Jinmeng Hu

Stimulated-Brillouin-scattering-suppressed high-power single-frequency polarization-maintaining Raman fiber amplifier with longitudinally varied strain for laser guide star

An up to 44 W, 1 MHz linewidth, 1178 nm CW laser is obtained by Raman amplification of a distributed feedback diode laser in a variably strained polarization-maintaining fiber with a record-high optical efficiency of 52%, pumped by a linearly polarized 1120 nm fiber laser. A polarization extinction ratio of 30 dB is achieved due to the all-polarization-maintaining configuration and the polarization dependence of Raman gain. The strain distribution is designed according to the signal power evolution along the fiber. A 20 times reduction in the effective stimulated Brillouin scattering coefficient is achieved. A 24.3 W 589 nm laser is generated by an external resonant doubling cavity with an optical efficiency of 68.5%. The laser is locked to 589.1591 nm for a laser guide star.

A 100 W all-fiber linearly-polarized Yb-doped single-mode fiber laser at 1120 nm

A 100 W-class all-fiber linearly-polarized single-mode fiber laser at 1120 nm with an optical efficiency of 50% was demonstrated. The laser consists of a 4.2 m long Yb-doped polarization maintaining fiber with a core diameter of 10 μm and a pair of FBGs written in matched passive fiber. Linearly polarized output with a polarization extinction ratio of 15 dB is achieved by a cavity that selects both wavelength and polarization. Pulsed operations with square shaped pulses varying from 100 μs to 1 ms duration are achieved without relaxation oscillation.

Density functional theoretical determinations of electronic and optical properties of nanowires and bulks for CdS and CdSe

The authors present density functionaltheoretical results of electronic and optical properties of wurtzite-type CdS and CdSesemiconductornanowires and bulks. The results show that quantum confinement will increase the energy gap, decrease the dielectric function, change the sign of birefringence, and increase the absolute value of birefringence at low-frequency region, as the dimensions of CdS and CdSe are reduced from the bulk to a nanowire with diameter of several nanometers. The optical spectral peaks of CdSenanowires show redshifts as compared with the corresponding ones of CdSnanowires.

Linearly Polarized 1180-nm Raman Fiber Laser Mode Locked by Graphene

In this paper, we demonstrate a linearly polarized 1180-nm passively mode-locked Raman fiber laser using graphene-based saturable absorber (SA). The pump source is a linearly polarized ytterbium-doped fiber laser at 1120 nm. Stable nanosecond mode-locked pulses with a repetition rate of 0.4 MHz are generated. The combination of Raman technology and the graphene-based ultrawide bandwidth SA offer a prospect of real wavelength-versatile mode-locked laser source. The mode-locked laser operating at 1180 nm is suitable for frequency doubling to yellow light after amplification.

First-principles study: size-dependent optical properties for semiconducting silicon carbide nanotubes

Using first-principles calculations, we investigate the effect of tube size on optical properties of the zigzag, armchair, and chiral SiC nanotubes. The results indicate that the optical spectra of SiC nanotubes are dependent on the diameter and chirality, and that optical anisotropy is observed for different light polarizations. For a given chirality of SiCNTs, redshifts or blueshifts of the peaks in the dielectric function and energy loss function with increasing tube diameter are possible due to the competition between the size effect and pi orbitals overlapping, and the shifts become smaller as the tube diameter increases. The unusual optical properties of semiconducting SiC nanotubes present an opportunity for applications in electro-optical devices.

High power room temperature 1014.8 nm Yb fiber amplifier and frequency quadrupling to 253.7 nm for laser cooling of mercury atoms

An 8 W continuous wave linearly-polarized single-frequency 1014.8 nm fiber amplifier working at room temperature is developed with commercial double-clad single-mode Yb-doped silica fiber. Re-absorption at the laser wavelength and amplified spontaneous emission at longer wavelength are managed by optimizing the amplifier design. The laser has a linewidth of ~24 kHz without noticeable broadening after amplification. Using two resonant cavity frequency doublers, 1.03 W laser at 507.4 nm and 75 mW laser at 253.7 nm are generated with 4 W 1014.8 nm laser. Both absorption and saturated absorption spectra of the (1)S(0) - (3)P(1) transition of atomic mercury are measured with the 253.7 nm laser.

A periodic density functional theory study on the effects of halides encapsulated in SiC nanotubes

In this paper we present results of density functional theory calculations on the configurations, band structures, and optical properties of halides MCl (M=K,Ag) intercalated single-wall SiC nanotubes. The results show that the M-Cl distances perpendicular to the tube axis are slightly smaller than the ones parallel to the tube axis, which could be due to the axial strain of MCl. The electronic and optical properties of the resulting MCl@SiCNT composite are modified with respect to both the bulk halide and the empty nanotube. It is shown that AgCl affects the structures and properties of SiC nanotubes more significantly than KCl, and that the interaction between the nanotube and the encapsulated halide is stronger for narrower SiC nanotube. The AgCl encapsulation into SiCNTs results in band gap narrowing of AgCl@SiCNTs.

Tunable all-fiber dissipative-soliton laser with a multimode interference filter

We report on a tunable all-fiber dissipative-soliton laser with a multimode interference filter that consists of a multimode fiber spliced between two single-mode fibers. By carefully selecting the fiber parameters, a filter with a central wavelength at 1032 nm and a bandwidth of 7.6 nm is constructed and used for spectral filtering in an all-normal-dispersion mode-locked ytterbium-doped fiber laser based on nonlinear polarization evolution. The laser delivers 31 mW of average output power with positively chirped 7 ps pulses. The repetition rate of the pulses is 15.3 MHz, and pulse energy is 2.1 nJ. Tunable dissipative-soliton over 12 nm is achieved by applying tension to the single-mode-multimode-single-mode filter.

Efficient linearly polarized ytterbium-doped fiber laser at 1120 nm

We report a 20 W linearly polarized, spectrally clean Yb-doped fiber laser at 1120 nm with an optical conversion efficiency of 54%. An excellent polarization extinction ratio of more than 23 dB is obtained using fiber Bragg gratings (FBGs) polarization selection technique at all power levels. The results reveal that a Yb-doped fiber laser at 1120 nm could be a promising replacement compared to Raman fiber lasers.

589 nm laser generation by frequency doubling of a single-frequency Raman fiber amplifier in PPSLT

A high-power single-frequency 1178 nm continuous-wave laser is generated in a two-stage stimulated-Brillouin-scattering-suppressed all-polarization-maintaining Raman fiber amplifier pumped by 1120 nm fiber lasers. A polarization-extinction-ratio of 30 dB is achieved due to the all-polarization-maintaining configuration and the polarization dependence gain of Raman scattering. Single-pass frequency doubling with a homemade periodically poled near-stoichiometric LiTaO(3) crystal (PPSLT) produces an up to 7 W narrow-linewidth laser at 589 nm. The thermally induced dephasing effect is found to be the key issue for improving second-harmonic efficiency.