Environmentally stable ytterbium figure-of-eight fiber laser producing 177-fs pulses

Pulses of 177 fs and 1035 nm, with average power of 1.2 mW, have been generated directly from a passively mode-locked Yb-doped figure-of-eight fiber laser, with a nonlinear optical loop mirror for mode-locking and pairs of diffraction gratings for intracavity dispersion compensation. To our knowledge, these are the shortest pulses ever to come from a passively mode-locked Yb-doped figure-of-eight fiber laser. This represents a 5-fold reduction in pulse duration compared with that of previously reported passively mode-locked Yb-doped figure-of-eight fiber lasers. Stable pulse trains are produced at the fundamental repetition rate of the resonator, 24.0 MHz.     

Generation and transmission simulation of 60 G millimeter-wave by using semiconductor optical amplifiers for radio-over-fiber systems

A novel method of the millimeter-wave (MMW) generation is proposed for Radio-over-fiber systems with low phase noise by using semiconductor optical amplifiers (SOAs). The simulation results show that the method is correct. When a pump light and a signal light are input into the SOA, the converted light induced by four-wave mixing (FWM) effect is generated. The optical MMW is generated between the signal light and converted light after filtering the pump light. The electrical MMW is obtained by beating the signal light and converted light via a photo-detector. The phase noise of the system is low because the phase difference between the signal light and converted light is stable for the FWM effect. The power of MMW is increased with the increase of the pump light power and the pump current of the SOA, is decreased with the increase of the polarization azimuths of the pump light.     

Phase measurements in nonlinear optics

Measurement of the phase, and not only the intensity, of the nonlinear optical response of a system is important in many applications which are reviewed here. We demonstrate and compare several techniques for direct measurement of the phase of the nonlinear susceptibilities through nonlinear interferometry. Different ways of imparting a controllable phase shift are discussed. Unless the coherence length is impractically large, the preferred method is to use a variable-pressure gas cell to control the phase difference between the input laser pulse and the nonlinear optical signal.Prof. F. P. Schäfer on the occasion of his 65th birthday.     

S1 singlet excited-state absorption of DODCI

1 excited-state absorption cross-section spectrum of DODCI in ethylene glycol is determined in the wavelength range from 500 nm to 750 nm. The S₁ state is populated by amplified femtosecond dye laser pulses (wavelength 592 nm) and the S₁-state absorption and emission behaviour is probed with a femtosecond light continuum. A general analysis procedure is developed to extract absolute excited-state absorption cross-sections from the measured transmissions. For DODCI in ethylene glycol the wavelength regions of saturable absorption (mode-locking application), reverse saturable absorption (optical limiter application), and effective stimulated emission (laser application) are determined. Received: 25 July 1996     

Ferroelectric domain inversion in near-stoichiometric lithium niobate for high efficiency blue light generation

LiNbO₃ single crystals with a composition close to stoichiometry ([Li]/[Li+Nb]=0.496), 16 mm in diameter and 40 mm in length were grown by the Czochralski method using K₂O flux. The domain reversal characteristics of near-stoichiometric LiNbO₃ single crystals were investigated. The switching field required for 180° ferroelectric domain reversal in the near-stoichiometric crystal at room temperature was 7.5 KV/mm. This is about one third of the switching field required for conventional LiNbO₃ crystals. Domain reversal (180°) in near-stoichiometric LiNbO₃ samples of 1.0 mm thickness has been achieved. Samples have been evaluated by second harmonic generation and conversion efficiencies of up to 32% have been obtained. Received: 8 November 2000 / Accepted: 29 January 2001 / Published online: 20 June 2001     

Double line stimulated Raman scattering in benzene

Simultaneous stimulated Raman scattering at the 992 cm^–1 and the 3063 cm^–1 line of benzene is observed by mode-locked ruby laser pulse excitation. The double line stimulated Raman scattering is initiated by self-focusing. The influence of small-scale self-focusing, self-phase modulation, and cross-phase modulation on the double line stimulated Raman scattering is discussed. At low pump pulse intensities, before the onset of small-scale self-focusing, the steady-state Raman gain factors of both Raman lines are determined by Raman energy conversion efficiency measurements.     

Theory and experiment of CW dye laser injection locking and its application to second harmonic generation

High-power single-mode operation of a cw ring dye laser has been obtained by injection of cw single-mode radiation. The intracavity power of this system was used to generate tunable single-mode uv radiation by frequency doubling in a temperature phase-matched ADA crystal: up to 45 W intracavity fundamental power and up to 70 mW extracted uv power have been observed. A theoretical treatment of the injection locked cw ring dye laser system is given for the stationary state. Expressions for the intracavity intensities as a function of the small-signal gain and the saturation intensity are derived.     

Optical fiber transmission of multipleQ-switch Nd: YAG laser pulses with microsecond interpulse separations

Up to sixQ-switch pulses with interpulse separations of between 2 and 100 s are extracted during single flashlamp pulses of a Nd:YAG laser (1.06 m) by opening the Pockels cell in up to six stages. The interpulse separations and output energies are adjustable for the individual pulses of the 10 Hz repetitive laser bursts. Measurements of maximum fiber transmission and stimulated backscattering are reported for 1 mm diam fused-silica step-index fibers.     

Phase transition in C60-2-thioxo-l, 3dithiole cycloadduct

Quadratic electrooptic coefficient (QEOC) measurements have been made for fullerene C₆₀) and its derivative C₆₀-2-thioxo-l,3-dithiole. An anomaly in C_p has been revealed at about — 60°C that corresponds to the appearance of a structural phase transition. Correlation with a temperature anomaly in the QEOC is revealed. This leads to the conclusion that the QEOC for fullerene depends mainly on vibrational and rotational contributions. The contribution arising from charge distribution asymmetry is most important in the fullerene derivative. The observed temperature anomalies of the QEOC result in the possibility of using the QEOC as a sensitive tool for observing low-temperature phase transitions in the fullerene derivatives.     

Picosecond pulse generation in a benzene raman generator amplifier system

Picosecond ruby laser pulses generate simultaneously Stokes pulses of the 992 cm^–1 ring breathing mode and of the 3063 cm^–1 CH-stretching mode of benzene in a Raman generator cell by stimulated Raman scattering under self-focusing conditions. The Raman generator light is spectrally filtered, collimated, and amplified in three Raman amplifier cells pumped by ruby laser pulses. Both first Stokes lines have been selectively amplified to short, low divergence, intense light pulses.