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.
Three products based on VCSEL chips are developed for intelligent driving Lidar and driver monitor system. The line beam products used for long-distance detection achieved a 0.1°horizontal divergence angle, 23° vertical divergence angle, and the vertical beam uniformity more than 80%. For the area beam products used in medium and short distance detection, has achieved the field of view 125°×25°. For the super wide field of view area beam product, can applied in driver monitor system, the FOV is 160°×120°. These three products all have excellent performance in a wide temperature range (- 40 degrees centigrade ~ 110 degrees centigrade).
Due to the maturity of VCSEL supply chain promoted by the VCSEL applications in smart phones, and the increasing peak power of multi-junction VCSEL chip,VCSELs are considered to have great advantages and potential as the transmitter light sources of automotive low-cost LIDAR devices. Here we introduce a kind of VCSEL line-beam module with unique optical shaping design for LiDAR applications. The module has a uniform line beam with a peak power larger than 200W, a pulse width of 4ns, a divergence angle of 0.12° @ 1/e2, and the vertical axis intensity uniformity is better than 80%. The experimental data showed that over a wide temperature range from - 40 °C to 110 °C the power variation of the line beam module is less than 20%, the variation of horizontal divergence angle is less than 5%, and the temperature drift coefficient is 0.066nm/°C, which greatly reduces the performance requirements of the receiver detector for the Lidar system. In addition, we introduce a prototype of new line-beam modules with peak power higer than 1000W we are developing, which can meet further requirement of long-distance LiDAR system.
Passively Q-switched solid-state laser is potentially a very advantageous light source for automotive LiDAR application. The key challenge is the ability of wide temperature range operation. In this work we investigated high-power diode laser bar pumped passively Q-switched Nd:YAG/Cr:YAG solid-state laser with a stable output over a wide temperature range. Firstly we studied the impact of the pump light wavelength and the laser crystal temperature on the pulse energy and threshold, and results showed that to obtain the stable output of a solid-state laser in a wide temperature range, both the diode output and the laser crystal temperature should be stabilized in a reasonable small range. Further we designed and fabricated solid-state laser modules with a single active temperature control for both laser diode and crystal, which had stable pulse energy of millijoules with a pulse width of about 2 ns and a repetition rate of 30 Hz over a wide temperature range from -30 oC to 90 oC.
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.
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