Broadband tunable Raman soliton self-frequency shift to mid-infrared band in a highly birefringent microstructure fiber

Raman soliton self-frequency shifted to mid-infrared band（λ 〉 2 μm） has been achieved in an air-silica microstructure fiber（MF）. The MF used in our experiment has an elliptical core with diameters of 1.08 and 2.48 μm for fast and slow axis. Numerical simulation shows that each fundamental orthogonal polarization mode has two wide-spaced λZDW and theλZDW pairs located at 701/2110 nm and 755/2498 nm along the fast and slow axis, respectively. Using 810-nm Ti：sapphire femtosecond laser as pump, when the output power varies from 0.3 to 0.5 W, the furthest red-shift Raman solitons in both fast and slow axis shift from near-infrared band to mid-infrared band, reaching as far as 2030 and 2261 nm. Also, midinfrared Raman solitons can always be generated for pump wavelength longer than 790 nm if output pump power reaches0.5 W. Specifically, with pump power at 0.5 W, the mid-infrared soliton in slow axis shifts from 2001 to 2261 nm when the pump changes from 790 nm to 810 nm. This means only a 20 nm change of pump results in 260 nm tunability of a mid-infrared soliton.

Six-bit all-optical quantization using photonic crystal fiber with soliton self-frequency shift and pre-chirp spectral compression techniques

In this paper, we propose an optical quantization scheme for all-optical analog-to-digital conversion that facilitates photonics integration. A segment of 10-m photonic crystal fiber with a high nonlinear coefficient of 62.8 W-1/kin is utilized to realize large scale soliton self-frequency shift relevant to the power of the sampled optical signal. Furthermore, a 100-m dispersion-increasing fiber is used as the spectral compression module for further resolution enhancement. Simulation results show that 317-nm maximum wavelength shift is realized with 1550-nm initial wavelength and 6-bit quantization resolution is obtained with a subsequent spectral compression process.

Optimizational 6-bit all-optical quantization with soliton self-frequency shift and pre-chirp spectral compression techniques based on photonic crystal fiber

In this paper, we optimize a proposed all-optical quantization scheme based on soliton self-frequency shift(SSFS)and pre-chirp spectral compression techniques. A 10m-long high-nonlinear photonic crystal fiber(PCF) is used as an SSFS medium relevant to the power of the sampled optical pulses. Furthermore, a 10m-long dispersion flattened hybrid cladding hexagonal-octagonal PCF(6/8-PCF) is utilized as a spectral compression medium to further enhance the resolution. Simulation results show that 6-bit quantization resolution is still obtained when a 100m-long dispersion-increasing fiber(DIF)is replaced by a 6/8-PCF in spectral compression module.

Polarisation-sensitive four-wave mixing and soliton self-frequency shift effect in the highly birefringent photonic crystal fibre

By adjusting the polarisation state of the pump at 805 nm parallel to slow （x） and fast （y） axes of the highly birefringent photonic crystal fibre with zero dispersion wavelengths 790 nm and 750 nm, this paper demonstrates the efficient polarisation-sensitive four wave mixing involved in pump, anti-Stokes and Stokes signals and soliton self- frequency shift effects induced by the phase-matching between red-shifted solitons and blue-shifted dispersive waves. If the reduction of coupling efficiency to the circular pump laser mode or other circular fibres due to asymmetry of the core is neglected, more than 98% of the total input power is kept in a single linear polarisation. Controlled dispersion characteristic of the doublet of fundamental guided-modes results in achieving light field strongly confined in principal axes of photonic crystal fibre, and enhancing the corresponding nonlinear-optical process through the remarkable nonlinear birefringence.

Study on the relationships between Raman shifts and temperature range for α-plane GaN using temperature-dependent Raman scattering

In this paper,Raman shifts of a-plane GaN layers grown on r-plane sapphire substrates by low-pressure metal-organic chemical vapor deposition（LPMOCVD） are investigated.We compare the crystal qualities and study the relationships between Raman shift and temperature for conventional a-plane GaN epilayer and insertion AlN/AlGaN superlattice layers for a-plane GaN epilayer using temperature-dependent Raman scattering in a temperature range from 83 K to 503 K.The temperature-dependences of GaN phonon modes（A1（TO）,E2（high）,and E1（TO）） and the linewidths of E2（high） phonon peak are studied.The results indicate that there exist two mechanisms between phonon peaks in the whole temperature range,and the relationship can be fitted to the pseudo-Voigt function.From analytic results we find a critical temperature existing in the relationship,which can characterize the anharmonic effects of a-plane GaN in different temperature ranges.In the range of higher temperature,the relationship exhibits an approximately linear behavior,which is consistent with the analyzed results theoretically.

