YAG Laser System Research Articles

Interferometric laser measurement of multi-axial mechanical properties exhibited by carbon nanotubes

Interferometric optical experiments for measuring changes in fringe irradiance patterns dependent on optical and mechanical responses associated to carbon nanotubes are reported. Thin solid films conformed by multiwall carbon nanotubes were prepared by an aerosol pyrolysis method. A Michelson optical interferometer with a highly stable 488nm wavelength was employed for evaluating the studied sample. According to the interferometric results, the strain of the carbon nanotubes presented a nonlinear behavior resulting from applied multiaxial forces. On the other hand, for further investigating the effect of the variation of the mechanical properties and the optical characteristics of the tubes, nonlinear optical experiments were performed when the sample was exposed to a mechanical action. The third order nonlinear optical response was explored with the assistance of the second harmonic provided by a Nd:YAG laser system in a two-wave mixing configuration. Potential applications for mechano-optical modulation by nanosystems based on carbon nanotubes are contemplated.

Studies on pulsed Nd:YAG laser cutting of thick stainless steel in dry air and underwater environment for dismantling applications

Abstract Dismantling of old equipments and structures is an important application in nuclear facilities and shipping industry. This paper presents a study on process optimization during pulsed Nd:YAG laser cutting of thick stainless steel (AISI SS304) sheets having a thickness in the range of 4–20 mm in dry air and underwater environment. Laser cutting experiments have been performed using a 500 W average power long pulse Nd:YAG laser system with fiber optic beam delivery. A water shielded laser cutting nozzle with coaxial gas jet was specifically developed to form a local dry cavity around the laser beam during the cutting experiments in underwater condition. It was found that for a given pulse energy, a higher cutting speed is possible with optimal value of pulse duration, spot overlapping, and assist gas pressure. Cutting speed of 20 mm thick SS sample was enhanced to about three times by means of increase in pulse duration from 14 ms to 20 ms and reduction in the required spot overlapping from a value of 80% to 40% using oxygen as the assist gas. A comparison of the cutting speed and heat affected zone in dry air and underwater environment has been performed. These results will be highly useful in laser based dismantling of old steel structures in radioactive and underwater environment to save time and minimize radiation dose consumption as compared to conventional dismantling methods.

Impact of pulse duration on Ho:YAG laser lithotripsy: treatment aspects on the single-pulse level.

Holmium-YAG (Ho:YAG) laser lithotripsy is a multi-pulse treatment modality with stochastic effects on the fragmentation. In vitro investigation on the single-pulse-induced effects on fiber, repulsion as well as fragmentation was performed to identify potential impacts of different Ho:YAG laser pulse durations. A Ho:YAG laser system (Swiss LaserClast, EMS S.A., Nyon, Switzerland) with selectable long- or short-pulse mode was tested with regard to fiber burn back, the repulsion capacity using an underwater pendulum setup and single-pulse-induced fragmentation capacity using artificial (BEGO) stones. The laser parameters were chosen in accordance with clinical application modes (laser fiber: 365 and 200 µm; output power: 4, 6 and 10 W in different combinations of energy per pulse and repetition rate). Evaluation parameters were reduction in fiber length, pendulum deviation and topology of the crater. Using the long-pulse mode, the fiber burn back was nearly negligible, while in short-pulse mode, an increased burn back could be observed. The results of the pendulum test showed that the deviation induced by the momentum of short pulses was by factor 1.5-2 higher compared to longer pulses at identical energy per pulse settings. The ablation volumes induced by single pulses either in short-pulse or long-pulse mode did not differ significantly although different crater shapes appeared. Reduced stone repulsion and reduced laser fiber burn back with longer laser pulses may result in a more convenient handling during clinical application and thus in an improved clinical outcome of laser lithotripsy.

