Advanced Solid-State Lasers: feature issue introduction.

This joint issue of Optics Express and Optical Materials Express features 23 peer-reviewed articles primarily by authors who participated in the Advanced Solid State Lasers conference, which was part of the Optica Laser Congress held in Tacoma, Washington, USA on October 8-12, 2023. This review provides a brief summary of these articles covering the latest developments in laser gain materials and nonlinear crystals, mode-locked lasers, fiber lasers and amplifiers, nonlinear optical sources, and novel concepts in laser design.

Rapid calculation of the efficiency of self-terminating four-level Q-switched lasers.

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.

Enhanced mid-infrared emission of Pr ions in solids through a "3-for-1" excitation process - quantified.

Evidence is presented that a "three-for-one" process based on two cross-relaxations between Pr ions efficiently populates the mid-infrared-emitting H manifold in a Pr-doped low-maximum-phonon-energy host. The concentration dependence of infrared fluorescence spectra and lifetimes of polycrystalline Pr:KPbCl initially excited to the F manifolds indicate that the 3500-5500-nm fluorescence becomes strongly favored over shorter-wavelength infrared emission bands in the higher-concentration sample. The strong concentration dependence of the F and H manifold lifetimes suggests that both of these decay by cross-relaxation processes, resulting in more than one ion excited to H for each ion initially excited to F.

Cladding-pumped, Yb:YAG-core, fiber-like waveguide laser: modeling and experiment.

We developed a model describing the performance of the cladding-pumped, Yb:YAG-core, fiber-like waveguide laser with a large cladding-to-core area ratio. We analyzed how pump absorption and laser output efficiencies depend on the Yb-doping level as well as the waveguide parameters, such as clad-to-core area ratio and waveguide length. We also determined the conditions that maximize both pump and laser efficiency.

Pr:RbPbCl: temperature dependent spectra, dynamics and three-for-one excitation: erratum.

We present an erratum regarding the contents of Table 1.

Low-loss 'crystalline-core/crystalline-clad' (C4) fibers for highly power scalable high efficiency fiber lasers.

We report the latest progress in fabrication and laser performance of the fully crystalline double-clad 'Yb:YAG-core/undoped-YAG-clad' fibers grown by the hybrid crystal growth method. The single-crystalline ytterbium (Yb) doped yttrium aluminum garnet (YAG) fiber cores were grown by the laser heated pedestal growth (LHPG) method, and the single-crystalline undoped YAG claddings were grown by the liquid phase epitaxy (LPE) technique, in which the single-crystalline Yb:YAG cores were used as the growth seeds. The key parameters of the hybrid-grown 'crystalline core/crystalline clad' (C4) fibers, including material composition, crystal structure, and fiber propagation loss, were characterized.

Pr:RbPbCl: temperature dependent spectra, dynamics and three-for-one excitation.

The temperature dependence of the absorption, fluorescence, and fluorescence lifetimes of states relevant to short-wave-infrared and mid-infrared laser operation have been measured in Pr:RbPbCl. The 3600-5500-nm fluorescence grows strongly with temperature, and at room temperature represents the large majority of the observed photon flux. Intra-ionic decay processes cannot explain this dominance, but a combination of two cross-relaxation processes provides good agreement with the data.

Nanoparticle doping for high power fiber lasers at eye-safer wavelengths.

A nanoparticle (NP) doping technique was developed for fabricating erbium (Er)- and holmium (Ho)-doped silica-based optical fibers for high energy lasers. Slope efficiencies in excess of 74% were realized for Er NP doping in a single mode fiber based master oscillator power amplifier (MOPA) and 53% with multi-Watt-level output in a resonantly cladding-pumped power oscillator laser configuration based on a double-clad fiber. Cores comprising Ho doped LaF and LuO nanoparticles exhibited slope efficiencies as high as 85% at 2.

High-efficiency, 154 W CW, diode-pumped Raman fiber laser with brightness enhancement.

