Stable dual-wavelength oscillation of an erbium-doped fiber ring laser at room temperature

We propose a simple Er-doped fiber laser configuration for achieving stable dual-wavelength oscillation at room temperature, in which a high birefringence fiber Bragg grating was used as the wavelength-selective component. Stable dual-wavelength oscillation at room temperature with a wavelength spacing of 0.23nm and mutually orthogonal polarisation states was achieved by utilising the polarisation hole burning effect. An amplitude variation of less than 0.7dB over 80s period was obtained for both wavelengths.

Thulium-doped all-fiber mode-locked laser based on NPR and 45°-tilted fiber grating

A nonlinear polarization rotation based all-fiber passively modelocked Tm3+-doped fiber laser is demonstrated by using a 45° tilted fiber grating (TFG) as an in-line polarizer. The 45° TFG centered at 2000 nm with polarization dependent loss (PDL) of >12 dB at 1850 nm∼2150 nm range was UV inscribed for the first time in SM28 fiber using a 244 nm Ar+ continuous wave laser and a phase mask with 25 mm long uniform pitch and titled period pattern of 33.7° with respect to the fiber axis. Stable soliton pulses centered at 1992.7 nm with 2.02 nm FWHM bandwidth were produced at a repetition rate of 1.902 MHz with pulse duration of 2.2 ps and pulse energy of 74.6 pJ. As increased pump power, the laser also can operate at noise-like regime with 18.1 nm FWHM bandwidth and pulse energy of up to 250.1 nJ. Using the same 45° TFG, both stable soliton and noise-like mode-locking centered at ∼1970 nm and ∼2050 nm, were also achieved by shortening and extending the length of Tm3+-doped fiber, respectively, exhibiting advantages of broadband and low insertion loss at 2 μm band.

All-fiber 250 MHz fundamental repetition rate pulsed laser with tilted fiber grating polarizer

We demonstrated a high fundamental repetition-rate pulsed erbium-doped fiber laser with all-fiber-integrated configuration. A novel scheme using a 45°-tilted fiber grating as the in-fiber polarizing element was employed to shorten the total cavity length and, thus, increase the fundamental repetition rate of the laser. Dissipative soliton pulses mode-locked with a fundamental repetition rate of 251.3 MHz and pulse duration of 96.7 fs have been achieved from the compact and all-fiber ring cavity laser. Additionally, passively Q-switched pulses were observed from this high fundamental repetition-rate fiber laser, which is the first report on Q-switched fiber laser using a tilted fiber grating.

Passively harmonic mode locked erbium doped fiber soliton laser with carbon nanotubes based saturable absorber

We have proposed and demonstrated passive harmonic mode locking of an erbium doped fiber laser with soliton pulse shaping using carbon nanotubes polyvinyl alcohol film. Two types of samples prepared by using filtration and centrifugation were studied. The demonstrated fiber laser can support 10th harmonic order corresponding to 245 MHz repetition rate with an output power of ~12 mW. More importantly, all stable harmonic orders show timing jitter below 10 ps. The output pulses energies are between 25 to 56 pJ. Both samples result in the same central wavelength of output optical spectrum with similar pulse duration of ~1 ps for all harmonic orders. By using the same laser configuration, centrifugated sample exhibits slightly lower pulse chirp. © 2012 Optical Society of America.

Higher-order soliton generation in hybrid mode-locked thulium-doped fiber ring laser

A thulium-doped all-fiber laser passively mode-locked by the co-action of nonlinear polarization evolution and single-walled carbon nanotubes operating at 1860-1980 nm wavelength band is demonstrated. Pumped with the single-mode laser diode at 1.55 μm laser generates near 500-fs soliton pulses at repetition rate ranging from 6.3 to 72.5 MHz in single-pulse operation regime. Having 3-m long cavity average output power reached 300 mW, giving the peak power of 4.88 kW and the pulse energy of 2.93 nJ with slope efficiency higher than 30%. At a 21.6-m long ring cavity average output power of 117 mW is obtained, corresponding to the pulse energy up to 10.87 nJ and a pulse peak power of 21.7 kW, leading to the higher-order soliton generation.

