Low Threshold Microlasers Based on Organic-Conjugated Polymers

Conjugated polymers have emerged as ideal organic laser materials for the excellent optoelectrical properties and facile processability. During a typical lasing process, resonator configurations with specific geometry are essential to provide optical feedback and then amplified light. Herein, we summarized the geometry and working mechanism of several typical resonator configurations formed with conjugated polymers. Meanwhile, recent advances in fabrication techniques and lasing performance are also discussed to provide new ideas for the design and optimization of microcavity geometries. Followed by the advances of practical applications in fields of laser sensing, bioimaging, and laser illumination/display, we make a summary of the existing bottlenecks and future perspectives of electrically driven organic lasers toward laser display and illumination.

Radiation-Induced Phenomena in Wide-Gap Laser Materials Used in High-Radiation Areas

The analysis of the surface states in experimental reflection spectra is carried out peculiarities of the formation of defects of the electronic structure of irradiation corundum crystals is considered. It is shown that change of crystals reflectional ability is related to radiative growth forced by aluminum ions. The processes of radiative growth depend on the type and energy of irradiating high-energy particles. Kinetic of that growth is presented, which relates the intensity of zones with free aluminum ions to the concentration of such zones in near-surface layer.

Pilot Study on the Use of the “Monocyte-Rich” Platelet-Rich Plasma in Combination with 1927 nm Fractional and 308 nm Excimer Lasers for the Treatment of Vitiligo

Background and objectives: Vitiligo is an acquired chronic and idiopathic skin disorder, characterized by selective loss of melanocytes and resulting in a cutaneous depigmentation. Treatment for vitiligo remains a challenge for dermatologists; thus, it is frustrating both for physicians and patients. The objective of this study was to evaluate a combination treatment characterized by the use of a leukocyte-rich platelet-rich plasma, which is particularly rich in monocytes (defined here as monocyte-rich PRP), in combination with a 1927 nm fraxel laser and a 308 nm excimer laser. Materials and Methods: Treatment with monocyte-rich PRP combined with 1927 nm fraxel laser and 308 nm excimer laser was performed in nine sessions in 80 days and the median follow-up of the patients was 10 months. A total of 27 Caucasian patients were included in the present study. The median age of patients was 41 years, ranging between 20 and 69 years. Results: A re-pigmentation occurred in 16 cases (59%) with a reduction of the Vitiligo Extent Score (VES) and absence of re-pigmentation in untreated areas. Performing a rank correlation between VES and re-pigmentation in the treated areas, we found that there was a significant correlation (p < 0.0001). The presence of progressive vitiligo (p = 0.1) and the anatomic areas (p = 0.1) did not influence the treatment. Untreated areas did not show any improvement of the depigmented lesions, except in one case (p < 0.0001). Conclusions: in this report, we show for the first time how PRP rich in monocytes, in combination with laser therapies, gives a long therapeutic response, which persists even after 10 months of follow-up.

Energy Transfer and Cross-Relaxation Induced Efficient 2.78 μm Emission in Er3+/Tm3+: PbF2 mid-Infrared Laser Crystal

An efficient enhancement of 2.78 μm emission from the transition of Er3+: 4I11/2 → 4I13/2 by Tm3+ introduction in the Er/Tm: PbF2 crystal was grown by the Bridgman technique for the first time. The spectroscopic properties, energy transfer mechanism, and first-principles calculations of as-grown crystals were investigated in detail. The co-doped Tm3+ ion can offer an appropriate sensitization and deactivation effect for Er3+ ion at the same time in PbF2 crystal under the pump of conventional 800 nm laser diodes (LDs). With the introduction of Tm3+ ion into the Er3+: PbF2 crystal, the Er/Tm: PbF2 crystal exhibited an enhancing 2.78 μm mid-infrared (MIR) emission. Furthermore, the cyclic energy transfer mechanism that contains several energy transfer processes and cross-relaxation processes was proposed, which would well achieve the population inversion between the Er3+: 4I11/2 and Er3+: 4I13/2 levels. First-principles calculations were performed to find that good performance originates from the uniform distribution of Er3+ and Tm3+ ions in PbF2 crystal. This work will provide an avenue to design MIR laser materials with good performance.

Comparison of Percent Tissue altered in Topography Guided and Wavefront Optimized Laser-assisted in situ Keratomileusis using Zeiss MEL 80 Excimer Laser

Introduction: Laser-assisted in situ Keratomileusis (LASIK) is the most commonly performed refractive surgical procedure. The amount of tissue ablated in LASIK affects the safety and long-term outcome. The objective of this study was to compare the percent tissue altered (PTA) in topography guided (TG) and wavefront optimized (WFO) LASIK using Zeiss MEL 80 excimer laser. Materials and methods: This retrospective observational study was conducted at a tertiary eye center. Patients with moderate myopia who underwent LASIK between June 2016 and January 2019 were divided into two groups (Group I: TG LASIK, 69 eyes; Group II: WFO LASIK, 70 eyes). The groups were compared for preoperative parameters [spherical equivalent (SE), keratometry and pachymetry], intraoperative parameters [ablation depth (AD), PTA and residual stromal bed thickness (RSBT)] and postoperative parameters (vision, SE). Results: Among preoperative parameters, SE and keratometry were similar while thinnest pachymetry was significantly less in group I. Among the intraoperative parameters, PTA (P < 0.01) and AD (P < 0.01) were significantly less in group I while RSBT (P = 0.54) was not significantly different. Postoperatively at 6 months, 92.75% (64) eyes in group I and 90% (63) eyes in group II had visual acuity of 6/6 or better (P = 0.57). 98.55% (68) and 97.14% (68) eyes in group I and group II respectively had SE refraction within ± 0.5 dioptres. Conclusion: TG LASIK induces less tissue alteration for given refractive error with similar visual outcome as compared to WFO LASIK which makes TG apparently safer and is the preferred technique for borderline thin corneas.

Measurements at laser materials processing machines: spectrum deconvolution including uncertainties and model selection

Laser materials processing of workpieces using ultra-short pulsed lasers can lead to unwanted X-ray emission. Their dose rate and spectral distribution have been precisely determined. The measurements were carried out using a thermoluminescence detector (TLD)-based spectrometer in which 30 TLD planes are arranged one behind the other, the first 10 layers made of polymethyl methacrylate, while the remaining 20 layers are interspaced by absorbers with, from the front to the back, increasing atomic charge and thickness. The penetration depth of the radiation into the spectrometer depends on its energy, so that the energy-resolved spectrum of the radiation can be calculated from the TLD dose values by means of mathematical methods (Bayesian deconvolution). The evaluation process also takes into account both the uncertainties of all input quantities and the possibility of adopting different models for the spectrum form. This allowed the resulting spectra to be associated with their realistic uncertainty. The measurements are traceable to the Système international d'unités (SI), i.e. the International System of Units. The results not only provide manufacturers and users of ultra-short pulsed lasers with important information on the design of the machines with regard to radiation protection, but were also included in the recently concluded legislative procedure in the field of radiation protection in Germany.