YAG Laser Cavity Research Articles

Micro-CT analysis and leakage of bioceramic retrofillings after ultrasonic and Er:YAG laser cavity preparations: an in vitro study.

The purpose of the study was to determine the influence of preparation techniques on marginal adaptation and sealing of Biodentine™ and TotalFill® RRM bioceramic retrograde fillings. Fifty-two single-root teeth extracted for periodontal reasons were used. Root canals were instrumented using Reciproc Blue #25 and obturated using a single cone technique with an AH Plus® root canal sealer. Retrograde cavities were prepared with Piezomed device (Piezo), Er:YAG laser in short-pulse(SP) and quantum square pulse(QSP) modes and filled with Biodentine™ (BD) or TotalFill® RRM (TF). There were 6 groups (n=8): (1) Piezo BD, (2) Piezo TF, (3) SP BD, (4) SP TF, (5) QSP BD, and (6) QSP TF, and positive and negative controls (n=2). Micro-CT analysis was performed on two samples from each group. Percentage volumes of internal and external voids in apical 1.5 mm were determined. Rhodamine B dye leakage was done on six samples. The samples were cut longitudinally and examined under a stereomicroscope. Digital recordings were analyzed in ImageJ software. The deepest penetration of color in mm was recorded. The data were statistically analyzed using ANOVA and Duncan's test at the level of significance α=0.05. TotalFill® RRM performed significantly better than Biodentine™ in terms of sealing (p<0.05) and marginal adaptation, as evaluated by micro-CT. Sealing was significantly better in SP compared to QSP mode preparations (p<0.05). Differences between Piezomed and laser modes were not significantly different (p>0.05). Sealing was statistically significantly better with TotalFill® RRM compared to Biodentine™ and in Er:YAG SP preparations compared to Er:YAG QSP.

THERMALLY INDUCED BIREFRINGENCE AND MODE SELECTION IN CAVITY OF PASSIVELY Q-SWITCHED DIODE PUMPED Nd:YAG LASER

Operating regimes of an optical system consisted of compact pulsed master diode-pumped Q-switched Nd:YAG laser and triple-crystal (KTP) ring cell of the optical parametric oscillator have been investigated. It has been experimentally shown that frequency-selective properties of a passive Q-switched unit in the “natural mode selection” are enhanced by creating a polarization interference filter Lyot with the phase plate in the form of a laser active element with the thermally induced birefringence and a polarizer. Such filter Lyot appears in the Nd:YAG laser cavity during operation at relatively high energy and repetition rate of radiation pulses (60–100 mJ, 20 Hz). The combined action of the “natural mode selection” process and the Lyot filter ensures the stable operation of a passive Q-switched Nd:YAG laser in the single frequency lasing mode (the lasing bandwidth is less than 57 MHz). The master single frequency pulsed Nd:YAG laser (λ = 1.06 μm) allows reducing the energy of pulses applied to the input of the optical parametric oscillator by more than 1.5 times while maintaining the specified energy level of the output pulses (30 mJ, λ = 1.57 μm). An additional increase in the efficiency of the optical parametric oscillator conversion is achieved by introducing&#x0D; a two-lens 1.3x telescope into the master laser cavity.

High energy (0.8 J) mechanically Q-switched 2.94 μm Er:YAG laser.

We report a flashlamp pumped mechanically Q-switched (MQS) 2.94 μm Er:YAG laser based on a spinning mirror with a highest output energy of 805 mJ at a pulse duration of 61 ns and 13 MW of peak power at 1 Hz repetition rate. This record output energy was achieved with the use of 300 mm long MQS Er:YAG laser cavity consisting of a 70% output coupler, 7 × 120 mm AR coated Er(50%):YAG crystal, and 4200 rad/s angular speed of the spinning mirror. The pulse jitter was also measured by using optical triggering and was smaller than 10 ns for 150 ns Q-switched pulses, which could be applicable to many laser applications where precise synchronization of pulses is required.

Molybdenum Disulfide Film Saturable Absorber Based on Sol-Gel Glass and Spin-Coating Used in High-Power Q-Switched Nd:YAG Laser.

