Types Of Laser Systems Research Articles

Influence of the pulse duration at the laser processing of nitride ceramics

This paper presents results on laser ablation of AlN and Si3N4 ceramics by laser pulses with different duration. Three types of laser systems, a Nd:YAG one, operated at wavelength of 1064 nm and pulse duration of 15 ns, a Nd:YAG, operated at wavelength of 1064 nm and pulse duration of 10 ps, and a femtosecond laser system, operated at 800 nm, with a pulse duration of 75 fs, are used for experiments. Details on the ablation efficiency, surface morphology, and the chemical composition of the irradiated zones as a function of the pulse duration are given and discussed. It is demonstrated that the ablation rate (ablation depth per pulse) is highest for processing with nanosecond pulses and it is lowest for the femtosecond regime. The laser ablation results in significant change of the surface morphology, as its characteristics are influenced by the pulse duration. For all pulse durations conditions for formation of ripples structures are found. The ablation process is realized by decomposition of the ceramics and the composition of the remaining surface layer is governed by oxidation and carbonization.

Fiber Lasers – Advancing the Frontier of High Power Light

During the last two and a half decades fiber lasers underwent a revolutionary transformation in their power from initially operating at Watt level to currently capable of producing multi-kW beams. This enabled a widespread use of fiber lasers in a wide range of industrial and defense applications. These revolutionary advances in power and energy are continuing, mostly along the path of coherent and incoherent combining of multiple fiber lasers, which exploits the advantage inherent in fiber technologies for monolithic integration to achieve compact and robust systems even with a large number of parallel laser channels. This is a particularly promising pathway for scaling powers and energies of ultrashort pulse lasers for driving secondary radiation sources of energetic accelerated electrons and positrons, as well as generating high energy neutrons, protons, gamma rays and high-brightness X-rays, which promise new application areas ranging from fundamental science to material science, biology, medicine, and numerous new industrial uses. This summer school lecture will cover fundamentals of rare-earth doped fiber lasers, will describe numerous innovations that enabled ultra-large core fibers constituting the foundation of high power lasers, will survey state-of-the-art performance of different types of laser systems, and will review recent progress in coherently combined fiber lasers.

Effect of Laser Irradiation on the Apical Root Canal Sealing

Cleaning and shaping of the root canal system are essential for the successful outcome of endodontic treatment. In addition to the routinely used irrigating solutions, other technologies have been investigated for the treatment of root canal dentine, such as different types of laser systems. Purpose: The aim of our in vitro study was to evaluate the effect of different types of laser irradiation (Er:YAG , Nd:YAG, diode laser and photodynamic therapy) on the intracanal dentin and their interference in the apical seal of filled root canals. Methodology: 72 human single rooted teeth were randomly assigned into 6 groups. Root canal preparation was done using ProTaper Universal rotary system up to F3. The laser irradiation was performed at the end of the traditional endodontic preparation as a final means of decontaminating the endodontic system. Teeth were filled with a core-carrier system Guttacore (Dentsply, Sirona) and sealer AH- plus. Results: Statistical analysis showed that all groups had significantly less leakage in apical third than the control group. The laser-treated groups presented better results than Group II (Classical disinfection protocol), without statistically significant difference. The morphological changes on the apical intraradicular dentin surface caused by Nd:YAG and Er:YAG laser irradiation resulted at least linear dye apical leakage. Conclusions: Laser irradiation may improve the apical seal of the root canal. Different type of laser systems with appropriate parameters are recommended to be used as an adjunct to the current chemical root canal disinfection protocols.

LASER TECHNOLOGIES – MASTER’S PROGRAM BETWEEN TWO EUROPEAN UNIVERSITIES OF APPLIED SCIENCES FROM LATVIA AND GERMANY

Laser equipment and laser technologies are among the most modern, fastest growing and most promising branches of science and technology in the 21st century. The first laser was created in 1960 and for about 55 years, today there is hardly any area of our lives in which lasers and related technologies are not applied. Laser systems and related innovative technologies ensuring high precision, productivity and quality of production have been developed and proposed worldwide from hundreds of scientific research institutes and companies. The Master's program is accredited in two European universities in Germany and Latvia and allows for the production of double diplomas. The course is based on international experience and reflects the most recent advances in laser techniques and technologies. The program examines the physical fundamentals and technical realization of various types of laser systems and their specific characteristics. First the necessary foundations of the laser physics, optics and the interaction of radiation with matter are presented, followed by more detailed examination of the problems of laser technology in various fields of science, technology and industrial production. Basic physical and technical solutions of the building blocks of lasers are presented in details, such as: optical resonators, active environments, excitation systems, management systems, laser generation. As well as specific issues and practical examples of industrial applications are described.

