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Femtosecond laser

Kathrin J Mohler, Bernhard J Bohn, Ming Yan, Gwénaëlle Mélen, Theodor W Hänsch, Nathalie Picqué
We extend the technique of multiplex coherent Raman spectroscopy with two femtosecond mode-locked lasers to oscillators of a pulse repetition frequency of 1 GHz. We demonstrate a spectra of liquids, which span 1100  cm<sup>-1</sup> of Raman shifts. At a resolution of 6  cm<sup>-1</sup>, their measurement time may be as short as 5 μs for a refresh rate of 2 kHz. The waiting period between acquisitions is improved 10-fold compared to previous experiments with two lasers of 100-MHz repetition frequencies...
January 15, 2017: Optics Letters
A I Chernov, M A Kozhaev, I V Savochkin, D V Dodonov, P M Vetoshko, A K Zvezdin, V I Belotelov
In most of the previous studies of the spin wave optical generation in magnetic dielectrics, the backward volume spin waves were excited. Here we modified the parameters of the circularly polarized optical pump beams emitted by femtosecond laser to reveal surface spin waves in bismuth iron garnet thin film. Beams that are larger than 10 μm in diameter generate both surface and volume spin waves with only one spectral peak near the ferromagnetic resonance. On the contrary, narrower beams excite predominantly surface spin waves of higher frequency, providing an additional peak in the spin wave spectrum...
January 15, 2017: Optics Letters
Jason C Ng, Peter R Herman, Li Qian
Second harmonic generation (SHG) is demonstrated in femtosecond laser written waveguides in fused silica through a combination of thermal poling and laser-based quasi-phase-matching (QPM) techniques. Quasi-phase-matching was controlled by the periodic erasure of induced nonlinearity through femtosecond laser erasure. A maximum SHG conversion efficiency of 6.6±0.5×10<sup>-5</sup>%/W is reported for the fundamental wavelength of 1552.8 nm with a phase-matching bandwidth of 4.4 nm for a 10.0 mm long waveguide...
January 15, 2017: Optics Letters
S Mondal, Q Wei, W J Ding, H A Hafez, M A Fareed, A Laramée, X Ropagnol, G Zhang, S Sun, Z M Sheng, J Zhang, T Ozaki
We demonstrate an intense broadband terahertz (THz) source based on the interaction of relativistic-intensity femtosecond lasers with aligned copper nanorod array targets. For copper nanorod targets with a length of 5 μm, a maximum 13.8 times enhancement in the THz pulse energy (in ≤20 THz spectral range) is measured as compared to that with a thick plane copper target under the same laser conditions. A further increase in the nanorod length leads to a decrease in the THz pulse energy at medium frequencies (≤20 THz) and increase of the electromagnetic pulse energy in the high-frequency range (from 20-200 THz)...
January 10, 2017: Scientific Reports
Christophe Panthier, Florent Costantini, Jean Claude Rigal-Sastourné, Antoine Brézin, Chadi Mehanna, Mikael Guedj, Dominique Monnet
PURPOSE: To compare the shape of the capsulotomy, its change, and its impact on visual quality over 1 year using the femtosecond laser system from the manual technique. METHODS: In this two-center cross-sectional study from May 2012 to June 2013, each patient had femtosecond laser-assisted cataract surgery in one eye (FLACS group) and conventional phacoemulsification cataract surgery in the other eye (CPCS group). An evaluation of the capsulotomy was performed using retroillumination slit-lamp photographs at 7 days, 6 months, and 1 year after surgery...
January 1, 2017: Journal of Refractive Surgery
Gustavo K Marino, Marcony R Santhiago, Steven E Wilson
PURPOSE: To characterize the location and regularity of the opaque bubble layer (OBL) in the corneal stroma after femtosecond laser-assisted LASIK (FS-LASIK) flap generation. METHODS: In this prospective study, 30 eyes of 15 patients who had FS-LASIK surgery for myopia, astigmatism, and/or hyperopia were included. Screen captures were obtained at the end of the flap creation and the eyes with hard type OBL were immediately imaged with anterior segment optical coherence tomography...
January 1, 2017: Journal of Refractive Surgery
Rohit Shetty, Rushad Shroff, Kalyani Deshpande, Roshan Gowda, Sumeet Lahane, Chaitra Jayadev
PURPOSE: To analyze refractive outcomes of wavefront-optimized (WFO) ablation and topography-guided custom ablation (TCAT) profiles using the Allegretto Wave excimer laser platform (Alcon Laboratories, Inc., Fort Worth, TX) in the treatment of myopia. METHODS: Sixty eyes of 30 patients who underwent LASIK were included in this prospective interventional study. WFO ablation was performed in one eye (WFO group) and TCAT in the fellow eye (TCAT group). The WaveLight FS200 femtosecond laser (Alcon Laboratories, Inc...
