Observation of Optical Second Harmonic Generation in Wet-Spun Films of Na-DNA

The observation of optical second harmonic generation (SHG) from wetspun films of Na-DNA is reported. The SHG signal is stronger at a relative humidity of 92% (corresponding to the B conformation of Na-DNA) than at low humidity of -33% (corresponding to a disordered conformation of Na-DNA). The strength of the SHG signal is also dependent on the orientation of the incident laser beam polarization with respect to the DNA helical axes.     

Second-harmonic generation in a near-field optical-fiber probe

Second-harmonic generation (SHG) in a near-field optical-fiber probe was observed. The tip of the probe consists of a triple-tapered fiber with an aluminum coating. For a fiber probe with an aperture size of 100 nm, the SHG conversion factor was 2.0 x 10(-11)cm(2)/W , which is as large as that of a 5-mm KDP crystal. In a probe-to-probe experiment, we demonstrated that SHG took place at the aluminum coating on the fiber probe.     

Continuous-wave quasi-phase-matched generation of 60 mW at 465 nm by single-pass frequency doubling of a laser diode in backswitch-poled lithium niobate

We report continuous-wave single-pass second-harmonic generation (SHG) in 4-mum -period 0.5-mm-thick backswitch-poled lithium niobate. Pump sources at 920-930 nm include both Ti:sapphire and diode-oscillator-amplifier lasers. SHG of a Ti:sapphire laser at 6.1%/W efficiency, producing 61 mW of power at 460 nm, is demonstrated in 50-mm-long periodically poled lithium niobate samples with a nonlinear coefficient d(eff) approximately 9pm/V, and 60 mW at 465 nm and 2.8%/W efficiency is obtained by SHG of a laser-diode source.     

Implementation and evaluation of a detector for forward propagated second harmonic signals

Second harmonic generation (SHG) is emerging as an alternative non-linear imaging method. The fact that most commercial multi-photon microscopes can be easily adapted to image SHG makes it appealing to explore the kind of sample information given by SHG. Here we describe an SHG detection implementation designed to optimize the collection of forward propagating light. A Hamamatsu H957-08 PMT is inserted at the back-focal plane of the condenser on an inverted Nikon TE300, and controlled by the existing electronics of a BioRad 1024MP system. Evaluation of the performance was done on common SHG generating preparations, KH₂PO₄ crystals and collagen. We concluded that positioning a detector at the back focal plane of the condenser provides a highly efficient detection system for second harmonic signals, with many advantages over a detector sited at the lamp housing.     

NaNO_2晶体线性和非线性光学系数的计算

使用从头计算平面波赝势方法,计算了NaNO2晶体电子能带结构,并使用改进的倍频公式计算了它的线性折射率和静态二级非线性系数,所得到的结果和实验值相符.采用实空间原子切割方法分析了阳离子和阴离子基团对光学性质的贡献.计算表明(NO2)-基团对双折射率和倍频系数的贡献占主要地位,从而进一步验证了阴离子基团理论的正确性.     

Second-harmonic generation in periodically poled nonlinear polymer waveguides

We demonstrate quasi-phase-matched (QPM) second-harmonic generation (SHG) at the optical communication wavelengths with side-chain polymer waveguides. A ridge waveguide structure is designed to support fundamental mode guiding at both the pump and the second harmonics, leading to a high field overlap integral of the guided modes. The nonlinearity contrast in the +/0 type QPM waveguide is maximized under a QPM poling electrode width of nearly half the coherence length. Using these configurations, we record a normalized SHG efficiency of 2.2% W(-1) cm(-2) in the polymer waveguide.     

银表面光学二次谐波参数的研究

本文测量了几种玻璃-银膜界面反射二次谐波随入射光偏振角的变化,测量了超高真空中多晶银基底上冷凝银膜表面退火前后的反射二次谐波,以及超高真空中纯度为99.99%多晶银表面的反射二次谐波,计算了垂直和平行表面谐波电流参数a、b,得到对棱镜-银界面b=-0.97;α=2.1,多晶银表面α=-9,冷凝银膜退火前后α分别为7和-5.结果表明.α对表面状况极为敏感.     

