State Key Laboratory of Laser Technology

We demonstrate the characteristics of relatively low saturation intensity using co-doped Nd, Cr:YAG as saturable absorber for passively mode locking the Nd:YAG laser. The difference of the saturation intensity between Q-switched and mode-locked operation in co-doped Nd, Cr:YAG was only one to two orders of magnitude, while Cr:YAG was generally reported at a difference of five orders of magnitude. More than 80% mode locking modulation depth was achieved at an incident pump power of 4.4W, corresponding to an intracavity intensity of 6×104W/cm2, using a 68cm long plano-concave cavity.

Abstract Sm‐doped bismuth titanate and random oriented Bi 4– x Sm x Ti 3 O 12 (BST) thin films were fabricated on Pt/Ti/SiO 2 /Si substrates using a pulsed laser deposition method. The structures and the ferroelectric properties of the films were investigated. Sm doping leads to a marked improvement in the remanent polarization ( P r ) and the coercive field ( E c ). At an applied electric field of 100 kV/cm, P r and E c of a BST ( x = 0.8) film annealed at 650 °C are 20.5 µC/cm 2 and 60 kV/cm, respectively. However, after 3 × 10 10 switching cycles, 20% degradation of 2 P r is observed in the film. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

We investigate the effects of the higher-order space-charge field on the self-deflection of photovoltaic bright solitons in a photovoltaic photorefractive crystal by both numerical and perturbation methods under steady-state conditions. Our results indicate that there exits a characteristic value of photovoltaic fields for photovoltaic bright solitons. When the photovoltaic field is less than the characteristic value, these solitons always bend in the direction opposite to the crystal's c axis, and the absolute value of the spatial shift that is due to the first-order diffusion term alone is always larger than that which is due to both the first-order diffusion term and the higher-order terms acting together. If the strength of the photovoltaic field is larger than the characteristic value, soliton bending in both the same direction as and in the direction opposite to the crystal's c axis is possible. Whether the direction is in the same or in the opposite direction will depend on the strength of the photovoltaic field and on the input intensity. Specifically, self-deflection cannot occur for photovoltaic bright solitons if the strength of the photovoltaic field and the intensity of the input beam are appropriately selected. We provide some relevant examples to confirm our prediction.

We propose a new kind of optical spatial solitons in biased photovoltaic-photorefractive materials when the self-trapping beam couples coherently with a pump beam by codirectional degenerate two-wave mixing. Such solitons are a result of double balance, i.e., loss is balanced by gain provided by the pump beam via two-wave mixing, and diffraction is balanced by nonlinearity that is due to the spatially nonuniform screening of the applied field, the photovoltaic effect, and the periodic modulation of the refractive index via two-wave mixing. These solitons possess some unique properties, are stable relative to small perturbations, and can become screening-photovoltaic solitons if the pump beam is switched to a background illumination.

The stochastic resonance phenomenon in a single-mode laser system driven by multiplicative and additive Gaussian white noises without external periodic force is studied. We find that there are multiple extrema (maximum) in the curve of the mean output laser intensity versus the logarithm of multiplicative noise level. This phenomenon reveals that the mean output laser intensity can be amplified at several values of the multiplicative noise intensity, whose peaks are likely modulated by a sinusoidal function.

The electronic structures of two ferromagnetic polynuclear copper(II) complexes, derived from end-to-end azido ligand and tridentate (NNN donor) Schiff base ligand, have been studied using the full-potential linearized augmented plane-wave method based on the density-functional theory. They are [Cu(L1)(micro-1,3-N3)]n(ClO4)n (1) and [Cu(L2)(micro-1,3-N3)]n(ClO4)n (2). The result shows that the spin populations in these two complexes are mainly distributed on the equatorial planes of a square pyramidal that surround the copper(II) ions. There are large and positive spin populations on copper(II) ions, small and positive spin populations on the three nitrogen atoms of tridentate Schiff base ligand, and the two terminal nitrogen atoms of asymmetrical end-to-end azido ligand, while weak and negative spin populations on the central nitrogen atoms of asymmetrical end-to-end azido ligand. Ferromagnetic coupling through the asymmetrical azido ligand in these two complexes has been mainly attributed to the spin delocalization, also with weak spin-polarization effect.

