This PDF file contains the front matter associated with SPIE Proceedings Volume 11982, including the Title Page, Copyright information, Table of Contents, and Conference Committee listings.

Low SWAP (low size and weight and power-efficient) laser diode has been a major focus of research in the laser industry. However, achieving high output power by a wavelength-stabilized laser diode with low SWaP and high airtightness is still challenging. Herein, using lightweight aluminum material and a compact structure design, BWT has developed a laser diode that outputs 200 W from 105 μm core diameter NA 0.22 fiber with the weight of 190 g and size of 144×52×17 mm³. The leakage rate of the diode laser is lower than 9.9×10^-9 Pam³ s ^-1. At 11 A, the electro-optical efficiency is higher than 50% with 200 W power output. The module’s mass-to-power ratio is lower than the commercially available 200W laser diode from BWT. It is a relatively low-cost approach to low SWaP laser diode applications without complex structural design.

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.

BWT introduced the idea of dense spatial beam combination(DSBC) and proved it experimentally with kW level pump source. Currently, the output power of single emitters has reached 15W~30W@BPP≈5-12mm·mrad with electro-optical efficiency<60%. This makes it possible for the high-power pump source with optical fiber output to maintain high brightness, small volume, and light weight. With commercial available chips, BWT achieved 420W output locked at 976nm from a fiber of 135μm core diameter and NA0.22, and mass of ≈500g. Also 1000W output at 976nm (or 915nm) from a 220μm core diameter 0.22NA fiber is obtained and mass of ≈400g. In the future, with increasing diode chip brightness and electro-optical efficiency, the pump source with high power and mass ratio will have an important role in small size and high power fiber lasers, which will become an active driver for defence and industrial applications.

A compact, lightweight, laser transmitter using space-qualified heritage oscillator from the currently on-orbit ICESat-2 transmitter was built and tested. The Nd:YVO₄ oscillator’s cavity length was reduced by 30% compared with ICESat-2 transmitter and achieved an intermediate 1064 nm energy of ~180 μJ. Final 532 nm output performance after external cavity frequency doubling and beam shaping showed pulse energies <80 μJ and pulse widths < 1 ns. The system was engineered and packaged for an overall dimension of 5.4” L × 3.1” W × 4.1” H and a total mass <1.5 kg. The laser housing and optics were hermetically sealed for contamination control to reduce laser damage and improve reliability. Environmental testing was done, and this packaging design is intended for future space-qualified operation.

Recent advancements in diffraction-limited output from tapered diode laser amplifiers represent a disruptive technology breakthrough that is poised to revolutionize the LIDAR market. Output powers which were previously only achievable using doped fiber, glass, or crystal laser architectures are now possible directly from the semiconductor chip. For example, diffraction-limited an output power of just a few watts at 1550 nm is sufficient for continuous wave frequency modulated (FMCW) automotive LIDAR. We report here a new world record of >3.0 W output power with nearly diffraction-limited beam quality (M^2 ~1.2) from a 1550 nm tapered diode laser amplifier; this source is suitable for direct use in numerous LIDAR and remote sensing applications.

Thermoelectric (TE) coolers are solid-state heat pump systems with no moving parts that directly use electric power to cool. Benefits are very small size, extremely light weight, low cost, vibration free operation, refrigerant-free, and excellent durability and reliability. Conventional TE (CTE) systems have limited capability to cool quantum infrared detectors because of insufficient cooling capacity and the inability to achieve the low operating temperatures required by high performance systems. Our studies show the capabilities of TE systems can be significantly improved by using Distributed Transport Properties (DTP) technology, which has the potential to make practical, inexpensive, light weight and highly reliable deep cooling systems and thus enable a new class of deep cooled infrared sensors. Our studies demonstrate the feasibility of creating a single-stage TE device operating in cooling mode with a maximum temperature differential that exceeds state-of-the-art TE systems by more than 35%. The enabling technology is the optimization of transport property distribution within the TE legs. We project that coefficient of performance (COP) and cooling power increase greater than 150% and 200% respectively at high temperature differentials. We also show that such TE devices will have superior performance under all operating conditions (both nominal and off-nominal) and can be smaller than conventional TE devices. Using DTP technology in multi-stage devices (and appropriately optimizing DTP within each stage), the large temperature differentials required to provide temperature control to quantum infrared sensors becomes achievable.

