Showing papers on "Supercontinuum published in 1997"

Generation of Coherent X-rays in the Water Window Using 5-Femtosecond Laser Pulses

Abstract: Coherent extreme-ultraviolet radiation extending to wavelengths below the carbon K edge at 4.37 nanometers (nm) has been generated at a repetition rate of 1 kilohertz by focusing 5-femtosecond near-infrared (780 nm) laser pulses into a helium gas jet. The incident light field performs just a few oscillations, which results in the emission of an x-ray supercontinuum rather than discrete harmonics. Owing to the extremely short rise time of the driving pulses, neutral atoms can be exposed to high fields before they are depleted by ionization. As a result, the observed x-ray radiation extends well into the water window and is delivered in a well-collimated beam (divergence less than 1 milliradian). The high repetition rate and spatial coherence result in a brightness of about 5 × 108 photons per square millimeter per square milliradian per second in a 1-percent bandwidth at 4.37 nm, the carbon edge of the water window. The compact laboratory system holds promise as a source for biological holography and nonlinear optics in the x-ray regime.

Supercontinuum self-Q-switched ytterbium fiber laser

Abstract: We have discovered a new mechanism for passive Q switching of fiber lasers. 10-kW peak power pulses with ∼2-ns pulse widths are reported from a diode-pumped ytterbium-doped fiber laser. The laser generates a high-brightness Raman-dominated supercontinuum spectrum covering the complete window of transparency of silica fiber in the infrared from 1.06 to 2.3 µm

Flatly broadened supercontinuum spectrum generated in a dispersion decreasing fibre with convex dispersion profile

Abstract: Dispersion design in a single-mode fibre is investigated experimentally and numerically for generating a supercontinuum with a flatly broadened spectrum. It is found to be important both that group velocity dispersion is a convex function with two zero-dispersion wavelengths and also that it decreases with fibre length. A calculated spectrum explains well that obtained experimentally. The mechanism of the spectral evolution of supercontinuum is examined.

Femtosecond Stokes shift in styryl dyes: Solvation or intramolecular relaxation?

Abstract: Transient absorption and gain spectra of the styryl dye LDS-750 in solution have been studied by the pump/supercontinuum probe (PSCP) technique with excitation at 530 nm. The pump/probe intensity correlation width was 70 fs, providing a time resolution of 40 fs. Spectra were detected in the range 400–800 nm with 1.5 nm resolution. Before 70 fs, prominent spectral structure is observed due to resonant Raman scattering from a 1500 cm−1 active mode of the chromophore. At later time, the gain spectrum undergoes an ultrafast redshift and change of shape, with time constants of ∼200 and ∼600 fs for acetonitrile and chloroform solutions, respectively. At high pumping energy (1.2 μJ), the final emitting state is reached by internal conversion from higher electronic states without a further essential Stokes shift. The emitting state is assigned to an excited isomeric form of the molecule. At low pumping energy (0.3 μJ), the first excited electronic state isomerizes in an ultrafast process followed by a slower process, the dynamics of which is controlled by the solvent. The geometrical and electronic nature of these processes and their coupling to the solvent needs further clarification.

1.4 Tbit/s (200 Gbit/s × 7 ch) 50 km optical transmission experiment

Abstract: A 14 Tbit/s (200 Gbit/s OTDM/spl times/7 channel WDM) signal is successfully transmitted in a 50 km dispersion shifted fibre A supercontinuum pulse source and arrayed waveguide grating are used to generate WDM channels with 600 GHz spacing, and high-speed TDM techniques are used to multiplex/demultiplex a 200 Gbit/s signal

Artificial eye for in vitro experiments of laser light interaction with aqueous media.

Abstract: An artificial eye has been designed and assembled that mimics the focusing geometry of the living eye. The artificial eye’s focusing characteristics are measured and compared with those of the in vivo system. The artificial eye is used to measure several nonlinear optical phenomena that may have an impact on the laser damage thresholds of the retina produced by ultrashort laser pulses. We chose a focal length of 17 mm to simulate the rhesus monkey eye, with a visual cone angle of 8.4 deg for a 2.5-mm diameter laser beam input. The measured focal point image diameter was 5.661 mm, which was 1.5 times the calculated diffractionlimited image diameter. This focusing system had the best M2 of all the systems evaluated. We used the artificial eye to measure the threshold for laser-induced breakdown, stimulated Brillouin scattering, supercontinuum generation, and pulse temporal broadening due to group velocity dispersion.