UV-Inscribed optical fiber gratings in Mid-IR range and their laser applications

We have UV-inscribed fiber Bragg gratings (FBGs), long-period gratings (LPGs), and tilted fiber gratings (TFGs) into mid-IR 2μm range using three common optical fiber grating fabrication techniques (two-beam holographic, phase mask, and point-by-point). The fabricated FBGs have been evaluated for thermal and strain response. It has been revealed that the FBG devices with responses in mid-IR range are much more sensitive to temperature than that in near-IR range. To explore the unique cladding mode coupling function, we have investigated the thermal and refractive index sensitivities of LPGs and identified that the coupled cladding modes in mid-IR range are also much more sensitive to temperature and surrounding medium refractive index change. The 45° tilted fiber gratings (45°-TFGs) as polarizing devices in mid-IR have been investigated for their polarization extinction characteristics. As efficient reflection filters and in-cavity polarizers, the mid-IR FBGs and 45°-TFGs have been employed in fiber laser cavity to realize multi-wavelength 2 μm Tm-doped CW and mode locked fiber lasers, respectively.

Laser-MAG-hybridihitsauksen käyttöönotto laivan rungon valmistuksessa

Perinteisten kaarihitsausmenetelmien suhteellisen suuri lämmöntuonti aiheuttaa huomattavia muodonmuutoksia laivan rungon valmistusprosessin alkuvaiheessa. Muodonmuutosten seurauksena rakenteiden mitta- ja muototarkkuus heikkenee, mikä lisää oikaisu- ja sovitustyötä myöhemmissä työvaiheissa. Hitsausmuodonmuutoksia voidaan vähentää siirtymällä käyttämään laser-MAG-hybridihitsausta, jossa lämmöntuonti on merkittävästi pienempi kuin kaarihitsauksessa. Näin kyetään oleellisesti leikkaamaan oikaisu- ja sovitustyöstä syntyviä kustannuksia. Tämän diplomityön tavoitteena oli kehittää tuotantovalmiiksi kuitulaser- ja MAG-hitsauksen yhdistelmäprosessi Aker Yards Oy:n Turun telakalla loppuvuoden 2006 aikana. Hitsauslaitteiston asennus oli valmistunut kesäkuussa 2006, minkä jälkeen aloitettiin luokituslaitoksen hyväksymän koeohjelman hitsaukset. Käyttöönotto suunnitelmaan sisältyvä koehitsausohjelma oli laadittu Det Norske Veritaksen julkaisemaa ohjetta (Guidelines no. 19) mukaillen. Ensimmäiseksi määritettiin hitsauskokeiden avulla prosessille laadun ja tehokkuuden suhteen optimaalinen railogeometria. Seuraavaksi optimoitiin prosessin hitsausparametrit 6 mm:n aineenpaksuudelle hyödyntäen Taguchi-koesuunnittelumenetelmää. Tämän jälkeen optimiparametreilla hitsattiin koekappale väsytyskokeisiin, jotka suoritettiin Teknillisen korkeakoulun laivalaboratoriossa. Väsytyskoetulokset täyttivät luokituslaitoksen vaatimukset. Myös hitsauksen menetelmäkoe suoritettiin hyväksytetysti. Viimeinen koeohjelman mukainen hitsauskoesarja tehtiin prosessiparametrien sallittujen vaihtelurajojen määrittämiseksi. Diplomityön tavoite täyttyi joulukuussa 2006, jolloin 'laivan kansipaneeli hitsattiin ensimmäistä kertaa uudella hitsausprosessilla. Hitsauksen laatu korreloi hyvin menetelmäkokeen tulosten kanssa ¿ hitsit olivat tasalaatuisia ja ne täyttivät B-luokan vaatimukset.

