This PDF file contains the front matter associated with SPIE Proceedings Volume 12515, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

We have developed a proprietary Triple Junction laser diode at eye-safe 1550nm based on AlInGaAs/InP material systems for LiDAR and laser range finding applications. Three monolithic laser structures with tunnel junction layers are designed to reduce mechanical stress with superior heat dissipation. It achieves 3x output power and 2x wall plug efficiency of a single junction with low operating voltage and high slope efficiency at 1W/A. A 1550nmTriple Junction laser diode allows a LiDAR or laser rangefinder to achieve the longest detection range compared to a single junction or 905nm laser diode. Here we demonstrate the high reliability of Triple Junction high power laser diodes at 1550nm for adoption in various applications. The life test was performed on Triple Junction samples with 95μm aperture and 2.5mm cavity length in a TO9 package. They were driven at average power of 700mW in pulse width of 100 μsec and 10% duty cycle at 60°C. Such stressed electrical and thermal condition is almost 20 times higher than standard operation for automotive LiDAR. We have accumulated over 1000 hours of life test on 17 devices. Based on Arrhenius conditions the estimated MTTF (mean time to failure) is 75k hours at 20°C and 17k hours at 50°C operating temperature, which is respectively 9.3x and 2.5x more than the required 8k hours in automotive applications. We also tested Triple Junction laser diodes up to 100°C and it shows no sign of COD (catastrophic optical damage). Under a high stress CW operating condition at 5W, Triple Junction laser diodes exhibit thermal rollover but return to normal performance under pulsed operation.

High-power, narrow-linewidth blue laser sources with excellent beam quality are important for wide variety of applications including directed energy and underwater communication and sensing. Achieving narrow spectral linewidth from high-power blue semiconductor diode arrays is still a challenge. Our experimental efforts focused on two external cavity schemes involving single broad-area blue diodes and arrays of high-power blue diodes. We demonstrated narrowing the linewidth down to a few dozens of pm. The center wavelength of this narrow optical mode was tunable in the range of several nm and tunability was controlled by the angle of the surface grating providing optical feedback.

Complex spatio-temporal dynamics can be observed in single broad-area semiconductor lasers under external optical feedback. Yet, non-linear dynamics is mostly unexplored in large 1D-arrays of lasers. In our recent investigations, we demonstrated both numerically and experimentally that single-mode and broad-area laser arrays in a V-shape external cavity can generate complex spatio-temporal dynamics with typical frequencies in the GHz range as well as periodic and chaotic phase-locking. Feedback misalignment and feedback strength are key parameters to warrant that diode lasers in the array display a variety of dynamics. Potential applications may include directed energy, LIDAR, and random number generators.

Crytur recently introduced MonaLIGHT, a novel ultrabright light source built on an integrated OSARAM 5W laser diode pumping a single crystal phosphor element in a transmission configuration. The module can produce a luminous flux of 1200 lm and luminous intensity of 8000 cd, unattainable with existing LED technology. This new fit-for-purpose light source (Modular Narrow Angle Light) is characterized by a very low étendue <0.2mm².sr and brings high system efficiency in a very compact and energy efficient package. The phosphor is an optical element of the system which can produce excellent beam characteristics with a viewing angle as low as 4 degrees without the use of secondary optics. The internal quantum efficiency (QE) of the phosphor is 0.96 and external QE is greater than 0.55. The non-coherent emission spectrum is broad and continuous from 500 to 700 nm with no speckle pattern with applications in head up displays, micro projectors, navigation and instrument lighting, dazzlers, endoscopy, microscopy, and optical communications.

We study, via wave-optics simulations, the behavior of spatiotemporal (ST) Bessel–Gauss beams in atmospheric turbulence. ST Bessel-Gauss beams are a type of space-time-coupled light field that carries a ST optical vortex: a phase vortex coupling space and time. We provide a brief theoretical discussion of ST Bessel-Gauss beams before simulating their propagation through atmospheric turbulence of varying strengths. We examine the average irradiances (space-time profiles) and mutual coherence functions and compare/contrast those quantities to the free-space results. We conclude with a brief discussion of future work.

