Noncollinear phase matching in fluorescence upconversion

We investigate noncollinear sum-frequency generation in a time-resolved fluorescence upconversion experiment to eliminate group-velocity mismatch (GVM), a major mechanism that deteriorates time resolution. The noncollinear geometry inherently causes phase-front mismatch (PFM) that also spoils time resolution. The effects of GVM and PFM on the time resolution are studied by numerical calculations and experiments. Based on the investigation, a fluorescence upconversion apparatus with time resolution better than 45 fs (FWHM) is demonstrated.     

基于角色散的非共线匹配宽带三倍频技术

宽带光打靶可以有效降低激光等离子体相互作用过程中非线性效应。提出一种基于角色散的非共线匹配宽带三倍频方案,利用宽带基频与窄带二倍频的非共线和频产生宽带三倍频,和频过程中通过特殊设计的渐变光栅实现不同频率的基频光束以特定角度入射,补偿了波长差异引入的位相失配使得全波段满足位相匹配条件。理论模拟表明,采用KDP晶体Ⅱ类位相匹配,将中心波长为1058 nm、带宽10 nm的宽带基频光与526.5 nm的二倍频光进行非共线匹配和频,可以实现高效宽带三倍频转换。     

Noncollinear optical frequency doubling in strontium barium niobate

The observation of a novel noncollinear optical second-harmonic generation mechanism is reported. In strontium barium niobate crystals, a circular cone of second-harmonic light is generated when a fundamental beam of intensive laser light is directed along the crystallographic c axis. It can be shown that the effect is caused by the nonlinear polarization of antiparallel ordered ferroelectric microdomains.     

Noncollinear folded mixing geometries for difference-frequency far infrared generation

Noncollinear folded geometries for far infrared generation by difference-frequency mixing of CO₂ lasers are analyzed, and are shown theoretically to provide orders of magnitude increase in the far infrared output compared with the simple noncollinear geometry used previously. The basic principle of the folded geometry has been verified experimentally.     

Efficient phase conjugation by Brillouin enhanced four wave mixing

It is shown that frequency detuning and phase mismatch effects can strongly effect the reflection coefficient of Brillouin enhanced four-wave mixing. Extremely large reflectivities (R > 10⁶) can be obtained if the intensities and frequency of the pump beams and the length of the interaction region all take on certain critical values. This theory accounts for the high reflectivity which has been reported by another author.     

Noncollinear phase-matched four-photon mixing of CO2 laser radiation in germanium

Noncollinear four photon mixing of two TEA CO₂ laser beams in germanium at room temperature has been used to obtain phase-matched generation of step tunable radiation in the 8.7 μm region which is of interest for the uranium isotope separation. Using an 8.3 cm long crystal of germanium, peak output power of ≈10kW (corresponding to 1 mJ per pulse) was obtained at 8.7 μm with 3 MW peak input power from each of the two CO₂ lasers operating at 9.6 μm and 10.6 μm.     

Noncollinear double quasi phase matching in one-dimensional poled crystals

We demonstrate simultaneous phase matching of two different nonlinear processes, using a noncollinear interaction in periodically poled crystal with single grating. The noncollinear scheme provides phase-matching solutions over continuous regions of the optical spectrum and can be used for multiple-harmonic generation as well as all-optical effects. We have demonstrated experimentally third-harmonic generation of a 3 microm pump wavelength in a noncollinear configuration using a periodically poled LiNbO3 crystal. We observed, in good agreement with theoretical calculation, very broad spectral and thermal acceptance bandwidths, as well as a relatively narrow angular bandwidth.     

Generalised dispersive phase and its effect on four wave mixing in fibers

A generalised method of calculating the efficiency of four wave mixing products in an optical fiber is presented in this paper. Apart from indicating the insufficiency of the existing theoretical model, this work brings out the importance of calculating the dispersive phase shift more precisely in combination with the nonlinear phase shift to predict the efficiencies of sideband generation. The experimental results for the generation of the first and second order sidebands are analysed. Contrary to expectations, higher powers and longer lengths of fiber do not result in larger number of sidebands. An attempt is made to understand this aspect as well as the experimentally observed fluctuations in the four wave mixing products.     

Pseudo-scalar photon mixing in a magnetized medium

Axions are pseudo-scalar particles, those which arise because of breaking of Peccei Queen (PQ) symmetry. Axions have a tree level coupling to two photons. As a consequence there exists a tree level coupling of axion to photon in a magnetic field. However, in an external magnetic field, there exists a new loop induced, axion photon vertex that gives rise to axion photon coupling. The strength of the tree level axion photon coupling in magnetic field is known to be model dependent. However, in a magnetic field, the new loop induced coupling has some interesting features. This note discusses the new axion photon vertex in a magnetized medium and the corrections arising from there. The magnitude of the correction to axion photon coupling, because of magnetized vacuum and matter, is estimated in this note. While making this estimate we note that the form of the axion photon vertex is related to the axial polarization tensor. This vertex is shown to satisfy the Ward identity. The coupling is shown to have a momentum dependent piece in it. Astrophysical importance of this extra modification is also pointed out.     

