[1]红外动目标识别跟踪系统的dsp+fpga实现




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Femtosecond and Attosecond Pulse


147

Author(s): Zhou, W (Zhou Wei); Liu, XL (Liu XiuLi); Lu, XH (Lue XiaoHua); Li, JS (Li JiaSong); Luo, QM (Luo QingMing); Zeng, SQ (Zeng ShaoQun)

Title: Monitor and control of neuronal activities with femtosecond pulse laser

Source: CHINESE SCIENCE BULLETIN, 53 (5): 687-694 MAR 2008

Abstract:

Combined with the fluorescence labeling technique, two-photon microscopy excited with femtosecond pulse laser has become an important tool for neuroscience research. In this research, the calcium signals from neurons in rat cortex slice were monitored by a custom-built two-photon microscopy, and the spontaneous calcium signals and the pharmacological responses as well as the responses to femtosecond pulse laser stimulation were recorded. The results showed that the amplitude of the calcium signals increased in direct proportion to the corresponding electrical activities. Glutamate induced a calcium transient, but continuous application resulted in smaller response. Simultaneous monitoring of neuronal populations distinguished the neurons of different microcircuits. The femtosecond pulse laser induced local or global calcium signals in the pyramidal neurons. The approach of interrogation and control of neural activities using femtosecond pulse laser is non-contact, nondestructive, repeatable, and without any additional substrates, which will contribute to the development of neuroscience.


Addresses: Huazhong Univ Sci & Technol, Wuhan Natl Lab Optoelect, Britton Chance Ctr Biomed Photon, Wuhan 430074, Peoples R China

Reprint Address: ZENG, SQ, HUAZHONG UNIV SCI & TECHNOL, WUHAN NATL LAB OPTOELECT, BRITTON CHANCE CTR BIOMED PHOTON, WUHAN 430074, PEOPLES R CHINA

Author's E-mail: sqzeng@mail.hust.edu.cn

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148

Author(s): von Vacano, B; Rehbinder, J; Buckup, T; Motzkus, M

Title: Microanalytical nonlinear single-beam spectroscopy combining an unamplified femtosecond fibre laser, pulse shaping and interferometry

Source: APPLIED PHYSICS B-LASERS AND OPTICS, eFIRST

Abstract:

Nonlinear vibrational spectroscopy using a single beam of femtosecond pulses from an unamplified fibre laser oscillator is demonstrated. To achieve high spectral resolution and sensitive signal detection with the picojoule pulse energies available, pulse shaping and integrated interferometric detection is employed. The spectroscopic technique used is coherent anti-Stokes Raman scattering (CARS), which yields well-resolved spectra of molecular vibrations in the 100-350 cm-1 domain of halomethane samples in the liquid phase. We explore the implications of phase control for the interferometric detection of weak signals. The presented combination of a fiber laser, pulse shaping and CARS microspectroscopy is a first example of simplified schemes for compact and robust nonlinear spectroscopic detection and sensing, which is demonstrated exemplarily by on-line monitoring of the chemical composition in a microfluidic flow cell.

Addresses: Physikalische Chemie, Philipps-Universitaet Marburg, Marburg, 35043, Germany

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149

Author(s): Kosareva, OG (Kosareva, O. G.); Panov, NA (Panov, N. A.); Uryupina, DS (Uryupina, D. S.); Kurilova, MV (Kurilova, M. V.); Mazhorova, AV (Mazhorova, A. V.); Savel'ev, AB (Savel'ev, A. B.); Volkov, RV (Volkov, R. V.); Kandidov, VP (Kandidov, V. P.); Chin, SL (Chin, S. L.)

Title: Optimization of a femtosecond pulse self-compression region along a filament in air

Source: APPLIED PHYSICS B-LASERS AND OPTICS, 91 (1): 35-43 APR 2008

Abstract:

We have identified the pulse self-compression region in a filament produced by 55 fs, 4 mJ, 805 nm radiation propagating in air without geometrical focusing. In our experiment the pulse self-compression region is attained by the propagation distance, where the shortest wavelength in the supercontinuum blue wing reaches a minimum, and the growing conversion efficiency to white light has a large gradient. Numerical tracking of the pulse along the filament shows a single-peak 9 fs pulse with a flat spectral phase at the optimum compression distance.

