Reflection coefficient determination of the complex resonator mirrors in solid state laser

On the basis of pulse-energy measurement of Nd–YAG laser emission, the reflection coefficient of complex mirror is determined as a function of pumping energy and resonator parameters. It is shown that the reflection coefficient of complex mirror has the tendency to stabilize with increasing pumping energy above the threshold energy. The practical interest of this work is to determine the reflection coefficient of resonant mirror without using calibrated mirrors.     

Total reflection x‐ray fluorescence spectrometer with parallel primary beam

A new type of x‐ray optical device with two curved mirrors was tested experimentally for total reflection x‐ray fluorescence (TXRF). When focusing optics are used to increase the primary beam intensity at the sample position of TXRF spectrometers, it is always associated with an increase in the angular divergence, which is tolerable to only a limited extent. The possibility of improving the divergence by means of an additional curved mirror was reported in the past. One may hope that this additional mirror will correct some of the adverse characteristics of conventional x‐ray sources, such as the angular divergence and the intensity at the sample position. Copyright © 2005 John Wiley & Sons, Ltd.     

Experimental study of the stability and reflective properties of depleted uranium thin films at a wavelength of 4.5 nm

A technology of depleted uranium thin films, which can be used as high-reflectivity X-ray mirrors at a wavelength of 4.5 nm, is presented. The coefficient of X-ray reflection by these mirrors varies from 90 to 10% at grazing angles between 1° and 10°. The stability of the reflection coefficients for 200-Å-thick depleted uranium films covered by a protective carbon layer 100 and 200 Å in thickness and for 200-Å-thick uranium-nickel films with a nickel content of 9 and 23 wt % is studied. A high-reflectivity mirror is fabricated with the goal of increasing the X-ray radiation intensity in RKK-1-100 X-ray calibration equipment. Advice on fabrication of X-ray mirrors based on depleted uranium films is given.     

Measurement of transport mean-free path of light in thin systems

We extensively investigate in-plane light diffusion in systems with thicknesses larger than but comparable with the transport mean free path. By exploiting amplified spontaneous emission from dye molecules placed in the same holder of the sample, we obtain a directional probe beam precisely aligned to the sample plane. By comparing spatial intensity distribution of laterally leaking photons with predictions from random walk simulations, we extract accurate values of transport mean free path, opening the way to the investigation of a previously inaccessible kind of sample.     

偏振无关的旋光双反射结构的实验研究

完成了偏振无关双旋光晶体双反射结构的实验研究. 根据其偏振补偿特点对双旋光晶体双反射结构进行简化, 提出了一种偏振无关的单旋光晶体双反射结构. 实验表明, 两种反射结构的偏振保持度均能达到99.97%以上. 作为对比, 分别测试了单个反射镜反射90°和两个反射镜反射90°时的输出光偏振态. 该条件下, 无保偏处理的反射镜的偏振保持度分别只有92.1%和76.2%. 关键词： 偏振态 偏振无关反射 旋光晶体     

顶部反射镜对GaN基共振腔发光二极管性能的影响研究

本文在Ga N基共振腔发光二极管(RCLED)顶部设计制备了高反膜结构分布式布拉格反射镜(DBR)和滤波器结构DBR,对比分析了两种反射镜的反射率曲线特征以及对应的RCLED器件的光输出纵模模式、光谱线宽和输出光强等性能差异,详细研究了顶部反射镜的光反射特性对RCLED器件输出光谱性能的影响机理.研究结果表明,顶部反射镜是RCLED的重要组成部分,其反射率曲线特征决定器件的光输出性能.常规高反膜结构DBR顶部反射镜的反射率曲线具有较宽的高反射带,将其作为顶部反射镜可有效压窄RCLED发光纵模线宽,但是发光光谱仍呈现多纵模光输出特征.滤波器结构DBR顶部反射镜的反射率曲线在中心波长处具有较窄的透光凹带,利用透光凹带对输出光的调制作用,器件可实现单纵模光输出,在光通信、光纤传感等领域展示了广阔的应用前景.通过进一步设计RCLED顶部反射镜结构,可以改变其反射率曲线特性,进而优化RCLED器件的输出光谱特性,以满足器件在多个领域的应用需求.     

原子在两个平行镜面间两层电介质板中的自发辐射率

利用光子的闭合轨道理论,我们研究了原子在两个平行镜面间两层电介质板（折射率分别为n1,n2）中的自发辐射率. 自发辐射率呈现出多周期的振荡结构。自发辐射率的傅立叶变换中的每一个峰和光子从原子出发到返回原子的一条闭合轨道相对应。结果表明自发辐射率和两层电介质的宽度和折射率有关。和只有一层电介质的辐射率比较,当两层电介质的折射率n1 和 n2 差别很小时, 两层电介质之间分界面的反射效应可以忽略;但是当二者的差别很大时,发射效应变得非常重要且自发辐射率中的振荡减弱。本文的结果为原子在不同电介质间的自发辐射率的研究提供了新的理解。     