In recent years, many different kinds of nonlinear optical materials have been applied to passively Q-switched solid-state lasers. However, the average output powers of these lasers are typically limited to 1 W due to the low damage threshold of the materials. In this study, a molybdenum-disulfide-doped glass-composite absorber was synthesized using the sol-gel method and spin-coating technique. The optical damage threshold of the absorber reached 3.17 J/cm2. Saturation intensity, modulation depth, and nonsaturable loss are 9.35 MW/cm2, 8.41%, and 9.14%, respectively. After inserting the absorber into a linear Nd:YAG laser cavity, the maximum average output power (3.22 W) and stable Q-switched laser pulses duration (132 ns) were obtained.

Effect of Er:YAG laser cavity preparation on the bond strength of 2-hydroxyethyl methacrylate-free and 2-hydroxyethyl methacrylate-rich self-etch adhesive systems: An in vitro study

Despite many advantages of lasers and reduction of the risk of surface bonding errors with newer self-etch systems, they have not been thoroughly researched. This study was done to evaluate the effect of Er:YAG laser cavity preparation on the microtensile bond strength of 2-hydroxyethyl methacrylate (HEMA)-rich and HEMA-free one-step self-etch adhesive systems. In this in vitro study, eighty freshly extracted human premolars were collected. Cavities were prepared in 40 teeth with carbide bur (Group 1) and in other 40 teeth with Er:YAG LASER (490 mJ and 15 Hz) (Group 2). Subgroups of twenty teeth each were made according to the adhesive systems used. After placement of restoration, the mean values of the bond strength were calculated using universal testing machine. Data were then tabulated and analyzed using descriptive statistics (Significant at P < 0.05). The overall microtensile bonding strength was higher when the cavities were prepared with bur compared to those with Er:YAG laser. Mean bond strengths of single-bottle self-etching seventh-generation dentin bonding agents to bur-prepared cavities were higher than those to laser-prepared cavities irrespective of the adhesive system (P = 0.01). No statistically significant difference was observed between HEMA-free and HEMA-rich self-etch adhesive systems. The effect of Er:YAG laser for cavity preparation did not show improved performance when evaluated using microtensile bond strength with seventh-generation bonding agents, Adper Easy One and G-Bond. More studies are required to assess the effect of lasers.

Qualitative evaluation of hybrid layer formation using Er:YAG laser in QSP mode for tooth cavity preparations.

The purpose of this study was to evaluate the thickness and qualitative characteristics of the hybrid layer after two cavity preparation methods, using Er:YAG laser in QSP mode and conventional carbide burs. Additionally, two different adhesive techniques were investigated using etch-and-rinse and self-etch adhesive systems. Sixty sound human third molars were used and were randomly divided into four groups (n = 15). In the first two groups, large (4mm length, 3mm wide, and 3mm deep) class I cavities were prepared using Er:YAG laser (2.94μm) in QSP mode, while in the other two groups, the cavities were prepared using carbide burs. After cavity preparations, two different adhesive techniques with GLUMA® 2 Bond (etch-and-rinse) and Clearfil™ Universal Bond Quick (self-etch) were applied. For the qualitative evaluation of the formed hybrid layer, photomicrographs were taken using SEM, and elemental semi-quantitative analysis was performed using EDS to confirm the extent of the hybrid layer. One-way ANOVA was applied to verify the existence of statistically significant differences, followed by Tukey test for post hoc comparisons (Bonferroni corrected), and the level of significance was set at a = 0.05. The laser-treated groups exhibited higher hybrid layer thickness than bur-treated groups (p < 0.001). Between the laser-treated groups, etch-and-rinse technique presented higher hybrid layer thickness than self-etch technique (p < 0.001), while between the bur-treated groups, no significant differences were detected (p = 0.366). Er:YAG laser cavity preparations in QSP mode may be advantageous for adhesion of composite restorations, but more data are necessary to confirm its clinical effectiveness.

