The performances of the diode-pumped CW and free running pulsed (Q-CW) 3-μm Er:YLF lasers, operating at room and cryogenic temperatures (RT and LNT), were compared theoretically and experimentally. It is shown that cryogenic cooling considerably enhances laser output power and efficiency in both modes of operation. On the other hand, our prediction for a Q-switched mode is that cryogenic performance can be so severely limited by amplified spontaneous emission (for some gain element designs) that the RT Q-switching may result in substantially higher pulse energies, albeit at lower efficiency.

An Er:YAG master-oscillator (MO)/power amplifier (PA) system with a dual-end pumped, 4-pass, zig-zag, slab amplifier was experimentally and theoretically investigated. Both the Q-switched MO and PA were in-band diode-pumped at 1532 nm. With the MO seed pulse energy of 17 mJ, our MOPA yielded 70 mJ pulses with a duration of ∼ 80 ns at a pulse repetition frequency (PRF) of 1 kHz, thus delivering 70 W of average power at 1645 nm.

All-ceramic channel waveguides (CWGs) in Yb:YAG transparent ceramics have been fabricated for the first time, to the best of our knowledge, via direct ink write (DIW) and their laser performance has been demonstrated. Single filaments of Yb:YAG nanoparticle-loaded ink were extruded into undoped YAG; the Yb:YAG filaments formed the CWGs, surrounded by undoped cladding. Elemental mapping confirmed the Yb doping profile and waveguide integrity. Optical characterization showed low cladding scatter losses (<1.3%/cm at 1.3 µm), and laser testing with a 940 nm Ti:sapphire pump demonstrated efficient lasing at 1030 nm. The best-performing waveguide, with an elliptical cross-section (100 µm × 60 µm and a length of 1.4 cm), achieved a slope efficiency of 61% and a roundtrip loss of 12.4%. These results identify DIW as a promising approach for fabricating high-performance channel waveguides in transparent ceramics.

We thoroughly investigate the spectral kinetics of a diode-pumped, free-running, pulsed 3 μ m Er:YLF laser at cryogenic and room temperatures and show that spectroscopically-derived emission cross-sections of the 3 μ m laser transitions in Er 3+ do not allow correctly predicting the experimentally observed multiwavelength spectral kinetics of the laser output. ‘True’ emission cross-sections were determined through detailed modeling of the laser dynamics, anchored by experimentally derived thresholds for successively lasing inter-Stark transitions between the 4 I 11/2 and 4 I 13/2 manifolds. These revised cross-sections also finally eliminate the existing major discrepancies in the literature data on emission cross-sections in Er:YLF.

Ultra-low maximum-phonon energy of the ternary-halide crystalline hosts and multi-millisecond-long 3H5 level lifetimes of Pr3+ dopant make them promising gain media for mid-infrared lasers in the 4.6-5.1 µm spectral domain with “3-for-1” enhanced laser efficiency.

In this work, we present the results of our recent spectroscopic investigation on Dy3+-doped Ga2Ge5S13 (Dy:GGS) glass, aiming to explore its potential for mid-infrared (3-5 µm) laser applications. Under 910 nm excitation, the studied Dy:GGS glass displayed broad emission bands centered at ~2.9 µm and ~4.35 µm corresponding to 6H13/2 --> 6H15/2 and 6H11/2 --> 6H13/2, respectively. The measured fluorescence decay time of the 6H11/2 manifold (upper laser level for 4.35 µm laser transition) was found to be in the millisecond range, demonstrating similarity to other sulfide glasses doped with Dy3+. Spectroscopic results and data modeling including the temperature dependent emission and decay dynamics, concentration dependent studies, Judd-Ofelt analysis, and transition cross-sections, will be presented.

We have developed a simple approach to deriving the efficiency of Q-switched four-level lasers, valid even for arbitrarily long lower laser level lifetimes. By eliminating time dependence from the calculation, numerical solutions can be obtained very rapidly. Its threshold and limiting slope efficiency values provide useful estimates for free-running pulsed four-level lasers as well as Q-switched.

Comprehensive study of spectral kinetics of a free-running, pulsed, ~3-µm Er:YLF laser versus Er3+ concentration, pump energy and temperature eliminates discrepancy in existing data on emission cross-sections of inter-Stark transitions between the 4 I 11/2 and 4 I 13/2 manifolds.

