The photoemission optogalvanic effect in a Ne-Nd hollow cathode

Laser-induced photoelectric and photoemission optogalvanic effects in a Ne-Nd hollow cathode discharge have been studied using a continuous wave laser source. The potential barrier for photoinduced electron emission from the cathode decreases as the applied voltage is increased. Owing to secondary electron emission in the plasma, the photocurrent is greater than that without discharge. The multiplication of secondary electrons and the quantum efficiency are also investigated.

Nitrogen laser excited fluorescence of some rare earth doped alkaline earth fluorides

The present study is mainly concéntrated on the visible fluorescence of Ho3+ ,nd 3+ and Er 3+rare earths in alkaline earth fluoride hosts(caF2,srF2,BaF2) using a nitrogen laser excitation. A nitrogen laser was fabricated and its parametric studies were first carried out.

Development and parametric studies of pulsed nitrogen and d-switched nd:glass lasers and some of their applications

Laser engineering is an area in which developments in the existing design concepts and technology appear at an alarming rate. Now—a-days, emphasis has shifted from innovation to cost reduction and system improvement. To a major extent, these studies are aimed at attaining larger power densities, higher system efficiency and identification of new lasing media and new lasing wavelengths. Todate researchers have put to use all the ditferent Forms of matter as lasing material. Laser action was observed For the first time in a gaseous system - the He-Ne system. This was Followed by a variety of solidstate and gas laser systems. Uarious organic dyes dissolved in suitable solvents were found to lase when pumped optically. Broad band emission characteristics of these dye molecules made wavelength tuning possible using optical devices. Laser action was also observed in certain p-n junctions of semiconductor materials and some of these systems are also tunable. The recent addition to this list was the observation of laser action from certain laser produced plasmas. The purpose of this investigation was to examine the design and Fabrication techniques of pulsed Nitrogen lasers and high power Nd: Glass laserso Attempt was also made to put the systems developed into certain related experiments

Nanostructured europium oxide thin films deposited by pulsed laser ablation of a metallic target in a He buffer atmosphere

Nanostrucured europium oxide and hydroxide films were obtained by pulsed Nd:YAG (532 nm) laser ablation of a europium metallic target, in the presence of a 1 mbar helium buffer atmosphere. Both the produced film and the ambient plasma were characterized. The plasma was monitored by an electrostatic probe, for plume expansion in vacuum or in the presence of the buffer atmosphere. The time evolution of the ion saturation current was obtained for several probe to substrate distances. The results show the splitting of the plume into two velocity groups, being the lower velocity profile associated with metal cluster formation within the plume. The films were obtained in the presence of helium atmosphere, for several target-to-substrate distances. They were analyzed by Rutherford backscattering spectrometry, x-ray diffraction, and atomic force microscopy, for as-deposited and 600 degrees C treated-in-air samples. The results show that the as-deposited samples are amorphous and have chemical composition compatible with europium hydroxide. The thermally treated samples show x-ray diffraction peaks of Eu(2)O(3), with chemical composition showing excess oxygen. Film nanostructuring was shown to be strongly correlated with cluster formation, as shown by velocity splitting in probe current versus time plots. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3457784]

Processamento de materiais carbonáceos por pulsos intensos de laser em alta pressão

Neste trabalho foi desenvolvida uma câmara de alta pressão com janela de safira para processamento de filmes finos com pulsos de laser de alta potência, num regime de resfriamento ultra-rápido e geometria confinada. As amostras estudadas consistiram de filmes finos de carbono amorfo depositados sobre substratos de cobre. Os processamentos foram realizados com um laser pulsado Nd:YAG com energia de até 500 mJ por pulso, com duração de 8 ns, focalizada numa região de cerca de 1,5mm2, gerando uma região de elevada temperatura na superfície da amostra durante um intervalo de tempo bastante curto, da ordem do tempo de duração do pulso do laser. Para evitar a evaporação do filme de carbono, aplicava-se através da câmara, uma pressão de 0,5 a 1,0 GPa, confinando a amostra e eliminando o efeito da ablação. Este sistema tornou possível produzir taxas de resfriamento extremamente elevadas, com supressão da formação de uma pluma durante a incidência do laser, sendo o calor dissipado rapidamente pelo contato com os substratos de cobre e safira, ambos com elevada condutividade térmica. As amostras processadas foram analisadas por micro-espectroscopia Raman e os resultados revelaram a formação de estruturas com cadeias lineares de carbono, “carbynes”, caracterizadas pela presença de um pico Raman intenso na região de 2150 cm-1. Outro conjunto de picos Raman foi observado em 996 cm-1, 1116 cm-1 e 1498 cm-1 quando o filme fino de carbono amorfo foi processado dentro da câmara, com uma seqüência de mais de três pulsos consecutivos de laser. Várias tentativas foram feitas para investigar a natureza da fase que origina estes picos. Apesar da similaridade com o espectro Raman correspondente ao poliacetileno (CnHn), não foi possível constatar evidências experimentais sobre a presença de hidrogênio nos filmes de carbono processados. Estes picos Raman não foram observados quando o filme de carbono era depositado sobre outros substratos metálicos, a não ser em cobre. O conjunto de resultados experimentais obtidos indica que estes picos estariam relacionados a pequenos aglomerados lineares de átomos de carbono, diluídos numa matriz de átomos de cobre, formados durante os pulsos subseqüentes de laser e retidos durante o resfriamento ultra-rápido da amostra. A comparação dos resultados experimentais com a simulação do espectro Raman para diferentes configurações, permite propor que estes aglomerados seriam pequenas cadeias lineares, com poucos átomos, estabilizadas frente à formação de grafenos pela presença de átomos de cobre em abundância. Foram também realizados processamentos de materiais carbonáceos por pulsos de laser em meios líquidos, através de câmaras especialmente construídas para este fim. Os resultados, em diversos materiais e configurações, mostraram apenas a formação de estruturas grafíticas, sem evidência de outras fases.

