Effects Of Pulsed Nd Research Articles

Pulsed Neodymium-Doped Yttrium Aluminum Garnet Laser Heating of Multiwalled Carbon Nanotube Film

A multiwalled carbon nanotube (MWCNT) film surface was irradiated with a single pulse from a neodymium-doped yttrium aluminum garnet (Nd:YAG) laser. When an MWCNT film is irradiated with a pulsed Nd:YAG laser of 23.7 mJ/cm2, the calculated maximum surface temperature becomes 304 °C. The surface temperature increases from 595 to 2968 °C with an increase in laser power from 59.4 to 469 mJ/cm2. The MWCNT film is examined by increasing the intensity of the two characteristic Raman shifts ID (defect-induced mode: D-band) and IG (graphite-induced mode: G-band) to clarify the effect of pulsed Nd:YAG laser heating. Moreover, a new original image analytical method is developed to characterize CNTs from scanning electron microscopy (SEM) images. This method is useful for measuring the diameter of as-grown CNTs and those after annealing with a pulsed Nd:YAG laser. The number of detected diameters between 40 and 60 nm increases with an increase in laser energy density from 181 to 268 mJ/cm2.

Non-vitrectomizing vitreous surgery for premacular haemorrhage

We report three cases illustrating an alternative treatment option for premacular haemorrhage. This retrospective interventional case study included three eyes in three patients with premacular haemorrhage caused by idiopathic thrombocytopenic purpura in the first case, trauma in the second case and retinal arterial macroaneurysm in the third case. All patients underwent non-vitrectomizing vitreous surgery. Visual acuity as well as slit-lamp and indirect ophthalmoscopic examinations were performed pre- and postoperatively to evaluate the resolution of premacular haemorrhage and changes in lenticular opacity. At postoperative day 1, visual acuity had improved from counting fingers (CF) to 6/12 in case 1, from CF to 6/20 in case 2 and from CF to 3/60 in case 3. Examination of the fundus showed resolution of the premacular haemorrhage with mild vitreous haemorrhage in all cases. Final best corrected visual acuities were 6/6, 6/7.5 and 6/15, respectively. The lens remained clear in two of two phakic eyes at the last follow-up visit. In these selected cases, non-vitrectomizing vitreous surgery was a useful and safe alternative for the treatment of premacular haemorrhage.

Pulsed Nd:YAG laser heating and treatment on multi-walled carbon nanotubes film

Multi-walled carbon nanotubes (MWCNTs) film surface was flashed with the second harmonic ( λ = 532 nm) of a single pulse of Nd:YAG laser in air, vacuum (0.03Pa) and nitrogen. When MWCNTs film is irradiated with a pulsed Nd:YAG laser of 23.7 mJ/cm 2, the calculated value of maximum surface temperature becomes 304 °C. The surface temperature increases from 595 °C to 2968 °C with the increase of laser power from 59.4 mJ/cm 2 to 469 mJ/cm 2. MWCNTs film was examined by Raman spectroscopy to clarify the effect of Pulsed Nd:YAG laser heating. Raman spectra of MWCNTs films before and after irradiation were measured. The intensity of the two characteristic Raman shifts I D (defect-induced mode: D-band) and I G (graphite-induced mode: G-band) was examined. Moreover, I G/ I D ratio and normalized D-band FWHM (Full Width at Half Maximum) of MWCNTs film were measured from Raman spectra and compared with the calculated results of maximum temperature of MWCNTs film surface. The purification and graphitization of as-prepared MWCNTs occurred after irradiation.