Optical fiber and light source apparatus

Abstract: High peak pulse light is incident on an optical fiber having a dispersion decreasing region which serves as a main region for generating supercontinuum or idler light and in which the chromatic dispersion does not increase but at least partially decreases in the direction in which light travels. The fiber can be applied to broad band width idler light generation with both light transmission directions. Four wave mixing upon incidence of the light on the dispersion decreasing region of the optical fiber are efficiently obtained.

Broader and flatter supercontinuum spectra in dispersion-tailored fibers

Abstract: In summary, we find experimentally that dispersion decreasing (DD) fiber produces broader and smoother supercontinuum (SC) spectra than dispersion increasing (DI) or constant dispersion fiber. At 24.3 W peak input power, the SC spectrum of DD fiber is over 100 nm wide, over twice that created by constant dispersion fiber. The spectrum is also relatively flat over the 20-nm range from 1545-1565 nm. We will also report applications of the multiwavelength SC source to erbium doped fiber amplifiers and wavelength-division multiplexed fiber characterization.

Dispersion-flattened and decreasing fiber for ultra-broadband supercontinuum generation

Abstract: Dispersion-flattened and decreasing fiber is found highly effective for ultra-broadband supercontinuum generation through simulations, for the first time. Actually manufactured fiber produces 280 nm bandwidth supercontinuum with an input pulse peak power of only 12 W.

Nearly transform-limited 1.4 [micro sign]m picosecond pulse generation by supercontinuum and pulse amplification in Tm-doped optical amplifier

Abstract: Transform-limited 10 GHz picosecond pulse generation is experimentally demonstrated in the 1.4 /spl mu/m wavelength region by amplifying supercontinuum pulses in a Tm-doped optical amplifier. Through bit error rate measurements, power penalties of <1.5 dB are found in the range 1450-1470 nm.

Observation of spectral broadening caused by self-phase modulation in highly multimode optical fiber.

Abstract: We observed spectral broadening caused by self-phase modulation in 400-and 600-µm core diameter fibers using amplified, Q -switched, Nd:YAG laser pulses with peak powers to 150 kW. The degree of spectral broadening was not dependent linearly on the fiber length as in single-mode fibers because of the more complicated modal evolution in highly multimode fiber. Furthermore, even slight stress near the input end of the fiber reduced the observed broadening. The results have significant implications for the delivery of high-peak-power laser beams through optical fiber with high-output beam quality for industrial applications.

Chromatic dispersion measurement in the 1-2 /spl mu/m spectral region using a high brightness supercontinuum fiber laser source

Abstract: We demonstrate a novel, diode-pumped ytterbium-doped fiber laser, which combines the unique characteristics of a high brightness supercontinuum together with simplicity of operation and compactness for application in dispersion measurement using both time delay and interferometric techniques and has considerable potential for implementation into a simple yet highly practical apparatus for dispersion measurement. The high brightness and intensity of the source is particularly applicable to nondestructive dispersion-distribution measurements as well as real time control of dispersion during fiber drawing. The potential of these have been examined.

Q-switched fibre laser

Abstract: A Q-switched fibre laser system comprising a doped fibre gain medium 2 that is continuously pumped by a pump source 6. Back reflection within the system is insufficient to support continuous wave lasing because reflection from the output end is suppressed.. A light storage means 8, such as a fibre loop, is coupled to the doped fibre gain medium and gathers light produced by spontaneous decay from the excited state. This gathered light generates back reflected light through a distributed back scattering, such as Rayleigh scattering. The back scattered light is resonated in a loop, and provides a delayed nonlinear feedback into the doped fibre. As the population inversion increases, then the amount of light stored within the light storage means 8 increases until the back scattering reaches a threshold amount that is sufficient to stimulate a pulse of laser light within the doped fibre gain medium 2. An optical isolator 10 and/or a cleaved end face 12 may be used at one end of the laser cavity to inhibit continuous wave lasing. As an alternative to the fibre loop 8, a length of single mode fibre 14 may be used,or for self Q-switching, feedback may also be achieved as result of back scattering from the doped fibre itself. The Q-switched fibre laser produced results in pulses of laser light sufficiently intense to result in a frequency supercontinuum. Repetition rate may be controlled by controlling the pump output of the pump source 6. The repetition rate may be stabilised by modulating the pump output.

