Full 3D modelling of pulse propagation enables efficient nonlinear frequency conversion with low energy laser pulses in a single-element tripler

Although new optical materials continue to open up access to more and more wavelength bands where femtosecond laser pulses can be generated, light frequency conversion techniques are still indispensable in filling the gaps on the ultrafast spectral scale. With high repetition rate, low pulse energy laser sources (oscillators) tight focusing is necessary for a robust wave mixing and the efficiency of broadband nonlinear conversion is limited by diffraction as well as spatial and temporal walk-off. Here we demonstrate a miniature third harmonic generator (tripler) with conversion efficiency exceeding 30%, producing 246 fs UV pulses via cascaded second order processes within a single laser beam focus. Designing this highly efficient and ultra compact frequency converter was made possible by full 3-dimentional modelling of propagation of tightly focused, broadband light fields in nonlinear and birefringent media

Near-infrared, mode-locked waveguide lasers with multi-GHz repetition rates

In this work, we discuss mode-locking results obtained with low-loss, ion-exchanged waveguide lasers. With Yb3+-doped phosphate glass waveguide lasers, a repetition rate of up to 15.2 GHz was achieved at a wavelength of 1047 nm with an average power of 27 mW and pulse duration of 811 fs. The gap between the waveguide and the SESAM introduced negative group velocity dispersion via the Gires Tournois Interferometer (GTI) effect which allowed the soliton mode-locking of the device. A novel quantum dot SESAM was used to mode-lock Er3+, Yb3+-doped phosphate glass waveguide lasers around 1500 nm. Picosecond pulses were achieved at a maximum repetition rate of 6.8 GHz and an average output power of 30 mW. The repetition rate was tuned by more than 1 MHz by varying the pump power

The acute phase of inflammatory response involved in the wound-healing process after excimer laser treatment

Mirko Resan,1,2 Miroslav Vukosavljevic,1,2 Danilo Vojvodic,2,3 Brigitte Pajic-Eggspuehler,4 Bojan Pajic2,4–6 1Eye Clinic, Military Medical Academy, Belgrade, Serbia; 2Faculty of Medicine of the Military Medical Academy, University of Defense, Belgrade, Serbia; 3Department for Clinical and Experimental Immunology, Institute for Medical Research, Military Medical Academy, Belgrade, Serbia; 4Eye Clinic ORASIS, Swiss Eye Research Foundation, Reinach AG, Switzerland; 5Department of Physics, Faculty of Science, University of Novi Sad, Novi Sad, Serbia; 6Division of Ophthalmology, Department of Clinical Neurosciences, University Hospitals of Geneva, Switzerland Purpose: To evaluate the participation of proinflammatory cytokines in the acute phase of corneal wound-healing response after excimer laser treatment. Methods: The study included 68 myopic eyes up to -3.0 diopters divided into two groups: 1) eyes treated with laser in situ keratomileusis (LASIK) (n=31) and 2) eyes treated with photorefractive keratectomy (PRK) (n=37). Each group was then divided into three subgroups based on tear sampling times: before (0 hours), 1 hour after, and 24 hours after treatment. The tear fluid was sampled from lower lateral tear meniscus using a cellulose microsurgical sponge. The levels of tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, IL-6, and IL-8 in tear fluid were determined by flow cytometry method. Results: Statistical significance was observed in the concentrations of TNF-α (P=0.0421) and IL-1β (P=0.0225) between samples collected 1 and 24 hours after PRK treatment in favor of samples collected 1 hour after treatment. IL-6 concentration changes showed a significant increase in the PRK group in both time intervals following treatment compared to pretreatment (0 hour/1 hour, P=0.0031; 0 hour/24 hours, P=0.0059). For IL-8 concentrations, significant differences were observed between control and experimental groups in samples collected 1 hour after LASIK and 1 hour after PRK treatment (P<0.001 for both groups), and IL-8 concentrations between control and experimental groups in samples collected 24 hours after LASIK and 24 hours after PRK treatment were greater after PRK treatment (P=0.0005). Comparison of average concentration values of proinflammatory cytokines in all the tested samples between LASIK and PRK groups showed significantly higher levels of IL-1β in the LASIK group 24 hours after treatment (P=0.0134), and of IL-6 in the PRK group 24 hours after treatment (P=0.0031). Conclusion: The acute phase of corneal wound healing after excimer laser treatment is defined by an intensive inflammatory response. After PRK treatment, there were increased concentrations of TNF-α and IL-1β in tear samples 1 hour after treatment, IL-6, 1 and 24 hours after treatment, and IL-8, 1 and 24 hours after treatment. After LASIK treatment, there were increased concentrations of IL-8 in tear samples 1 hour after treatment and IL-1β, 24 hours after treatment. Both PRK and LASIK methods are characterized with a significant inflammatory response. However, tear findings following PRK method showed more intensive inflammatory response than the findings after LASIK method. Keywords: LASIK, PRK, tears, proinflammatory cytokines, wound healin

