Nanosecond laser ablation of metals in gases observed by photoacoustic and imaging techniques

Abstract

Laser ablation of some metals in gases induced by nanosecond Nd:YAG laser has been studied by both photoacoustic and fast imaging techniques. Photoacoustic technique using piezoelectric polymer film revealed the change of coupling among laser radiation, ablated matter, plasma and target as a function of the laser fluence. Nanosecond imaging technique showed surface phenomena during and immediately after the ablating laser pulse.Photoacoustic signal intensity as a function of laser fluence was measured at constant pulse energy. It is constant at low fluence, starts to increase with fluence at certain threshold, reaches the maximum and then decreases gradually with increasing fluence. At fluence higher than about 7 J/cm2, there appeared jet-like plasma growing toward incident laser beam at velocities of as high as 1 o ms' in addition to the laser induced plume. The jet grew during the laser pulse and when the pulse terminated, its rapid growth stopped. At lower fluence, laser induced plasma expanding at about 1 O ms' was observed. The growth speed of the jet-like plasma depended on laser fluence and gas atmosphere but did not change for different metals.

Reconstruction of pulse noisy images via stochastic resonance

“…Their results suggest a general method of reconstructing images by seeding instability in nonlinear imaging systems. While, the nanosecond pulse images is widely used in optical processing 8 9 10 . Especially, in remote light detection and transmission, the nanosecond pulse images are usual low-level and relatively low repetition frequency.…”

Nonlinear restoration of pulse and high noisy images via stochastic resonance

“…As with other kinds of stochastic resonance, signal amplification occurs at the expense of the noise background, leading to reconstruction of the noise-hidden images 3 . Nowadays, the nanosecond pulse images have been widely used in optical processing and are usually low-level in remote light detection and transmission 7 8 9 10 . Considering the rapid development of the pulse images and their practical applications, it is urgent to investigate the stochastic resonance with a simple structure and flexible design, which will promote the detection sensitivity of weak and high noisy images.…”