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• We firstly propose a cascaded Kerr beam self-cleaning scheme that combines multiple MMFs to further improve multimode beam quality. • Radial offset between fiber 1 and fiber 2 of the cascaded multimode fiber system should be as small as possible for cascaded beam self-cleaning. • Our results also suggest that an increased number of HOMs with negligible energy along with a higher number of cascaded fibers contribute to superior multimode beam quality. Spatial beam self-cleaning has shown a nonlinear improvement in beam quality in multimode fibers (MMFs), proving its value in high-power fiber lasers and nonlinear biomedical imaging. In this Letter, we propose a novel cascaded Kerr beam self-cleaning scheme that combines multiple MMFs to further improve beam quality. Through this scheme, the initially speckled beam gradually evolves into a well-defined bell-shaped, primarily dominated by the fundamental mode, after undergoing two or three cascaded self-cleaning processes. Simulation results also suggest that an increased number of high-order modes (HOMs) with negligible energy along with a higher number of cascaded fibers contribute to superior beam quality. This phenomenon is attributed to the new excited HOMs acting as attractor and facilitating an energy cascade towards the fundamental mode. [ABSTRACT FROM AUTHOR]

Ultrafast electron pulses generated using femtosecond lasers offer a direct means for investigating ultrafast processes, but the yield of electron emission remains a significant practical limitation. This study demonstrates a substantial enhancement in yield of electron emission from carbon nanotubes induced by two-color (ω + 2 ω) pulses with an 80 MHz repetition rate and this enhancement is non-delay-dependent. Compared to the sum of photocurrents induced by each color pulse individually, the combined two-color pulses result in a remarkable enhancement in yield of electron emission by more than 25 times. We attribute this enhanced yield to carrier-assisted optical field emission: carbon nanotubes sustain high carrier concentration state under laser radiation thereby enhancing yield of electron emission. We propose the carrier migration emission model to provide a semi-quantitative description for the carrier-assisted optical field emission. This phenomenon introduces a new method to increase the yield of ultrafast electron pulses from CNTs and paves the way for next-generation ultrafast electron emitters and on chip ultrafast optoelectronic device. [Display omitted] [ABSTRACT FROM AUTHOR]

• A new method to detect liquid level is proposed and experimentally demonstrated. • The significant improvement as compared to the traditional demodulation method. • Enable measurement without specialized installation for easier deployment. This study presents a fiber optic liquid level sensor (FOLLS) by acquiring information from the amplitude of spectral fast Fourier transform (FFT) in a specified narrow wavelength range. The sensing light path is simply formed by embedding a section of Panda-type polarization-maintaining fiber (PMF) into the sensing arm of a conventional Michelson interferometer (MI) structure. The output composite spectrum consists of two parts: the fine interference fringes due to MI optical path difference (OPD) and the envelope fringes stemming from the PMF's birefringence. By applying liquid level variations on the sensing structure, shifts in envelope wavelength indicate a sensitivity of −0.193 nm/cm, and a liquid level resolution of 1 mm can be easily acquired. Furthermore, by demodulating the amplitude after spectral FFT in a specific narrow wavelength range, and intensity sensitivity of 1.906 dB/cm is achieved, leading to a greatly improved overall resolution of 0.03 mm in liquid level measurement. Besides, the sensing element is sealed and packaged by two sheets of silicone rubber, which can be thrown into liquid when in use, thus easing the sensor installation. Moreover, due to the proposed demodulation method, the sensor is insensitive to the light source power jitter, reference arm phase shift and optical spectral analyzer wavelength shift. Therefore, the merits of the proposed sensor include high precision, high stability, ease of installation, which are beneficial in pore water pressure and liquid level monitoring. [ABSTRACT FROM AUTHOR]

• Low-cost fiber MI temperature sensor is formed by filling SCF with polymer-UV glue. • High sensitivity is obtained due to the great thermal properties of UV glue. • Our sensor shows advantages of robust, small size, and low cost. • The reflective tip structure enable for remote sensing in practical applications. A low-cost fiber tip temperature sensor is proposed and experimentally demonstrated. It is based on the Michelson interferometer (MI) structure which is partially filled with polymer-UV glue in the suspended core fiber (SCF). Due to the greater thermal properties of UV glue compared with the silica optical fiber, the length of the inner cavity in the MI structure is susceptible to temperature modulation, resulting in the interference wavelength drift. Experimental results show that the sensor achieves a sensitivity of −164 pm/°C in the temperature range of 25–60 °C, and the sensor offers good wavelength and power stability at room temperature. In addition, the sensor has advantages such as robust, small size, and low cost, especially the reflective tip structure is more suitable for remote sensing in practical applications. [ABSTRACT FROM AUTHOR]

• A highly-sensitive pressure sensor with sensitivity of 80.8 pm/kPa. • Low temperature cross sensitivity of 2.2 kPa/°C. • Experimental results in good agreement with the "Two-beam" interference model. • Simple fabrication technique without fiber machining, and possible for mass production. We propose and demonstrate a simple highly-sensitive gas pressure sensor based on harmonic Vernier effect. By fusion splicing two hollow silica capillaries, a cascaded Fabry-Perot (FP) cavity is formed. Without special photonics crystal fibers or laser machining involved, the fabrication process is greatly simplified. The interplay between the two interferometers consisting the FP cavity leads to optical Vernier effect. By properly adjusting the length of the silica capillaries harmonic of optical Vernier effect is observed and can be served as a sensitive probe for diagnosing gas pressure. Our results showed a sensitivity of 80.8 pm/kPa from 1 to 101 kPa with good linearity of 99.7%, and a low temperature cross sensitivity of 2.22 kPa/°C, a factor of three lower than that of the microstructure fiber-based gas pressure sensors. Combining both ease of fabrication and high sensitivity, this sensor can be a good candidate for mass production in fields of gas sensing and environmental safety monitoring. [ABSTRACT FROM AUTHOR]