Innovation in diode laser design and technology, assembly techniques and optical design are used to realize high-brightness pump modules for application in pumping of fiber lasers. In a first demonstration, monolithically grating-stabilized diode lasers with wavelength around 970 nm are integrated into prototype modules that deliver 500 W of continuous wave TE-polarized optical power at a conversion efficiency ⪆ 55% within a spectral width of 1.2 nm (95% power) in a narrow beam, suitable for low-loss coupling into a 200-µm core fiber. An especially simple opto-mechanical configuration is developed, without need for external volume Bragg gratings.
The performance characteristics of two stack modules (emitting near 780 nm) each consisting of 24 wide-aperture (1200 μm) diode laser chips is presented and the results are discussed. The stack modules are constructed using diode lasers from two different epitaxial design iterations. Compared to the first iteration, the second iteration was optimized for higher conversion efficiency and optical in-pulse power (lower losses), without compromising the beam characteristics. The stack modules make use of an established (field-proven) FBH design that utilizes innovative edge-cooling of both sides of the diode stack with large-channel (micro-channel free), water-cooled, thermally-expansion-matched heatsinks. We investigate here their performance up to high duty cycles and results for pulse width up to 10 ms at high duty cycle (50 %) operation is presented. Test of the completed modules show that the iteration 2 (power-optimized) chips deliver about 15 % more optical power without compromising the beam propagation ratio. Specifically, the stack module with first iteration chips delivers approx. 1.4 kW whereas the stack module with the optimized chips delivers approx. 1.6 kW. For the stack module that uses the first chip iteration a fiber coupling to a 1 mm core fiber was demonstrated with approx. 90 % coupling efficiency and loss channels are discussed. Finally, very high duty cycle operation (50 %) is demonstrated for the first time, using an iteration 1 stack module.
Mid-infrared (MIR) solid state lasers based on thulium and holmium-doped crystals are of increasing interest in applications in medicine, material processing and particle physics. Thulium-doped lasers can be efficiently pumped at wavelengths around 780 nm and diode laser pumps with high conversion efficiency and high intensity are sought at this wavelength. Diode lasers integrated in laser stacks suitable for high duty cycle pumping are of particular interest for high energy class applications, especially when realizable without need for the additional cost and reliability hazard of microchannel cooling. However, high efficiency and reliable power is more challenging to realize at 780 nm than around 940…980 nm, due to limitations on the capability of the available semiconductor materials. Progress is therefore presented here in the design, realization and test of 780 nm pump sources suitable for high energy class pump applications, using GaAs-based TM-polarized diode lasers. We show how power per device can be increased from 4 W for conventional single emitters (90…100 μm) up to 60 W at high duty cycle (10%) and long pulse length (10 ms) for high brightness large aperture emitters (with 1200 μm aperture, equivalent to around 500 W per bar), at the cost of reduced operating efficiency (from 60 to 50%). We show progress in integrating these large aperture emitters into novel passively (macro-channel) edge-cooled stacks, that are then suitable for use in pumping high energy class Th:YAG laser systems.
Progress is presented on ongoing research and development into ultra-high power and efficiency bars that achieve significantly higher useful optical output power and higher brightness than are currently commercially available. In previous work (2017), the authors reported on bars that deliver over 1 kW continuous wave (cw) diode laser power, when cooled using 15°C water. Our current studies are focused on increasing the usable output power (power within a targeted beam angle), which is essential for real world industrial applications. These ongoing studies have enabled the first demonstration of 500 W cw output power from a 10 mm x 6 mm laser diode bar with a lateral far field angle of only 8°. In efforts to further improve brightness, we also present our latest progress on high power SMEBs (Single Mode Emitter Bars). These emitters operate in a close to diffraction limited optical mode (M² < 1.5, laterally and vertically). This new technology enables a significant increase in Diode Laser brightness. We demonstrate in excess of 55% electro optical efficiency at > 200 W cw laser bar power for SMEBs.
de lasers are key components in material processing laser systems. While mostly used as pump sources for solid state or fiber lasers, direct diode laser systems using dense wavelength multiplexing have come on the market in recent years. These systems are realized with broad area lasers typically, resulting in beam quality inferior to disk or fiber lasers. We will present recent results of highly efficient ridge waveguide (RW) lasers, developed for dense-wavelength-beamcombining (DWBC) laser systems expecting beam qualities comparable to solid state laser systems and higher power conversion efficiencies (PCE).
The newly developed RW lasers are based on vertical structures with an extreme double asymmetric large optical cavity. Besides a low vertical divergence these structures are suitable for RW-lasers with (10 μm) broad ridges, emitting in a single mode with a good beam quality. The large stripe width enables a lateral divergence below 10° (95 % power content) and a high PCE by a comparably low series resistance. We present results of single emitters and small test arrays under different external feedback conditions. Single emitters can be tuned from 950 nm to 975 nm and reach 1 W optical power with more than 55 % PCE and a beam quality of M2 < 2 over the full wavelength range. The spectral width is below 30 pm FWHM. 5 emitter arrays were stabilized using the same setup. Up to now we reached 3 W optical power, limited by power supply, with 5 narrow spectral lines.
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