两片掺铒玻璃样品级联荧光光谱的实验研究

介绍一种掺铒玻璃样品的制作方法，实验测量了单片及两片掺铒玻璃样品的荧光特性.结果表明：两片掺铒玻璃样品级联的荧光强度比单片掺铒玻璃样品的荧光强度高，半值宽度与高浓度单片样品的半值宽度近似相等；在两片掺铒玻璃样品级联的形式中，浓度高的样品靠近抽运光源时的荧光强度比浓度低的样品靠近抽运光源时的荧光强度高；两种低浓度样品组合的荧光强度相对于其单片样品荧光强度的增幅比两种高浓度样品组合的荧光强度相对于其单片样品荧光强度的增幅要高. 关键词： 掺铒玻璃样品 级联 荧光光谱强度 半值宽度     

Coating stainless steel with diamond-like carbon using the hot filament chemical vapor deposition system,and its effects on fusion devices

Internal mirrors are used widely for plasma diagnostics in fusion devices. Therefore, keeping them in good optical condition is essential. The results of this experiment show that coating stainless steel 316l (S.S.316l) mirrors with diamond-like carbon (DLC) reduces the erosion rate and contamination of plasma by evaporation and sputtering and also increases the optical lifetime of these mirrors. For this purpose, firstly two similar S.S.316l samples were chosen. One of these samples was coated with DLC by a Hot Filament Chemical Vapor Deposition device, while the other was kept intact as a reference for investigating the effect of DLC coating. Then, in order to study the coating effects, these samples were exposed to 200 shots of the hydrogen plasma, with a total duration of 7 s in tokamak. Before and after the exposure, samples were analyzed by the atomic force microscopy, scanning electron microscopy, Raman Spectroscopy, and Spectrophotometer. It was found that the uncoated sample was damaged severely and its reflection dropped significantly, and the sample showed some cracks and some melting lines, while no significant change was observed on the surface characteristic of coated sample. Moreover, the weight loss of the uncoated was more in comparison to the coated, sample. Therefore, the results of this experiment showed that coating of S.S.316l by DLC is a useful method to strengthen this material against plasma erosion, and with further optimization, it could possibly be used in preparing plasma diagnostics mirrors.     

Second-harmonic generation in a doubly resonant semiconductor microcavity

We demonstrate second-harmonic generation in a doubly resonant semiconductor microcavity. The monolithic cavity consists of an AlGaAs active medium sandwiched between two AlGaAs/AlAs dual-wavelength mirrors. The mirrors do not have any apparent periodicity because, unlike single- or dual-wavelength Bragg reflectors, they are engineered with dispersion taken into account. Quasi-phase matching is obtained by addition of the appropriate phases at reflection so as to compensate for the dephasing between the fundamental and the second-harmonic fields.     

Laser cavities and polarization optics for soft X-rays and the extreme ultraviolet

Addressed here are polarization optics for extreme-ultraviolet and soft X-ray wavelengths, especially as relevant to laser cavities. It is pointed out that the whisper-gallery mirrors studied by Vinogradov can serve as weak polarizers and, more importantly, as birefringent elements. The application of multilayer technology to polarizing mirrors and beamsplitters is also considered. It is shown that multilayer beamsplitters can function both as reflective and transmissive polarizers. Their behavior is surprising in some cases, with the same polarization being preferred in both reflection and transmission. Three polarizing cavity schemes are proposed, each incorporating a polarizing beamsplitter as its output coupler. Cavity optimization issues are discussed.     

Optimization of self-frequency doubling in periodically and quasi-periodically poled nonlinear crystals

The theory of self-frequency doubling in a periodically poled nonlinear crystal is generalized to the case of varied domain thickness (quasi-periodically poled crystals). A particular statistical model of quasi-periodicity is considered. The effect of quasi-periodicity on the output emission intensity is calculated. The degree of quasi-periodicity allowable for practical applications is estimated, and the advantages of quasi-periodically poled crystals are discussed. The problem of maximization of the output emission intensity for periodically and quasi-periodically poled crystals is considered. The dependence of the output emission intensity on the crystal length is investigated, and an upper estimate for the maximum intensity is obtained. A formula for the optimal reflection coefficient of the output mirror as a function of the crystal length is derived.     

Improvement of the Reproducibility and Sensitivity of Laser Microspectral Analysis

The possibility for the concentration sensitivity improvement and the limit of detection of the elements at a laser microspectral analysis is studied by means an absorbtion decrease of the laser emission in the plasma torch.

From the investigations at an incline of 0°, 30°, 45°, 60° on the surface of the sample in the laser emission direction it is established, that the most intensive spectra are obtained at an incline of 45°. At an incline of 45° the intensity of certain spectral lines increases up 3 times in comparison with that of the horizontal surface of the sample. The limit of detection increases with one or two orders. The gradution curves for the determination of Si, Mn, Fe.     

Correlation between alkali concentration,surface potential,and exoelectronic emission of thin films

For several types of thin films (insulators, semiconductors, and metals) a maximum in exoelectron emission and a minimum in work function have been found for the same concentration in alkaline dopants. These results are in accordance with theoretical models predicting a decrease in'intensity with the work function, such as the thermionic model for insulators or the Auger emission for conductors.     

