Zhaohui Shi

Dual-core antiresonant hollow core fibers

In this work, dual-core antiresonant hollow core fibers (AR-HCFs) are numerically demonstrated, based on our knowledge, for the first time. Two fiber structures are proposed. One is a composite of two single-core nested nodeless AR-HCFs, exhibiting low confinement loss and a circular mode profile in each core. The other has a relatively simple structure, with a whole elliptical outer jacket, presenting a uniform and wide transmission band. The modal couplings of the dual-core AR-HCFs rely on a unique mechanism that transfers power through the air. The core separation and the gap between the two cores influence the modal coupling strength. With proper designs, both of the dual-core fibers can have low phase birefringence and short modal coupling lengths of several centimeters.

Study on LD-pumped Nd:YAG laser cutter

The theory of laser cutter and the technology neck is analyzed. We can conclude that it is almost impossible to deal with the waste thick silicon wafers which are yielded in producing silicon wafers by conventional eroding or diamond cutting, while it is also unperfected with ecumenical laser cutter without good beam quality or precise laser and optics system. It is represented that high average power and high repetition rate laser with good beam quality and precise laser and optics system are pivotal to obtain excellent cutting effect such as thick groove depth, rapid cutting speed, fine kerf section without considering the effect of technique. Considering laser medium thermal lens effect and thermal focal length changing with pumping power, using plano-convex high reflectivity mirror as the back cavity mirror to compensate the heat lens influence, aλ/4 waveplate to compensate heat-induced birefraction, utilize the Nd:YAG self-aperture effect, more than 50 W average power 1.064 um IR output is obtained with beam quality factor (M2) equals 3.19. Through the LD-Pumped Nd:YAG laser cutter we developed with short focus length negative spherical aberration focusing lens, double axis linear step motor positioning system, suitable beam expander multiplying factor, appropriate diameter of exit beam aperture, proper repetition rate, when the cutting velocity equals 400mm/min, 0.75mm thick silicon wafer can be penetrated; when the cutting velocity equals 100mm/min, double-layer 0.75mm thick silicon wafer can be penetrated. The cross section is fine and the groove is narrow, the cutting quality meets the expecting demand.

Research on LD-pumped dual wavelength Nd:YAG laser with high beam quality for machining

Considering laser medium thermal lens effect and thermal focal length changes with pumping power, conventionally, lasers are designed to operate in the middle of thermal stable zones, where the fundamental mode size is insensitive to thermal perturbation, while this method seems impossible when large fundamental mode size is required. Through self-select mode cavity, lasers are designed to work at the border of stable zone instead, where large fundamental mode size in gain media can be reached. With increase of pumping power and self-aperture mode-selective effect, mode size would grow up automatically to a certain value suitable for monomode resonance. With double 180 W pump modules, acoustic Q-switch and LBO external frequency-doubled, over 28 W which M2 equals 4.5 quasi-CW output green laser and 52W 1.064 um IR output is obtained simultaneity. With the insertion or not of the harmonic separator by footswitch high beam quality green IR, and green & IR lasers are obtained conveniently.