High-Q measurements of fused-silica microspheres in the near infrared

Measurements of the quality factor Q approximately 8x10(9) are reported for the whispering-gallery modes (WGM's) of quartz microspheres for the wavelengths 670, 780, and 850 nm; these results correspond to finesse f approximately 2.2x10(6) . The observed independence of Q from wavelength indicates that losses for the WGM's are dominated by a mechanism other than bulk absorption in fused silica in the near infrared. Data obtained by atomic force microscopy combined with a simple model for surface scattering suggest that Q can be limited by residual surface inhomogeneities. Absorption by absorbed water can also explain why the material limit is not reached at longer wavelengths in the near infrared.     

Cu2+离子注入的石英光波导的特性研究

利用Cu2+离子注入的方式在熔融石英和石英晶体上分别制备了平面光波导结构.通过棱镜耦合实验测试了两种光波导的导模特性,结果表明:在同样的注入条件下熔融石英上形成了增加型的光波导结构,而石英晶体上形成了位垒型的光波导结构.研究了退火温度对两种光波导导模折射率的影响,熔融石英光波导中导模的折射率随着退火温度的升高而降低,而石英晶体光波导中导模的折射率随着退火温度的升高先增加后降低.为了进一步分析离子注入两种材料形成光波导的微观机理,利用SRIM模拟了Cu2+离子注入两种材料的电子能量损失和核能量损失,并且模拟了两种光波导结构的折射率分布.模拟结果表明:熔融石英光波导的主要形成原因是离子注入表面的折射率大于其体材料的折射率,而石英晶体光波导的主要形成原因是离子射程末端的折射率小于其体材料的折射率.因此,在熔融石英光波导的形成中电子能量损失起主要作用,而在石英晶体光波导的形成中核能量损失起主要作用.     

Fused silica as a composite nanostructured material

A method for calculating the refractive index of optical fused silica by applying the model of effective permittivity of composite homogeneous media is proposed and realized. The calculation was performed using the tabular data of the refractive index of crystalline α quartz and the ratio of the quartz glass and α quartz densities. It was suggested that fused silica contains nanosized pores with a glass filling number q immersed in a matrix with a density differing from the α quartz density by a factor of κ, where κ is slightly less than unity. It was established that the Maxwell-Garnett model makes it possible to calculate the refractive index of quartz glass and its dispersion in the transparency range (404 nm ≤ λ ≤ 671 nm) with a deviation less than 0.0002 from the tabular values. The calculated and experimental values coincide at q = 0.155 and κ = 0.986.     

Crystallinity of pure silica glass studied by positron annihilation

The crystallinity of silica glass fused from Brasilian quartz is demonstrated by positron annihilation lineshape measurements using a high resolution Ge(Li)-detector as well as by positron lifetime measurement.     

Diagnose Parameters of Plasma Induced by Femtosecond Laser Pulse in Quartz and Glasses

Electron plasma induced by a focused femtosecond pulse (130 fs, 800 nm) in quartz, fused silica, K9 glass, and Soda Lime glass was investigated by pump-probe technology. Pump and probe shadow imaging and interferometric fringe imaging have been used to determine plasma density, relaxation time, and electron collision time in the conduction band. In these materials, the electron collision time is about several femtoseconds when the electron density is in the 10¹⁹cm⁻³ range. The electron relaxation processes are different: lifetime is about 170 fs in pure quartz and fused silica, and about 100 ps in K9 and Soda Lime glass. The modified electron band by doped ions is regarded to be responsible for the difference of decay time in these materials.     