This issue of Acta, printed and electronic

The cover illustration shows a painting of Allvar Gullstrand painted in 1915, 4 years after he received the Nobel Prize for medicine. This issue is dedicated to the centennial of Allvar Gullstrand’s Nobel Prize. He is the only ophthalmologist ever to receive this prestigious price. Stefan Seregard writes an editorial commemorating this event. This is followed by an historical article by Ehinger and Grzybowski on the life and times of Allvar Gullstrand. Yilmaz et al. in USA, Spain and Ireland review the use of intravitreal bevacizumab for diabetic macular oedema. This is an extensive review of the literature for this new and important treatment modality. Lundström et al. in Sweden and Australia found the Catquest questionnaire useful for measuring self-assessed visual function before and after cataract surgery. Mönestam and Behndig found that light scattering and glistening in intraocular lenses does not affect visual acuity. Gazieva et al. in Denmark performed LASIK with two types of laser systems, both which effectively reduce high degrees of myopia with reasonable but slightly different predictability. Rijneveld et al. in the Netherlands found that emergency corneal grafts fail mostly due to host factors, not the quality of the donor tissue. Reinshagen et al. in Switzerland and Germany used mesenchymal stem cell in rabbits to treat total limbal stem cell deficiency. Heijl et al. in Sweden and USA report that intraocular pressure reduction with drug treatment depends on the baseline IOP level and suggest that the baseline IOP level should be documented when reporting treatment effect on intraocular pressure. Larsson et al. in Sweden used the Heidelberg retina tomography system to evaluate optic nerve heads in children. Lin et al. in Taiwan describe lacrimal canaliculitis in a series of patients. Mehlsen et al. in Denmark found that a calcium channel blocker and an angiotensin converting enzyme inhibitor did not influence retinal autoregulation in diabetic patients. Kook et al. in Germany found that intravitreal bevacizumab and/or triamcinolone do not provide long-term improvement for diabetic macular oedema. Kofoed et al. in Copenhagen found that hyperbaric oxygen exposure influenced electrophysiological components related to bipolar in Müller cells. It did not influence retinal thickness. Holton et al. in Denmark examined the influence of light source on contrast sensitivity in patients with AMD. They found that full spectral radiance incandescent light sources seem optimal. Available on http://www.actaophthalmologica.com Stalmans and a large international group review extensively the use of colour Doppler imaging in ocular blood flow research. Founti et al. in Greece and USA found good reproducibility between technicians in imaging retrobulbar blood flow in healthy volunteers. Frøen et al. in Norway and Hungary found that cells from the iris pigment epithelium have limited capabilities as retinal stem cells. Andjelić et al. in Slovenia found that lens capsule contraction with changing in calcium levels or mechanical stimulus. Sieving in USA explains Medline indexing and keywords. Bull in Bergen proposes that fireworks should be banned to reduce eye injuries. Basit et al. in Trondheim describe a case of Wernicke’s encephalopathy in a young boy. Russo et al. in Liverpool found scleral calcification in a case of recurrent melanoma after brachytherapy. Rama et al. in Italy report severe keratitis following corneal cross-linking for keratoconus. Jonas and Jonas in Germany compare peripapillary scleral thickness in glaucoma patients and normal subjects. Lim and An in Korea report good results after epiretinal membrane removal. Kernt et al. in Germany had good experiences with focal and panretinal photocoagulation with a navigated laser. Fielden et al. in Canada describe a cluster of cases with intraocular inflammation following bevacizumab injection. Bloch et al. in Denmark and Egypt describe neovascular membrane contraction and retinal pigment epithelial rupture following verteporfin and bevacizumab treatment. Caramoy et al. in Germany found recurrent choroidal neovascular membrane after autologous RPE transplantation. I wish all readers a Merry Christmas and a Happy New Year and hope that they enjoy reading ACTA during the holidays.