Fabrication and optical testing of hybrid SiO2: azo-polymer based planar waveguides for NLO/SHG laser emission

Predesigned push-pull azo-dye polymers were homogeneously dispersed within a SiO2 sol-gel matrix synthesized via the sonogel (SG) route. High-quality spin-coated films were obtained with these hybrid structures in the liquid sol-phase. The spectroscopic UV- Vis analyses reveal the appropriate insertion of these organic compounds within the highly pure SG-environment whereas the thermal (DSC) analysis and photoacoustic measurements evidence the thermomechanical stability of the amorphous hybrid layers. As the optical attenuation, refractive index and film thickness values of the obtained films are adequate for opto-electronic applications; these hybrid films were implemented to fabricate optical waveguiding prototypes. In this sense, functional planar waveguides were fabricated for nonlinear optical (NLO) applications after performing a molecular ordering via a corona DC-poling procedure in order to achieve a macroscopic polar order (ferroelectric and noncentrosymmetric arrangement of the organic chromophores). The poled films were then able to exhibit stable NLO-waveguiding effects as excited with a Nd:YAG laser system in order to generate second harmonic waves travelling within the planar layer.

Enhanced random lasing from a colloidal CdSe quantum dot-Rh6G system

In this letter, we report random laser action in a system where optical amplification is provided by colloidal CdSe quantum dots (CQDs) triggered by the emission from Rhodamine 6G. The laser emission from CdSe QDs is optically excited by Rh-6G which in turn is photo-pumped by a frequency-doubled Q-switched Nd : YAG laser system at an excitation wavelength of 532 nm. At intensities greater than the threshold value, laser emission is characterized by narrowing peaks.

Photothermal, photoconductive and nonlinear optical effects induced by nanosecond pulse irradiation in multi-wall carbon nanotubes

Abstract The influence of the optical absorption exhibited by multi-wall carbon nanotubes on their photothermal, photoconductive and nonlinear optical properties was evaluated. The experiments were performed by using a Nd:YAG laser system at 532 nm wavelength and 1 ns pulse duration. The observations were carried out in thin film samples conformed by carbon nanotubes prepared by an aerosol pyrolysis method; Raman spectroscopy studies confirmed their multi-wall nature. Theoretical and numerical calculations based on the heat equation allow us to predict the temporal response of the induced effects associated to the optical energy transference. A two-wave mixing method was employed to explore the third order nonlinear optical response exhibited by the sample. A dominant thermal process was identified as the main physical mechanism responsible for the optical Kerr effect. Potential applications for developing a monostable multivibrator exhibiting different time-resolved characteristics were analyzed.

Enhanced fluorescence emitted by microdroplets containing organic dye emulsions.

In this paper, laser beam resonant interaction with pendant microdroplets that are seeded with a laser dye (Rhodamine 6G (Rh6G)) water solution or oily Vitamin A emulsion with Rhodamine 6G solution in water is investigated through fluorescence spectra analysis. The excitation is made with the second harmonic generated beam emitted by a pulsed Nd:YAG laser system at 532 nm. The pendant microdroplets containing emulsion exhibit an enhanced fluorescence signal. This effect can be explained as being due to the scattering of light by the sub-micrometric drops of oily Vitamin A in emulsion and by the spherical geometry of the pendant droplet. The droplet acts as an optical resonator amplifying the fluorescence signal with the possibility of producing lasing effect. Here, we also investigate how Rhodamine 6G concentration, pumping laser beam energies and number of pumping laser pulses influence the fluorescence behavior. The results can be useful in optical imaging, since they can lead to the use of smaller quantities of fluorescent dyes to obtain results with the same quality.

Laser Source for Wireless Power Transmission in Space

For many years the attempts to create a super long conductive channel were taken in order to study the upper atmosphere and to settle special tasks, related to the energy transmission. There upon the program of “Impulsar” creation represents a great interest, as this program in a combination with high-voltage high repetition rate electrical source can be useful to solve the above mentioned problems. It looks like as some kind of “renaissance of N. Tesla ideas” for the days of high power lasers. In the experiments the GDL CO2-laser and solid state Nd YAG laser systems had been used. Theoretical and experimental investigation of high repetition rate P-P mode of operation for high power lasers (COIL, HF/DF) had been provided. The experimental realization of P-P regime has been demonstrated for 100 KW GDL and 1 kW LD pumped SSL. More than two orders of magnitude ratio of peak to average power with minimal energy loss have been obtained. High efficiency and excellent beam quality of disk laser mean that it can be widely used in modern science and industry. Disk laser idea, suggested by N. G. Basov 52 years ago, after implementation in the mono-module disk geometry can be used effectively for many important challenges faced by science and technological advances of the future. Today we can say that creation of megawatt class mono-module P-P disk laser with a large cross section of the active medium opens up great prospects for its use for solving of the set of problems: small satellites launching by lasers, formation of super-long conducting channels in space (vacuum and atmosphere), cleaning of the near-Earth space from the debris and so on.