Addresses: Moscow MV Lomonosov State Univ, Dept Phys, Ctr Int Laser, Moscow 119991, Russia

FSUE SPA Astrophys, Moscow 125424, Russia

Univ Laval, Ctr Opt Photon & Laser, Quebec City, PQ G1K 7P4, Canada

Univ Laval, Dept Phys Genie Phys & Opt, Quebec City, PQ G1K 7P4, Canada

Reprint Address: KOSAREVA, OG, MOSCOW MV LOMONOSOV STATE UNIV, DEPT PHYS, CTR INT LASER, MOSCOW 119991, RUSSIA

Author's E-mail: kosareva@phys.msu.ru

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150

Author(s): Ghotbi, M (Ghotbi, M.); Esteban-Martin, A (Esteban-Martin, A.); Ebrahim-Zadeh, M (Ebrahim-Zadeh, M.)

Title: Tunable, high-repetition-rate, femtosecond pulse generation in the ultraviolet

Source: OPTICS LETTERS, 33 (4): 345-347 FEB 15 2008

Abstract:

We report efficient generation of tunable femtosecond pulses in the ultraviolet (UV) by intracavity doubling of a visible femtosecond optical parametric oscillator (OPO). The OPO, based on a 400 mu m BiB3O6 crystal and pumped at 415 nm in the blue, can provide visible femtosecond signal pulses across 500-710 nm. Using a 500 mu m crystal of beta-BaB2O4 internal to the OPO cavity, efficient frequency doubling of the signal pulses into the UV is achieved, providing tunable femtosecond pulses across 250-355 nm with up to 225 mW of average power at 76 MHz. Cross-correlation measurements result in UV pulses with durations down to 132 fs for 180 fs blue pump pulses. (c) 2008 Optical Society of America.

Addresses: ICFO Inst Ciencies Foton, Barcelona 08860, Spain

Inst Catalana Rec & Estudis Avancats, Barcelona 08010, Spain

Reprint Address: EBRAHIM-ZADEH, M, ICFO INST CIENCIES FOTON, MEDITERRANEAN TECHNOL PK, BARCELONA 08860, SPAIN

Author's E-mail: majid.ebrahim@icfo.es

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151

Author(s): Kornaszewski, L (Kornaszewski, Lukasz); Kohler, M (Kohler, Markus); Sapaev, UK (Sapaev, Usman K.); Reid, DT (Reid, Derryck T.)

Title: Designer femtosecond pulse shaping using grating-engineered quasi-phase-matching in lithium niobate

Source: OPTICS LETTERS, 33 (4): 378-380 FEB 15 2008

Abstract:

The generation of tailored femtosecond pulses with fully engineered intensity and phase profiles is demonstrated using second-harmonic generation of an Er:fiber laser in an aperiodically poled lithium niobate crystal in the undepleted pump regime. Second-harmonic pulse shapes, including Gaussian, stepped, square, and multiple pulses have been characterized using cross-correlation frequency-resolved optical gating and have been shown to agree well with theory. (C) 2008 Optical Society of America.

Addresses: Heriot Watt Univ, Ultrafst Opt Grp, Sch Engn & Phys Sci, Edinburgh EH14 4AS, Midlothian, Scotland

Uzbek Acad Sci, NPO Akadempribor, Tashkent 700125, Uzbekistan

Reprint Address: KORNASZEWSKI, L, HERIOT WATT UNIV, ULTRAFST OPT GRP, SCH ENGN & PHYS SCI, EDINBURGH EH14 4AS, MIDLOTHIAN, SCOTLAND

Author's E-mail: lwk1@hw.ac.uk

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152

Author(s): Klaiber, M (Klaiber, Michael); Hatsagortsyan, KZ (Hatsagortsyan, Karen Z.); Muller, C (Mueller, Carsten); Keitel, CH (Keitel, Christoph H.)

Title: Coherent hard x rays from attosecond pulse train-assisted harmonic generation

Source: OPTICS LETTERS, 33 (4): 411-413 FEB 15 2008

Abstract:

High-order harmonic generation from atomic systems is considered in the crossed fields of a relativistically strong infrared laser and a weak attosecond pulse train of soft x rays. Due to one-photon ionization by the x-ray pulse, the ionized electron obtains a starting momentum that compensates the relativistic drift, which is induced by the laser magnetic field, and allows the electron to efficiently emit harmonic radiation upon recombination with the atomic core in the relativistic regime. This way, short pulses of coherent hard x rays of up to 40 keV energy can be generated. (C) 2008 Optical Society of America.

Addresses: Max Planck Inst Kernphys, D-69117 Heidelberg, Germany

Phys Inst Univ, D-79104 Freiburg, Germany

Reprint Address: KEITEL, CH, MAX PLANCK INST KERNPHYS, SAUPFERCHECKWEG 1, D-69117 HEIDELBERG, GERMANY

Author's E-mail: keitel@mpi-hd.mpg.de

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153

Author(s): Ruchon, T (Ruchon, T.); Hauri, CP (Hauri, C. P.); Varju, K (Varju, K.); Mansten, E (Mansten, E.); Swoboda, M (Swoboda, M.); Lopez-Martens, R (Lopez-Martens, R.); L'Huillier, A (L'Huillier, A.)

