Measurements of the optical properties of tissue in conjunction with photodynamic therapy

A simple optical dosimeter was used to measure the light intensity in rat liver and muscle in vivo with fibers positioned at different depths to investigate whether the light penetration changed during photodynamic therapy (PDT). The results were then correlated with measurements of the three optical-interaction coefficients μ(s), μ(a) and g for wavelengths in the range 500-800 nm for PDT-treated and nontreated rat liver and muscle tissue in vitro. Adistinct increase in the absorption coefficient was seen immediately after treatment, in agreement with the decreasing light intensity observed during the treatment, as measured with the optical dosimeter. The collimated transmittance was measured with a narrow-beam setup, and an optical integrating sphere was used to measure the diffuse reflectance and total transmittance of the samples. The corresponding optical properties were obtained by spline interpolation of Monte Carlo-simulated data. To ensure that the measured values were correct, we performed calibration easurements with suspensions of polystyrene microspheres and ink.     

基于光源平移恢复物体法线和材质的算法

提出了一种基于光源平移恢复物体法线和材质的算法.光源平移时获得一组输入图像.根据输入图像将物体表面上的点分成纯漫反射点和混合点(包含漫反射和镜面反射的点).首先,根据镜面反射的原理求出混合点的法线.然后根据求出的法线用全局优化的迭代方法来恢复物体的材质.最后,根据不同输入图像中光源与物体的相对位置的不同,通过一个三角函数来恢复物体表面纯漫反射点的法线.分析对比实验结果和场景的真实参数表明,算法能够有效地恢复物体的法线和材质.     

NIST High Accuracy Reference Reflectometer-Spectrophotometer

A new reflectometer-spectrophotometer has been designed and constructed using state-of-the-art technology to enhance optical properties of materials measurements over the ultraviolet, visible, and near-infrared (UV-Vis-NIR) wavelength range (200 nm to 2500 nm). The instrument, Spectral Tri-function Automated Reference Reflectometer (STARR), is capable of measuring specular and diffuse reflectance, bidirectional reflectance distribution function (BRDF) of diffuse samples, and both diffuse and non-diffuse transmittance. Samples up to 30 cm by 30 cm can be measured. The instrument and its characterization are described.     

Dispersive optical constants of thermally deposited AgIn5S8 thin films

AgIn₅S₈ thin films were obtained by the thermal evaporation of AgIn₅S₈ crystals onto ultrasonically cleaned glass substrates. The films are found to exhibit polycrystalline cubic structure. The calculated lattice parameter of the unit cell (a) is 10.78 Å. The transmittance data of the as grown films which was recorded at 300 K in the incidence wavelength (λ) range of 320-1000 nm are used to calculate the refractive, n(λ). The transmittance and reflectance data are also used to calculate the absorption coefficient of the as grown AgIn₅S₈ thin films. The fundamental absorption edge is found to be corresponding to a direct allowed transitions energy band gap. This band-to-band transition energy is found to be 1.78 eV and it is consistent with that reported for AgIn₅S₈ single crystals.     

Surface textured molybdenum doped zinc oxide thin films prepared for thin film solar cells using pulsed direct current magnetron sputtering

In this study, we examined the effect of etching on the electrical properties, transmittance, and scattering of visible light in molybdenum doped zinc oxide, ZnO:Mo (MZO) thin films prepared by pulsed direct current magnetron sputtering. We used two different etching solutions - KOH and HCl - to alter the surface texture of the MZO thin film so that it could trap light. The experimental results showed that an MZO film with a minimum resistivity of about 8.9 × 10^− 4 Ω cm and visible light transitivity of greater than 80% can be obtained without heating at a Mo content of 1.77 wt.%, sputtering power of 100 W, working pressure of 0.4 Pa, pulsed frequency of 10 kHz, and film thickness of 500 nm. To consider the effect of resistivity and optical diffuse transmittance, we performed etching of an 800 nm thick MZO thin film with 0.5 wt.% HCl for 3-6 s at 300 K. Consequently, we obtained a resistivity of 1.74-2.75 × 10^− 3 Ω cm, total transmittance at visible light of 67%-73%, diffuse transmittance at visible light of 25.1%-28.4%, haze value of 0.34-0.42, and thin film surface crater diameters of 220-350 nm.     