Imaging theory of nonlinear second harmonic and third harmonic generations in confocal microscopy

ItisreportedrecentlythatnonlinearopticalphenomenonofSHGandTHGhasbeenobservedinmanybiologicaltissues[16].SHGandTHGhavebeenusedtoperformthethree-dimensionalimaginginlivingtissuesandhaveattractedmuchattentionrecently.TherearemanyadvantagesofusingSHGandTHGtoperformthethree-dimensionalimaginginlivingtissues,suchasnoninvasiveandnophotobleaching,inadditiontotheimagingpropertiesofmulti-photonfluorescenceimaging[7—9].Firstly,unlikeinthesingle-andmulti-photonfluorescenceprocesses,onlyvirtualstat…     

不同表压下芪盐单层LB膜二次谐波的研究

在不同表压下制备芪盐的单层LB薄膜,测量LB膜的二次谐波信号.在低表压得到增强的二次谐波信号.对比芪盐的透射光谱,认为在LB膜中,芪盐以固相态存在,低表压时的固相态聚集体的吸收峰351nm使四阶非线性极化率x(4)(-2ω;ω,ω,ω,-ω)产生共振增强,四阶光学非线性现象对二次谐波信号产生影响.     

NaNO2晶体线性和非线性光学系数的计算

使用从头计算平面波赝势方法,计算了NaNO₂晶体电子能带结构,并使用改进的倍频公式计算了它的线性折射率和静态二级非线性系数,所得到的结果和实验值相符.采用实空间原子切割方法分析了阳离子和阴离子基团对光学性质的贡献.计算表明(NO₂)-基团对双折射率和倍频系数的贡献占主要地位,从而进一步验证了阴离子基团理论的正确性 关键词： 电子结构 非线性光学系数 从头计算方法     

应用级联倍频方法提高倍频系统输出稳定性研究

提出应用级联倍频方法提高倍频系统输出稳定性,并就该方法的有效性进行了理论分析和模拟计算.分析和计算结果不但证明级联倍频方法能实现倍频系统稳定输出,而且还表明可以通过仔细调节第一块倍频晶体中波矢方向 k 与光轴间夹角、两块倍频晶体间的间隔,能调节改变实现倍频系统最稳输出时所需第二块晶体的理论计算长度,使之与第二块倍频晶体的实际加工长度一致,最终实现系统稳定倍频输出.级联倍频方法在实现高输出稳定性的同时能实现高的倍频转换效率,对应用于光参量啁啾脉冲放大系统的高稳定抽运源系统的设计建造具有重要参考意义. 关键词： 级联倍频 稳定倍频输出 光参量啁啾脉冲放大     

Second-harmonic generation in quasi-periodically domain-inverted Sr(0.6) Ba(0.4) Nb(2)O(6) optical superlattices

One-dimensional Fibonacci-type quasi-periodically domain-inverted structures have been successfully fabricated in a strontium barium niobate crystal by electric field poling. With a single such structure, type I phase-matched second-harmonic generation (SHG) has been demonstrated at several wavelengths from red to near ultraviolet. The spectral positions of the observed SHG peaks are in good agreement with theoretical predictions. The range of measured conversion efficiencies is 2-10%.     

High-power, Yb-fiber-laser-pumped, picosecond parametric source tunable across 752-860 nm

We report a stable, high-power source of picosecond pulses in the near-infrared based on intracavity second harmonic generation (SHG) of a MgO:PPLN optical parametric oscillator synchronously pumped at 81 MHz by a mode-locked Yb-fiber laser. By exploiting the large spectral acceptance bandwidth for Type I (oo→e) SHG in β-BaB2O4 and a 5 mm crystal, we have generated picosecond pulses over 752-860 nm spectral range under minimal angle tuning, with as much as 3.5 W of output power at 778 nm and >2 W over 73% of the tuning range, in good beam quality with TEM00 spatial profile and M2<1.4. The SHG output pulses have durations of 15.2 ps, with a spectral bandwidth of ～3.4 nm at 784 nm. In addition, the oscillator simultaneously provides a signal power of >1 W over 1505-1721 nm (25 THz) and idler power >1.8 W over 2787-3630 nm (25 THz), corresponding to a total (signal plus idler) tuning range of 1059 nm. The SHG, signal, and idler output exhibit passive long-term power stability better than 1.6%, 1.3%, and 1.6% rms, respectively, over 14 h.     

用SHG-FROG方法测量超短光脉冲的振幅和相位

介绍了二次谐波振荡频率分辨光学快门(SHGFROG)测量超短脉冲的实验系统和二维相位恢复算法,这种方法可以实现对超短脉冲振幅和相位的完全测量.利用矩阵方法数值模拟了几种常见超短脉冲的SHGFROG迹线,并用主元素广义投影算法(PCGPA)从这些无噪音的SHGFROG迹线中恢复了脉冲的振幅和相位,误差接近收敛的标准.研究结果表明,这种测量方法结构简单,算法可靠,是测量超短脉冲的理想方法之一.     

