100 W, tunable in-band thulium fiber amplifier pumped by incoherently combined 1.9 µm fiber lasers.

We detail the design and performance of a high efficiency in-band pumped thulium fiber amplifier operating at the 100 W level. Using a novel pumping architecture based on three incoherently combined thulium fiber oscillators at 1904 nm and a seed laser tunable from 1970-1990 nm, efficient amplification is demonstrated in a high dopant concentration 25/65/250 µm thulium fiber. Here we use the 65 µm pedestal surrounding the core as a pump cladding to increase the cladding to core overlap and improve the overall pump absorption. Up to 89% slope efficiency is obtained with ∼100 W output power at 1990 nm. These results indicate that in-band pumping is a viable route to circumvent the thermal limitations associated with 793 nm diode pumping and provide a pathway for development of multi-kW laser sources in the 2 µm spectral window.

Efficient coupling of a quantum cascade laser to a few-mode chalcogenide fiber: erratum.

The authors wish to acknowledge an additional funding source which was absent from our manuscript.

Efficient coupling of a quantum cascade laser to a few-mode chalcogenide fiber.

We report efficient coupling of a quantum cascade laser (QCL) into step-index chalcogenide fibers (As 2S 3). Mechanically robust and low-loss chalcogenide fibers were fabricated using a hybrid, multi-material thermal drawing process. With suitable free-space optics, more than 160 mW of optical power was coupled into the fiber with predominantly single-mode excitation. Antireflection coatings on the fiber facets enabled 88.9% transmission with strong core confinement. By accurately tailoring the core diameter and antireflection-coating thickness, these fibers offer a versatile platform for high-power and low-loss transmission across the infrared spectrum. This work introduces an attractive alternative to the use of hollow-core fibers or multimode solid-core fibers for diffraction-limited infrared beam delivery.

High-power spectral beam combining of linearly polarized Tm:fiber lasers.

To date, high-power scaling of Tm:fiber lasers has been accomplished by maximizing the power from a single fiber aperture. In this work, we investigate power scaling by spectral beam combination of three linearly polarized Tm:fiber MOPA lasers using dielectric mirrors with a steep transition from highly reflective to highly transmissive that enable a minimum wavelength separation of 6 nm between individual laser channels within the wavelength range from 2030 to 2050 nm. Maximum output power is 253 W with M(2)<2, ultimately limited by thermal lensing in the beam combining elements.

High peak-power mid-infrared ZnGeP2 optical parametric oscillator pumped by a Tm:fiber master oscillator power amplifier system.

We report on the utilization of a novel Tm:fiber laser source for mid-IR ZnGeP2 (ZGP) optical parametric oscillator (OPO) pumping. The pump laser is built in a master oscillator power-amplifier configuration delivering up to 3.36 W of polarized, diffraction limited output power with 7 ns pulse duration and 4 kHz repetition rate. This corresponds to a peak power of ∼121 kW and a pulse energy of ∼0.84 mJ. With this source, we generated 27.9 kW of total mid-IR peak power in a doubly resonant oscillator (DRO) configuration. This is, to the best of our knowledge, the highest ever demonstrated mid-IR peak power from a directly Tm:fiber laser pumped ZGP OPO. Moreover, a DRO output with about 284 µJ of total mid-IR pulse energy was demonstrated using 100 ns pump pulses. The wavelength tuning of the idler was extended to 6 µm with lower output power in another OPO experiment.

Highly polarized all-fiber thulium laser with femtosecond-laser-written fiber Bragg gratings.

We demonstrate and characterize a highly linearly polarized (18.8 dB) narrow spectral emission (<80 pm) from an all-fiber Tm laser utilizing femtosecond-laser-written fiber Bragg gratings. Thermally-dependent anisotropic birefringence is observed in the FBG transmission, the effects of which enable both the generation and elimination of highly linearly polarized output. To our knowledge, this is the first detailed study of such thermal anisotropic birefringence in femtosecond-written FBGs.