Investigation of Spatial Chirp Induced by Misalignments in a Parallel Grating Pair Pulse Stretcher

Detrimental effects of period-chirped gratings in pulse compressors

We present a comprehensive simulative and experimental investigation of how period-chirped pulse compression gratings affect the compressed pulses. A specifically developed ray-tracing tool was used for the simulative investigations. It is shown that the chirp creates a characteristic spatio-spectral error pattern, which leads to a degradation of the beam quality and an increase of the pulse duration. The experimental investigations, for which both a narrow-bandwidth continuous-wave and a pulsed laser beam were guided through a Treacy-compressor comprised of period-chirped gratings, confirm the simulation results and present methods on how to identify the chirp's characteristic error pattern in practice.

Femtosecond laser induced damaging inside fused silica detected by a single-pulse ultrafast measurement system

The dynamics of damage inside the fused silica induced by a femtosecond laser has been characterized by a single-pulse ultrafast measurement system that is built upon the pump-probe mechanism. Our investigation disclosed the quantitative relationship between the size of the damaged area and the pulse energy. The dynamic measurement experiments showed that the radial size of the damaged area increased rapidly from 0 to 21 µm within ∼10 ps before stabilizing at 21 µm with the pulse energy of 1.1 mJ, which follows the rule of Boltzmann function. Moreover, we demonstrated that the structure inside the damaged area kept changing for about 200 ps before the formation of a double-void structure. The developed system alongside the proposed analysis method is expected to be of great importance in understanding the dynamics of laser-induced damage process in laser micromachining.

Diffraction based single pulse measurement of air ionization dynamics induced by femtosecond laser

A single pulse diffraction method to probe the plasma column evolution of the air ionization induced by the femtosecond laser pulse has been proposed. By utilizing a linearly chirped pulse as the probe light, the spatiotemporal evolution spectrum of the plasma column can be acquired in a single measurement. A method based on the Fresnel diffraction integral is proposed to extract the evolution of the phase shift after the probe light is crossing through the plasma column. Results show that the plasma expands rapidly within 7 ps due to the ionization, and then reaches a steady state with a diameter of about 80 μm with the pump pulse energy of 1 mJ. Furtherly, the temporal profile of the free electron density and the refractive index in the plasma region were determined using the corresponding physical models. The single-shot method can be expected to broaden the way for detecting the dynamics of the femtosecond laser-induced plasma.