All- optical phase encoded 4-to-1 phase multiplexer using four wave mixing in semiconductor optical amplifier

Optics has already showed its potency over its electronic complements in case of superfast computing and communication systems. Semiconductor optical amplifier, (SOA) with its several nonlinear properties, plays a very crucial role in the development of high-speed all-optical processor. Multiplexer and demultiplexer are the extremely important element of the processor which takes part in utilizing different actions like encoding, decoding, routing, and the different process of data conversion and generation, etc. In this paper, the authors have proposed a scheme of phase encoded all-optical phase multiplexer using four wave mixing (FWM) property of semiconductor optical amplifier. Thus, the improved tolerance against fiber-nonlinearity and higher receiver sensitivity of phase encoding method with the fast occurring processes like FWM in SOA offers higher speed in this proposed scheme of multiplexing.     

Generation of photon pairs in dispersion shift fibers through spontaneous four wave mixing: Influence of self-phase modulation

Correlated signal and idler photon pairs with small detuning in the telecom band can be generated through spontaneous four-wave mixing in dispersion shift fibers. However, photons originated from other nonlinear processes in optical fibers, such as Raman scattering and self-phase modulation, may contaminate the photon pairs. It has been proved that photons produced by Raman scattering are the background noise of photon pairs. Here we show that photons induced by self-phase modulation of pump pulses are another origin of background noise. After studying the dependence of self-phase modulation induced photons in signal and idler bands, we demonstrate that the quantum correlation of photon pairs can be degraded by the self-phase modulation effect. The investigations are useful for characterizing and optimizing an all fiber source of photon pairs.     

Optical Bloch equations with dual photon excitation explain the polarization dependence of four wave mixing quantum beats

We explain the polarization dependence of four wave mixing (FWM) quantum beats for semiconductors as essentially due to the spin phase correlations of photo-excited electrons, rather than to Coulomb interaction between the electrons. A theoretical analysis is given within the framework of optical Bloch equations for the light–semiconductor interactions and the Luttinger–Kohn model for the band structure. Residual Coulomb interactions between charge carriers are ignored. The results suggest that the polarization dependence of FWM quantum beats is a purely coherent effect of dual photon excitations, rather than, e.g., exciton–exciton Coulomb interaction. We show that the coherence transfer between the excited states is responsible for the FWM in a configuration with orthogonally polarized pump and probe.     

Phase matched vectorial three-wave mixing in isotropic Kerr media

A theoretical analysis of vectorial three-wave mixing in isotropic Kerr media is presented. The analysis based on the coupled-wave equations describes the amplification of a weak wave by coupling with a strong pump wave phase matched by optically induced change of average refractive index. The phase matching condition for interacting waves with different polarizations is calculated, allowing a large amplification of a weak wave by three-wave mixing in thick Kerr media. The main conclusions of our theoretical analysis are supported by the results of experiments in CS₂ liquid medium.     

四波混频光相位运算器原理及其噪声性能研究

推导了抽运消耗情形下简并和非简并四波混频(FWM)闲频光幅度和相位的统一解析表达式.采用极限方法,计算证明了非相敏放大模式下闲频光相位与输入光初始相位之间的关系,揭示了FWM相位加减混合运算器的工作原理.以四相相移键控信号为例,对基于非简并FWM的相位运算器进行了设计,重点分析了三种基本加减混合运算的噪声转移性能及其对光纤长度、输入光波长和功率的依赖特性.计算表明:该运算器的噪声指数约为1.1 dB;当输入光信号的信噪比大于24 dB时无纠错编码的符号错误率可低于10~(-3).     

A method of implementation of frequency encoded all optical encryption decryption using four wave mixing

All optical encryption decryption method using frequency encoding is proposed based on semiconductor optical amplifiers. The plain text and key are encoded in frequency encoding format i.e. the states of information ‘0’ and ‘1’ are represented by two different frequencies in the c-band. The ultra fast speed of operation of the devices used for the implementation of this system makes it very attractive for future all optical secure communication network. A simple method of conversion of frequency encoded data stream and intensity encoded data stream is also described, which enables us to use same technology of production and detection of intensity encoded data signals until new techniques based on frequency encoding comes out.     

New experimental limit on photon hidden-sector paraphoton mixing

We report on the first results of a search for optical-wavelength photons mixing with hypothetical hidden-sector paraphotons in the mass range between 10⁻⁵ and 10⁻² electron volts for a mixing parameter greater than 10⁻⁷. This was a generation-regeneration experiment using the “light shining through a wall” technique in which regenerated photons are searched for downstream of an optical barrier that separates it from an upstream generation region. The new limits presented here are the most stringent limits to date on the mixing parameter. The present results indicate no evidence for photon-paraphoton mixing for the range of parameters investigated.     

Resonant four wave mixing in n-type silicon

We observe a strong resonance in the third order nonlinear optical susceptibility of n-type silicon corresponding to the valley orbit splitting of the 1s-states of phoshorous and antimony donors. Cross-sections for valley orbit Raman scattering near 10 μm obtained from our data agree with calculations based on an intraband model. The expression for the cross-section resulting from this model is equivalent to that of Jain et al.     

Microwave frequency shifting using photon acceleration

Using a Bostick Gun as a plasma source, we have been investigating the effects of a moving plasma front on the frequency of an incident R.F. signal. We have been able to measure frequency shifts of 10 MHz frequency with a 2.6 GHz signal. The density is such that the plasma frequency is well above the transmitter frequency 1.3 meters from the plasma source. No magnetic field is used.