Effect of various Er:YAG laser conditioning energies on dentin surface: micromorphological investigation and dentin-resin shear bond strength test.

The aim of this study is to assess the influence of various Er:YAG laser energies on dentin surface micromorphology and dentine-resin shear bond strength (SBS). Eighty dentin specimens were prepared and divided randomly into ten groups: control group (CG), phosphoric acid-etched group (AG), four laser-conditioned groups treated with various pulse energies of 40, 60, 80, and 100 mJ (L40, L60, L80, L100), and four laser-conditioned acid-etched groups (LA40, LA60, LA80, LA100). Two specimens from each group underwent scanning electron microscopy examination, while the remaining six were subjected to the dentin-resin SBS test. Statistical analyses included Welch's analysis of variance (ANOVA), followed by post hoc Tamhane's T2 multiple comparisons test, Pearson's correlation, and Fisher's exact test. Pulse energies of 60, 80, and 100 mJ fully exposed the dentin tubule orifices, although 100 mJ lead to microcracks. Laser-conditioned surfaces exhibited smaller tubule diameters compared to acid-etched surfaces, and tubule diameters positively correlated with dentin-resin SBS. Laser-conditioned groups showed lower SBS values, while laser-conditioned acid-etched groups demonstrated higher SBS values. No significant relationship was observed between dentin surface roughness and SBS. The range of laser energies used for dentin conditioning had limited effects on SBS or failure modes. Laser conditioning with energies ranging from 40 to 100 mJ effectively removes the smear layer from the dentin surface. However, to enhance dentin-resin bond strength, further acid etching of the laser-conditioned surface is necessary.

Analysis of the effects of concentrated growth factor and low-level laser therapy on the bone healing.

Purpose: The aim of this study is to evaluate whether concentrated growth factor (CGF) and photobiomodulation (PBMT) can show synergistic effect on bone healing process. Methods: In vivo osteogenesis studies were performed in a rabbit critical-sized calvarial defect model. Four 8 mm critical-sized bone defects were created on each rabbit calvarium, and these 4 defects were randomly divided into 4 groups: 1-control (defect filled with autologous blood clot); 2-CGF (defect filled with CGF); 3-LLLT (defect filled with autologous blood clot and received Nd:YAG low-level laser irradiation); 4-CGF + LLLT (defect filled with CGF and received LLLT). 15 Japanese big-ear white rabbits were operated on using the same procedure in this study. Then, 5 rabbits were selected randomly and sacrificed at 4th, 6th and 8th week postoperatively and respectively. The calvariums were harvested and scanned by micro-CT. The volumes of new bone formation of these defects were calculated by analyzing the micro-CT image. Data were analyzed as mean values of each group, comparisons were made for statistical analysis with the group and among the 4 groups using analysis of variance (ANOVA, P < 0.05). Results: At the 4th, 6th and 8th weeks, compared with the control group, the volume of new bone formed in each experimental group was significantly increased. Both CGF and LLLT can accelerate bone healing, but the effect of LLLT is better than that of CGF, and the difference between the two is statistically significant (P < 0.01). There was no statistically significant difference in the osteogenic effect between the combined application of CGF + LLLT and the application of CGF alone. And the osteogenic effect of the former two groups was weaker than that obtained by laser irradiation alone. Conclusions: Both CGF and LLLT can promote osteogenesis effectively, but the combination of the two did not show a synergistic effect. The pro-osteogenic effect of Nd:YAG low-level laser irradiation is superior to that of CGF, and also superior to the combined effect of the two.

Precise determination of energy transfer upconversion coefficient for the erbium and ytterbium codoped laser crystals.

