Zhang Xue-Ru

Nonresonant Saturation Absorption in Electrostatic Self-Assembly Films Containing Methanofullerene

Ultrathin films containing methaofullerene are prepared by electrostatic layer-by-layer self-assembly of a positively charged trifluoroacetic acid salt of monoamino-substituted methanofullerene (TMAF) derivative and a negatively charged poly (sodium 4-styrenesulfonate) (PSS). Absorptive optical nonlinearities of 30 bilayer TMAF/PSS films and TMAF in water solution are measured using the Z-scan technique at 532 nm. Nonresonant saturation absorption is observed in the film sample, whereas reverse saturation absorption was for TMAF in water. The saturation-absorption behaviour is interpreted by a special formula. The saturation intensity is extracted to be 15.2±0.8 MW/cm2. The mechanism of saturation absorption in the TMAF/PSS film is discussed.

NONLINEAR REFRACTION IN MULTILEVEL MOLECULAR SYSTEMS

The intensity-dependent nonlinear refraction phenomena in a non-resonant multilevel molecular system is studied using rate equations in steady state, including saturable refraction, reverse saturable refraction, and the turnover between these two effects. The relationship between the refraction saturation and the optical Kerr effect is also discussed.

Nonlinear optical properties in double-sided nonlinear media with Z-scan technique based on the Huygens--Fresnel principle

We present a theoretical model to analyse the propagation of a Gaussian laser beam through double-sided nonlinear media. This model is based on the Huygens?Fresnel diffraction integral method. This theoretical model is not only consistent with the cascade structure model for a small nonlinear phase-shift but also can be used for a large nonlinear phase-shift. It has been verified that it is suitable to characterize the double-sided nonlinear media compared with the cascade structure model. A good agreement between the experimental data and the results from the theoretical model is obtained. It will be useful for the design of multi-sided nonlinear materials.

Optical limiting effect in two phthalocyanines observed by picosecond pulsed laser

Optical limiting (OL) properties of two phthalocyanines were investigated by using picosecond laser pulses at 532nm. The relative ratios k of the absorption cross section of the first singlet excited state to that of the ground state were approximately obtained by the analysis of the experimental results in which the reverse saturable absorption model of the three-energy-level scheme was employed. A significant comparison with fullerene C60 was presented for OL. The OL mechanisms have been analysed in detail.

Measurement of Ultrashort Laser Pulse Width in a Wide Spectrum Range Using Dimethyl Sulfoxide by Optical Kerr Effect Technique

We illustrate that applying the optical Kerr effect technique to dimethyl sulfoxide (DMSO) can determine the width of laser pulses in a wide spectrum range that is transparent. Different from many other simple molecular liquids, such CS2, and toluene, DMSO responds to both 130 fs 800nm laser pulses and 248 fs 400 nm laser pulses with electronic motions only. Therefore, the observed signal as a function of time reflects the temporal distribution of the intensity. We verify our illustration by both the autocorrelation technique and spectra analysis.

Theory of Z-scan technique using Gaussian-Bessel beams with a phase object

This paper reports the theoretical study of combining Z-scan technique with Gauss–Bessel (GB) beams beside a phase object (PO) to measure the third-order nonlinear susceptibility components. By using this method, the sign of refractive index which depends on the shape of the close aperture Z-scan curve can be easily determined. Meanwhile, the magnitude of nonlinear coefficients can also be deduced by theoretical fit. The proposed method is advantageous for high sensitivity and imposes a lower stress in the cases of fragile materials, since small pulse energy is enough for the measurement of nonlinear coefficients. Predictions of the models are compared with Gaussian Z-scan measurement and GB Z-scan measurement. By using GB beams with a PO, the sensitivity of Z-scan measurements is found to be a factor of over 60 times greater than for Gaussian beams and 2 times greater than for Gaussian-Bessel beams.

Identification of Ag37Sn33Te30 Phase-Change Films for Optical Data Storage

The Ag37Sn33Te30 film has been investigated to determine its suitability as phase change optical recording alloy based on static tester and atomic force microscopy measurements. Switching properties and the recording bit topography of the film are studied. With a writing pulse of power 2.5 mW, width 10 μs, and an erasure pulse of power 0.25 mW, width 10 μs, optical contrast of 31.8% is obtained. Re-crystallization experiments identify the Ag37Sn33Te30 film as a suitable phase change material for optical data storage with a complete erasure time of 1.1 μs at low erasure power.

Crystallization Kinetics of Amorphous In44Sb20Te36Phase-Change Optical Recording Films on a Nanosecond Scale

We propose a simple method to investigate the crystallization kinetics of amorphous In44Sb20Te36 films on a nanosecond scale, based on local reflectivity measurements of the nanosecond laser-induced crystallization using a static tester. The pulse condition in terms of laser power and pulse width required for the onset of crystallization is established. Applying this pulse condition and Kissingers analysis, an activation energy of 0.57 eV is estimated for the crystallization. This value deviates substantially from the activation energy determined at lower sample temperatures where crystallization proceeds in a time scale of seconds rather than nanoseconds.