Fiber-coupled high-power external-cavity semiconductor lasers for real-time Raman sensing.

High-power, external-cavity semiconductor lasers with narrow bandwidth and fiber-coupled output are designed and constructed. An output power of 540 mW is coupled out of a 100-mum multimode fiber with coupling efficiency of 72% when the laser is operated at 1.1 A. The emission linewidth is as narrow as 22 GHz, and the wavelength is tunable from 779.7 to 793.0 nm. Application of such lasers to remote real-time Raman sensing of materials is also demonstrated.

Application of Raman spectroscopy to metal-sulfide surface analysis.

The surface products of electrochemically oxidized pyrite (FeS(2)) are investigated as a function of applied potential by using Raman spectroscopy. The parameters necessary for sulfur formation on the pyrite surface were determined. An optical multichannel apparatus, consisting of an argon laser, a triple spectrograph, and a charge-coupled-device detector, was utilized for the Raman measurements. The advantages of this system for surface characterization include high resolution and high sensitivity as well as the capability of identifying compounds and making in-situ measurements.

Spherical particle sizing by optical correlation using ternary phase-amplitude filters.

Computer simulations and experimental data are presented for various ternary phase-amplitude filters used to size opaque spherical particles. We first report on nearly unlimited spatial frequency ternary phase-amplitude filters derived directly from the classical matched filter for opaque spherical particles in the size range of 100 to 400 microm. Next we investigate the increasing influence of the cutoff frequency on the optical correlator as the particles become smaller. Using limited-order ternary phase-amplitude filters, we report on sizing opaque spherical particles in the size ranges of 100 to 400, 15 to 100, and 5 to 25 microm.

Application of charge-coupled device technology for measurement of laser light and fluorescence distribution in tumors for photodynamic therapy.

Laser and fluorescence light distributions with applications for photodynamic therapy were measured in mouse tumors using a non-invasive electronic optical imaging system. The system consists of a liquid-nitrogen-cooled, charge-coupled-device (CCD) array camera under computer control with 576 x 384 detection elements having dimensions of 23 microns x 23 microns. The available dynamic range of the array is approx. 10(3), and the effective wavelength range is 400-1000 nm. An interstitially placed cylindrical diffusing optical fiber was used to provide tumor illumination. The light distribution pattern from the fiber was determined by immersing the cylindrical diffusing tip in a fluorescing solution and recording the emission image. Fluorescence imaging facilitates an accurate measurement of light intensity distribution while avoiding problems associated with the directional nature of other detection methods used with diffusing fibers. Radiation-induced fibrosarcoma tumors on C3H mice were grown to about 1 cm diameter for in vivo recording of light distribution from the tumor volume and for determination of effective light penetration distance at 18 wavelengths in the range 458-995 nm. Endogenous tumor fluorescence and Photofrin II fluorescence intensity were measured over the wavelength range 585-725 nm to investigate the possible application of CCD imaging technology for drug distribution measurements. Model experiments were begun to evaluate the relative importance of potential distortions of light distribution measurements using this approach.

Spherical particle sizing based on the VanderLugt correlator.

We present a flexible architecture for particle sizing based on the VanderLugt correlator with a multiplexed matched spatial filter. Theoretical and experimenal data obtained using opaque spherical particle projections demonstrate the potential uses and simplicity of the architecture. The system is capable of handling spherical and nonspherical particles and shows potential for handling high particle concentrations.

Reflection display of rainbow holograms.

In this paper experimental results and a detailed analysis of a method for reflection display of rainbow holograms are presented. A method for noncontact reflection display is put forward. High quality reconstructed images can be obtained by simply placing a mirror at a proper distance behind the holograms. Essential requirements are derived to avoid interference fringes and unacceptable image blur. The diffraction efficiency which may be close to or even higher than that of transmission display in some conditions is also discussed. Experimental results are presented which fully coincide with the analysis.

Dedicated monitoring of anesthetic and respiratory gases by Raman scattering.

The monitoring of respiratory and anesthetic gases in the operating room is important for patient safety. This study measured the accuracy and response time of a multiple-gas monitoring instrument that uses Raman light scattering. Measurements of oxygen, carbon dioxide, nitrogen, nitrous oxide, halothane, enflurane, and isoflurane concentrations were compared with a gas mixer standard and with measurements made with an infrared anesthetic agent analyzer. Correlation coefficients were all greater than 0.999, and probable errors were less than 0.43 vol% for the gases and less than 0.03 vol% for the volatile anesthetics. Response time was 67 ms with a sample flow rate of 150 ml/min. There was some signal overlap between nitrogen and nitrous oxide and between the volatile anesthetic agents. Such overlap can be compensated for by linear matrix analysis. The Raman instrument promises a monitoring capability equivalent to the mass spectrometer and should prove attractive for the monitoring of respiratory and anesthetic gases in the operating room.

Sizing dielectric spheres and cylinders by aligning measured and computed resonance locations: algorithm for multiple orders.

An algorithm for determining the size of dielectric spheres and cylinders by aligning measured and computed resonance locations is presented. The orders of the resonance locations need not be known a priori. The algorithm is applicable to several types of scattering and emission spectra of spheres and cylinders if the index of refraction including dispersion is known and uniform, or nearly uniform, throughout the sphere or cylinder. The algorithm performs well when tested with groups of computed resonance locations of spheres (synthetic data) and with measured fluorescence emission spectra of spheres exhibiting as many as 5 orders of resonance.

Proposed method of intracordal injection and gelation of poly (vinyl alcohol) solution in vocal cords: polymer considerations.

Intracordal polymer solution and/or suspension injection has potential in the swelling of paralysed or partially removed vocal cords to the midline laryngeal position. This technique allows the normally functioning cord to vibrate against the swollen one in order to produce sound. Polymeric systems which may possibly be used for the treatment of vocal cords are presented and analysed with special reference to poly(vinyl alcohol). Aqueous poly(vinyl alcohol) solution in concentrations of 3% to 10% (wt/wt) are gelled by glutaraldehyde. The gelation kinetics are followed and the gelation point, final crosslinking density and structure are determined in terms of the initial molar ratio of crosslinking agent to polymer. The mechanical properties of poly(vinyl alcohol) gels are discussed. Finally a proposed technique for the application of these systems for the treatment of certain vocal cord impairments is presented.

Angular distribution of fluorescence from liquids and monodispersed spheres by evanescent wave excitation.

Experimental data on the angular distribution of fluorescence from thick liquid dye layers excited by evanescent waves are found to agree well with Fresnel theory and with an effective thickness formulation. Qualitative agreement of theory with fluorescence data obtained from monodispersed spherical particles having diameters comparable to the wavelength of the incident evanescent radiation and impregnated with dye molecules is also attained. From our results, the optimum incident and observation angles and polarizations to enhance the contrast and SNR for inelastic ATR reemission spectroscopy applied to studying micron or submicron layers of particulates can be predicted.