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Irradiation of intense ultrafast laser pulses in glasses can lead to formation of nanogratings whose periods are significantly smaller than the incident irradiation wavelength. The mechanism of the exotic phenomenon is still under hot debate. Here, we access the snapshots of morphologies in the laser affected regions in a porous glass which reveal the evolution of the formation of nanogratings with increasing number of laser pulses. Combined with further theoretical analyses, our observation provides important clues which suggest that excitation of standing plasma waves at the interfaces between areas modified and unmodified by the femtosecond laser irradiation plays a crucial role for promoting the growth of periodic nanogratings. The finding indicates that the formation of volume nanogratings induced by irradiation of femtosecond laser pulses is initiated with a mechanism similar to the formation of surface nanoripples.

Ultrafast lasers pulses induced ablation of nickel-titanium (NiTi) alloy substrates immersed in deionized water yielded a high-throughput of polycrystalline core - amorphous shell NiTi nanoparticles (NPs) owing to the high pulse energy of femtosecond (fs) lasers. In this study, the alloy NPs were fabricated by varying the laser fluences from 15 to 45 J/cm2. The polycrystalline core - amorphous shell NiTi were confirmed by selected area diffraction patterns via High resolution - Transmission Electron microscopy. Theoretical investigations were carried out via hybrid simulation approach of molecular dynamics simulation and analytical modelling. Molecular dynamics study revealed the spatial and temporal evolution of electron and lattice temperature of NiTi melt pool due to ablation at various laser fluences. The subsequent temporal dynamics of melt-pool temperature along the depth revealed the phase separation via spinodal decomposition process after 40 picoseconds post irradiation of NiTi with ultrafast laser pulse. The analytical modelling incorporating phase explosion theory estimated the thermophysical expansion of ablated chunks and subsequent fragmentation of NiTi melt pool in liquid-vapor co-existing phase. The parameters of mathematical modelling were evaluated in-conjunction with the experimental results of size distribution of NPs at the laser fluence of 15 J/cm2. Later, the hybrid mathematical model was employed to predict the size of NiTi NPs ablated at higher laser fluences of 30 J/cm2 and 45 J/cm2 and the results were experimentally verified.

Date of Conference: 16–21 May 2010 Conference name: Conference on Lasers and Electro-Optics 2010 Controlled modification of implant surfaces using femtosecond, picosecond and nanosecond pulses from home-built all-fiber-integrated lasers is demonstrated. Picosecond and femtosecond pulses offer superior control over the surface texture. Increasing cell attachment to surface is discussed. ©2010 Optical Society of America.

Infrared multiphoton adsorption at 3.1 μm in crystalline GaAs depends on the crystal alignment to the laser polarization. This reveals the roles electron mass and band structure play in multiphoton ionization inside solids., Also found at: https://ieeexplore.ieee.org/document/5950673, 2011 Conference on Lasers and Electro-Optics, CLEO 2011, May 1-6, 2011, Baltimore, MD, USA

A self-starting, passively stabilized, monolithic all-polarization- maintaining femtosecond Yb-fiber master oscillator / power amplifier with very high operational and environmental stability is demonstrated. The system is based on the use of two different photonic crystal fibers. One is used in the oscillator cavity for dispersion balancing and nonlinear optical limiting, and another one is used for low-nonlinearity final pulse recompression. The chirped-pulse amplification and recompression of the 232-fs, 45-pJ/pulse oscillator output yields a final direct fiber-end delivery of 7.3-nJ energy pulses of around 297 fs duration. Our laser shows exceptional stability. No Q-switched modelocking events were detected during 4-days long observation. An average fluctuation of only 7.85 x 10(-4) over the mean output power was determined as a result of more than 6-hours long measurement. The laser is stable towards mechanical disturbances, and maintains stable modelocking in the temperature range of at least 10 - 40 (0)C.

[EN]The dispersion scan (d-scan) technique has emerged as a simple-to-implement characterization method for ultrashort laser pulses. D-scan traces are intuitive to interpret and retrieval algorithms that are both fast and robust have been developed to obtain the spectral phase and the temporal pulse profile. Here, we shortly review the second harmonic generation d-scan technique, focusing predominantly on results obtained at the Lund Laser Centre. We describe and compare recent implementations for the characterization of few- and multi-cycle pulses as well as two different approaches for recording d-scan traces in a single shot, thus showing the versatility of the technique., Vetenskapsrådet (2013-8185, 2016-04907, 2019-06275); European Research Council (654148 Laserlab-Europe, proof of concept grant SISCAN-789992); Knut och Alice Wallenbergs Stiftelse; Junta de Castilla y León (SA136P20, SA287P18); Ministerio de Economía y Competitividad (EQC2018-004117-P, FIS2017-87970-R); Agência Nacional de Inovação (045932, 04/SI/2019, Projetos ID industrial à escala, PT2020); Fundação para a Ciência e a Tecnologia (‘Ultragraf’ M-ERA -NET4/0004/2016, PTDC/FIS-OTI/32213/2017, UIDB/04968/2020); Programa Operacional Temático Factores de Competitividade (NORTE-01-0145-FEDER-022096).

Photonic devices that can guide, transfer, or modulate light are highly desired in electronics and integrated silicon (Si) photonics. Here, we demonstrate for the first time, to the best of our knowledge, the creation of optical waveguides deep inside Si using femtosecond pulses at a central wavelength of 1.5 mu m. To this end, we use 350 fs long, 2 mu J pulses with a repetition rate of 250 kHz from an Er-doped fiber laser, which we focused inside Si to create permanent modifications of the crystal. The position of the beam is accurately controlled with pump-probe imaging during fabrication. Waveguides that were 5.5 mm in length and 20 mu m in diameter were created by scanning the focal position along the beam propagation axis. The fabricated waveguides were characterized with a continuous-wave laser operating at 1.5 mu m. The refractive index change inside the waveguide was measured with optical shadowgraphy, yielding a value of 6 x 10(-4), and by direct light coupling and far-field imaging, yielding a value of 3.5 x 10(-4). The formation mechanism of the modification is discussed. (C) 2017 Optical Society of America

International audience; We demonstrate phase-matched difference frequency generation in the emerging nonlinear crystal La3Ga5.5Ta0.5O14. Tunable wavelengths between 1.4 and 4.7 μm are generated by using femtosecond sources. We also report on the measurements of the optical damage threshold in the femtosecond regime and on the nonlinear refractive index n2.