Effects of Dentin Ablation by a Q-Switching Er:YSGG Laser with a High Pulse Repetition Rate.

Objective: The aim of the study was to evaluate the characteristics of dentin ablation with a high pulse repetition rate Q-switching 2.79 µm laser. Materials and methods: Dentin was ablated using a homemade Q-switching Er:YSGG laser with a high pulse repetition rate. Er:YSGG radiation was applied with a pulse energy of 1 or 10 mJ for 100 or 3 Hz pulse repetition rate, respectively. A scanning electron microscope (SEM) was used to observe the microstructures of dentin samples after ablation. Teeth were irradiated in vitro with a 100 Hz pulse repetition rate under two different modes: free running and Q-switching. A thermocouple was applied to measure the temperature in the pulp cavity during ablation. Results: A 100 or 3 Hz Q-switching laser was used to irradiate dentin for 30 and 100 sec, respectively. There was no significant difference in ablation mass loss between the two conditions. The SEM photographs showed more dentinal tubules and no damage in the ablation area when using the 100 Hz Q-switching laser. The temperature of the pulp cavity was maintained below 41°C when using a Q-switching laser. Conclusions: The Q-switching Er:YSGG laser with a high pulse repetition rate exhibited greater ablation efficiency and better morphology than the low pulse repetition rate Q-switching laser. The experimental results also demonstrate the significant advantage of the Q-switching laser over free-running lasers for protecting dental pulp tissue. The Q-switching Er:YSGG laser with a high pulse repetition rate is expected to become an efficient new dental tool.

High-conversion-efficiency tunable mid-infrared BaGa4Se7 optical parametric oscillator pumped by a 2.79-µm laser.

A mid-infrared BaGa4Se7 optical parametric oscillator with high conversion efficiency and beam quality is demonstrated, which is pumped by a 2.79-µm electro-optically Q-switched Cr, Er:YSGG laser. A pulse energy of 3.5 mJ with a pulse width of 21 ns at 10 Hz is obtained in the range of 3.94-9.55 µm, and the beam quality factors are measured to be Mx2=5.0 and My2=4.6. The optical-to-optical conversion efficiency is 18.9%, and the slope efficiency is 31.6%, which is a 59% improvement on the best of the previously reported slope efficiencies for BaGa4Se7-based OPOs.

Widely tunable and narrow-bandwidth pulsed mid-IR PPMgLN-OPO by self-seeding dual etalon-coupled cavities.

Integrating narrow-bandwidth and wavelength tunability together is crucially important in upgrading the applications of optical parametric oscillators (OPO). Here, we have demonstrated a widely tunable, narrow-bandwidth and efficient mid-IR OPO pumped by a single-longitudinal-mode pulsed Yb-fiber laser. By restricting the bandwidth of the oscillated signal via self-seeding dual etalon-coupled cavities, the bandwidth of the idler can be suppressed to about 0.35 nm, with a wide tunable range of 2.85-3.05 µm, which can be achieved by synergistically adjusting the temperatures of PPMgLN crystal and one of the etalons. The maximum idler power at 3.031 µm is 2.67 W with an optical-to-optical conversion efficiency of 17.4%.

Mid-infrared ZGP-OPO with a high optical-to-optical conversion efficiency of 75.7.

We experimentally demonstrate a ZnGeP2 based optical parametric oscillator (ZGP-OPO) with a record of the optical-to-optical conversion efficiency. To improve the conversion efficiency, we design and construct a double-pass pumped high-gain OPO and a matched large-sized high-peak-power pump beam to suppress the spatial walk-off and conversion. Pulse energy of 19 mJ with pulse width of 27.8 ns at 5 Hz in the mid-infrared 3-5 µm waveband is obtained in the doubly resonated ZGP-OPO, the beam quality M2 is about 9.6, and the corresponding optical-to-optical conversion efficiency reaches up to 75.7%.