Temporally and spectrally resolved imaging of laser-induced plasmas

We report a hybrid imaging technique capable of performing measurements of the spatial, temporal, and spectral emission characteristics of laser-induced plasmas by use of a single detection system. We apply this technique to study the plasma produced by laser ablation of LiNbO3 and observe phenomena not seen in such detail with standard instruments. These include extreme line broadening up to a few nanometers accompanied by self-absorption near the target surface, and expansion dynamics that differ strongly between the different species. Overall, the wealth of quantitative information provided by this novel technique sheds new light on processes occurring during plasma expansion.     

On the spectrally resolved thermoluminescence of alumina

Summary The thermoluminescence of α-alumina was investigated by recording light emission simultaneouslyvs. temperature and wavelength. Samples were prepared, starting from amorphous alumina, by means of thermal treatments in the 850 to 1400°C temperature range. The recorded light exhibits two spectral bands at 553 and 706 nm emitted at temperatures close to 500 K, which reappear in the 700 K region with reduced intensity. The 553 nm band fades away in samples treated at temperatures exceeding 1200°C. The results are compared to a kinetic model which explains the most significant experimental features. Some qualitative arguments are advanced which could be useful in identifying the nature of the lattice defects responsible for the thermoluminescent emission observed.

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Riassunto Si è studiata la termoluminescenza dell'α-alumina registrando l'emissione di luce in funzione, simultaneamente, della temperatura e della lunghezza d'onda. Partendo da allumina amorfa, i campioni sono stati preparati mediante trattamenti termici nell'intervallo di temperatura da 850 a 1400°C. La luce registrata mostra due bande spettrali a 553 e 706 nm, emesse a temperature vicine a 500 K. Queste bande riappaiono nella regione attorno a 700 K con intensità ridotta. La banda a 553 nm svanisce nei campioni trattati a temperature al di sopra di 1200°C. I risultati sono paragonati ad un modello cinetico che spiega gli aspetti sperimentali più significativi. Vengono proposti alcuni argomenti qualitativi che potrebbero essere utili per identificare la natura dei difetti reticolari responsabili dell'emissione termoluminescente osservata.

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Резюме Исследуется термолюминесценция α-корунда, регистрируя интенсивность светового излучения в зависимости от температуры и длины волны. Образды изготавливаются из аморфного корунда, используя термическую обработку в области температур от 850°C до 1400°C. Термолюминесценция обнаруживает две спектральных зоны 553 и 606 нм, излучаемые при температурах, близких к 500 K, которые снова появляются в области 700 K с уменьшенной интенсивностью. Зона 553 нм затухает в образцах, обработанных при температуре выше 1200°C. Этот результат сравнивается с кинетической моделью, которая объясняет наиболее сушественные экспериментальные особенности. Приводятся некоторые качественные аргументы, которые могут быть полезны для идентификации природы дефектов решетки, ответственных за наблюдаемое термолюминесцентное излучение.

     

Demonstration of spectrally resolved x-ray scattering in dense plasmas

We present the first spectrally resolved x-ray scattering measurements from solid-density plasmas. The scattering spectra show the broadened Compton down-shifted feature allowing us to determine the electron temperature and density with high accuracy. In the low temperature limit, our data indicate that the ionization balance reflects the electrons in the conduction band consistent with calculations that include quantum mechanical corrections to the interaction potential.     

Long-range spectrally and spatially resolved radiation from filaments in air

The distance-resolved spectral intensity distribution of the backscattered light from long filaments generated in air using ultra-short and intense laser pulses is presented. A clean fluorescence spectrum from N₂ molecules and ions, which is produced by the high peak intensity inside the plasma filament of the fundamental pulse, was clearly resolved from the backscattered supercontinuum. The supercontinuum generated by both the fundamental and the third-harmonic pulses developed progressively and became fully developed only at the end of the filamentation.     

Evaluation of spectral phase in spectrally resolved white-light interferometry: Comparative study of single-frame techniques

Spectral phase in a white-light interferogram contains information about the absolute optical path difference (OPD) in the interferometer. Evaluation of spectral phase is therefore important in applications such as profilometry with white light. In spectrally resolved white-light interferometry (SRWLI) the white-light interferogram is spectrally decomposed by a spectrometer in order to determine this phase. Several single-frame techniques in SRWLI have been proposed for the evaluation of the phase including Fourier transform, Hilbert transform, spatial phase shifting, windowed Fourier transform and wavelet transform. In this paper we present a comparative study of these techniques in this application in relation to the temporal phase-shifting technique which is a multi- frame method. Further, we also propose a modified method to remove the influence of source spectrum modulation in Hilbert transform procedure.     