January 1, 2017: Journal of Refractive Surgery
Sizuo Luo, Wenhui Hu, Jiaqi Yu, Ruihan Zhu, Lanhai He, Xiaokai Li, Pan Ma, Chuncheng Wang, Fuchun Liu, Wim G Roeterdink, Steven Stolte, Dajun Ding
Rotational dynamics of quantum state selected and un-selected CH3I molecules in intense femtosecond laser fields has been studied. The orientation and alignment evolutions are derived from a pump-probe measurement and in good agreement with the numerical results from the time dependent Schrödinger equation (TDSE) calculation. The different rotational transitions through nonresonant Raman process have been assigned from the Fourier analysis of the orientation and alignment revivals. These revivals are derived from a pump-probe measurement and in good agreement with the numerical results from the time dependent Schr¨odinger equation (TDSE) calculation...
January 9, 2017: Journal of Physical Chemistry. A
Heewon Yang, Byungheon Han, Junho Shin, Dong Hou, Hayun Chung, In Hyung Baek, Young Uk Jeong, Jungwon Kim
Ultrafast electron-based coherent radiation sources, such as free-electron lasers (FELs), ultrafast electron diffraction (UED) and Thomson-scattering sources, are becoming more important sources in today's ultrafast science. Photocathode laser is an indispensable common subsystem in these sources that generates ultrafast electron pulses. To fully exploit the potentials of these sources, especially for pump-probe experiments, it is important to achieve high-precision synchronization between the photocathode laser and radio-frequency (RF) sources that manipulate electron pulses...
January 9, 2017: Scientific Reports
Santosh Karki, Habiballah Sistani, Jieutonne J Archer, Fengjian Shi, Robert J Levis
Charge state distributions are measured using mass spectrometry for both native and denatured cytochrome c and myoglobin after laser vaporization from the solution state into an electrospray (ES) plume consisting of a series of solution additives differing in gas-phase basicity. The charge distribution depends on both the pH of the protein solution prior to laser vaporization and the gas-phase basicity of the solution additive employed in the ES solvent. Cytochrome c (myoglobin) prepared in solutions with pH of 7...
January 6, 2017: Journal of the American Society for Mass Spectrometry
Jing Zhao, Yang Shen, Mi Tian, Ling Sun, Yu Zhao, Xiaoyu Zhang, Xingtao Zhou
PURPOSE: To investigate the feasibility of allotransplanting extracted lenticules after femtosecond laser-assisted small incision lenticule extraction (SMILE) in rabbits and the subsequent healing process. METHODS: Fourteen New Zealand white rabbits were divided evenly into 2 groups. The rabbits in group A received SMILE procedures with a -6.00 D correction. The lenticules from group A were immediately inserted into a femtosecond laser-created corneal stromal pocket in group B...
February 2017: Cornea
Carlos H Gordillo, Juan C Grandin, Roger Zaldivar, Roberto Zaldivar, Adriana C Lotfi
PURPOSE: To evaluate outcomes, efficacy, and safety of intrastromal corneal ring segment implantation for treatment of keratoconus combined with collagen cross-linking (CXL) with 1-year follow-up. METHODS: One hundred nineteen eyes of 82 patients with keratoconus (37 females) underwent femtosecond (Intralase FS; Abbott Medical Optics, Inc) laser-assisted intrastromal corneal ring segment implantation (INTRASEG; Gamma Vision) with flash CXL (18 mW/cm for 5 minutes)...
February 2017: Cornea
Marcelo F Ciappina, J Perez-Hernandez, Alexandra Landsman, William Okell, Sergey Zherebtsov, Benjamin Förg, Johannes Schötz, Lennart Seiffert, Thomas Fennel, Tahir Shaaran, Tomas Zimmermann, Alexis Chacón, Roland Guichard, Amelle Zair, John Tisch, J Marangos, Tobias Witting, Avi Braun, Stefan Maier, Luis Roso, Michael Krüger, Peter Hommelhoff, Matthias Kling, Ferenc Krausz, Maciej Lewenstein
Recently two emerging areas of research, attosecond and nanoscale physics, have started to come together. Attosecond physics deals with phenomena occurring when ultrashort laser pulses, with duration on the femto- and sub-femtosecond time scales, interact with atoms, molecules or solids. The laser-induced electron dynamics occurs natively on a timescale down to a few hundred or even tens of attoseconds, which is comparable with the optical field. For comparison, the revolution of an electron on a 1s orbital of a hydrogen atom is 152 as...