Transmyocardial Revascularization

Low-powered lasers were first used in the 1980s to produce transventricular channels as an adjunct to coronary artery bypass surgery. High-powered lasers, which were introduced in the 1990s, are powerful enough to create transmyocardial channels with minimal damage to surrounding tissues. Clinical studies were first carried out in patients with inoperable coronary artery disease and angina pectoris refractory to medical therapy. Based on these studies, the Food and Drug Administration granted approval of transmyocardial revascularization (TMR) as a sole therapy. Recently, TMR has been combined with coronary artery bypass surgery and 2 types of laser systems are currently available which have not been compared. The results of clinical trials provide contrasting findings regarding benefit, and the procedure is associated with potential morbidity and mortality risk. Furthermore, the mechanism of action of TMR remains undefined. Additional studies need to be done with TMR to assess whether it is a useful treatment or an addition to the list of placebo therapies initially thought to have been of benefit in the therapy for angina pectoris.

The influence of the pulse length on the drilling of metals with an excimer laser

Laser parameters, which significantly influence laser-material interaction processes, are the wavelength, the energy, and the power density. Additionally, there are parameters, like the pulse length, which also strongly influence processing speed and quality. Studies where different types of lasers have been used indicate that long pulses are beneficial for processing speed. However, when different types of laser systems are used to study the effect of the pulse length, a direct comparison of the results is difficult because the use of different lasers involves a simultaneous variation of other parameters (e.g., wavelength) as well. In this study a technique of pulse length variation is used in which the pulse length is the only varied parameter and thus enables the desired direct comparison. Pulses with different lengths are sliced out of pulses of a long pulse XeCl excimer laser, keeping all other laser parameters unchanged. Results are shown of hole drilling experiments in 125 μm nickel, 25 μm aluminum, and 125 μm aluminum foil with pulse lengths between 9 and 150 ns. The influence of the pulse length on material processing is discussed in connection with energy and power of the pulses. The experiments show that both for pulses with the same energy and the same power long pulses remove more material than short pulses and, moreover, long pulses can yield higher quality of the drilled holes.

Transmyocardial laser revascularization.

Low-powered lasers were first used in the early 1980s to produce transventricular channels as an adjunct to coronary artery bypass graft surgery (CABG). Early results were encouraging, but because of the combined procedure, could not be attributed directly to use of the laser [1]. High-powered lasers were introduced into clinical practice in 1990 [2]. These lasers are powerful enough to create a transmyocardial channel with minimal thermal damage to surrounding tissues [3]. Clinical studies, using transmyocardial laser revascularization (TMR) as the sole operative therapy for patients with severe and diffuse coronary artery disease (CAD) who have Class III or IV angina, and are on medical therapy, have been conducted since 1993. Based on the results of these studies, the FDA granted approval for the use of TMR as a sole therapy. Clinical studies are currently underway to assess the results of combined TMR and CABG [4]. Results of four controlled randomized studies have been published [5-8]. The data from two of these studies formed the basis for FDA approval of two different types of laser systems. The results of these studies have not provided any additional insights into the mechanism of action of TMR, which remains the Achilles' heel of this procedure. In this review, background information about the TMR procedure will be discussed along with an analysis of the recently published randomized studies.

Laserlithotripsy of salivary stones: A comparison between the pulsed dye laser and the Ho-YSGG laser

The feasibility of laser lithotripsy of salivary stones was investigated. Two types of laser systems were evaluated: a 504 nm flashlamp pumped dye laser and a Ho-YSGG laser. With the dye laser, plasma flashes and acoustic phenomena could be observed. The number of laser shots per unit mass necessary to fragment the stone decreased in proportion to the energy per laser pulse to the power −2.7. With the Ho-YSGG laser, a more ablative kind of stone decomposition was observed. Here the number of shots per unit mass necessary for fragmentation was inversely proportional to the energy per laser pulse. For both lasers the total time necessary to fragment the stones is much too long to compete with conventional stone removal.

Lens design for laser systems*

Lenses for focusing laser beams can be designed by use of conventional methods, but since laser beams are monochromatic, and have angular divergences that are limited by diffraction, the requirements for an optimized design are different than those for an ordinary lens. In particular, in a weakly focused beam, the axial locations of the paraxial focus and the gaussian beam waist do not coincide. Although the focus shift is small for a beam of low f number, when the f number is as large as f/1000 (a common value in certain types of laser systems), the shift may be comparable to the focal length. Such a shift should be taken into account in an optimized focusing system, although the extremely large depth of focus obtained with a beam of such large f number makes the resultant image blur rather small.