单色仪波长定标中狭缝设置的影响分析

单色仪作为一种分光仪器，在传感器的辐射定标等方面具有重要应用。在实际应用过程中，其波长和带宽的设置对传感器的精确定标具有重要影响。使用低压汞灯作为波长标准光源，通过对其特征谱线扫描的方法，研究了传感器定标过程中，设置单色仪不同的狭缝宽度，对传感器精确定标具有重要影响。结果显示，当出射入射狭缝相同，同时改变其宽度的情况下，与典型校准状态(出射入射狭缝宽度设置为0.5 mm)相比，波长偏差量达到0.17 nm；当入射狭缝与出射狭缝不一致时，与典型校准状态相比，波长偏差量达到0.18 nm；当光源未充满入射狭缝与充满入射狭缝相比，最大误差达到0.02 nm，该影响几乎可以忽略。在相关的传感器光谱辐射定标实验研究中，单色仪的定标精度和准确性评估等方面具有重要应用。     

Cassegrain激光发射系统的光路设计

为了提高激光探测系统激光的发射功率,在出射激光为基模的高斯光束的光路设计中,根据高斯光束经过光学系统的变换与传输特性,分析了系统采用Cassegrain望远镜时,其遮拦比以及入射光束束腰半径对光功率透过率的影响。通过具体的数值计算得出,随着遮拦比及入射光束束腰半径的增大,系统光功率透过率将减小,给出了望远镜遮拦比与发射孔径处光斑尺寸之间的最佳匹配关系,最后讨论了离焦误差（安装误差）为0.2mm时对出射光斑尺寸的影响。     

照度对测量三代微光像增强器MTF的影响分析

通过探讨像增强器MTF测试仪用光源的出射光照度对测量结果的影响,对透过测量狭缝的光强分布进行了分析.调节狭缝面的入射光照度,对不同照度作用下的调制传递函数进行了对比测量,经与微光像增强器的饱和输出亮度比较,得出:三代微光像增强器的MTF测试值随入射光照度分布呈抛物线分布,其最大值与微光像增强器的自动亮度控制特性有关.适当选择入射光照度,可确保被测像增强器既有足够的输出信噪比,而不进入饱和区域.     

折射型光限幅器中参量的最优化设计研究

以衍射理论为基础,用箝位输出功率表征限幅器的限幅效果,推导了折射型光限幅器出射功率的表达式.数值计算了连续激光照射下,限幅器出射功率、限幅能力和最佳限幅位置的变化规律.结果表明:限幅器的出射功率随入射功率的增加衰减振荡,其振荡周期取决于介质相对于光束焦点的位置;限幅器的限幅能力随入射光束腰半径和光阑孔径的变大而减弱;入射功率范围固定,入射光束腰半径和光阑孔径增大时,介质的最佳限幅位置向入射光束的焦点靠近,但是在某些入射功率范围内会存在多个最佳限幅位置;光限幅器的箝位输出功率随光阑线性透过率的增加存在线性增加和非线性增加两个不同区域,实际应用中应在线性增加区域确定光阑孔径的大小.     

折射型光限幅器中参量的最优化设计研究

以衍射理论为基础,用箝位输出功率表征限幅器的限幅效果,推导了折射型光限幅器出射功率的表达式.数值计算了连续激光照射下,限幅器出射功率、限幅能力和最佳限幅位置的变化规律.结果表明：限幅器的出射功率随入射功率的增加衰减振荡,其振荡周期取决于介质相对于光束焦点的位置;限幅器的限幅能力随入射光束腰半径和光阑孔径的变大而减弱;入射功率范围固定,入射光束腰半径和光阑孔径增大时,介质的最佳限幅位置向入射光束的焦点靠近,但是在某些入射功率范围内会存在多个最佳限幅位置;光限幅器的箝位输出功率随光阑线性透过率的增加存在线性增加和非线性增加两个不同区域,实际应用中应在线性增加区域确定光阑孔径的大小.     

光栅光谱仪的光谱重建

用光栅光谱仪进行光谱测量,不同的入射缝、出射缝宽度导致测量得到的光谱不同,狭缝宽度越大,测得的光谱越不准确.为了消除入射缝、出射缝的影响,需要对测量光谱进行数学处理以获得尽可能真实的光谱,这就是光谱重建.本文通过光谱与入射缝、出射缝的关系,用实验测得的谱线,通过出射缝还原、入射缝还原,直接恢复重建真实光谱.     

