Capítols de llibre
http://hdl.handle.net/2117/3219
2024-03-29T09:38:56ZWavelet transform applied to internal defect detection by means of laser ultrasound
http://hdl.handle.net/2117/178862
Wavelet transform applied to internal defect detection by means of laser ultrasound
Mohamed Selim, Hossameldin; Piñal Moctezuma, Juan Fernando; Delgado Prieto, Miquel; Trull Silvestre, José Francisco; Romeral Martínez, José Luis; Cojocaru, Crina
Laser-generated ultrasound represents an interesting nondestructive testing technique that is being investigated in the last years as performative alternative to classical ultrasonic-based approaches. The greatest difficulty in analyzing the acoustic emission response is that an in-depth knowledge of how acoustic waves propagate through the tested composite is required. In this regard, different signal processing approaches are being applied in order to assess the significance of features extracted from the resulting analysis. In this study, the detection capabili-ties of internal defects in a metallic sample are proposed to be studied by means of the time-frequency analysis of the ultrasonic waves resulting from laser-induced thermal mechanism. In the proposed study, the use of the wavelet transform considering different wavelet variants is considered due to its multi-resolution time-frequency characteristics. Also, a significant time-frequency technique widely applied in other fields of research is applied, the synchrosqueezed transform.
2020-02-28T08:02:22ZMohamed Selim, HossameldinPiñal Moctezuma, Juan FernandoDelgado Prieto, MiquelTrull Silvestre, José FranciscoRomeral Martínez, José LuisCojocaru, CrinaLaser-generated ultrasound represents an interesting nondestructive testing technique that is being investigated in the last years as performative alternative to classical ultrasonic-based approaches. The greatest difficulty in analyzing the acoustic emission response is that an in-depth knowledge of how acoustic waves propagate through the tested composite is required. In this regard, different signal processing approaches are being applied in order to assess the significance of features extracted from the resulting analysis. In this study, the detection capabili-ties of internal defects in a metallic sample are proposed to be studied by means of the time-frequency analysis of the ultrasonic waves resulting from laser-induced thermal mechanism. In the proposed study, the use of the wavelet transform considering different wavelet variants is considered due to its multi-resolution time-frequency characteristics. Also, a significant time-frequency technique widely applied in other fields of research is applied, the synchrosqueezed transform.Strong-field-enhanced forward scattering of high-order harmonics
http://hdl.handle.net/2117/86376
Strong-field-enhanced forward scattering of high-order harmonics
Serrat Jurado, Carles
We show that scattering of ultrashort XUV pulses from strong-field driven electron wave packets is enhanced as compared with normal weak scattering from bound or free electrons. We predict large XUV amplification in high-order harmonic generation. Recent measurements have corroborated the main effect that we report. Parametric amplification of attosecond pulse trains at 11 nm has been observed to occur only if the seed pulse-train is perfectly synchronized to the driving laser pulse in the amplifier as predicted here theoretically: J. Seres et al. Scientific Reports 4:4254 (2014).
This is a copy of the author 's final draft version of an article published in the journal Ultrafast phenomena XIX: proceedings of the 19th international conference, Okinawa Convention Center, Okinawa, Japan, July 7-11, 2014.
The final publication is available at Springer via
http://dx.doi.org/10.1007/978-3-319-13242-6_24
2016-04-28T13:14:03ZSerrat Jurado, CarlesWe show that scattering of ultrashort XUV pulses from strong-field driven electron wave packets is enhanced as compared with normal weak scattering from bound or free electrons. We predict large XUV amplification in high-order harmonic generation. Recent measurements have corroborated the main effect that we report. Parametric amplification of attosecond pulse trains at 11 nm has been observed to occur only if the seed pulse-train is perfectly synchronized to the driving laser pulse in the amplifier as predicted here theoretically: J. Seres et al. Scientific Reports 4:4254 (2014).Chiral modes in 2D PT-symmetric nanostructures
http://hdl.handle.net/2117/80912
Chiral modes in 2D PT-symmetric nanostructures
Botey Cumella, Muriel; Herrero Simon, Ramon; Turduev, M.; Kurt, H.; Staliunas, Kestutis
We propose the stabilization of the output beam of Broad Area Semiconductor (BAS) amplifiers through the introduction of a spatially periodic modulated potential. We show that a periodic modulation of the pump profile in transverse and longitudinal directions, under certain ‘resonance’ condition, can solve two serious problems of BAS amplifiers (and possibly lasers), which are (i) the lack of an intrinsic spatial mode selection mechanism in linear amplification regimes and (ii) the modulation instability (also called Bespalov-Talanov instability) in nonlinear regimes. The elimination of these two drawbacks can significantly improve the spatial quality of the emitted beam in BAS amplifiers.
2015-12-18T14:45:43ZBotey Cumella, MurielHerrero Simon, RamonTurduev, M.Kurt, H.Staliunas, KestutisWe propose the stabilization of the output beam of Broad Area Semiconductor (BAS) amplifiers through the introduction of a spatially periodic modulated potential. We show that a periodic modulation of the pump profile in transverse and longitudinal directions, under certain ‘resonance’ condition, can solve two serious problems of BAS amplifiers (and possibly lasers), which are (i) the lack of an intrinsic spatial mode selection mechanism in linear amplification regimes and (ii) the modulation instability (also called Bespalov-Talanov instability) in nonlinear regimes. The elimination of these two drawbacks can significantly improve the spatial quality of the emitted beam in BAS amplifiers.Stochastic competition between two populations in space
http://hdl.handle.net/2117/28093
Stochastic competition between two populations in space
Pigolotti, Simone; Benzi, Roberto; Jensen, Mogens H.; Perlekar, Prasad; Toschi, Federico
2015-05-28T11:12:08ZPigolotti, SimoneBenzi, RobertoJensen, Mogens H.Perlekar, PrasadToschi, FedericoMulti-stability and transient chaotic dynamics in semiconductor lasers with time-delayed optical feedback
http://hdl.handle.net/2117/8886
Multi-stability and transient chaotic dynamics in semiconductor lasers with time-delayed optical feedback
Zamora Munt, Jordi; Masoller Alonso, Cristina; García Ojalvo, Jordi
We investigate numerically the chaotic transient dynamics of a semiconductor laser with time-delayed optical feedback. This transient behavior is seen in the low-frequency fluctuations (LFF) regime ocurring when the laser is pumped close to thereshold and is subjected to moderate feedback strengths. We characterize the transient dynamics in terms of its duration, the time intervals between consecutive dropouts, and the total in each transient event. We statistically analyze these quantities as a function of the noise strength and other system parameters related to different nonlinear mechanisms of light-matter interaction inside the laser active medium.
2010-09-15T16:57:59ZZamora Munt, JordiMasoller Alonso, CristinaGarcía Ojalvo, JordiWe investigate numerically the chaotic transient dynamics of a semiconductor laser with time-delayed optical feedback. This transient behavior is seen in the low-frequency fluctuations (LFF) regime ocurring when the laser is pumped close to thereshold and is subjected to moderate feedback strengths. We characterize the transient dynamics in terms of its duration, the time intervals between consecutive dropouts, and the total in each transient event. We statistically analyze these quantities as a function of the noise strength and other system parameters related to different nonlinear mechanisms of light-matter interaction inside the laser active medium.