Studying the Nonlinear Optical Properties of Fluoride Laser Host Materials in the Ultraviolet Wavelength Region

Fluoride host materials doped with trivalent cerium ions have previously been demonstrated as successful laser materials in the ultraviolet wavelength region. However, the nonlinear optical properties of the fluoride hosts in this wavelength region have not been investigated yet, although nonlinearity could result in undesirable effects such as self-focusing and pulse distortion when these fluoride materials are used as gain media in high-power, ultrashort pulse laser oscillator and amplifier systems. In this work, the nonlinear refractive index of lithium calcium aluminum fluoride (LiCaAlF6), lithium strontium aluminum fluoride (LiSrAlF6), lanthanum fluoride (LaF3), and yttrium lithium fluoride (YLiF4) fluoride host materials are determined using the Kramers–Krönig relation model in the ultraviolet wavelength region. Self-focusing conditions, particularly at the peak laser emission wavelength of these materials, are further analyzed. Results show that LiCaAlF6 has the smallest nonlinear refractive index and self-focusing, making it an ideal host material under the conditions of ultrashort pulse and ultrahigh-power laser generation.

Laboratory and Greenhouse Performance of Five Commercial Light Traps for Capturing Mosquitoes in China

ABSTRACT Mosquito light traps for household use are popular because they are small, cheap, user friendly, and environment friendly. At present, there are many variations and specifications of mosquito traps intended for household use on the market. The light traps claim they are powerful, but research and evaluation are lacking. Key parameters such as capture rates in the laboratory and field of 5 popular mosquito traps were evaluated as intended for household use. This study found that in the laboratory experiments, the capture rate of the mosquito traps selected was between 34.7% and 65.0%. Field tests in greenhouses found that the 5 mosquito traps had high catch rates for Culex quinquefasciatus. The percentage of Cx. quinquefasciatus, Aedes albopictus, Anopheles sinensis, and other flying insects captured was 51.76%, 25.29%, 14.12%, and 8.82%, respectively. There was no significant difference in the capture rate of Ae. albopictus and An. sinensis by the 5 mosquito traps in the greenhouse, but a significant difference in the catch rate of Cx. quinquefasciatus. The analysis showed that the fan speed and design of the air guide of the traps are important factors that affect the mosquito catch rate and that the ultraviolet wavelength (395–400 nm) used by the traps did not impact mosquito catch rates. Therefore, the mosquito traps intended for household use can be improved by adjusting the fan speed and optimizing the air guide.

The Effect of Ultraviolet Wavelength on Corrosion Behavior of 7075 Aluminum Alloy in the Marine Atmospheric Environment

The influence of ultraviolet rays on the corrosion behavior of 7075 aluminum alloy in the marine atmosphere was studied by salt spray corrosion test. Electrochemical methods and surface analysis techniques were used to analyze and compare the corrosion laws of 7075 aluminum alloy in the marine atmosphere under ultraviolet radiation with wavelengths of 0 nm, 185 nm, 254 nm, and 365 nm. The results showed that ultraviolet light irradiation could promote the corrosion of 7075 aluminum alloy. Oxygen was prone to chemical reactions to form oxygen atoms after being irradiated by ultraviolet rays, and oxygen atoms recombined with oxygen to form ozone in the marine atmosphere. The 7075 aluminum alloy in the marine atmosphere accelerated corrosion due to the increasing ozone content. Although there were passivation films with different degrees of protection on the surface of aluminum alloy under ultraviolet irradiation, the surface of 7075 aluminum alloy in the marine atmosphere failed to form a stable passivation film after pitting, and the corrosion rate was the fastest when the ultraviolet wavelength was 185 nm.

Performance Evaluation of a Novel Optical Sensing System for Detecting Rail Lubricity Conditions

This paper presents a laboratory evaluation of a novel optical sensing system mounted on a moving platform for detecting the presence and adequacy of Top-of-Rail (TOR) friction modifiers and flange greases. The friction modifiers are applied on the top of rail for managing the coefficient of friction to reduce wear while maintaining stable traction. Flange greases are intended to reduce wear that happens when wheel flange makes contact with the rail gage-face during curving. Additionally, friction modifiers and flange greases could influence fuel consumption. The U.S. railroads have made the application of TOR adopted on the mainlines. The tools, however, for evaluating the rail lubricity condition are limited and there is often uncertainty about the required or “optimal” amount of friction modifiers, except for the trained eye of the track engineer. The proposed sensing system provides an innovative non-contact method by using the optical laser’s reflective and scattering properties when directed at the rail surface to assess the friction modifiers’ conditions. In addition, the laser’s near-UV (Ultraviolet) wavelength is able to excite fluorescent elements in the flange grease and detect any top-of-rail contamination of grease that may exist. The design and working principles of the system are demonstrated and explained in this paper. Static and dynamic tests are performed in the lab under a controlled environment for various lubricity conditions, in order to experimentally validate and evaluate the performance of the optical sensing system. The lab evaluation indicates that the proposed optical sensing system is capable of successfully detecting the diverse lubricity conditions and shows a great potential to be widely tested and used in the field on revenue-service tracks.

Experimental study of lateral resistance of bolted joints using Japanese cedar (Cryptomeria japonica) treated with resin impregnation

The development of wooden joints possessing high resistance performance has become an important issue for the construction of newer buildings. This study attempts to strengthen the lateral resistance of bolted joints using the previously reported plasticizing technique. This technique consists of two processing stages: incising the surface of the wood using an ultraviolet wavelength short-pulse laser and impregnating the resin into the incised area. This technique makes it possible to plasticize only a local part of the wood surface. Bolted joint specimens were assembled using plasticized wood around the bolt hole, and the lateral tests were conducted. Acrylic monomer and urethane prepolymer were used as the impregnating resins and their incision depths were set as 4 and 10 mm. When the lateral load acted parallel to the grain, changes in the lateral resistance characteristics were observed, especially for the stiffness and yield load. For example, when acryl was used, and the incision depth was 10 mm, an increment of 73% in the yield load was observed, as compared to the non-impregnated specimens. The specimen groups impregnated with acryl exhibited greater changes in their properties than those using urethane. When loaded perpendicular to the grain, an increase in properties were observed; however, these increments were lower than those of the groups loaded parallel to the grain.