Li Zaiguang

Photostimulated aggregation of ultradispersoidal silver particles into fractal clusters

In this paper, studies of the photostimulated aggregation of ultradispersoidal silver particles into fractal clusters observed in colloidal solutions irradiated by different types of pulsed and continuous-wave lasers and by non-monochromatic light are described. A photoaggregation mechanism is suggested, on the basis of mutual opposite charging of different sized particles due to the equalization of their size-dependent Fermi energies in a conducting medium.

Coupling losses and mode properties in planar waveguide resonators

Abstract In this paper the coupling losses in planar waveguide resonators are calculated and the coupling losses for the EH 11 mode of various planar waveguides are presented as a function of mirror curvature and position. It is shown that there exist two special geometries to provide low coupling losses which is different from the square waveguide. The design and the mode properties of a planar waveguide resonator are discussed.

Efficiency and optical feedback of traveling-wave semiconductor laser amplifier to single-mode fiber coupling: theory and experiment

Abstract This paper analyzes the coupling efficiency and optical feedback of the tapered fiber end with a high-index hemiellipsoidal microlens. Such a device has been used as a coupler of traveling-wave semiconductor laser amplifier (TW-SLA) to single mode fiber (SMF). A theory of the calculation of coupling efficiency and optical feedback is presented including the effects of spherical aberration and Fresnel reflection of thick lens. In consideration of the large beam divergency of the TW-SLA chip, the finite transmission aperture is introduced. The calculations are in agreement with experiment results and a group of optimum structure parameters of the coupler are given.

Reflection and refraction of Gaussian beam on wavy surface in airborne ocean lidar

According to the statistical description of direction distribution on wavy surface by Cox, we have set up a physical model of reflection and refraction of Gaussian beam on wavy surface, derived that a beam reflected and refracted by wavy surface is also a Gaussian beam when the incident beam is a Gaussian beam, and set up the relationship between Gaussian beams light spot size and wind speed over sea surface.

Electron diffusion in a non-uniform electric field and a uniform magnetic field

A Monte Carlo simulation technique has been used to model the electron transport behavior, especially the electron diffusion motion, in the cathode fall region of a glow discharge under the influence of a non-uniform electric field and a transverse magnetic field perpendicular to the cathode sheath electric field. Three types of collisions (elastic, excitation and ionization) are taken into account in our model. The electron free flying time is determined by the electron-neutral atom collision frequency. We focus attention on the electron diffusion distance and velocity. The electron-neutral atom collision processes and the electron drift velocity are also studied. The results indicate that with the increase of the magnetic field the electron diffusion distance increases and the electron diffusion velocity decreases. The results also show that the collision processes are enhanced by the magnetic field, this is in agreement with the experimental result. However, the axial magnetic field does not affect the electron transport behavior.

Photon-Number Distributions of Lasers Generated via Pump-Noise Suppression*

The photon-number distribution of lasers generated via pump-noise suppression is derived in the photon-number representation. The derivation shows that the negative probability emerging in the calculation of the photon-number distribution in the photon-number representation is not caused by the representation itself but by the truncation of the master equation. Here without truncating the master equation we derive the characteristic function and the distribution function of the photon-number distribution of the laser system with regular pump and with spontaneous atomic decays being eliminated. It is convenient to use the characteristic function to calculate any order of the moment of the photon-number distribution. Such a method can be used to some more general cases, in which the laser system has imperfectly regular pump and the spontaneous atomic decays are also considered.

First-Order-Like Transition in Inhomogeneously Broadened Two-Mode Ring Laser Gain-Noise Model*

An inhomogeneously broadened two-mode ring laser gain-noise model taking account of both full saturation effects and multiplicative noise induced by gain fluctuations is investigated. By using a corresponding Fokker–Planck equation and perturbation theory proposed by Graham et al. the joint stationary distribution for light intensities is obtained. It is found that a first-order-like transition occurs when laser is operated off resonance.

The Photon-Number Distribution of the Lasers with Binomial Pump Model*

A method on how to take into account pump statistics and spontaneous atomic decays when calculating the photon-number distribution of lasers in photon-number representation is presented. The intracavity phonon-number and extracavity photocount distributions with binomial pump and spontaneous atomic decays are calculated. In two limit cases, the results of calculations transit respectively to the photon-number distributions of systems with common Poissonian pump and regular pump, and both with the spontaneous atomic decays being suppressed.

THE RELATION BETWEEN THE TWO METHODS FOR DESCRIBING MARKOVIAN NOISES

A general method used to calculate the time-dependent probability distribution from the switching time distribution and the transition probability for Markovian noises is presented, and the way how to describe the noises treated as diffusion processes such as noise by the jump model (namely, and ) is given, which makes it possible to apply the stochastic trajectory technique and the definition method to the above noises.

Investigation Of All Sealed Transverse Flow 5 Kw Cw With Helium-free Co/ sub 2/ Laser

Water-operated heat exchanger since line-narrowed outputs can be obtained maintaining the continuous wavelength tunability. In this paper, we demonstrate 10 GHz active frequency shift using a high-pressure CO, laser. The experimental apparatus is shown in Fig. 1. The main section of the system was an injection-locked high-pressure CO, laser with a gain volume of 1 X 1 X 30 cm’. The laser can operate at a pressure up to 10 atm. Then, the maximum input energy density was 1000 J/t. In addition to a main cavity consisting of a rear reflector (RR) and an output coupler (OC), a subcavity was constructed by the RR and a total reflector (TR). The RR was mounted on the laser tube in order to shorten the cavity length. The lengths of the main cavity and the subcavity were 95 cm and 105 cm, respectively. An A 0 frequency shifter instaIled in the subcavity was driven at a frequency of 40 MHz. The experiment was carried out at around the 1OP (20) line since no dispersive element for coarse tuning was used. Figure 2 shows the frequency shift as a function of the gate pulse width of the PC. The slope of 9.5 GHz/ ks agreed well with the value of 9.4 GHz/ks calculated from the round-trip frequency shift of 80 MHz and the round-trip time of 8.5 ns in the subcavity. The maximum frequency shift obtained was 9 GHz at a pressure of 8 atm. At higher pressures the maximum frequency shift was decreased by the reduction of the gain duration time although the gain bandwidth became wider. In order tu select other wavelength regions, we replaced the RR by a low-dispersive (50 lines/”) diffraction grating. The frequency shift was successfully obtained without degrading the tuning linearity and the maximum frequency shift. “Department of Physics, Science University of Tokyo, 1-3 Kagurazaka, Shinjyuku-ku, Tokyo 262, IAPAN