We have demonstrated direct and stable flat-top beam emission from a passively Q-switched microchip laser, featuring an intracavity spot-defect for mode selecting. By adjusting the distance between the focusing lens and the microchip laser, the Gaussian, flat-top, and doughnut-shaped mode can be achieved separately. The flat-top mode is obtained due to the equally weighted superposition of Gaussian and doughnut-shaped mode. By using the self-injection seeding technique, the timing jitter of these three kinds of mode can be reduced effectively.
A simple, efficient, and low-cost method is proposed to reduce the timing jitter in passively Q-switched microchip lasers by self-injection seeding. A portion of the output pulse of the microchip laser was incident into the fiber delay line, and then, the backward reflection light induced the formation of the pulse. With different lengths of fiber, it was found that the timing jitter of the microchip laser could be reduced effectively when the repetition rate of the microchip laser was about 0.8 times the reciprocal of the delay time. The standard deviation of the microchip laser was reduced from several hundred nanoseconds to less than 181 ps.
We studied the pulsed laser diode (LD)-pumped saturable output coupler (SOC) passively Q-switched Nd:YVO4 transmission microchip laser both numerically and experimentally. We demonstrated numerically that the timing jitter decreased with increasing pump power both in the continuous wave (CW) LD pump scheme and the pulsed LD pump scheme. Compared with the CW pump scheme, the pulsed LD pump scheme showed a better performance in timing jitter control due to the much higher peak power and shorter duration of the pulses. Experiments were also carried out to verify the theoretical analysis results. As the pump power of the CW LD increased, the timing jitter value of our laser decreased from 1.68% at 30 mW pump power to a constant around 0.86% at 90 mW. The output frequency can be controlled by changing the pump spot size in the rectangular shape pulsed pump scheme, and it was achieved from 333.3 to 71.4 kHz, while the relative timing jitter decreased from 0.10% to 0.03% accordingly. Additionally, the microchip laser had a good stability of output power, and the power fluctuation was below 2% in a 2-h measurement.
We studied the cw LD and rectangular pulsed LD pumped saturable output coupler (SOC) passively Q-switched Nd:YVO4 transmission microchip laser experimentally. We demonstrated that the SOC passively Q-switched Nd:YVO4 transmission microchip laser pumped by a highly stabilized narrow bandwidth pulsed LD has a much lower timing jitter than pumped by a continuous wave (CW) LD, especially at low output frequency regime. By changing the pump beam size in the rectangular shape pulsed pump scheme, the output frequency can be achieved from 333.3 kHz to 71.4 kHz, while the relative timing jitter decreased from 0.09865% to 0.03115% accordingly. Additionally, the microchip laser has a good stability of output power, the power fluctuation below 2%.
Semiconductor saturable absorber mirror (SESAM) mode locked Yb doped ultrafast lasers have been widely used in industrial applications. High laser stability against environment change and delivery process are required for industrial laser systems. A double Z-type ultrafast laser cavity was demonstrated experimentally and theoretically. Compared with the conventional Z-type cavity, this double Z-type cavity SESAM mode locked laser is less sensitive to misalignment and can tolerate more arm length changes while still staying cw mode locking.
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