Title: Macroscopic effects in attosecond pulse generation - art. no. 025027

Source: NEW JOURNAL OF PHYSICS, 10: 25027-25027 FEB 29 2008

Abstract:

We examine how the generation and propagation of high-order harmonics in a partly ionized gas medium affect their strength and synchronization. The temporal properties of the resulting attosecond pulses generated in long gas targets can be significantly influenced by macroscopic effects, in particular by the intensity in the medium and the degree of ionization which control the dispersion. Under some conditions, the use of gas targets longer than the absorption length can lead to the generation of compressed attosecond pulses. We show these macroscopic effects experimentally, using a 6 mm-long argon-filled gas cell as the generating medium.

Addresses: Lund Univ, Dept Phys, SE-22100 Lund, Sweden

ENSTA, CNRS, Ecole Polytech, Lab Opt Appl,UMR 7639, F-91761 Palaiseau, France

Reprint Address: L'HUILLIER, A, LUND UNIV, DEPT PHYS, POB 118, SE-22100 LUND, SWEDEN

Author's E-mail: anne.lhuillier@fysik.lth.se

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154

Author(s): Peng, LY (Peng, Liang-You); Pronin, EA (Pronin, Evgeny A.); Starace, AF (Starace, Anthony F.)

Title: Attosecond pulse carrier-envelope phase effects on ionized electron momentum and energy distributions: roles of frequency, intensity and an additional IR pulse - art. no. 025030

Source: NEW JOURNAL OF PHYSICS, 10: 25030-25030 FEB 29 2008

Abstract:

The effects of the carrier-envelope phase (CEP) of a few-cycle attosecond pulse on ionized electron momentum and energy spectra are analyzed, both with and without an additional few-cycle IR pulse. In the absence of an IR pulse, the CEP-induced asymmetries in the ionized electron momentum distributions are shown to vary as the 3/2 power of the attosecond pulse intensity. These asymmetries are also found to satisfy an approximate scaling law involving the frequency and intensity of the attosecond pulse. In the presence of even a very weak IR pulse (having an intensity of the order of 10(11)-10(12)W cm(-2)), the attosecond pulse CEP-induced asymmetries in the ionized electron momentum distributions are found to be significantly augmented. In addition, for higher IR laser intensities, we observe for low electron energies peaks separated by the IR photon energy in one electron momentum direction along the laser polarization axis; in the opposite direction, we find structured peaks that are spaced by twice the IR photon energy. Possible physical mechanisms for such asymmetric, low-energy structures in the ionized electron momentum distribution are proposed. Our results are based on single active electron solutions of the three-dimensional, time-dependent Schrodinger equation including atomic potentials appropriate for the H and He atoms.

Addresses: Univ Nebraska, Dept Phys & Astron, Lincoln, NE 68588 USA

Peking Univ, State Key Lab Mesoscop Phys, Beijing 100871, Peoples R China

Peking Univ, Dept Phys, Beijing 100871, Peoples R China

Reprint Address: PENG, LY, UNIV NEBRASKA, DEPT PHYS & ASTRON, LINCOLN, NE 68588 USA

Author's E-mail: astarace1@UNL.edu

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155

Author(s): Lorin, E (Lorin, E.); Chelkowski, S (Chelkowski, S.); Bandrauk, AD (Bandrauk, A. D.)

Title: Attosecond pulse generation from aligned molecules - dynamics and propagation in H-2(+) - art. no. 025033

Source: NEW JOURNAL OF PHYSICS, 10: 25033-25033 FEB 29 2008

Abstract:

The dynamics and propagation effects in attosecond (asec) pulse generation from high-order harmonic generation (HHG) of aligned one-dimensional (1D) H-2(+) molecules are investigated from numerical solutions of fully coupled Maxwell and time-dependent Schrodinger equations ( Maxwell-TDSEs), in the highly nonlinear nonperturbative regime of laser - molecule interaction. Density, laser-phase and propagation length effects are studied on the total electric field and nonlinear polarization from the Maxwell-TDSE for intense few cycle (800 nm) laser pulses interacting with a 1D H-2(+) gas. We show how single and double asec pulses can be generated and propagated as a function of the phase of individual harmonics created by ultrashort intense laser pulses in aligned H-2(+) molecules. We find furthermore extension of maximum HHG plateaux with increasing gas pressure.

