Laser diode advances enable performance and cost breakthroughs for high-power lasers.
Petawatt (1015 or one quadrillion watts) lasers are used by large research facilities for the exploration of a multitude of cutting-edge scientific investigations. Potential commercial applications for these extremely high-powered lasers span across several different industries:
- Cancer treatment—particle accelerators can enable promising high-energy proton beam cancer therapy, but the size and cost of these facilities present a significant barrier.
- Novel imaging technologies—novel techniques like ultrafast spectroscopy could allow for new insights in a wide variety of research, including high energy density science, planetary science, and astrophysics.
- Fusion energy—power generation that uses abundant fuel supplies with zero greenhouse gas emissions or radioactive waste.
While petawatt lasers may offer the key to important research in fields that benefit mankind, challenging barriers to accessibility exist. Most of today’s petawatt laser systems are powered with flashlamps and operate at very low pulse repetition rates. These systems can occupy entire buildings, with operational costs prohibitive for many applications. New capabilities in high-efficiency laser diodes could introduce a paradigm shift by making them more compact, reliable, and capable of running at much higher repetition rates, such as tens of shots per second, expanding the practical applications in medical and science fields.
Traditional Designs & Challenges
Regardless of the system design and implementation, all current methods rely on stretching the pulses of a relatively low-power ultrafast seed laser, then amplifying and recompressing the pulse to attain the desired petawatt peak power levels. Traditional designs often rely on flashlamps to power the pump lasers or amplifier stages. Flash lamps’ spectrally broadband output results in lost energy as waste heat. Designing for the removal or dissipation of this excessive heat impacts system design, and operating cost, and effectively caps the repetition rate.
Major advances have resulted from Lawrence Livermore National Lab (LLNL)’s collaboration with the European Union’s Extreme Light Infrastructure (ELI) Beamlines in the development of the High-Repetition-Rate Advanced Petawatt Laser System.
The HAPLS design goal was to produce petawatt pulses with an energy of ≥30 J and pulse widths of <30 fs at a 10 Hz repetition rate. Numerous innovations in lasers and control systems would be necessary to achieve what, at the time, was unprecedented performance.
Leonardo semiconductor pump laser diodes are at the core of HAPLS’ breakthrough advances:
- Higher output power is achieved through innovations in coating and facet passivation of the epitaxial structure. These process improvements alone exceeded the HAPLS design specifications, consistently achieving over 1.5 kW per bar.
- Addressing pitch (how closely the laser diode bars can be packed together) increases brightness while reducing the traditional tradeoff between brightness, performance, and lifetime.
The final design of the laser diode bars used for HAPLS pump modules broke a world record for brightness. What’s next for this technology?