Phase retrieval algorithm applied to high-energy ultrafast lasers.

A standardized phase retrieval algorithm is presented and applied to an industry-grade high-energy ultrashort pulsed laser to uncover its spatial phase distribution. We describe in detail how to modify the well-known algorithm in order to characterize particularly strong light sources from intensity measurements only. With complete information about the optical field of the unknown light source at hand, virtual back propagation can reveal weak points in the light path such as apertures or damaged components.

Measurement of stress-induced birefringence in a thin-disk laser with full-Stokes polarimetry.

Stress-induced birefringence leads to losses in solid-state laser resonators and amplifiers with polarized output beams. A model of stress-induced birefringence in thin disks is presented, as well as measurements of stress-induced birefringence in a thin disk in a multi-kilowatt oscillator. A full-Stokes imaging polarimeter was developed to enable fast and accurate polarimetric measurements. Experimental and simulated results are in good agreement qualitatively and quantitatively and show that the polarization loss due to stress-induced birefringence is negligible for ytterbium-doped thin disks with a thickness around 100 µm but becomes relevant in thicker disks. It is concluded that stress-induced birefringence should be taken into consideration when designing a thin-disk laser system.

Process monitoring based on plasma emission for power-modulated glass welding with bursts of subpicosecond laser pulses.

Defects and process irregularities influence the bonding strength and thus the stability and lifetime of welded glass components. The present paper proposes to monitor the laser-based glass welding process by means of a single photodetector that records the radiation emitted from the laser-induced plasma. It is shown that the plasma emission provides information about irregularities of the welded seam height, gap bridging, process interruptions, and the position of the seam. The method is suitable for different welded glass types.

Ultrafast thin-disk multi-pass amplifier system providing 1.9 kW of average output power and pulse energies in the 10 mJ range at 1 ps of pulse duration for glass-cleaving applications.

An ultrafast Yb-doped thin-disk multi-pass laser amplifier system with flexible parameters for material processing is reported. We can generate bursts consisting of four pulses at a distance of 20 ns and a total energy of 46.7 mJ at a repetition rate of 25 kHz. In single-pulse operation, 1.5 kW of average output is achieved at 400 kHz when optimizing for a beam quality of M2 = 1.5. Alignment for maximum output power provides 1.9 kW at the same repetition rate. All results are obtained without chirped-pulse amplification in the multi-pass set-up. The application potential of the system is demonstrated exploring its performance in materials processing of dielectrics. Cleaving of 3.8-mm-thick SCHOTT borofloat glass with a velocity of 1200 mm/s is demonstrated with 300 W of input power. Single-pass modification of 30 mm borosilicate glass is enabled with a Bessel beam at 1 kW of average power delivered by four-pulse bursts of an energy of 30 mJ.