Structural, optical and electrical properties of undoped polycrystalline hematite thin films produced using filtered arc deposition

Thin films of α-Fe₂O₃ (hematite) were deposited using filtered arc deposition. The structural, optical and electrical properties of the films have been characterized. High-purity hematite films were produced, free from other iron oxide phases and impurities. The films exhibit preferred orientation, with the c-axis of the hexagonal structure aligned perpendicular to the substrate. The films have an upper uncertainty bound of the porosity of 15%, with a microindentation hardness of 17.5 ± 1 GPa and elastic modulus of 1235 ± 5 GPa. The indirect and direct band gap energies were found to be approximately 1.9 eV and 2.7 eV, respectively. The refractive index, and the extinction and absorption coefficients were determined from total reflectance and direct transmittance measurements. The thin films exhibit a high resistivity (≥ 10⁵ Ω cm) which indicates pure α-Fe₂O₃. An activation energy of 0.7 eV was calculated from an Arrhenius plot of the conductivity.     

Optical constants of platinum octaethyl porphyrin in single-layer organic light emitting diode studied by spectroscopic ellipsometry

We studied the optical properties of platinum octaethyl porphyrin (PtOEP) emitting layer in single-layer organic light emitting diode (OLED) device and in thin film grown on quartz plate using a phase modulated spectroscopic ellipsometry. Spectra of optical constants (refractive index n and extinction coefficient k) were obtained for PtOEP in the visible-ultraviolet spectral range. Difference was observed in the n and k spectra between the thin film evaporated on quartz plate and the encapsulated OLED. Additionally, difference was found between the layer thickness estimated by quartz oscillator and thickness estimated from the ellipsometry measurement. Discussion is given on contamination by oxygen and moisture in the unsealed thin film.     

Z-scan measurement for the nonlinear absorption of Bi2.55La0.45TiNbO9 thin films

Bi_2.55La_0.45TiNbO₉ (BLTN-0.45) thin films with layered aurivillius structure were fabricated on fused silica substrates by pulsed laser deposition technique. Their structure, fundamental optical constants, and nonlinear absorption characteristics have been studied. The film exhibits a high transmittance (> 60%) in visible-infrared region. The optical band gap energy was found to be 3.44 eV. The optical constant and thickness of the films were characterized using spectroscopic ellipsometric (SE) method. The nonlinear optical absorption properties of the films were investigated by the single-beam Z-scan method at a wavelength of 800 nm laser with a duration of 80 fs. We obtained the nonlinear absorption coefficient β = 4.64 × 10^− 8 m/W. The results show that the BLTN-0.45 thin film is a promising material for applications in absorbing-type optical device.     

A statistical parameter study of indium tin oxide thin films deposited by radio-frequency sputtering

In order to optimize the electrical and optical properties of indium tin oxide (ITO) thin films, a statistical analysis called Taguchi design was employed. It is shown that the sheet resistance and transmittance are inversely proportional to each other as a function of the process parameters. Additionally, the preferred orientation of crystalline ITO film is distinguishably changed with the increase of sputtering temperature and oxygen fraction (O₂/O₂+Ar) in the sputtering ambient. The change in crystallinity results from the content of incorporated oxygen, which significantly affects the electrical and optical properties of ITO films and causes a rearrangement of atoms to form preferred closed-packed plane orientation. Finally, the microstructure of the ITO films becomes denser with the increasing oxygen fraction. As a result of this work, we have successfully achieved low sheet resistance (7.0 Ω/□) and high transmittance (~90%) for 300 nm thick films.     

Determination of optical constants of thin films from transmittance trace

A simple method is depicted in this communication to determine the optical constants of transparent thin films from transmittance versus wavelength traces, showing no fringes, for evaluating thickness. The strength of this technique is apparent when applied to Zn_1 − xMg_xO films.     

