be more than 8.5 dyne/W. In the plasma channel, the detonation wave generation with the air ionization is found to be the propulsive source.