KEYWORDS: Semiconductor lasers, Absorption, Solid state lasers, Temperature metrology, Nd:YAG lasers, Crystals, Resistance, High power lasers, Laser development, Heatsinks
High power diode laser stack is widely used in pumping solid-state laser for years. Normally an integrated temperature control module is required for stabilizing the output power of solid-state laser, as the output power of the solid-state laser highly depends on the emission wavelength and the wavelength shift of diode lasers according to the temperature changes. However the temperature control module is inconvenient for this application, due to its large dimension, high electric power consumption and extra adding a complicated controlling system. Furthermore, it takes dozens of seconds to stabilize the output power when the laser system is turned on. In this work, a compact hard soldered high power conduction cooled diode laser stack with multiple wavelengths is developed for stabilizing the output power of solid-state laser in a certain temperature range. The stack consists of 5 laser bars with the pitch of 0.43mm. The peak output power of each bar in the diode laser stack reaches as much as 557W and the combined lasing wavelength spectrum profile spans 15nm. The solidstate laser, structured with multiple wavelength diode laser stacks, allows the ambient temperature change of 65°C without suddenly degrading the optical performance.
A novel marco channel cooler (MaCC) has been developed for packaging high power diode vertical stacked (HPDL) lasers, which eliminates many of the issues in commercially-available copper micro-channel coolers (MCC). The MaCC coolers, which do not require deionized water as coolant, were carefully designed for compact size and superior thermal dissipation capability. Indium-free packaging technology was adopted throughout product design and fabrication process to minimize the risk of solder electromigration and thermal fatigue at high current density and long pulse width under QCW operation. Single MaCC unit with peak output power of up to 700W/bar at pulse width in microsecond range and 200W/bar at pulse width in millisecond range has been recorded. Characteristic comparison on thermal resistivity, spectrum, near filed and lifetime have been conducted between a MaCC product and its counterpart MCC product. QCW lifetime test (30ms 10Hz, 30% duty cycle) has also been conducted with distilled water as coolant. A vertical 40-MaCC stack product has been fabricated, total output power of 9 kilowatts has been recorded under QCW mode (3ms, 30Hz, 9% duty cycle).
KEYWORDS: Semiconductor lasers, Packaging, High power lasers, Reliability, Copper, Laser bonding, Near field, High power diode lasers, Laser systems engineering
The package structure critically influences the major characteristics of diode laser, such as thermal behavior, output power, wavelength and smile effect. In this work, a novel micro channel cooler (MCC) for stack array laser with good heat dissipation capability and high reliability is presented. Numerical simulations of thermal management with different MCC structure are conducted and analyzed. Based on this new MCC packaging structure, a series of QCW 500W high power laser arrays with hard solder packaging technology has been fabricated. The performances of the laser arrays are characterized. A narrow spectrum of 3.12 nm and an excellent smile value are obtained. The lifetime of the laser array is more than 1.38×109 shots and still ongoing.
KEYWORDS: Semiconductor lasers, High power diode lasers, Laser development, Indium, Resistance, Reliability, High power lasers, Numerical simulations, Gold
The high power diode lasers have been widely used in many fields. In this work, a sophisticated high power and high performance horizontal array of diode laser stacks have been developed and fabricated with high duty cycle using hard solder bonding technology. CTE-matched submount and Gold Tin (AuSn) hard solder are used for bonding the diode laser bar to achieve the performances of anti-thermal fatigue, higher reliability and longer lifetime. This array consists of 30 bars with the expected optical output peak power of 6000W. By means of numerical simulation and analytical results, the diode laser bars are aligned on suitable positions along the water cooled cooler in order to achieve the uniform wavelength with narrow spectrum and accurate central wavelength. The performance of the horizontal array, such as output power, spectrum, thermal resistance, life time, etc., is characterized and analyzed.
Due to their high electrical-optical conversion efficiency, compact size and long lifetime, high power diode lasers have
found increased applications in many fields. As the improvement of device technology, high power diode laser bars with
output power of tens or hundreds watts have been commercially available. With the increase of high current and output
power, the reliability and lifetime of high power diode laser bars becomes a challenge, especially under harsh working
conditions and hard-pulse operations. The bonding technology is still one of the bottlenecks of the advancement of high
power diode laser bars. Currently, materials used in bonding high power diode laser bars are commonly indium and goldtin
solders. Experimental and field application results indicates that the lifetime and reliability of high power diode laser
bars bonded by gold-tin solder is much better than that bonded by indium solder which is prone to thermal fatigue,
electro-migration and oxidization. In this paper, we review the bonding technologies for high power diode laser bars and
present the advances in bonding technology for single bars, horizontal bar arrays and vertical bar stacks. We will also
present the challenges and issues in bonding technology for high power diode laser bars and discuss some approaches
and strategies in addressing the challenges and issues.
