Optical parametric oscillator for flow diagnostics

Cluster hopping effects and frequency instabilities prevent a wide use of doubly-resonant optical parametric oscillators (DROPOs) in the field of optical diagnostics, especially in the nanosecond regime. By using a two-cavity device, we demonstrate here that stable single-mode output can be obtained, provided that the length of each cavity is carefully chosen.     

Optical spectra analysis for breast cancer diagnostics

Minimally invasive probe and optical biopsy system based on optical spectra recording and analysis seem to be a promising tool for early diagnostics of breast cancer. Light scattering and absorption spectra are generated continuously as far as the needle-like probe with one emitting and several collecting optical fibers penetrates through the tissues toward to the suspicious area. That allows analyzing not only the state of local site, but also the structure of tissues along the needle trace. The suggested method has the advantages of automated on-line diagnosing and minimal tissue destruction and in parallel with the conventional diagnostic procedures provides the ground for decision-making.     

二维及三维流场的光学测量方法

对于复杂的非定常流动 ,流场的测量往往要求无干扰、非接触 ,并且能够瞬时记录流场的二维甚至三维信息。对近年来流场测量领域发展快速、应用广泛的几种光学测量方法 ,如 PIV技术及其由此发展而来的 DPIV和 HPV技术 ,做一些介绍和比较。     

等离子体诊断用Schwarzschild显微镜的光学设计

基于三级像差理论设计了用于激光等离子体诊断的极紫外Schwarzschild显微镜光学系统。显微镜的工作波长为18.2 nm,数值孔径为0.1,放大倍数为10。光学设计得到中心视场空间分辨力达0.3 μm,±1 mm视场内分辨力约0.4 μm的结果。分析了Schwarzschild成像系统的物镜装配、系统装调及光学元件加工误差对像质的影响,结果显示光学元件局部面形误差是影响系统成像分辨力的主要因素。通过提高系统装调的精度,可以有效补偿像距误差、两镜间距误差及曲率半径误差对像质的影响。综合考虑实际加工和装调能力,制定了系统整体公差方案,考虑公差后光学系统能够在±1 mm视场内获得3 μm的空间分辨力,达到了等离子体诊断的要求。     

等离子体诊断用Schwarzschild显微镜的光学设计

 基于三级像差理论设计了用于激光等离子体诊断的极紫外Schwarzschild显微镜光学系统。显微镜的工作波长为18.2 nm,数值孔径为0.1,放大倍数为10。光学设计得到中心视场空间分辨力达0.3 μm,±1 mm视场内分辨力约0.4 μm的结果。分析了Schwarzschild成像系统的物镜装配、系统装调及光学元件加工误差对像质的影响,结果显示光学元件局部面形误差是影响系统成像分辨力的主要因素。通过提高系统装调的精度,可以有效补偿像距误差、两镜间距误差及曲率半径误差对像质的影响。综合考虑实际加工和装调能力,制定了系统整体公差方案,考虑公差后光学系统能够在±1 mm视场内获得3 μm的空间分辨力,达到了等离子体诊断的要求。     

Optical diagnostics for particle-cleaning process utilizing laser-induced shockwave

The dynamics of laser-induced plasma/shockwave and the interaction with a surface in the laser shock cleaning process are analyzed by optical diagnostics. Shockwaves are generated by a Q-switched Nd:YAG laser in air or with N₂, Ar, and He injection into the focal spot. The shock velocity is measured by monitoring the photoacoustic probe–beam deflection signal under different conditions. In addition, nanosecond time-resolved images of shockwave propagation and interaction with the substrate are obtained by the laser-flash shadowgraphy. The results reveal the effect of various operation parameters of the laser shock cleaning process on shockwave intensity, energy-conversion efficiency, and flow characteristics. Discussions are made on the cleaning mechanisms based on the experimental observations. PACS 81.65.Cf; 42.62.-b; 47.40.Nm     