Direct identification of the carbonate intermediate during water-gas shift reaction at Pt-NiO interfaces using surface-enhanced Raman spectroscopy

Noble metal-reducible oxide interfaces have been regarded as one of the most active sites for water-gas shift reaction.However,the molecular reaction mechanism of water-gas shift reaction at these interfaces still remains unclear.Herein,water-gas shift reaction at Pt-NiO interfaces has been in-situ explored using surface-enhanced Raman spectroscopy by construction of Au@Pt@NiO nanostructures.Direct Raman spectroscopic evidence demonstrates that water-gas shift reaction at Pt-NiO interfaces proceeds via an associative mechanism with the carbonate species as a key intermediate.The carbonate species is generated through the reaction of adsorbed CO with gaseous water,and its decomposition is a slow step in water-gas shift reaction.Moreover,the Pt-NiO interfaces would promote the formation of this carbonate intermediate,thus leading to a higher activity compared with pure Pt.This spectral information deepens the fundamental understanding of the reaction mechanism of water-gas shift reaction,which would promote the design of more efficient catalysts.

Quantification of radiation damage in natural and synthetic zircon by Raman spectroscopy:application to low-temperature thermochronology

Due to its ubiquitous occurrence in igneous,metamorphic,and sedimentary rocks and its wide application in geochronology and geochemistry,zircon has become the most widely used accessory mineral in the geological community.Nevertheless,the decay of U and Th causes radiation damage to the zircon structure,resulting in various degrees of metamictization,which can affect the accuracy of U–Pb dates and Hf and O isotope results.If the degree of zircon radiation damage can be quantified,the influence on geochemical analyses can be evaluated,and the results can be corrected more precisely.In this paper,synthetic and natural zircon crystals with different crystallization ages were selected for Raman spectroscopy analysis,cathodoluminescence imaging,and determination of the U and Th concentrations.The results show that Raman FWHM(full width at half bandmaximum)and Raman shift correlate with alpha dose(Da)ofzirconsfollowingtheseequations,FWHM=44.36(±2.32)×[1-exp(-2.74×Da)]-+1.7(±0.19),Raman Shift=-6.53×Da+1007.69.Analysis of synthetic zircon crystals shows that doped REEs(rare earth elements and P)can also lead to an increase in the FWHM.However,this effect can be ignored for natural zircon samples with REE contents at a normal level of hundreds to a few thousand ppm.The FWHM and Raman shift can be used as proxies to measure the degree of zircon radiation damage.Using the updated equations to calculate the latest age when zircon began to accumulate radiation damage,a more accurate and more meaningful“radiation damage age”can be obtained.

纳秒可见光全固态拉曼激光器的研究进展

纳秒脉冲可见波段激光在遥感、相干雷达系统、精密加工、激光清洗、液态染料激光器泵浦等领域广泛应用,全固态激光器以其结构紧凑、占用空间小、成本低、寿命长等特点备受青睐。近年来,纳秒可见光全固态激光器发展迅速,本文简述了传统激光二极管泵浦掺Nd ^(3+)、Yb ^(3+)等稀土离子晶体输出近红外光的二阶非线性频率变换产生纳秒脉冲可见光固体激光器的技术水平。从非线性频率变换角度介绍了几种出光波段丰富的纳秒脉冲可见光全固态拉曼激光器的技术特点,重点介绍了拉曼频移、拉曼混频和金刚石拉曼,对其性能特点和技术瓶颈进行了综述,并在最后做了总结和展望。

高温高压下NaCl-H_2O体系的Raman光谱分析:一种新的流体包裹体盐度测定方法

利用水热金刚石压腔研究了高温高压下0.0%、5.0%、10.0%和20.0%的NaCl-H_2O体系的Raman光谱,研究结果发现:对于盐度一定的NaCl-H_2O体系,当压力不变时,水的Raman伸缩谱峰的波数变化量△v_((O-H))随温度的升高而不断增加;当压力不同时,△v_((O-H))随温度的变化关系(偏移斜率S)不受压力的影响,而只与盐度相关。利用该性质可以用来确定流体包襄体的盐度(W),其计算公式如下:W=123.25S^2-128.11S+32.40,误差为0.46%。