Laser Cutting of Austenitic Stainless Steel with a High Quality Laser Beam

The thin disk and fiber lasers are new solid-state laser technologies that offer a combinationof high beam quality and a wavelength that is easily absorbed by metal surfacesand are expected to challenge the CO2 and Nd:YAG lasers in cutting of metals ofthick sections (thickness greater than 2mm). This thesis studied the potential of the disk and fiber lasers for cutting applications and the benefits of their better beam quality. The literature review covered the principles of the disk laser, high power fiber laser, CO2 laser and Nd:YAG laser as well as the principle of laser cutting. The cutting experiments were made with thedisk, fiber and CO2 lasers using nitrogen as an assist gas. The test material was austenitic stainless steel of sheet thickness 1.3mm, 2.3mm, 4.3mm and 6.2mm for the disk and fiber laser cutting experiments and sheet thickness of 1.3mm, 1.85mm, 4.4mm and 6.4mm for the CO2 laser cutting experiments. The experiments focused on the maximum cutting speeds with appropriate cut quality. Kerf width, cutedge perpendicularity and surface roughness were the cut characteristics used to analyze the cut quality. Attempts were made to draw conclusions on the influence of high beam quality on the cutting speed and cut quality. The cutting speeds were enormous for the disk and fiber laser cutting experiments with the 1.3mm and 2.3mm sheet thickness and the cut quality was good. The disk and fiber laser cutting speeds were lower at 4.3mm and 6.2mm sheet thickness but there was still a considerable percentage increase in cutting speeds compared to the CO2 laser cutting speeds at similar sheet thickness. However, the cut quality for 6.2mm thickness was not very good for the disk and fiber laser cutting experiments but could probably be improved by proper selection of cutting parameters.

Laser cladding with scanning optics

Scanning optics create different types of phenomena and limitation to cladding process compared to cladding with static optics. This work concentrates on identifying and explaining the special features of laser cladding with scanning optics. Scanner optics changes cladding process energy input mechanics. Laser energy is introduced into the process through a relatively small laser spot which moves rapidly back and forth, distributing the energy to a relatively large area. The moving laser spot was noticed to cause dynamic movement in the melt pool. Due to different energy input mechanism scanner optic can make cladding process unstable if parameter selection is not done carefully. Especially laser beam intensity and scanning frequency have significant role in the process stability. The laser beam scanning frequency determines how long the laser beam affects with specific place local specific energy input. It was determined that if the scanning frequency in too low, under 40 Hz, scanned beam can start to vaporize material. The intensity in turn determines on how large package this energy is brought and if the intensity of the laser beam was too high, over 191 kW/cm2, laser beam started to vaporize material. If there was vapor formation noticed in the melt pool, the process starts to resample more laser alloying due to deep penetration of laser beam in to the substrate. Scanner optics enables more flexibility to the process than static optics. The numerical adjustment of scanning amplitude enables clad bead width adjustment. In turn scanner power modulation (where laser power is adjusted according to where the scanner is pointing) enables modification of clad bead cross-section geometry when laser power can be adjusted locally and thus affect how much laser beam melts material in each sector. Power modulation is also an important factor in terms of process stability. When a linear scanner is used, oscillating the scanning mirror causes a dwell time in scanning amplitude border area, where the scanning mirror changes the direction of movement. This can cause excessive energy input to this area which in turn can cause vaporization and process instability. This process instability can be avoided by decreasing energy in this region by power modulation. Powder feeding parameters have a significant role in terms of process stability. It was determined that with certain powder feeding parameter combinations powder cloud behavior became unstable, due to the vaporizing powder material in powder cloud. Mainly this was noticed, when either or both the scanning frequency or powder feeding gas flow was low or steep powder feeding angle was used. When powder material vaporization occurred, it created vapor flow, which prevented powder material to reach the melt pool and thus dilution increased. Also powder material vaporization was noticed to produce emission of light at wavelength range of visible light. This emission intensity was noticed to be correlated with the amount of vaporization in the powder cloud.

