Quantitative characterization of the optical properties of absorbing polymer films: Comparative investigation of the internal reflection intensity analysis method

Nondestructive, three‐dimensional refractive‐index measurements are used for the determination of both the crystallinity and orientation in thin polymer films. The prism wave‐guide coupler is particularly suited for three‐dimensional isotropic and anisotropic thin‐film studies because of the quantitative character of the information obtained and the ease of data acquisition. It has been limited, however, to determining only the refractive index of transparent or weakly absorbing thin‐film samples. On the basis of thin‐film optics, this study develops a new internal reflection intensity analysis (IRIA) method, which uses the intensity information rather than the conventional mode angle values to acquire both the refractive index and the extinction coefficient over a range of transparent to highly absorbing polymer films. Therefore, the IRIA method overcomes the limitations of this prism wave‐guide coupler technique, which can only measure the refractive index of a weakly absorbing sample. With a Metricon PC‐2010 as the skeletal framework, a prototype instrument has been developed to apply and test the IRIA method. A study comparing both the refractive index and extinction coefficient obtained with ellipsometry, ultraviolet–visible/near‐infrared reflectometry, and IRIA for solvent blue 59 dyed polystyrene films confirms that the IRIA method is effective for obtaining the three‐dimensional refractive indices and extinction coefficients of polymer films. In addition, the refractive index and extinction coefficient spectrum (400–800 nm) of solvent blue 59 have been determined with the effective media theory. Furthermore, the three‐dimensional complex refractive indices of highly absorbing black electrical tape, inaccessible to other optical measurement because of its surface character, has been determined by the IRIA method. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 842–855, 2003     

Development of a modified grating coupler in application to geosciences

A grating coupler system has been developed to measure refractive index gradients with high spatial (6.7 μm) and temporal (milliseconds) resolution. The system was applied to two-phase model systems consisting of water and non-aqueous pollution liquids. Refractive index gradients at the interfaces between the aqueous and organic phase of 1-butanol, hexane, and 1-heptanol were monitored under steady-state conditions. The temporal resolution was utilized in diffusion experiments with glycerol and sodium chloride in water, where the formation of a concentration gradient was studied. In a further application, the grating coupler system was modified to monitor low-level concentrations of aqueous pollution profiles as are caused by bacterial degradation in the aqueous phase. Toluene was selected as contaminant. The sensor sensitivity was improved by coating the sensor with the pre-concentrating polymers polydimethylsiloxane and Teflon® AF-2400. With the grating coupler setup, a multi-purpose instrument was created to measure high-resolution refractive index gradients with high temporal and spatial resolution in different fields of application. The new sensor system can be used to measure absolute refractive indices by covering parts of the sensing area with cover media of known refractive index. Coatings can be used for sensitivity improvement by pre-concentrating the sample, for selectivity by utilizing filtering properties of the coating, and as calibration standard for absolute refractive index measurements.     

固定光路可变焦宽调角表面等离子共振成像装置

设计了一种折反式棱镜耦合单元, 用于简化表面等离子共振系统的角度调节操作, 并基于此单元构建了固定光路可变焦宽调角表面等离子共振成像装置. 该装置通过旋转折反式棱镜耦合单元即可实现角度调节, 调节范围可达40°~80°, 结合1~2倍的变焦成像系统, 可对1~4 cm²传感芯片成像, 且可分辨至少3600 Point/cm². 以蔗糖溶液为研究对象, 考察了该装置的灵敏度, 结果表明其灵敏度可达7×10^-6 RIU(Refractive index unit), 共振角与折射率的线性相关系数为0.99953. 将该装置用于研究抗牛血清白蛋白抗体与其它蛋白的实时相互作用, 所得结果与理论相符. 该表面等离子共振成像装置将在实时并行分析方面具有广阔的应用前景.     