光学石英玻璃纳米划痕性能仿真研究

基于分子动力学方法,对石英玻璃进行了三维的纳米划痕仿真,用来研究其纳米加工性能。采用熔融-淬火的办法建立了石英玻璃的模型,并通过观察模型的截面图,分析了在制备过程中内部微观孔隙的形成过程和原因。在仿真过程中,观察了石英玻璃的变化和孔隙周围原子的运动,得到了切削力的曲线,重点研究了内部的微观空隙对划痕过程的影响。仿真结果表明:当石英玻璃冷却时,由于内部共价键的重组,会形成平均半径为0.25 nm的微观的孔隙,而且其降低了石英玻璃的纳米加工性能,使得切削力的曲线发生一定程度的波动。当磨粒划过表面后,会在表面以下形成厚度为2 nm的原子密集堆积区。由于稠密区的原子共价键键长的变化,失去了原有共价键的强度,所以会形成加工的损伤层。因此在对石英玻璃超精密加工时,应采用少量多次的加工方法来提高材料的加工性能。     

Ultrafast laser-induced melting of glass

The interaction of intense femtosecond laser pulses with wide band-gap fused silica and quartz is investigated. It is shown that during target irradiation, melting of SiO₂ occurs. Laser pulses with fluences above the damage threshold induce partial phase transition of fused silicia into quartz and vice-versa. PACS 42.62.-b; 61.46.+w; 81.30.Hd     

The sol-gel glass transformation of silica

Abstract

Large monolithic xerogel silica glasses were successfully made from tetramethyl-orthosilicate and distilled water using the combination of an acidic drying control chemical additive (DCCA) and a specially designed drying chamber. The acidic DCCA increases the gel strength by formation of a fibrillar ultrastructure, and the drying chamber reduces the catastrophic capillary forces inside the wet gel body.

Partially densified monolithic gels up to 850°C were routinely made for physical property tests and compared to commercial fused silicas. Although the mechanical properties of the porous gel-silica monoliths such as microhardness, Young's modulus, toughness, flexural strength, density are relatively lower than fused silica, the optically transparent porous gel silica has a UV cut-off ranging from 250–300 nm. Such a porous gel with excellent optical transmission and a highly uniform pore radius of 10–50 Å offers a unique, chemically stable matrix for impregnation with a second phase of optically active organic or inorganic compounds.

The processing and properties of Types I and II fused quartz optics and Types III and IV synthetic fused silica optics are compared with the new organometallic sol-gel derived gel-silica optics. Fully dehydrated and densified gel-silica has excellent transmission from 165 nm to 4400 nm with no OH absorption peaks. This optical transmission is equivalent to the best Type IV fused silica. The other physical properties and structural characteristics of the dehydrated dense gel-silica are similar to fused quartz and fused silica. However, the dense gel-silica has a lower coefficient of thermal expansion of 2.0 × 10^?7 cm/cm compared with 5.5 × 10^?7 cm/cm for standard vitreous silicas. The CTE value is temperature independent from 80 K to 500 K. Sol-gel silica optics can be made as complex shapes by casting of the sol into inexpensive plastic molds.     

Laser etching of transparent materials at a backside surface adsorbed layer

The laser etching using a surface adsorbed layer (LESAL) is a new method for precise etching of transparent materials with pulsed UV-laser beams. The influence of the processing parameters to the etch rate and the surface roughness for etching of fused silica, quartz, sapphire, and magnesium fluoride (MgF₂) is investigated. Low etch rates of 1 nm/pulse and low roughness of about 1 nm rms were found for fused silica and quartz. This is an indication that different structural modifications of the material do not affect the etching significantly as long as the physical properties are not changed. MgF₂ and sapphire feature a principal different etch behavior with a higher etch rate and a higher roughness. Both incubation effects as well as the temperature dependence of the etch rate can be interpreted by the formation of a modified near surface region due to the laser irradiation. At repetition rates up to 100 Hz, no changes of the etch rate have been observed at moderate laser fluences.     

Heat treatment of pure silica glass studied by positron annihilation

The crystallinity of silica glass fused from Brazilian quartz was studied by Doppler-broadening techniques after heat treatment in the temperature range between 1000°C and 1500°C. Paper F13 presented at 4th Internat'l Conf. Positron Annihilation, Helsing?r, Denmark (August 1976)     

Dosimetry techniques

The formation and annealing of defects in ion implanted silicon dioxide layers and in connection with them the refractive index change are of high interest for the production of electronic and integrated optical devices.

