Direct measurement of dispersion of the group refractive indices of quartz crystal by white-light spectral interferometry

We present a white-light spectral interferometric technique employing a low-resolution spectrometer for a direct measurement of the dispersion of the ordinary and extraordinary group refractive indices of a quartz crystal over the wavelength range approximately from 480 to 860 nm. The technique utilizes a dispersive Michelson interferometer with the quartz crystal of known thickness to record a series of spectral interferograms and to measure the equalization wavelength as a function of the displacement of the interferometer mirror from the reference position, which corresponds to a balanced non-dispersive Michelson interferometer. We confirm that the measured group dispersion agrees well with that described by the dispersion equation proposed by Ghosh. We also show that the measured mirror displacement depends, in accordance with the theory, linearly on the theoretical group refractive index and that the slope of the corresponding straight line gives precisely the thickness of the quartz crystal.     

Measurement of complex refractive index of human blood by low-coherence interferometry

In this article, the usefulness of the optical technique for measurements of blood complex refractive index has been examined. Measurement of optical properties of human blood is difficult to perform because of its nonuniform nature. However, results of my investigation have shown the usefulness of low-coherence interferometry for measurement complex refractive index of human blood. Furthermore, mathematical analysis of spectrum of measured signal have made possible to determined relationship between complex refractive index and hematocrit level in human blood.     

利用白光干涉技术测量块状材料的群折射率

对群折射率的精确而快速测量是光学工程领域一个基础而又亟需解决的难题,本文提出了一套光谱型迈克尔逊白光干涉系统的解决方案.该系统充分利用了微型光纤光谱仪一次测量便可获得所有干涉信息的特点,无需机械扫描装置,具有结构简单和测量快速的优点.与传统的窗口傅里叶变换算法相比,本文采用小波变换直接从干涉信号的小波脊中提取群延迟,减小了由相位求导得到群延迟过程中引入的误差放大效应,进而提高了群折射率的测量精度.基于此迈克尔逊白光干涉系统,在不同干涉位置处对两块不同厚度的石英和BK7玻璃进行了测量,实验结果表明此方法在宽 关键词： 白光干涉 群折射率 小波变换 傅里叶变换     

High-precision index measurement in anisotropic crystals using white-light spectral interferometry

White-light spectral interferometry appears an excellent tool for precise determination of indices, and has already been successfully applied to different isotropic or weakly dispersive materials such as glass or rhodamine films. In this paper, we extend the spectral method to the measurement of anisotropic media with strong dispersion. The method is discussed below and allows an accuracy of the order of 10^-5 on the principal indices of a birefringent silver thiogallate (AgGaS₂) crystal.     

All-reflective self-referenced spectral interferometry for single-shot measurement of few-cycle femtosecond pulses in a broadband spectral range

An all-reflective self-referenced spectral interferometry based on the transient grating(TG)effect is proposed for single-shot measuring of the amplitude and phase of ultrashort pulses in a broadband spectral range.Except for a thin third-order nonlinear medium,which was used to generate the TG signal,no transmitted optics were used in the proposed device,and few-cycle pulses in a broad spectral range from deep UV to mid-IR can be characterized.With a homemade compact and alignment-free device,a 5.0 fs pulse at 800 nm corresponding to about two cycles and a 14.3 fs pulse at 1800 nm corresponding to less than three cycles were successfully characterized.     

Kramers-Kronig analysis on the real refractive index of porous media in the terahertz spectral range

We present a terahertz time-domain experimental technique for the detection of scattering from porous media. The method for detection of the scattering enables one to make a decision when Fresnel or Kramers-Kronig (K-K) analysis can be applied for a porous medium. In this study the real refractive index of a tablet is calculated using the conventional K-K dispersion relation and also using a singly subtractive K-K relation, which are applied to the extinction coefficient obtained from the Beer-Lambert law. The advantage of the K-K analysis is that one gets estimates both for absolute refractive index and also dispersion of the porous tablet, whereas Fresnel analysis provides only the absolute value of the index.     

Direct measurement of group dispersion of optical components using white-light spectral interferometry

We present a simple white-light spectral interferometric technique employing a low-resolution spectrometer for a direct measurement of the group dispersion of optical components over a wide wavelength range. The technique utilizes an unbalanced Mach-Zehnder interferometer with a component under test inserted in one arm and the other arm with adjustable path length. We record a series of spectral interferograms to measure the equalization wavelength as a function of the path length difference. We measure the absolute group refractive index as a function of wavelength for a quartz crystal of known thickness and the relative one for optical fiber. In the latter case we use a microscope objective in front and a lens behind the fiber and subtract their group dispersion, which is measured by a technique of tandem interferometry including also a Michelson interferometer.     

Measurement of the group refractive index of air by two-wavelength interferometry

The group refractive index of air at 3.44 μm is directly measured with an accuracy of 2 × 10^-7 using two-wavelength simultaneous interferometry with a 3.51- and 3.37-μm simultaneous operation He-Xe laser.     