The influence of hydrogen chloride doping level on the complex refractive indices of anisotropic polyaniline film: Application of a new internal reflection waveguide coupling technique

Nondestructive three‐dimensional refractive‐index measurements are used for the determination of both crystallinity and orientation in thin polymer films. The prism waveguide coupler is particularly suitable for three‐dimensional isotropic and anisotropic thin‐film studies because of the quantitative character of the information obtained and the ease of data acquisition. It has been limited, however, to measuring the refractive index of optically transparent or weakly absorbing films. This study shows that a modified prism waveguide coupler can be used to determine the complex refractive index over a range from transparent to highly absorbing films from the internally reflected light intensity. Thus, both the refractive index, n, and the extinction coefficient, k, can be obtained. This method is used to determine the anisotropic three‐dimensional n and k values of spin‐coated emeraldine base and hydrogen chloride doped emeraldine salt polyaniline films. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2481–2490, 2001     

High‐refractive‐index and high‐barrier‐capable epoxy‐phenoxy‐based barrier film for organic electronics

A barrier film is a fundamental component of the fast growing organic electronic device industry that is necessary to sustain long‐term stability. The barrier film prevents the permeation of environmental moisture and oxygen into the organic electronic device. Superior barrier property is the most crucial characteristic of a barrier film, in addition to a high refractive index. A high‐refractive‐index barrier film has the potential to reduce the refractive‐index mismatch between a device and a protective film, consequently, reducing the energy costs by increasing the light output. In this work, six epoxy and phenoxy resin composite compositions are synthesized separately, each with a different cross‐linker. POL‐TE1/PET and POL‐HD1/PET films show enhanced refractive indexes of 1.726 (at 750 nm) and 1.721 (at 500 nm), allowing only 71.7% and 70.4% permeation, respectively, compared to those of POL/PET, while exhibiting more than 80% transparency and excellent properties. The films are fabricated using a straightforward process, from a solution, at low temperature and under atmospheric conditions, using an applicator and bar coating.     

Optically trapped microsensors for microfluidic temperature measurement by fluorescence lifetime imaging microscopy

The novel combination of optical tweezers and fluorescence lifetime imaging microscopy (FLIM) has been used, in conjunction with specially developed temperature-sensitive fluorescent microprobes, for the non-invasive measurement of temperature in a microfluidic device. This approach retains the capability of FLIM to deliver quantitative mapping of microfluidic temperature without the disadvantageous need to introduce a fluorescent dye that pervades the entire micofluidic system. This is achieved by encapsulating the temperature-sensitive Rhodamine B fluorophore within a microdroplet which can be held and manipulated in the microfluidic flow using optical tweezers. The microdroplet is a double bubble in which an aqueous droplet of the fluorescent dye is surrounded by an oil shell which serves both to contain the fluorophore and to provide the refractive index differential required for optical trapping of the droplet in an external aqueous medium.     

Fluorescent liquid-core/air-cladding waveguides towards integrated optofluidic light sources

We have demonstrated fluorescent liquid-core/air-cladding (LA) waveguides suitable for use as integrated optofluidic light sources. These waveguides were fabricated by conventional soft lithography using poly(dimethylsiloxane) (PDMS). Two-phase stratified flows of air and ethylene glycol with fluorescent dye were generated along the PDMS channel. Compared to the liquid-core/liquid-cladding (L(2)) waveguide, the larger refractive index contrast of the LA waveguide resulted in stronger optical confinement. Specifically, the larger refractive index contrast led to experimentally achievable captured fractions (the amount of light to be coupled into the liquid core) as high as 22.8% and the measured propagation losses as low as 0.14 dB cm(-1). Furthermore, in our LA waveguides, diffusional mixing of the core and cladding fluids did not occur and the size of the core stream could be reversibly tuned simply by adjusting the flow rates of the two contiguous phases.     

