Dissection of dispersed off‐resonant femtosecond degenerate four‐wave mixing of O2

Simultaneous time and frequency detection in off‐resonant femtosecond degenerate four‐wave mixing (fs‐DFWM) experiments displays spectral features that are covered in standard, nondispersed, frequency‐integrated measurements. The application of laser fields with finite bandwidths, narrower than or comparable to the rotational Raman bands, affects the observed coherent signals. Information available from such experiments is split between the time and frequency domains and an improved measurement necessitates a combined detection. Rotational recurrences of oxygen (O₂), measured by dispersed fs‐DFWM at room temperature, exhibit spectral characteristics, using 800‐nm laser pulses with ∼100 fs duration. Analysis of the detected signals in both dimensions incorporating temporal and spectral trends can assist in the extraction and interpretation of chemicophysical quantities from the experiment. The dispersed recurrent signals are in accordance with simulations. Copyright © 2011 John Wiley & Sons, Ltd.     

Degenerate and two‐color resonant four‐wave mixing of C2− in a molecular beam environment

In this paper, we demonstrate that degenerate and two‐color resonant four‐wave mixing spectroscopy is applicable for the sensitive and selective characterization of negative ions in a molecular beam environment. Results are shown for C , which is produced by discharging a mixture of acetylene and argon prior to supersonic expansion. Substantial signal‐to‐noise ratios of ≈ 150 show that the method is generally applicable for high‐resolution optical double‐resonance spectroscopy of negative ions. A detection sensitivity for C of ≈ 10⁷ ions/cm³ is estimated. Copyright © 2010 John Wiley & Sons, Ltd.     

Flame temperature diagnostics with water lines using mid‐infrared degenerate four‐wave mixing

The feasibility of using degenerate four‐wave mixing (DFWM) for hot gas thermometry in the mid‐infrared spectral region is, for the first time, demonstrated by probing molecular ro‐vibrational transitions of water. DFWM spectra of hot water were recorded in specially designed flames, providing a series of temperatures varying from 1000 to 1900 K and, the dramatic spectral structure variations were used as temperature indicator. The intensity ratios between two hot water line groups at around 3231 cm⁻¹ were especially studied and composed into a calibration table for flame temperature measurement using DFWM spectra. The saturation properties of different lines were also studied by recording the line intensity ratios as a function of laser power, and the results indicated that saturated excitation was in favor of reliable temperature measurements. As validation, infrared DFWM spectra in an φ = 1.52 flat premixed methane/air flame were recorded, and a good temperature value was obtained. Moreover, the recently released HITEMP2010 database as well as its previous version HITEMP2000 were adopted to simulate the hot water spectra and to analyze the line intensity ratios. Copyright © 2011 John Wiley & Sons, Ltd.     

Six‐wave mixing induced by free‐carrier plasma in silicon nanowire waveguides

Nonlinear wave mixing in mesoscopic silicon structures is a fundamental nonlinear process with broad impact and applications. Silicon nanowire waveguides, in particular, have large third‐order Kerr nonlinearity, enabling salient and abundant four‐wave‐mixing dynamics and functionalities. Besides the Kerr effect, in silicon waveguides two‐photon absorption generates high free‐carrier densities, with corresponding fifth‐order nonlinearity in the forms of free‐carrier dispersion and free‐carrier absorption. However, whether these fifth‐order free‐carrier nonlinear effects can lead to six‐wave‐mixing dynamics still remains an open question until now. Here we report the demonstration of free‐carrier‐induced six‐wave mixing in silicon nanowires. Unique features, including inverse detuning dependence of six‐wave‐mixing efficiency and its higher sensitivity to pump power, are originally observed and verified by analytical prediction and numerical modeling. Additionally, asymmetric sideband generation is observed for different laser detunings, resulting from the phase‐sensitive interactions between free‐carrier six‐wave‐mixing and Kerr four‐wave‐mixing dynamics. These discoveries provide a new path for nonlinear multi‐wave interactions in nanoscale platforms.

     

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.     