Addresses: Ctr Rech Math, Montreal, PQ H3T 1J4, Canada

Univ Sherbrooke, Fac Sci, Chim Theor Lab, Sherbrooke, PQ J1K 2R1, Canada

Reprint Address: LORIN, E, UNIV ONTARIO INST TECHNOL, FAC SCI, 2000 SIMCOE ST N, OSHAWA, ON L1H 7Y4, CANADA

Author's E-mail: Emmanuel.Lorin@uoit.ca

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156

Author(s): Nabekawa, Y (Nabekawa, Y.); Midorikawa, K (Midorikawa, K.)

Title: Interferometric autocorrelation of an attosecond pulse train calculated using feasible formulae - art. no. 025034

Source: NEW JOURNAL OF PHYSICS, 10: 25034-25034 FEB 29 2008

Abstract:

The autocorrelation trace of an attosecond pulse train (APT) directly revealed the pulse envelope in our recent experiment on measuring the two-photon Coulomb explosion of a nitrogen molecule as a correlation signal. Although the spatial overlap of the two replicas of the APT in the correlation measurement was only achieved near the focal region owing to the spatial split of the measured APT field, which is a situation quite different from that of the correlation measurement using a Michelson interferometer, the interference fringes clearly appeared on the correlation envelope and proved the odd symmetry of the electric field to the time translation with a half-period of the driving laser field. In this paper, we show a simple and practical analysis for the propagation and the nonlinear interaction of an APT to simulate the experimental result of the interferometric autocorrelation of the spatially split APT. The spatial convolution of the focused electric field is essential for obtaining the fringes. We also discuss how the autocorrelation should be described in the context of the second-order perturbation theory within a dipole approximation.

Addresses: RIKEN, Laser Technol Lab, Wako, Saitama 3510198, Japan

Reprint Address: NABEKAWA, Y, RIKEN, LASER TECHNOL LAB, HIROSAWA 2-1, WAKO, SAITAMA 3510198, JAPAN

Author's E-mail: nabekawa@riken.jp

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157

Author(s): Mendoza-Yero, O (Mendoza-Yero, Omel); Minguez-Vega, G (Minguez-Vega, Gladys); Lancis, J (Lancis, Jesus); Tajahuerce, E (Tajahuerce, Enrique); Climent, V (Climent, Vicent)

Title: Spectral analysis of femtosecond pulse diffraction through binary diffractive optical elements: theory and experiment

Source: OPTICS EXPRESS, 16 (4): 2541-2546 FEB 18 2008

Abstract:

We report on the changes in the spectrum of a femtosecond pulse originated by diffraction of the ultrashort waveform through a circularly symmetric binary diffractive optical element. The analysis is performed in the framework of the Rayleigh-Sommerfeld formulation of the diffraction, where an analytical expression for the monochromatic amplitude distribution close to the optical axis is obtained. To corroborate our results, we experimentally measure the variations of the pulse spectrum within the collecting area of a spectrometer located at the output plane. Multiple splitting of the pulse spectrum in the vicinity of a focal position and a phase singularity are shown. (C) 2008 Optical Society of America.


Addresses: Unic Jaume I, Dept Fis, GROC, E-12080 Castellon de La Plana, Spain

Reprint Address: MENDOZA-YERO, O, UNIC JAUME I, DEPT FIS, GROC, E-12080 CASTELLON DE LA PLANA, SPAIN

Author's E-mail: omendoza@uji.es

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158

Author(s): Orlando, G (Orlando, Gianfranco); Castiglia, G (Castiglia, Giuseppe); Corso, PP (Corso, Pietro Paolo); Fiordilino, E (Fiordilino, Emilio)

Title: Bremsstrahlung from a repulsive potential: attosecond pulse generation - art. no. 055601

Source: JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS, 41 (5): 55601-55601 MAR 14 2008

Abstract:

The collision of an electron against a repulsive potential in the presence of a laser field is investigated. It is found that a sufficiently strong laser field forces the electron to remain in the neighbourhood of the repulsive potential causing bremsstrahlung. By appropriately filtering the emitted signal, an electron in the presence of a repulsive potential is capable of generating attosecond pulses.


