Temperature investigation of low SWaP thulium-doped fiber lasers.

We investigate the temperature dependence of an in-band core-pumped thulium-doped fiber laser with a low SWaP (size, weight, and power) architecture. The temperature investigation is carried out both experimentally and numerically by a simulation model. We demonstrate experimentally that the investigated setup is resistant for temperatures till 353 K. In addition, we explain the observed behavior by considering the temperature depended spectroscopic parameters of thulium-doped silica fibers. Finally, a numerical investigation is carried out for higher temperatures up to 573 K and higher output powers up to 12 W as well as for different wavelengths and show that the considered fiber lasers works still efficient at these temperature ranges. We show the reliability of the considered thulium-doped fiber laser architecture for applications in harsh environment.

High average power Q-switched Ho3+:YAG laser with a single-line emission at 2122 nm.

We present an efficient Q-switched dual-crystal Ho3+:YAG laser resonator achieving an output power of 56 W at an incident pump power of 100.7 W with a slope efficiency of 64.4%. The setup was pump power limited. Notably, by carefully tuning multiple etalons placed within the cavity, we achieved a single-line spectral emission at 2122 nm. This deviates from the typical emission wavelengths of 2090 nm or 2096 nm for Ho3+:YAG at comparable output powers in Q-switched operation. The laser exhibited very good beam quality, approaching diffraction-limited performance with an excellent M2- < 1.2. At the maximum output power, a pulse FWHM of 100 ns was measured.

Alignment-insensitive end-pumped continuous-wave crossed-Porro prism Ho3+:YAG laser.

A continuous-wave crossed-Porro prism Ho3+:YAG laser is presented and compared with a corresponding mirror resonator. A maximum output power of 30.7 W is reached with a slope efficiency of 67.4% with respect to the absorbed pump power. The laser output beam shows a very good beam quality of better than M2 < 1.2 which clearly surpasses that of the mirror resonator. In terms of alignment sensitivity, the crossed-Porro prism resonator is superior to the mirror resonator due to the retro-reflective nature of the prisms in the axis around the apex.

High-power continuous-wave Tm3+:Ho3+-codoped fiber laser operation from 2.1 µm to 2.2 µm.

A Tm3+:Ho3+-codoped free-space single-oscillator fiber laser is under investigation with special focus on the power scalability of emission wavelengths from 2.1 µm to 2.2 µm. Using a tunable diffraction grating, a 200-nm tunable laser source is built. Laser output powers above 10 W are delivered from 1990 nm up to 2190 nm, demonstrating the range for stable high-power laser operation. By replacing the diffraction grating by a highly reflective, narrow linewidth volume Bragg grating, power scaling is performed at 2.1 µm and is even enabled at a wavelength of 2.2 µm. Using a volume Bragg grating (VBG) at 2.1 µm, a slope efficiency of 49% is measured with an output power of 262 W. Using another VBG with a center wavelength of 2.2 µm, the fiber laser delivers a record power of 77 W with a slope efficiency of 29%.

Mid-infrared optical parametric oscillator pumped by a high-pulse-energy, Q-switched Ho3+:YAG laser.

A high-pulse-energy mid-infrared light source is presented, based on a zinc-germanium-phosphide optical parametric oscillator (ZGP OPO) pumped by an actively $Q$-switched high-pulse-energy ${{\rm Ho}^{3 +}}{:}{\rm YAG}$ laser. The ${{\rm Ho}^{3 +}}{:}{\rm YAG}$ pump laser source is capable of generating a pulse energy of 15 mJ from a single ${{\rm Ho}^{3 +}}{:}{\rm YAG}$ rod at room temperature at a pulse repetition frequency (PRF) of 700 Hz. A maximum power of 20.1 W at a central wavelength of 2090 nm can be obtained in continuous operation, with a slope efficiency of 45.1%. A good beam quality with an ${{\rm M}^2}$ better than 1.3 was achieved in $Q$-switched operation. The presented laser architecture was used as a suitable pump source for a ZGP-based OPO. Operated at a PRF of 2 kHz and pumped with a pulse energy of 8 mJ, a low conversion threshold of 1.5 W and a maximum total output power of 6.3 W could be obtained in a linear ZGP-based OPO. At maximum power, the peak power of the generated mid-infrared radiation exceeded 120 kW, while the beam quality was affected by the strong gain lens building inside the nonlinear material as a consequence of the high-energy pump pulses.

Nanosecond pulsed single-frequency two-stage holmium-doped fiber MOPA at 2054 nm and 2090 nm.

A single-frequency polarization-maintaining holmium-doped fiber master oscillator power amplifier operating at signal wavelengths of $2054\;{\rm nm}$ and $2090\;{\rm nm}$ is presented. The two-stage setup delivers up to $240\;{\rm W}$ peak power and $6.7\;\unicode{x00B5} {\rm J}$ pulse energy for a pulse width of $30.2\;{\rm ns}$ at a repetition rate of $100\;{\rm kHz}$. The first amplifier stage is designed by simulation, tailored for high gain at the signal wavelength range, favoring amplification at $2090\;{\rm nm}$. The design is discussed, and the measured values are compared with the simulation. The second stage is investigated regarding the efficiency for co- and counter-pumping. Stimulated Brillouin scattering was found to be the limiting factor for pulse peak power scaling in the second stage. The measured output pulse shapes are discussed and compared to pulse shapes derived with the Frantz-Nodvik model.