The Effect of PIPS on Three Different Types of Dentin: A Surface Observational Study

ABSTRACT Aim To study the effect of 17% EDTA with PIPS on dentinal surfaces of pediatric, adolescent and geriatric teeth using scanning electron microscope (SEM). Background data The debriding ability of an Er:YAG laser system equipped with a new tapered and stripped tip of 400 micron diameter and auxiliary irrigating solutions after mechanical preparation. Materials and methods For each group, 20 single rooted human mandibular premolars were selected. The groups were categorized as group 1 pediatric, group 2 adolescent and group 3 geriatric. These groups were further divided as subgroup A (control)—saline and subgroup B—EDTA and PIPS. Access opening was done for all the samples and respective irrigation protocol was followed. The samples were then sectioned and observed under SEM. Results The observational study shows that the efficacy of smear layer removal was better in the pediatrics group followed by adolescent and geriatric groups. Conclusion The PIPS technique resulted in effective debriding and decontamination of the root canal system in all the three types of dentin. How to cite this article Hegde V, Vangala A, Jain P, Srilatha S, Dixit V. The Effect of PIPS on Three Different Types of Dentin: A Surface Observational Study. World J Dent 2015;6(1):5-9.

Resection of Calcified Aortic Heart Leaflets In Vitro by Q-Switched 2 µm Microsecond Laser Radiation

Transcatheter aortic valve implantation (TAVI) can result in paravalvular leakage and stent deformation in the presence of severe calcification. This study was undertaken to determine the efficacy of laser-assisted resection of calcific aortic valve leaflets as a method to minimize the effects of calcium on perivalvular leakage during TAVI. A Q-switched Tm:YAG laser emitting at a wavelength of 2.01 μm was used to evaluate the cutting efficiency on highly calcified human aortic leaflets in vitro (N = 10). A pulse energy of 4.3 mJ, a pulse duration of 0.8-1 μs, and a repetition rate of 1 kHz were used. The radiation was transmitted via a 200 µm core diameter quartz fiber. Resection was performed in a fiber-tissue contact mode on water-covered samples in a dish. The remnant particles were analyzed with respect to quantity and size by light microscopy. A resection rate of 40.4 ± 22.2 mg/min on highly calcified aortic leaflets was achieved. This corresponds to a cutting speed of approximately 1 cm/min; a laser dissection time of 3 min per leaflet is expected. The majority of the remnant particles (85.4%) were <6 μm in diameter, with only 0.1% exceeding 300 μm. The Q-switched Tm:YAG laser system showed promising results in cutting calcified aortic valves, by transmitting sufficient energy through a small flexible fiber. Catheter-based removal of aortic valve calcification may help to improve TAVI technology.

A theoretical and experimental investigation for wavelength switchable TmYAG laser modulated by Tm:YAG crystal length

Abstract Based on the analysis of the quasi-three-level side pumped Tm:YAG laser system, the oscillating conditions of this laser are predicted from the point of pump threshold. The laser oscillation at 2.02 µm with larger stimulated emission sections is suppressed when the crystal length is larger than ~85 mm with a 5% output coupling and then an efficient side-diode-pumped rod Tm:YAG laser operating at 2.07 µm is realized. Experimental results are reported from single-module and two-modules Tm:YAG laser and compared with the predictions obtained from the model. The experimental results show that the center wavelength of the Tm:YAG laser is shifted to 2.07 μm when the Tm:YAG crystal length is switched from 69 mm to 138 mm, which is in well agreement with the predictions obtained from the model.

Impact of pulse duration on Ho:YAG laser lithotripsy: fragmentation and dusting performance.