Energy transfer upconversion (ETU) coefficient plays a crucial role in investigating complex laser systems as it greatly influences both the laser output behavior and heat generation. For some quasi-three-energy-level lasers based on Er3+ doped, Ho3+ doped and codoped gain media, the available theoretical studies relied on some unreasonable approximations due to the lack of spectroscopic data, notably the ETU coefficient. We put forward what we believe is a novel approach to overcome the difficulties caused by wavelength jump occurred in aforementioned laser systems. Based on net gain cross-section analysis and rate equations modelling, the functional relationship between the ETU coefficient, the laser power and pump power at the jumping wavelength are established. ETU coefficients and their temperature dependences of Er,Yb:YAB crystals with different crystal doped concentrations are experimentally determined for the first time. The results reveal that the ETU process in Er,Yb:YAB laser system is 5∼35 times stronger than that in Er3+ and Yb3+ codoped phosphate glass. The determination of these spectroscopic data paves the way for precise modelling of laser system based on Er,Yb:YAB or similar gain media.

Wavelength tuning of solid-state continuous-wave single frequency 1.5†µm laser by manipulating net gain spectra.

A wavelength tuning method suitable to watt-level continuous-wave single frequency solid-state laser (CWSFL) at 1.5 µm was proposed. Based on a dual-gain-medium resonator design, the laser wavelength can be tuned by manipulating the combined net gain spectrum. Comparing with the traditional tuning method, the wavelength tuning range was eight times broader and extended to 0.438 nm, the maximum laser power was raised up to 0.64 W, which was the highest record for the 1.5 µm CWSFL to the best of our knowledge. The laser intensity noise reached the shot noise limit at the analysis frequency above 3.5 MHz. Wider wavelength tuning band of 5.58 nm can be expected when the same resonator design including two gain media with different doped concentrations was used, according to our theory.

Real time deterministic quantum teleportation over 10†km of single optical fiber channel.

A real time deterministic quantum teleportation over a single fiber channel was implemented experimentally by exploiting the generated EPR entanglement at 1550 nm. A 1342 nm laser beam was used to transfer the classical information in real time and also acted as a synchronous beam to realize the synchronization of the quantum and classical information. The dependence of the fidelity on the transmission distance of the fiber channel was studied experimentally with optimizing the transmission efficiency of the lossy channel that was established to manipulate the beam of the EPR entanglement in Alice's site. The maximum transmission distance of the deterministic quantum teleportation was 10 km with the fidelity of 0.51 ± 0.01, which is higher than the classical teleportation limit of 1/2. The work provides a feasible scheme to establish metropolitan quantum networks over fiber channels based on deterministic quantum teleportation.

In vitro evaluation of the effectiveness of bleaching agents activated by KTP and Nd:YAG laser.

AIM: To compare two different laser sources, a KTP laser with a wavelength of 532 nm and a Nd:YAG laser with a wavelength of 1064 nm, to investigate the relation between laser source and bleaching gel during laser irradiation. METHODS: Extracted human teeth were stained and randomly divided into six groups. Two in-office bleaching gels, Beyond and Opalescence Boost, were applied to stained teeth and then irradiated at either 532 nm or 1064 nm. The temperature change of pulp chamber was measured. The color change (ΔE*) was evaluated at the following time points: immediately after bleaching, 7, 14 and 30 days after the end of bleaching. RESULTS: Boost irradiated by KTP laser showed the higher temperature increase when compared with Beyond irradiated KTP and Nd:YAG. Boost irradiated by Nd:YAG presented lower temperature increase than by KTP. All groups showed a certain color change. After bleaching, Nd:YAG laser irradiation did not increase the ΔE* value significantly compared with gels without laser (p >  0.05). At each time point, Boost activated by KTP laser showed higher ΔE* value compared with other groups (p < 0.05), but decreased significantly 15 days after the end of bleaching. The other groups showed a relatively small change in ΔE* value after 30 days (p > 0.05). CONCLUSIONS: KTP laser achieved better results than the Nd:YAG laser regarding tooth color change when associated with the Opalescence Boost bleaching gels.

Influence of energy-transfer upconversion and excited-state absorption on a high power Nd:YVO4 laser at 1.34 µm.

