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.
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.
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.
For current 905nm pulsed laser diode(PLD) for LiDAR applications, most of them are single channel chips each with a power range of 75W-120W designed for scanning multiple single points. In this work, kilowatt 905nm light source based on eight channel 905nm PLD mini-bars had been designed and packaged using flip chip bonding technology. A series of kilowatt 905nm PLD modules were fabricated and characterized. The maximum output power of 982W limited by the pulse driver was obtained for the first time under the condition of 100V@5ns,100kHz at room temperature. The spectral width of FWHM and FW90%E was 5.1nm and 7.2nm, respectively. The far field divergence test data indicated that the fast axis divergence@1/e2 and slow axis divergence@1/e2 was 0.38°and 27.59°, respectively. In the future, the fast axis divergence@1/e2 and the slow axis FoV can be designed and optimized for any particular LiDAR system.
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.
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.
High power diode lasers (HPDLs) offer the highest wall-plug efficiency, highest specific power (power-to-weight ratio), arguably the lowest cost and highest reliability among all laser types. However, the poor beam quality of commercially HPDLs is the main bottleneck limiting their direct applications requiring high brightness at least in one dimension. In order to expand the applications of HPDLs, beam shaping and optical design are essential. In this work, we report the recent progresses on maximizing applications of HPDLs by synergizing diode laser light source and beam shaping micro-optics. Successful examples of matching of diode laser light sources and beam shaping micro-optics driving new applications are presented.
Thermal management is one of the most important factors affecting the performance of high power diode lasers. In this paper, transient thermal behavior of conduction-cooled high power diode lasers has been studied using finite element method. The effects of heat sink geometry, ceramics size on the junction temperature of high power diode laser packages have been analyzed. Based on the simulations, heat dissipation capability of high power diode laser packages is improved and compact conduction-cooled diode laser array packages with 3 bars and 5 bars are fabricated. The power ~ current and spectrum of the optimized high power diode laser array packages at different operation parameters are characterized at different pulse widths, repetition frequencies and TEC temperatures. The effects of temperature on the output power and spectrum are discussed. The lifetime test of high power diode laser array packages is also performed. It shows that the conduction-cooled high power diode laser array packages have good optical performance.
High power diode laser arrays have found increasing applications in the field of pumping solid-state lasers and fiber lasers. Due to the thermal crosstalk across diode laser arrays and non-uniformity of local flow rate within microchannel cooler, junction temperature distribution becomes inhomogeneous, consequently leading to spectrum broadening and large beam divergence of diode laser pumping sources. In this work, an analytical method and numerical heat transfer based on finite volume method were employed to optimize the inner structure of microchannel cooler so as to obtain low thermal resistance and uniform junction temperature distribution for the diode laser arrays. Three-dimensional numerical models were developed to study the fluid flow and heat transfer of copper stacked microchannel coolers with different dimensions and arrangements of inner channels and fins. More uniform junction temperature distribution of diode laser array package could be achieved by self-heating compensation with specific coolant covering width. These results could provide significant guidance for the design of microchannel coolers of high power diode laser arrays for better performance.
High power diode lasers have been widely used in many fields. To meet the requirements of high power and high reliability, passively cooled single bar CS-packaged diode lasers must be robust to withstand thermal fatigue and operate long lifetime. In this work, a novel complete indium-free double-side cooling technology has been applied to package passively cooled high power diode lasers. Thermal behavior of hard solder CS-package diode lasers with different packaging structures was simulated and analyzed. Based on these results, the device structure and packaging process of double-side cooled CS-packaged diode lasers were optimized. A series of CW 200W 940nm high power diode lasers were developed and fabricated using hard solder bonding technology. The performance of the CW 200W 940nm high power diode lasers, such as output power, spectrum, thermal resistance, near field, far field, smile, lifetime, etc., is characterized and analyzed.
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).
The solid state laser relies on the laser diode (LD) pumping array. Typically for high peak power quasi-CW (QCW) operation, both energy output per pulse and long term reliability are critical. With the improved bonding technique, specially Indium-free bonded diode laser bars, most of the device failures were caused by failure within laser diode itself (wearout failure), which are induced from dark line defect (DLD), bulk failure, point defect generation, facet mirror damage and etc. Measuring the reliability of LD under QCW condition will take a rather long time. Alternatively, an accelerating model could be a quicker way to estimate the LD life time under QCW operation. In this report, diode laser bars were mounted on micro channel cooler (MCC) and operated under QCW condition with different current densities and junction temperature (Tj ). The junction temperature is varied by modulating pulse width and repetition frequency. The major concern here is the power degradation due to the facet failure. Reliability models of QCW and its corresponding failures are studied. In conclusion, QCW accelerated life-time model is discussed, with a few variable parameters. The model is compared with CW model to find their relationship.
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.
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.
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.
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.
High power diode lasers have increased application in many fields. In this work, a sophisticated high power and high performance conduction cooled diode laser stack has been developed for long pulse duration and high duty cycle using gold-tin (AuSn) bonding technology. The transient thermal behavior and optical simulation of the laser diode stack module are investigated to optimize the laser device structure. CTE-matched submount and AuSn hard solder are used for bonding the laser diode bar to achieve higher reliability and longer lifetime. Guided by the numerical simulation and analytical results, conduction cooled diode laser stack with high power, long pulse duration and high duty cycle is fabricated and characterized. Compared with the conventional indium bonding technology, the new design is a promising approach to obtain improved performance with high reliability and long lifetime.
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 improvement of output power, efficiency and reliability, high power semiconductor lasers have been applied in more and more fields. In this paper, a conduction-cooled, high peak output power semiconductor laser array was studied and developed. The structure and operation parameters of G-Stack semiconductor laser array were designed and optimized using finite element method (FEM). A Quasi-continuous-wave (QCW) conduction-cooled G-Stack semiconductor laser array with a narrow spectrum width was fabricated successfully.
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.
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.
In this article different experiments are carried out to exam some key elements that influence the performance of PCSS
(Photoconductive semiconductor switches). The experiments include the bias voltage over the switch, the trigger pulse
energy and position. From the results we got the relationship among the elements and the output impulses. The bias
voltage controls the output linearly; the rise of trigger energy increase the export voltage but when the energy get over
280μJ this trend slow down and the export voltage go to a fixed value; different positions change the export voltage and
the peak value appears at the area near the cathode. The results were analyzed and explanations were given. From the
discussion we give the evidences in helping to explain the linear mode, and point out an efficient way to use the laser
energy for PCSS. Some tests methods are introduced and will be done in the future.
Epitaxial layers and monolayer of Ga0.98 In0.02As0.24Sb0.76 quaternary alloys lattice matched to GaSb substrates were grown by our home-made low pressure metal organic chemical vapor deposition (LP-MOCVD). Lattice mis-match (Δa/a~2.5%) between Ga0.98In0.02As0.24Sb0.76 quaternary alloys and GaSb substrate was obtained. Mirrorlike surface
morphologies were investigated by SEM and AFM. Undoped Ga0.98In0.02As0.24Sb0.76 epitaxial layers grown on semi-insulated GaAs substrates indicates n-type with carrier density of 1.8×1017cm-3 and electron mobility of 2551 cm2v-1 s-1. Growth at this temperature yielded a root-mean-square (rms) surface roughness of 160 nm. The effects of growth parameters on epitaxial layers were discussed. It is shown that under proper growth conditions, containing growth temperature (570~620°C), V/III ratios (2~6) and flux of carrier gas, smooth and high quality Ga0.98In0.02As0.24Sb0.76 epitaxial layers can be achieved.
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