Addresses: Univ Palermo, CNISM, I-90123 Palermo, Italy

Univ Palermo, Dipartimento Sci Fis & Astron, I-90123 Palermo, Italy

Reprint Address: ORLANDO, G, UNIV PALERMO, CNISM, VIA ARCHIRAFI 36, I-90123 PALERMO, ITALY

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159

Author(s): Liu, WH (Liu Wei-Hua); Song, XZ (Song Xiao-Zhong); Wang, YS (Wang Yi-Shan); Liu, HJ (Liu Hong-Jun); Zhao, W (Zhao Wei); Liu, XM (Liu Xue-Ming); Peng, QJ (Peng Qin-Jun); Xu, ZY (Xu Zu-Yan)

Title: Experimental research of supercontinuum generation by femtosecond pulse in highly nonlinear photonic crystal fiber

Source: ACTA PHYSICA SINICA, 57 (2): 917-922 FEB 2008

Abstract:

We pumped a 1m long highly nonlinear photonic crystal fiber by a Ti: sapphire laser and generated a supercontinuum with the wavelength extension form 420-1700 nm, of which the output power was about 170 mW and we conversion efficiency was above 20%. The experiment result was particularly analyzed and compared with calculated result, and we consider the main reasons of supercontinuum generation was fission of high-order solitons and four-wave mixing. We also researched the supercontinuum generation under different pump power and wavelength conditions. With the pump power increased gradually in the same fiber, the output spectrum can be divided into initial broadening stage, dramatic broadening stage and saturation broadening stage. When the output spectrum is in the initial broadening stage or saturation broadening stage, there exists some residual pump, when the output spectrum is in the dramatic broadening stage, the highest conversion efficiency is obtained. When the pump wavelength is in the anomalous dispersion region of the fiber, the spectrum width is far broader than that in the zero dispersion region, but the shapes of the spectra are very similar. These conclusions provide valuable reference for supercontinuum system optimization and control.


Addresses: Wuhan Polytech Univ, Dept Math & Phys, Wuhan 430023, Peoples R China

Chinese Acad Sci, Xian Inst Opt & Precis Mech, State Key Lab Transient Opt & Technol, Xian, Peoples R China

Chinese Acad Sci, Inst Phys, Lab Opt Phys, Beijing 100080, Peoples R China

Reprint Address: LIU, WH, WUHAN POLYTECH UNIV, DEPT MATH & PHYS, WUHAN 430023, PEOPLES R CHINA

Author's E-mail: liuwhsky@126.com

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160

Author(s): Kosareva, O; Panov, N; Uryupina, D; Kurilova, M; Mazhorova, A; Savel' ev, A; Volkov, R; Kandidov, V; Chin, S

Title: Optimization of a femtosecond pulse self-compression region along a filament in air

Source: APPLIED PHYSICS B-LASERS AND OPTICS, eFIRST

Abstract:

We have identified the pulse self-compression region in a filament produced by 55 fs, 4 mJ, 805 nm radiation propagating in air without geometrical focusing. In our experiment the pulse self-compression region is attained by the propagation distance, where the shortest wavelength in the supercontinuum blue wing reaches a minimum, and the growing conversion efficiency to white light has a large gradient. Numerical tracking of the pulse along the filament shows a single-peak 9 fs pulse with a flat spectral phase at the optimum compression distance.


Addresses: International Laser Center, Physics Department, M.V. Lomonosov Moscow State University, Moscow, 119991, Russia

FSUE "SPA Astrophysica , Moscow, 125424, Russia

Centre d' Optique, Photonique et Laser (COPL) and Departement de Physique, de Genie Physique et d' Optique, Universite Laval, Quebec, Quebec, G1K 7P4, Canada

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161

Author(s): Li, X (Li Xia); Mang, H (Mang Hui); Mang, XY (Mang Xiang-Yun); Mang, SA (Mang Shi-An); Chen, GL (Chen Guo-Liang); Wang, ZG (Wang Zu-Geng); Sun, ZR (Sun Zhen-Rong)

Title: High resolution mode-selective excitation by adaptive femtosecond pulse shaping

Source: CHINESE PHYSICS LETTERS, 25 (2): 528-531 FEB 2008

Abstract:

High resolution mode-selective excitation in the mixture of C6H6 (992 cm(-1)) and C6D6 (945 cm(-1)) is experimentally achieved by adaptive femtosecond pulse shaping based on the genetic algorithm (GA), and second harmonic generation frequency-resolved optical gating (SHG-FROG) is adopted to characterize the original and optimal laser pulses, and its mechanism is experimentally validated by tailoring the frequency components of the pump pulses at the Fourier plane. It is indicated that two-pulse coherent mode-selective excitation of the Raman scattering mainly depends on the effective frequency components of the pump pulse related to specific molecular vibrational mode. The experimental results have attractive potential applications in the complicated molecular system.