A self-consistent theoretical model considering both energy-transfer upconversion (ETU) and excited-state absorption (ESA) effects, as well as the couplings among the temperature distribution in the laser crystal, the thermal fractional loading, the upper state population involved in the ETU and ESA effects, the laser output and other temperature-dependent parameters, was developed to simulate the behaviors of diode-end-pumped continuous-wave (CW) single-transverse-mode (TEM00) lasers. Based on the theoretical and experimental investigations of the influences of ETU and ESA effects on laser performance, a high power CW TEM00 Nd:YVO4 1.34 µm laser dual-end pumped at 880 nm was achieved with a maximum output power of 16 W. The measured laser beam quality was M2x = M2y = 1.17 and the stability of the laser output was better than ± 0.9% in a given four hours. The theoretical predictions considering both ETU and ESA effects are in good agreement with experimental results.

Comparison of phase quadrature squeezed states generated from degenerate optical parametric amplifiers using PPKTP and PPLN.

Phase quadrature squeezed states at 1550 nm generated from degenerate optical parametric amplifiers (DOPAs) using periodically poled KTiOPO4 (PPKTP) and periodically poled lithium niobate (PPLN) are compared. A squeezing of 6.8 dB was produced from the DOPA using PPKTP with the phase matching temperature of 34.5 °C. By contrast, a measured squeezing of 4.9 dB was generated using PPLN with the phase matching temperature of 135.2 °C. The degradation of squeezing using a nonlinear crystal with a high phase matching temperature is explained by a theoretical model of DOPAs including the extra phase noise caused by the guided acoustic wave Brillouin scattering within the nonlinear crystal.

High-power stable continuous-wave single-longitudinal-mode Nd:YVO4 laser at 1342 nm.

A universal model about the sufficient condition of stable single-longitudinal-mode (SLM) operation is established and applied to the theoretical analysis of a high power unidirectional ring Nd:YVO4 laser at 1342 nm with energy transfer upconversion and excited stimulated absorption taken into account. A stable continuous-wave SLM laser with 1342 nm power of 11.3 W and 671 nm power of 0.3 W is fabricated by optimizing the transmission of output coupler and the temperature of LiB3O5 crystal. Mode-hopping-free laser operation with a power stability better than ± 0.5% and a frequency fluctuation less than ± 88 MHz is achieved during a given three hours.

Distribution of continuous variable quantum entanglement at a telecommunication wavelength over 20 km of optical fiber.

The distribution of continuous variable (CV) Einstein-Podolsky-Rosen (EPR)-entangled beams at a telecommunication wavelength of 1550 nm over single-mode fibers is investigated. EPR-entangled beams with quantum entanglement of 8.3 dB are generated using a single nondegenerate optical parametric amplifier based on a type-II periodically poled KTiOPO4 crystal. When one beam of the generated EPR-entangled beams is distributed over 20 km of single-mode fiber, 1.02 dB quantum entanglement can still be measured. The degradation of CV quantum entanglement in a noisy fiber channel is theoretically analyzed considering the effect of depolarized guided acoustic wave Brillouin scattering in optical fibers. The theoretical prediction is in good agreement with the experimental results.

Theoretical and experimental investigation of singly resonant optical parametric oscillator under double-pass pumping.

The singly resonant optical parametric oscillator (SRO) under double-pass pumping in a two-mirror linear cavity is investigated theoretically and experimentally. Different output couplers are used in the periodically poled lithium niobate based SRO to optimize the extracted signal output. When the 2.5% output coupler is used, a pump threshold as low as 3.7 W is achieved, and 6.2 W of signal at 1.56 µm with the linewidth of 62.5 kHz is obtained at pump power of 14.5 W. The measured signal frequency drift and peak-to-peak power fluctuation are less than ±40 MHz and ±0.9% in a given 1 h, respectively.

400 mW low noise continuous-wave single-frequency Er,Yb:YAl3(BO3)4 laser at 1.55 µm.

We build up a LD end-pumped Er,Yb:YAB laser at 1.55 µm and improve the laser performance by end cooling the gain medium efficiently through a sapphire plate. 680 mW cw single transverse mode laser output was obtained with the slope efficiency of 16.3%. Using an etalon placed in the laser cavity, 400 mW cw single frequency 1.55 µm laser output was achieved with the slope efficiency of 11.8%. The laser power fluctuation was less than ± 1.3% in a given period of 1.5 hours. The 1.55 µm laser presents low noise properties, that the intensity and the phase noise reach the shot noise level for the analysis frequencies higher than 4 MHz and 5 MHz, respectively.

