Gao Chun-Qing

Laser Performance of Nd:GGG Operating at 938 nm

We report an efficient diode-pumped Nd-doped Gadolinium gallium garnet (GGG) continuous-wave (CW) laser operating at 938 nm. Laser action of 1.6at.% Nd-doped GGG crystals with different lengths and temperatures are also investigated. The maximum output power of 620 mW is obtained at the incident pump power of 5.0 W with a slope efficiency of 15%.

Study on holographic grating diffraction for Laguerre--Gaussian beam generation

Laguerre–Gaussian beams, as a special model with spiral phase structure, have been intensively investigated. Holographic grating method is a convenient method of generating Laguerre–Gaussian beams and measuring their orbital angular momenta. But due to some inevitable adverse factors such as lateral displacement, angular deflection and elliptical incident profile of incident beam, the practical effectiveness should be reevaluated. This paper is devoted to the study on the influences of the abovementioned three adverse factors on the holographic grating method. The characteristics of the mode decomposition of diffractive order and the relative powers of the orbital angular momentum eigen-states are also given.

Orbital angular momentum of the laser beam and the second order intensity moments

From the wave equation of a generalized beam the orbital angular momentum is studied. It is shown that the orbital angular momentum exists not only in the Laguerre-Gaussian beam, but in any beam with an angular-dependent structure. By calculating the second order intensity moments of the beam the relation between the orbital angular momentum and the second order moments (x θy), (y θx) is given. As an example the orbital angular momentum of the general astigmatic Gaussian beam is studied.

Resonantly pumped 1.645 μm single longitudinal mode Er:YAG laser with intracavity etalons

We report on a 1.645 μm single longitudinal mode Er:YAG laser that was resonantly pumped by a 1.532 μm fiber laser, using intracavity etalons to generate single longitudinal mode operation. We obtained 0.749 W single longitudinal mode output power at 1.645 μm from an Er:YAG laser with two intracavity etalons. The M2-factors of the Er:YAG laser were 1.041 and 1.068 in the x and y directions, respectively.

Diode-Pumped Quasi-Three-Level Passively Q-Switched Nd:GGG Laser with a Codoped Nd,Cr:YAG Saturable Absorber

We demonstrate the first quasi-three-level passively Q-switched Nd:GGG laser at 937 nm using a Nd,Cr:YAG crystal as the saturable absorber. The dependences of the average output power, the repetition rate and the pulse width on the incident pump power are obtained. A maximum average output power of 1.18 W with repetition rate of 35 kHz and pulse width of 45 ns is achieved at an incident pump power of 18.3 W. The corresponding optical-to-optical and slope efficiencies are 6% and 10%, respectively.

Laser Diode-Pumped Nd:LuVO4 Acousto-Optic Q-Switched Laser at 916 nm

A compact laser diode-pumped solid-state Nd:LuVO4 acousto-optic Q-switched laser is demonstrated at 916 nm of a quasi-three level for the first time. A pulse width of 130 ns is observed when the pulse-repetition frequency is 10 kHz. The laser experiment shows that the Nd:LuVO4 crystal can be used for efficient diode-pumped Q-switched lasers.

Passively Mode-Locked Quasi-Three-Level Nd:LuVO4 Laser with Semiconductor Saturable Absorber Mirror

We demonstrate a passively cw mode-locked Nd:LuVO4 laser operating on the quasi-three-level at 916 nm with a Z-folded resonator. Using a semiconductor saturable absorber mirror (SESAM) as the passive mode-locking device, we achieve stable cw mode locking with 6.7 ps pulse duration at repetition rate of 133MHz and 88mW average output power under the pump power of 17.1 W.

Generation of the Stigmatic Beam with Orbital Angular Momentum

The stigmatic beam with orbital angular momentum is generated by transforming the Hermite-Gaussian beam of a diode-pumped Nd:YAG laser through a rotated cylindrical optical system. Behind the transformation optics, the output beam has an intensity distribution of ring shape and a twist phase. The beam transformation is theoretically calculated and the result has been confirmed in the experiments.

Efficient Pumping Scheme by Direct Excitation of Upper Laser Level in Nd:CNGG

We report an efficient pumping scheme which involves a direct excitation of the upper lasing level of a four-level laser in a Nd-doped Ca3(NbGa)2-xGa3O12 (Nd:CNGG) by using a tunable Tr.sapphire, 700–920 nm, cw pump source. The slope efficiency is improved from 10.5% of the traditional band pumping at 808nm to 21.8% of the direct pumping at 882 nm. The influence of pumping wavelength on lasing is discussed. We present a scheme of double pumping for lasing.

Spiral spectrum separation for information transmission by using orbital angular momentum of light beam

Orbital angular momentum (OAM) can be used in information transmission since OAM states can construct high dimensional Hilbert space. We propose a method to separate such OAM states quantitatively, i.e. spiral spectrum, according to the rotational Doppler effect (RDE).