Search results for "LASER"
showing 10 items of 3161 documents
Novel non-destructive inspection techniques for laser powder deposition inspection
2013
A novel non-destructive testing (NDT) techniques for inspection of parts and components manufactured by Additive Manufacturing Processes (AMP), in particular Laser Metal Deposition (LMD), has been developed. LMD is a technology that has been maturing over the last 20 years and has found application in repair, coatings, hybrid build and 3D near net shape manufacture of small intricate parts that can be used in aero and automobile engines to improve efficiency. Currently this technology cannot be used to supply some of these parts because absence of flaws, which might be left in the component during manufacture, cannot be guaranteed. Today, quality is assessed by sample destructive testing, w…
Phase-delayed laser diode array allows ultrasonic guided wave mode selection and tuning
2013
Selecting and tuning modes are useful in ultrasonic guided wave non-destructive testing (NDT) since certain modes at various center frequencies are sensitive to specific types of defects. Ideally one should be able to select both the mode and the center frequency of the launched waves. We demonstrated that an affordable laser diode array can selectively launch either the S0 or A0 ultrasonic wave mode at a chosen center frequency into a polymer plate. A fiber-coupled diode array (4 elements) illuminated a 2 mm thick acrylic plate. A predetermined time delay matching the selected mode and frequency was employed between the output of the elements. The generated ultrasound was detected by a 215…
Reaktiovoimantuotto, nopeus ja tekniikka pituushypyn ponnistusvaiheessa
2011
Pituushypyn tulokseen vaikuttavat ponnistusvaiheessa eniten kehon massakeskipisteen lähtönopeus, mutta myös sekä massakeskipisteen lähtökorkeus että lähtökulma. Pi-tuushyppyä on aikaisemmin tutkittu melko laajasti – eniten liikeanalyysimenetelmin. Sen sijaan reaktiovoimatutkimuksia löytyy paljon vähemmän. Tämän tutkimuksen tarkoitus olikin selvittää pituushyppysuorituksen kannalta keskeisiä reaktiovoimamuuttujia ja no-peuksia valmentajien tueksi ja arvioida niiden soveltuvuutta testipatteristoon. Menetelmät. Koehenkilöinä oli kaksi kansallisen tason naishyppääjää ja yksi kansallisen tason mieshyppääjä (ikä 22,3 ± 1,5 vuotta, pituus 174,3 ± 11,1 cm, paino 58,7 ± 2,5 kg, ennätys 6,25 ± 0,67 m…
Reaktiovoimantuotto, nopeus ja tekniikka kolmiloikassa
2011
Johdanto. Kolmiloikka on seka fyysisesti etta teknisesti erittain vaativa ja herkka laji, jossa tutkimus on tahan asti ollut vahaista ja lahinna liikeanalyysiin perustuvaa. Erityisesti huipputuloksiin vaadittavista reaktiovoimista ei ole juuri tietoa saatavilla. Taman tutkimuksen tarkoituksena oli koota saatavilla oleva tutkimustieto lajista seka pyrkia maarittamaan tarkeimpia reaktiovoimamuuttujia uuden testipatteriston muodostamiseksi valmennuksen tueksi. Lisaksi tutkimuksen yhteydessa testattiin lasermittausjarjestelman soveltuvuutta suorituksen aikaisten nopeuden muutosten mittaamisessa. Menetelmät. Koehenkiloina tutkimukseen osallistui yhteensa kolme kansallisen tason mieshyppaajaa (ik…
Laser a diodi in odontostomatologia: la nostra esperienza
Experimental investigation of the optical Kerr effect at large laser intensity: impact on the propagation of a short and intense laser pulse
2010
Talk given by O. Faucher; International audience
Higher-order Kerr terms allow ionization-free filamentation in gases
2010
Talk given by J. Kasparian; International audience; Higher-order nonlinear indices, rather than plasma, provide the main defocusing contribution to filamentation in gases at 800 nm. Developing generalized Miller formulae, we discuss the generality of this as a function of the laser wavelength
Optical Absorption of Excimer Laser‐Induced Dichlorine Monoxide in Silica Glass and Excitation of Singlet Oxygen Luminescence by Energy Transfer from…
2021
An optical absorption (OA) band of interstitial dichlorine monoxide molecules with peak at 4.7 eV and halfwidth 0.94 eV is identified in F2 laser - irradiated (photon energy=7.9 eV) synthetic silica glass bearing both interstitial O2 and Cl2 molecules. Alongside with intrinsic defects, this OA band can contribute to solarization of silica glasses produced from SiCl4. While the formation of ClClO is confirmed by its Raman signature, its structural isomer ClOCl may also contribute to this induced OA band. Thermal destruction of this band between 300C and 400C almost completely restores the pre-irradiation concentration of interstitial Cl2. An additional weak OA band at 3.5 eV is tentatively a…
Efficient interrogation method of forward Brillouin scattering in optical fibers using a narrow bandwidth long-period grating
2020
A new technique, to the best of our knowledge, for the characterization of the effective refractive index modulation in optical fibers due to transverse acoustic mode resonances excited by electrostriction is reported. The resonances excited by an optical pulse are probed by a narrow bandwidth long-period grating (LPG) inscribed in the fiber, which is interrogated by a continuous wave (CW) beam. The LPG used in this experiment has a narrow bandwidth and high sensitivity to small mode index perturbations, allowing the measurement of index variations from below 10 − 9 to 10 − 6 . Radial and torsional-radial acoustic modes were characterized up to 1.1 GHz. The linewidth of resonances was found…