In this paper we discuss recent progress in exploring short-term and long-term stability of high power Yb-doped fiber lasers and amplifiers. Long-term stability is associated with photodarkening effects that can significantly reduce operational lifetime of a high-power laser system. Short-term stability is associated with so-called transverse modal instabilities that degrade output beam quality at average powers above a certain threshold. In this paper we review ongoing studies that provide experimental characterization, and explore physical causes and mitigation strategies of the different physical phenomena involved. Those studies are critical for achieving stable operation of high power fiber lasers.
Cavity-enhanced photosensitivity of As2S3 chalcogenide glass films is measured using planar micro-disk resonators. We observed infrared index trimming by 1550 nm wavelength light, cavity instability and confirmed the absence of two photon absorption.
We introduce the Optical Materials Express feature issue that celebrates historic and recent advances in optical glass. In honor of the United Nations declaring 2022 to be the International Year of Glass (IYOG), this issue comprises a collection of twenty-seven manuscripts that highlight processing, characterization/metrology and applications where glass has changed our world.
Phosphate glasses are ideal candidates to substitute traditional silicate bioactive glasses as they can exhibit controlled ion release. Furthermore, phosphate glasses possess congruent dissolution and also resistance to crystallization, two properties that are favorable for the processing of 3D porous scaffolds. However, most of the phosphate glasses also exhibit a fast dissolution rate, which is inappropriate for bone tissue regeneration. In this context, a new bioresorbable phosphate glass within the 45P2O5- 2.5B2O3- 2.5SiO2- 10Na2O- 20CaO- (20-x) SrO- (x)MgO (in %mol) composition was developed. Magnesium is substituted for strontium in order to promote bone formation but in the present study, its role is mainly to favor sintering at lower temperatures without crystallization. The in vitro dissolution in simulated body fluid was assessed for glass particles <38 μm (pH, ICP, SEM-EDS). All glasses were found bioresorbable, rather than bioactive. The newly developed phosphate glasses containing Sr and Mg were found to have a slower dissolution rate when compared to traditional metaphosphate glasses while maintaining their congruent dissolution and hot forming ability. All glasses were 3D printed into scaffolds with controlled pore size and without apparent crystallization. The substitution of SrO for MgO was shown to be highly effective in enhancing the sintering ability of the material by enabling sintering at lower temperatures while avoiding the risk of crystallization leading to the processing of scaffolds with mechanical properties, in compression, above that of the cancellous bone.
Using three-dimensional (3D) second-harmonic generation (SHG) scanning microscopy, we unravel the formation and distribution of distinct and highly localized persistent luminescent (PeL) microparticles of varied hierarchical levels in glasses prepared using the direct doping method. The PeL microparticles were added in the glasses at different doping temperatures and the glasses were quenched after different dwell time. The SHG maps of the PeL microparticles in the glass, prepared with a doping temperature of 975°C and a dwell time of 3 min, reveal grating-like microscopic domains. This suggests that a large arrangement of PeL crystals spanning several micrometers in three dimensions is manifested by the imbued PeL microparticle. In contrast, the SHG maps of the PeL microparticles inside the glass prepared at doping temperature of 1025°C and dwell time of 10 min, show the existence of single, highly localized and most importantly, submicrometer-sized PeL crystals. These findings substantiate well with the expected behavior of the PeL microparticles in glasses and their physical disintegration in the form of nanoparticles at high doping temperatures and dwell times. The SHG microscopy technique is shown to circumvent the fundamental challenges of traditional and usually destructive imaging methods to detect and visualize PeL nanoparticles in a glass matrix and expected to open a new avenue to evidence the presence of crystals in glasses.
Planar microdisk optical resonators fabricated from Ge 23 Sb 7 S 70 chalcogenide glass on a silicon substrate are applied for cavity-enhanced spectroscopic measurement of chemical molecular absorption fingerprint. A 0.02 cm - 1 detection limit for these devices is demonstrated. This detection limit represents a threefold improvement as compared to a straight waveguide sensor, while the physical device length is reduced by 40-fold. The reduction in device footprint with enhanced sensitivity makes the structure attractive for ldquosensor-on-a-chiprdquo device applications. We also present a design optimization approach for cavity-enhanced IR absorption spectroscopy using traveling-wave resonators, which indicates that further performance improvement can be achieved in optimally coupled, low-loss resonant cavities.
Abstract Here, we report on core–clad bioactive borosilicate fibers, that we have prepared both with round and rectangular cross‐section profile. The exposed approach, which relies on the stacking and drawing of glass slabs, demonstrates our ability to develop bioactive‐based glass fibers with tailored cross‐section profiles. Tens‐of‐meters‐long fibers were successfully drawn, although suffering from elevated losses in the case of the rectangular ones. The response of the fibers in simulated body fluid was studied for both geometries. We found that a round cladding can act as protective layer, tempering effects of the corrosion. We also noticed that rectangular fibers are more prone to degradation, the enhanced corrosion beginning from their sharp corners as they accumulated residual tensile stress during drawing. To the best of our knowledge, this is the first report on the effect of residual tensile stresses from surface tension deformations applied to the corrosion of rectangular fibers. As geometry plays a critical role on the biodegradation behavior of the fiberglass, we believe the enclosed results could lead to the design of fiber devices with tailored cross‐section profile in order to tune their rate of degradation on solely based geometrical effects.
This review focuses on the radiation-induced changes in germanate and tellurite glasses. These glasses have been of great interest due to their remarkable potential for photonics, in terms of extended transmission window in the mid-infrared, ability of rare-earth loading suitable with a laser, and amplification in the near- and mid-infrared or high nonlinear optical properties. Here, we summarize information about possible radiation-induced defects, mechanisms of their formation, and the influence of the glass composition on this process. Special attention is paid to laser-induced structural modification of these glasses, including possible mechanisms of the laser-glass interaction, laser-induced crystallization, and waveguide writing. It is shown that these methods can be used for photostructuring of the glass and have great potential for practical applications.
