Yield stress of 80 μm thick glass wafer chip diced with fs-laser μ-processing was investigated with varying the repetition
rate of laser pulse and scanning speed under constant number of shot. By using constant laser fluence, the yield stress is
almost invariant at lower repetition rate less than 20 kHz, but abruptly drops to the half of initial yield stress. Based on
the effect of the ambient gas on the transition point of yield stress changes, we propose an empirical relation between the
yield stress and cumulative stress caused by temperature increment with changing the laser repetition rate.
The temporal coupling of femtosecond and nanosecond laser induces a remarkable increase in the processing efficiency
12 times more than that with an independent laser exposure. When femtosecond laser arrives before nanosecond laser,
the dependence of the ablation efficiency on the time delay between the femtosecond and nanosecond laser pulses is very
resemble to nanosecond laser traces. When femtosecond laser arrives after nanosecond laser, however, we observed an
apparent delayed decaying component with a time constant of several hundreds of nanosecond in the ablation efficiency
curve. Based on the current observation, we have explained the rather large enhancement in femtosecond laser ablation
efficiency with synchronization between femtosecond and nanosecond laser in terms of silicon surface metallization due
to the proceeding nanosecond laser. Such a progress in femtosecond laser micro processing makes it possible to
maximize the processing speed and reduce the processing threshold energy. The current findings prominently reduce a
various high order nonlinear effects which are frequently confronted when we focus high-power femtosecond laser
pulses on the target under atmospheric conditions.
Terahertz transmission filters have been manufactured by perforating metal surface structures with various geometric shapes which all support near-unity transmission at specific frequencies determined by geometric shape, symmetry, polarization, and lattice constant. Our results show that the structures specifically designed by the shape resonance are extremely versatile, dependable, easy to control and easy to make the multifunctional filters.
We present that size of Ge nanoparticle can be controlled by changing the angle between ultrafast laser polarization and crystal axis using ultrafast laser irradiation. The nanoparticle size dependence on the laser polarization with respect to the Ge crystal axis exhibits a sinusoidal function with a minimum size at (100) axis. Moreover, the measurement of transient reflection reveals the presence of large anisotropies in both its amplitude and its relaxation dynamics with a minimum at (100) crystal axis. This implies that the observed anisotropic dependence of nanostructure size of Ge is followed by a different carrier density as well as its relaxation process depending on the orientation of Ge crystal axis only at near and above threshold fluence.