A new mechanism of ultra-deep (up to tens of microns per pulse, sub-mm total hole depths) plasma-assisted ablative drilling of optically opaque and transparent materials by high-power nanosecond lasers proposed by <i>Kudryashov et al</i>. has been studied experimentally using average drilling rate and photoacoustic measurements. In the drilling experiments, average multi-micron crater depth per laser shot and instantaneous recoil pressure of ablated products have been measured as a function of laser energy at constant focusing conditions using optical transmission and contact photo acoustic techniques, respectively. Experimental results of this work support the theoretical explanation of the ultra-deep drilling mechanism as a number of stages including ultra-deep "non-thermal" energy delivery by a short-wavelength radiation of the surface high-temperature ablative plasma, bulk heating and melting of these materials, accompanied by the following subsurface boiling in the melt pool and resulting melt expulsion off of the target.
Femtosecond lasers show much promise as potential sources of choice in a number of laser micromachining applications, including semiconductors, photonics and biomedicine. Their ability for minimal damage and precise processing has been thoroughly researched for the past few years. One of the requirements for precise processing is high precision beam steering. Acousto-optic devices (AODs) are commonly used in laser direct writing systems to steer the beam with high precision and speed. However AODs cannot be applied for steering femtosecond laser beams, because, dispersion associated with acousto-optic interaction will cause serious spatial deformation on the writing spot. A detailed study of the AOD dispersion and the method to compensate this dispersion have been discussed in this paper.
A photomask is a high precision plate used in the lithographic process for the fabrication of microcomponents and it is an important prerequisite for microfabrication. A binary photomask is composed of tranasparent and opaque elements wich from one layer of a pattern. Photomasks are currently fabricated using lithographic process, which is complex and time consuming because of several steps involved in the fabrication process. In order to address this issue, a simple technique is reported in this paper which is a single-step process. The required pattern is transferred to mask blank by direct writing with femtosecond laser pulses without the aid of photoresist. The opaque layer of the mask blank is removed by femtosecond laser ablation. An acousto-optic device based non-mechanical scanning system immune to effects of vibration has been developed to scan the laser beam with high positional accuracy and scan speed. The applicability of this technique for microfabrication has been proved conclusively by fabricating microfeatures with the photomask fabricated by this technique.