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1. High-power diode laser spectrally narrowed with prism–etalon feedback

   https://doi.org/10.1063/5.0203666  

   Muller, A (September 2024, Review of Scientific Instruments)

   A simple method for reducing the linewidth of a diode laser while maintaining high output power is described. It is based on a dispersive prism and a thin etalon for retroreflective feedback. The etalon creates two weak external cavities that provide spectral selectivity that is periodic with a period equal to the etalon’s free spectral range. The method was applied to a multimode blue laser diode, which in the absence of feedback features a linewidth of several nanometers. The spectral properties of the laser were investigated for different etalon thicknesses and operating currents and tested in the presence of temperature fluctuations. With a SF11 equilateral uncoated prism near Brewster’s angle and a 0.3 mm-thick uncoated fused silica etalon, the linewidth was reduced 20-fold to 70 pm (3.6 cm−1) with an output power of 3 W at a current of 2.15 A. The largest diode current probed was 2.75 A, which resulted in a linewidth of 100 pm (5.1 cm−1) and an output power of 4 W. In contrast to the use of, for example, a volume Bragg grating, a high degree of flexibility is afforded as the same prism–etalon pair can be used across the visible and near infrared. 

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2. Generation of 14.0  W of single-frequency light at 770  nm by intracavity frequency doubling

   https://doi.org/10.1364/OL.45.000339  

   Kwon, Minho; Yang, Peiyu; Huft, Preston; Young, Christopher; Ebert, Matthew; Saffman, Mark (January 2020, Optics Letters)

   We present a continuous, narrow-linewidth, tunable laser system that outputs up to 14.0 W at 770 nm. The light is generated by frequency doubling 18.8 W of light from a 1540 nm fiber amplifier that is seeded by a single-mode diode laser achieving $><\#comment/>74\mathrm{\%<\#comment/>}$conversion efficiency. We utilize a lithium triborate crystal in an enhancement ring cavity. The low intensity noise and narrow linewidth of the 770 nm output are suitable for cold atom experiments. 

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3. High-power narrow spectrum GaSb-based DBR lasers emitting near 2.1  µm

   https://doi.org/10.1364/OL.422536  

   Jiang, Jiang; Shterengas, Leon; Kipshidze, Gela; Stein, Aaron; Belyanin, Alexey; Belenky, Gregory (April 2021, Optics Letters)

   Stable high-power narrow-linewidth operation of the 2.05–2.1 µm GaSb-based diode lasers was achieved by utilizing the sixth-order surface-etched distributed Bragg reflector (DBR) mirrors. The DBR multimode devices with 100 µm wide ridge waveguides generated $\sim <\#comment/>850\mathrm{m}\mathrm{W}$in the continuous wave (CW) regime at 20°C. The device CW output power was limited by thermal rollover. The laser emission spectrum was defined by Bragg reflector reflectivity at all operating currents in a wide temperature range. The devices operated at DBR line with detuning from gain peak exceeding 10 meV. 

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4. All-Solid State Iron Resonance Lidar for Measurement of Temperature and Winds in the Upper Mesosphere and Lower Thermosphere

   Collins, R.; Li, J.; Wiliams, B.; Kaifler, B.; Thorsen, D. (October 2022, 30th International Laser Radar Conference (ILRC-30))

   The Arctic atmosphere and subauroral region are a natural laboratory for understanding plasma-neutral and dynamical coupling in the atmosphere and geospace. During geomagnetically active periods the auroral electrojet and auroral precipitation are overhead at the High-Frequency Active Auroral Research Program (HAARP) facility in Gakona, Alaska (62°N, 145°W) and facilitate active experiments. Iron resonance lidar systems are uniquely suited for these active investigations as naturally occurring iron layers extend from the upper mesosphere to the middle thermosphere (~70-150 km). A novel lidar system has been demonstrated at the German Aerospace Center using an Nd:YAG laser that operated at a minor line at 1116 nm and was tripled to the iron resonance line at 372 nm. This prototype laser was fully solid-state without liquid dyes or flashlamps and with diode pumping. We are developing a lidar system based on this prototype system that can operate robustly at the remote location of HAARP. We will employ a diode-pumped Nd:YAG laser with second and third harmonic generation. The laser will be injection-seeded by a tunable diode laser allowing the laser to frequency scan the iron line. The laser pulse spectra will be recorded on a shot-by-shot basis using an etalon imaging system with a spectral reference. The lidar system is will operate at 372 nm, with a pulse repetition rate of 100 pps, a pulse energy of 30 mJ, and a 0.9-m diameter telescope. We present the system specifications and the expected performance of the system. 

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5. All-Solid State Iron Resonance Lidar for Measurement of Temperature and Winds in the Upper Mesosphere and Lower Thermosphere

   Collins, R; Li, J; Wiliams, B; Kaifler, B; Thorsen, D (October 2022, 30th International laser radar Conference (ILRC-30))

   The Arctic atmosphere and subauroral region are a natural laboratory for understanding plasma-neutral and dynamical coupling in the atmosphere and geospace. During geomagnetically active periods the auroral electrojet and auroral precipitation are overhead at the High-Frequency Active Auroral Research Program (HAARP) facility in Gakona, Alaska (62°N, 145°W) and facilitate active experiments. Iron resonance lidar systems are uniquely suited for these active investigations as naturally occurring iron layers extend from the upper mesosphere to the middle thermosphere (~70-150 km). A novel lidar system has been demonstrated at the German Aerospace Center using an Nd:YAG laser that operated at a minor line at 1116 nm and was tripled to the iron resonance line at 372 nm. This prototype laser was fully solid-state without liquid dyes or flashlamps and with diode pumping. We are developing a lidar system based on this prototype system that can operate robustly at the remote location of HAARP. We will employ a diode-pumped Nd:YAG laser with second and third harmonic generation. The laser will be injection-seeded by a tunable diode laser allowing the laser to frequency scan the iron line. The laser pulse spectra will be recorded on a shot-by-shot basis using an etalon imaging system with a spectral reference. The lidar system is will operate at 372 nm, with a pulse repetition rate of 100 pps, a pulse energy of 30 mJ, and a 0.9-m diameter telescope. We present the system specifications and the expected performance of the system. 

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