Multifocal femto-PresbyLASIK in pseudophakic eyes

Background: Presbyopia treatment in pseudophakic patients with a monofocal IOL is challenging. This study investigates the refractive results of femto-PresbyLASIK and analyzes presbyopia treatment in pseudophakic eyes. Methods: 14 patients with 28 pseudophakic eyes were treated with femto-PresbyLASIK. The dominant eye was targeted at a distance and the non-dominant eye at −0.5 D. The presbyopic algorithm creates a steepness in the cornea center by using an excimer laser that leads to corneal multifocality. Results: 6 months after surgery a refraction of −0.11 ± 0.13 D (p = 0.001), an uncorrected distance visual acuity of 0.05 ± 1.0 logMAR (p < 0.001) and an uncorrected near visual acuity of 0.15 ± 0.89 logMAR (p = 0.001) were achieved in the dominant eye. For the non-dominant eye, the refraction was −0.28 ± 0.22 D (p = 0.002), the uncorrected distance of visual acuity was 0.1 ± 1.49 logMAR, and the uncorrected near visual acuity was 0.11 ± 0.80 logMAR (p < 0.001). Spherical aberrations (Z400) were reduced by 0.21–0.3 µm in 32% of eyes, and by 0.31–0.4 µm in 26% of eyes. Conclusion: By steepening the central cornea while maintaining spherical aberrations within acceptable limits, PresbyLASIK created a corneal multifocality that safely improved near vision in both eyes. Thus, femto-PresbyLASIK can be used to treat presbyopia in pseudophakic eyes without performing intraocular surgery

Orthogonal frequency division multiplexing (OFDM) in photonic communications

OFDM has emerged as a promising modulation technique in long-haul and access optical networks because of a number of advantages: Scalable spectrum partitioning, good spectral efficiency, dispersion tolerance, and a natural suitability for software-defined transmission. However, there are also issues inherent in OFDM: High peak-to-average power ratio making the system more susceptible to nonlinearity, sensitivity to frequency offset and phase noise, and the required computational complexity. With the advent of powerful digital signal processors and by exploiting all-optical signal processing, some of these obstacles can be overcome

Urinary transferrin as an early biomarker of diabetic nephropathy

© 2019 Inst. Sci. inf., Univ. Defence in Belgrade. All rights reserved. Background/Aim: Diabetic nephropathy is one of the leading cause of chronic kidney disease and end-stage renal disease. It occurs in 20%-40% of patients with diabetes mellitus and microal-buminuria is still considered as the first sign of diabetic nephropathy. Low sensitivity and specificity of microalbuminuria lead to more sensitive biomarkers that may be used to detect diabetic nephropathy at an earlier stage with a higher accuracy. This study was carried out to determine whether urinary transferrin can serve as an indicator of diabetic nephropathy. Methods: Our study included 80 type 2 diabetic patients who were classified into two groups: group 1 - normoalbuminuric patients (albumin excretion up to 30 mg/d); group 2 - microalbuminuric patients (albumin excretion from 30-300 mg/d), and 10 healthy controls. All patients were older than 18, having the diabetic disease more than one year, glomerular filtration rate more than 60 mL/min/1.73 m2. Serum creatinine, glycosylated hemoglobin (HbA1c), and concentration of transferrin in the 24 h urine samples as well as in spot urine were measured using a highly sensitive one-step sandwich enzyme immunoassay kit. Results: Urinary transferrin was significantly higher in the microalbuminuric patients than in the normoalbuminuric ones and healthy control subjects. When comparing these goups according to the urinary transferrin concentration, we found a statistically significant positive correlation r = 0.584 (p < 0.001). There was no correlation between level of urinary transferrin and glycoregulation, and no correlation was found between transferrin and duration of diabetes. Conclusions: The results from this study provide the evidence that the urinary transferrin levels could be used as an early marker of diabetic nephropathy