Frequency doubling of dual frequency injection seeding laser pulses

High power RF intensity modulated pulses at 532 nm are achieved via dual-frequency injection seeding a Q-switched laser at 1064 nm and frequency doubling. A dual-frequency laser signal with beat-note frequency of 200 MHz is injected into a Q-switched Nd:YAG laser cavity, the injected power is 40 mW, two adjacent longitudinal modes of the cavity with mode spacing from 223 to 227 MHz are locked to the injected signal respectively. The output pulses are RF intensity modulated due to the interferences between the two modes. By changing the power transmission index of the output coupler of the Q-switch laser, the pulse durations from 16 ns to 20 ns are observed. When the transmission of the output coupler is 44%, the pulse energy is 7 mJ and pulse width is 16 ns, corresponding a peak power of 437 kW. The RF modulated laser pulse at 1064 nm is frequency doubled by a KTP crystal. The SHG pulse energy is 2.27 mJ with a pulse duration of 12 ns, corresponding to a peak power of 189 kW. Two modulation frequencies at 223 MHz and 446 MHz are observed in the second harmonic wave. The high-power RF intensity modulated pulsed light source at 532 nm has potential applications in long-distance underwater detections.

Randomly polarised beam produced by magnetooptically Q-switched laser

Diode-pumped solid-state micro lasers are compact (centimetre-scale), highly stable, and efficient. Previously, we reported Q-switched lasers incorporating rare-earth substituted iron garnet (RIG) film. Here, the first demonstration of the magnetooptical (MO) Q-switch in an Nd:YAG laser cavity is performed. We fabricate a quasi-continuous-wave (QCW) diode-pumped Nd:YAG laser cavity, which is shortened to 10 mm in length and which contains an RIG film and a pair of small coils. This cavity yields a 1,064.58-nm-wavelength pulse with 25-ns duration and 1.1-kW peak power at a 1-kHz repetition ratio. Further, the polarisation state is random, due to the isotropic crystal structure of Nd:YAG and the fact that the MO Q-switch incorporating the RIG film does not require the presence of polarisers in the cavity. This is also the first report of an MO Q-switch producing random polarisation.

Investigation of the Er: YAG laser and diamond bur cavity preparation on the marginal microleakage of Class V cavities restored with different flowable composites.

The purpose of this study was to evaluate the efficiency of the Er:YAG laser and diamond bur cavity preparation on the marginal microleakage of Class V cavities. Group 1: bur preparation (bp) + Vertise Flow (VF); Group 2: laser preparation (lp) + VF; Group 3: bp + Adper Easy One (AEO) + Filtek Ultimate Flowable Composite (FUFC); Group 4: lp + AEO + FUFC; Group 5: bp + Clearfil S3 Bond (CSB) + Clearfil Majesty Flow (CMF); Group 6: lp + CSB + CMF. Data were analyzed by Kruskal-Wallis and Mann-Whitney U tests (p < .05). More microleakage was observed in cervical regions compared to occlusal regions in all groups (p < .05). No significant difference was observed among all groups in terms of occlusal and cervical surfaces, respectively (p > .05). The use of the Er:YAG laser for cavity preparation with different adhesive systems and flowable composites did not influence microleakage.

Holmium laser with an acousto-optic paratellurite filter

Experimental results on a solid-state holmium laser (Ho : YAG) with an intracavity acousto-optic paratellurite filter are presented. The laser power in cw and repetitively pulsed regimes is determined experimentally. It is shown that the use of an acousto-optic filter in the Ho : YAG laser cavity makes it possible to solve several important problems such as obtaining repetitively pulsed lasing, wavelength tuning and linearly polarised emission.

Passively Q-switched Nd:YAG laser with a MoS2 solution saturable absorber

This study presents a passively Q-switched Nd:YAG laser using a MoS2 solution as a saturable absorber. The prepared MoS2 solution saturable absorber features adjustable optical absorption, high heat dissipation, and non-contact damage. By inserting the MoS2 solution saturable absorber into a Z-type Nd:YAG laser cavity, a stable Q-switched laser with the maximum repetition rate of 20.8 KHz centered at 1064.24 nm was achieved, with the shortest pulse width at 2.8 μs. The results experimentally confirm the potential application of a MoS2 solution saturable absorber for high performance Q-switched solid-state lasers.