Addresses: E China Normal Univ, Dept Phys, State Key Lab Precis Spect, Shanghai 200062, Peoples R China

E China Normal Univ, Dept Math, Shanghai 200062, Peoples R China

Reprint Address: SUN, ZR, E CHINA NORMAL UNIV, DEPT PHYS, STATE KEY LAB PRECIS SPECT, SHANGHAI 200062, PEOPLES R CHINA

Author's E-mail: zrsun@phy.ecnu.edu.cn

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162

Author(s): Kanai, T (Kanai, Takuya); Suda, A (Suda, Akira); Bohman, S (Bohman, Samuel); Kaku, M (Kaku, Masanori); Yamaguchi, S (Yamaguchi, Shigeru); Midorikawa, K (Midorikawa, Katsumi)

Title: Pointing stabilization of a high-repetition-rate high-power femtosecond laser for intense few-cycle pulse generation - art. no. 061106

Source: APPLIED PHYSICS LETTERS, 92 (6): 61106-61106 FEB 11 2008

Abstract:

We have developed a beam stabilization system for high-power femtosecond lasers operating at a repetition rate of 1 kHz. The beam pointing at a hollow fiber input was stabilized to within 1 mu m rms and the fluctuations of the broadened spectra and power were significantly improved. This technique enables us to increase the input power to a hollow fiber for intense few-cycle pulse generation. (c) 2008 American Institute of Physics.


Addresses: Tokai Univ, Dept Phys, Kanagawa 2591292, Japan

RIKEN, Wako, Saitama 3510198, Japan

Reprint Address: KANAI, T, TOKAI UNIV, DEPT PHYS, 1117 KITA KANAME, KANAGAWA 2591292, JAPAN

Author's E-mail: asuda@riken.jp

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163

Author(s): Cai, WJ (Cai, Wenjian); Piestun, R (Piestun, Rafael)

Title: Low pulse-energy micromachining in bulk glass with a short-cavity femtosecond oscillator - art. no. 124301

Source: OPTICAL ENGINEERING, 46 (12): 24301-24301 DEC 2007

Abstract:

We report the first experiments showing structural changes in borosilicate glass using just a short-cavity Ti:sapphire oscillator at 800 nm and 90 MHz. Micromachining is achieved with infrared femto-second pulses having record-low energies. We show 3-D patterning capability, including waveguides and 3-D gratings embedded in the volume of a glass slab. (c) 2007 Society of Photo-Optical Instrumentation Engineers.


Addresses: Univ Colorado, Dept Phys, Boulder, CO 80309 USA

Univ Colorado, Dept Elect & Comp Engn, Boulder, CO 80309 USA

Reprint Address: CAI, WJ, UNIV COLORADO, DEPT PHYS, BOULDER, CO 80309 USA

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164

Author(s): Nuzzo, V (Nuzzo, Valeria); Plamann, K (Plamann, Karsten); Savoldelli, M (Savoldelli, Michele); Merano, M (Merano, Michele); Donate, D (Donate, David); Albert, O (Albert, Olivier); Gardeazabal Rodriguez, PF (Gardeazabal Rodriguez, Pedro Felipe); Mourou, G (Mourou, Gerard); Legeais, JM (Legeais, Jean-Marc)

Title: In situ monitoring of second-harmonic generation in human corneas to compensate for femtosecond laser pulse attenuation in keratoplasty - art. no. 064032

Source: JOURNAL OF BIOMEDICAL OPTICS, 12 (6): 64032-64032 NOV-DEC 2007

Abstract:

The application of femtosecond lasers in corneal transplant surgery requires high pulse energies to compensate for the strong optical scattering in pathological corneas. However, excessive energies deteriorate the quality of the incisions. The aim of this study is to demonstrate the dependence of side effects on local radiant exposure, numerical aperture, and tissue properties, to quantify the penetration depth of the laser for individual corneas, and to provide a method for optimizing the energy in the volume of the cornea. We examine histological and ultrastructural sections of clear and edematous corneas with perforating and lamellar incisions performed at different pulse energies. We demonstrate that the augmented energies in edematous corneas may result in unwanted side effects even when using high numerical apertures. The dependence of the laser beam penetration depth on pulse energy is evaluated by histology and an exponential decrease is observed. We show that the penetration length can be determined by evaluating the back-scattered second-harmonic emission associated with the nonlinear optical properties of the tissue. This approach represents a noninvasive method for the in situ quantification of the laser beam attenuation, enabling us to adapt the pulse energy accordingly. Experiments using adapted energies show that the side effects are minimized. (C) 2007 Society of Photo-Optical Instrumentation Engineers.


