The high reliability and efficiency of high-power conduction cooled annular diode laser stack are critical to the side pump solid-state laser head in a DPSSL system. To obtain the higher reliability and efficiency, a high-power conduction cooled annular diode laser stack packaged by AuSn hard solder has been presented. The CTE-matched wedge-shaped submounts are designed and applied in bonding GaAs-based diode laser bars with the cavity length of 1.5 mm on a conduction cooled annular heatsink. The mechanical structural design and thermal design are conducted to evaluate the capability of the annular packaging. The bar bonding process is optimized to reduce the thermal stress and improve the spectral performances of this package. After optimizing the multiple bar bonding process, a series of 808nm QCW ⪆2000W annular diode laser stacks with a narrow spectral width are achieved, which has the average FWHM and FW90%Energy value of approximately 2.6 nm and approximately 3.6 nm at 65 °C, respectively. Also, the FW90% Energy value at 65 °C is significantly reduced from 8.03 nm to 3.84 nm. Of particular importance is the elimination of the left shoulder of the spectral profile after optimizing the multiple bar bonding process.
The line-scanning LiDAR (Light Detection and Ranging) has the advantages of relatively simple structure and longdistance detection, so it is widely adopted by many key players. However, one challenge of this method lies in the realization of the line-beam laser module with high peak power, small divergence angle, high reliability, and low cost. In this work, we introduce our line-beam laser modules based on 905nm triple-junction EEL with unique optical and structure design. The modules have a uniform line beam with a peak power larger than 800W, a pulse width of less than 6ns and repetition rate of 100 kHz. The divergence angle of the line beam is less than 0.15°@ 1/e2. The FOI (field of illumination) is 25° and the intensity uniformity is better than 90%. The Low/High-temperature-operation test data showed that over a wide temperature range from - 40 ℃ to 85 ℃ the power variation of the line beam module is less than 10%, and the variation of the divergence angle is less than 0.02 deg. Other reliability tests including temperature cycling from -40 ℃ to 120 ℃, and lifetime were also introduced.
We report the latest development of a high power conductively cooled laser module using a novel design approach. The laser bar is directly bonded to two heatsinks in a sandwich configuration without employing submounts as buffers for stress relief caused by CTE mismatch. Simulations were performed to aid the laser module design. The accuracy of the simulations was verified by experimental tests on the laser modules. Production data were collected and used to determine the key performance parameters, statistical distribution, lifetime, and failure mechanism. The laser module thermal rollover could reach 480W at 500A drive current under CW running mode. Furthermore, it could continuously operate under a harsh-hard pulse driving condition at 300A drive current with 300ms pulse width and 1Hz repetition rate.
In this study, a high-power diode laser bar assembly is developed with good heat dissipation in long pulse operation mode. The thermal behavior and stress distribution are investigated in order to characterize the cooling capability and reliability. The optimal thermal resistance reaches 0.81K/W for each bar, based on the custom designed cooling plate, which is 0.6K/W lower than conventional coolers. The maximum thermal stress of laser bar is 39.4MPa under the working condition, which is less than half of the stress for previous conventional diode laser. Reliability of the device is improved as the diode laser works in a low stress status with long pulse width mode. The light power of the diode laser achieves 120W/bar with pulse duration of 30ms in 10Hz, and 200W/bar with 10ms, 10Hz, respectively. The diode laser of lifetime test passed 4.5×107 shots under the condition of 30ms, 10Hz@120A.
With the development of laser technology, high power diode lasers have found the increasing various applications in many fields, including industry, advanced manufacturing, aerospace, Lidar and medical systems etc.. The near field non-linearity (Smile) and lasing uniformity of emitters for high power diode laser arrays are critical to high reliable optically coupled modules and laser heads in a cladding system. In order to obtain the lower smile and higher lasing uniformity, two CTEmatched substrates (Copper Tungsten-CuW) are employed to bond a single GaAs-based diode laser array with the cavity length of 2mm on a Micro Channel Cooler (MCC) using Gold-Tin hard solder. This double-CuW MCC-packaged structure is called DMCC which enables a diode laser array bonded on a CuW/MCC/CuW structure with all AuSn solder. Structural optimization has been carried out to reduce the thermal stress and smile for this package. Simulation results indicate that the smile and thermal stress is lowered 0.24μm and 16MPa, respectively. According to the simulation results, single bar DMCC-packaged diode lasers with lower Smile value are fabricated and characterized. The experimental results show that the ratio of Smile (average smile ~0.87μm) ⪅1μm is ~71% and higher ~19% than that of conventional structure (average smile ~1.2μm). Importantly, the quantity ratio of lasing emitters (≥46 emitters) in a diode laser array is significantly raised from ~62% to 85% after the optimization of CuW submount.
