In this paper, safety-related experiments with ultra-short laser pulses (down to 30 fs) on various components (goggles, curtains) for laser protection are presented. The damage and failure behaviour of protective devices has been investigated dependent on practical conditions such as pulse duration, laser fluence, pulse number, and repetition rate.
The effects of laser-irradiation on materials can be roughly divided into transient ones like laser-induced transmission (LIT) or short-lived colour centres and permanent damages like the stable colour centres and ablation. The former effects are particularly important for transparent devices like laser goggles.
To obtain a complete overview on laser safety issues and the prevention of failure there are two important fields of investigation:
1. the effects of laser radiation on human eyes and skin, and
2. on the possible protection materials.
Both fields have been addressed during the recently finished German project SAFEST (safety aspects in femtosecond technology). The amount of safety data available in the ultrashort pulse region has been increased remarkably. This allows for a re-evaluation of known laser protection materials for this region of pulse durations and for the evaluation of new designs that promise high protection levels while being light-weight and convenient to use.
The authors' research on the laser interaction with semiconductors, high-performance ceramics, oxides, and glasses with pulse durations of 30 fs and 130 fs is reviewed. Near-ablation threshold investigations were concerned with the generation of periodic nanostructures and their correlation with physico-chemical properties of the solid phase such as e.g. the material-dependent surface energy. Molecular dynamic modeling in the sub-picosecond time domain considered ultrafast opto-electronic processes triggering surface reorganization reactions. Fluid containment of solid interfaces showed strong influence on the resulting micro- and nanostructures due to its drastic reduction of the surface energy. The phenomena are discussed in respect to the minimization of the surface free energy in dependence of material composition and interfacial structure.
For the development of standard measurement procedures in optics characterization, comparative measurement campaigns (Round-robin experiments) are indispensable. Within the framework of the CHOCLAB project in the mid-90s, several international Round-robins were
successfully performed qualifying procedures for e. g. 1 on 1-LIDT, laser-calorimetry and total scattering. During the recent years, the demand for single pulse damage investigations has been overtaken by the more practically relevant S on 1-LIDT. In contrast to the
industrial needs, the comparability of the multiple-pulse LIDT has not been proven by Round-robin experiments up to now. As a consequence of the current research activities on the interaction of ultra-short pulses with matter as well as industrial applications, numerous fs-laser systems become available in universities and research institutes. Furthermore, special problems for damage testing may be expected because of the intrinsic effects connected with the interaction of ultrashort pulses with optical materials. Therefore, a Round-robin experiment on S on 1-damage testing
utilizing fs-pulses was conducted within the framework of the EUREKA-project CHOCLAB II. For this experiment, seven parties investigated different types of mirrors and windows. Most of the partners were guided by the International Standard ISO 11254-2, but one partner employed his own damage testing technique. In this presentation, the results of this comparative experiment are compiled demonstrating the problems induced by special effects of damage testing in the ultra-short pulse regime.