Optical anisotropy of polymeric films measured by waveguide propagation mode determination

Extruded thin films of a liquid-crystalline charge-conjugated rigid-rod polymer poly(p-phenylenebenzobisthiazole), PBT, and a semicrystalline thermoplastic polyethylene-terephthalate (Mylar) were fabricated and examined for film thickness, refractive index, and linear attenuation coefficient. Optical waveguide modes were successfully induced on the polymeric films using a prism coupler at λ = 633 and 1300 nm. Highly consistent thickness values were obtained for the polymeric films. In addition, the anisotropic nature of the optical properties was determined using TE and TM propagation modes. A refractive index as high as 2.3 was observed on PBT film. The refractive index data suggested that the PBT and Mylar films were optically anisotropic with refractive indices n? (out-of-plane) invariably smaller than n∥ (in-plane). Large anisotropy was also discovered in the linear attenuation coefficient α, with α_∥/α_? ≈ 50 for the Mylar films. Complementary polarimetric and spectroscopic interference measurements were also applied to investigate the optical anisotropy of the extruded polymeric films. © 1992 John Wiley & Sons, Inc.     

Quantitative 3-dimensional profiling of channel networks within transparent lab-on-a-chip microreactors using a digital imaging method

We have developed a method for the quantitative 3-dimensional profiling of micron sized channel networks within optically transparent "lab-on-a-chip" microreactor devices. The method involves capturing digitised microscope images of the channel network filled with an optically absorbing dye. The microscope is operated in transmission mode using light filtered through a narrow bandpass filter with a maximum transmission wavelength matching the wavelength of the absorbance maximum of the dye solution. Digitised images of a chip filled with solvent and dye solution are analysed pixel by pixel to yield a spatially resolved array of absorbance values. This array is then converted to optical path length values using the Beer-Lambert law, thereby providing the 3D profile of the channel network. The method is capable of measuring channel depths from 10 to 500 microm (and probably even smaller depths) with an accuracy of a few percent. Lateral spatial resolution of less than 1 microm is achievable. It has been established that distortion of the measured profiles resulting from a mismatch in refractive index between the dye solution and the glass of the microreactors is insignificant. The method has been successfully used here to investigate the effects of thermal bonding and etch time on channel profiles. The technique provides a convenient, accurate and non-destructive method required to determine channel profiles; information which is essential to enable optimisation of the operating characteristics of microreactor devices for particular applications.     

Micro flow modules with combined fluid flow channel and optical detection waveguide - hyper Rayleigh scattering as a case study

Micro flow modules with optical detection have been fabricated in a way which enables optical waveguiding inside and a defined interaction length along the fluid channel. Because of the usually lower refractive index of the solution compared with that of the substrate, so-called "leaky" optical wave-guiding must be employed. The combination of the fluid flow channel function with that of the optical waveguide has advantages for all miniaturized optical detection cells. It has been shown for hyper Rayleigh scattering (HRS) that improvement of the analytical principle is inherent in the miniaturization. The detection limit can be enhanced by at least a factor of 20. The applied HRS measurement procedure also enables simultaneous detection of two photon absorption (TPA) fluorescence. The severe boundary conditions of capillary electrophoresis were used as micro flow module design constraints to enable the transfer of the approach to other types of analysis.     

磷酸铁纳米薄膜复合光波导氨气传感元件的制备

将硝酸铁和甲醇、磷酸溶液按一定比例混合后,通过旋涂法制备了磷酸铁（FePO₄）纳米薄膜,测定了匀胶机转速对膜厚及烘干温度对膜厚和折射率的影响,并发现薄膜的烘干温度超过150 ℃时,薄膜的厚度（130 nm）和折射率(1.7)变化不大。将该薄膜固定在钾离子交换玻璃光波导表面,研制出FePO₄膜/K⁺交换玻璃复合光波导。酸碱指示剂溴百里酚兰（BTB）作为敏感试剂,固定在复合光波导表面,研制了BTB膜-FePO₄膜/K⁺交换玻璃复合光波导氨气传感元件。采用自装的光波导气体传感检测系统对不同浓度的氨气进行了检测。结果表明,该传感元件能够检测0.35 mg/m³浓度的氨气,并具有响应（10 s）及恢复（90 s）速度快、可逆性好、连续使用等特点。     

Epoxy-based Polymer Containing Imidazole-type Azo Chromophores for Integrated Waveguide Applications