ObjectivesIn vitro investigations of Ho:YAG laser-induced stone fragmentation were performed to identify potential impacts of different pulse durations on stone fragmentation characteristics.Materials and methodsA Ho:YAG laser system (Swiss LaserClast, EMS S.A., Nyon, Switzerland) with selectable long or short pulse mode was tested with regard to its fragmentation and laser hardware compatibility properties. The pulse duration is depending on the specific laser parameters. Fragmentation tests (hand-held, hands-free, single-pulse-induced crater) on artificial BEGO stones were performed under reproducible experimental conditions (fibre sizes: 365 and 200 µm; laser settings: 10 W through combinations of 0.5, 1, 2 J/pulse and 20, 10, 5 Hz, respectively).ResultsDifferences in fragmentation rates between the two pulse duration regimes were detected with statistical significance for defined settings. Hand-held and motivated Ho:YAG laser-assisted fragmentation of BEGO stones showed no significant difference between short pulse mode and long pulse mode, neither in fragmentation rates nor in number of fragments and fragment sizes. Similarly, the results of the hands-free fragmentation tests (with and without anti-repulsion device) showed no statistical differences between long pulse and short pulse modes.ConclusionThe study showed that fragmentation rates for long and short pulse durations at identical power settings remain at a comparable level. Longer holmium laser pulse duration reduces stone pushback. Therefore, longer laser pulses may result in better clinical outcome of laser lithotripsy and more convenient handling during clinical use without compromising fragmentation effectiveness.

The Effect of Laser Focus Position on Laser Induced Plasma Characteristics

Laser induced plasma is a relatively complex process which is closely related to many factors. In this paper, using a short pulse Nd:YAG laser and CCD photoelectric detection system, the variation of laser focus position effected by spectral intensity, the ratio of signal to background as well as the self-absorption of the plasma spectral lines with the standard spectra sample of aluminum for analysis samples was studied. Results show that: when the laser focus position is about 5mm under the surface of the sample, the relative intensity and the ratio of signal to background of the spectral lines are the strongest, and the spectral lines are sharp without obvious self-absorption.

Optimisation of Pulsed Nd: YAG Laser Processing of Gray Cast Iron for Enhanced Surface Properties

This paper presents laser surface modification of gray cast iron for enhanced surface hardness properties. A 300 W high power Nd:YAG laser system with pulse mode was used to modify gray cast iron samples surface. Laser processing was conducted using a 33 full factorial design. Three controlled parameters were laser power, pulse duration and overlap percentage. The modified surface was characterised for metallographic study, roughness and hardness. Metallographic study and surface morphology were conducted using optical microscope while hardness properties were measured using Vickers scale. Surface roughness was measured using a 2D stylus profilometer. The results show that hardness of laser modified surface increased due to grain refinement. The overlapping rates increased significantly with decreasing laser scanning speed which affected sample surface integrity. Low surface roughness obtained at the highest scanning speed of 1400 mm/min, and low power of 830 W with pulse repetition frequency of 50 Hz. Process optimization was carried out for maximum surface hardness and laser modified depth, and minimum surface roughness. These findings indicate potential application of cast iron for high wear resistant applications through laser surface modification.

Edge profile measurements using Thomson scattering on the KSTAR tokamak.

In the KSTAR Tokamak, a "Tangential Thomson Scattering" (TTS) diagnostic system has been designed and installed to measure electron density and temperature profiles. In the edge system, TTS has 12 optical fiber bundles to measure the edge profiles with 10-15 mm spatial resolution. These 12 optical fibers and their spatial resolution are not enough to measure the pedestal width with a high accuracy but allow observations of L-H transition or H-L transitions at the edge. For these measurements, the prototype ITER edge Thomson Nd:YAG laser system manufactured by JAEA in Japan is installed. In this paper, the KSTAR TTS system is briefly described and some TTS edge profiles are presented and compared against the KSTAR Charge Exchange Spectroscopy and other diagnostics. The future upgrade plan of the system is also discussed in this paper.

Thermal stability study of nitro-rich triazole derivatives using temperature dependent time resolved pulsed photoacoustic (PA) technique

The paper reports the pulsed laser based photoacoustic pyrolysis technique to study the thermal stability of novel nitro-rich 1H-1,2,3-triazole derivatives of high energy materials (HEMs) for the first time. We have employed 532nm wavelength, 7ns duration pulses at 10Hz repetition rate obtained from Q-switched Nd:YAG laser system to record the time resolved temperature dependent PA spectra in a specially designed PA pyrolysis system. The study has been carried out between the 30 and 350°C temperature range. Thermally stable HEMs are insensitive to temperature and they release very small amount of volatile compounds such as H2O, NO2, and NO at high temperatures. The combined results obtained from PA and TG–DTA techniques open a new channel to understand the molecular dynamics of HEMs which is responsible for energy storage mechanism of these compounds in terms of free NO2 at different temperature ranges. In addition, the experimental findings lead to develop a new tool to scale the efficiency of these molecules as a fuel.