We demonstrate a high-power, high-efficiency Raman fiber laser pumped directly by laser diode modules at 978 nm. 154 W of CW power were obtained at a wavelength of 1023 nm with an optical to optical efficiency of 65%. A commercial graded-index (GRIN) core fiber acts as the Raman fiber in a power oscillator configuration, which includes spectral selection to prevent generation of the second Stokes.

Scalable waveguide design for three-level operation in Neodymium doped fiber laser.

We have constructed a double clad neodymium doped fiber laser operating on the three-level F→I transition. The laser has produced 11.5 W at 925 nm with 55% slope efficiency when pumped at 808 nm, comparable to the best previous results for a double-clad fiber configuration on this transition.

Thermal characterization, crystal field analysis and in-band pumped laser performance of Er doped NaY(WO(4))(2) disordered laser crystals.

Undoped and Er-doped NaY(WO4)2 disordered single crystals have been grown by the Czochralski technique. The specific heat and thermal conductivity (κ) of these crystals have been characterized from T = 4 K to 700 K and 360 K, respectively. It is shown that κ exhibits anisotropy characteristic of single crystals as well as a κ(T) behavior observed in glasses, with a saturation mean free phonon path of 3.

Resonantly cladding-pumped Yb-free Er-doped LMA fiber laser with record high power and efficiency.

We report the results of our power scaling experiments with resonantly cladding-pumped Er-doped eye-safe large mode area (LMA) fiber laser. While using commercial off-the-shelf LMA fiber we achieved over 88 W of continuous-wave (CW) single transverse mode power at ~1590 nm while pumping at 1532.5 nm.

Resonantly diode-pumped Ho3+:Y2O3 ceramic 2.1 µm laser.

We report what is believed to be the first laser operation based on Ho3+-doped Y2O3. The Ho3+:Y2O3 ceramic was resonantly diode-pumped at ~1.93 µm to produce up to 2.

Principal modes in fiber amplifiers.

The dynamics of the state of polarization in multimode fiber amplifiers is presented. The experimental results reveal that although the state of polarizations at the output can vary over a large range when changing the temperatures of the fiber amplifiers, the variations are significantly reduced when resorting to the principal states of polarization in single-mode fiber amplifiers and principal modes in multimode fiber amplifiers.

Fiber amplification of radially and azimuthally polarized laser light.

The results of amplifying either radially or azimuthally polarized light with a fiber amplifier are presented. Experimental results reveal that more than 85% polarization purity can be retained at the output even with 40 dB amplification and that efficient conversion of the amplified light to linear polarization can be obtained.

Temperature dependence of a diode-pumped cryogenic Er:YAG laser.

We report the laser performance of resonantly diode-pumped Er:YAG from liquid nitrogen temperature to above room temperature. Relative to incident pump power, the best performance was observed at approximately 160 K. Spectroscopy and modeling show that this is due primarily to the changing efficiency of diode pump absorption as the absorption lines broaden with temperature.

Ultralow quantum-defect eye-safe Er:Sc2O3 laser.

Resonantly pumped Er(3+):Sc(2)O(3) laser operation is achieved with a quantum defect (QD) of 1.5% at liquid nitrogen temperature. The laser, in-line pumped at 1535 nm, operated at 1558 nm with a slope efficiency of over 45%.

Concentration quenching in fine-grained ceramic Nd:YAG.

We have studied the concentration dependent fluorescence decay kinetics of ceramic Nd:YAG, to resolve inconsistencies in the previous literature. Our data indicate that earlier reports of single exponential lifetimes even at Nd concentrations of a few percent were due to the effects of long-pulse excitation. Under short-pulse excitation the fluorescence decay is nonexponential for concentrations greater than about 1% atomic.

Ultrahigh-gain bulk solid-state stimulated Brillouin scattering phase-conjugation material.

We report what is believed to be the first observation of phase conjugation by stimulated Brillouin scattering (SBS) in TeO2 single crystal. The observed very low threshold for phase-conjugate mirror (PCM) formation, high PCM reflectivities in this initial experiment, and commercial availability of material hold promise for a host of practical applications in the near future. The resultant steady-state gain parameter, approximately 100 cm/GW, is to our knowledge the largest ever reported for any SBS material.