半导体微结构物理效应及其应用讲座第三讲半导体的激子效应及其在光电子器件中的应用

人们对半导体中的电子空穴对在库仑互作用下形成的激子态及其有关的物理性质进行了深入研究.激子效应对半导体中的光吸收、发光、激射和光学非线性作用等物理过程具有重要影响,并在半导体光电子器件的研究和开发中得到了重要的应用.与半导体体材料相比,在量子化的低维电子结构中,激子的束缚能要大得多,激子效应增强,而且在较高温度或在电场作用下更稳定.这对制作利用激子效应的光电子器件非常有利.近年来量子阱、量子点等低维结构研究获得飞速的进展,已大大促进了激子效应在新型半导体光源和半导体非线性光电子器件领域的应用.     

Propagation of sound and spectrally resolved rayleigh scattering in weakly ionized plasmas

The scattering mechanisms possible in weakly ionized plasmas are reviewed. The different cases can be discerned by means of the magnitude of three characteristic parameters: 2π/ωτ _c being the ratio of scattering time and mean free collision time, y=1/kλ _c being the scattering parameter defined as the ratio of scattering length and mean free collision path, and χω/c _{s, T} ² being the ratio between the product of thermometric conductivity and scattering frequency to the square of the adiabatic or isothermal sound velocity. For \({{2\pi } \mathord{\left/ {\vphantom {{2\pi } {\omega \tau _c<< 1}}} \right. \kern-0em} {\omega \tau _c<< 1}}\) quantum mechanical formulae have to be used, whereas in the opposite case classical treatments are applicable. The classical methods are Boltzmann equation formalisms ify?1, and fluid dynamics ify?1. In the fluid dynamical case there appear two waves for low frequencies, \({{\chi \omega } \mathord{\left/ {\vphantom {{\chi \omega } {c_{s, T}^2 }}} \right. \kern-0em} {c_{s, T}^2 }}<< 1\) , an adiabatic one which can propagate with weak damping and an isobaric one which cannot propagate, both wave types yielding together three scattered lines. In the opposite case of high frequencies, \({{\chi \omega } \mathord{\left/ {\vphantom {{\chi \omega } {c_{s, T}^2 }}} \right. \kern-0em} {c_{s, T}^2 }} > > 1\) , the scattering behavior is different from ordinary hydrodynamics. Here also do exist two types of waves, isochoric and isothermal, but none of them can propagate. Since the intensity of the scattered isochoric wave can be neglected, there is only one scattered line. Local temperatures and particle densities can be determined from the scattered spectrum. On the other hand, transport coefficients like shear and bulk viscosity as well as thermometric conductivity can be derived from sound absorption or Rayleigh scattering experiments if an independent temperature measurement is performed at the same time. The general formalism is applied to a weakly ionized hydrogen arc plasma.     

Atomic state reduction and energy balance relation in spectrally resolved resonance fluorescence

The paper is devoted to a study of properties of the reduced atomic state directly after detection of a resonance fluorescence photon that passed through a spectral (Fabry–Perot) filter. We establish the energy balance relation for the reduced state and discuss its observable consequences.     

Recording the temporal radiation characteristics of spectrally resolved light signals

It is proposed to extract data on the temporal characteristics of an optical signal by spectrally resolving the radiation and recording the nonlinear-optics effect of the resolved radiation. The recording should be made in two planes, with the spectrum image sharp in one of them and out-of-focus in the other. The dependence of the nonlinear effect on the phase relations of the spectral components of the radiation is analyzed. It is shown that if the spectral instrument is suitably chosen it is possible to determine (to within inessential constants) the phases of the spectral components from the frequency dependence of the nonlinear effect.Translated from Preprint No. 174 of the Lebedev Physics Institute, Academy of Sciences of the USSR, Moscow, 1990.     

Spatially,temporally, and spectrally resolved measurement of laser-induced plasma in air

Images and emission spectra of sparks produced by laser-induced breakdown in air were investigated with a high degree of spatial and temporal resolution. The laser-induced breakdown was generated by focusing a 532-nm nanosecond pulse from a Q-switched Nd:YAG laser. The data were collected using a framing intensified charged coupled device (CCD) camera and a multi-fiber Cassegrain optics system coupled to an intensified CCD spectrometer. The results provided information about the different stages of laser-induced breakdown. The plasma shape and emission spectrum were very reproducible. Different ionization levels in the plasma kernels, which were observed using the high spatial resolution of the multi-fiber Cassegrain optics system, occurred during the plasma formation and cooling and at different locations within the plasma. This was due mainly to the thickness of the plasma relative to the laser wavelength, which created different ionization levels and energy absorption rates throughout. These observations were correlated with the plasma visualizations obtained with the framing ICCD camera. The plasma emission analysis permitted us to study the temperature evolution along the plasma during the laser-induced breakdown process. The analysis demonstrated the validity of a laser-supported wave model during the first stages of laser-induced breakdown and illustrated the weak dependence of the plasma temperature on the input energy. PACS 52.50.Jm; 52.70.-m; 51.50.+v     

Hybrid laser-plasma system for processing and testing microelectronic devices

The possibility of using a new technique (a hybrid laser-plasma system) for processing microelectronic devices is discussed. The method will allow one to increase significantly the production rate preserving a sharp space pattern obtained by the laser beam of a given profile.     