Optical properties of ytterbium films in the far and the extreme ultraviolet

The optical properties of thin film of ytterbium in the 53.6-183.6-nm spectral range are described. Yb film were deposited in ultrahigh-vacuum conditians, and their transmittance and reflectance were measured in situ. Transmittance measurements showed that Yb has a certain window of lower absorption at approximately 54-100 nm, which makes Yb an interesting material for filters in this difficult spectral range. The optical constants were obtained from transmittance measurements and from multiangle reflectance measurements. These are what we believe are the first reported optical measurements of fresh Yb films at wavelengths shorter than 107.8 nm. Aging studies were performed both under vacuum and in a desiccator and showed that the optical properties of Yb are strongly modified on aging.     

Diffuse reflectance and transmittance spectra of an interference layer. 2. Evaluation of tin oxide-coated glass

A model for the calculation of diffuse reflectance and transmittance of a single interference layer on a transparent substrate is applied to pyrolytically deposited tin oxide films on glass. Total as well as diffuse reflectance and transmittance spectra were measured in an integrating sphere, and scattering levels between 0.002 and 0.1 were recorded. The optical constants and the thickness of the films were determined from the total reflectance and transmittance spectra. The wavelength-dependent effective root-mean-square roughness of aluminum-coated tin oxide front surfaces was determined by the application of the scalar scattering theory. Surface roughness values between 5 and 25 nm were obtained. The obtained effective rms roughness values of the air-film interface were used together with the other film parameters to calculate the diffuse reflectance and transmittance spectra of the tin oxide-coated glass substrates. A comparison between calculated and experimental spectra showed good agreement for diffuse reflectance, diffuse transmittance, and total integrated scattering spectra.     

Calculation of electric field and absorption distributions in thin film structures

It will be shown how, by s straightforward extension of the usual matrix formalism for the calculation of transmittance and reflectance of thin film optical structures, the internal electric field distribution can be calculated. Consideration of the energy flux then allows one to calculate the distribution of absorption in the structure. The effects of absorption are included without approximation so that there is no restriction on the nature of the substrate or of any of the thin film media. Absorbing dielectrics, semiconductors or metal layers are allowed. Examples will be given of the application of the theory to antireflection coatings, high reflectance mirrors and interference filters.     

Bistability of a self-standing film caused by photothermal displacement

We report on the bistability of a self-standing thin film caused by photothermal displacement. The sample consisted of a self-standing thin film placed in front of a mirror. By irradiating the self-standing thin film with continuous wave laser light, the self-standing thin film deflected with thermoelastic bending moment. Since a standing wave of the laser light was generated by the reflection of the mirror, the bending moment generated on the film was periodic along the optical axis. The displacement of the film was found to be bistable with the laser light intensity. Simultaneously, the light intensity reflected from the sample was also bistable. These phenomena are explained by the photothermal displacement of thin film in the standing wave of laser light.     

Polarization and incidence angle-dependent transmittance of transparent nickel electrodes with various thicknesses

The polarization and incidence angle-dependent transmittance of thin nickel film with various thicknesses deposited on glass substrates was first investigated by using a modified UV-Vis spectrometer. The thin nickel films showed relatively high uniform transmittance over a wide range of wavelengths, 300-1100 nm. The thickness-dependent dielectric and optical constants extracted from the experimental transmittance are significantly distinct from those of the thick nickel film. In particular, the p-polarized light transmittance largely increases with larger incidence angle, but the s-polarized light transmittance behavior is opposite from that of p-polarized light. The difference of the polarization-dependent transmittance increases parabolically with the incidence angle.     