Ultra-broad band supercontinuum produced by terawatt femtosecond laser

Abstract: The characteristics of supercontinuum produced by high-intensity femtosecond pulses were investigated under different interaction lengths, various pump intensities, different pump wavelengths at the fundamental 800 nm and its second-harmonic 400 nm. High transfer-efficiency supercontinuum with flat-top in liquid media was produced. As the main nonlinear mechanisms, the effects of self-phase modulation (SPM) and four-photon parametric emission were also investigated.

Ultrafast transient phenomena in semiconductor microcavities

Abstract: The excitation of semiconductor microcavity modes (ZnSe films on Cr and Cu surfaces) were investigated by femtosecond pump- supercontinuum probe spectroscopy in wide spectral region 300 - 800 nm. Photoinduced red shift of cavity modes due to parametric pump of ZnSe film and film-metal interface and the generation of coherent phonon oscillations in ZnSe were observed.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Optical TDM transmission techniques toward Tbit/s

Abstract: Ultra-high speed optical time-division-multiplexed (TDM) transmission is one of the key technologies to realize future Tbit/s optical networks. We reported 400 Gbit/s optical TDM transmission using high-speed optical techniques such as short pulse generation by mode-locked fiber-ring-laser (ML-FRL) combined with supercontinuum (SC), time-division multiplexing by the planar-lightwave-circuits (PLC), prescaled phase-lock-loop (PLL) timing extraction using four-wave-mixing (FWM) in a semiconductor laser amplifier, and all-optical demultiplexing using FWM. We show the experimental setup of a 400 Gbit/s transmission experiment. We used 0.98 ps transform-limited optical pulses and the 400 Gbit/s signal was successfully transmitted through 40 km.

Study on optimum designs of optical fiber for generating supercontinuum pulses

Abstract: 2.シミュ レーシ ヨンの試行 シミュレーシ ョンはSplit-Step Fourier法 。SCは フ ァイバ中の非線形現象で起 こると考 えられるが、今 回は誘導 ラマ ン散乱は無視 し、光カー効果のみを考慮 、通常の 分散 シフ トファイバ(DSF)、 及び分散 フラットファイバ(DfF) について検討した。分散スロープの値は、前者が0.07ps/nm2/km 、 後者が0.01ps/nm2/kmで あ り、その他のパラメータは同条件で、 分散値Dは0.2ps/nm/km、 ファイバ長Lは3km 、非線形屈折率 馬は2.8×10-20m2/W、 実効 コア断面積Aoffは50μm2と した。例 と して、FWHM3.5ps、 ピークパワー1.5Wの ソリトンパルスをDFF に入射 させた場合の出射スベク トルを図1に 示す。図より平坦 な 領域がほ とん どなく、スペク トル幅 も数THzに とどまっているこ とが分かる。また、DSFに 入射させた場合は更に帯域は狭い結果 となっていた。この理 由として は(1)ラ マ ン散乱を無視 してい るため、(2)実 験のファイバ の分散値が長手方向に揺 らいでい るための二つが推測される。ここでは(2)に 着 目して更に検討 を続けた。

Photoinduced processes in silicate glasses exposed to IR femtosecond pulses

Abstract: The optical properties variation in silicate glasses after exposure to high-power femtosecond laser radiation at 0.85 micrometers have been studied. The laser spectral line broadening leading to the supercontinuum generation in visible and UV spectral regions was observed in all studied glasses. Color center generation and intrinsic luminescence were found in boro- and alkali-silicate glasses. It is believed that these processes result from linear and/or two-photon absorption of the short-wavelength part of this supercontinuum which causes glass matrix ionization. No color center absorption in the visible region was observed in fused silica at irradiances up to the laser damage threshold. It was concluded that there is no significant ionization of fused silica under exposure to IR femtosecond laser pulses with irradiance below laser induced damage threshold.