Impact of the non-measured infrared spectral range of the imaginary refractive index on the derivation of the real refractive index using the Kramers-Kronig transform

A quantitative analysis to asses the influence of a non-measured imaginary index spectrum on the extracted real refractive index is presented. The investigation was done on the Mid-IR spectral range, where the ‘‘measured’’ imaginary spectrum is defined between 800 and 4500 cm⁻¹. The influence of bands of various locations and shapes in the non-measured IR spectral region (0-800 cm⁻¹) on the n values obtained by the computational procedure of the Kramers-Kronig transform was investigated. Additional analysis was conducted to estimate the relevance of different assumptions that are commonly made with regard to the non-measured range (e.g. linear extrapolation or the effect of uncertainty in the precise band location). The results show that the contribution of an unmeasured band at any wavenumber is well described by a simple function of the band location and , regardless of the band shape. Furthermore, the error caused by incorrect band location can also be described by a simple function of the band location, the band location error and . The simple functions can be used to estimate the impact that ignoring or misplacing a band will have on the extracted n spectrum, without performing the whole KK integration. These relationships were validated on two data sets of optical constants of crystalline ammonium sulfate and water in the Mid-IR range.     

Single-shot measurement of carrier-envelope phase changes by spectral interferometry

We demonstrated single-shot measurements of spectral interference between a white-light continuum generated in a hollow-fiber and its second harmonic. The interference has information on the carrier-envelope phase of an input pulse to the fiber and the time delay of the blue wing of the continuum. By analyzing the observed spectral interference, we estimated shot-by-shot changes of the carrier-envelope phase. This method is useful for determining the carrier-envelope phase changes of a low-repetition-rate, high-intensity laser.     

Proposal for nonlinear refractive index measurement using spectral ratio in modulated OFRR dynamics

A novel method for measuring the nonlinear refractive index of an optical fiber using a spectral ratio between the modulation frequency and a harmonic component in a modulated optical fiber ring resonator (OFRR) is proposed. The spectral ratio between the modulation frequency and the 2nd-harmonics generated by phase-modulation through the OFRR is increased with increasing the input light power and has peaks above 5 W input power, however, the peaks was shifted to the lower input power below 1 W by averaging taken into account of the phase distribution. A experimental setup consisted of an OFRR system and an Ar-laser as a pump light source was used to determine the nonlinear refractive index of an optical fiber. In the experimental results, the peaks of the spectral ratio as a function of the input power was found out at 0.8 W and 0.45 W of the input power corresponding to the input source line at 488.0 nm and 514.5 nm, respectively. The profile was similar to that obtained by the simulation and the nonlinear refractive index of a optical fiber was determined as 1.0 × 10⁻²² m²/V² by a relationship between the input power giving the peak and the nonlinear refractive index.     

Determination of the refractive index of IR surface plasmons by static asymmetric interferometry

A new method has been proposed for determining the complex refractive index of terahertz surface plasmons. This method implements the concept of asymmetric static interferometry in the planar version, where the interference pattern is formed by surface rather than bulk waves. The information about the real part of the refractive index is carried by the interference pattern period, while its imaginary part can be found from the illumination magnitudes in the pattern extrema. Original Russian Text ? G.D. Bogomolov, G.N. Zhizhin, A.P. Kiryanov, A.K. Nikitin, O.V. Khitrov, 2009, published in Izvestiya Rossiiskoi Akademii Nauk. Seriya Fizicheskaya, 2009, Vol. 73, No. 4, pp. 562–565.     

Design of an optoelectronic refractometer having an adjustable range of refractive index measurement

A real-time optoelectronic refractometer having an adjustable range of refractive index measurement is presented. The adjustment is achieved by obtaining a shift in the zero-reflected intensity point at the interface following the introduction of a glass plate of refractive index different from that of the constituent prism. The sensitivity remains reasonably high over the enhanced range of refractive index measurement. The experimental results are in qualitative agreement with the theoretical calculations. This refractometer sensor, which is based on the detection of modulation in emergent light intensity, has a sturdy and user-friendly design.     

悬浊液光谱透射法测量烟尘粒子的复折射率

光谱复折射率是计算烟尘粒子散射特性的重要参数。该文在光谱透射法反演烟尘粒子复折射率理论的基础上,将烟尘粒子弥散于水中形成烟尘粒子悬浊液,通过可见光分光光度计测量该悬浊液的光谱透射率,通过激光粒度仪获得烟尘粒子的粒径分布,利用悬浊液光谱透射法对烟尘粒子的复折射率进行了反演。研究结果表明,烟尘粒子在可见光波长范围内没有明显吸收带,但随着波长的增加,透过率逐渐降低。烟尘粒子复折射率的反演结果与KBr样片法的反演结果吻合较好。利用悬浊液光谱透射法测量烟尘粒子的复折射率,实验过程简单,约束条件少,并可利用红外分光光度计测量透射率后,拓展至红外波段。     

Use of multibeam interferometry to determine the refractive index of liquids

Journal of Applied Spectroscopy -     

A new method for complex spectral measurement in millimeter and submillimeter wave range

New method for measuring complex transmission or reflection coefficients has been proposed and demonstrated using a simple setup. High measurement quality was achieved: phase sensitivity 0.005 rad., amplitude reproduceability 1%, dynamic range to 10⁷ ÷ 10⁸ (previously 10⁴), phase shift range to be measured 10⁵. It is effective for BWT-Spectroscopy due to the absence of any mechanical adjustments during electronic frequency scan.     

Real-time analysis of 3-D axisymmetric refractive index field by photorefractive holographic interferometry

A real-time test method for determining the refractive index distributions of 3-D axisymmetric temperature field around a flame with the use of a photorefractive holographic interferometer is proposed. Some techniques in data processing for improving the quality of resultant interferogram are developed. Experimental results, which show the effectiveness of this method and agree with theoretical expectations, are also given.