Power handling capabilities of broad-area high-power diode lasers are limited by the heat extraction capabilities of the device packaging. Traditional methods of heat extraction rely on conductive heat extraction from the diode chip and an emitting facet in contact with either quiescent or naturally convecting air. This leads to a thermal profile in the lasing direction of the cavity and a hot emitting facet. A hot facet accelerates material degradation, reducing the mean time to failure and limiting the safe operating power. Direct contact between the facet and a liquid coolant could enable higher levels of heat extraction compared to traditional cooling pathways. An innovative approach to cooling high-power, broad-area diode lasers via total immersion in liquid coolant is proposed and tested. In this study, we demonstrate that single emitters can operate with the emitting facet in direct contact with static coolant, with no negative change to device power or efficiency. Thermal analysis and models show that immersed diodes operate with improved thermal pathways, yielding lower total thermal resistance with the greatest improvement to thermal resistance at the facet-fluid interface.

Variation of lasing wavelength with temperature is a key factor to determine packaging thermal resistance in laser diodes. Using proprietary mounting technology that clamps laser bars instead of using soldering material we can precisely control the stress applied on the laser bars. We experimentally demonstrate that uniaxial stress in the normal direction of the p-n junction (which results in tensile stress in the lattice) increases the temperature characteristic of laser diodes. We report a temperature characteristic raise between 10% and 50% under different stress conditions.

We have developed a novel small SmartLaser^TM plug and play laser module that can be employed to house and power most CW semiconductor diode lasers and small TO type diode-pumped solid-state lasers offered by Advanced Photonic Sciences (APS). These include blue, visible, and near-infrared diode lasers operating from 404 nm to 980 nm, and TO solid-state devices producing output at 532 nm, 1064 nm, and 1535 nm. The innovative laser, mechanical, electrical, and software engineering efforts have resulted in the first smart laser micro-module. This is powered by a simple USB and is fully connected to the internet through a dongle that incorporates a Radio Frequency (RF) link, Analog to Digital converters (ADC), and live-streamed output. A new APS website is also demonstrated, showing the ability to monitor laser performance from any location and at any time. We believe that this new product is the first to offer full internet connectivity, and the ability to remotely monitor laser behavior. Applications of this new plug and play and monitor device are many and include remote monitoring of experiments utilizing lasers in universities and other laboratories, hazardous or environmental unfriendly locations, while traveling, as well as documentation of laser output power in situations involving eye-safety.

Silica fibers are successful at delivering high-power high-energy signals in the near-infrared and visible but suffer from high absorption and color formation in the UV spectrum. Hollow-core negative-curvature antiresonant fibers are promising alternatives as UV radiation has a low overlap with the guiding microstructure. However, their power scaling is hindered by the microstructure power handling and only a few tens to a few hundreds of milliwatt were reported delivered from the nano to the femtosecond regimes. We report on a record single-mode delivery of 23.3W (155μJ) with 89.1% transmission from a 343 nm, 10 ns, 150 kHz laser source developed by Bloom Lasers.

As 248nm DUV lithography tools pursue resolution of smaller features, the transition towards higher numerical aperture optics in these tools is pushing the development of high-performance anti-reflection coatings on large-area, highly curved transmitting optics present in these systems. We present the results of one such effort to coat multi-layered Al₂O₃ and MgF₂ antireflection coatings on substrates of planar, spherical, and aspherical geometries. The spectral, surface quality, and pulsed laser damage performance of these coatings are presented.

The light flux of laser based digital projectors is constantly growing. Further, the setup gets more compact. This leads to increasing spatial dependent power densities inside color channel controlling optical systems of high-end laser cinema projectors. It was surprisingly found that high power blue laser irradiation leads to solarization of optical glass, resulting in a decrease of transmission over time. Therefore, SCHOTT started to develop blue laser solarization stable optical glass. A blue laser irradiation setup and spectral photometer measurement facility was established to characterize the solarization effect on optical glass. First very promising results of the development show that it is possible to significantly increase the stability of optical glass against blue laser solarization. This paper discusses the actual status of the development of blue solarization stable optical glass used for digital projection. Solarization results are shown as a function of time and wavelength. Additionally the intensity dependence and saturation of blue laser solarization is addressed.

Vertical-cavity surface-emitting lasers (VCSELs) have recently paved their way into the 3D sensing market, specifically in mobile device applications. Vertical emission of VCSELs enables arranging single emitters into high-power 2D arrays. Thus, VCSEL arrays require efficient heat management which can be implemented by the means of packaging, both to improve thermal conductivity and to keep VCSEL chips intact. This becomes particularly important when considering also very high-density laser arrays and 2D matrices for quantum computing targeting a larger number of parallel outputs. Despite VCSELs decreased temperature sensitivity, their internal efficiency strongly depends on the internal temperature rise, which is defined by the dissipated power and thermal impedance of the laser assembly. Thermal impedance effect is more notable in the proximity to the gain medium, resulting into a drastic temperature gradient due to relatively thick substrate and its poor thermal conductivity. This prevents efficient heat dissipation in the gain media and creates a need for additional heat sinking. In this work, the improved heat sinking is implemented by packaging VCSEL arrays onto AIN sub mounts and subsequently encapsulating them into a thermally conductive and optically transparent epoxy. Thus, the closest proximity of the gain media to the heat sink is established, leading to an enhanced heat flow. Quantitative evaluation of the heat flow is performed by determining thermal resistance, defined as a ratio of the shift rates in the emission spectrum produced by varying pumping current and the heat sink temperature. The evaluation of thermal resistance of the devices with and without epoxy, not reported earlier, is performed to quantitively demonstrate the obtained improvements in the heat flow, efficiency, and output power.