Optical diagnostics of intermittent flows

The efficiency of combined use of different optical techniques for flow diagnostics is demonstrated with the practically important case of intense swirling flows. It is shown that, when applied separately, commonly used optical measuring techniques, such as laser Doppler anemometry and particle image velocimetry, frequently give erroneous results, especially for the transition flow and developed nonstationary flow. However, their combined use in diagnostics of unsteady (intermittent) flows significantly improves both the temporal and spatial resolution of measurements. Such a complex approach is for the first time applied for diagnostics of the flow pattern in a closed cylinder with a rotating end face with the aim of studying the changeover from the steady axisymmetric to unsteady asymmetric flow over a wide range of flow parameters. It is found that such a transition is notable for azimuthal disturbances with characteristic modes and frequencies.     

Optical diagnostics of the atmosphere

The theoretical principles of the method of polarized laser probing of an aspherical atmospheric aerosol, oriented in space, are considered. An approach to estimating the effectness of methods of spectroscopic diagnostics of organic molecules, based on the study of photophysical processes occurring in them, is described. The possibilities of optical diagnostics of gaseous and aerosol media by short and ultrashort pulses on the basis of nonsteady and nonlinear effects are demonstrated. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 87–101, August, 1998.     

Optical diagnostics of dispersing He plasma

An experimental study has been made of the characteristics of radiation from a dispersing helium plasma. From measurements of the space-time dependence of the line intensities of the helium 2³P — n³D series we obtained the distribution of the populations of the n³D levels for n=3–10. The study has shown that over a wide range of conditions the high-lying levels (n=5–10) are in equilibrium with electrons while a substantial deviation from equilibrium is observed for levels n=3, 4. From the energy distribution of the populations of the upper levels we determined the space-time dependence of the electron temperature, which reflects the process of effective electron cooling during dispersal of the plasma. The gas temperature was estimated from the populations of helium singlet and triplet levels with n=5. The time distribution of the electron density in the plasma was found from the Stark broadening of the spectral lines.Deceased.V. D. Kuznetsov Siberian Physicotechnical Institute, Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 15–19, November, 1992.     

Optical emission diagnostics of laser-induced plasma for diamond-like film deposition

Optical emission from a laser-induced plasma plume is recorded during KrF excimer laser ablation of graphite in a gas mixture of Ar and H₂ (3%) for deposition of diamond-like thin films. At sub-GW/cm² laser intensities the spectrum is dominated by the bands of C₂ and CN. From the band intensities, the vibrational temperatures of both radicals are calculated to be 12–15×10³ K, and their concentrations are estimated to be 5×10¹⁴ cm^–3 and 2×10¹⁴ cm^–3, respectively.     

激光等离子体诊断用Wolter型X射线显微镜的设计

围绕着稠密等离子体硬X射线成像诊断,提出了一种基于阿贝正弦条件的Wolter型X射线显微镜的光学系统设计。详细介绍了Wolter显微镜的结构特点和设计方法,进行了参数优化,定量分析了包括物距、放大倍数、掠入射角和双曲面镜镜长在内的初始结构参数对物镜性能的影响。由光线追迹可以得出,在约±260 μm的视场范围内分辨率优于1 μm;在±460 μm范围内优于3 μm。有效视场可达约1 mm,几何集光立体角约为6.1×10^-5sr。同时,该系统具备平响应系统特性,在mm级的视场范围内,系统响应效率的一致性优于93.7%。     

A new tool for painting diagnostics: Optical coherence tomography

Nondestructive techniques have seen successful growth in the last few years, and, among them, optical ones are widespread and extremely well received in the field of painting diagnostics because of their effectiveness and safety. At present, many techniques for nondestructive investigations of paintings are available; nevertheless, none of them is suitable for a quantitative characterization of varnish. However, varnish removal, either partial or complete, is a fundamental part of the cleaning process, which is an essential step in painting conservation. This critical process has been carried out, up to now, without the possibility of any non-destructive measurement for assessing the actual varnish thickness, but with microscopic observation of a detached microfragment. Optical coherence tomography (OCT) is a noninvasive technique that is well established for biomedical applications. In this work, we present a novel application of OCT to measure the varnish film thickness for painting diagnostics. The text was submitted by the authors in English.     

