Cheng Bingying

The influence of hole shape on enhancing transmission through subwavelength hole arrays

The extraordinary light transmission through a 200-nm thick gold film when passing through different subwavelength hole arrays is observed experimentally. The sample is fabricated by electron beam lithography and reactive ion etching system. A comparison between light transmissions shows that the hole shape changing from rectangular to diamond strongly affects the transmission intensity although both structures possess the same lattice constant of 600 nm. Moreover, the position of the transmission maximum undergoes a spectral red-shift of about 63 nm. Numerical simulations by using a transfer matrix method reproduce the observed transmission spectrum quite well.

CRYSTALLIZATION OF DIELECTRIC SPHERES IN LASER STANDING WAVE FIELD

Experimental study on crystallization of polystyrene spheres and SrTiO3 particles in laser standing wave field is presented. The diameter of polystyrene, which are able to be trapped, is 7 times smaller than that reported by Burns, the corresponding lattice constant is reduced to 1.5 μm. The crystallization effect of SrTiO3 particles with a refractive constant of 2.5 in the visible range is observed for the first time. Based on the results above we believe that it is possible to construct photonic crystal with lattice constant extended to visible wave range by this method.

Competition between stimulated Raman scattering and resonant laser emission

Competitive phenomena between stimulated Raman scattering and resonant laser emission in atomic lead are studied through photodissociation of PbCl2 with a UV laser. The different dependences of their intensities on the UV power, the density of PbCl2 and the pressure of buffer gases are investigated. The results indicate that under the conditions of high pump intensity and low buffer gas pressure SRS can have the advantage of RLE.

THE REFLECTIVE PROPERTIES OF BROADBAND OPTICAL MULTILAYERS

Binary multilayers with a certain kind of disorder may exhibit high reflection range over a very wide bandwidth. The dependencies of this bandwidth on the center wavelength, random layers sequence, refractive contrast of the coating materials, layer thickness errors and the angle of incidence have been studied numerically. Our simulations have shown that broadband reflectors can be designed for various applications. The reflective curves for staggered multilayers are also computed. The results show that the broadening effect of irregular multilayers is dominated by its degree of disorder. A broadband TiO2-SiO2 multilayer is fabricated. The measured width of the transmittance less than 1% for this multilayer covers 400 nm, from 700 to 1100 nm, which is just the tuning range of Ti: sapphire lasers.

Study on light localization of one-dimensional disordered multilayer

Antimonite and cryolite are used as the high and low refractive index coating materials to be evaporated alternately to the glass substrates. All cryolite layers have the same thickness d/4na, and the thickness of antimonite layers varies randomly around an average value d/4nb, with =650 nm, na and nb their refractive indices. Three kinds of multilayer are prepared, they possess the same degree of thickness disorder, but different total lengths, i.e., 10, 15 and 21 periods. We measure the transmission and reflection spectrum after the light passing through these multilayers. The exponential intensity variation versus total length is experimentally demonstrated, and the light localization length is then obtained. Our experimental results can be fitted very well with the numerical simulation. Based on the measured and calculated localization length, the effects of phase coherent Bragg reflection and Anderson localization are discussed.

Stimulated Emission Originated from Collision of Long Life Zn

Under the resonant excitation of Zn atomic 4p 3P1 state a strong stimulated emission at 481.0 nm is produced, which corresponds to the transition between 5s 3S1 and 4p 3P2 of Zn. If N2 molecular gas is used as buffer gas instead of rare gas He or Ar, the stimulated emission may be enhanced by several orders of magnitude. The dependences of intensity on density of atomic Zn and N2 pressure are studied experimentally. The mechanism which causes population inversion is proposed.

Emission Spectrum of Zn2 Excimers

Under laser excitation of vaporized zinc to 4s4p 3P10 metastable level, the emission bands at violet and ultraviolet ranges were observed. The radiative decay time of 20 ns has been measured for both bands. The temporal behavior and excitation condition indicate that they are possibly from the same state 3Σu+ of Zn2 molecule. The wavelength range of the two bands coincides with theoretical predication.

GENERATION OF STIMULATED-EMISSION BY VISIBLE MULTIPHOTON DISSOCIATION OF PBCL2 MOLECULES

Stimulated emission was generated at the 722.9nm line of neutral lead atoms by multiphoton dissociation of PbCl2 molecules with a DPS dye laser. Anti-Stokes Raman scattering around 283.3nm was also observed. The effects of the heat-pipe oven temperature and pump laser energy on the 722.9nm radiation was studied. The energy conversion efficiency of the 722.9nm laser is about 5%. It provides a way for frequency conversion by multiphoton dissociation of simple molecules with a visible laser.

Experimental study on stimulated Raman scattering originated from metastable population of atomic Pb

Under excitation of 355nm or 266nm UV radiation some strong emissions have been observed in PbI2 vapor. Analysis shows that they are 1st, 2nd order Stokes and 1st anti-Stokes components of 355nm laser and 1st order Stokes and anti-Stokes components of 266nm laser. The initial states of Raman transition are 6p2 3P1 and 6p2 3P2 metastable states of atomic Pb, respectively. The population on it is created by photodissociation of PbI2. The dependences of Raman components on pump power, PbI2 density and pressure of buffer gas are investigated experimentally.

Coherent wave mixing process by using metastable atoms

In PbCl2 vapor under the mutual interaction of two laser beams with wavelengths at λ1=266nm and λ2=280.2nm (or 282.3nm), a strong coherent emission at 405.8nm is generated, which corresponds to transition between states 6p7s 3P10 and 6p2 3P2 in atomic Pb. The dependences of its intensity I405.8 on the power and detuning of λ2 are measured. The results show that it is caused by a four-wave mixing process in Pb, in which the initial state is a metastable state, 6p2 3P2.