128 mJ/Pulse, Laser-Diode-Pumped, Q-Switched Tm:YAG Laser

We demonstrated a high-pulse-energy, laser-diode-pumped Tm:YAG laser in AO Q-switched operation. In laser experiments, we introduced a composite-type Tm:YAG laser rod with undoped endcaps. The rod was pumped by 785-nm quasi-continuous-wave laser diodes in a side-pumping configuration. To obtain a high energy and high beam quality, we designed a Tm:YAG laser cavity utilizing the thermal lens effect of the laser rod. A Q-switched output energy of 128 mJ at 10 Hz with a pulse width of 160 ns was obtained from the laser oscillator at room temperature, and the slope efficiency reached 14%. A high beam quality in the TEM 00 mode was also realized.

Low-power pulsed Nd:YAG laser irradiation for pre-emptive anaesthesia: A morphological and histological study.

To determine if tooth structure or dental pulp of normal healthy human premolar teeth to be extracted for orthodontic reasons exhibit morphological or histological changes following dental anaesthesia by pulsed Nd:YAG laser and subsequent cavity preparation (CP). Materials (Subjects) and Methods: 54 bilateral paired of human, healthy premolar teeth identified for inclusion in a clinical trial of Nd:YAG-induced anaesthesia and subsequently extracted for orthodontic reasons, were randomly divided into 4 treatment groups: Group 1 - teeth (n=44) were irradiated with 150 µs pulsed Nd:YAG laser-1064 nm (American Dental Laser, dLase300, Sunrise Technologies Inc., Folsom, CA, USA; Average power: 1.1 ± 0.2 W, power density: 39+ 0.7 W/cm(2), area 0.28 cm(2), 15 Hz; energy density:0. 260+ 0.047 J/cm(2)) +Sham EMLA (cream without active component) followed by cavity preparation (CP); Group 2 - Teeth (n=44) - were treated with EMLA + Sham Laser (1 mW 632.8-nm He:Ne laser aiming beam only) with CP; Group 3 Teeth (n=10) - were irradiated with pulsed Nd:YAG laser as above but minus CP; Group 4 (n=10)- was a Control group with teeth untreated (no Laser, EMLA or CP). Clinical anaesthesia was assessed by electric pulp testing (EPT) and CP. Teeth in each of the 4 groups were processed for examination by i) scanning electron microscopy (SEM); ii) longitudinal undecalcified ground sectioning (LUGS); iii) light microscopy of pulpal tissues or iv) dye penetration. Both Laser and EMLA groups demonstrated no alteration to mineralized tooth structure and dentinal permeability. Mild superficial pulpal changes were found in both groups (3/18 teeth) and of no statistical difference (p>0.99, the McNemar test). Neither Laser nor the Control groups minus CP, showed pulpal changes. Low-power pulsed Nd:YAG laser dose, as used in the clinical trial to induce anaesthesia, does not cause morphological damage to the mineralized tooth structure. Both Laser and EMLA groups showed minor superficial pulpal change following cavity preparation which was not statistically significant. Laser and Control groups minus preparation had no pulpal changes.

Coherent polarization locking: an approach to mitigating optical damage in a pulsed Ho:YAG laser

Intracavity optical damage is mitigated in a pulsed Ho:YAG laser cavity using the coherent polarization locking (CPL) technique. By splitting the available pump power into two individual Ho:YAG laser rods, we passively coherently locked two orthogonal polarization lasers with 9.13 mJ output pulse energies and 14 ns pulsewidths, and operating at 800 Hz repetition rate. A conventional Ho:YAG laser cavity with the same pump and cavity configuration results in severe optical damage when operating at <2 kHz repetition rate, thus limiting the output pulse energies to <5 mJ. We also demonstrated, to the best of our knowledge, the first pulsed operation within the entire CPL Ho:YAG laser cavity by Q-switching in one of the polarization arms, producing nanosecond pulses with no sign of pulse instability.

Preserving a diffraction-limited beam in Ho:YAG laser using coherent polarization locking

We overcome several thermal issues present in Ho:YAG lasers by distributing the gain over a larger volume and achieve a diffraction-limited beam using coherent polarization locking. Increased single-pass absorption, suppression of output power saturation, and improvement in beam quality were shown using the coherent polarization locking technique as compared to a conventional Ho:YAG laser cavity with the same pump and cavity configuration. Ten watts of CW Ho:YAG laser power was generated with >96% coherent combining efficiency.

