Novel High-Power, High Repetition Rate Laser Diode Pump Modules Suitable for High-Energy Class Laser Facilities

• Main Authors: Marko Hübner, Ingo Will, Jörg Körner, Jürgen Reiter, Mathias Lenski, Johannes Tümmler, Joachim Hein, Bernd Eppich, Arnim Ginolas, Paul Crump
• Format: Article
• Language: English
• Published: MDPI AG 2019-07-01
• Series: Instruments
• Subjects: diode laser; diode stacks; 100 Hz pumping; high duty cycle; fibre coupled; EuPRAXIA
• Online Access: https://www.mdpi.com/2410-390X/3/3/34

The latest generation of high-energy-class pulsed laser facilities, under construction or planned, such as EuPRAXIA, require reliable pump sources with high power (many kW), brightness (>1 MW/cm²/sr) and electro-optical conversion efficiency (>50%). These new facilities will be operated at high repetition rates (around 100 Hz) and only diode lasers are capable of delivering the necessary performance. Commercial (quasi-continuous wave, QCW) diode laser pulse-pump sources are, however, constructed as low-cost passively cooled stacked arrays that are limited either in brightness, efficiency or repetition rate. Commercial continuous wave diode laser pumps constructed using microchannel coolers (as used in high-value industrial machine tools) can fulfil all requirements, but are typically not preferred, due to their cost and complexity and the challenges of preventing cooler degradation. A custom solution is shown here to fill this gap, using advanced diode lasers in a novel passive side-cooling geometry to realize 100 … 200 Hz pump modules (10%−20% duty cycle) that emit peak power of 6 kW at wavelength = 940 nm. The latest performance of these modules is summarized and compared to literature. We show that a brightness >1 MW/cm²/sr can be efficiently delivered across a wide range of laser pulse conditions with 10% duty cycle (pulse width: 100 µs … 100 ms … cw, repetition rate up to 1 kHz). Furthermore, we describe how these pumps have been used to construct and reliably operate (>10⁹ pulses without degradation) in high-energy-class regenerative and ring amplifiers at the Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie (MBI). We also show first results on 100 Hz pumping of cryogenically cooled solid-state Yb:YAG slab amplifiers, as anticipated for use in the EuPRAXIA laser, and note that peak temperature is disproportionately increased, indicating that improved cooling and more detailed studies are needed.