Huilong Liu

Flat-topped vortex hollow beam and its propagation properties

In this paper, a flat-topped vortex hollow beam, which is a new mathematical model for dark hollow beams, has been introduced. The propagation properties of a flat-topped vortex hollow beam of circular and elliptical symmetry are investigated. According to the Collins formula under paraxial conditions, analytical formulas of the average intensity and the effective beam radius of a flat-topped vortex hollow beam are derived. Compared with a general flat-topped hollow beam by using numerical simulation, the propagation characteristics of a flat-topped vortex hollow beam are studied in detail. The relationships between the effective beam radius and propagation distance z are also provided graphically. From the graphical outputs of the receiver plane, it is observed that a flat-topped vortex hollow beam propagating to the far field still maintains a dark hollow spot and the radius of the dark hollow spot will get gradually larger as the propagation distance is extended. Furthermore, the flat-topped vortex hollow beam carrying the orbital angular momentum can be widely applied in atomic optics.

Orthogonally polarized dual-wavelength Nd:YAlO(3) laser at 1341 and 1339 nm and sum-frequency mixing for an emission at 670 nm.

We report a diode-pumped continuous wave (cw) orthogonally polarized dual-wavelength laser at 1339 and 1341 nm with a single b-cut Nd:YAlO(3) (Nd:YAP) crystal. By adjusting the tilt angle of the uncoated glass plate inserted in the laser cavity, we can control the cavity losses of two polarized directions. The output wavelengths are 1339 nm in a-axis polarization and 1341 nm in c-axis polarization, respectively, which are orthogonal to each other. At an incident pump power of 17.3 W, the cw output power obtained at 1339 and 1341 nm is 1.6 and 2.3 W, respectively. Furthermore, intracavity sum-frequency mixing at 1339 and 1341 nm was then realized in a KTiOPO(4) (KTP) crystal to reach the red range. To our knowledge, this is the first work realizing an orthogonally polarized dual-wavelength Nd:YAP laser based on the (4)F(3/2-)-(4)I(13/2) transition. Such a dual-wavelength laser would be especially valuable as a compact laser source to generate terahertz emission because the frequency difference between 1339 and 1341 nm is about 0.9 THz.

Influences of uniaxial crystal on partially coherent multi-Gaussian Schell-model vortex beams

The evolution properties and the spectral degree of coherence of a partially coherent multi-Gaussian Schell-model vortex (MGSMv) beam propagating in uniaxial crystals orthogonal to the optical axis are studied. Propagation expression for the cross-spectral density and the average intensity of the partially coherent MGSMv beam propagating in uniaxial crystals are derived. Some analyses are illustrated by numerical examples related to the propagation properties and coherence vortices of the partially coherent MGSMv beam in uniaxial crystals. Numerical results show that, upon propagating in uniaxial crystals, the partially coherent MGSMv beam loses its initial dark center distribution. After propagating for sufficient distances, the partially coherent MGSMv beam will also evolve into a flat-topped beam. The evolution behavior of average intensity and coherent vortices depends on the crystal including the ratio of extraordinary and ordinary refractive indices, and beam parameters including the spatial correlation length and topological charge of the beams, as well as the propagation distance.

Simultaneous triple 914 nm, 1084 nm, and 1086 nm operation of a diode-pumped Nd:YVO4 laser

We report a diode-pumped continuous-wave (cw) triple-wavelength Nd:YVO4 laser operating at 914, 1084, and 1086 nm. A theoretical analysis has been introduced to determine the threshold conditions for simultaneous triple-wavelength laser. Using a T-shaped cavity, we realized an efficient triple-wavelength operation at 4F3/2→4I9/2 and 4F3/2→4I11/2 transitions for Nd:YVO4 crystal, simultaneously. At an absorbed pump power of 16 W (or 25 W of incident pump power), the maximum output power was 2.3 W, which included 914 nm, 1084 nm, and 1086 nm three wavelengths, and the optical conversion efficiency with respect to the absorbed pump power was 14.4%.

Fine wavelength control in 1.3 μm Nd:YAG lasers by electro-optical crystal lens

A diode-pumped tunable and multi-wavelength continuous-wave Nd:YAG laser based on the 4F3/2−4I13/2 transition has been demonstrated for the first time. The combination of the glass plane positioned at the Brewster angle and the electro-optical crystal KH2PO4 (KDP) lens formed a Lyot filter in the cavity and compressed the available gain bandwidth. With an adjustable voltage applied to the KDP crystal lens, the laser wavelength could be tuned from 1333.8 to 1338.2 nm. Moreover, we can also realize cw dual-wavelength and triple-wavelength lasers with smaller wavelength separation by adjusting the free spectral range of the Lyot filter.

Radial phased-locked partially coherent flat-topped vortex beam array in non-Kolmogorov medium.

The analytical expressions for the cross-spectral density, the average intensity and the complex degree of spatial coherence of a radial phased-locked partially coherent flat-topped vortex beam array propagating through non-Kolmogorov medium are obtained by using the extended Huygens-Fresnel principle. The evolution behaviors of a radial phased-locked partially coherent flat-topped vortex beam array propagating through non-Kolmogorov medium are studied in detail. It is shown that the evolution behaviors of average intensity depend on beam parameters including the spatial correlation length, the radius of the beam array, as well as the propagation distance. A radial phased-locked partially coherent flat-topped vortex beam array with high coherence evolves more rapidly than that with low coherence.

Evolution properties of partially coherent standard and elegant Hermite–Gaussian beams in uniaxial crystals

The propagation properties of a partially coherent elegant Hermite-Gaussian beam (EHGB) and a partially coherent standard Hermite-Gaussian beam (SHGB) in uniaxial crystals orthogonal to the optical axis are studied. The propagation expression for the cross-spectral density of the partially coherent EHGB and SHGB propagating in a uniaxial crystal is derived. With the help of the derived formula, some analyses are illustrated by numerical examples related to the evolution properties of the spectral density, the spectral degree of coherence, and the effective beam width of the partially coherent EHGB and SHGB in a uniaxial crystal. It is shown that propagation properties of the partially coherent EHGB and SHGB in an isotropic crystal are much different from the evolution properties in an anisotropic crystal. The evolution behavior of spectral density and the spectral degree of coherence depends on the parameters of the uniaxial crystals (the ratio of extraordinary and ordinary refractive indices), and beam parameters including the coherence length and the beam order, as well as the propagation distance.

Generation and propagation dynamics of Airy beam with the tunable tail

We introduce a new kind of Airy beam called Airy beam with the tunable tail, which can be generated from the elliptical flat-topped Gaussian beam. The analytical formula of Airy beam with the tunable tail is derived. Airy beam with the single tail can be obtained by adjusting the ration of the beam width of elliptical flat-topped Gaussian beam. The tail length of Airy beam can be controlled by the order N of incident beam. The normalized intensity distributions of Airy beam with the tunable tail propagating in free space are studied, and the propagation dynamics of Airy beam with the single tail are investigated. Compared with the Airy beam generated from the fundamental Gaussian beam or the flat-topped Gaussian beam, some interesting and useful information has been found.