Temporally and spectrally resolved sampling imaging with a specially designed streak camera

We present a novel sampling imaging technique capable of performing simultaneous two-dimensional measurements of the temporal and spectral characteristics of light-emission processes by use of a specially designed streak camera. A proof-of-principle experiment was performed with a homemade multifocal multiphoton fluorescence microscope. The system was calibrated with a Fabry-Perot etalon and a standard fluorophore solution (rhodamine 6G in ethanol) and was shown to have temporal and spectral resolution of 6.5 ps and 3 nm, respectively, as well as high accuracy and reproducibility in lifetime and spectrum measurement. Temporally and spectrally resolved images of 4 x 4 foci on the sample can be obtained with a snapshot.     

半导体微结构物理效应及其应用讲座第1讲布拉格衍射效应在半导体光电子器件中的应用与发展

文章对布拉格衍射效应在半导体光电子材料和光电子器件，特别是在光纤通信中的光电子器件的应用和发展进行了详细的介绍．文中以布拉格光栅衍射效应的光反馈和选模功能为主线，逐一介绍了X射线双晶布拉格衍射技术在半导体材料、特别是在量子阱和应变量子阱超薄层晶体生长和质量控制方面的作用，介绍了内建布拉格光栅对光通信用光信号源的发展所起的重要作用，波导光栅在复用和解复用过程中的作用，以及光纤布拉格光栅在全光纤通信系统中的应用及发展等．     

Special techniques for the Auger analysis of microelectronic devices

Microelectronic devices are becoming more complex and device features are getting smaller as the level of integration continues to increase. Although scanning Auger microscopy has been applied extensively to the analysis of microelectronic devices with a great deal of success, the analysis of current and future devices is presenting new challenges. The major limitations are (1) features of interest in microelectronic circuits are often comparable in size to the beam diameter of commercial Auger microprobes, and (2) the electron beam tends to drift about on the specimen surface because of mechanical instability and differential thermal expansion of the apparatus. In this paper, we present two different techniques developed to overcome these limitations. In the specimen modulation technique, the modulating signal is applied to the electrically isolatable regions of a device instead of to the electron energy analyzer. This method of modulation permits the detection of only the Auger electrons that are emitted from the modulated region. Spurious contributions from adjacent areas inadvertently illuminated by the analyzing beam are suppressed. In the position modulation technique, the analyzing beam is scanned repetitively across the feature to be analyzed and the Auger signal is synchronously detected at the scan frequency. The resulting Auger signal magnitude is shown to be unaffected by beam drift. This method of signal detection eliminates the error and uncertainty caused by beam instability during long-term depth profiling, but is applicable only to specimens with certain geometries.     

Sensitive measurement of nonlinear refraction and two-photon absorption by spectrally resolved two-beam coupling

A simple and very sensitive method for determining refractive and absorptive nonlinearities based on spectral resolution of two-beam coupling is demonstrated. Nonlinear phase shifts as small as ~10(-6) rad and two-photon absorption coefficients as small as 10(-4) cm/GW are readily observed by use of this technique with nanojoule pulses from a mode-locked laser.     

Laser and ion beams graphene oxide reduction for microelectronic devices

Reduced graphene oxide (rGO) is a two-dimensional material, which is attracting increasing attention due to its special properties. It can be obtained by laser or ion beam irradiations of pristine graphene oxide (GO). It shows high mechanical resistance, considerable electric and thermal conductivity. All these rGO characteristics together with the high number of molecular species that can be embedded between its layers, make graphene oxide a potential material for electronic sensors or efficient support on which conductive strips, condensers, and micrometric electronic devices can be designed. In particular, as it is described in this paper, it is possible to carry out high spatial resolution lithography in GO by using a focused laser or micro ion beam in order to design macro, micro, and submicron geometrical structures. The use of the reduced graphene oxide for the laser and ion beam fabrication of electrical resistances and capacitances is presented.     

Beat structure in spectrally resolved four-wave mixing under crosslinear polarization in GaAs quantum wells

The polarization dependence of beat structure in spectrally resolved four-wave mixing was investigated on 50 Å GaAs multiple quantum wells. Under crosslinear polarization we observed a beating structure at higher energy region of the main spectral peak due to biexciton–exciton transition. The beat has a period of 0.95 ps and is constructive at delay time T=0 ps, which suggests the corresponding double Feynman diagrams to be of the same type. By shortening the central wavelength of the sub-ps laser, we observed the distinctive peak corresponding to the beat period. Even in GaAs system, which is generally believed to have a small biexcitonic effect, there are two effective 2-exciton states with well-defined energies which are required to describe the third-order optical nonlinearly.