Inherent intensity noise suppression in a mode-locked polycrystalline Cr:ZnS oscillator.

We developed a diode-pumped, mode-locked polycrystalline Cr:ZnS oscillator using single-walled carbon nanotubes as a saturable absorber. The oscillator exhibits self-start mode-locking operation, generating sub-100 fs pulses with an average power of 300 mW. We found a unique feature in which the intensity noise originating from relaxation oscillation is suppressed by inherent second harmonic generation in polycrystalline Cr:ZnS. The observed noise suppression is reproduced by a theoretical model that includes an instantaneous nonlinear loss.

Antimonene Nanoflakes: Extraordinary Photoacoustic Performance for High-Contrast Imaging of Small Volume Tumors.

Photoacoustic imaging (PAI) has evolved to a stage that high-performance exogeneous contrast agents are urgently needed for imminent biomedical and clinical applications. Given that a material meets the basic criteria of efficient photoacoustic conversion, high biocompatibility, and fast excretion, great effort has been devoted to evaluating various materials for developing advantageous contrast agents to explore the full potentials of PAI. One focus is through modification of the current agents to boost their PA performance; whilst the other focus is to develop novel agents. Antimonene (AM) has emerged as a promising candidate for next generation of electronics among 2D materials due to its outstanding properties. Herein, it is reported that liquid-phase exfoliated antimonene exhibits extraordinary photoacoustic performance, which is not only more advantageous than other 2D materials, such as black phosphorus, graphene oxide, and transition metal dichalcogenides, but also superior to the commonly used PA contrast agents, such as ICG and gold nanorods. An insight analysis reveals that the unique thermal property of AM, including intrinsic low thermal conductivity and the morphology-related high interfacial thermal conductivity, might interpret the high photothermal conversion efficiency, and thus the excellent photoacoustic performance. The prodigious performance allows sensitive monitoring of intracellular events and high-quality in vivo tumor imaging.

All-normal-dispersion passive harmonic mode-locking 220 fs ytterbium fiber laser.

We report a stable passive second-harmonic mode-locked all-normal-dispersion ytterbium fiber laser based on nonlinear polarization evolution. This fiber laser has two polarization beam splitter output ports for optimizing the output spectrum 5 ps duration pulses with 187 mW average power being generated at the harmonic repetition rate of 99.6 MHz. By use of a pair of gratings to extracavity compensate the chirp, the pulse is further compressed to 220 fs. We measured that the peak-to-pedestal extinction of the radio frequency is about 80 dB corresponding to a pulse-to-pulse energy fluctuation of 0.32% and timing jitter of 3.2 ps.