简并四波混频中相位共轭波强度的振荡特性研究

一、引言 文献1中用波长为0．53μm，脉宽为35ps的激光脉冲作泵浦源，以对称激励的形式，研究了透明以及可饱和吸收介质的筒并四波混频（DFwM）中后向相位共轭波能量E与读出光束相对于写入光束延迟到达非线性介质的时间△t之间的关系，     

多通道简并的四波混频

使用脉冲调QNd:YAG倍频激光辐射,香豆素152染料二氯乙烷溶液作混频介质,研究了四通道简并的四波混频。各通道后向波转换效率为4％左右。     

氟化锂晶体F3^＋色心四波混频研究

利用简并四波混频技术观测到LiF晶体中F_3~+色心的非线性光学相位共轭效应,以脉冲染料激光为泵浦光得到最大相位共轭反射率约为0.1%,根据LiF晶体F_3~+色心的能级特点从理论上阐明了F_3~+色心系统非线性饱和吸收和四波混频的物理起源。     

The mechanism and dynamics of transient thermal grating diffraction in nematic liquid crystal films

We have studied the mechanism and the dynamics of degenerate four-wave mixing in a nematic liquid crystal film. Nanosecond laser pulses are used to generate an index grating associated with the changes in the density and in the order parameter. We have measured and analyzed the contributions from these two mechanisms, their interference effects rise and decay time constants, and have also performed a detailed analysis of the diffraction efficiency. This study quantitatively characterizes the potential usefulness of nematie films for four-wave mixing based applications.     

Quantitative nonlinear spectroscopy: a direct comparison ofdegenerate four-wave mixing with cavity ring-down spectroscopy appliedto NaH

Cavity ring-down spectroscopy and degenerate four-wave mixing have been applied for spectroscopic studies, temperature determination, and measurement of relative dipole transition moments of photochemically produced sodium hydride. In our experiment, NaH was formed within a heat-pipe oven after 3p excitation of sodium in a hydrogen atmosphere with a second dye laser. The reaction product NaH was probed in the near ultraviolet part of the spectrum at 382 nm with 1-4-μs delay to the excitation pulse using both a linear and nonlinear spectroscopic technique with a pulsed dye laser source (pulsewidth 15-ns full-width half-maximum). The strengths and limitations of these two spectroscopic techniques are discussed. Since the two processes depend on different parameters and the image-forming beams have different properties, it is difficult to define a single criterion for comparison. But our measurements indicate that cavity ring-down spectroscopy is a powerful tool with a sensitivity better than 10⁹ particles per cm³ and quantum state which is comparable to degenerate four-wave mixing in our case     

利用四波混频消除图像畸变的局限性

一、引言 在大多数理论研究中,人们仅在平面泵浦和探测波的条件下研究四波混频产生位相共扼波的机理、手段。然而在实际应用简并四波混频共轭波补偿大气干扰时,入射到位相共轭镜上的探测波不可能是理想平面波。但是在大多用相位共轭消畸变的方案中都忽略了畸变探测波在简并四波混频中产生什么样的“共轭波”这个问题。本文将讨论利用简并四波混频消除通过湍流大气传输图像的畸变问题。     

Transient coherent degenerate four-wave mixing

A set of coupled equations is derived and used to analyze transient coherent degenerate four-wave mixing (DFWM) in a two-level system. The numerical results show that in the case of near-resonance, intense pumping, and short pulses, the properties of degenerate four-wave mixing have interesting coherent interaction characteristics, such as quasi-periodicity in the pump pulse area, probe pulse areas, and energy reflectivity, oscillatory behavior of the DFWM pulse, and generation of a DFWM signal in the case of delayed incidence, where the three incident pulses do not overlap in the medium     

紫外飞秒激光的脉宽测量方法

相对于近红外波段的飞秒激光脉冲，紫外波段的飞秒脉冲由于具有单光子能量高、聚焦特性好、电离率高和成丝阈值低等优点，在高功率密度光场的产生、等离子体光物理等领域有着越来越广阔的应用前景，成为激光技术的研究热点。随着紫外飞秒激光技术的发展，传统的脉宽测量方法不能满足需求。指出了紫外飞秒激光脉宽测量研究的主要进展，讨论了目前可用于紫外飞秒激光脉宽的测量方法，主要有双光子荧光测量法、互相关法、简并四波混频法、多光子电离法，介绍了相关测量原理与特点。在此基础上，对紫外飞秒激光脉宽测量技术研究前景进行了展望。     

Investigation of transient nonlinear optical mechanisms using avariable pulselength laser

We show a variable pulselength laser to be extremely useful when investigating the dynamics and parameters of optomechanical nonlinarities in optical materials. Pulselength variability allows observation of the transient nonlinear behavior using nanosecond pulses and determination of the underlying physical mechanisms using subnanosecond pulses. It also enables observation of the transition response between the two time regimes where intrinsic polarizabilities compete with optomechanical effects. We examine the transient nonlinear scattering properties of an optical power limiter, platinum ethynyl, and compare it to carbon disulfide using degenerate four-wave mixing. Intensity, polarization, and pulselength control allow us to measure acoustic scattering and decay parameters, χ⁽³⁾ magnitudes, and the transient laser-induced grating behavior     