Addresses: Polytecn CNRS UMR 7639, ENSTA Ecole, Lab Opt Appl, F-91761 Palaiseau, Essone, France

Univ Paris 05, Hop Hotel Dieu, Lab Biotechnol & Aeil, F-75181 Paris, France

Ecole Natl Super Tecn Avancees, CNRS, UMR 7639, Lab Opt Appl Chemin Huniere, F-91761 Palaiseau, France

Reprint Address: NUZZO, V, POLYTECN CNRS UMR 7639, ENSTA ECOLE, LAB OPT APPL, F-91761 PALAISEAU, ESSONE, FRANCE

Author's E-mail: valeria.nuzzo@ensta.fr

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165

Author(s): Gale, BJS (Gale, B. J. S.); Sun, JH (Sun, J. H.); Reid, DT (Reid, D. T.)

Title: Towards versatile coherent pulse synthesis using femtosecond laser and optical parametric oscillators

Source: OPTICS EXPRESS, 16 (3): 1616-1622 FEB 4 2008

Abstract:

Pulses from a tunable near-infrared femtosecond optical parametric oscillator and its Ti:sapphire pump laser were phase-locked by matching their carrier-envelope phase-slip frequencies to one quarter of their common pulse repetition frequency. Interferometric second-order crosscorrelation and spectral interferometry traces demonstrated their mutual coherence for periods of at least 20 ms, compared with individual coherence times of 0.1 ms estimated from their phase-noise power spectra. This result is a prerequisite for versatile coherent pulse synthesis. Implications for the synthesis of arbitrary waveforms from multi-colour pulses are discussed.


Addresses: Heriot Watt Univ, Sch Engn & Phys Sci, Ultrafast Opt Grp, Edinburgh EH14 4AS, Midlothian, Scotland

Reprint Address: GALE, BJS, HERIOT WATT UNIV, SCH ENGN & PHYS SCI, ULTRAFAST OPT GRP, EDINBURGH EH14 4AS, MIDLOTHIAN, SCOTLAND

Author's E-mail: bjsg1@hw.ac.uk

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166

Author(s): Siegel, J (Siegel, J.); Gawelda, W (Gawelda, W.); Puerto, D (Puerto, D.); Dorronsoro, C (Dorronsoro, C.); Solis, J (Solis, J.); Afonso, CN (Afonso, C. N.); de Sande, JCG (de Sande, J. C. G.); Bez, R (Bez, R.); Pirovano, A (Pirovano, A.); Wiemer, C (Wiemer, C.)

Title: Amorphization dynamics of Ge2Sb2Te5 films upon nano- and femtosecond laser pulse irradiation - art. no. 023516

Source: JOURNAL OF APPLIED PHYSICS, 103 (2): 23516-23516 JAN 15 2008

Abstract:

Phase transformations of crystalline Ge2Sb2Te5 films upon pulsed laser irradiation have been studied using in situ reflectivity measurements with temporal resolution. Two different configurations allowed point probing with nanosecond temporal resolution and imaging with subpicosecond temporal and micrometer spatial resolution. The role of the pulse duration and laser fluence on the dynamics of the phase change and the degree of amorphization is discussed. Several advantageous features of femtosecond compared to nanosecond laser-induced amorphization are identified. Moreover, a high-resolution study of the amorphization dynamics reveals the onset of amorphization at moderate fluences to occur within similar to 100 ps after arrival of the laser pulse. At high fluences, amorphization occurs after similar to 430 ps and the molten phase is characterized by an anomalously low reflectivity value, indicative of a state of extreme supercooling. (C) 2008 American Institute of Physics.


Addresses: CSIC, Inst Opt, E-28006 Madrid, Spain

UPM, EUITT, Ingn Circuitos & Sistemas, Madrid 28031, Spain

STMicroelect, I-20041 Agrate Brianza, Italy

CNR INFM, MDM Lab, I-20041 Agrate Brianza, Italy

Reprint Address: SIEGEL, J, CSIC, INST OPT, SERRANO 121, E-28006 MADRID, SPAIN

Author's E-mail: j.siegel@io.cfmac.csic.es

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167

Author(s): Petrovic, JS (Petrovic, Jovana S.); Mezentsev, V (Mezentsev, Vladimir); Schmitz, H (Schmitz, Holger); Bennion, I (Bennion, Ian)

Title: Model of the femtosecond laser inscription by a single pulse

Source: OPTICAL AND QUANTUM ELECTRONICS, 39 (10-11): 939-946 AUG 2007

Abstract:

A comprehensive model of processes involved in femtosecond laser inscription and the subsequent structural material modification is developed. Different time scales of the pulse-plasma dynamics and thermo-mechanical relaxation allow for separate numerical treatments of these processes, while linking them by an energy transfer equation. The model is illustrated and analysed on examples of inscription in fused silica and the results are used to explain previous experimental observations.