Real-time monitoring of laser scribing process utilizing high-speed camera

Currently, laser scribing is growing material processing method in the industry. Benefits of laser scribing technology are studied for example for improving an efficiency of solar cells. Due high-quality requirement of the fast scribing process, it is important to monitor the process in real time for detecting possible defects during the process. However, there is a lack of studies of laser scribing real time monitoring. Commonly used monitoring methods developed for other laser processes such a laser welding, are sufficient slow and existed applications cannot be implemented in fast laser scribing monitoring. The aim of this thesis is to find a method for laser scribing monitoring with a high-speed camera and evaluate reliability and performance of the developed monitoring system with experiments. The laser used in experiments is an IPG ytterbium pulsed fiber laser with 20 W maximum average power and Scan head optics used in the laser is Scanlab’s Hurryscan 14 II with an f100 tele-centric lens. The camera was connected to laser scanner using camera adapter to follow the laser process. A powerful fully programmable industrial computer was chosen for executing image processing and analysis. Algorithms for defect analysis, which are based on particle analysis, were developed using LabVIEW system design software. The performance of the algorithms was analyzed by analyzing a non-moving image from the scribing line with resolution 960x20 pixel. As a result, the maximum analysis speed was 560 frames per second. Reliability of the algorithm was evaluated by imaging scribing path with a variable number of defects 2000 mm/s when the laser was turned off and image analysis speed was 430 frames per second. The experiment was successful and as a result, the algorithms detected all defects from the scribing path. The final monitoring experiment was performed during a laser process. However, it was challenging to get active laser illumination work with the laser scanner due physical dimensions of the laser lens and the scanner. For reliable error detection, the illumination system is needed to be replaced.

Estudo do comportamento mecânico e microestrutural de um aço maraging após soldagem a laser e tratamentos térmicos

Pós-graduação em Engenharia Mecânica - FEG

Implantes nanotopograficamente modificados pela ação do laser Yb-YAG

Titanium has proven its suitability as an implant material in surgery over many years. Excellent biocompatibility and corrosion resistance are outstanding features. Implant surfaces always causes concern and interest in scientific communities, due to its close relationship with the time required for osseointegration. Surface modification can be performed by several methods, being laser irradiation one of them. Titanium implants with two different surfaces were inserted in rabbits: Group I (G-I: machined surface, control group), and group II (G-II: laser irradiated, test group) being processed 30 and 60 days after surgery for histological analysis. Surface characterization was performed with SEM-EDS, contact angle measurement, and mean roughness (Ra) parameters. Surface analysis in the GII group showed a nanomorphology affected by melt and quick solidification zones following laser irradiation (SEM), as well as total wettability and Ra mean values significantly higher than in the G-I group. The laser treatment resulted in a homogenized, porous surface, with increased surface area and volume. Histological analysis of bone-implant contact linear extension (BIC) showed better results in G-II at 30 days (39.26 ± 18.23 and 68.41 ± 13.68 for G-I and G-II groups, respectively). Titanium implants modified by laser irradiation showed important features that may accelerate early osseointegration.

Mechanical and microstructural characterization of laser-welded joints of 6013-T4 aluminum alloy

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Laser locking to the Hg-199 S-1(0)-P-3(0) clock transition with 5.4x10(-15)/root tau fractional frequency instability

With Hg-199 atoms confined in an optical lattice trap in the Lamb-Dicke regime, we obtain a spectral line at 265.6 nm for which the FWHM is similar to 15 Hz. Here we lock an ultrastable laser to this ultranarrow S-1(0) - P-3(0) clock transition and achieve a fractional frequency instability of 5.4 x 10(-15) / root tau for tau <= 400 s. The highly stable laser light used for the atom probing is derived from a 1062.6 nm fiber laser locked to an ultrastable optical cavity that exhibits a mean drift rate of -6.0 x 10(-17) s-(1) (-16.9 mHzs(-1) at 282 THz) over a six month period. A comparison between two such lasers locked to independent optical cavities shows a flicker noise limited fractional frequency instability of 4 x 10(-16) per cavity. (c) 2012 Optical Society of America

Experimental implementation of a biometric laser synaptic sensor

We fabricate a biometric laser fiber synaptic sensor to transmit information from one neuron cell to the other by an optical way. The optical synapse is constructed on the base of an erbium-doped fiber laser, whose pumped diode current is driven by a pre-synaptic FitzHugh–Nagumo electronic neuron, and the laser output controls a post-synaptic FitzHugh–Nagumo electronic neuron. The implemented laser synapse displays very rich dynamics, including fixed points, periodic orbits with different frequency-locking ratios and chaos. These regimes can be beneficial for efficient biorobotics, where behavioral flexibility subserved by synaptic connectivity is a challenge.