R. Staske

Bio: R. Staske is an academic researcher from Leibniz Association. The author has contributed to research in topics: Laser & Energy conversion efficiency. The author has an hindex of 3, co-authored 5 publications receiving 193 citations.

Efficient High-Power Laser Diodes

Abstract: High-power broad-area diode lasers are the most efficient light sources, with 90-μm stripe GaAs-based 940-980 nm single emitters delivering > 10 W optical output at a power conversion efficiency ηE(10 W) > 65%. A review of efforts to increase ηE is presented here and we show that for well-optimized structures, the residual losses are dominated by the p -side waveguide and nonideal internal quantum efficiency ηi . The challenge in measuring efficiency to sufficient precision is also discussed. We show that ηE can most directly be improved using low heat sink temperature THS with ηE(10 W) reaching > 70% at THS = -50 °C. In contrast, increases in ηE at THS = 25 °C require improvements in both material quality and design, with growth studies targeting increased ηi and reduced threshold current and design studies seeking to mitigate the impact of the p-side waveguide. “Extreme, double asymmetric” (EDAS) designs are shown to substantially reduce p-side losses, at the penalty of increased threshold current. The benefit of EDAS designs is shown here using diode lasers with 30-μm stripes, (in development as high beam quality sources for material processing). Efficiency increases of ~ 10% relative to conventional designs are demonstrated at high powers.

High-power, high-efficiency 1150 nm quantum well laser

Abstract: Edge emitting diode lasers with highly strained InGaAs quantum wells and GaAs waveguide layers emitting at 1150 nm were investigated focusing on the impact of the waveguide design on the laser performance. Using a thick GaAs waveguide layer broad area devices with low vertical divergence of 20/spl deg/ FWHM and reliable operation at a power level of 80-mW//spl mu/m stripe width were demonstrated.

Passively Cooled TM Polarized 808-nm Laser Bars With 70% Power Conversion at 80-W and 55-W Peak Power per 100- $\mu$ m Stripe Width

Abstract: Many solid state laser systems rely on transverse- magnetic polarized 808-nm diode lasers, whose efficiency is limited by the transparency current of the quantum well and whose peak power is limited by facet failure. Using optimized epitaxial growth, low voltage designs, and optimized facet reflectivity, we demonstrate 70% power conversion efficiency at 80 W in 1-cm laser bars under continuous-wave (CW) test conditions. We assess peak power limits in single emitters and find that 100-mum stripe lasers roll thermally under the CW condition at 13 W without failure, then reach >50 W under 300-ns pulse condition, where they fail at internal defects.

5.5 W output power from 100 μm stripe width lasers at 670 nm with a vertical far-field angle of 32 degrees

Abstract: 670 nm broad area diode lasers with an output power of 55 W and a conversion efficiency of 40% will be presented Reliable operation over 1800 h at more than 1 W will be demonstrated

Efficient High-Power Laser Diodes

Abstract: High-power broad-area diode lasers are the most efficient light sources, with 90-μm stripe GaAs-based 940-980 nm single emitters delivering > 10 W optical output at a power conversion efficiency ηE(10 W) > 65%. A review of efforts to increase ηE is presented here and we show that for well-optimized structures, the residual losses are dominated by the p -side waveguide and nonideal internal quantum efficiency ηi . The challenge in measuring efficiency to sufficient precision is also discussed. We show that ηE can most directly be improved using low heat sink temperature THS with ηE(10 W) reaching > 70% at THS = -50 °C. In contrast, increases in ηE at THS = 25 °C require improvements in both material quality and design, with growth studies targeting increased ηi and reduced threshold current and design studies seeking to mitigate the impact of the p-side waveguide. “Extreme, double asymmetric” (EDAS) designs are shown to substantially reduce p-side losses, at the penalty of increased threshold current. The benefit of EDAS designs is shown here using diode lasers with 30-μm stripes, (in development as high beam quality sources for material processing). Efficiency increases of ~ 10% relative to conventional designs are demonstrated at high powers.

Double-lattice photonic-crystal resonators enabling high-brightness semiconductor lasers with symmetric narrow-divergence beams.