Addresses: Aston Univ, Photon Res Grp, Birmingham B4 7ET, W Midlands, England

Reprint Address: PETROVIC, JS, ASTON UNIV, PHOTON RES GRP, BIRMINGHAM B4 7ET, W MIDLANDS, ENGLAND

Author's E-mail: j.petrovic@physics.ox.ac.uk

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168

Author(s): Kojiri, T (Kojiri, Takashi); Misawa, K (Misawa, Kazuhiko); Lang, R (Lang, Roy)

Title: Photoisomerization of all-trans retinal triggered with femtosecond phase-locked pulse Pairs - art. no. 014708

Source: JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 77 (1): 14708-14708 JAN 2008

Abstract:

We investigate dependence of photo-isomerization compositions on the time interval of a femtosecond phase-locked pulse pair used for excitation. The compositions were analyzed directly by high-performance liquid chromatograpy. Coherent enhancement of the isomerization from all-trans to 13- and 9-cis retinals was observed via the two-photon excited Ag state. We determined the dephasing time of the excited-state wave-packets to be less than 80 fs.


Addresses: Tokyo Univ Agr & Technol, Dept Appl Phys, Tokyo 1848588, Japan

Japan Sci & Technol Agcy, Core Res Evolut Sci & Technol, Chiyoda Ku, Tokyo 1020075, Japan

Reprint Address: KOJIRI, T, TOKYO UNIV AGR & TECHNOL, DEPT APPL PHYS, 2-24-16 NAKA CHO, TOKYO 1848588, JAPAN

Author's E-mail: kmisawa@cc.tuat.ac.jp

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169

Author(s): Boschetto, D (Boschetto, D.); Gamaly, EG (Gamaly, E. G.); Rode, AV (Rode, A. V.); Luther-Davies, B (Luther-Davies, B.); Glijer, D (Glijer, D.); Garl, T (Garl, T.); Albert, O (Albert, O.); Rousse, A (Rousse, A.); Etchepare, J (Etchepare, J.)

Title: Small atomic displacements recorded in bismuth by the optical reflectivity of femtosecond laser-pulse excitations - art. no. 027404

Source: PHYSICAL REVIEW LETTERS, 100 (2): 7404-7404 JAN 18 2008

Abstract:

Subtle atomic motion in a Bi crystal excited by a 35 fs-laser pulse has been recovered from the transient reflectivity of an optical probe measured with an accuracy of 10(-5). Analysis shows that a novel effect reported here-an initial negative drop in reflectivity-relates to a delicate coherent displacement of atoms by the polarization force during the pulse. We also show that reflectivity oscillations with a frequency coinciding with that of cold Bi are related to optical phonons excited by the electron temperature gradient through electron-phonon coupling.


Addresses: Ecole Polytech, ENSTA, Lab Opt Appl, Palaiseau, France

Australian Natl Univ, Res Sch Phys Sci & Engn, Laser Phys Ctr, Canberra, ACT 0200, Australia

Reprint Address: BOSCHETTO, D, ECOLE POLYTECH, ENSTA, LAB OPT APPL, PALAISEAU, FRANCE

Author's E-mail: davide.boschetto@ensta.fr

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170

Author(s): Song, ZM (Song Zhen-Ming); Zhang, GX (Zhang Guang-Xiao); Cao, SY (Cao Shi-Ying); Pang, DQ (Pang Dong-Qing); Chai, L (Chai Lu); Wang, QY (Wang Qing-Yue); Zhang, ZG (Zhang Zhi-Gang)

Title: Simulation of femtosecond pulse propagation through hollow fibre filled with noble gases of gradient temperature

Source: CHINESE PHYSICS LETTERS, 25 (1): 129-132 JAN 2008

Abstract:

We propose a novel technique for generating intense few to mono-cycle femtosecond pulses. The simulation demonstrate that for the temperature difference of 300K, the spectrum of the output pulses is increased by 67% and the transform limited pulse width is reduced almost by half, compared with those obtained with hollow fibres in uniform temperature.


Addresses: Tianjin Univ, Coll Precis Instrument & Optoelect Engn, Ultrafast Laser Lab, Key Lab Optoelect Informat Tech Sci, Tianjin 300072, Peoples R China

Peking Univ, Sch Elect Engn & Comp Sci, Inst Quantum Elect, Beijing 100871, Peoples R China

Reprint Address: SONG, ZM, TIANJIN UNIV, COLL PRECIS INSTRUMENT & OPTOELECT ENGN, ULTRAFAST LASER LAB, KEY LAB OPTOELECT INFORMAT TECH SCI, TIANJIN 300072, PEOPLES R CHINA

Author's E-mail: song.zm@163.com


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