ラバーダム装着から除去後に至るまでのＮｄ：ＹＡＧレーザーによる疼痛緩和効果に関する経時的変化

The purpose of this study was to compare the pain-relieving effects of pulsed Nd:YAG laser irradiation with topical anesthetic application during placement of a rubber dam clamp.Twenty-two students, aged 22 to 31 years (mean 24.05), who had not experienced either endodontic or cervical restorative treatment of first permanent molars, participated in this study. In this study, the same tooth for the same patient was tested three times every week. The following were the conditions of each site: 1) control site: no pretreatment before placement of the rubber dam clamp, 2) topical anesthetic site: application of topical anesthetic 60 seconds before placement of the rubber dam clamp and wash-out by three-way syringe water, 3) Nd:YAG laser irradiation site: Nd:YAG laser irradiation before placement of the rubber dam clamp. The irradiation conditions were 120 mJ, 1.2 W, 10 pps, and irradiation time was 30 sec twice. The efficacy of pain-relief was assessed by visual analogue scale (VAS) at the start, before placement of the rubber dam clamp, after placement of the rubber dam clamp, and until 20 minutes at 2-minute intervals. The clamp was removed 14 minutes after the start. Pain-relieving effects were also examined by questionnaire.The VAS levels of both placement and removal of the rubber dam clamp were high for all sites. On placement of the rubber dam clamp, the VAS level with Nd:YAG laser irradiation was statistically significantly lower than with no preparation (P<0.05: Wilcoxon signed-ranks test). During placement of the rubber dam clamp, the VAS level with Nd:YAG laser irradiation and topical anesthetic application were statistically significantly lower than with no preparation (P<0.05: Wilcoxon signed-ranks test).

Parametric study of hole circularity in Nd:YAG laser microdrilling of alumina aluminium (Al&lt;SUB align=right&gt;2O&lt;SUB align=right&gt;3 Al) interpenetrating phase composite

In the present research, pulsed Nd:YAG laser microdrilling operation has been carried out on alumina?aluminium (Al2O3?Al) Interpenetrating Phase Composites (IPC). These composites are widely used in structural application in aircraft and space stations. The effect of pulsed Nd:YAG laser drilling parameters on the hole circularity at entry and exit has been investigated using Response Surface Methodology (RSM). Mathematical modelling of Nd:YAG laser performance criteria correlating the various process parameters has been done. This research also includes evaluation of the optimum laser drilling parameters to achieve maximum hole circularity at entry and exit.

Effect of pulsed Nd:YAG laser melting treatment on microstructural and corrosion behaviour of AZ91C Mg alloy

In the present study, an attempt was made to improve the corrosion resistance and microhardness of a cast magnesium–aluminium–zinc alloy by laser surface melting. A 400 W pulsed Nd:YAG laser was used to melt and rapidly quench the surface of the cast AZ91C alloy to improve the corrosion resistance. This was evaluated using potentiodynamic polarisation and EIS studies. The microstructure of the melt pool was examined using optical microscopy and scanning electron microscopy (SEM) along with energy dispersive spectroscopy (EDS), X-ray diffraction studies (XRD) and X-ray fluorescence (XRF). The work revealed that laser melting improves the corrosion resistance of as cast AZ91C alloy because of its fine microstructure and extensive solubility of aluminium in eutectic (β phase). The microhardness of the laser surface melted layer was also increased from 74 HV to 99–124 HV.

The effects of pulsed Nd:YAG laser irradiation on surface energy of copper

The effect of laser surface treatment on the surface energy of copper plate was investigated in terms of the surface microstructure analysis and theoretical computation in this paper. The surfaces of the copper plates were treated by Nd:YAG pulsed laser with different powers. The microstructures of the treated copper plates were analyzed by optical microscopy and X-ray diffraction (XRD), and the wetting experiment was performed to evaluate the variation of surface energy. The results showed that the surface microstructure and the corresponding surface energy of copper, changed with the variation of the laser power. The experimental results further explained by XRD results and theoretical calculation, demonstrated that the surface energy changed when the crystal structure in the surface layer was re-oriented in a preferred orientation after laser irradiation.

Effects of Pulsed Nd:YAG Laser on Microleakage of Composite Restorations in Class V Cavities

The purpose of this study was to evaluate the effects of pulsed Nd:YAG laser on decrease of dentinal microleakage beneath the restoration. Thirty-two sound extracted premolar teeth were subjected to two standardized, V-shaped, class V cavity preparations on both buccal and lingual surfaces. Cavities were located at 1-2 mm below the cemento-enamel junction (CEJ) line. The teeth were divided into two groups of experimental and control in an random manner. Both 20 and 15 mJ/pulse laser energies were tested. Etching, bonding, and filling were performed using Tetric ceram composite material. All samples were thermocycled for 1000 cycles, followed by an immersing period of 1 week in 2% basic fuchsin solution. Specimens were then sliced longitudinally and evaluated under a digital scanner for the extent of dye penetration. Our results indicated that the level of microleakage of laser-treated cavities was significantly less than that of untreated cavities (p < 0.05) for 20 mJ/pulse laser energy. No significant decrease in microleakage level was observed for the 15 mJ/pulse laser energy. The short pulsed Nd:YAG laser with the energy of 20 mJ/pulse and aforementioned features appeared to be able to reduce microleakage toward pulp.