Optical constants and band edge of amorphous zinc oxide thin films

The optical characteristics of amorphous zinc oxide (a-ZnO) thin films grown by radio frequency reactive magnetron sputtering on various substrates at temperature < 325 K have been investigated in the spectral range 340-1600 nm. The amorphous nature of the a-ZnO films was verified by X-ray diffraction and the optical constants were obtained by analysis of the measured ellipsometric spectra using the Cauchy-Urbach model. Refractive indices and extinction coefficients of the films were determined to be in the range 1.67-1.93 and 3.9 × 10^− 8-0.32, respectively. The band edge of the films on Si (100) and quartz has been determined by spectroscopic ellipsometry (3.39 ± 0.05 eV) and spectrophotometric (3.35 ± 0.05 eV) methods, respectively. From the angle dependence of the p-polarized reflectivity we deduce a Brewster angle of 60.5°. Measurement of the polarized optical properties shows a high transmissivity (81%-99%) and low absorptivity (< 5%) in the visible and near infrared regions at different angles of incidence. Also, we found that there was a higher absorptivity for wavelength < 370 nm. This wavelength, ∼ 370 nm, therefore indicated that the band edge for a-ZnO thin films is about 3.35 eV.     

Nonlinear optical properties of laser deposited CuO thin films

In this work we investigate the third-order optical nonlinearities in CuO films by Z-scan method using a femtosecond laser (800 nm, 50 fs, 200 Hz). Single-phase CuO thin films have been obtained using pulsed laser deposition technique. The structure properties, surface image, optical transmittance and reflectance of the films were characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy and UV-vis spectroscopy. The Z-scan results show that laser-deposited CuO films exhibit large nonlinear refractive coefficient, n₂ = − 3.96 × 10^− 17 m²/W, and nonlinear absorption coefficient, β = − 1.69 × 10^− 10 m/W, respectively.     

On the determination of the optical constants n(λ) and α(λ) of thin supported films

A general method was developed to determine the optical constants n(λ) and α(λ) for a thin semiconducting or metallic supported film from five or three measurements of the transmittance and the reflectance.Exact formulae were deduced for oblique incidence transmittance and reflectance considering multiple coherent reflections in the films and incoherent reflections in the non-absorbing substrate. A computer program was developed that, when used as a subroutine of a European Organization for Nuclear Research program called MINUIT, allowed the method to be tested for gold, silicon, CdS, Cu₂S (chalcocite) and Cu_1.96S (djurleite) polycrystalline films.A residual function shows good agreement between the calculated and measured values of the transmittance and the reflectance when a careful choice of the value of the thickness is made.     

Refractive index, optical bandgap and oscillator parameters of organic films deposited by vacuum evaporation technique

In this work, the organic thin films of 8-hydroxyquinoline aluminum (Alq₃), 9,10-bis-(β-naphthyl)-anthrene (ADN), and aluminum (III) bis-(2-methyl-8-quninolinato)-4-phenylphenolate (BAlq) were deposited by vacuum evaporation technique, and the optical and dielectric properties of the films were investigated. The optical constants such as refractive index, extinction coefficient, dielectric constant and dissipation factor were determined from the measured transmittance spectra using the envelope method. Meanwhile, the dispersion behavior of the refractive index was studied in terms of the single-oscillator Wemple-DiDomenico (W-D) model, and the physical parameters of the average oscillator strength, average oscillator wavelength, average oscillator energy, the refractive index dispersion parameter and the dispersion energy were achieved. Furthermore, the optical bandgap values were calculated by W-D model and Tauc model, respectively, and the values obtained from W-D model are in agreement with those determined from the Tauc model. These results provide some useful references for the potential application of the thin films in optoelectronic devices.     

Effect of sample thickness on the extracted near-infrared bulk optical properties of Bacillus subtilis in liquid culture

In order to determine the bulk optical properties of a Bacillus subtilis culture during growth phase we investigated the effect of sample thickness on measurements taken with different measurement configurations, namely total diffuse reflectance and total diffuse transmittance. The bulk optical properties were extracted by inverting the measurements using the radiative transfer theory. While the relationship between reflectance and biomass changes with sample thickness and the intensity (absorbance) levels vary significantly for both reflectance and transmittance measurements, the extracted optical properties show consistent behavior in terms of both the relationship with biomass and magnitude. This observation indicates the potential of bulk optical properties for building models that could be more easily transferable compared to those built using raw measurements.