Packaging is an important part of high power diode laser (HPLD) development and has become one of the key factors affecting the performance of high power diode lasers. In the package structure of HPLD, the interface layer of die bonding has significant effects on the thermal behavior of high power diode laser packages and most degradations and failures in high power diode laser packages are directly related to the interface layer. In this work, the effects of interface layer on the performance of high power diode laser array were studied numerically by modeling and experimentally. Firstly, numerical simulations using finite element method (FEM) were conducted to analyze the effects of voids in the interface layer on the temperature rise in active region of diode laser array. The correlation between junction temperature rise and voids was analyzed. According to the numerical simulation results, it was found that the local temperature rise of active region originated from the voids in the solder layer will lead to wavelength shift of some emitters. Secondly, the effects of solder interface layer on the spectrum properties of high power diode laser array were studied. It showed that the spectrum shape of diode laser array appeared “right shoulder” or “multi-peaks”, which were related to the voids in the solder interface layer. Finally, “void-free” techniques were developed to minimize the voids in the solder interface layer and achieve high power diode lasers with better optical-electrical performances.
9xx nm CW mini-bar diode lasers and stacks with high brightness and reliability are desired for pumping fiber lasers and direct fiber coupling applications. For the traditional cm-bar with 1mm-2mm cavity, it can provide CW output power up to 80W-100W and high reliability, whereas the brightness is relatively low. In comparison, mini-bar based diode lasers with 4mm cavity offer a superior performance balance between power, brightness, and reliability. However, the long cavity and large footprint of mini-bar diode laser renders its sensitivity towards thermal stress formed in packaging process, which directly affects the performances of high bright mini-bar diode lasers. In this work, the thermal stress correlating with package structure and packaging process are compared and analyzed. Based on the experiment and analysis results, an optimized package structure of CW 60W 976 nm mini-bar diode lasers is designed and developed which relieves thermal stress.
High power diode lasers have been widely used in many fields. For many applications, a diode laser needs to be robust under on-off power-cycling as well as environmental thermal cycling conditions. To meet the requirements, the conduction cooled single bar CS-packaged diode laser arrays must have high durability to withstand thermal fatigue and long lifetime. In this paper, a complete indium-free bonding technology is presented for packaging high power diode laser arrays. Numerical simulations on the thermal behavior of CS-packaged diode laser array with different packaging structure were conducted and analyzed. Based on the simulation results, the device structure and packaging process of complete indium-free CS-packaged diode laser array were optimized. A series of high power hard solder CS (HCS) diode laser arrays were fabricated and characterized. Under the harsh working condition of 90s on and 30s off, good lifetime was demonstrated on 825nm 60W single bar CS-packaged diode laser with a lifetime test of more than 6100hours achieved so far with less 5% power degradation and less 1.5nm wavelength shift. Additionally, the measurement results indicated that the lower smile of complete indium-free CS-packaged diode laser arrays were achieved by advanced packaging process.
With the increasing applications of high power semiconductor lasers in industry, advanced manufacturing, aerospace,
medical systems, display, entertainment, etc., semiconductor lasers with high power and high performances are required.
The performance of semiconductor lasers is greatly affected by packaging structure, packaging process and beam
shaping. A novel macro channel cooler (MaCC) for stack array laser with good heat dissipation capacity and high
reliability is presented in this work. Based on the MaCC package, a high power stack array diode laser is successfully
fabricated. A series of techniques such as spectrum control and beam control are used to achieve narrow spectrum and
high beam quality. The performances of the semiconductor laser stack array are characterized. A high power 20kW
QCW hard solder packaged stack array laser is fabricated; a narrow spectrum of 3.94 nm and an excellent rectangular
beam shape are obtained. The lifetime of the stack array laser is tested as well.
Laser cladding has become a useful tool in materials processing for improving the surface properties of the substrate
materials, and has been widely used in industry in recent years. In this paper, we study the 3000W CW laser cladding
system based on the high power diode lasers. The beam control method is proposed to reduce the collimated beam
pointing errors caused during the packaging of the laser stack. At the input current of 84A, the output power and the
optical coupling efficiency of this laser cladding system are 3738W and 93.7%, respectively, and at work face the beam
spot size is 2.5mm*7.9mm with symmetry intensity distribution. The laser cladding system is also used in cladding the
nickel powder onto the iron substrate and the nickel powder can be clothed onto steel plate uniformly.
High power semiconductor laser arrays have found increased applications in many fields. In this work, a hard soldering
microchannel cooler (HSMCC) technology was developed for packaging high power diode laser array. Numerical
simulations of the thermal behavior characteristics of hard solder and indium solder MCC-packaged diode lasers were
conducted and analyzed. Based on the simulated results, a series of high power HSMCC packaged diode laser arrays
were fabricated and characterized. The test and statistical results indicated that under the same output power the HSMCC
packaged laser bar has lower smile and high reliability in comparison with the conventional copper MCC packaged laser
bar using indium soldering technology.
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