Origin of spectral interferences in femtosecond stimulated Raman microscopy

In femtosecond stimulated Raman microscopy (FSRM), a spectrally narrow (Raman pump) pulse and a broad (Raman probe) laser pulse are employed to generate the Raman spectra of microscopic objects. The resulting spectra exhibit, in addition to the Raman bands, spectral modulations of comparable amplitude. Here a model is devised that attributes these modulations to a four‐wave mixing (FWM) process. Two light fields of the probe pulse and one field of the pump pulse serve as input fields. The resulting FWM field experiences a heterodyne amplification by the probe field. Simulations based on this model reproduce the appearance of the spectral modulations. Furthermore, the amplitude of the modulations exhibits dependences on the energies of pump and probe pulses as well as on the nonlinear refractive index n₂, which are in line with the model. Copyright © 2011 John Wiley & Sons, Ltd.     

Investigation of tunable trap filter utilizing intense signal four wave mixing model in highly non-linear fiber

Tunable trap filter based on highly non-linear fiber (HNLF) utilizing degenerate four wave mixing (FWM) model has been proposed and investigated. The output powers in a FWM configuration are calculated as a function of the input signal power, with the result that new-wavelength is efficiently generated, leading to about −26 dB signal depletion. The signal loss spectra are also simulated under the condition of different initial signal powers, injected wavelengths, and fiber lengths.     

瑞利型非简并四波混频:一种研究超快过程的新方法

文章提出了用瑞利型非简并四波混频来研究物质的超快过程，与传统的时间领域技术不同，瑞利型非简并四波混频是一种频率领域的光谱学方法，它的时间分辨率与激光的脉冲宽度无关。     

近简并四波混频相位共轭介质中的光强分布

从求解耦合波方程出发，详细研究了非线性光学介质中由近简并四波混频所产生的相位共轭过程。以上述波方程的解为基础，给出作为混频结果的反射传播相位共轭波沿介质轴向的光强分布，得到比以往文献中所报道的更为精确的结果，从而为选择工作物质的最佳尺寸提供了理论依据。     

Carrier relaxation dynamics in InAs/InGaAlAs quantum dashes

We characterize size-dependent carrier relaxation dynamics of partial laser structures containing quantum dashes by time-resolved degenerate four wave mixing between 1.2 and 1.6 μm.     

Opportunities for wavelength conversion with on‐chip diamond ring resonators

Recent progress in the fabrication of high‐quality synthetic diamond and of diamond waveguide structures has enabled photonics researchers to start exploiting the unique optical properties of diamond for various applications. In this article the promise of on‐chip diamond ring resonators for wavelength conversion based on Kerr and Raman‐resonant four‐wave mixing is numerically demonstrated. After examining to what extent both dispersion‐engineered phase‐matching and “automatic” quasi‐phase‐matching can be established in diamond ring converters, it is shown that such a “double‐matching” approach can yield high conversion efficiencies for a wide range of wavelengths in the near‐infrared/mid‐infrared domain, as well as in the ultraviolet/visible domain.     

偶氮化合物中级联作用引起的高阶多波混频的研究

用三维简并四波混频的实验装置，在偶氮化合物中观察到了多波混频效应，在接收屏上，除了三个泵浦光斑，还观察到了由于多波耦合产生的另外１４个排列整齐的信号光斑，这个现象可望被广泛用光计算，信息处理和光互连中。     

单模光纤中四波混频的自诱导相位匹配

报道了无双折射单模光纤中四波混频的一种新型相位匹配方式,这种相位匹配仅由抽运光产生的自相位调制和互相位调制的共同作用即可提供,文中报道了实验结果,并从理论上成功地解释了该四波混频相位匹配的机理,与实验符合得很好。     

Temporally Correlated Narrowband Biphoton Interference Based on Mach–Zehnder Interferometer

Since early 1990s, Mach–Zehnder interferometer has been used to investigate the interference of biphoton wave packets. Due to subpicosecond time coherence of biphoton generated by spontaneous parametric downconversion process, some physical processes are ignored in the interferometer, most likely the biphoton time‐domain interference. Here, the two‐photon interference phenomenon based on the Mach–Zehnder interferometer is theoretically studied, where the correlated photon pairs are produced by the four‐wave mixing in atomic system. In particular, the quantum interference effect to effectively control the coherent time of two‐photon by adjusting the input delay is used. In the damped Rabi oscillation regime, two‐photon bunching and antibunching effects are observed. In addition, in the group‐delay regime, the interference between biphoton precursor, slow‐light wave packets and also in between the precursor and the slow‐light wave packets is observed, which had never been reported before. These results may have potential applications in the fields of biphoton shaping and quantum information processing.     