Q-switching and mode-locking in a diode-pumped frequency-doubled Nd : YAG laser

A new method for obtaining Q-switching simultaneously with mode-locking using one travelling-wave acousto-optic modulator in a frequency-doubled Nd : YAG laser cavity is described. Further shortening of output laser pulses (from 40 to 3.25 ps) is achieved by forming a Kerr lens in the frequency-doubling crystal. At an average power of ∼ 2 W and a Q-switching rate of 2 kHz, the peak power of the stably operating reached ∼ 50 MW.

Laser-Induced Defects in a Bulk GaAs Used as an Output Coupler in an Nd : YAG Laser Cavity

By using bulk GaAs as an output coupler as well as a saturable absorber, with changing of concentration of defects inside the laser cavity, Q-switching of flashlamp-pumped Nd : YAG laser has been studied. It is shown that the formation of the laser pulses, in a wide range of duration, which were reported in a lot of previous papers is caused by the intracavity changes of the defect concentration in GaAs. The factor of increase in defect concentration is estimated by modeling of the pulse formation process.

Temperature rise during Er:YAG cavity preparation of primary enamel

This study aimed to assess in vitro thermal alterations taking place during the Er:YAG laser cavity preparation of primary tooth enamel at different energies and pulse repetition rates. Forty healthy human primary molars were bisected in a mesio-distal direction, thus providing 80 fragments. Two small orifices were made on the dentin surface to which type K thermocouples were attached. The fragments were individually fixed with wax in a cylindrical Plexiglass® abutment and randomly assigned to eight groups, according to the laser parameters (n = 10): G1 - 250 mJ/ 3 Hz, G2 - 250 mJ/ 4 Hz, G3 - 250 mJ/ 6 Hz, G4 - 250 mJ/10 Hz, G5 - 250 mJ/ 15 Hz, G6 - 300 mJ/ 3 Hz, G7 - 300 mJ/ 4 Hz and G8 - 300 mJ/ 6 Hz. An area of 4 mm(2) was delimited. Cavities were done (2 mm long × 2 mm wide × 1 mm thick) using non-contact (12 mm) and focused mode. Temperature values were registered from the start of laser irradiation until the end of cavity preparation. Data were analyzed by one-way ANOVA and Tukey test (p ≤ 0.05). Groups G1, G2, G6, and G7 were statistically similar and furnished the lowest mean values of temperature rise. The set 250 mJ/10 and 15 Hz yielded the highest temperature values. The sets 250 and 300 mJ and 6 Hz provided temperatures with mean values below the acceptable critical value, suggesting that these parameters ablate the primary tooth enamel. Moreover, the temperature elevation was directly related to the increase in the employed pulse repetition rates. In addition, there was no direct correlation between temperature rise and energy density. Therefore, it is important to use a lower pulse frequency, such as 300 mJ and 6 Hz, during cavity preparation in pediatric patients.

Passive Q-switching of the diode-pumped Er:YAG laser cavity with the Q-switch based on the Fe2+:ZnSe crystal

Repetitive-pulse generation of the diode-pumped Er:YAG laser (λ = 2.94 µm) in the free mode and in the mode of cavity passive Q-switching was achieved using a Q-switch based on the Fe2+:ZnSe crystal. When using pump pulses 3 ms long, the pulse-average output power of the Er:YAG laser in the free generation mode was 0.5W. In the passive Q-switching mode, giant pulses 180 ns long with an energy of 3 µJ were obtained.

Demonstration and selection of a single-transverse higher-order-mode beam with radial polarization

Single-transverse higher-order radially polarized beams with multiple rings are selectively generated from a Nd:YAG laser cavity by using a reflectivity-modified and polarization-selective photonic crystal mirror. As predicted by theoretical analysis [A. A. Tovar, J. Opt. Soc. Am. A 15, 2705 (1998)], the intensity distribution and propagation characteristics of the higher-order radially polarized beams are expressed by a Laguerre-Gaussian formula.