In this work, an epoxy-based polymer containing 2-phenylazo-4, 5-dicyanoimidazole chromophores (BP-IZ-DC) was synthesized and characterized by spectroscopic methods. The polymer showed unusual photo-bleachable property and the refractive index of the polymer could be readily modified by irradiation with a laser beam at visible wavelength. The irradiation with a laser beam at 488 nm caused a much more significant change of the refractive index than irradiation with 532 nm laser light. Upon the irradiation with the laser beam (488 nm, 100 mW/cm²) for 1 h, the refractive index decreased from 1.6512 to 1.5802. By using the photo-bleachable azo polymer, channel waveguide was fabricated by light irradiation through a mask and the light-transmission ability of the waveguide was evaluated.     

Fibre optic coupler as a detector for microfluidic applications

A new construction of a fibre optic coupler is presented in the paper. Two polymer optical fibres were used to build a coupler in which coupling efficiency of optical power depends on the refractive index of liquid delivered to a microchannel formed by the fibres. The coupler was tested as a detector in saccharose concentration measurements, and was used in absorbance measurements. A red light emitting diode and a spectrometer were used as a light source and a photodetector, respectively. Experiments confirmed that the coupler can be used for the real time monitoring of the changes in the refractive index of a saccharose solution exhibiting repeatable changes in the signal, with no hysteresis. Absorbance tests were performed with a solution of bromothymol blue at different pH.     

Rapid fabrication of a microfluidic device with integrated optical waveguides for DNA fragment analysis

The fabrication and performance of a microfluidic device with integrated liquid-core optical waveguides for laser induced fluorescence DNA fragment analysis is presented. The device was fabricated through poly(dimethylsiloxane) (PDMS) soft lithography and waveguides are formed in dedicated channels through the addition of a liquid PDMS pre-polymer of higher refractive index. Once a master has been fabricated, microfluidic chips can be produced in less than 3 h without the requirement for a cleanroom, yet this method provides an optical system that has higher performance than a conventional confocal optical assembly. Optical coupling was achieved through the insertion of optical fibers into fiber-to-waveguide couplers at the edge of the chip and the liquid-fiber interface results in low reflection and scattering losses. Waveguide propagation losses are measured to be 1.8 dB cm(-1) (532 nm) and 1.0 dB cm(-1) (633 nm). The chip displays an average total coupling loss of 7.6 dB due to losses at the optical fiber interfaces. In the electrophoretic separation and detection of a BK virus PCR product, the waveguide system achieves an average signal-to-noise ratio of 570 +/- 30 whereas a commercial confocal benchtop electrophoresis system achieves an average SNR of 330 +/- 30. To our knowledge, this is the first time that a waveguide-based system has been demonstrated to have a SNR comparable to a commercially available confocal-based system for microchip capillary electrophoresis.     

Fabrication of Channel Waveguides by Photochemical Self-Developing in Doped Sol-Gel Hybrid Glass

Sol-gel derived inorganic-organic hybrid glass (HYBRIMER) films doped with benzildimethylketal (BDK) were prepared. Refractive index and film thickness increase by UV exposure due to photoinduced polymerization and photolocking of high refractive index BDK. This enables the channel waveguides in HYBRIMER film to be fabricated without using a developing process, which is called photochemical self-developing (PSD). The waveguides consist of three layers with under-cladding and over-cladding of undoped HYBRIMER films and core of BDK-doped HYBRIMER film. A 1 × 4 splitter of waveguides was fabricated and demonstrated.     

Novel microfabricated device for electrokinetically induced pressure flow and electrospray ionization mass spectrometry

A novel microchip device for electrospray ionization has been fabricated and interfaced to a time-of-flight mass spectrometer. Fluid is electrokinetically transported through the chip to a fine fused-silica capillary inserted directly into a channel at the edge of the device. Electrospray is established at the tip of the capillary, which assures a stable, efficient spray. The electric potential necessary for electrospray generation and the voltage drop for electroosmotic pumping are supplied through an electrically permeable glass membrane contacting the fluidic channel holding the capillary. The membrane is fabricated on the microchip using standard photolithographic and wet chemical etching techniques. Performance relative to other microchip electrospray sources has been evaluated and the device tested for potential use as a platform for on-line electrophoretic detection. Sensitivity was found to be approximately three orders of magnitude better than spraying from the flat edge of the chip. The effect of the capillary on electroosmotic flow was examined both experimentally and theoretically.     

