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.
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.
When an intense ultrafast laser pulse is focused into a free-flowing water film, broadband terahertz (THz) radiation is emitted through the interaction between strong laser fields and liquid water molecules. Experimental results show that THz waves generated from liquid water have very different characteristics in comparison to those from other THz sources such as solids and gases. The mechanism for the THz wave generation process is currently attributed to the plasma formation in the bulk water. This demonstration may find potential applications in biological imaging and provide new tools in the field of nonlinear laser-liquid interactions.