透过率及其测试中的几个问题

<正> 透过率是光学系统的一项重要的性能指标,通常定义为出射光通量和入射光通量的比值。分别测出入射通量和出射通量即可得出透过率值。透过率的定义和测量方法都十分简单直观,但在实际测试中,却往往由于不注意其严谨的定义和不明确其严格的测量条件,致使测量结果没有良好的重复性。因此,为客观、     

双边缘技术多普勒测风激光雷达标准具的优化

 优化了基于双边缘技术的直接测风多普勒激光雷达中F-P标准具的工作参数。确定激光谱宽后，选择适当的F-P标准具自由谱间距，可正确消除瑞利背景噪声的影响。分析了标准具镜面缺陷、非严格平行和入射光束发散角对其透过率曲线的影响。将标准具透过率函数表达为唯一系统参数，即反射精细度的函数；通过计算散粒噪声极限时的相对测量误差，可确定最优反射精细度以及激光频率相对标准具透过率中心频率的最佳偏置；由最优反射精细度可得到入射到标准具光束的最大发散角和标准具的最小通光口径。     

碳纳米管悬浮液的光限幅特性实验研究

 通过超声波降解法制备了多壁碳纳米管的水-表面活性剂悬浮液,测量了其对于1 064 nm,脉宽10 ns Nd:YAG调Q脉冲激光的光限幅曲线。实验发现：入射激光能量密度较低时,出射能量密度随入射能量密度的增加而线性增加;当入射能量密度为160 mJ/cm²时,出射能量不再线性增加并且逐渐趋近于光限幅器的嵌位输出值,约16 mJ,同时,对激光的透过率从71%下降到15%。通过Z扫描和探针光实验以及45°散射角下散射能量、散射率随入射激光能量变化曲线的测量,对碳纳米管悬浮液的光限幅机理进行了研究。结果表明：其限幅机理可能源于碳纳米管吸收激光能量后升华产生的膨胀的碳气泡对入射激光产生的非线性散射;另外,非线性折射对光限幅效果也有一定的作用。     

波状结构二维光子晶体负折射现象的研究

结合波状结构二维(2D)光子晶体(PC)与入射介质两者的等频面结构分析了PC内部的负折射现象，采用时域有限差分(FDTD)方法模拟了高斯光束在波状结构2DPC内的负折射，分别得到了折射角/入射角以及折射角/入射波长之间的关系曲线，当入射角为45°，入射波段在1485—1530nm区域时，波状结构2DPC的负折射角与入射波长近似呈线性变化关系，并带有明显的PC超棱镜效应，采用端面投影方法对波状结构2DPC的入射端面和出射端面进行处理，改善了负折射时的透过率. 关键词： 光子晶体 负折射 等频面     

Influence of grooves in the electromagnetic transmission of a periodic metallic grating filter

The light transmittance of metal film with periodic slits and grooves structure has been investigated. It was demonstrated that the grooves significantly affect the transmittance of the metal film. The structure excavating two grooves symmetric to the central slit in a cell of a period grating displays a dent in the transmission spectrum comparing with the structure with only one slit in the cell. Deepening the grooves moves the dents to the longer wavelengths in the transmission spectrum. An analytical equation is also provided to approximately locate the dents. The grooves in the grating filter supply the advantage of removing the needless transmission of certain frequency.     

Quantitative spectrally resolved imaging through a spectrograph

A grating spectrograph can be used for spectrally selective two-dimensional imaging if it is operated with a broad entrance slit. The resulting intensity distribution in its exit plane is a one-dimensional convolution of the spatial and spectral distributions of incident light. We present a dedicated deconvolution filter to reconstruct the spatial image from the spectrograph output. The algorithm is illustrated on Raman imaging of an underexpanded dry air jet. Recorded Raman images correspond to density maps convolved with the Raman spectrum of air; the latter essentially acts as a blurring function for the density map. The deconvolution filter combines the individual images recorded in the O2 and N2 Raman bands into a single image of relative air density.     

Enhanced optical transmission by V-shaped nanoslit in metal film

In this paper,we reveal that the enhanced transmission through a perforated metal film can be further boosted up by a V-shaped nanoslit,which consists of two connected oblique slits.The maximum transmission at resonance can be enhanced significantly by 71.5%in comparison with the corresponding vertical slit with the same exit width.The value and position of transmission resonance peak strongly depend on the apex angle of the V-shaped slit.The optimum apex angle,at which the transmission is maximal,is sensitive to the slit width.Such phenomena can be well explained by a concrete picture in which the incident wave drives free electrons on the slit walls.Moreover,we also simply analyze the splitting of the transmission peak in the symmetry broken V-shaped slit,originating from the resonances of different parts of the V-shaped slit.We expect that our findings will be used to design the nanoscale light sources based on the metal nanoslit structures.     