Composite‐Assisted Phase‐Matching: Efficient Wavelength Conversion in Nonlinear Optical Composite Materials Containing Metal Nanoparticles

A novel phase‐matching scheme which is based on the dispersion compensation in the nonlinear optical composite materials containing metal nanoparticles is proposed. Anomalous dispersion originating from the plasmon resonance in metal nanoparticles compensates the dispersion of the host nonlinear material, leading to the perfect phase‐matching and high efficiency of nonlinear optical wavelength conversion. The effectiveness of this approach is theoretically demonstrated, taking third‐order nonlinear processes such as the direct third‐harmonic generation and four‐wave mixing in ZnO composites containing silica‐core–silver‐shell nanoparticles as examples. The results show that with the proposed phase‐matching scheme, unprecedentedly high conversion efficiency can be obtained compared with preceding results in third‐order nonlinear optical solid‐state materials.     

Observation of four-wave mixing in caesium atoms using a noncycling transition

In this paper the generation of four-wave mixing (FWM) signal using a noncycling transition of caesium atoms is investigated when the pumping laser is locked to the transition $6{\rm S}_{1/2}F=4\to6{\rm P}_{3/2}F'=4$, and meanwhile the probe frequency is scanned across the $6{\rm S}_{1/2}F=4 \to6{\rm P}_{3/2}$ transition. The efficiency of the four-wave mixing signal as a function of the intensity of the pumping beams and the detuning of the pumping beams is also studied. In order to increase the detection efficiency, a repumping laser which is resonant with $6{\rm S}_{1/2} F=3\to 6{\rm P}_{3/2}F'=4$ transition is used. A theoretical model is also introduced, and the theoretical results are in qualitative agreement with experimental ones.     

双KTP内腔参量下转换产生量子相关孪生光子对

使用双ＫＴＰ晶体串接，经光学参量振荡腔内参量下转换，在３００ｍＷ泵浦功率下，获得总功率约２３ｍＷ的强度相关的孪生光束，在１．２５ＭＨｚ处其强度差噪声功率较散离噪声极限降低５０％（３ｄＢ）。     

对称型二烷氨基蒽醌的三阶非线性光学性质研究

研究了对称型二烷氨基蒽醌的三阶非线性光学性质。通过三维简并四波混频实验对１１种低浓度溶液样品的测试，其三阶非线性极化率｜χ（３）｜达１．８～３．４×１０－１３ｅｓｕ，分子的三阶非线性超极化率γ达１．９～３．５×１０－３１ｅｓｕ。讨论了分子结构对三阶非线性光学性质的影响。     

Lower Order and Higher Order Entanglement in Four‐Wave Mixing Process

Possibilities of generation of lower order and higher order intermodal entanglement in four‐wave mixing (FWM) process are rigorously investigated using Sen‐Mandal perturbative technique. The investigation has revealed that for a set of experimentally realizable parameters, one can observe lower order and higher order intermodal entanglement between pump and signal modes and signal and idler modes in a FWM process. In addition, trimodal entanglement involving pump, signal and idler modes is also reported.     

足球烯分子三阶非线性光学性质的研究

报道了有关足球烯分子甲苯溶液中简并四波混频实验.测量出足球烯C_(70)分子和C_(60)分子的三阶超极化率张量y_(1111)分量分别为1.2×10~(-30)esu和4.0×10~(-31)esu.对应于固体样品的三阶非线性光学系数X_(1111)分量分别是2.5×10~(-8)esu和8.5×10~(-9)esu.此结果表明了足球烯分子是现有的非线性光学材料中具有较大三阶非共振电子极化率材料之一.文中还利用自由电子模型解释了非线性光学极化率的起源.