Geng You-Fu

Efficient Compound-Cavity Eye-Safe KTP OPO at 1.57 μm Pumped by an Electro-Optic Q-Switched Nd:YAG Laser

An efficient high-energy eye-safe optical parametric oscillator (OPO) based on a type-II non-critically phase-matched KTP crystal is demonstrated. The KTP OPO is pumped by a quasi-cw diode side-pumped electro-optic Q-switched Nd:YAG laser in a compound-cavity configuration. The maximum output energy of the signal wavelength at 1.57 μm is 66.5 mJ, corresponding to an electrical-to-optical conversion efficiency of 4.47% and an optical-to-optical conversion efficiency of 12.1%. The pulse width (FWHM) is about 3.6ns with a peak power of 18.5 MW. The output energy is insensitive to repetition rate and demonstrates good stability.

Low Loss Plastic Terahertz Photonic Band-Gap Fibres

We report a numerical investigation on terahertz wave propagation in plastic photonic band-gap fibres which are characterized by a 19-unit-cell air core and hexagonal air holes with rounded corners in cladding. Using the finite element method, the leakage loss and absorption loss are calculated and the transmission properties are analysed. The lowest loss of 0.268 dB/m is obtained. Numerical results show that the fibres could liberate the constraints of background materials beyond the transparency region in terahertz wave band, and efficiently minimize the effect of absorption by background materials, which present great advantage of plastic photonic band-gap fibres in long distance terahertz delivery.

Green-Beam Generation of 40 W by Use of an Intracavity Frequency-Doubled Diode Side-Pumped Nd:YAG Laser

A cw diode side-pumped Nd:YAG laser is frequency doubled to 532nm with an intracavity KTP crystal in a V-shaped arrangement, achieving an output power of 40 W corresponding to an optical–optical conversion efficiency of 9.7%. The instabilities and the M2 -parameters of the laser are measured at different output powers after the beam is filtered.

Bend-Induced Distortion in Large Mode Area Holey Fibre

A simplified scheme of bend-induced mode distortion is introduced into bent holey fibres, the distorted mode distribution and mode effective area reduction are investigated using the finite difference method. Numerical results show that the modes of bent holey fibres with small bend radius shift away from the core and are deformed greatly, and the mode areas drop significantly as the bend radius decreases, which severely affects the fibre laser performance. The propagation characteristics of bent holey fibres at given wavelength are determined by fill factor and normalized bend radius. Finally, the transition normalized bend radius that represents the location of the mode area beginning to fall off is obtained.