Magnitude Of Refractive Index Change Research Articles

Theoretical study of polarization insensitivity of carrier-induced refractive index change of multiple quantum well.

Characteristics of polarization insensitivity of carrier-induced refractive index change of 1.55 μm tensile-strained multiple quantum well (MQW) are theoretically investigated. A comprehensive MQW model is proposed to effectively extend the application range of previous models. The model considers the temperature variation as well as the nonuniform distribution of injected carrier in MQW. Tensile-strained MQW is expected to achieve polarization insensitivity of carrier-induced refractive index change over a wide wavelength range as temperature varies from 0°C to 40°C, while the magnitude of refractive index change keeps a large value (more than 3 × 10-3). And that the polarization insensitivity of refractive index change can maintain for a wide range of carrier concentration. Multiple quantum well with different material and structure parameters is anticipated to have the similar polarization insensitivity of refractive index change, which shows the design flexibility.

Noninvasive Intratissue Refractive Index Shaping (IRIS) of the Cornea with Blue Femtosecond Laser Light

To test the feasibility of intratissue refractive index shaping (IRIS) in living corneas by using 400-nm femtosecond (fs) laser pulses (blue-IRIS). To test the hypothesis that the intrinsic two-photon absorption of the cornea allows blue-IRIS to be performed with greater efficacy than when using 800-nm femtosecond laser pulses. Fresh cat corneas were obtained postmortem and cut into six wedges. Blue laser pulses at 400 nm, with 100-fs pulse duration at 80 MHz were used to micromachine phase gratings into each corneal wedge at scanning speeds from 1 to 15 mm/s. Grating lines were 1 μm wide, 5 μm apart, and 150 μm below the anterior corneal surface. Refractive index (RI) changes in micromachined regions were measured immediately by recording the diffraction efficiency of inscribed gratings. Six hours later, the corneas were processed for histology, and TUNEL staining was performed to assess whether blue-IRIS causes cell death. Scanning at 1 and 2 mm/s caused overt corneal damage in the form of bubbles and burns. At faster scanning speeds (5, 10, and 15 mm/s), phase gratings were created in the corneal stroma, which were shown to be pure RI changes ranging from 0.037 to 0.021 in magnitude. The magnitude of RI change was inversely related to scanning speed. TUNEL staining showed cell death only around bubbles and burns. Blue-IRIS can be performed safely and effectively in living cornea. Compared with near-infrared laser pulses, blue-IRIS enhances both achievable RI change and scanning speed without the need to dope the tissue with two-photon sensitizers, increasing the clinical applicability of this technique.

Potentiation of Femtosecond Laser Intratissue Refractive Index Shaping (IRIS) in the Living Cornea with Sodium Fluorescein

To assess the effectiveness of intratissue refractive index shaping (IRIS) in living corneas and test the hypothesis that it can be enhanced by increasing the two-photon absorption (TPA) of the tissue. Three corneas were removed from adult cats and cut into six pieces, which were placed in preservative (Optisol-GS; Bausch & Lomb, Inc., Irvine, CA) containing 0%, 0.25%, 1%, 1.5%, or 2.5% sodium fluorescein (Na-Fl). An 800-nm Ti:Sapphire femtosecond laser with a 100-fs pulse duration and 80-MHz repetition rate was used to perform IRIS in each piece, creating several refractive index (RI) modification lines at different speeds (between 0.1 and 5 mm/s). The lines were 1 mum wide, 10 microm apart, and approximately 150 microm below the tissue surface. The RI change of each grating was measured using calibrated, differential interference contrast microscopy. TUNEL staining was performed to assess whether IRIS or Na-Fl doping causes cell death. Scanning at 0.1 mm/s changed the RI of undoped, living corneas by 0.005. In doped corneas, RI changes between 0.01 and 0.02 were reliably achieved with higher scanning speeds. The magnitude of RI changes attained was directly proportional to Na-Fl doping concentration and inversely proportional to the scanning speed used to create the gratings. IRIS can be efficiently performed in living corneal tissue. Increasing the TPA of the tissue with Na-Fl increased both the scanning speeds and the magnitude of RI changes in a dose-dependent manner. Ongoing studies are exploring the use of IRIS to alter the optical properties of corneal tissue in situ, over an extended period.

Structural Modification in Borosilicate Glass by Use of Femtosecond Fiber Laser at 1.56 µm

By focusing intense femtosecond laser pulses inside a transparent material, one can induce localized structural modifications including a refractive-index change. This technique can be applied to the fabrication of three-dimensional photonic devices. In this paper, we study on the structural modifications in borosilicate glass by using an amplified femtosecond Er-fiber laser system producing 947-fs optical pulses at a repetition rate of 155.1 kHz and a wavelength of 1.56 μm. In order to optimize the irradiation condition, we investigate the dependence of structural modification on the incident pulse energy, exposure time, and focusing condition. In a static exposure experiment, it is found that refractive-index change can be induced with a wider range of pulse energies compared to silica glass. The magnitude of refractive-index change is estimated to be 1.2 × 10 by measuring the diffraction efficiencies of a Raman-Nath grating fabricated in borosilicate glass.

Femtosecond laser direct writing of embedded optical waveguides in aluminosilicate glass

Using tightly focused femtosecond laser pulses to irradiate lines in aluminosilicate glass, embedded lines with increased refractive index, which function as optical waveguides were observed. The pulse energy (4.5–11.2 μJ) and writing speed (50–700 μm/s) were shown to affect the resultant optical properties of the waveguides such as the magnitude of refractive index change, core diameter and propagation mode. At pulse energies above 5 μJ, two types of structures were observed, namely an inhomogeneous void-like structure and a cross-sectional crack-like structure. These structures were found to affect significantly the resultant waveguiding properties of the irradiated lines. Using pulse energy of 5 μJ or below, single mode waveguides were fabricated. Raman spectroscopy showed that the fs laser pulses generated structural changes to the aluminosilicate glass. The fabrication of a 1×4 splitter was also demonstrated.

Photoinduced refractive index changes in organic polysilane-inorganic hybrid thin films

Ultra-violet (UV) light induced refractive index change has been observed in organic polysilane (PS)-silica and PS-titania hybrid thin films prepared by a sol-gel method. The magnitude of refractive index change is found to be extremely large; 0.16 for 50 wt% PS-silica and 0.18 for 50 wt% PS-titania hybrid thin films. It is demonstrated that the refractive index change of the hybrid thin films is due to photodecomposition of PS. These findings indicate potential usefulness of the hybrid thin films as optical devices with refractive index modulated structures.

Measurements of the Parameters Involved in the Theory of Radio Scattering in the Troposphere

Booker and Gordon have recently proposed a theory of radio scattering in the troposphere. Using atmospheric inhomogeneities in refractive index, the scattered power was shown to be a function of the intensity and scale of the existing turbulent variations. Lacking experimental data on the nature of the refractive index variations which may be present in the atmosphere, they predicted the magnitude of refractive index changes on the basis of limited temperature fluctuation measurements. Measurements have been made of refractive index and associated temperature fluctuations by the Electrical Engineering Research Laboratory of The University of Texas since 1948 with a somewhat detailed study being made from 10 inches to 50 feet above the ground since December, 1949. This paper includes a brief discussion of the recording refractometer and recording thermometer used for these studies, a meteorological analysis of the problem, and tracings of the refractive index and temperature fluctuations for several various conditions of the lower atmosphere.