Several studies have shown that the ion implantation in fused silica leads to a compaction of the material and in consequence to an increasing of the refractive index.^1–6 On the other hand the defect formation in crystalline quartz is connected with a decreasing of the refractive index up to nearly the same value for ion implanted quartz and fused silica layers in the high dose region.^1,5 On the base of this effects optical waveguides had been produced by ion implantation in both material.^2,7–12 However, the nature of the mechanisms responsible for the defect formation and for the changes of the optical properties are not well understood.

This paper reports on the ion dose and annealing temperature dependence of several defects in connection with the refractive index change.     

激光陀螺新型槽片

根据激光陀螺的使用要求,针对传统槽片在结构和材质上给加工和陀螺性能所带来的不利因素,设计一种集微晶玻璃和熔石英玻璃的优点于一体的新型槽片结构。其基体采用与陀螺腔体材料相同的底膨胀系数的微晶玻璃,反射片采用抛光表面特性很好的熔石英玻璃,通过光胶接合组成一个完整的新型槽片。并针对新的槽片结构提出了与之相应的陀螺腔体贴片面加工方案,使其既能配合新结构的槽片又不增加腔体的制造难度。同时还提出和实现了在加工中采取球面部件与槽片基体分开加工的方式,使得新结构槽片不仅解决了长期困扰陀螺制造行业的因石英槽片易漏氦而引起的陀螺存储寿命相对较短的问题,同时还降低了球面基片超光滑表面加工难度和加工成本。     

Parametric instabilities and their control in advanced interferometer gravitational-wave detectors

A detailed simulation of Advanced LIGO test mass optical cavities shows that parametric instabilities will excite 7 acoustic modes in each fused silica test mass, with parametric gain R up to 7 and only 1 acoustic mode with R approximately 2 for alternative sapphire test masses. Fine-tuning of the test mass radii of curvature causes the instabilities to sweep through various modes with R as high as approximately 2000. Sapphire test mass cavities can be tuned to completely eliminate instabilities using thermal g-factor tuning. In the case of fused silica test mass, instabilities can be minimized but not eliminated.     

Third-order nonlinear optical response in transparent solids using ultrashort laser pulses

The third-order optical nonlinearity, χ ⁽³⁾, is measured in transparent glasses (BK7 and fused silica) and crystals (BaF₂ and quartz) using 36-fs, 800-nm laser pulses and the optical Kerr gate (OKE) technique; values are found to lie in the range 1.3–1.7×10^-14 esu, in accordance with theoretical estimates. We probe the purely electronic response to the incident ultrashort laser pulse in fused silica and BK7 glass. In BaF₂ and quartz, apart from the electronic response we also observe contribution from the nuclear response to the incident ultrashort pulses. We observe oscillatory modulations that persist for ～400 fs. The response of the media (glasses and crystals) to ultrashort pulses is also measured using two-beam self-diffraction; the diffraction efficiency in the first-order grating is measured to be in the range of 0.06–0.13 %. Third harmonic generation due to self-phase matching in the transient grating geometry is measured as a function of temporal delay between the two incident ultrashort pulses, yielding the autocorrelation signal.     

熔石英再沉积层结构的纳米级表征和杂质分析

利用原子力显微镜观察熔石英不同蚀刻时间的表面形貌,结合二次离子质谱分析,研究了熔石英的再沉积层结构和杂质分布。结果表明,熔石英表面深度10nm的再沉积层内存在大量微裂纹和杂质,经蚀刻展开形成nm级划痕和坑点,其分布随着深度增加呈指数衰减。根据nm级划痕密度、宽深比随蚀刻深度变化的规律,估算出再沉积层厚度,估算结果与二次离子质谱测得的杂质嵌入深度基本一致。杂质元素嵌入深度与抛光微裂纹分布特征的关联性表明,杂质很有可能藏匿在抛光微裂纹中。     

