Liang’en Ding

Efficient tunable diode-pumped Yb:LYSO laser

We demonstrated efficient laser action of a new ytterbium-doped oxyorthosilicate crystal Yb:LuYSiO(5) (Yb:LYSO) under high-power diode-pumping. The spectroscopic features and laser performance of the alloyed oxyorthosilicate crystal are compared with those of ytterbium-doped lutetium and yttrium oxyorthosilicates. In the continuous-wave laser operation of Yb:LYSO, a maximal slope efficiency of 96% and output power of 7.8 W were respectively achieved with different pump sources. The Yb:LYSO laser exhibits not only little sensitivity to the pump wavelength drift but also a broad tunability. By using a dispersive prism as the intracavity tuning element, we demonstrated that the continuous-wave Yb:LYSO laser exhibit a continuous tunability in the spectral range of 1014-1091 nm.

Single-photon routing by time-division phase modulation in a Sagnac interferometer

In this letter, we report the experimental demonstration of a single-photon router based on a time-division Sagnac interferometer, wherein differential phase shifts are applied on either the clockwise or counterclockwise quasi-single-photon pulses to determine the single photon interference and consequently output photon routing. High fidelity (>85%) of single-photon routing was demonstrated over a long-distance Sagnac loop. Stable performance was guaranteed by passive compensation of stress and temperature dependent drifts of the fiber-optic path. Experimental data show that time-division single-photon routing can be realized by controlling the applied electric pulses on the integrated phase modulators in the Sagnac loop, which makes this setup suitable for a practical quantum cryptography system.

Femtosecond laser pulse energy transfer induced by plasma grating due to filament interaction in air

We experimentally demonstrate the formation of a thin plasma grating lasted for several tens of picosecond induced by the strong interaction between two noncollinear femtosecond filaments in air. A time-delayed second-harmonic pulse propagating along one of the incident filaments is coupled and nonlinearly diffracted by the thin plasma grating, leading to an energy transfer to the other noncollinearly crossed femtosecond filament. The dependences of the plasma grating on the intensity ratios and relative polarizations between the input pulses are investigated.

Plasma waveguide array induced by filament interaction

We demonstrate that interference-assisted coalescence of two noncollinearly overlapped filaments creates a wavelength-scale periodic plasma density modulation to guide the input pulses equivalently as a photonic crystal plasma waveguide. The periodic self-channeling is evidenced by the direct observation of the filament coalescence, which reveals wavelength-scale spatial widths and periodicity dependent on the crossing angles and intensity ratios between the incident filaments.

Efficient diode-pumped Yb:Gd2SiO5 laser

An efficient diode-pumped laser was demonstrated by using an ytterbium-doped laser crystal, Yb:Gd2SiO5 (Yb:GSO), wherein Yb3+ ions exhibit the largest ground-state splitting among all the ytterbium-doped crystals. The Yb:GSO laser can be operated at a low pumping threshold, and the most efficient laser occurs around 1088nm since the corresponding emission band has the largest emission cross section and the lowest thermal population. A slope efficiency of 75% was demonstrated for a continuous-wave Yb:GSO laser at 1094nm, and self-pulsed lasers were achieved within the tunable range of 1091–1105nm, which are the longest laser wavelengths achieved for Yb3+ lasers.

Diode-pumped continuous-wave and passively mode-locked Yb:GSO laser.

We report on both continuous-wave and passively mode-locked laser actions of a new ytterbium-doped laser crystal Yb:Gd(2)SiO(5) (Yb:GSO) under high-power diode-end-pumping. Due to the anisotropic and compact crystal structure, Yb:GSO exhibits a large manifold splitting of Yb(3+) ions, and a Yb:GSO laser can be operated efficiently with negligible reabsorption losses at emission wavelengths. In the continuous-wave operation, a Yb:GSO laser was operated with a slope efficiency of 49% near 1094 nm--the longest laser wavelength achieved for Yb(3+) lasers. Passive mode locking was obtained with a semiconductor saturable-absorber mirror. At a pump power of 6.23 W, a maximum average output power of 638 mW was obtained with the repetition rate of 145.5 MHz.

Intense ultrafast light kick by rotational Raman wake in atmosphere

We report that intense ultrafast light can be particlelike kicked through the rotational Raman wake of the impulsively pre-excited diatomic molecules in atmosphere, manifested by controllable repulsion and attraction of intense pulses delayed by molecular alignment revival periods, and by mutual fusion of orthogonally polarized intense pulses nearby zero time delay. The rotational Raman wake facilitates longer ranges of interaction on the intense ultrafast light kicks than the plasma wake and Kerr effect.

Continuous-Wave and Passively Mode-Locked Yb:GYSO Lasers Pumped by Diode Lasers

We report both continuous-wave and passively mode-locked laser actions in a Yb3+-doped gadolinium yttrium oxyorthosilicate Yb:GdYSiO5 (Yb:GYSO) crystal. Continuous-wave (CW) laser operations were compared under different pump conditions with high-power diodes of different wavelengths and fiber cores. CW mode-locking was obtained with a semiconductor saturable absorber mirror.

The formation of an intense filament controlled by interference of ultraviolet femtosecond pulses

We experimentally investigated the formation of a wavelength-scale photonic plasma grating induced by interference-assisted coalescence of two noncollinear ultraviolet femtosecond laser pulses. The period of the created plasma grating decreased with the crossing angle of the interacting laser pulses. For a proper small crossing angle, the noncollinear ultraviolet filaments were coalesced and an intense single ultraviolet filament was formed with a diameter of 5 μm which was below the focused limitation. This may provide a way to control ultraviolet femtosecond filamentation.

Spectral modulation of ultraviolet femtosecond laser pulse by molecular alignment of CO2, O2, and N2

We demonstrate efficient third harmonic generation of a near infrared femtosecond pulse through cascaded frequency doubling and sum-frequency generation processes, where the group velocity mismatching between the involved fundamental and generated second harmonic pulses, before they are sent to frequency mixing, are precompensated with a properly inserted nonlinear crystal. The spectrum of the generated third harmonic pulse with energy of 1.1 mJ is further modulated by using impulsive molecular alignments of CO2, O2, and N2, where significantly broadened spectrum in the ultraviolet spectral region is observed due to the additional cross-focusing effect from the parallel aligned molecules and the consequently enhanced self-phase modulation.