Spatial Splitting and Intensity Suppression of Four-Wave Mixing in V-Type Three-Level Atomic System

We illustrate our experimental observation of coexisting the controllable spatial splitting and intensity suppression of four-wave mixing （FWM） beam in a V-type three-level atomic system. The peak number and separation distance of the FWM beam are controlled by the intensities and frequencies of the laser beams, as well as atomic density.     

Beam-size effect in time-delayed laser-induced double gratings

We have studied theoretically the effect of the probe-beam size on time-delayed laser-induced double gratings by assuming that the probe beam is described as a Gaussian beam. LettingE _s1 andE _s2 be the Four-Wave Mixing (FWM) signals originating from the diffraction of the probe beam by the gratings, the condition for the occurrence of the FWM signal modulation is that the divergence angle ofE _s1 andE _s2 is larger than half of the intersection angle between the propagation directions ofE _s1 andE _s2. We have also proposed methods to increase the modulation contrast.     

Enhancing and suppressing four‐wave mixing in electromagnetically induced transparency window

We demonstrate the enhancement and suppression of four‐wave mixing (FWM) in an electromagnetically induced transparency (EIT) window in Y‐type ⁸⁵Rb atomic system. The generated two‐photon FWM signal can be selectively enhanced and suppressed via an EIT window. The EIT of probe as well as the enhancement and suppression of FWM signals can be modified by the sequential‐cascade double dressing. The influence of different probe polarization configurations is also studied. Different polarization states of the probe laser can select different transitions among Zeeman sublevels and different dressing strengths. Copyright © 2010 John Wiley & Sons, Ltd.     

Effect of Ag Nanoparticles on Optical Properties of R6G Doped PMMA Films

The composite PMMA films containing Ag nanoparticles and rhodamine 6G are prepared. We investigate the fluorescence properties and nonlinear optical properties of R6G/PMMA films influenced by Ag nanoparticles. The fluorescence enhancement factor is about 3.3. The corresponding nonlinear refractive index is measured to be -2.423 ×10^-8 esu using the Z-scan technique, which is much enhanced compared with the R6G/PMMA film. The results indicate that these enhancements are attributed to surface plasmon resonance of Ag nanoparticles.     

Highly efficient inelastic four-wave mixing using dual induced transparency and coherently prepared states

We investigate a life time broadened and coherently prepared five-state system for multi-wave mixing processes. We show that very efficient wave mixing occurs, producing an unconventional mixing wave that has the characteristics of both conventional four-wave mixing (FWM) and stimulated hyper-Raman (SHR) emission. In addition, we show interesting multiple simultaneous multi-photon interference effects at large propagation distances and demonstrate more than 10 orders of magnitude suppression of populations of the probe wave terminal state and the near three-photon resonance mixing wave generating state. These new type of multi-photon interference based induced transparency effects, which are critically dependent on two distinctive relaxation processes involving both an external supplied and an internally generated fields, are fundamentally different from the conventional three-state electromagnetically induced transparency effect which does not depend on propagation. As a consequence, both the probe and the wave-mixing field to propagate nearly free of absorption and distortions in a highly dispersive medium.     

Polarization enhancement and suppression of four-wave mixing in multi-Zeeman levels

Polarization dependence of the enhancement and suppression of four-wave mixing (FWM) in a multi-Zeeman level atomic system is investigated both theoretically and experimentally. A dressing field applied to the adjacent transition can cause energy level splitting. Therefore, it can control the enhancement and suppression of the FWM processes in the system due to the effect of electromagnetically induced transparency. The results show that the pumping beams with different polarizations select the transitions between different Zeeman levels that, in turn, affect the enhancement and suppression efficiencies of FWM.     

Efficient four-wave mixing of a coupled double quantum-well nanostructure

We propose an efficient four-wave mixing (FWM) scheme in an asymmetric semiconductor double quantum-well (SDQW) structure based on intersubband transitions, and obtain the corresponding explicit analytical expressions for the input probe and generated FWM pulsed fields by use of the coupled Schrödinger-Maxwell approach. Under the resonant and phase-matched conditions, the FWM efficiency versus several variables is also discussed in details and the maximum FWM efficiency of the system under study is greater than 25%. Such a semiconductor system is much more practical than its atomic counterpart because of its flexible design and the controllable interference strength. This nonlinear optical process in the SDQW solid-state material can be used for efficiently generating coherent short-wavelength radiation.     

