Near-Infrared Femtosecond Laser for Studying the Strain in Si1-xGex Alloy Films via Second-Harmonic Generation

The second-harmonic generation (SHG) from Si1-xGex alloy films has been investigated by near-infrared femtosecond laser. Recognized by s-out polarized SHG intensity versus rotational angle of sample, the crystal symmetry of the fully strained Si0.83Ge0.17 alloy is found changed from the O-h to the C-2 point group due to the inhomogeneity of the strain. Calibrated by double crystal X-ray diffraction, the strain-induced chi((2)) is estimated at 5.7 x 10(-7) esu. According to the analysis on p-in/s-out SHG, the strain-relaxed Si0.10Ge0.90 alloy film is confirmed to be not fully relaxed, and the remaining strain is quantitatively determined to be around 0.1%.

Decay dynamics of excited CS2 and NH3 investigated by femtosecond laser

By using the home-made femtosecond laser system and the time-of-flight mass spectrometer, the decay dynamics of excited carbon disulfide (CS2) and ammonia (NH3) are investigated in real time by pump-probe multiphoton ionization detection. The estimated lifetime constant of the NH3 (A) over tilde (1)A(2)' state (51+/-4 fs) agreed quite well with the literature report. For the first time, the decay lifetime constants of the NH3 (E) over tilde'(1)A(1)' state (937+/-93 fs), the CS2 (a) over tilde (3)A(2) state (153+/-10 fs), and the CS2 Rydberg state [(3)/(2)]6ssigma(g) ((3)Pi(g)) (948+/-23 fs) are obtained.

Interactions of a femtosecond intense laser with rare gas clusters in a dense jet\

A study on the interactions of high intensity (similar to 10(16) W/cm(2)) femtosecond laser pulses with rare gas clusters in a dense jet is performed. Energy absorption by Ar and Xe clusters is measured and it can be as high as 90%. Very energetic ions produced in the laser interaction with a dense cluster jet are detected by time-of-flight spectrometry and the maximum ion energy of Xe is up to 1.3 MeV. The average ion energies are found to increase with increasing cluster size and get saturated gradually. The average ion energies also show a strong directionality and the average ion energy in the direction parallel to the laser polarization vector is 40% higher than that perpendicular to it. The findings are discussed in terms of a model of charge-dependent ion acceleration.

Femtosecond pulse laser-induced self-organized nanostructures on the surface of ZnO crystal

This paper reports self-organized nanostructures observed on the surface of ZnO crystal after irradiation by a focused beam of a femtosecond Ti:sapphire laser with a repetition rate of 250 kHz. For a linearly polarized femtosecond laser, the periodic nanograting structure on the ablation crater surface was promoted. The period of self-organization structures is about 180 nm. The grating orientation is adjusted by the laser polarization direction. A long range Bragg-like grating is formed by moving the sample at a speed of 10 mu m/s. For a circularly polarized laser beam, uniform spherical nanoparticles were formed as a result of Coulomb explosion during the interaction of near-infrared laser with ZnO crystal.