Raman Spectroscopy of Nitrogen Clathrate Hydrates

Nitrogen hydrate samples were synthesized using liquid nitrogen and powder ice at 16 MPa and 253 K. Confocal laser Raman spectroscopy was used to investigate the characteristics of nitrogen clathrate hydrates. The results show that the Raman peaks of N-N and O-H stretching vibration in nitrogen hydrates are observed at 2322.4 and 3092.1 cm^-1, respectively, which are very similar to those in natural air clathrate hydrates. For comparison, we measured the Raman peaks of N-N stretching vibration both in liquid nitrogen and nitrogen molecules saturated water, which appear at 2326.6 and 2325.0 cm^-1, respectively. The Raman spectroscopic observations on the dissociation process suggest that nitrogen molecules occupy both the large and small cages in nitrogen clathrate hydrates. However, only one Raman peak is observed for N N stretching vibration because the difference of the environment of nitrogen molecules between large and small cages is too small to be differentiated by Raman spectroscopy.

色散管理孤子中 Raman效应引起的时移及定时抖动(英文)

给出了色散管理孤子中 Raman效应所引起的脉冲中心位置时移的解析表达式并讨论了孤子脉宽的波动所引起的 Raman定时抖动 .结果表明 :时移的演化和不同的色散配置有关 ,并且色散管理孤子 Raman时移和常规孤子一样与传输距离及平均色散的平方成正比 。

Third-order nonlinear wavelength conversion in chalcogenide glass waveguides towards mid-infrared photonics

The increasing demand in spectroscopy and sensing calls for infrared(mid-IR)light sources.Here,we theoretically investigate nonlinear wavelength conversion of Ge_(28)Sb_(12)Se_(60)chalcogenide glass waveguide in the mid-IR spectral regime.With waveguide dispersion engineering,we predict generation of over an octave wavelength(2.8μm-5.9μm)tuning range Raman soliton self-frequency shift,over 2.5 octaves wavelength cover range supercontinuum(1.2μm-8.0μm),as well as single soliton Kerr comb generated in suspended Ge_(28)Sb_(12)Se_(60)waveguide.Our findings evidenced that Ge_(28)Sb_(12)Se_(60)chalcogenide glass waveguides can simultaneously satisfy the generation of Raman soliton self-frequency shift,supercontinuum spectrum,and Kerr frequency comb generation through dispersion engineering towards mid-IR on chip.

激光加热效应在硅显微Raman光谱测量中的影响

本文从理论和实验两方面研究了显微Raman光谱测量中,激光功率对单晶硅样品测量的影响。由于显微Raman光谱仪对激光的聚焦作用,使得激光对不同厚度的样品具有微区加热作用,被测样品产生不同程度的温升,从而对显微Raman光谱仪在硅材料应力和温度的测量中产生影响。实验结果证明,对无限厚硅样品,20mW的激光使Raman频移达到0.15cm-1;而对2μm厚的热薄硅样品,26mW的激光使Raman频移达到4.47cm-1。

基于光谱信息的拉曼成像技术助力生物质材料结构设计研究进展

近年来研究人员对生物质材料进行了诸多结构设计,以提升其性能并获得高性能生物质材料。其中,拉曼光谱技术因其高分辨率、无损检测等特点,被广泛应用于生物质材料的多尺度结构表征。介绍了拉曼成像技术,并详细总结了课题组基于拉曼峰位、拉曼峰偏移、拉曼峰强度及偏振拉曼等光谱信息对生物质材料进行拉曼成像,以辅助验证材料结构的研究进展。此研究进展为拉曼成像技术在其他材料上的扩展应用提供了参考。

多孔硅薄膜纵向分辨Raman谱研究

采用高灵敏度的micro Raman系统研究了多孔硅(PS)在纵向的Raman效应,并研究了多孔硅尺寸对Raman谱的影响.实验中采用脉冲电化学腐蚀和直流电化学腐蚀两种方法制备PS样品,纵向Raman光谱的结果表明,在纵向不同深度,用脉冲电化学腐蚀方法制备的PS,Raman光谱不存在频移,而用直流电化学腐蚀方法制备的PS在多孔层深度为70～90μm处的Raman光谱有向低波数方向约40cm-1的移动,它是由于常规电化学腐蚀方法制备的PS不同深度的尺寸分布对量子效率的影响引起的.