Long-term effect of pulsed Nd:YAG laser irradiation on cultured human periodontal fibroblasts

The purpose of this study was to investigate the long-term effect of Nd:YAG laser irradiation on cultured human periodontal fibroblasts (hPF). The cultured hPF were irradiated by pulsed Nd:YAG laser. The power delivery was 50 mJ x 10 pps (pulse per second) with irradiation duration 60, 120, 180, or 240 seconds. The viability and collagen content of laser-irradiated hPF were assessed on day 5 after laser treatment. Light microscope and transmission electron microscope (TEM) were used to observe cytomorphological change. The irradiated hPF cultured in mineralizing medium for 28 days were examined by alizarin red S and Von Kossa stain. The cellular viability and collagen content of hPF decreased after Nd:YAG laser irradiation. Cell damage was noted with retraction of cellular processes, loss of normal architecture, and lysis of some cells. However, survived hPF proliferated and migrated to the cell-debris-associated deposits. The electron-dense cytoplasm and amorphous organelles in laser-damaged cells was revealed by TEM. In vitro mineralization was demonstrated in the long-term laser-irradiated hPF cultured in mineralizing medium. Nd:YAG laser irradiation induced partial loss of cellular viability and collagen content. The co-existence of viable cells and progressive degeneration of laser-damaged cells was associated with the in vitro mineralization of hPF.

Effects of pulsed Nd:YAG laser on microleakage of composite restorations in class V cavities

The purpose of this study was to evaluate the effects of the pulsed Nd:YAG laser on the decrease of dentinal microleakage beneath the restoration. Materials and method: 32 sound extracted premolar teeth were subjected to two standardized, V shaped, class V cavity preparations on both buccal and lingual surfaces. Cavities were located at 1–2 mm below the Cemento–Enamel Junction (CEJ) line. The teeth were divided into two groups of experimental and control in a random manner. Both 20 and 15 mJ/ pulse laser energies were tested. Etching, bonding and filling were performed using Tetric ceram composite material. All samples were thermocycled for 1000 cycles followed by an immersing period of 1 week in 2% basic fuchsin solution. Specimens were then sliced longitudinally and evaluated under a digital scanner for the extent of dye penetration. Result: results indicated that the level of microleakage of laser-treated cavities was significantly less than that of untreated cavities ( P<0.05) for 20 mJ/pulse laser energy. No significant decrease in microleakage level was observed for the 15 mJ/pulse laser energy. Conclusion: The short pulsed Nd:YAG laser with the energy of 20 mJ/pulse and aforementioned features appeared to be able to reduce microleakage toward pulp.

The effect of pulsed Nd–YAG laser irradiation on acid resistance of dentin

The purpose of this study was to examine the effect of tip–object distance in Nd–YAG laser irradiation on the acid resistance and morphological change of dentin. Freshly extracted human premolars were used. Each crown was cut in half transversally. Samples were randomly assigned to five groups as follows. Group 1: noncontact laser irradiated with 100 mJ, 10 pps (tip–object distance was approximately 2 mm). Group 2: contact laser irradiated with 100 mJ, 10 pps. Group 3: noncontact laser irradiated with 200 mJ, 10 pps. Group 4: contact laser irradiated with 200 mJ, 10 pps. Group 5: control. For acid resistance testing, they were individually immersed in acetic buffer solution (0.2 M, pH 4.2). The amount of dissolved Ca 2+ in each solution was determined by sequential plasma spectrometry. The laser-irradiated dentin surface had morphological characteristics such as a cracker or lava. The dissolved Ca 2+ from lased dentin was significantly less than that of the control group. In the group of noncontact lased dentin, the dissolved Ca 2+ lased with 100 mJ is less than that of lased with 200 mJ. In the contact lased group, the dissolved Ca 2+ lased with 200 mJ is less than that lased with 100 mJ. These results lead the optimum pulsed Nd–YAG laser-irradiated condition of different tip–object distance on acid resistance of dentin.