光栅光谱仪分辨率及波长范围计算公式的研究

对水平对称式Ebert-Fastie型光谱仪的参量及性能进行了分析研究.基于水平对称式Ebert-Fastie型光谱仪工作时的光路图,用几何方法推导出了入射光线与衍射光线的夹角、入射角、衍射角、可测光谱级次及波长适用范围的计算公式,该公式可通过简单编程计算结果.基于理论分辨率计算公式,并考虑到狭缝宽度导致实际分辨率低于理论分辨率,推导出了分辨率与狭缝宽度等结构参量之间关系的计算公式,对该公式求导得出提高分辨率的方法,并举例计算得出考虑狭缝宽度后的实际分辨率为理论分辨率的83％.     

Efficient directional excitation of surface plasmon polaritons by partial dielectric filling slit structure

In this paper, we investigate the excitation of surface plasmon polariton (SPP) in the metallic slit partly filled with dielectric by using the finite-difference time-domain method. It is found that the slit structure displays high asymmetry in the field distribution and SPP excitation due to the difference in matching degree of SPP wavevector on the two sides of slit exit. At certain incident wavelengths, the power flow carried by SPP modes on one side of slit exit is over three orders of magnitude greater than that on the other side, an efficient directional excitation is achieved. The SPP generation efficiencies on both sides of slit exit can be periodically adjusted by the dielectric width, but their changes are not synchronous, implying that such slit structure could be acted as a directional splitter/coupler. Moreover, the asymmetry degree of SPP excitation can also be modulated by the refractive index of dielectric layer.     

Analysis on diffraction properties of the transmission phase grating

Diffraction properties of the transmission phase grating are analyzed in terms of the Fourier optics theory. The analysis results show that the diffraction intensity distribution of the transmission phase grating is closely related to the optical thickness of the grating and the wavelength of the incident light, and not only determined by the grating's period and slit width. For monochromatic incident light, more than 80% of the diffraction energy will concentrate to the first diffraction order under certain conditions. For white incident light, the energy of the first order of diffraction spectrum may be much higher than other orders. Based on these results, some possible applications of the transmission phase grating are discussed.     

Influence of slit width on the electromagnetic transmission of a periodic metallic grating

The light transmittance of a periodic metallic grating with varied slit widths has been investigated. The transmission peaks move to the shorter wavelength direction with an increase in the width of slits while keeping the other parameters unchanged. It was demonstrated that the slit width affects the spectral transmittance of the metal grating significantly. It was also found that the effective refractive index and cavity modes in slits are responsible for this phenomenon. Cavity modes play an important role in extraordinary transmission of the sub-wavelength aperture grating. When a complete resonant mode forms in the slits, a high transmission will appear. A wider slit results in a smaller efficient refractive index and thus affects the cavity mode in the slits. These two elements cause the transmission peaks to move to the shorter wavelength direction with widening of slits. The results obtained here may provide a useful guide to design metallic slit grating devices.     

倾斜入射楔形薄膜滤光片的透射光谱研究

角度调谐薄膜滤光片因较大的波长调谐特性和良好的矩形度在密集波分复用系统中得到了广泛的应用。在倾斜入射时薄膜滤光片透射光谱的透射率和半宽不仅受到入射角度的影响,还跟滤光片两端面间的非平行度即楔角的大小有关。详细分析了楔角对对滤光片透射率以及半宽的影响,发现适当的楔角和角度取向能够改善倾斜入射状态下滤光片的透射光谱特性。设计制备了楔角为0.8°的楔形薄膜角度调谐滤光片,实验结果证明保持该楔角的方向与倾斜入射角度相同时会严重的劣化透射光谱的透射率和矩形度,方向相反时则可以提高光谱的透射率以及矩形度,并使器件的波长调谐范围增大约10 nm。     

Spatiotemporal shaping of terahertz pulses

We report temporal shaping of few-cycle terahertz pulses, using a slit in a conductive screen as a high-pass filter. The filter's cutoff frequency was tuned by changing the width of the slit; the slope of the cutoff transition was altered by changing the thickness of the screen. We measured the transmission function of the filters, using large-aperture photoconducting antennas to create and detect the incident and transmitted electric field. Our experimental results were in excellent agreement with the performed finite-difference time-domain simulations of the propagation of the pulse through the slit. When the screen thickness was greater than the slit width, the filter was well modeled by a short, planar waveguide. Using a simple transfer function, we accurately describe the sharp cutoff and dispersion of such a filter.