High energy laser applications of the future are the targets of diode laser research at Berlin’s Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, (FBH). Teams of scientists and technologists are working on what FBH calls “a new generation of ultra-high energy lasers,” adding in a statement, released this week, “These are tools for basic science, for novel medical applications and, not least, for laser-induced fusion.”

”Ultra-high power laser systems require diode lasers that are not just extremely capable, but also manufacturable at low costs in high volumes,” the R&D lab commented. “Specifically diode lasers bars in the wavelength range 930 to 970nm are the fundamental building blocks for pump sources for ytterbium-doped crystals in large laser facilities, wher optical pulses are generated with petawatt class peak energies and picosecond pulse widths. The individual laser bars in these pump sources have a typical output power between 300 and 500W.”

The FBH says it is currently optimizing both the necessary design and technology as a part of the Leibniz project “CryoLaser”. The FBH presented the latest results from CryoLaser at CLEO 2015, when it reported demo nstrating for the first time that a single 1cm laser bar can deliver at least 2kW of optical output power, when cooled to 203K (-70°C).

Paul Crump, who leads the FBH team that made the recent CLEO presentation, commented, “If the cost per photon is to fall, a higher optical power density must be generated, reducing the amount of material needed. The co nversion efficiency must also be dramatically improved for enhanced system efficiency. CryoLaser uses a novel design concept, developing innovative structures that are optimized for operation at 203K. The performance of diode lasers is substantially improved at these temperatures.”

Paul Crump: FBH team leader.

Technical specification

The latest work builds on advances in epitaxial design and packaging technology; FBH bars deliver output around 940nm at 203 K. This is said to be “a worldwide best achievement of 2 kW peak power per bar at a current of 2 kA, with a pulse width of 200μs and10 Hz repetition rate, correspo nding to a pulse energy of 0.4 J. Peak power is limited by the available current.

To date, such powers could o nly be achieved by combining the optical beams from at least four single bars. Co nversion efficiency was 65% at 1 kW output and 56% at 2 kW. Such bars have the potential to play an im portant role in future high-energy-class laser facilities. Currently, the FBH team is working to further increase the electro-optical co nversion efficiency of these bars.

The FBH is respo nsible for the full value chain within this development project, from design to co nstruction of first prototypes. The final pump sources are being e valuated for potential use in high-energy-class diode-pumped solid-state laser systems together with the world- leading groups in the field.