熔石英表面杂质元素在酸蚀过程中的变化

为了探寻熔石英表面痕量杂质元素种类以及随HF酸蚀刻过程中的变化情况,用质量分数为1%HF酸溶液对熔石英进行长达24,48,72,96 h的静态蚀刻实验。结合飞行时间二次离子质谱（TOF-SIMS）和X射线光电子能谱（XPS）测试分析结果发现,熔石英试片表面的痕量杂质元素主要含有B,F,K,Ca,Na,Al,Zn和Cr元素,其中绝大部分都存在于贝氏层中,在亚表面缺陷层检测到有K,Ca元素。所含有的K,Na杂质元素会与氟硅酸反应生成氟硅酸盐化合物。分析表明,在HF酸蚀刻的过程中一部分杂质元素将被消除,一部分杂质元素和生成氟硅酸盐化合物会随着蚀刻液逐渐从熔石英表面向表面纵深方向扩散并被试片吸附沉积,且随着深度的加深各元素的相对含量逐渐减少。     

Comparison of parametric instabilities for different test mass materials in advanced gravitational wave interferometers

Following the recognition that parametric instabilities can significantly compromise the performance of advanced laser interferometer gravitational wave detectors, we compare the performance of three different test mass configurations: all fused silica test masses, all sapphire test masses and fused silica inboard test masses with sapphire end test masses. We show that the configuration with sapphire end test masses offers the opportunity for thermal tuning on a time scale comparable to the ring up time of oscillatory instabilities. This approach may enable significant reduction of parametric gain.     

Muon-spin-rotation study of muon polarization losses in plastic scintillators and quartz

Muon polarization losses in plastic scintillators of two types and in fused quartz have been studied by the μSR method. The muon and muonium spin precession spectra have been measured on the μSR setup placed at the output of the muon channel of the Gatchina synchrocyclotron. It has been shown that a significant fraction of stopped muons participate in the formation of the muonium. As a result, these muons lose their polarization completely. The magnitude of muon depolarization depends considerably on the type of plastic. It has been found that the muon spin precession frequency in fused quartz in an external magnetic field (F _{Q, μ} = 0.116 ± 0.002 MHz) is shifted with respect to that in plastic scintillators (F _{1, μ} = 0.101 ± 0.005 MHz and F _{2, μ} = 0.101 ± 0.002 MHz).     

Using Ion-beam etching to smooth fused silica surfaces

The roughness of fused silica, silicon, and sapphire substrates from different manufacturers is studied. Features of the substrates for imaging optics in the soft X-ray (SXR) and extreme UV (EUV) ranges are discussed. The first results from smoothing quartz substrates by etching with neutralized 50–500-eV argon beams are reported. Surface smoothing has been observed in the spatial-frequency range of 10^-1-10^-2 μm^-1.     

塑性加工条件下射流颗粒冲击去除效应

针对在微观上存在尖锐突起、凹坑和划痕等缺陷的光学元件,提出用低质量分数磨料水射流冲击的方式对其进行处理。从弹性接触出发,对射流中粒子与元件发生塑性接触的临界速度进行了推导,并引入了塑性转入脆性加要的临界速度,从而对射流的塑性去除阶段作了明确的界定。针对常用的两种光学材料K9和石英玻璃,结合具体参数对使其处于塑性去除阶段的射流速度进行了模拟计算,利用单颗粒冲击去除模型,在塑性去除范围内对两种材料的冲击去除进行了模拟计算。结果表明:石英玻璃进入塑性去除的临界速度高于K9玻璃,而进入脆性去除的临界速度低于K9玻璃,因而使石英玻璃处于塑性去除阶段的射流速度范围为K9玻璃相应速度范围的子区间;在塑性去除阶段,各材料的去除量皆随着冲击速度的增大而增大,但较硬的石英玻璃更不耐冲击,较K9玻璃更容易被去除。