Transient dynamics of pulsating polarization rotating dual solitons in an ultrafast fiber laser.

The state of polarization is essential for a full description of ultrashort pulses. We experimentally observe the transient vector dynamics of pulsating vector solitons with rotating polarizations in a single-wall carbon nanotube mode-locked fiber laser. We acquire the single-shot polarization evolution of two different dual soliton pulsations using a homemade real-time wavelength-resolved state of polarization measurement system. We identify experimentally two different types of dual-soliton pulsations with longer and shorter pulsating periods respectively, and we find that dispersive-caused wave-caused energy exchange may be the reason for the distinct single soliton polarization evolution in multi-soliton cases. Our results are crucial for understanding the essence of soliton behaviour and developing novel potential applications of ultrafast fiber lasers.

High speed surface defects detection of mirrors based on ultrafast single-pixel imaging.

High speed surface defects detection of mirrors is of great significance, for detecting the quality of the mirrors on-site, and ultimately for monitoring the operating states of laser systems. The speeds of conventional proposals are relatively low as they utilize mechanically scanning methods or two-dimensional charge-coupled devices. Here, we propose a high speed surface detection method based on ultrafast single-pixel imaging, which consists of a spatial Fourier optical module for frequency-space mapping and a dispersive Fourier transform module for frequency-time mapping. An optical grating is utilized to map the wideband spectrum of dissipative soliton into the spatial domain under far-field diffraction, where the mirror is inspected. Dispersive Fourier transform is used to map the surface-defects-coded spectral information into the temporal domain, then recorded by a high speed single-pixel detector. The detection system permits continuous single-shot spectra measurement with a frame rate equivalent to the pulse repetition rate (8.4 MHz). We extract amplitude defects by demodulating light intensity, and obtain phase defects by demodulating the interference spectrum with a Mach-Zehnder interferometer structure. Experimental results show that the damaged mirror with a two-dimensional width of 10 × 13 mm can be obtained with a spatial resolution of 90 µm. The obtained phase accuracy after Hilbert transformation is 0.00217 rad, corresponding to a depth resolution of 51 nm. This scheme can find promising applications for surface defects detection of large aperture mirrors, and real-time monitoring of laser systems with high energy.

Dynamic phase retrieval method for ultrafast and precise vibration sensing based on time stretching.

We demonstrate a method for retrieving the phase information from single-shot interference spectra obtained by dispersive Fourier transform, through which the error accumulation during phase retrieval is restrained. A Mach-Zehnder interferometer is proposed for vibration sensing with high speed. We find that relative phase trends at different time delays can be precisely retrieved to improve the signal-to-noise ratio when the time interval jitter between pulses within two arms is less than four times the pulse width. The verification experiment achieves a phase resolution of 5.3 mrad and a high-speed refresh frame rate of 51.8 MHz. Numerical simulations and experiments show that the method is effective for phase demodulation of dynamic interference spectra, and provides a reliable strategy for high-speed, precision sensing.

Self-Powered Intelligent Water Meter for Electrostatic Scale Preventing, Rust Protection, and Flow Sensor in a Solar Heater System.

Triboelectric nanogenerators (TENGs) have been investigated for mechanical energy harvesting because of their high-energy conversion efficiency, low cost, ease of manufacturing, and so on. This paper deals with designing a kind of water-fluid-driven rotating TENG (WR-TENG) inspired by the structure of a water meter. The designed WR-TENG is effectively integrated into a self-powered electrostatic scale-preventing and rust protection system. The WR-TENG can generate a constant DC voltage up to about 7.6 kV by using a voltage-doubling rectifier circuit (VDRC) to establish a high-voltage electrostatic field in the water tank. A WR-TENG, a VDRC, and an electric water heating tank are the components of the whole system. The system is convenient to be installed in any waterway system, effectively preventing the rusting of stainless steel and restraining the formation of scale when the water is heated to 65 ± 5 °C. Moreover, the approximately linear relationship between the short-circuit current and the rotation rate of the WR-TENG makes employing it as a self-powered water flow sensor possible. This work enables a facile, safe, and effective approach for electrostatic scale prevention, rust protection, and flow sensing in solar heaters, which will enrich the high-voltage applications of TENGs.