Shibing Liu

Two-dimensional periodic structure induced by single-beam femtosecond laser pulses irradiating titanium.

A novel two-dimensional (2-D) periodic structure on the ablated hole wall is formed by using the method of single-beam femtosecond laser pulses irradiating a titanium target. This 2-D structure on the ablated surface, after consecutive irradiation of 10000 pulses, presents different spatial periods which characters a 1500 nm period along the hole wall in the vertical direction and a 400 nm period in the azimuthal direction of the hole. The reported experimental results can be well interpreted by a prophetic theoretical model of Bonch-Bruevich (A. M. Bonch-Bruevich et al., Opt. Eng. 31, 718 (1992)).

Electromagnetic field quantization in an anisotropic absorbing medium

In this paper, we extend the Langevin noise (LN) scheme to an anisotropic medium which shows loss and dispersion. And the results are compared with previous work.

Quantum theory of Cherenkov radiation in an anisotropic absorbing media

A fully quantum mechanical treatment is presented for the Cherenkov radiation stimulated by a uniformly moving charge particle in both isotopic medium and anisotropic medium. The relation between Cherenkov radiation intensity and dielectric tensor is analyzed, and the result is compared with previous work.

Influence of femtosecond laser pulse energy on the surface reflection of black silicon in alkaline solution

A highly efficient approach for reducing the reflection of the black silicon surface is demonstrated, in which the black silicon is fabricated in alkaline solution via a femtosecond laser irradiation. The junglelike microstructures are formed on the surface of the black silicon. Compared to the polished silicon, the black silicon can significantly suppress the surface reflection. Throughout the region of visible light, the average minimum reflectance of the blackened surface is about 5.6%. Meanwhile, in order to get an optimal laser energy, we investigated the evolution on silicon surface as a function of incident pulse energy. Taking into account the height of junglelike microstructures and the reflectance of black silicon samples, the optimal laser energy is 1400 μJ. By choosing the right laser energy, it is possible to fabricate the highly absorptive black silicon. These results are of extreme importance in the control of surface morphology and the modification of material surface.

Structuring features of micro- and nano-ripples induced by oblique incident linear polarized femtosecond laser irradiating metal surface

The periodic ripple structures with micro- and nano-scales on the metal surface are fabricated experimentally by using an oblique incident linear polarized femtosecond laser pulses with 800nm wavelength. The structuring features show a material difference in the s- and p-polarized laser irradiations. Besides the ripples are perpendicular to the polarized direction of applied laser, in the p-polarized laser irradiation the interspace between ripples increases with the incident angle when it exceeds a threshold angle, and differently the interspace is unaltered with the incident angle in the s-polarized laser irradiation. Especially, when the incident angle is larger than the threshold angle, the spacial structured cycle (SSC) is larger than the wavelength of incident lase. Meanwhile, with the incident fluence increasing, the threshold is become small.The periodic ripple structures with micro- and nano-scales on the metal surface are fabricated experimentally by using an oblique incident linear polarized femtosecond laser pulses with 800nm wavelength. The structuring features show a material difference in the s- and p-polarized laser irradiations. Besides the ripples are perpendicular to the polarized direction of applied laser, in the p-polarized laser irradiation the interspace between ripples increases with the incident angle when it exceeds a threshold angle, and differently the interspace is unaltered with the incident angle in the s-polarized laser irradiation. Especially, when the incident angle is larger than the threshold angle, the spacial structured cycle (SSC) is larger than the wavelength of incident lase. Meanwhile, with the incident fluence increasing, the threshold is become small.

Study on ultrafast imaging of silicon surface ablated by a single nanosecond laser pulse

We present a technology of ultrafast imaging using femtosecond laser as probe light and ICCD camera as imaging instrument. And we obtained time-resolved ICCD images of a single nanosecond laser pulse (30 ns laser pulse with a wave length of 1064 nm) ablation of silicon surface taking advantage of this technology. This research shows that when a single nanosecond laser pulse was focused onto the silicon target, it induced plasma firstly. The produced plasma was very much and its propagation was very fast at first. And when the nanosecond laser pulse passed, the amount and propagation of the plasma didn’t increase any more until it disappeared.We present a technology of ultrafast imaging using femtosecond laser as probe light and ICCD camera as imaging instrument. And we obtained time-resolved ICCD images of a single nanosecond laser pulse (30 ns laser pulse with a wave length of 1064 nm) ablation of silicon surface taking advantage of this technology. This research shows that when a single nanosecond laser pulse was focused onto the silicon target, it induced plasma firstly. The produced plasma was very much and its propagation was very fast at first. And when the nanosecond laser pulse passed, the amount and propagation of the plasma didn’t increase any more until it disappeared.

QUANTUM THEORY OF RADIATION IN LASER PLASMA

Based on the Langevin noise approach, a full quantum theory of radiation in laser plasma is explored, where the laser intensity is limited to the range of 1010 W/cm2 to 1012 W/cm2 and the plasma is considered as a homogeneous dielectric background. By numerical calculation, the results show that the radiation is generated from the resonance of the plasma and the emitted rate of photons depends on the angular relation between the directions of radiation fields and the motion of the unbounded free electrons. In addition, the photons are more easily created under the lower collision frequency.