Abstract: Achieving high brightness (where brightness is defined as optical power per unit area per unit solid angle) in semiconductor lasers is important for various applications, including direct-laser processing and light detection and ranging for next-generation smart production and mobility. Although the brightness of semiconductor lasers has been increased by the use of edge-emitting-type resonators, their brightness is still one order of magnitude smaller than that of gas and solid-state/fibre lasers, and they often suffer from large beam divergence with strong asymmetry and astigmatism. Here, we develop a so-called ‘double-lattice photonic crystal’, where we superimpose two photonic lattice groups separated by one-quarter wavelength in the x and y directions. Using this resonator, an output power of 10 W with a very narrow-divergence-angle (<0.3°) symmetric surface-emitted beam is achieved from a circular emission area of 500 μm diameter under pulsed conditions, which corresponds to a brightness of over 300 MW cm−2 sr−1. In addition, an output power up to ~7 W is obtained under continuous-wave conditions. Detailed analyses on the double-lattice structure indicate that the resonators have the potential to realize a brightness of up to 10 GW cm−2 sr−1, suggesting that compact, affordable semiconductor lasers will be able to rival existing gas and fibre/disk lasers. An optimized design for a broad-area surface-emitting photonic-crystal laser leads to high brightness of over 300 MW cm–2 sr–1 and an output power of 10 W under pulsed excitation.

Indoor Optical Wireless Power Transfer to Small Cells at Nighttime

Abstract: The application of wireless backhaul communication and power transfer to outdoor small cells (SCs) could significantly decrease their installation cost. In this paper, the concept of indoor optical wireless power transfer to SCs is investigated in the absence of ambient light, i.e., during darkness hours. An experimental study is conducted by the use of up to four red laser diodes (LDs), a crystalline silicon solar panel and cell placed at $5.2$ m. A value of $69$ % is measured for the fill factor of the solar panel. Also, a total power efficiency of $3.2$ % is measured for an optical wireless (OW) link with an average efficiency of two LDs of $26.8$ %, a solar cell efficiency of $13.3$ % and only $10.6$ % of geometrical losses. A comparison of this link with a state-of-the-art inductive power transfer system shows an improvement of the total power efficiency by $2.7$ times. Another OW link is implemented with a divergence of full width at $36.8$ % of the peak intensity of $3$ and $5.75$ mrad along the small and large axes of the beam, respectively. The experimental levels of harvested power are in the order of mW, whereas approximately $1$ W is required for the operation of a SC. Therefore, a $42$ laser-based transmitter is designed both analytically and by the use of the simulation tool Zemax. The respective results show the feasibility of delivering $7.2$ W of optical power to a solar cell of up to $30$ m distance with geometrical losses of only $2$ %, but a beam enclosure is also required due to eye safety restrictions.

Root-Cause Analysis of Peak Power Saturation in Pulse-Pumped 1100 nm Broad Area Single Emitter Diode Lasers

Abstract: Many physical effects can potentially limit the peak achievable output power of single emitter broad area diode lasers under high current, pulse-pumped operation conditions. Although previous studies have shown reliable operation to high pump levels (240 A, 300 ns, and 1 kHz), power was found to saturate. We present here results of a systematic study to unambiguously determine the sources of this power saturation. A combination of detailed measurements and finite element device simulation were used for the diagnosis. We find that the measured power saturation is dominated by electron leakage caused by band bending at high bias due to the low mobility of the p-type waveguide. However, the power saturation is only fully reproduced when longitudinal spatial hole-burning is included. Higher powers are expected to be achieved if higher energy barriers and lower confinement factors are used to mitigate leakage and longitudinal hole-burning, respectively.

Comparative theoretical and experimental studies of two designs of high-power diode lasers

Abstract: Design and technology developments targeted at increasing both power conversion efficiency and optical output power of GaAs-based diode lasers are under intense study worldwide, driven by the demands of commercial laser systems The conversion efficiency at the operation point is known to be limited by electrical and optical losses in the p-side waveguide In this paper an ‘extreme, double asymmetric’ design to mitigate the impact of the p-side waveguide is studied and compared with a more conventional design An increase of the efficiency at the highest power is demonstrated, but it is less than expected from simulations