锥形微纳光纤激发相干反斯托克斯拉曼散射光谱研究

从数值仿真和实验测量方面验证了使用锥形微纳光纤代替聚焦物镜产生相干拉曼散射信号的可行性。通过数值计算以及实验测量分析了超短脉冲在锥形微纳光纤中的传输特性,证明锥区长度为5cm的锥形微纳光纤可以有效保证超短脉冲在其中传输时的时域和谱域特性,并且功率衰减较小,850~1100nm波长范围内的实测插入损耗最大值不超过1.05dB,平均值0.84dB。然后,使用锥形微纳光纤成功探测到环己烷在2853cm^(-1)位置处的拉曼共振峰,证明了使用锥形微纳光纤激发相干拉曼光谱的可行性。使用锥形微纳光纤激发相干拉曼光谱具有信号激发灵活方便,摆脱了传统空间光学的约束,为相干反斯托克斯拉曼散射(coherent anti-Stokes Raman scattering,CARS)系统在内窥成像领域和微创检测领域的发展提供了一种新的途径。

Fluctuations of optical phase of diffracted light for Raman–Nath diffraction in acousto–optic effect

The Raman–Nath diffraction in acousto–optic effect was studied theoretically and experimentally in the paper. Up to now, each order of diffracted light in Raman–Nath diffraction was still considered simply to be just frequency-shifted and to be a plane wave. However, we find that the phase and frequency shifts occur simultaneously and individually in Raman–Nath diffraction. The findings demonstrate that, in addition to the frequency shift, the optical phase of each order of diffracted light is also shifted by the sound wave and fluctuates with the sound wave and is related to the location in the acoustic field from which the diffracted light originates. As a result, the wavefront of each order of diffracted light is modulated to fluctuate spatially and temporally with the sound wave. Obviously, these findings are significant for applications of Raman–Nath diffraction in acousto–optic effect because the optical phase plays an important role in optical coherence technology.

Magnetic field measurement based on a stimulated two-photon Raman transition

The magnetic field in the microwave interaction zone of the fountain atomic clock was measured by stimulated Raman transitions. By measuring the two-photon transition frequency between the Zeeman levels of the two ground states, we achieved a magnetic field measurement accuracy of the order of 0.28 nT, This method is immune to the Doppler shift and the AC Stark shift. The second order Zeeman shift of the fountain clock is 170.7 × 10^-15, with the uncertainty of 7,2 × 10^-16.

Raman Spectroscopy of Garnet-group Minerals

The Raman spectra of the natural end members of the garnet-group minerals, which include pyrope, almandine and spessarite of Fe-Al garnet series and grossularite, andradite and uvarovite of Ca-Fe garnet series, have been studied. Measured Raman spectra of these minerals are reasonably and qualitatively assigned to the intemal modes, translational and rotatory modes of SiO4 tetrahedra,as well as the translational motion of bivalent cations in the X site. The stretch and rotatory Alg modes for the Fe-Al garnet series show obvious Raman shifts as compared with those for the Ca-Fe garnet series, owing to the cations residing in the X site connected with SiO4 tetrahedra by sharing the two edges. The Raman shifts of all members within either of the series are attributed mainly to the properties of cations in the X site for the Fe-Al garnet series and in the Y site for the Ca-Fe gamet series.

Ultraviolet and mid-infrared continuum generation by cross-phase modulation between red-shifted solitons and blue-shifted dispersive waves in a photonic crystal fiber

Using a photonic crystal fiber with a zero dispersion wavelength of the fundamelItal mode at 780 nm designed and fabricated in our lab, the ultraviolet and mid-infrared continua are generated by cross-phase modulation between red-shift solitons and blue-shift dispersive waves. The dependences of continuum on the pump power and wavelength are investigated. With the pump working at 820 nm, when the pump power increases froul 300 to 500 mW, the bandwidths of ultraviolet and mid-infrared continua change from 80 to 140 nm and 100 to 200 nm, respectively. The wavelength of ultraviolet continuum is below 246 nm, and the wavelength of mid-infrared continuum exceeds 2500 nm. Moreover, the influences of pump power on wavelength and conversion efficiency of different parts of continua are also demonstrated.