Progress in high-energy-class diode laser pump sources

Abstract

A new generation of diode-pumped high-energy-class solid-state laser facilities is in development that generate multijoule pulse energies at around 10 Hz. Currently deployed quasi-continuous-wave (QCW) diode lasers deliver average inpulse pump powers of around 300 W per bar. Increased power-per-bar helps to reduce the system size, complexity and cost per Joule and the increased pump brilliance also enables more efficient operation of the solid state laser itself. It has been shown in recent studies, that optimized QCW diode laser bars centered at 940…980 nm can operate with an average in-pulse power of > 1000 W per bar, triple that of commercial sources. When operated at pulsed condition of 1 ms, 10 Hz, this corresponds to > 1 J/bar. We review here the status of these high-energy-class pump sources, showing how the highest powers are enabled by using long resonators (4…6 mm) for improved cooling and robustly passivated output facets for high reliability. Results are presented for prototype passively-cooled single bar assemblies and monolithic stacked QCW arrays. We confirm that 1 J/bar is sustained for fast-axis collimated stacks with a bar pitch of 1.7 mm, with narrow lateral far field angle (< 12° with 95% power) and spectral width (< 12 nm with 95% power). Such stacks are anticipated to enable Joule/bar pump densities to be used near-term in commercial high power diode laser systems. Finally, we briefly summarize the latest status of research into bars with higher efficiencies, including studies into operation at sub-zero temperatures (-70°C), which also enables higher powers and narrower far field and spectra.

Heading to 1 kW levels with laser bars of high-efficiency and emission wavelength around 880 nm and 940 nm

“…A further improvement of the WPE at high currents is expected from bars with increased fill-factor and also from bars operated at sub-zero temperatures like in [1][2][3]. …”

“…Therefore the epitaxial structure with low internal losses, with a strong carrier confinement at high currents, and with a low resistivity is the key for the kWperformance of the laser bar. Another approach to lower the operating temperature is operating of the laser bars under subzero temperatures of the heat-sink [2][3]. Moreover, operating power at kW-output power range require a passivation of the laser facets.…”

Phase measurement and far-field reconstruction on externally coupled laser diode arrays

“…Their high (electro-)optic conversion efficiencies in combination with a typically small footprint would make them an ideal competitor to established but comparatively bulky and inefficient high power systems. Nevertheless, upper limits to the feasible dimensions of LDs limit to either a good beam quality but moderate power [3] or vice versa [4]. While hybrid concepts have been developed [5], typical applications such as laser cutting demand for much higher output powers.…”

Long-Term Reliability of 915-nm Broad-Area Laser Diodes Under 20-W CW Operation

“…ECENTLY, high-power and high-efficiency 9xx-nm broad-area laser diodes (BA-LDs) have attracted much attention as pumping sources for fiber lasers, light sources for laser material processing [1]- [3]. These applications require higher output power and the long-term reliability for the BA-LDs.…”