Antibacterial Effects of Pulsed Nd:YAG Laser Radiation at Different Energy Settings in Root Canals

The in vitro study aimed at the determination of the bacterial reduction in root canals used pulsed Nd:YAG laser radiation without a photosensitizing dye. In addition the temperature change in the root canals was determined during laser irradiation. The study sample was 114 root canals of extracted single-rooted human teeth that have been enlarged mechanically, sterilized, and randomly assigned to two experimental units. The source of radiation was a Nd:YAG laser device emitting pulsed infrared radiation at a wavelength of 1.064 microm, a pulse duration of 100 micros, and a pulse repetition rate of 20 pps. Samples of each experimental unit were inoculated with Escherichia coli (ATCC 25922) or Staphylococcus aureus (ATCC 25923), respectively, and divided into subgroups of 13 teeth each for irradiation for 20 s at 100 mJ or 200 mJ. One subgroup was left untreated as positive control and one subgroup was rinsed with 0.5 ml of sodium hypochloride. After laser treatment or rinsing with sodium hypochloride the number of bacteria in each root canal was determined using the surface spread plate technique. Statistical analysis of the results was performed with ANOVA and Scheffé test at a level of significance of 5% (p < 0.05). In case of E. coli the number of bacteria was reduced from 8.67 x 10(6) (+/-4.11 x 10(5)) colony-forming units (CFU)/ml to 4.39 x 10(4) (+/-1.72 x 10(4)) CFU/ml after laser radiation at 200 mJ. Regarding S. aureus the number of bacteria decreased from 1.44 x 10(6) (+/-1.59 x 10(5)) CFU/ml to 3.8 x 10(4) (+/-1.06 x 10(4)) CFU/ml at a radiation energy of 200 mJ. Rinsing with sodium hypochloride reduced the number of bacteria to 1.03 x 10(3) (+/-4.02 x 10(2)) CFU/ml regarding E. coli and to 1.84 x 10(3) (+/-7.4 x 10(2)) CFU/ml in case of S. aureus. The temperature increase at 100 mJ was 24.3 degrees C (+/-3.9) and that at 200 mJ was 61.8 degrees C (+/-4.2). The Nd:YAG laser radiation has antimicrobial effects in root canals even in the absence of photosensitizing dyes but also causes considerable temperature increase.

Effect of pulsed Nd:YAG laser irradiation on acid demineralization of enamel and dentin.

The purpose of this study was to investigate the effect of Nd:YAG laser irradiation on the acid demineralization of enamel and dentin by spectrophotometry. A mechanism of acquired acid resistance is also proposed. The ability of Nd:YAG laser irradiation to the enhanced resistance to artificial caries formation is still controversial. A pulsed Nd:YAG laser at 1.064-micron wavelength was used to irradiate the human enamel and dentin samples from 20 extracted human molars at the parameters of 1, 2, and 3 W and 20 pps for a total of 9 sec after painting with black ink. Samples were then subjected to 2 microliters of 0.1 M lactic acid solution (pH 4.8) for 24 h at 36 degrees C. The parts per million (ppm) of calcium ion (Ca2+) dissolved in each solution was determined by atomic absorption spectrophotometry and the morphological changes were also investigated by scanning electron microscopy (SEM). The lowest mean Ca2+ ppm was recorded in the samples irradiated at 3 W, in those by irradiated at 2 W and 1 W. The unlased samples showed the highest Ca2+ ppm. SEM observation showed that in the lased areas, the smear layer was partially melted and the underlying primary enamel or dentin seemed to be thermally degenerated. The results of this study suggested that melted smear layer and underlying enamel or dentin degenerated thermally by the heat treatment of Nd:YAG laser might play a major role to enhance resistance to artificial caries-like formation.

