In this work we propose a simulation tool to analyze the case of conduction-driven thermal blooming and compare the results with measurements at the 2055 nm absorption line of CO2. Using a split-step beam propagation method and incorporating the spatial refractive index change related to the absorption-driven radial temperature gradient resulting from conduction, the effect of beam distortion can be described for arbitrary wavelengths and various atmospheric conditions. The model is benchmarked by experimental investigations using a tunable 100-W thulium fiber laser.
We report on the scaling of a polarization-maintaining MOPA at a signal wavelength of 2048 nm, designed for pumping an optical parametric oscillator (OPO). By utilizing the MOPA structure to design suitable OPO pump pulses the overall mid-IR conversion efficiency is enhanced enabling the scaling of the mid-IR average power. 60 W of average power is achieved and applied to pump different ZGP OPOs. The resonator designs are investigated and compared regarding scalability and beam quality.
We present our latest results in power scaling of Midwave-Infrared (MWIR) Optical Parametric Oscillators (OPOs) based on a Zinc Germanium Phosphide (ZGP) crystal, utilizing a single oscillator fiber laser as pump source. To obtain a compact and complexity-reduced pump source emitting at ≥ 2.09 μm, a Q-switched Tm3+:Ho3+- codoped fiber laser was developed. Based on this pump source at an emission wavelength of 2.1 μm, we achieved an MWIR output power of 12.2W with pulse energies of up to 270 μJ and a conversion efficiency exceeding 43 %. This result exceeds the published power records of ZGP-based OPOs pumped by 2 μm Q-switched fiber lasers by 50 % and sets a new benchmark for average power scaling and pulse energy of Q-switched pump sources.
An actively Q-switched diode-pumped Tm3+-doped fiber laser (TDFL) operating at 2050 nm is reported based on a flexible Photonic Crystal Fiber (PCF) with a core diamter of 50 μm. Using a fiber length of 3 m, the TDFL delivers gaussian shaped pulses with a maximum pulse energy of 1.5 mJ, corresponding to a peak power of 16 kW and a pulse width of 88 ns. The measured output spectrum shows a single peak at 2050 nm with a 3-dB-linewidth of 100 pm and 10-dB-linewidth of 270 pm. For a longer fiber length of 7 m, the effective gain is redshifted by reabsorbtion, increasing the achievable pulse energy up to 1.9 mJ. The average output power of the pulsed TDFL can be scaled to more than 100 W with a slope efficiency of 46 %. In all configurations the TDFL delivers nearly diffraction limited beam quality (M2 ⪅1.3).
A polarization-maintaining (PM) pulsed three-stage master oscillator power amplifier (MOPA) emitting at 2047 nm is reported, generating 19.8W of output power (396 μJ pulse energy) for a 50 ns pulse width at a repetition rate of 50 kHz. The output signal is linearly polarized and a diffraction limited beam quality is achieved. This MOPA laser is used to pump a doubly resonant ZnGeP2 (ZGP) optical parametric oscillator (OPO) in a linear cavity. A mid-IR output power of 8.1W, accordingly 162 μJ of pulse energy, and a conversion efficiency of 44 % are obtained in the 3-5 μm band.
A diode-pumped actively Q-switched Tm3+-doped fiber laser is reported generating pulse energies of 800 μJ, pulse widths of 43 ns and peak powers of 17.5 kW. By using the single-oscillator as a pump source for nonlinear frequency conversion, mid-IR pulse energies of 230 μJ are extracted from a ZnGeP2 (ZGP) optical parametric oscillator (OPO).
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