RESUMEN
In free-space optical communication, the propagation of a laser beam through the atmosphere causes wavefront distortions that decrease the coupling efficiency (CE) from free space to single-mode fiber. This tremendously degrades the performance of the communication channel even in the case of weak turbulence regime. In this Letter, we demonstrate that a multi-actuator adaptive lens working in closed loop with a wavefront sensor can strongly reduce the effect of turbulence while reducing the system complexity with respect to correction systems using deformable mirrors or liquid crystal spatial light modulators. We obtain a three-fold increase in the CE in weak turbulence regime.
RESUMEN
We have developed a theoretical model for the regenerative amplification of ultrashort mid-infrared radiation in high-pressure transverse electric discharge CO2 lasers. This model is based on counter-propagating wave equations that are combined with Boltzmann equation, six-temperature, and circuit-coupled kinetic models. For the first time to our knowledge, the effect of spontaneous emission is taken into account. The model describes noise behavior, contrast ratio, and self-lasing of amplified spontaneous emission. The proposed scheme allows the attainment of a few-picosecond pulse with GW-level peak power and contrast ratio on the order of 106 in the 9 µm range.
RESUMEN
In this paper, we experimentally evaluated the performance of underwater optical communications using 1 Mbit/s on-off keying signals of perfect optical vortices. Perfect optical vortices generated by Fourier transformation of the Bessel-Gaussian beam are propagated through a 2.6 m underwater medium and affected by various water conditions such as stagnant water, water flow, temperature difference, and air bubbles, so beam wander and fluctuation of the signal are studied. Air bubbles have the maximum effect on signal fluctuations and beam wanders. Measurement of the system bit error rate (BER) based on the signal-to-noise ratio (SNR) for these situations matches the results of wandering and fluctuations. The system BER is studied for different values of SNR, and its value is more degraded due to the air bubbles.
RESUMEN
This publisher's note identifies an error in the paper title of Appl. Opt.57, 9148 (2018)APOPAI0003-693510.1364/AO.57.009148.
RESUMEN
Perfect optical vortices (POVs) are beams whose topological charges are independent of radius, unlike conventional optical vortices. POVs are the Fourier transformation of Bessel-Gaussian (BG) beams and can be seen in the far-field diffraction of BG beams. In this paper, we present the generation of POVs of arbitrary charge using curved fork grating (CFG) illuminated by BG beam. For this purpose, first, a theoretical study of the Fresnel-Kirchhoff integral for diffraction of a BG beam by CFG is completed. The analytical results show the presence of vortex beams with various topological charges in diffraction orders. Then, diffraction of the BG beam with the order (l) by CFG with a topological charge (p) is numerically simulated. Additionally, experimental results prove the generation of POVs in diffraction orders. Also, experimental interference patterns obtained by interfering a POV and Gaussian beam confirm the ability of analytical solutions to determine the topological charges of vortex beams. Comparison of the results reveals the validity of the analytical, simulation, and experimental results.
RESUMEN
A new method is presented to measure chlorine concentration more accurately than conventional method in exhaust gases of a jet-type singlet oxygen generator. One problem in this measurement is the existence of micrometer-sized droplets. In this article, an empirical method is reported to eliminate the effects of the droplets. Two wavelengths from a fiber coupled LED are adopted and the measurement is made on both selected wavelengths. Chlorine is measured by the two-wavelength more accurately than the one-wavelength method by eliminating the droplet term in the equations. This method is validated without the basic hydrogen peroxide injection in the reactor. In this case, a pressure meter value in the diagnostic cell is compared with the optically calculated pressure, which is obtained by the one-wavelength and the two-wavelength methods. It is found that chlorine measurement by the two-wavelength method and pressure meter is nearly the same, while the one-wavelength method has a significant error due to the droplets.