墨汁塗布の有無によるＮｄ：ＹＡＧレーザー照射のとう痛緩和効果

The purpose of this study was to evaluate the pain relief effects of pulsed Nd: YAG laser irradiation with and without Chinese ink. Twenty mandibular canines and the mucogingival areas were examined in this study (10 males, 10 females; aged 25 to 30 years; the mean age, 26.5 years). The right areas were irradiation sites (with and without Chinese ink), and the left areas were control sites without irradiation. The conditions for irradiation were laser energy 1.5w, pulses per second 15pps, and irradiation time 60sec. And the laser was irradiated on mucogingival surfaces stained with and without Chinese ink. Also, pain relief effects were evaluated as to pulp thermal sensitivity and surface anesthetic effect. (1) Evaluation of pulp thermal sensitivity: The buccal surfaces of canines were heated to 65°C with the tip of a heat probe, and each subject reported an immediate response to pulp thermal sensitivity. And, the degree of pulp thermal sensitivity was measured by a pain thermometer on irradiation sites and control sites. (2) Evaluation of surface anesthetic effect: The mucobuccal folds were penetrated with a 30G cartridge needle, and each subject reportedan immediate response to needle penetration on the irradiation site and the control site. The pain was classified into the following three grades: grade 1, no pain; grade 2, slight pain; grade 3, pain. For these results of pain relief effects on pulp thermal sensitivity and surface anesthetic effects, there was a statistically significant difference in the pain relief effects between the irradiation site and the control site (P<0.05: Wilcoxon signed-ranks test). In the irradiation site, the pain relief effect of Nd: YAG laser irradiation with Chinese ink was significantly more effective than that without Chinese ink (P<0.001: Wilcoxon signed-ranks test). This study suggested that Nd: YAG laser irradiation with Chinese ink may be useful for pain relief.

Effects of pulsed Nd:YAG laser irradiation on smear layer at the apical stop and apical leakage after obturation.

This study evaluated the removal of smear layer at the apical stop by pulsed Nd:YAG laser irradiation with or without black ink, and the degree of apical leakage after obturation in vitro. Sixty extracted human single-rooted teeth were used in this study. The teeth were instrumented up to a size 40 K-file, and then divided into three groups of 20 teeth each: group 1 was unlased as a control group; group 2 was treated with a laser; group 3 was treated with a laser and black ink. The laser was operated at 2 W and 20 pp for 2 s, and irradiation was performed twice with a 30-s interval. In each group, 10 teeth for the leakage study were obturated and immersed in rhodamine B solution for 48 h at 37 degrees C, and the others were used for evaluation of remaining smear layer. All teeth were bisected longitudinally and observed by stereoscopy or scanning electron microscopy. The smear layer in the laser-treated groups almost melted or evaporated, and was removed significantly compared with the control group (P < 0.05). Leakage was observed in 60% of samples in group 1 and in 20% of samples in group 2. No leakage was observed in group 3, which was significantly different from the control (P < 0.05). These results suggest that pulsed Nd:YAG laser irradiation with black ink increases the removal of smear layer compared with that without black ink, and reduces apical leakage after obturation significantly.

A histopathological study of the effects of pulsed Nd:YAG laser irradiation on infected root canals in dogs

The effects of pulsed Nd:YAG laser irradiation during root canal treatment of infected teeth were investigated histopathologically in dogs. One hundred and eight teeth with a single root in 15 healthy adult beagle strain dogs were used in this study. After inducing infected teeth, each root canal was shaped with up to at least a #40 K-file; then, after coating with black ink, the canal was irradiated using the following parameters: 1 W, 30 pps, for 1 and 2 s, and 2 W, 30 pps, for 2 s. The degree of inflammation of the periapical regions at 2, 4, and 8 wk was examined histopathologically by light microscopy. Inflammation of the periapical regions in the laser-treated groups was significantly less than that in the control group at 4 and 8 wk (p < 0.05). These results suggest that pulsed Nd:YAG laser is useful for root canal treatment of infected teeth, if appropriate parameters are selected.

A histopathological study of the morphological changes at the apical seat and in the periapical region after irradiation with a pulsed Nd:YAG laser

In this study, the effects of pulsed Nd:YAG laser irradiation on the apical seat and periapical region of instrumented root canals were investigated. One hundred and ninety-two teeth, including incisors and molars (239 root canals), in 18 healthy adult beagle dogs were used. After extirpation of the pulp under anaesthesia, each root canal was shaped up to at least a size 40 K-file, and then laser irradiated using the following parameters: 1 W, 15 pps for 2, 3, and 4 s; 2 W, 15 pps for 2 s. The effectiveness of debris removal and carbonization on the root canal walls immediately laser irradiation were examined and inflammation of the periapical region at 1, 2, and 4 weeks after laser irradiation was examined using light microscopy. Effective debris removal was observed in most cases in the laser-treated groups and was dependent on irradiated energy. Carbonization was observed in the irradiated root canals except at the parameter of 1 W for 2 s. Periapical inflammation was observed at 1 W for 2 s to the same extent as in the control group (P > 0.01). These results suggest that the pulsed Nd:YAG laser is useful for debris removal with no adverse effects immediately after extirpation of the pulp if appropriate parameters are selected.