Stable, 12 W, continuous-wave single-frequency Nd:YVO4 green laser polarized and dual-end pumped at 880 nm.

Based on a polarized and dual-end pumping scheme and a ring resonator, a stable, high power and high beam quality continuous-wave single-frequency Nd:YVO4 green laser directly pumped at 880 nm has been fabricated. A measured maximum output power of 12 W at 532 nm was obtained with a conversion efficiency of 23.1%. The stability of the output was better than ±0.5% and no mode hopping was observed over a period of five hours. The output beam was almost diffraction limited with a measured beam quality of M2(x)=1.03 and M2(y)=1.02. The intensity noise reached the shot noise limit (SNL) for analysis frequencies above 3.5 MHz, and the phase noise was 1.3 dB above the SNL in the range of 2 to 20 MHz.

Stable continuous-wave single-frequency Nd:YAG blue laser at 473 nm considering the influence of the energy-transfer upconversion.

We report a continuous-wave (cw) single frequency Nd:YAG blue laser at 473 nm end-pumped by a laser diode. A ring laser resonator was designed, the frequency doubling efficiency and the length of nonlinear crystal were optimized based on the investigation of the influence of the frequency doubling efficiency on the thermal lensing effect induced by energy-transfer upconversion. By intracavity frequency doubling with PPKTP crystal, an output power of 1 W all-solid-state cw blue laser of single-frequency operation was achieved. The stability of the blue output power was better than +/- 1.8% in the given four hours.

Quantum noise limited tunable single-frequency Nd:YLF/LBO laser at 526.5 nm.

We describe continuous wave single-frequency operation of an intracavity frequency-doubled Nd:YLF ring laser end-pumped by a fiber-coupled laser diode. Output power of 770 mW has been achieved at 526.5 nm. The amplitude noise of the laser reaches the quantum noise limit for frequencies above 5 MHz, and the phase noise reaches the quantum noise limit for frequencies above 10 MHz. The laser's emission frequency can be tuned over 12 GHz by using an intracavity LiTaO3 electro-optic crystal based Fabry-Perot etalon.

Noise suppression, linewidth narrowing of a master oscillator power amplifier at 1.56 microm and the second harmonic generation output at 780 nm.

We have demonstrated a 2 W cw single frequency 1.56 microm laser using a diode laser seeded Erbium doped fiber power amplifier, and a 715 mW cw single-frequency 780 nm laser by an external cavity enhanced second-harmonic-generation. The performance of the system was improved greatly by the seed diode laser optical locked to the resonant frequency of confocal F-P cavity. The linewidth of the 1.56 microm laser was narrowed from 2 MHz to 200 kHz, meanwhile, the intensity and phase noises were suppressed by 10 dB and 12 dB, respectively. The linewidth of the 780 nm laser was narrowed from 2 MHz to 300 kHz, meanwhile, the intensity and phase noises were suppressed by 11 dB and 13 dB, respectively.

Four watt long-term stable intracavity frequency-doubling Nd:YVO(4) laser of single-frequency operation pumped by a fiber-coupled laser diode.

The longitudinal-mode stability of a single-frequency intracavity frequency-doubling laser can be enhanced by increasing the ratio between the nonlinear spectral bandwidth and the gain bandwidth of the laser. A 4 W long-term stable cw single-frequency green laser is obtained using an etalon inside the laser cavity as a spectral filter. No mode hopping is observed when the laser operates for 6 h and the power fluctuation is less than +/-1.2%. In contrast, in the situation of no etalon inside the laser cavity, mode hopping can be observed at irregular intervals and the power fluctuation is +/-3.8% when the laser operates for 4 h.

High-efficiency generation of a continuous-wave single-frequency 780 nm laser by external-cavity frequency doubling.

We demonstrated a 670 mW continuous-wave single-frequency laser source at 780 nm by using external-cavity-enhanced second-harmonic generation of a seeded fiber amplifier in periodically poled lithium niobate. A maximum second-harmonic conversion efficiency of 58% was achieved. The source can work stably over 1 h by locking the frequency-doubling cavity, while the power stability is less than 2%.