Cross-coupled phase conjugation through two-frequency four-wave mixing in dyes

Two-frequency four-wave mixing in a dye is demonstrated, in which degenerate four-wave mixing is performed simultaneously within the absorption and emission frequency spectra, with two separate sets of beams. The coupling between the two bands gives rise to backward output waves at both frequencies, which are proportional to the phase conjugate of a single probe which can be at either of the two frequencies. Forward-propagating waves which are not conjugated are also generated at both frequencies. The frequency shifted outputs are tunable over the bandwidth of the spectrum in which they lie. A theoretical analysis is performed which is based on a four-level system model of the ground and first excited singlet states in a dye. Resulting are coupled equations, which are solved to yield the efficiencies of the various outputs. Experiments give results in good agreement with the theory.     

Optical correlation in Bi12SiO20 at 632.8 nm

Optical image correlation with a low-power HeNe laser has been demonstrated using the phenomenon of degenerate four-wave mixing in Bi12SiO20. Preliminary results for character recognition, using a compact two-dimensional image processor, are presented.     

Terahertz generation based on four-wave mixing difference frequency by resonance-enhanced third-order nonlinear of media

Using nanosecond pulse near-infrared and mid-infrared laser pulses as the pump source, we obtain terahertz wave sources via four-wave difference frequency mixing. From the coupled wave theory, we analyze the four-wave mixing process of GaSe crystal and alkali metal vapor in detail, get the analytical expression of terahertz wave output power, and discuss the conditions for achieving phase matching. By adjusting the pump frequency, the third-order nonlinear polarization of alkali metal vapor is r...     

Optical sampling using nondegenerate four-wave mixing in asemiconductor laser amplifier

Picosecond optical sampling using nondegenerate four-wave mixing in a semiconductor laser amplifier (SLA) is demonstrated for the first time. High-peak-power pulses and electrical gating of the SLA produce an optical sampling signal with a high signal-to-noise ratio     

Nanometer wavelength conversion of picosecond-optical pulses usingcavity-enhanced highly nondegenerate four-wave mixing in semiconductorlasers

We demonstrate 5.0-nm wavelength conversion of a mode-locked optical pulse train by cavity-enhanced highly nondegenerate four-wave mixing in a 1.53-μm injection-locked bulk InGaAsP V-groove laser. Input pulses having 17 ps duration are broadened to 61 ps due to the filtering imposed by the mixing laser. A simple two-mode rate equation model of an injection-locked semiconductor laser is used to explain the dependence of the output pulse broadening on bias current and injected pump power. The temporal response is improved by decreasing the laser bias current or increasing the injected pump power     

Picosecond optical sampling using four-wave mixing in fibre

An all-optical sampling system with 20 ps resolution realised by employing four-wave mixing in a fibre is demonstrated. Using only semiconductor laser sources, picosecond pulses are displayed on a microsecond time scale with a low speed receiver.<>     

Small-signal analysis of optical-frequency conversion in aninjection-locked semiconductor laser

A theory of optical-frequency conversion using nearly degenerate four-wave mixing (FWM) in an injection-locked semiconductor laser is presented by small-signal analysis. The bandwidth of the converted signal is determined by the relaxation resonance frequency of the laser. The greatest conversion efficiency appears when the pump-probe detuning frequency is equal to the relaxation resonance frequency. The influence of the bias of the laser, the pump power and the other injection-locking parameters on the frequency conversion efficiency is discussed. The theoretical results agree with experiments     

Laser mirror by degenerate four-wave mixing in a saturable amplifier

A phase conjugate mirror by degenerate four-wave mixing in a saturable gain medium has been successfully operated in a pulsed laser cavity. This mirror works with low-intensity pump beams when they are resonant with the nonlinear medium. The pump beams can thus be delivered by a continuous-wave, frequency stable laser of low power. In such a device, the pulsed laser emission displays automatic frequency locking to the pump waves without cavity length stabilization.     

Measurement of the stimulated carrier lifetime in semiconductor optical amplifiers by four-wave mixing of polarized ASE noise

We present a simple experiment aimed at measuring the stimulated carrier lifetime in semiconductor optical amplifiers (SOA's). The technique relies on polarization-resolved nearly degenerate four-wave mixing (FWM) of a laser source with an amplified spontaneous emission (ASE) noise source. The method can quickly characterize the bandwidth performance of active layers for application in a cross-gain or cross-phase wavelength converter.     

Infrared pulses of 1 picosecond duration tunable between 4 μmand 18 μm

The generation of infrared pulses via difference frequency mixing of Nd:glass laser pulses and infrared dye laser pulses is discussed. Tuning between 4 and 18 μm is achieved by various combinations of laser dyes (dye No. 5 and A 9860) and nonlinear crystals (AgGaS₂ and GaSe). The energy of the mid-infrared pulses is in the order of a microjoule; and the photon conversion efficiency is ≲2%. The duration of the nearly bandwidth limited pulses is measured to be 1 ps. The system operates with a repetition rate of 1 Hz