High pulse energy ZnGeP2 OPO directly pumped by a Q-switched Tm3+-doped single-oscillator fiber laser.

A mid-infrared ${{\rm ZnGeP}_2}$ optical parametric oscillator pumped by a ${{\rm Tm}^{3 +}}$-doped fiber laser is reported, providing pulse energies of $230 \;\unicode{x00B5}{\rm J}$, pulse widths of 40 ns, and peak powers of ${\sim}6\;{\rm kW} $ with excellent efficiency and beam quality. The pump source is an actively $Q$-switched single oscillator optimized to generate high pulse energies.

55 W actively Q-switched single oscillator Tm3+, Ho3+-codoped silica polarization maintaining 2.09 µm fiber laser.

A bidirectional 793 nm diode-pumped actively Q-switched Tm3+, Ho3+-codoped silica polarization-maintaining (PM) double-clad (DC) fiber laser is reported. With this fiber laser, 55 W of average output power with 100 ns pulse width at 200 kHz repetition rate and 2.09 µm wavelength is obtained. The pump power injection with end-caps fusion-spliced on fiber tips provides good power stability (< 1.1%) and beam quality factors (M2 < 1.7). The fiber laser output beam polarization factor is 97.5%. At 55 W, no thermal-induced damage is observed on any optical element, and power scaling of the laser is only pump-power-limited in the range of the total available pump power (180 W).

Optical parametric generation by a simultaneously Q-switched mode-locked single-oscillator thulium-doped fiber laser in orientation-patterned gallium arsenide.

Optical parametric generation is demonstrated in orientation-patterned gallium arsenide, pumped by a novel single-oscillator simultaneously Q-switched and mode-locked thulium-doped fiber laser, downconverting the pump radiation into the mid-infrared wavelength regime. The maximum output energy reached is greater than 2.0 µJ per pump pulse.

High-peak-power single-oscillator actively Q-switched mode-locked Tm3+-doped fiber laser and its application for high-average output power mid-IR supercontinuum generation in a ZBLAN fiber.

A single-oscillator actively Q-switched mode-locked (QML) thulium-doped silica fiber laser is presented and used to pump a ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fiber for mid-infrared (mid-IR) supercontinuum (SC) generation. The fiber laser provided high-peak-power levels directly from the oscillator delivering single mode-locked pulse energies up to 48 µJ, being 2-4 orders of magnitude higher than conventional continuous wave mode-locked lasers. By pumping a ZBLAN fiber specially designed for high-output-power SC generation, 7.8 W have been achieved in all spectral bands with a spectrum extending to 4.2 µm.

Actively mode-locked Tm(3+)-doped silica fiber laser with wavelength-tunable, high average output power.

A diode-pumped, actively mode-locked high-power thulium (Tm3+)-doped double-clad silica fiber laser is demonstrated, providing an average output power in mode-locked (continuous wave) operation of 53 W (72 W) with a slope efficiency of 34% (38%). Mode-locking in the 6th-harmonic order was obtained by an acousto-optic modulator driven at 66 MHz without dispersion compensation. The shortest measured output pulse width was 200 ps. Owing to a diffraction grating as cavity end mirror, the central wavelength could be tuned from 1.95 to 2.13 µm. The measured beam quality in mode-locked and continuous wave operation has been close to the diffraction limit.

Mid-infrared lasing from Ho(3+) in bulk InF(3) glass.

We report on an Ho3+:InF3 glass laser pumped by a Cr3+:LiSAF laser emitting at 889 nm. Ho3+:InF3 glass is a promising material for direct mid-infrared lasers around 4 µm. To evaluate the performances of this new material, we compared it to an Ho3+:BYF crystalline laser pumped by the same source. At 650 mJ pump energy, 7.2 mJ (46 mJ) was obtained with Ho3+:InF3 (Ho3+:BYF), respectively. This is, to the best of our knowledge, the first reported laser activity in this type of glass.

6.5 W ZnGeP(2) OPO directly pumped by a Q-switched Tm(3+)-doped single-oscillator fiber laser.

An efficient actively Q-switched Tm3+-doped single-oscillator fiber laser based on a silica polarization-maintaining (PM) double-clad fiber provided average powers of 23 W at pulse widths of 65 ns at 40 kHz pulse repetition frequency. It was used to directly pump a ZnGeP2 optical parametric oscillator (OPO). Up to 6.5 W were generated in mid-IR wavelength range.

Actively Q-switched and mode-locked Tm3+-doped silicate 2 µm fiber laser for supercontinuum generation in fluoride fiber.

A diode-pumped actively Q-switched and actively mode-locked Tm3+-doped double-clad silicate fiber laser is reported providing up to 5 W of average output power at ~60 kHz Q-switch envelope repetition rate and ~8 µJ subpulses with up to 2.4 kW peak power. Using this source as a pump laser for supercontinuum generation in a ZBLAN fiber, over 1080 mW of supercontinuum from 1.9 µm to beyond 3.6 µm was obtained at an overall efficiency of 3.3% with respect to the diode pump power.

High-power actively mode-locked sub-nanosecond Tm³âº-doped silica fiber laser.

A diode-pumped actively mode-locked Tm³âº-doped double-clad silica fiber laser providing up to 11.8 W of average output power and pulse widths in mode-locked operation of 38 ps at a repetition rate of 37.88 MHz is reported. Pulse energies of up to 314 nJ were obtained.