All material types are being considered, from crystals to ceramics and glasses, with focus on those RE3+ hosts with low maximum energy. In this work, a comparative study was performed on the mid-IR (3-5 um) spectroscopic properties of erbium doped in low-phonon fluoride (BaF2) and chloride (CsCdCl3) crystals as well as sulphide (Ga2Ge5S13) glasses. Among the studied materials, Er3+:CsCdCl3 showed the longest 4I9/2 emission lifetime of ~11 ms whereas the ~ 46 us observed from Er3+:BaF2 was the shortest 4I9/2 lifetime. These results reflect the reduced nonradiative rates through multiphonon relaxation in chloride crystals. Spectroscopic results and data modeling including the temperature dependent emission and decay dynamics, Judd-Ofelt analysis, and transition cross-sections will be presented.

The comparative analysis of Er3+- and Dy3+-doped low-phonon laser gain materials aiming to identify the best dopant for directly diode-pumped mid-infrared lasers operating in the 4.1-4.8 µm spectral domain has been performed for the first time.

With the goal of developing new mid-IR laser sources, Rare-earth doped low-phonon crystals and sulfide-based chalcogenide glasses are being explored. Low maximum 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 mid-IR spectroscopic study on Dy3+ doped sulfide-based chalcogenide glasses, as well as comparative results from similarly doped chloride and fluoride crystals. 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.

Transparent ceramic Er:YAG laser rods were fabricated via the direct ink write (DIW) method with engineered doping profiles featuring an Er-doped core with endcaps and core-clad structures. Laser rods up to 11 cm in length were produced which required development of a scalable process. To achieve this, multiple improvements were implemented, including printing the rods horizontally on a substrate, rather than vertically, eliminating the need for an external support structure and using a sacrificial drying layer to mitigate warping and defects. Highly transparent rods were achieved with optical scatter levels as low as 0.5%/cm (at 543 nm). A small refractive index difference of 5.7 ppm was measured at the interface between the Er-doped core and the Lu-doped endcaps and cladding. These results demonstrate DIW as a straightforward method for making good optical quality laser rods with engineered doping profiles to improve laser performance.

Development of new solid-state mid-infrared (mid-IR) laser sources for wide range of applications in remote sensing, free-space communications, materials processing, and medicine remains to be a challenge, and demands advanced laser material development. RE 3+ ions possess promising emission transitions in the mid-IR spectral region but require host materials with low maximum phonon energies to circumvent competing nonradiative multi-phonon relaxation (MPR), thus preserving high efficiency of mid-IR emission [1–3]. RE 3+ doped low-phonon fluoride $(300-450\ \text{cm}^{-1})$ and ternary chloride crystals $(200-250\ \text{cm}^{-1})$ are well studied as laser materials for mid-IR. Recently, interest in chalcogenide glasses increased significantly due to their chemical and mechanical durability, wide mid-IR transparency, sufficiently low phonon energies. Among RE 3+ ions, trivalent dysprosium Dy 3+ , holmium Ho 3+ , and erbium Er 3+ are known to be the most common laser active ions in solid host materials capable of producing laser output in the 3–5 $\upmu\mathrm{m}$ spectral range [1].

This Joint Issue of Optics Express and Optical Materials Express features 40 peer-reviewed articles written by authors who participated in the Advanced Solid State Lasers Conference, part of the Optica Laser Congress and Exhibition held in Barcelona, Spain from December 11-15, 2022. This review provides a brief summary of these articles covering the latest developments in laser host and nonlinear crystals, structured materials, fiber lasers and amplifiers, ultrafast mode-locked lasers and optical parametric amplifiers, frequency-doubled Raman lasers, vortex beams, and novel concepts in laser design.

We describe our progress in developing additively manufactured transparent optical ceramic gain media, including gradient-doped parts, thin disk gain elements, variously cladded slabs and rods, as well as planar and channel waveguides.

We have developed a simple approach to deriving the efficiency of Q-switched four- level lasers, valid for long lower laser level lifetimes. Its threshold and limiting slope efficiency provide useful estimates for free-running four-level lasers as well.