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In broadband terahertz waves generated by femtosecond lasers, spatial chirp will be simultaneously produced with the introduction of angular dispersion. The chirp characteristics of the terahertz wave will directly affect the frequency response, bandwidth response, and intensity response of the terahertz sensor. To enhance the capability of terahertz sensors, it is necessary to control and improve the chirped characteristics of broadband terahertz sources. We generate a chirped terahertz wave via optical rectification in a LiNbO3 prism using the technique of pulse front tilt. The effect of the pump-beam spot size on THz generation is systematically studied. The pump's spot size is manipulated using a telescope system. With a pump spot diameter of 1.8 mm, the scanning spectrum of the THz pulse is narrower and is divided into multiple distinct peaks. In contrast, using a pump spot diameter of 3.7 mm leads to increased efficiency in the generation of THz pulses. Also, we investigate the underlying properties governing the generation of chirped terahertz pulses using varying pump pulse spot diameters. [ABSTRACT FROM AUTHOR]

It is crucial to enhance the efficiency of terahertz radiation in a single crystal for the application of intense field terahertz waves. We devise a trapezoidal lithium niobate prism that, upon side incidence of the terahertz wave, retroreflects the femtosecond laser onto the crystal's symmetric plane. The conversion efficiency of pump power to THz pulse power for circular cavity increases by 36% compared to that of the conventional cavity. The findings demonstrate that the utilization of sample multiplexing pump can significantly enhance the efficiency of terahertz generation. [ABSTRACT FROM AUTHOR]

An effective approach to manipulate terahertz (THz) waves involves the utilization of a device structure. In this particular investigation, we have successfully fabricated a SnS2 nanofilm device using femtosecond laser direct ablation. The passive and active polarization‐sensitive characteristics of the SnS2 nanofilm device were examined within the THz frequency range, employing different line spaces of 500, 600, and 700 μm. The combination of the device effect and SnS2 absorption led to an enhanced passive polarization modulation. Moreover, when an external electric field was applied to the SnS2 nanofilm device along the device line, persistent switching and linear modulation of THz wave transmission were observed. These findings indicate that the integration of material properties and device structure in this SnS2 device renders it highly suitable for applications in ultrafast THz switches, filters, and modulation devices. [ABSTRACT FROM AUTHOR]

This study reports the growth of SnO2 nanocrystals (NCs) in mesoporous silica glasses and its great enhancement of Eu3+ photoluminescence at around 590 nm wavelength-band. Significantly different energy level character of Eu3+ was observed using photoluminescence (PL) spectra, which was attributed to the effect of the SnO2 crystal field. Remarkably, enhancement of Eu3+ as much as 116 times was achieved in the orange emission region by optimal SnO2 NCs addition. PL excitation spectra and decay curves verify the efficient energy transfer from SnO2 NCs to Eu3+. It is well understood that the highly enhanced emission originates from Eu3+ embedded in SnO2 NCs and the strong energy transfer between them. Our study has not only demonstrated an effective way to enhance down-conversion PL of rare earth ions in silica glasses, but also widened the applications of semiconductor oxides such as SnO2 NCs. [ABSTRACT FROM AUTHOR]

Blood sugar is an important biomedical parameter of diabetic patients. The current blood sugar testing is based on an invasive method, which is not very friendly for patients who require long-term monitoring, while the non-invasive method is still in the developing stage. In this paper, we design a non-invasive and highly sensitive terahertz wave detector with Co 3 Sn 2 S 2 semimetal thin film to test sugar concentration. As different concentrations have inconsistent responses to terahertz wave, we can deduce the concentration of the sugar solution to realize real-time highly sensitive detection of blood sugar concentration. This novel method can be further expanded to 6 G edge intelligence for non-invasive and real-time monitoring of blood sugar, and promote the development of 6 G technology., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 Optica Publishing Group.)

Upconversion (UC) materials have shown many applications in the solar cell industry, biomedical imaging, and LED lighting. For the first time, we report enhanced UC in Er 3+ /Yb 3+ -codoped silica glasses induced by the energy transfer between rare earth ions and indium tin oxide nanoparticles (ITO NPs), introduced by an in situ growth approach. The enhancements of the intensities of the emissions of red and green light were all more than 10 fold and in some cases up to 42 fold. This work in our opinion has contributed a novel method and materials for UC enhancement in Er 3+ /Yb 3+ -codoped silica glasses.