Applying statistical models optimize the process of multi-pass narrow-gap laser welding with filler wire

Laser welding of thick plates has been used in automobile and shipping industry owing to its focusing heat input, little welding deformation, and high productivity. Using narrow-gap technique can decrease the filling volumes of wire and increase the welding efficiency. However, its process is more complicated since it introduces filler wire to narrow-gap weld configurations. Usually the welding path, planning mainly depends on man’s experiences. Human factors have big influences on the quality of the joint. The aim of this paper is to study the interactions between welding parameters and the geometry of single bead using statistical methods. Then, the founded models were employed to plan the welding path, the number of filling passes, and layers in the multi-pass narrow nap joining. These results will provide supports for automatic multi-pass laser welding. The welding system includes a 10-kW Nd:YAG laser system, a KUKA robot, a Fronius wire feeder, and a 20-mm-thick high-strength ship steel with narrow gap. Laser power, welding speed, and wire feed rate are input variables. The responses include the transversal area of the added metals, bead width, bead height, and the ratio of bead width to height. Verification experiments indicate that all these models can forecast the responses within the factor domain. Transversal section micrographs of the joints show that this method can get welding joint with less defects.

Progress of the 10 J water-cooled Yb:YAG laser system in RCLF

Abstract The high repetition rate 10 J/10 ns Yb:YAG laser system and its key techniques are reported. The amplifiers in this system have a multi-pass V-shape structure and the heat in the amplifiers is removed by means of laminar water flow. In the main amplifier, the laser is four-pass, and an approximately 8.5 J/1 Hz/10 ns output is achieved in the primary test. The far-field of the output beam is approximately 10 times the diffraction limit. Because of the higher levels of amplified spontaneous emission (ASE) in the main amplifier, the output energy is lower than expected. At the end we discuss some measures that can improve the properties of the laser system.

Bactericidal effects of using a fiber-less Er:YAG laser system for treatment of moderate chronic periodontitis: preliminary results.

The purpose of this study was to evaluate the bactericidal effectiveness of using a fiber-less Er:YAG laser in the first stage of therapy for moderate chronic periodontitis and to compare it with conventional treatment. Two quadrants from 20 patients with moderate chronic periodontitis were treated with Gracey curettes (control), and the contralateral two quadrants in each patient were treated using an Er:YAG laser with total power of 1.5W (test). Subgingival plaque samples from the four deepest pockets in each quadrant were taken immediately before and 1 month after treatment, and the presence of nine marker bacteria was studied using real-time polymerase chain reaction technology. A significant reduction of total pathogens and bacteria from the red complex was observed 1 month after treatment with both procedures. The results were more significant for the test group (P = .003) than for the control group (P = .005). Qualitative analysis of sites that had a therapeutically significant number and proportion of marker bacteria also showed significant reduction after treatment. The results of the present study suggest that the Er:YAG laser possesses comparable with conventional treatment bactericidal effectiveness against periodontal pathogens in vivo in the initial treatment of moderate chronic periodontitis. More evaluations should be performed to prove these results for a longterm successful clinical outcome.

Enhancement of p-polarized output power in long pulse single rod Nd:YAG laser using a tilted 90° quartz rotator

We report a study on the enhancement of linearly p-polarized output power in long pulse (2–20ms) multimode operation of single rod Nd:YAG laser. Laser resonator was designed using a simple optical scheme with a tilted 90° quartz rotator and a re-entering feedback mirror placed at appropriate location. A p-polarized average output power of 215W has been achieved with a slope efficiency of 4.5%, which is on higher side for a typical long pulse single rod Nd:YAG laser system. It has been verified experimentally that the depolarization losses can be reduced significantly from a value of ~34% to ~9%. Further, this scheme has resulted in a significant enhancement (more than 80%) of p-polarized output power as compared to placing a polarizer in the resonator. This long pulse p-polarized laser will be useful in various material processing applications and nonlinear frequency conversions.