Starting from the Rayleigh diffraction integral, the propagation equation of ultrashort pulsed beams in dispersive media is derived without making the paraxial approximation and slowly varying envelope approximation (SVEA). The spatiotemporal properties of ultrashort pulsed beams in dispersive media, such as spectrum redshifting, narrowing and pulse distortion are illustrated with pulsed Gaussian beams. It is stressed that the ``antibeam'' behaviour of ultrashort pulsed beams can be avoided, if a suitable truncation function is chosen.

In this study, the finite difference time domain (FDTD) method was used to analyze light propagation in polymer nanoporous films. Compared with some theoretical models, it is found that the composite medium in series model is consistent with the results calculated by the FDTD method. In order to verify the theoretical model, we also fabricated several polymer nanoporous films, and obtained their effective indices of refraction and porosities with an ellipsometer and scanning electronic microscope (SEM), respectively. It is indicated that the composite medium in series model is also consistent with the experimental results.

We propose a simple method to generate a practical SU(2)-Schrödinger-cat state of a single trapped-ion vibration mode and the light field state, using the method based on a quantum system, which is composed of the one-dimensional trapped-ion motion and a single cavity field mode. Moreover, we discuss the methods proposed so far for the generation two-mode maximal quantum entangled state. The detection of such a state is also briefly discussed.

The ferromagnetic phenyl nitronyl nitroxide derivate alpha-phase 2-(2('),5(')-dihydroxyphenyl)- 4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxy-3-oxide has been studied by the electronic structure calculation based on the density functional theory. The result shows that the spin delocalization due to hyperconjugation effect plays an important role in the spin distribution and ferromagnetic coupling of the crystal.

A novel method based on photorefractive(PR) two-wave mixing to detect air turbulence is presented.The air turbulence is modulated on the input pump and signal beams of a PR crystal,thus creating a phase fluctuation for the input beams.Such a phase fluctuation results in an intensity fluctuation in the output beams and the intensity fluctuation can be detected by measuring the differential signals between the two output beams.Our experimental demonstration shows that air turbulence can be detected effectively based on the process of PR two-wave mixing and an electrical differential detection.This method may be widely used in future detecting applications.

We study theoretically the properties of nonlinear waveguides induced by one-dimensional steady-state screening-photovoltaic spatial solitons. It shows that the waveguides can be induced by both bright and dark spatial solitons in the biased photovoltaic-photorefractive crystal such as LiNbO3. We also derive wave equations for the probe beam in the general condition and low-amplitude condition.

Due to the polarization sensitivity of Raman gain and the random nature of PMD in the fiber the gain of fiber Raman amplifier not only depends on the polarization states of the input signal and pump but also fluctuates over a wide range during a relative long time. The fluctuations are related to the PMD parameter of the fiber and the pumping scheme. In this paper the statistics of the gain fluctuations in an amplifier employing bidirectionally pumping schemes is studied. The ratio of forward to total pumping power is optimized to achieve best trade-off between the OSNR and nonlinear distortions beforehand. The results obtained are useful for the further optimization of bi-directionally pumped amplifiers.

This paper introduces the system design、main specifications and characters of the Ho:YAG laser for the uriary tract lithotripsy and states the advantages over the other lithotripsy instruments.

Based on diffractive theory and experimental work, a binary optical resonator (BOR) was developed according to phase-conjugate principle. Replacing the sphere mirror of a high power CO/sub 2/ laser simi-confocal resonator (SCR) with a 16-levels binary optical mirror (BOM), having square aperture, a square-cross-section 10/sup th/ order super-Gaussian beam was specified as the eigenmode of the new resonator.