All-fiber mode-locked ytterbium-doped fiber laser with a saturable absorber based on the nonlinear Kerr beam cleanup effect.

We theoretically and experimentally demonstrate a novel, to the best of our knowledge, mode-locked ytterbium-doped fiber laser with a saturable absorber based on the nonlinear Kerr beam cleanup effect. The saturable absorber was formed by a 2-m graded-index multimode fiber, and a single-mode fiber segment served as a diaphragm. With an all-normal-dispersion-fiber configuration, the laser generated dissipative soliton pulses with pulse duration of 26.38 ps and pulse energy more than 0.25 nJ; output pulses could be compressed externally to 615.7 fs. Moreover, the self-starting mode-locking operation of this laser exhibited a high stability with a measured signal-to-noise ratio of 73.4 dB in the RF spectrum.

Miniaturized optical fiber tweezers for cell separation by optical force.

In advanced biomedicine and microfluidics, there is a strong desire to sort and manipulate various cells and bacteria based on miniaturized microfluidic chips. Here, by integrating fiber tweezers into a T-type microfluidic channel, we report an optofluidic chip to selectively trap Escherichia coli in human blood solution based on different sizes and shapes. Furthermore, we simulate the trapping and pushing regions of other cells and bacteria, including rod-shaped bacteria, sphere-shaped bacteria, and cancer cells based on finite-difference analysis. With the advantages of controllability, low optical power, and compact construction, the strategy may be possibly applied in the fields of optical separation, cell transportation, and water quality analysis.

High-efficiency near-degenerate PPMgLN optical parametric oscillator with a volume Bragg grating.

We demonstrate a high-efficiency near-degenerate periodically poled MgO:LiNbO(3) (PPMgLN) optical parametric oscillator (OPO) using a volume Bragg grating (VBG) output coupler (OC) pumped by a multilongitudinal Q-switched Nd:YVO(4) laser at 20 kHz repetition rate. A total parametric power of 4.3 W with a conversion efficiency of 60% is achieved in a double-pass pump configuration. The output power improvement over the case of a single-pass pump is nearly 60%. Both the signal and the idler bandwidths are less than 40 GHz and are confined within 170 GHz bandwidth at 2128.8 nm. Such efficiency is, to our knowledge, the highest ever achieved from a degenerate OPO using a VBG OC.

High average power 2 µm generation using an intracavity PPMgLN optical parametric oscillator.

An intracavity quasi-phase-matched optical parametric oscillator (OPO) has been developed for the purpose of generating radiation with high average power and high repetition rate in the 2 µm regime. The device is a degenerate OPO based on a 3 mm thick MgO-doped periodically poled LiNbO(3) (PPMgLN) crystal, which is pumped in turn within the cavity by a diode side-pumped, Q-switched 1 µm Nd:YAG laser operating at 10 kHz. Up to 20 W broadband 2 µm radiation can be generated with a compact configuration under the crystal temperature of 115 °C. The beam profile is close to circularly symmetric with M(2) ~ 10.

Generation of radially polarized beams based on thermal analysis of a working cavity.

The laser oscillation and polarization behavior of a side-pumped Nd:YAG laser are studied theoretically and experimentally by a thermal model for a working cavity. We use this model along with the Magni method, which gives a new stability diagram, to show important characteristics of the resonator. High-power radially and azimuthally polarized laser beams are obtained with a Nd:YAG module in a plano-plano cavity. Special regions and thermal hysteresis loops are observed in the experiments, which are concordant with the theoretical predictions.

The cavity dispersion noncoaxiality effects on broadband few-cycle pulse generation in Ti:sapphire laser.

The cavity dispersion noncoaxiality (CDN) effects on broadband few-cycle pulse generation of a Kerr-lens mode-locked Ti:sapphire laser is investigated theoretically and experimentally. It is found that the influence of CDN is comparable with that of self-focusing and self-phase-modulation in the frequency-dependent mode size (FDMS) effects. Spectra extending from 680 nm to 1020 nm with pulse duration shorter than three optical cycles are favorably generated under the minimum CDN in the vicinity of the coaxial point of the sub-cavity.