Dose response of thermoluminescence emission spectra of LiF:Mg,Ti with different Mg, Ti impurity concentrations

The dose response of the TL emission spectra of an LiF:Mg,Ti (TLD-100) sample and three LiF:Mg,Ti samples with different impurity concentrations (0–6 ppm Ti and 80–100 ppm Mg) have been measured. At a dose less than 22 Gy the emission spectrum of the TLD-100 sample comprises one emission band at 420 nm. The sample without Ti shows also one emission band but now at 620 nm. The spectra of the other two samples comprises two emission bands at 420 nm and 620 nm of which the intensity of the 420 nm band increases with increasing Ti concentration. The dose response of the glow peaks is different for peaks at different temperatures and emission bands. From these observations it can be concluded than in LiF:Mg,Ti at least some of the traps and luminescent centers are coupled.     

Combinatorial thin film sputtering investigation of cerium concentration in Lu2SiO5 scintillators

Lutetium oxyorthosilicate (LSO) thin films with a cerium thickness gradient were sputter deposited to investigate the optimum cerium concentration for emission intensity. Thin film cerium concentration ranged from 0.06 to 0.88 at%. To compare the thin film samples to single crystal LSO, a set of single crystal LSO samples were investigated with cerium concentrations of 0.0015, 0.0095 and 0.078 at%. The thin film samples showed peak photoluminescence emission intensity at a cerium concentration of 0.35 at%; however, the single crystal samples exhibited peak photoluminescence emission intensity at a lower cerium concentration of 0.0095 at%. The photoluminescence excitation and emission spectra as a function of concentration demonstrate the concentration quenching behavior and the mechanisms are speculated to be due to radiative (self-absorption) and non-radiative energy transfer, which may be phonon assisted.     

Feedback method of the noise suppression in wave-mixing amplifiers based on non-linear materials with photorefractive response in a reflection grating configuration

In the photorefractive wave-mixing system, fluctuation in the signal beam intensity of the photorefractive output with a reflection grating has been analyzed by employing pump feedback method. In this method, fluctuations of the photorefractive wave-mixing process not only induce the intensity fluctuation of the mixing waves but also induce phase fluctuation of the mixing waves. Thus, the phase of the pump and signal beams at the output surface fluctuates in time around a mean value. Using such a positive feedback method of a pump beams, the relative fluctuation in the photorefractive output signal beam intensity with respect to its mean intensity can be minimized significantly without reducing its mean intensity. The factors that control the fluctuation in the signal beam intensity, such as the phase fluctuation of the output pump beam, absorption strength of the material and the feedback reflectivity of the cavity mirrors, on the relative fluctuation of the output signal intensity in the photorefractive wave-mixing systems have been studied in detail. It has been found that the fluctuation of the output signal intensity relative to its mean intensity in the photorefractive wave-mixing system can be suppressed to larger extent by taking lower value of feedback reflectivity of the cavity mirrors which could exist at a higher value of absorption strength of the photorefractive materials.     

Dose dependence of room temperature photoluminescence from Si implanted SiO2

Photoluminescence from Si implanted silica is studied as a function of Si fluence and Si concentration profile in order to assess the effect of particle size and size distribution on emission spectra. Peaked (skewed Gaussian) concentration profiles were produced by implanting with 400 keV Si ions and uniform Si profiles were produced by a multi-energy implant sequences. Both as-implanted and annealed samples are shown to exhibit a distinct maximum in the emission intensity as a function of ion fluence, with the intensity increasing with fluence up to the maximum and then decreasing at higher fluences. Samples with a uniform Si profile are also shown to produce emission which is significantly red-shifted relative to that of samples with a peaked Si profile. This is consistent with the fact that such samples are expected to have a narrower particle size distribution (i.e. a greater fraction of larger particles).     

Ag nanoparticle mediated growth of CdS nanobelts

Catalytic growth of CdS have been carried out on large scale by evaporation of bulk CdS on Ag deposited Si (1 1 1) at atmospheric pressure. The as prepared CdS had wurtzite structure as evidenced by X-ray diffraction. The nanostructures were beltlike with several tens of micrometers length, several micrometers width and few nanometers to tens of nanometers thick as seen by scanning electron microscope and confirmed by TEM studies. The nanobelts were single crystalline in nature and showed reflection corresponding to (1 1 2) and (0 0 2) planes in SAED. The PL studies revealed the green band due to band gap emission and red band due to emission from the surface states. The higher intensity of the defect emission indicated the presence of considerable concentration of surface defects in the as prepared sample. The deposition of CdS could be explained on the basis of catalyst assisted vapor-liquid-solid and vapor-solid mechanism.     

Mirrors in optical schemes of ellipsometers

Expressions for Mueller matrices describing how the reflection from plane mirrors with an arbitrary orientation of the surface affects the polarization are obtained. The expressions can be useful in considering new ellipsometers’ optical schemes containing plane mirrors, as well as mirrors with a nonzero curvature of the surface.