High power diode laser systems with homogenized intensity distribution have been widely used in laser annealing, cladding and surface heating. New applications such as semiconductor wafer annealing prefer adjustable laser beam size for process optimization, especially during process development stage. Here we report a development of a diode laser system with an adjustable beam size and highly uniform line beam intensity. Beam size in two dimensions perpendicular to its propagation direction can be adjusted independently with higher than 97% intensity uniformity in length dimension. The beam width is adjustable from 60 to 90um (FWHM) and the beam length is adjustable from 11mm to 12mm (FWHM). The output power can reach 1500W at 808nm wavelength with a power density reaches ~170KW/cm². Detailed misalignment sensitivities of the Micro-Lens Arrays (MLAs), with respect to the lateral position, the rotating angle, and the distance between the two MLAs are studied. Beam back reflection isolation is also considered in the design to accommodate for high reflectivity materials processing. This new laser system can adapt to the requirement of different beam size quickly and precisely by simply adjusting the lens group position, without interrupting production process and increasing manufacturing cost.

In this contribution, we demonstrate the capabilities of additive manufacturing (AM) to transfer complex optical assemblies into function-integrated systems. The Fused Filament Fabrication (FFF) technique is combined with the print-pause-print (PpP) scheme and the possibilities of multi-material printing. Thereby conventional optics are fully embedded into a lightweight and compact 3D printed optomechanic for a solid-state laser system. An optical characterization of the laser system proves the functionality in comparison to setups with discrete conventional optomechanics. We show that AM is a technology that can increase the level of integration of optical technologies and offers the potential to rethink optics assembly and optomechanical systems design.

Coherent and Spectral beam combining are methods used to achieve very high output powers by combining beams from multiple fiber laser sources. In coherent beam combining, the seed laser source is common for all fiber amplifiers, while in spectral beam combining, each fiber amplifier needs a different seed laser due to the requirement of distinct wavelengths. This is a major disadvantage in spectral beam combining since each amplifier needs an independent single-frequency laser, line-broadener, temperature and current controller. This adds substantial component cost and complexity. However, spectral beam combining has advantages over coherent beam combining such as not requiring complex phase stabilization mechanisms and graceful degradation of system output to individual amplifier failure. What is desirable is a compact, single module seed laser source for spectral combining. In this work, we demonstrate such a system based on an electro-optic high repetition rate comb generator incorporating a line-broadener for stimulated Brillouin scattering (SBS) suppression and a de-multiplexer to provide distinct wavelengths in distinct fiber ports. In this system, the output wavelengths have a carrier separation of 50GHz in the C-band and tunable linewidth as required for SBS suppression, based on phase modulation with noise, from a single frequency to 4GHz. Further, we demonstrate that this system enables superior SBS control by allowing for suitable altering of the line-shape in the de-multiplexer. In fiber amplifiers, SBS is enhanced due to seeding by the back-reflected component of laser spectra. Here, we avoid it by reducing the power in the laser line-shape at the SBS band.

Interband and Quantum Cascade Lasers (ICLs and QCLs) offer coherent and high-power radiation in the mid-infrared range, which is crucial for infrared countermeasures, high-resolution gas spectroscopy and chemical sensing. Due to many advantages, Cascade Lasers were expected to mature quickly and to settle in large volume applications. Especially the semiconductor nature of ICLs and QCLs gave hope to make this technology largely scalable and cheap, as it happened with LEDs and VCSELs in the past. Dynamic growth has not fully materialized in the last years. The price of lasers still remains high (around few thousand dollars per piece), and the potentially “killer” applications have not come yet. Cascade Lasers can be mainly found in niche applications. The reason for that lies both in the technical bottlenecks, but also in the market which has not been ready to implement CL technology. The customers were very conservative and there were many other competitive techniques to choose from. Now the perspectives for the adoption are brighter. All bottlenecks preventing the wider use of Cascade Laser technologies are deeply discussed in this study.