Near-field probing of nanoscale nonlinear optical processes

We report a study of two nonlinear optical processes at the nanoscale level, using a near-field probe: (i) two-photon-pumped upconversion from ZnS:Mn nanoparticles encapsulated with 2-[{(?) -2-[4 -(ethylsulfonyl) phenyl]- 1-ethenyl} (methyl)anilino]- 1-ethanethiol and (ii) second-harmonic generation (SHG) from N -(4-nitrophenyl)- (L) -prolinol crystallites. The use of highly efficient nonlinear organic chromophores together with special processing on the nanometer scale made it possible to observe and characterize what are believed to be the smallest topographically distinguishable objects reported so far, using nonlinear optical techniques. Issues pertaining to the study of two-photon-excited emission and SHG by use of a near-field probe are discussed.     

Second harmonic generation of propagating collective excitations in Bose－Einstein condensates

We consider a possible second harmonic generation (SHG) of propagating collective excitations in a two-component Bose－Einstein condensate (BEC) with repulsive atom－atom interactions. We show that the phase-matching condition for the SHG can be fulfilled if the wave vectors and frequencies of the excitations are chosen adequately from different dispersion branches. We solve the nonlinear amplitude equations for the SHG derived using a method of multiple-scales and provide SHG solutions similar to those obtained for a SHG in nonlinear optical media. A possible experimental realization of the SHG for the propagating collective modes in a cigar-shaped two-component BEC is also discussed.     

Ultrasensitive second-harmonic generation frequency-resolved optical gating by aperiodically poled LiNbO3 waveguides at 1.5 microm

We retrieve intensity and phase profiles of 280 fs, 50 MHz optical pulses with 124 aJ coupled pulse energy (960 photons) by second-harmonic generation (SHG) frequency-resolved optical gating, using aperiodically poled LiNbO3 waveguides. The strong nonlinear interaction that is due to confinement within the micrometer-sized waveguide structure and the linearly chirped poling period contribute, respectively, to high SHG efficiency and broad phase-matching bandwidth. The achieved sensitivity is 2.7 x 10(-6) mW2, improving on the previous record for self-referenced complete pulse characterization by 5 orders of magnitude.     

Reflective-type configuration for nearly phase-matching cerenkov second-harmonic generation in a nonlinear-optical polymer waveguide

A new technique for achieving efficient Cerenkov-type second-harmonic generation (SHG) in a nonlinear-optical (NLO) polymer waveguide is presented. The configuration, which can prevent the losses of light caused by relatively long-distance propagation and the multiple reflections that appear in the conventional Cerenkov technique, exhibits ease of fabrication and compactness. We experimentally observed a conversion efficiency of 1.6% W(-1) cm(-1), which to our knowledge is the highest value reported for Cerenkov SHG in polymer, by tuning both the thickness and the refractive index of the polymer film close to phase matching between a guided fundamental wave and a guided harmonic wave. The experimental results agreed well with the theoretical prediction.     

Optical second-harmonic generation of Janus MoSSe monolayer

The transition metal dichalcogenides (TMD) monolayers have shown strong second-harmonic generation (SHG) owing to their lack of inversion symmetry. These ultrathin layers then serve as the frequency converters that can be intergraded on a chip. Here, taking MoSSe as an example, we report the first detailed experimental study of the SHG of Janus TMD monolayer, in which the transition metal layer is sandwiched by the two distinct chalcogen layers. It is shown that the SHG effectively arises from an in-plane second-harmonic polarization under paraxial focusing and detection. Based on this, the orientation-resolved SHG spectroscopy is realized to readily determine the zigzag and armchair axes of the Janus crystal with an accuracy better than ±0.6°. Moreover, the SHG intensity is wavelength-dependent and can be greatly enhanced (～ 60 times) when the two-photon transition is resonant with the C-exciton state. Our findings uncover the SHG properties of Janus MoSSe monolayer, therefore lay the basis for its integrated frequency-doubling applications.     

Evaluating cutaneous photoaging by use of multiphoton fluorescence and second-harmonic generation microscopy

The photoaging process of facial skin is investigated by use of multiphoton fluorescence and second-harmonic generation (SHG) microscopy. We obtain the autofluorescence (AF) and SHG images of the superficial dermis from the facial skin of three patients aged 20, 40, and 70 years. The results show that areas of AF increase with age, whereas areas of SHG decrease with age. The results are consistent with the histological findings in which collagen is progressively replaced by elastic fibers. The AF and SHG changes in photoaging are quantified by a SHG to autofluorescence aging index of dermis (SAAID). Our results suggest that SAAID can be a good indicator of the severity of photoaging.