High energy (>40 nJ), sub-100 fs, 950 nm laser for two-photon microscopy.

Compact and high-energy femtosecond fiber lasers operating around 900-950 nm are desirable for multiphoton microscopy. Here, we demonstrate a >40 nJ, sub-100 fs, wavelength-tunable ultrafast laser system based on chirped pulse amplification (CPA) in thulium-doped fiber and second-harmonic generation (SHG) technology. Through effective control of the nonlinear effect in the CPA process, we have obtained 92-fs pulses at 1903 nm with an average power of 0.89 W and a pulse energy of 81 nJ. By frequency doubling, 95-fs pulses at 954 nm with an average power of 0.46 W and a pulse energy of 42 nJ have been generated. In addition, our system can also achieve tunable wavelength from 932 nm to 962 nm (frequency doubled from 1863 nm to 1919 nm). A pulse width of ∼100 fs and sufficient pulse energy are ensured over the entire tuning range. Finally, we applied the laser in a two-photon microscope and obtained superior imaging results. Due to a relatively low repetition rate (∼ 10 MHz), similar imaging quality can be achieved at significantly reduced average power compared with a commercial 80 MHz laser system. At the same time, the lower average power is helpful in limiting the thermal load to the samples. It is believed that such a setup, with its well-balanced optical characteristics and compact footprint, provides an ideal source for two-photon microscopy.

Nanotube mode-locked, wavelength and pulsewidth tunable thulium fiber laser.

Mode-locked oscillators with highly tunable output characteristics are desirable for a range of applications. Here, with a custom-made tunable filter, we demonstrate a carbon nanotube (CNT) mode-locked thulium fiber laser with widely tunable wavelength, spectral bandwidth, and pulse duration. The demonstrated laser's wavelength tuning range reached 300 nm (from 1733 nm to 2033 nm), which is the widest-ever that was reported for rare-earth ion doped fiber oscillators in the near-infrared. At each wavelength, the pulse duration can be regulated by changing the filter's bandwidth. For example, at ~1902 nm, the pulse duration can be adjusted from 0.9 ps to 6.4 ps (the corresponding output spectral bandwidth from 4.3 nm to 0.6 nm). Furthermore, we experimentally and numerically study the spectral evolution of the mode-locked laser in presence of a tunable filter, a topic that has not been thoroughly investigated for thulium-doped fiber lasers. The detailed dynamical change of the mode-locked spectra is presented and we observed gradual suppression of the Kelly sidebands as the filter's bandwidth is reduced. Further, using the polarization-maintaiing (PM) cavity ensures that the laser is stable and the output laser's polarization extinction ratio is measured to exceed 20 dB.

Slowing down photocarrier relaxation in Dirac semimetal Cd3As2 via Mn doping.

In this Letter, we successfully introduce a long-lived non-radiative photocarrier decay component in a Dirac semimetal Cd3As2 thin film via Mn doping. The long-lived decay component is found to vary between 200 ps and 2.8 ns with different Mn concentrations and probing wavelengths. Most remarkably, the elongated transients persist over the important mid-infrared wavelengths (observed up to 4 µm). Saturable absorption measurement reveals stronger modulation effects for long-width pulses (∼80 ps) from the Mn-doped samples. Our results provide new insights into the effect of transition-metal doping on the ultrafast optical properties of Dirac semimetal Cd3As2 and establish Cd3As2 as a highly amendable material for mid-infrared photonic applications.

20 GHz actively mode-locked thulium fiber laser.

A high repetition-rate actively mode-locked thulium fiber laser is demonstrated where an electro-optic lithium niobate phase modulator is used to synchronize the longitudinal modes in the cavity. The repetition rate of the actively mode-locked laser is tunable from 14.6 MHz to 19 GHz, where the 19 GHz pulses exhibit a super-mode suppression ratio of 46 dB. Furthermore, the output pulse width could be manipulated through finely controlling the detuning frequency or repetition rate. We have also experimentally observed rational harmonic mode-locking in the laser and obtained 14 GHz and 21 GHz repetition rate pulses using a 7 GHz modulating signal. To the best of our knowledge, we have improved the repetition-rate of actively mode-locked thulium fiber laser by more than one order of magnitude. Such a high repetition source can be readily synchronized to a master clock, which makes it very suitable for high speed optical data processing, communication and remote sensing.

Angiogenesis and anti-angiogenesis activity of Chinese medicinal herbal extracts.

The aqueous extracts of 24 herbs traditionally used as curing ischemic heart disease in clinic in China were screened for their in vitro angiogenic activity, another twenty-four traditionally used as anti-tumor or anti-inflammatory remedies in China were screened for their in vitro anti-angiogenic activity. The activity of angiogenesis was determined by quantitation of vessels on chick embryo chorioallantoic membrane (CAM) model and cell proliferation of cultured bovine aortic endothelial cells (BAECs). Among the herbal extracts examined, the aqueous extracts of Epimedium sagittatum, Trichosanthes kirilowii and Dalbergia odorifera showed the strong angiogenetic activity both in CAM and BAECs models; and the aqueous extracts of Berberis paraspecta, Catharanthus roseus, Coptis chinensis, Taxus chinensis, Scutellaria baicalensis, Polygonum cuspidatum and Scrophularia ningpoensis elicited significant inhibition at a concentration of 1g dry herb /ml.