Analyse titanium surface irradiated with laser, with and without deposited of durapatite

OBJETIVO: Estudar a superfície de implantes osseointegráveis utilizando discos de titânio irradiados com feixe de laser. MÉTODOS: A amostra foi irradiada com feixes de laser de alta intensidade (Nd-YAG), posteriormente depositado hidróxiapatita e submetido a tratamento térmico. Foi analisada sob MEV (Microscópio Eletrônico de Varredura) e realizada análise morfológica qualitativa com microfotografias em vários aumentos. RESULTADOS: A superfície irradiada com laser apresentou deformidade superficial e característica isomórfica; a aplicação de hidroxiapatita pelo método de biomimético aumentou quantitativamente a área da superfície de titânio. CONCLUSÃO: A deposição de hidroxiapatita apresentou melhor característica isomórfica e aumento quantitativo da área superficial estudada, a amostra demonstrou características não encontradas nos implantes disposto no mercado.

Comparison between laser therapy and non-surgical therapy for periodontitis in rats treated with dexamethasone

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Laser ablation in titanium implants followed by biomimetic hydroxyapatite coating: Histomorphometric study in rabbits

Titanium surface texture and chemistry modification successfully improves the host response and consequently the bone-to-implant contact surrounding dental implants. The aim of the present study was to investigate, using histomorphometrical-analysis, the effects of titanium surface modification by laser-ablation (Nd:YAG) followed by thin chemical deposition of HA. Forty-eight rabbits received one implant by tibiae of AS-machined (MS), laser-modified (LMS), or biomimetic hydroxyapatite-coated (HA) surface. Bone-to-implant contact (BIC) and bone area (BBT) were evaluated after 4, 8, and 12 weeks, at cortical and cancellous regions. Average BIC in the cortical region was higher (P < 0.001) on the LMS and HA implants for all periods, with no differences between LMS and HA. For the cancellous area, the LMS and HA implants showed higher (P < 0.01) BIC than MS at the initial periods. The LMS and HA showed similar values in the cortical region, but a tendency of higher values for HA in the cancellous region was observed in all periods. For the BBT, the differences were found only between HA and MS after 4 weeks in the cortical region (P < 0.05), and after 12 weeks in the cancellous area (P < 0.05). Our results showed that HA biomimetic coating preceded by laser treatment induced the contact osteogenesis and allowed the formation of a more stable boneimplant interface, even in earlier periods. Microsc. Res. Tech., 2012. (C) 2012 Wiley Periodicals, Inc.

Biological Performance of Chemical Hydroxyapatite Coating Associated With Implant Surface Modification by Laser Beam: Biomechanical Study in Rabbit Tibias

Purpose: Considering the potential of the association between laser ablation and smaller scale hydroxyapatite (HA) coatings to create a stable and bioactive surface on titanium dental implants, the aim of the present study was to determine, by the removal torque test, the effects of a surface treatment created by laser-ablation (Nd:YAG) and, later, thin deposition of HA particles by a chemical process, compared to implants with only laser-ablation and implants with machined surfaces.Materials and Methods: Forty-eight rabbits received I implant by tibia of the following surfaces: machined surface (MS), laser-modified surface (LMS), and biomimetic hydroxiapatite coated surface (HA). After 4, 8, and 12 weeks of healing, the removal torque was measured by a torque gauge. The surfaces studied were analyzed according to their topography, chemical composition, and roughness.Results: Average removal torque in each period was 23.28, 24.0, and 33.85 Ncm to MS, 33.0, 39.87, and 54.57 Ncm to LMS, and 55.42, 63.71 and 64.0 Ncm to HA. The difference was statistically significant (P < .05) between the LMS-MS and HA-MS surfaces in all periods of evaluation, and between LMS-HA to 4 and 8 weeks of healing. The surface characterization showed a deep, rough, and regular topography provided by the laser conditioning, that was followed by the HA coating.Conclusions: Based on these results, it was possible to conclude that the implants with laser surface modification associated with HA biomimetic coating can shorten the implant healing period by the increase of bone implant interaction during the first 2 months after implant placement. (C) 2009 American Association of Oral and Maxillofacial Surgeons J Oral Maxillofac Surg 67:1706-1715, 2009