KEYWORDS: Semiconductor lasers, Packaging, Reliability, Laser development, High power diode lasers, Solid state lasers, Resistance, High power lasers, Corrosion, Continuous wave operation
There are strong demands at the market to increase power and reliability for high power diode laser. In parallel to this the requirements for cooler and package for the high power diode laser increase. Superior heat dissipation capability and low thermal resistance are some of the key attributes for the diode laser package design in the near future. The most common method of removing the large amounts of waste heat in a diode laser is using a micro-channel cooler. However, a microchannel cooler requires water to meet demanding specifications to avoid failures due to corrosion, which increases the overall cost to operate and maintain the laser. We demonstrate advances in a new macro-channel water cooling diode laser which are designed to eliminate the failure mechanisms associated with micro-channel coolers, and enhance the laser heat dissipation and the long-term reliability. For the package adopting the high thermal conductivity material, the maximum output power is 100 W per bar in CW mode. Due to the advantage of compact design, high power, high reliability and fast axis collimation, the new diode laser has the potential to be widely used in many fields, such as pumping solid state laser, hair removal, industry and research.
A high peak power annularly-stacked laser diode pump has been designed and manufactured for a solid state laser (SSL), which is constructed by 12 single annular stacks composed of 3-bar laser diode (LD) submodules. High peak power and high wavelength uniformity have been considered. Macro channel cooling has been used during the operation of the annular stacks, at typical coolant flow rate of 2L/min. Heat dissipation and stress of a single annular stack have been simulated by finite element software, which shows high temperature uniformity of 3-bar submodules (plus or minus 0.5℃) and low package stress (11.8MP).
The peak power of the annularly stacked laser diode pump has reached 234kW at a peak current of 450A or less. A high uniformity of centroid wavelength (802 plus or minus1nm) with a full width at half maximum (FWHM) of 4nm has been measured. More than 24 million shots have been verified for the 3-bar LD submodules.
We have simulated and optimized a conductive cooling structure including the distribution of temperature in active layer, and the deformation of laser to achieve high power operation with low SMILE value. Unlike the traditional conductive cooling structure, our structure improves the heat dissipation efficiency from three aspects: with angle structure in the front of heat sink; double side heat dissipation and without submount packaging technology. In this report, an output power of more than 250W CW from a 4 mm long laser bar with a filling factor of 50% is shown at 240A driving current with a power conversion efficiency of 65%. The thermal rollover of this packaging conductive cooling device can reach 385W at 400A driving current.
High power QCW diode laser stacks have been widely used in pumping applications for years. Different package structures of diode laser stacks are applied for pumping the cylindrical rod crystal, such as modular G-Stack, horizontal, vertical and annular arrays. Annular array is preferred in pumping of QCW mode with low duty cycle and short pulse width, due to the advantage of compact structural size, uniform light beam distribution and convenient electric connection. However, the development of annular diode laser array using hard solder is difficult because of the complex bonding process of diode laser on annular heatsink with conventional bonding fixture. Furthermore the stress and thermal behavior is yet to be well studied on the annular diode laser array. In this work, a sophisticated annular diode laser array was developed using hard solder. Optimized structure and thermal design were conducted to achieve uniform light beam distribution and good heat dissipation. Stress release structure of diode laser stack is applied to reduce the risk of chip crack and deviation of spatial spectrum. The annular diode laser array consists of 44 bars in a ring, with the peak output power of each bar over 500W. The maximum output power of each bar reaches 673 W.
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