Christian Jonin

Comparison of heat-affected zones due to nanosecond and femtosecond laser pulses using transmission electronic microscopy

This letter presents a method aimed at quantifying the dimensions of the heat-affected zone (HAZ), produced during nanosecond and femtosecond laser–matter interactions. According to this method, 0.1 μm thick Al samples were microdrilled and observed by a transmission electronic microscopy technique. The holes were produced at laser fluences above the ablation threshold in both nanosecond and femtosecond regimes (i.e., 5 and 2 J/cm2, respectively). The grain size in the samples was observed near the microholes. The main conclusion is that a 40 μm wide HAZ is induced by the nanosecond pulses, whereas the femtosecond regime does not produce any observable HAZ. It turns out that the width of the femtosecond HAZ is less than 2 μm, which is our observation limit.

High UV average power at 15 kHz by frequency doubling of a copper HyBrID vapor laser in β-barium borate

Abstract Second harmonic generation of a copper HyBrID laser oscillator was performed at 15 kHz. 5.1 W UV (255 nm) total average power at 15 kHz were generated in two β-barium borate (BBO) crystals by frequency doubling of two 511 nm beams from a single unpolarized HyBrID copper vapor laser. The beam quality factors of the UV emission are found to be M X 2 =30±2 and M Y 2 =24±2. These two UV beams, combined at the focal point of a focusing objective, may enable high repetition rate UV laser processing.

Micromachining with high-repetition-rate femtosecond laser sources

Ultrashort duration laser sources are considered as a promising tool for new micromachining applications: precise microdrilling and microcutting on various materials. As an illustration of the non thermal micromachining, we also paid attention to precious wood. Cutting is achieved without burning, and the cut surface remains undamaged. However, until now, only low-average-power sources are available. An average power level of 10 W appears to be the lowest limit for this type of laser to really become industrial. We are presently developing such a source based on the use of a 15kHz, 100W copper HyBrID laser as a pump laser. Thus, we intend to reach in a near future a typical drilling rate of one mm per second, for instance, in stainless steel compared with a 50 microns per second drilling rate obtained with presently available kHz and low-average-power sources. Micromachining obtained with out a 1 kHz source will be presented and discussed.