Apical Sealing Quality of In Vitro Apicectomy Procedures After Using Both Er:YAG and Nd:YAG

The aim of this study was to evaluate the apical sealing of dentinal tubules after root-end surface cutting by using Er:YAG and Nd:YAG lasers. After root-canal instrumentation and filling, apices of 50 extracted maxillary canine human teeth were resected by Er: YAG with 400 mJ, 10 Hz, for 30 sec. The samples were randomly assigned to five groups (n = 10): (GI) treated without root-end cavity, but with Nd: YAG (1.0W, 10 Hz, 20 sec) for dentinal tubules sealing; (GII) treated with root-end cavity without the use of Nd: YAG; (GIII) treated with root-end cavity and Nd: YAG application; (GIV) treated with root-end cavity made by Er: YAG with no focus and without Nd: YAG application; and (GV) treated without root-end cavity and without Nd: YAG application. The root-end cavities were performed by using Er: YAG at 300 mJ, 10 Hz, for 20 sec. Subsequently, all teeth were waterproofed and immersed in 2% methylene blue for 48 h in a vacuum environment. The samples were longitudinally sectioned, and microleakage was measured. ANOVA and the Fisher LSD test showed that GIV was less susceptible to microleakage than were the other groups (p < 0.05). Interestingly, the use of the Er: YAG with no focus showed superior dentinal tubule sealing in comparison with the other groups, even with or without root-end cavity and Nd: YAG application.

Assessment of external root temperature during root canal irradiation by Nd:YAG and Er:YAG lasers

Different types of laser have been widely studied for applicability in the oral health area. In the endodontic area, investigations with some types of laser have been conducted to establish safe parameters for clinical application in root canals. However, it has not been duly explained whether the temperature increase caused by laser irradiation could cause alteration in the temperature on the external surface of the root and, consequently, alterations in the cells of the periodontal ligament, causing resorption and even loss of the dental element. The proposal in this paper was to gauge the external root temperature in the apical and cervical regions of the roots of human teeth during root canal irradiation with Nd:yttrium aluminum garnet (YAG) and Er:YAG lasers using different parameters. The novel approach of this paper is the use of the technique of laser applications along the total length of the root canal with series of repetitive irradiation, however, using time of 1 s of irradiation associated with 1 s off to avoid cumulative thermal effects. Experimental results confirm the accuracy of the parameters and exposure regimen obtained. All the parameters used in this paper are acceptable from a clinical as well as a biological point of view. (C) 2009 Laser Institute of America.

Apatite coatings onto titanium surfaces submitted to laser ablation with different energy densities

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Time-resolved Z-scan and thermal lens measurements in Er+3 and Nd+3 doped fluoroindate glasses

In rare earth ion doped solids, a resonant non-linear refractive index, n2, appears when the laser pumps one of the ion excited states and the refractive index change is proportional to the excited state population. In these solids there are usually thermal and non-thermal lensing effects, where the non-thermal one is due to the polarizability difference, Δα, between excited and ground states of the ions. We have used the time resolved Z-scan and a mode-mismatched thermal lens technique with an Ar+ ion laser in Er+3 (20ZnF2-20SrF2-2NaF-16BaF2-6GaF3-(36 - x)InF3-xErF3, with x= 1, 2, 3 and 4 mol%) and Nd+3 (20SrF2-16BaF2-20ZnF2-2GdF3-2NaF-(40 - x)InF3-xNdF3, with x = 0.1, 0.25, 0.5-1 mol%) doped fluoroindate glasses. In both samples we found that the non-linear refraction is due to the thermal effect, while the non-thermal effect is negligible. This result indicates that in fluoride glasses Δα is very small (less than 10-26 cm3). We also measured the imaginary part of the non-linear refractive index (n″2) due to absorption saturation.

Evaluation of titanium implants with surface modification by laser beam. Biomechanical study in rabbit tibias

The purpose of the present study was to evaluate, using a biomechanical test, the force needed to remove implants with surface modification by laser (Nd:YAG) in comparison with implants with machined surfaces. Twenty-four rabbits received one implant with each surface treatment in the tibia, machined surface (MS) and laser-modified surface (LMS). After 4, 8 and 12 weeks of healing, the removal torque was measured by a torque gauge. The surfaces studied were analyzed according to their topography, chemical composition and roughness. The average removal torque in each period was 23.28, 24.0 and 33.85 Ncm for MS, and 33.0, 39.87 and 54.57 Ncm for LMS, respectively. The difference between the surfaces in all periods of evaluation was statistically significant (p < 0.05). Surface characterization showed that a deep and regular topography was provided by the laser conditioning, with a great quantity of oxygen ions when compared to the MS. The surface micro-topography analysis showed a statistical difference (p < 0.01) between the roughness of the LMS (R a = 1.38 ± 0.23 μm) when compared to that of the MS (R a = 0.33 ± 0.06 μm). Based on these results, it was possible to conclude that the LMS implants' physical-chemical properties increased bone-implant interaction when compared to the MS implants. © 2009 Sociedade Brasileira de Pesquisa Odontológica.