Resonantly pumped eye-safe Er3+:YAG SPS-HIP ceramic laser

Progress in Transparent Nano-Ceramics and Their Potential Applications

Transparent nano-ceramics have an important high-transmittance, material-integrating structure and function and a variety of potential applications, such as use in infrared windows, optical isolators, composite armors, intelligent terminal screens, and key materials of solid-state lasers. Transparent ceramics were originally developed to replace single crystals because of their low fabricating cost, controllable shape, and variable composition. Therefore, this study reviews and summarizes the development trends in transparent nano-ceramics and their potential applications. First, we review the research progress and application of laser nano-ceramic materials, focusing on the influence of controllable doping of rare earth ions on thermal conductivity and the realization of large-scale fabrication technology. Second, the latest research progress on magneto-optical transparent nano-ceramics, mainly including terbium gallium garnet (Tb₃Ga₅O₁₂, TGG) ceramics and terbium aluminum garnet (Tb₃Al₅O₁₂, TAG) ceramics, are summarized, and their performance is compared. Third, the research progress of transparent armor nano-ceramic materials, represented by MgAl₂O₃ and Aluminum oxynitride (AlON), are reviewed. Lastly, the progress in electro-optical transparent nano-ceramics and scintillation transparent nano-ceramics is reported, and the influence of the material-fabrication process on electro-optic effect or luminous intensity is compared. Moreover, the effect of particle diameter on fabrication, the relationship between nano powder and performance, and different sintering methods are discussed. In summary, this study provides a meaningful reference for low-cost and sustainable production in the future.

Pressure-assisted sintering and characterization of Nd:YAG ceramic lasers

Spark plasma sintering (SPS) is an advanced one-stage, rapid, near-net shape densification technique combining uniaxial pressure with resistive heating. Various transparent ceramics have been successfully fabricated by SPS, despite the existence of inherent carbon contamination and residual pores. Due to the disk-shape of SPS-processed samples, the technique may be suited for producing thin-disk ceramic laser materials. Nevertheless, an in-depth study of these materials has never been reported. With that goal in mind, the major focus of this study was to characterize the laser performance of Nd:YAG ceramics fabricated by one-stage SPS under conventional (60 MPa) and high (300 MPa) applied pressures. In addition to measuring the lasing slope efficiency and threshold, the passive losses associated with each sample were also evaluated. Surprisingly, it was found that in-line transmittance spectra do not provide accurate predictions of laser performance due to the nature of residual porosity. Moreover, homogeneity and beam quality were assessed, and comparisons were drawn between conventional and high-pressure SPS ceramics. This study lays the groundwork for the future of laser materials fabricated by SPS or similar pressure-assisted techniques.

Glass-Ceramics Processed by Spark Plasma Sintering (SPS) for Optical Applications

This paper presents a review on the preparation of glass-ceramics (GCs) and, in particular, transparent GCs by the advanced processing technique of spark plasma sintering (SPS). SPS is an important approach to obtain from simple to complex nanostructured transparent GCs, full densification in a short time, and highly homogeneous materials for optical applications. The influence of the different processing parameters, such as temperature, pressure, sintering dwell time on the shrinkage rate, and final densification and transparency, are discussed and how this affects the glass material properties. Normally, transparent glass-ceramics are obtained by conventional melt-quenching, followed by thermal treatment. Additionally, the GC scan is produced by sintering and crystallization from glass powders. Hot pressing techniques (HP) in which the source of heating is high-frequency induction can be also applied to enhance this process. In the case of transparent ceramics and glass-ceramics, spark plasma sintering is a promising processing tool. It is possible to enhance the material properties in terms of its compactness, porosities, crystallization, keeping the size of the crystals in the nanometric scale. Moreover, the introduction of a high concentration of active gain media into the host matrix provides functional glass-ceramics systems with enhanced luminescence intensity through reducing non-radiative transitions like multi phonon relaxation (MPR) and cross relaxations (CR), thus providing longer lifetimes. More effort is needed to better understand the sintering mechanisms by SPS in transparent GC systems and optimize their final optical performance.

Sapphire/Nd:YAG composite by pulsed electric current bonding for high-average-power lasers

As a new bonding technique for high-power laser optics, pulsed electric current bonding (PECB) of sapphire and Nd:YAG ceramics was demonstrated. The optical properties of the composite were measured, and its microstructure at the interface and laser performance was analyzed. The optical transmittance was equal to the theoretical value, and the transmitted wavefront was λ/3 (λ=633  nm); both are appropriate values for laser applications. The microstructural analysis indicated an absence of scattering sources such as pores or non-contact points at the sapphire/Nd:YAG interface, and the distance of yttrium diffusion into the sapphire was theoretically expected to be less than 10 nm, much smaller than that of ceramic materials bonded by conventional thermal diffusion techniques. The laser performance of the composite material showed an 18% higher output power with almost the same threshold power and slope efficiency as a Nd:YAG ceramic due to the sapphire-conductive cooling effect. This new PECB technique for different transparent materials has the potential to bond large aperture optical materials over 100 mm in diameter and could be especially effective for fabricating active laser media for high-average-power lasers having both high-pulse energy and high repetition rates.

Feature issue introduction: Advanced Solid-State Lasers 2017

The Advanced Solid State Lasers 2017 Conference (ASSL) was held from October 1 to 5, 2017. It was an extraordinary conference at the Nagoya Congress Center in Nagoya, Japan. ASSL 2017 again suggested an impressive platform where miscellaneous perceptions with a variety of approaches to optics, photonics, sensing, laser technology, laser systems, and solid state lasers were presented. This international meeting was highly selective, leading to high level contributions through one plenary conference, 17 invited presentations, 70 regular talks, and 121 posters. The present joint issue of Optics Express and Optical Materials Express features 27 articles written by ASSL 2017 authors and covering the spectrum of solid-state lasers from materials research to sources, and from design innovation to applications.