Optical methods for precision measurements

Contactless measuring techniques are becoming increasingly important for industrial applications. The use of a laser, solid-state detector arrays and powerful small computers leads to a very efficient fringe analysis in holography as well as in Moiré and speckle techniques. Due to the computer analysis, much more information can be extracted from interferograms, leading to higher sensitivities and accuracies. The application of different fringe analysis procedures is discussed, together with some potentials of the application of interferometry, holography, and speckle and Moiré techniques.     

Optical diagnostics on helical flux compression generators

Explosively driven magnetic flux compression (MFC) has been object of research for more than three decades. Actual interest in the basic physical picture of flux compression has been heightened by a newly started Department of Defense (DoD) Multi-University Research Initiative. The emphasis is on helical flux compression generators comprising a hollow cylindrical metal liner filled with high explosives and at least one helical coil surrounding the liner. After the application of a seed current, magnetic flux is trapped and high current is generated by moving, i.e., expanding, the liner explosively along the winding of the helical coil. Several key factors involved in the temporal development can be addresses by optical diagnostics. 1) The uniformity of liner expansion is captured by framing camera photography and supplemented by laser illuminated high spatial and temporal resolution imaging. Also, X-ray flash photography is insensitive to possible image blur by shockwaves coming from the exploding liner. 2) The thermodynamic state of the shocked gas is assessed by spatially and temporally resolved emission spectroscopy. 3) The moving liner-coil contact point is a possible source of high electric losses and is preferentially monitored also by emission spectroscopy. Since optical access to the region between liner and coil is not always guaranteed, optical fibers can he used to extract light from the generator. The information so gained will give, together with detailed electrical diagnostics, more insight in the physical loss mechanisms involved in MFC     

Development of particle image velocimetry for multiphase flow diagnostics

This paper discusses the suitability of PIV for measuring simultaneously the velocity field of every phase and the size and concentration field of the disperse phases in multiphase flows. Velocity and disperse phase information are both inferred either directly from the Young’s fringe pattern (far field diffraction function) or from its 2-D Fourier transform (autocorrelation function). In the first case, the velocity is inferred from the orientation and spacing of the fringes while the disperse phase size is inferred from the size of the diffraction halo that modulates the fringes. In the second case, the velocity and particle shape are related to the position and shape of the strongest autocorrelation peaks, respectively. Particle sizes are used to discriminate between phases on the velocity measurements. The technique has been demonstrated on a high speed air-particle flow, where the potential for determining air velocities and particle size and velocities are shown.     

Nonlinear acoustic methods of crack diagnostics

This paper is a brief overeview of experimental studies of nonlinear acoustic phenomena due to the presence of cracks in solids. The possibilities for using these phenomena in crack diagnostics are discussed. To explain the observed effects, we present the physical models of a single crack and a fractured medium.Institute of Applied Physics Russian Academy of Sciences, Nizhny Novgorod. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 38, Nos. 3–4, pp. 169–187, March–April, 1995.     

Optical coherence tomography in art diagnostics and restoration

An overview of the technique of optical coherence tomography (OCT) is presented, and a spectral OCT instrument especially designed for art diagnostics is described. The applicability of OCT to the stratigraphy of oil paintings is discussed with emphasis on examination of the artist’s signature. For the first time, OCT tomograms of stained glass are presented and discussed. The utilisation of Spectral OCT in real-time monitoring of varnish ablation is discussed with examples of ablation, melting and evaporation, and exfoliation of the varnish layer provided, for the first time. PACS  42.30.-Wb; 07.60.-j; 07.60.-Ly; 81.70.Fy; 79.20.Ds     

Optical oscilloscope for three-dimensional flow visualization

A previous article described a method for tomographic flow visualization by means of the scattering of a plane laser light sheet. This paper shows recent improvements of such a method using two-dimensional sweeps of a pencil laser, which allows three-dimensional visualization, particularly in internal flows.