Competition between Dispersion and Absorption of Doubly-Dressed Four-Wave Mixing and Dressed Six-Wave Mixing

We study the competition between dispersion and absorption of doubly-dressed four-wave mixing （DDFWM） and dressed six-wave mixing. In the case of weak coupling fields limit, we find DDFWM signal is affected by destructive interference between four-wave mixing（FWM） and six-wave mixing as wen as constructive interference between FWM and eight-wave mixing. By analysing the difference between two kinds of doubly dressing mechanisms （parallel cascade and nested cascade） in this opening five-level system, we can further understand the generated high-order nonlinear optical signal dressed by multi-fields.     

Enhancement and suppression of spatial splitting four-wave mixing in atomic medium

We experimentally report on the evolution from singly-dressed to doubly-dressed four-wave mixing (FWM) process by controlling the powers of the probe, the pump and the dressing fields respectively. The differences in the enhancement and the suppression of FWM signal between the two-level and cascade three-level atomic systems are observed and explained by the multi-dressed effect theoretically. Both the x direction and the y direction spatial splittings of the degenerate-FWM (DWFM) beams are obtained. We also investigate the switch between the enhancement and the suppression of the DWFM signals and between its spatial splittings in x direction and y direction. The spatial splittings in x direction and y direction can be controlled by the relative position and the intensity of the involved laser beams. Such a study can be useful for optimizing the efficiency of the FWM process and providing potential applications in spatial signal processing.     

Mid-infrared efficient generation by resonant four-wave mixing in a three-coupled-quantum-well nanostructure

We present a cascade configuration for the realization of highly efficient four-wave mixing (FWM) process in an asymmetric semiconductor three-coupled-quantum-well (TCQW) structure based on intersubband transitions (ISBTs). In the proposed TCQW scheme, the efficiency of the generated FWM mid-infrared (MIR) signal is significantly enhanced and the obtained maximum efficiency is greater than 50%. The corresponding explicit analytical expressions for the input probe and generated FWM pulsed fields are derived by use of the coupled Schrödinger-Maxwell approach and the FWM efficiency versus several variables is also discussed in details. Such a semiconductor system is much more practical than its atomic counterpart because of its flexible design and the wide adjustable parameters. This nonlinear optical process in the TCQW solid-state material can be used for efficiently generating coherent short-wavelength radiation.     

Experimental demonstration on 40 Gbit/s all-optical multicasting logic XOR gate for NRZ-DPSK signals using four-wave mixing in highly nonlinear fiber

We propose and demonstrate all-optical multicasting logic XOR gate for non-return-to-zero differential phase-shift keying (NRZ-DPSK) signals by using non-degenerate four-wave mixing (FWM) in a highly nonlinear fiber (HNLF). Theoretical analysis regarding the operation principle of NRZ-DPSK logic XOR gate is clearly described by deriving an analytical solution under the non-depletion approximation. The NRZ-DPSK logic XOR operation is attributed to the linear relationship of complex amplitudes between converted idlers and input NRZ-DPSK signals. By using three non-degenerate FWM processes in an HNLF, 40 Gbit/s all-optical multicasting logic XOR gate for NRZ-DPSK signals are successfully demonstrated in the experiment.     

Nonlinear Optical Properties of Novel Polymeric Rare Earth Phthalocyanine Studied Using Picosecond Z-Scan Technique

Three novel tri-dimensional phthalocyanine polymers, with lanthanum （LaPPc）, gadolinium （GdPPc） and ytterbium （YbPPc） as centric atoms, have been synthesized from a tetranuclear phthalonitrile. Third-order optical nonlinearities of these compounds in DMF solution are measured by a picosecond Z-sacn technique at 532 nm. It is found that all the compounds show reverse saturation absorption and nonlinear self-focus refraction effect. The second-order molecular hyperpolarizabilities are calculated to be 1.82×10^-23, 1.48×10^-23 and 1.45×10^-23 esu for LaPPc, GdPPc and YbPPc, respectively. The differences among their nonlinear optical properties are attributed to the special tri-dimensional structure and the variation in rare earth atoms.     

受限原子极化相干缀饰四波混频光谱

研究了两电介质面间级联四能级系统原子的缀饰四波混频(FWM)光谱.在缀饰场的作用下FWM信号可产生Autler-Townes (AT)分裂,分裂所产生的峰及凹陷的线型及缀饰场对FWM信号的抑制与增强效应均受原子极化相干及受限原子与光场相互作用瞬态机制的调制.     

Determination of Zero-Dispersion Wavelength by Four-Wave Mixing

We present an improved approach to determine the zero-dispersion wavelength by measurement of the four-wave mixing （FWM） effect employing the two-tunable-laser scanning method. The FWM behaviour of combined fibres with two different zero-dispersion wavelengths is investigated theoretically and experimentally. The results are compared with those by regular zero-dispersion wavelength test instrument using phase shift technique. The theoretical and experimental results confirm the feasibility of determination of zero-dispersion wavelength by FWM.     