Pulsed Nd:YAG laser application to one-visit treatment of infected root canals in dogs: a histopathological study.

In this study, the effects of pulsed Nd:YAG laser irradiation during root canal treatment of infected teeth were investigated histopathologically in dogs. Effects of Nd:YAG laser on infected root canal treatment have not been reported in vivo. One hundred thirty-five teeth with a single root, including incisors and premolars, in 15 healthy adult beagle-strain dogs were used in this study. After inducing infection in the teeth, each root canal was shaped with at least a # 40 K-file, then the canal was irradiated using the following parameters: 1 W, 30 pps for 1 and 2 sec; 2 W, 30 pps for 1 and 2 sec. Efficacy of debris removal and evaporation on the root canal walls at 2 weeks, and the degree of inflammation of the periapical region at 2, 4, and 8 weeks after laser irradiation were examined histopathologically by light microscopy. Effective debris removal was observed in all cases of the laser-treated groups. No evaporation was observed except at the conditions of 2 W for 2 sec. Inflammation of periapical region in the laser-treated groups was similar in the control group at 2 weeks, but was significantly less than that in the control group at 8 weeks (p < 0.05). These results suggest that pulsed Nd:YAG laser is useful for one-visit root canal treatment of infected teeth in dogs, if appropriate parameters are selected, and this is a potential therapy for human apical lesions of teeth.

Effects of pulsed Nd:YAG laser radiation on action potential conduction in nerve fibres inside teeth in vitro

Objective: This study aimed to simulate the effects of lasing dentine on pulpal nerve function. Methods: Rat spinal nerve roots were threaded through the prepared pulp canal of a 10 mm long tooth root segment which was mounted in a perspex bath. The protruding ends of the nerve were placed on platinum wire electrodes used to elicit and to record compound nerve action potentials (CAPs). Laser energy (average power = 0.3–3.0 W) was applied to the surface of the root segment using a pulsed Nd:YAG dental laser (dLase 300). Results: With the laser probe tip placed in static contact with the tooth surface, the nerve CAP was irreversibly abolished within 60 s of lasing at 1.0–3.0 W power. When the laser tip was moved to and fro over the root surface in a scanning mode, similar levels of radiation produced less marked effects. In the latter mode, CAP attenuation increased with increasing power and duration of lasing. After 60 s lasing at 0.3 W, the CAP size was 95% (± 5, S.D.) of the prelasing controls value; with 2.0 W the CAP was reduced to 54% (±33). The CAP recovered to 90% of control levels after lasing at powers up to 1.5 W, but reached only 72% of control values after lasing at 2.0 W power. Conclusions: Laser radiation applied to dentine caused a dose-dependent block of action potential conduction in nerve fibres in the underlying pulp chamber.

Effects of pulsed Nd:YAG laser irradiation on root canal wall dentin with different laser initiators

The effects of pulsed Nd:YAG laser irradiation with different laser initiators on the permeability and ultrastructure of the root canal wall dentin were investigated in vitro. Forty extracted human single-rooted teeth were randomly assigned to four groups. Group 1 teeth were not lased as a control. Group 2 specimens received four 10-s duration laser exposures for a total exposure of 40 s/canal. In group 3 specimens, the root canals were painted with black ink and then lased by the same method as group 2 teeth. In group 4 specimens, root canals were treated with 38% Ag(NH3)2F and then lased by the same method as group 2 teeth. Laser parameters were set at 2 W, 20 pps. After being placed in 0.6% rhodamine B solution for 48 h, the teeth were sectioned for study by stereoscope and scanning electron microscopy. Statistical analysis showed there were significant differences (p < 0.05) in dentin permeability in the apical areas between groups 3 and 1, 4 and 1, and 4 and 2. Scanning electron microscopic examination showed that laser treatment alone had no obvious effects on the root canal wall. The root canal surfaces prepared for by laser irradiation with black ink or 38% Ag(NH3)2F revealed melting, smear layer evaporation, and open dentinal tubules. Black ink was more effective than 38% Ag(NH3)2F as a Nd:YAG laser initiator.