Refractive index measurements of films with biaxial symmetry. 2. Determination of film thickness and refractive indices using polarized transmission spectra in the transparent wavelength range

A technique is formulated to determine both thickness and refractive indices of free-standing films with biaxial symmetry from polarized transmission spectra. The films must be transparent and show little dispersion in refractive indices in the wavelength range where the transmission spectra are collected. Methods are proposed to correct the errors caused by imperfect polarization of incident radiation and thickness variation across the sampling area. Anisotropic refractive indices and thickness of poly(biphenyl dianhydride-p-phenylenediamine) films which exhibit uniaxial optical anisotropy are determined from polarized transmission spectra. The refractive index and thickness values compare well to those obtained from waveguide prism coupler and profilometer measurements.     

可录型光盘(CD-R)中染料膜层的光谱性质和光学特性

本文利用光在多层膜介质中的传播模型,计算了可录型光盘（ＣＤ Ｒ）中染料媒体的光学特性．表明在适合于ＣＤ Ｒ光盘记录的７８０ｎｍ波长处,由于多层膜中光的干涉作用,样品反射率随薄膜的厚度变化发生振荡．振荡的幅度和周期依赖于染料薄膜的复数折射率（ｎ＋ｉｋ）．当记录介质层的复数折射率在２．１＋ｉ０．０２至２．８＋ｉ０．１２之间时,能够满足ＣＤ Ｒ光盘对染料介质的要求．通过对三种菁染料薄膜的光谱性质分析及光学参数的模拟计算,证实了该方法用于染料薄膜光学特性研究的合理性．并为选择适合于光记录的染料薄膜的厚度范围提供了简便的方法     

Comparison of Different High and Low Index Materials in the Manufacture of High Laser Damage Threshold Mirrors at the 351 nm Wavelength

Sol-gel material based mirrors have been produced by forming alternate layers of high refractive index and low refractive index thin films. These mirrors have proven to have a high laser induced damage threshold [LIDT]. Using nitric acid stabilized zirconia derived from zirconium-n-propoxide and base catalyzed silica, a 16 layer mirror with a reflectivity of better than 94% at 351 nm and 45° angle of incidence was fabricated. This had an LIDT of 7.7 J/cm2 at 351 nm with a 0.7 ns pulse width. Crazing prevented further layers being deposited. Both spin and dip coating were attempted with dip coating yielding the best results.The coating structure has been analyzed using XPS depth profiling and AES. The bulk materials have been investigated using transmission electron microscopy (TEM), X-ray diffraction (XRD) and TGA. High refractive index layers using Hafnia with nitric or acetic acid have also been investigated as prospective high LIDT mirrors.Alternative acidic routes to silica have been studied as a possible low index material and a route to preventing crazing.     

Monolithic column plastic microfluidic device for peptide analysis using electrospray from a channel opening on the edge of the device

Electrospray from a channel exit at the edge of a fluorocarbon coated cycloolefin copolymer microfluidic device has been investigated. The fluorocarbon coating facilitated generation of a stable electrospray, thereby enhancing the detectability of electrospray ionization (ESI) mass spectrometry (MS). A microfluidic device of integrated ESI emitters and monolithic liquid chromatography columns has been fabricated on a cycloolefin copolymer chip. The monolithic columns were polymerized in situ using UV irradiation with a photomask to confine the porous polymer monolith to the desired regions of the channels. The monolithic stationary phase was homogenous and well bonded to the channel surfaces, which had been functionalized by graft polymerization. The ESI potential was applied within the channel via a carbon ink line. The performance of this microfluidic device was demonstrated by analysis of a tryptic digest of bovine serum albumin on an ion trap MS instrument.