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.
We will report experimental results on the coherent laser operation of a bar of broad area lasers. The array is 1 cm wide and consists of 25 lasers of 200 micrometer width each. Under normal conditions the lasers possess no mutual coupling and, therefore, emit incoherently. The resulting beam quality is correspondingly very low and typically more than 2000-fold diffraction-limited. To coherently couple the emitters we operate them in an external cavity. Inside the cavity a multiplexing and mutual coupling is achieved by means of a 16 level diffractive optic (DO) designed as a 1:25 beam splitter. We show that a stable phase-locked laser mode can build up inside the resonator. Its pronounced central angular emission lobe possesses a beam quality of approximately 60 times diffraction limit. In a passive setup, in which the internal dynamics of the broad area lasers can be suppressed by use of a seeding laser of good beam quality (M<SUP>2</SUP><2), the central emission lobe is better than five times diffraction-limited.
Current commercially available diode lasers with output powers above a few watts lack beam quality, i.e. they have only limited possibility of small foci in combination with long Rayleigh lengths. Recent advances in coherent coupling of such lasers open view to a new generation of high power, high beam quality, low cost lasers suitable for a wide range of technical applications such as microshaping or cutting. Therefore, we performed experiments to couple the 25 diode lasers of a bar with specially coated low-reflection front facets. Mutual coherence can be improved in external resonators as opposed to the internal resonator absent in our case. Additional elements like mode stops can improve beam quality. Here we present results on the coupling of gain- guided broad-area diode lasers in external resonators, both of single emitters and bars of 25 emitters. In the single emitter case we achieved output powers up to 0.8 W at a beam quality of M<SUP>2</SUP> equals 16 or 0.4 W with M<SUP>2</SUP> equals 3.5 along slow axis. For the bars we achieved 10 W with M<SUP>2</SUP> equals 304.
Current commercially available diode lasers with output powers above a few watts lack beam quality, i.e. the ability to be precisely focused. Recent advances in coherent coupling 1,2 of such lasers open view to a new generation of high power, high beam quality, low cost lasers suitable for a wide range of technical applications such as microshaping or cutting. Therefore, we couple bars of 25 diode lasers with total output powers of 25-40 Watts and specially coated lowreflection front facets. Mutual coherence is achieved in external resonators as opposed to the internal resonator absent in our case. Additional elements like mode stops can improve beam quality. Here we present results on the coupling of gain-guided broad-area diode lasers in external resonators, both of single emitters and bars of 25 emitters. Also numerical simulations concerning the mutual coherence of the single emitters have been performed.