Effect of nanosecond- and microsecond-pulse Er,Cr:YSGG laser ablation on dentin shear bond strength of universal adhesives.

OBJECTIVE: The study aimed to evaluate the bond strength of universal adhesives to dentin after Er,Cr:YSGG laser irradiation with nanosecond-domain and microsecond-domain pulses. METHODS: Eighty extracted caries-free, sound human molars were divided into eight groups. The enamel was removed until the dentin occlusal flat dentin surface was exposed. Etch-and-rinse followed by adhesive was applied to group 1, and a self-etch adhesive was applied to group 2. Er,Cr:YSGG laser (3 mJ, 100 Hz, 100 ns), (3 mJ, 100 Hz, 150 µs), and (20 mJ, 100 Hz, 150 µs) were applied to groups 3-4, 5-6, and 7-8, respectively. The laser preparation was followed by self-etch adhesives or adhesives treatment. When the composite resin had been built up on the samples, the shear bond strength was tested, and the data were statistically analyzed using analysis of variance (ANOVA). RESULTS: Groups prepared with nanosecond-pulse laser showed significantly higher bond strength values than the microsecond-pulse laser groups and self-etch mode group, and the SEM photographs also showed more dentinal tubules and no damage in the ablation area. The shear bond strength of long pulse laser ablated was comparable to that of self-etching system when it was combined with a self-etch adhesive at low energy, but higher energy laser degraded shear bond strength. CONCLUSIONS: The pulse width of Er,Cr:YSGG laser affects the bond strength, nanosecond pulses of laser irradiation without water cooling can enhance bond strength, but microsecond pulses of laser cannot enhance bond strength.

2.79-µm efficient acousto-optic Q switched Er,Cr:YSGG laser with an LiNbO3 crystal modulator.

We fabricate a novel, to the best of our knowledge, acousto-optic Q switch in the 3-micron wavelength range using a longitudinal acoustic mode in a lithium niobate (LiNbO3) crystal. The device is designed based on properties of the crystallographic structure and material to obtain a high diffraction efficiency close to the theoretical prediction. The effectiveness of the device is verified by application in an Er,Cr:YSGG laser at 2.79 µm. The maximum diffraction efficiency reached 57% at the radio frequency of 40.68 MHz. At the repetition rate of 50 Hz, the maximum pulse energy was 17.6 mJ and the corresponding pulse width was 55.2 ns. The effectiveness of bulk LiNbO3 as an acousto-optic Q switch is verified for the first time.

High-peak-power electro-optically Q-switched laser with a gradient-doped Nd:YAG crystal.

We report on a high-peak-power electro-optically Q-switched laser emitting a near-diffraction-limited beam profile at 1064 nm by using a gradient-doped Nd:YAG crystal. The gradient-doped crystal features a unique combination of a reduced thermal lens effect through effectively spreading the heat load distribution within its volume. Its performance is compared with those of Nd:YAG crystals with uniform volume doping distribution operating in the Q-switched regime with the same laser configuration, demonstrating the higher average and peak power achievable with the gradient-doped crystal. The maximum average output power amounts to 6.9 W at a pulse repetition rate of 2 kHz, which corresponds to a maximum peak power of ∼585kW. Compared to homogeneous dopant crystals, the slope efficiency and average output power increased by 30.8% and 21.1%, respectively.

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%.

High peak power Q-switched Er:YAG laser with two polarizers and its ablation performance for hard dental tissues.

An electro-optically Q-switched high-energy Er:YAG laser with two polarizers is proposed. By using two Al(2)O(3) polarizing plates and a LiNbO(3) crystal with Brewster angle, the polarization efficiency is significantly improved. As a result, 226 mJ pulse energy with 62 ns pulse width is achieved at the repetition rate of 3 Hz, the corresponding peak power is 3.6 MW. To our knowledge, such a high peak power has not been reported in literature. With our designed laser, in-vitro teeth were irradiated under Q-switched and free-running modes. Results of a laser ablation experiment on hard dental tissue with the high-peak-power laser demonstrates that the Q-switched Er:YAG laser has higher ablation precision and less thermal damage than the free-running Er:YAG laser.