Single PCSEL devices have been demonstrated to have Watt-class output. Due to the inhomogeneous optical mode distribution, such large-area PCSEL devices may suffer from saturation of lasing efficiency under high biasing conditions when the spatial hole burning, and band distortion effects result in decreased gain to the fundamental mode and increased gain to the high-order modes. On the other hand, it has been a challenging task to achieve coherent beam combining and single-mode emission based on the VCSELs or DFB lasers. PCSEL architecture has stronger in-plane optical coupling control through the evanescent wave leakage between the cavities. In this paper, we present design and simulation of PCSEL arrays with experimental demonstration of single dominant spatial mode profile obtaining output power of 250 mW from 2-by-2 PCSEL arrays under pulsed operation. Our uncooled PCSEL arrays exhibit 0.22 nm linewidth above threshold compared to 0.075 nm for a single 100 µm PCSELs.

Forward Photonics (FP) is a company that specializes in developing and manufacturing high-brightness semiconductor lasers for defense and commercial applications, using its proprietary wavelength beam combination (WBC) technology. Direct semiconductor lasers can offer high efficiency output, however poor brightness has been a limiting factor in using them for applications which require long distance propagation or small spot sizes. WBC enables the generation of high brightness beams at various wavelengths, from UV to LWIR, by combining multiple laser diodes. WBC lasers have similar beam quality as fiber lasers, but with superior wavelength flexibility, efficiency, and reliability. In this presentation, FP will review recent power and form factor developments in its WBC laser systems, including quantum cascade lasers (QCLs) and direct-diode near-infrared lasers.

Fueled by recent technological advancements, high power laser systems are becoming an invaluable asset in a variety of applications. At the same time, there is a need for new architectural approaches that can reduce the size and cost of laser systems, as well as provide dynamic multi-beam control. While optical phased arrays (OPAs) can significantly reduce the size and cost of high power laser systems, their adoption is limited due to significant energy losses into spurious diffraction lobes. This presentation demonstrates the innate benefits of coherent field transformations (CFTs), enabling new architectural approaches and functionalities, with applications to directed energy, free-space optical communications, materials processing, and sensing.

We demonstrate a C-band gain-switched seed laser intended for a EDFA-based fiber laser meeting the performance, footprint, robustness, and cost targets for volume time-of-flight LiDAR systems. The technology reported here leverages Freedom Photonics high-power DFBs coupled with a Black Forest Engineering control ASIC in a low-inductance package. As a result, the overall package is a compact form factor that can fit within a 16-pin butterfly package. To date, our 1550 nm seed technology delivers more than 2.5 nJ pulse energy for a 480KHz repetition rate on a 4 ns pulse, which is 30 times higher than conventional seed lasers. This technology is the first of its kind to realize a 1550 nm high-pulse energy seed laser for volume deployment of time-of-flight fiber-laser-based LiDAR systems.

Lasers built on crystalline fibers are capable of producing significantly higher power output per fiber compared to their glass counterparts. This paper explores the barriers for the adoption and implementation of crystal fibers in high-power laser systems and recent advances in crystal fiber fabrication and testing. An overview and update of the crystal fiber work at NRL will be presented.

We are exploring the potential of Praseodymium (Pr³+) as a dopant in low-phonon chloride hosts, CsCdCl3 and CsPbCl3. Pr3+ possesses favorable absorption bands (3H4 → 3F3,4) in the ~1.5 µm range, amendable to efficient laser diode or fiber laser pumping, as well as group of energy levels with energy gaps enabling mid-IR emissions in the 3-5 micron wavelength range of practical interest. In this work, spectroscopic investigation of Pr3+ aimed to also determine whether the “three-for-one” processes boosting the efficiency of mid-IR emission can be observed in these new materials. Detailed spectroscopic results including Judd-Ofelt analysis, transitions cross-sections, and fluorescence dynamics will be discussed and their potential for efficient mid-IR laser operation will be evaluated.

We have studied the effect of radiation-induced degradation (RIGD) and recovery of the output optical power for erbium-doped fiber amplifiers (EDFAs) in a master oscillator power amplifier (MOPA) setup before and after radiation exposure using a 60Co gamma-ray source. Our preliminary results indicate that the fibers that are not optimized have a complete degradation of gain after exposure to a 10 kRad (100 Gy) dose, where all input signal power is absorbed. We present our efforts where we have improved the degradation to values where the fibers have a significant reduction in gain degradation after exposure. Results of our efforts for further improvement will be discussed.

With the goal of developing new mid-IR lasers, Rare Earth doped low-phonon sulfide-based chalcogenide glasses are being explored for their potential as sources emitting at ~3-microns. Such low phonon energy materials are necessary to minimize competing non-radiative decay processes such as multi-phonon relaxation (MPR). This work presents the results of a comprehensive spectroscopic study comparing the 3-micron laser potential of three different RE ions (Dy3+, Ho3+, and Er3+) doped into sulfide-based chalcogenide glass. Spectroscopic results will focus on absorption, fluorescence, and decay characteristics. From these measurements, laser relevant parameters such as cross sections and radiative lifetimes are calculated.

We will present our results on fabricating transparent ceramic gain media with endcaps, planar and channel waveguides made by additive manufacturing, thin-disk structures with an undoped “face cap”, and laser rods where the doped core is surrounded by a clad. The ceramic optics are based on various garnet and sesquioxide compositions as well as for SrF2. Various gain and laser oscillation results are included as feasibility demonstrations.

Employing Raman gain of optical materials is appealing for a variety of laser applications, to include fiber laser combiners. In order for a Raman combiner to be efficient, the Raman material must have high gain, low loss figure at 1st Stokes wavelength, and high loss figures at higher order Stokes wavelengths. This paper demonstrates an efficient double-clad fiber Raman combiner utilizing fused silica core as gain material with microstructured cladding designed with filtering properties implemented for suppression of higher order Stokes propagation in the core. Comprehensive study results of this Raman combiner will be presented.