Amplitude Regenerative Characteristics of RZ-DPSK Wavelength Converter Based on Four-Wave Mixing in SOA

We investigate the phase-preserving amplitude regenerative characteristics of the return-to-zero （RZ） differential- phase-shift-keying （DPSK） wavelength conversion based on four-wave m/xing （FWM） in a semiconductor optical amplifier （SOA）. The Q-factor and the optical signal-to-noise ratio （OSNR） before and after conversion are experimentally obtained and analysed in different input noise power levels. In both the continuous-wave and synchronous clock pumping cases, we find that there is amplitude clamping in the FWM conversion due to the gain saturation of SOA, which can suppress the amplitude fluctuation of the converted DPSK signal before and after demodulation. We have achieved 2-dB Q penalty improvement in our experiment demonstration of lOGbit/s RZ-DPSK signal with OSNR lower than 19dB.     

Non-perturbative wave-packet calculations of time-resolved four-wave-mixing signals

We extend a method proposed by Seidner et al. [J. Chem. Phys. 103, 3998 (1995)] to extract directional terms from a time-dependent molecular polarization to obtain time-resolved four-wave-mixing (FWM) signals. Instead of employing perturbation theory, the total polarization induced in the molecular sample by the interaction with several femtosecond laser pulses is determined by solving the time-dependent Schr?dinger equation for the nuclear dynamics in coupled electronic states numerically exact. Repeating the calculation for several combinations of relative phases of the involved fields leads to a linear system of equations for the contributions emitted in different directions. Gas-phase I₂ molecules serve as a numerical example. Received: 22 September 1999 / Published online: 30 June 2000     

Strangeness Suppression in e+e－ Light Flavour Jets

From the simple physical picture of quark combination model, we obtain the generate probabilities of various particles and relative ration in e⁺e^－→q₀q₀→h′s process, and find that the relationship between the ration of strange hadron to unstrange hadron γ and the strangeness suppression factor λ. Our results can be used to explain particle ration enhancement observed in experiments without assumption of strangeness suppression factor enhancement.     

Influence of Temperature on Stimulated Raman Scattering in Single-Mode Silica Fibre

One piece of single-mode silica fibre is used to study of temperature characteristics of stimulated Raman scattering (SRS), additional peaks (double-humped) are observed at both sides of pump light and 1^st-order Stokes light in the experiment. The frequency shift of the double-humped is calculated by stimulated Four--Photon mixing (SFPM) phase matching theory, the result is consistent with the frequency shift of this experiment. Simultaneously, the experimental conditions accord with the theoretical calculation of effective coherence length. We indicate that the double-humped phenomenon is caused by SFPM. The intensity of double-humped is first increased, then decreased and finally disappeared as the temperature increases. This phenomenon has been explained theoretically.     

Wave packet dynamics in different electronic states investigated by femtosecond time-resolved four-wave-mixing spectroscopy

This paper reviews results on wave packet dynamics investigated by means of femtosecond time-resolved four-wave-mixing (FWM) spectroscopy. First, it is shown that by making use of the various degrees of freedom which are offered by this technique information about molecular dynamics on different potential-energy surfaces can be accessed and separated from each other. By varying the timing, polarization, and wavelengths of the laser pulses as well as the wavelength of the detection window for the FWM signal, different dynamics are coherently excited and probed by the nonlinear spectroscopy. As a model system we use iodine in the gas phase. These techniques are then applied to more-complex molecules (gas phase: benzene, toluene, a binary mixture of benzene and toluene; solid state: polymers of diacetylene matrix-isolated in single crystals of monomer molecules). Here, ground-state dynamics are investigated first without any involvement of electronically excited states and then in electronic resonance to an absorption transition in the investigated molecules. Signal modulations result which are due to wave packet motion as well as polarization beats between modes in different molecules. Phase and intensity changes yield information about intramolecular vibrational energy redistribution, population decay (T₁), phase relaxation (T₂), and coherence times. Received: 12 October 1999 / Published online: 13 July 2000     

Interactions of Three Dual-Dressing Effects of Four-Wave Mixing in a Five-Level Atomic System

We study the four-wave mixing （FWM） in an opening five-level system with two dressing fields. There axe three kinds of doubly dressing mechanisms （parallel cascade, sequential cascade, and nested cascade） in the system for doubly dressed four-wave mixing. These mechanisms reflect different correlations between two dressing fields and different effects of two dressing fields to the FWM. Investigation of these mechanisms is helpful to understand the generated high-order nonlinear optical signal dressed by multi-fields.