Lack of critical communication components (external modulators, high-sensitivity detectors, amplifiers) has long hindered the development of high-speed free-space transmission in the 8-12 μm thermal atmospheric window. Unipolar quantum technology has emerged as a game-changer by developing key elements that outperform conventional direct-modulation schemes in terms of performance. In particular, we demonstrated a free-space communication at 30 Gbits/s. High-speed modulation of the 9 μm-wavelength beam from a quantum cascade laser is implemented with a Stark-effect external modulator while fast detection relies on a quantum well infrared photodetector. In between, a multi-pass cell allows increasing the propagation distance to 31 meters.

The scaling of fiber amplifiers and lasers to higher output powers is of considerable defense and industrial interests. However, above a given threshold power, parasitic nonlinearities arise that limit continued power scaling. Of the myriad of optical nonlinearities, transverse mode instability (TMI), driven by stimulated thermal Rayleigh scattering, stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SBS) are especially problematic as they generally exhibit the lowest threshold powers. Though power-scalable fibers are materially dominated by silica-based glasses, given their low optical losses and industrial maturity, single crystalline fibers have been long been contemplated as intriguing alternatives due to their significantly higher thermal conductivity, especially given recent advances in the growth of cladded single crystal fibers. A few prior efforts have explored the power-scaling potential of single crystal fibers but without considering TMI. Recently, we have developed a TMI model based on combining stimulated thermal Rayleigh scattering and a quasi- 3D fiber amplifier model which has been shown to fit experimentally measured TMI thresholds well. Here, TMI is studied in a double-clad single crystal Yb-doped YAG (Y₃Al₅O₁₂) and lutecia (Lu₂O₃) fiber lasers. The TMI threshold was found to be significantly higher in single crystal fiber lasers. Power scaling analysis was performed for Yb:silica, Yb:YAG and Yb:Lu₂O₃ fiber lasers with TMI considered. This work serves as a useful update to earlier works and shine significant lights on fiber and amplifier designs for maximum average powers.

Diode-pumped, passively-q-switched neodymium lasers at wavelengths near 1.3 μm based on the saturable absorber Vanadium:YAG have favorable properties as sources for longer-range, >300 m, 3D-imaging systems which are difficult to implement with semiconductor lasers. This wavelength enables eye safety at exposures above what is permitted at 1.5 μm. The lasers are simple, comprising two millimeter-scale crystals with all plano surfaces. We report a Nd:YVO₄ laser with a pulse repetition rate of approximately 500 kHz and a Nd:YAG laser with a pulse energy of 40 μJ, both with pulse durations below 2 nsec.

For several spectroscopy applications, there is a high demand for the small and economical fiber-coupled highpower laser system. In our case, a high-energy DPSS laser pulse was delivered by an optical fiber. For the reason of cost efficiency, we used commercially available “off the shelf” components, like pump diodes, multimode optical fibers and 3D printed components. In this case, the challenge is that the focused high-energy laser pulses can easily damage the optical fiber. To avoid this problem, we redesigned the entire laser cavity structure, optimizing the laser beam characteristics that fit a special fiber coupling module. In this work, we are presenting the development of a compact, low-price, high-energy Q-Switched Nd:YAG laser with a directly connected optical fiber using commercially available components.

Strontium fluoride ceramics have multiple prospective advantages over currently-used phosphate glass as a host for Nd ions in high-energy laser gain media, but fluoride ceramics have yet to be developed into usable gain media because of difficulties in processing. Past work on fluorides has primarily focused on processing from the liquid phase, such as fusion casting and hot forging. A powder processing route has been developed for strontium fluoride, achieving optical scatter as low as ~0.4%/cm at 1.3 μm, which is within the usable range for high-energy laser use. A series of hot-pressed samples exhibit decreasing optical scatter and increasing grain size with increasing process temperature.