Fiber Bragg gratings (FBGs) are well-known optical sensors, which have been widely used to perform temperature and strain measurements. Due to the cross-sensitivities of FBGs to both temperature and axial strain changes, using these fiber sensors for high-accuracy temperature measurements remained questionable. This paper presents an FBG sensor packaging technique that produces strain-free, multiplexable fiber temperature sensors. Using a precision CO2 laser heating process, a low-loss and mechanically robust fiber taper is formed near the FBG sensor, which relieves potential axial strain influence on FBG’s temperature measurements. FBG sensors with tapered junctions were housed in a two-hole PEEK tube. The entire structure is then inserted into a thicker hollow PEEK tubing and welded in place. This design protects the fiber sensor from mechanical breakage and isolates it from external stress. This paper reports highly accurate temperature measurements from 77k to 567k. It presents a viable approach to developing multiplexable temperature sensors for cryogenic environment applications.
Terahertz (THz) wave generation from laser-induced air plasma generally requires a short temporal laser pulse. In contrast, it was observed that THz radiation from ionized liquid water prefers a longer pulse, wherein the mechanism remains unclear. We attribute the preference for longer pulse duration to the process of ionization and plasma formation in water, which is supported by a numerical simulation result showing that the highest electron density is achieved with a subpicosecond pulse. The explanation is further verified by the coincidence of our experimental result and simulation when the thickness of the water is varied. Other liquids are also tested to assure the preference for such a pulse is not exclusive to water.
Nowadays, lasers, as innovation tools, provide extraordinary opportunities in a wide range of material processing and manufacturing applications. Here, we present using an ultra-short laser to fabricate a flute in a university’s lab on a syringe needle. By finely controlling the laser power and drilling time, holes can be drilled at one side but not penetrate the whole needle. With a set of holes arranged in a straight line, the needle acts as a “flute” when the gas flows into it. A microphone measures its acoustic frequency. Different tones were observed by changing the resonance length of the needle. Our work demonstrates the fabrication and testing of miniature flute on a syringe needle.
Liquid water was not considered as a favorable terahertz (THz) source due to its strongly absorption in THz frequency range. Recently, it has been experimentally demonstrated that broadband THz wave can be generated from liquid water under the excitation of ultrashort laser pulses. Here, we present the measured result of liquid lines as THz emitters. Selected liquids with different polarity, salinity and temperature on THz wave generation are investigated. Comparing with water with high polarity, lower polarity liquids produce stronger THz radiation with a broader bandwidth. α-pinene, a non-polar liquid produces strongest THz signals among all liquids we tested. Saline solutions produce weaker THz radiation compare to pure water. The THz signals from temperature with 8 ℃, 18℃, and 40℃ show marginal difference under our experiment’s conditions. In addition, sugar, acid, alkali solutions and a variety of milks were also tested. Our observations show that non-polar liquids are in favor than polar liquid as alternative THz sources.
The design study herein analyzes the design complexity of high zoom ratio lens systems in the visible, SWIR, and LWIR spectrums with four zoom groups (two internally moving). The aforementioned 12.5x zoom lens systems have been designed for use in the Coast Guard for maritime safety, security, and stewardship. To begin our comparative design study, the most advantageous solutions for distinct power groupings were found using a first order solution finder tool. The results showed that solutions with a PNNP, PNPP, and NPNP power grouping with the aperture stop in the third or fourth group had the most potential. At the end of the design process, a comparison was done for the three different wavebands to analyze the relative design complexity. Design complexity metrics were as follows: element count, number of aspheric surfaces, system total track length, element diameter, and tolerance sensitivity.