January 6, 2017: Reports on Progress in Physics
Oliver Kliebisch, Dirk C Heinecke, Thomas Dekorsy
An ultrafast time-domain spectroscopy system employing asynchronous optical sampling at a repetition rate of 10 GHz is presented. Two ultra-compact Ti:sapphire femtosecond ring lasers allow to achieve scan rates as high as 100 kHz for a 100 ps long time window and a time-delay resolution of 100 fs. The feasibility of this high-speed ASOPS system is evaluated by performing THz time domain spectroscopy on molecular gases where signal-to-noise ratios exceeding 30 dB for averaging times in the millisecond range have been obtained...
December 26, 2016: Optics Express
Wenlong Tian, Zhaohua Wang, Jiangfeng Zhu, Zhiyi Wei
We report a multi-gigahertz (GHz) repetition-rate femtosecond MgO:PPLN optical parametric oscillator (OPO) harmonically pumped by a 75.6 MHz Kerr-lens mode-locked Yb:KGW laser. By fractionally increasing the OPO cavity length, we obtained OPO operation up to the 493rd harmonic of the pump laser repetition rate, corresponding to a repetition rate as high as 37.3 GHz. Using a 1.5% output coupler, we are able to extract signal pulses with up to 260 mW average power at the 102nd harmonic (7.7 GHz) and 90 mW at the 493rd harmonic (37...
December 26, 2016: Optics Express
M Pergament, G Palmer, M Kellert, K Kruse, J Wang, L Wissmann, U Wegner, M Emons, D Kane, G Priebe, S Venkatesan, T Jezynski, F Pallas, M J Lederer
We present the main features of the final prototype of a pulsed optical laser, developed for pump-probe and other experiments in conjunction with the femtosecond x-ray beams at the European X-ray free-electron laser facility. Adapted to the temporal x-ray emission pattern of the facility, the laser provides 10 Hz bursts of up to 600 µs duration with intra-burst pulse frequencies as high as 4.5 MHz. In this mode, we have generated pulses as short as 12 fs at 350 W average power during the burst and with beam qualities close to the diffraction limit...
December 26, 2016: Optics Express
Stefan Lerch, André Stefanov
We apply the method of quantum state tomography for the reconstruction of classical laser pulses. The scheme is based on linear inversion, has no need for iterative inversion algorithm or deconvolution, and accounts for partial coherence. The reconstruction protocol is successfully tested on amplitude and phase shaped femtosecond pulses.
December 26, 2016: Optics Express
Runze Chen, Yuhua Tang, Xin Zheng, Tian Jiang
Layered black phosphorus nanosheets (BPNs) offer potential uses in nanoelectronic and photonics applications. This work demonstrates giant saturable absorption (SA) and two-photon absorption (TPA) of BPNs under femtosecond visible-to-mid-infrared laser-pulse excitation. In addition, the excited carrier dynamics of BPNs were also studied with ultrafast pump-probe technology. Measurements demonstrated that the nonlinear absorption properties of BPNs strongly depend on excitation wavelength and intensity. BPNs moved from SA to TPA under increasing laser intensities at 800, 1160, 1300, and 1550 nm but showed a purely TPA response at 2000 nm, as gauged by measuring BPN nonlinear absorption coefficients...
December 20, 2016: Applied Optics
Rui Li, Lingyan Du, Fei Tang, Yadong Jiang, Zhiming Wu
Microstructured Te-doped silicon is prepared via a femtosecond laser irradiating Si coated with Si-Te bilayer films, and photodiodes are successfully fabricated from this material. The samples are thermally annealed at 773 K for three different time durations. The effects of annealing time on microstructures, infrared absorptance, and photosensitivity of Te-doped silicon are investigated. From the scanning electronic microscope images and the optical absorptance spectra, the results show that the infrared absorptance decreases with the increase of annealing time durations, while the infrared photoresponse follows an opposite tendency...
December 20, 2016: Applied Optics
E A Zlobina, S I Kablukov, A A Wolf, A V Dostovalov, S A Babin
High beam quality and narrow spectrum have been obtained in a Raman fiber laser based on a 1.1 km long graded-index fiber directly pumped by a multimode 915 nm laser diode. The generation of a near-diffraction-limited beam at 954 nm with M<sup>2</sup>≤1.27 and Δλ=0.42  nm at an output power above 10 W is enabled by a cavity mirror made of a special fiber Bragg grating inscribed by a femtosecond technique in the central part of the graded-index fiber core.
January 1, 2017: Optics Letters
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