Reflectance spectrometry for real-time hemoglobin determination of placental vessels during endoscopic laser surgery for twin-to-twin transfusion syndrome.

Objective: The objective of the study was to develop a noninvasive technique to determine hemoglobin (Hb) content through spectral analysis of diffusely reflected broadband visible illumination from individual blood vessels during endoscopic fetal surgery for twin-to-twin transfusion syndrome (TTTS).

Methods: The reflection of an incoming xenon endoscopic light source was captured through a 630-mum-diameter optic fiber coupled to a fixed grating spectrometer (2-nm resolution). A 450- to 700-nm wavelength range was used for analysis.

Fourier transform spectroscopy using stressed liquid crystal.

A Stressed Liquid Crystal (SLC) is proposed for application as a single panel retardance element in a Fourier transform (FT) spectrometer. Volume alignment in SLCs increase the maximum retardance and subsequent FT resolution by creating greater path lengths. Here, the relationship between transmission and shear for thick SLC cells is characterized and the spectral resolution using the SLC phase modulators in a single and double pass FT spectrometer system is quantified.

Surgical performance with head-mounted displays in laparoscopic surgery.

Introduction: The difficulties of laparoscopic surgery include two-dimensional image projection and loss of alignment between the surgeon's hands and visual field. Head-mounted displays (HMDs) allow freedom from gazing at a stationary overhead monitor, thus improving ergonomics. Modern HMDs offer greatly improved image quality and reduced bulk and weight.

Electro-optical investigations of holographic-polymer-dispersed ferroelectric liquid crystals.

Uniform alignment of ferroelectric liquid-crystal domains encapsulated by a polymer binder was established through a holographic exposure process. The refractive index modulation in these thin films is modeled as a phase grating that can be electrically addressed to erase the optical diffractive properties. A phenomenological model is developed to take into account a distribution of domain sizes and an effective field that stabilizes the ferroelectric liquid-crystal domains.

Liquid-crystal materials find a new order in biomedical applications.

With the maturation of the information display field, liquid-crystal materials research is undergoing a modern-day renaissance. Devices and configurations based on liquid-crystal materials are being developed for spectroscopy, imaging and microscopy, leading to new techniques for optically probing biological systems. Biosensors fabricated with liquid-crystal materials can allow label-free observations of biological phenomena.

Switchable circular-to-point converter based on holographic polymer-dispersed liquid-crystal technology.

We demonstrate the use of a switchable circular-to-point converter (SCPC) device based on holographic polymer-dispersed liquid-crystal technology for application in lidar detection and optical telecommunication. A SCPC device converts the Fabry-Perot ring pattern into a single point or an array of points, while an external electrical field on the SCPC deactivates the conversion. Stacking different SCPC elements gives a random optical switch for applications in lidar detection and optical telecommunication.

Two-dimensional vectorial photonic crystals formed in azo-dye-doped liquid crystals.

A 2D, square lattice, vectorial photonic crystal is formed by vectorial holography using an azo-dye-doped liquid-crystal material. Four coherent beams are interfered to generate a highly stable, switchable polarization holography structure. The formation of the vectorial lattice by the liquid-crystal molecular orientation is confirmed by diffraction pattern and polarization microscopy analysis.

Holographic diffraction gratings using polymer-dispersed ferroelectric liquid crystals.

By controlling the morphology of holographic polymer-dispersed ferroelectric liquid crystals (FLCs), highly aligned FLC domains are obtained for diffractive optical applications. Rapid, thresholdless switching is observed for various grating pitch sizes between approximately 3 and approximately 12 microm. A simple phenomenological model is presented encompassing a distribution of domain sizes and an effective field that stabilizes the FLC domains to reflect the observed thresholdless switching and optical behavior.

Diffuse reflectance spectra of the palpebral conjunctiva and its utility as a noninvasive indicator of total hemoglobin.

The palpebral conjunctiva is an attractive location to qualitatively examine for the presence of anemia; however, this method of diagnosis has not been shown to be accurate. A spectroscopic examination of the palpebral conjunctiva enables the use of a quantitative parameter as a basis for diagnoses. Visible range diffuse reflectance spectra from the palpebral conjunctiva are examined from 30 patients and hemoglobin levels are extracted from these signatures using both a partial least-squares (PLS) multivariate regression model and a discrete spectral region model.

Surface-induced orientational order in stretched nanoscale-sized polymer dispersed liquid-crystal droplets.

We investigate orientational ordering in stretched polymer-dispersed liquid-crystal (PDLC) droplets using deuterium nuclear magnetic resonance, in the nematic and isotropic phases. In the latter case, we estimate the surface order parameter S(0) and the thickness of the interfacial layer from the temperature-independent surface ordering model for an elliptical cavity with a varying aspect ratio. A simple phenomenological model well describes the quadrupole splitting frequency of NMR spectra in the isotropic phase.

Chirped switchable reflection grating in holographic polymer-dispersed liquid crystal for spectral flattening in free-space optical communication systems.

We report the design and fabrication of a chirped switchable reflective grating (CSRG) recorded in a holographic polymer-dispersed liquid-crystal material. This CSRG is a spatial wavelength-selective flattener in a free-space dynamic gain equalizer for use in wavelength-division multiplexing (WDM) networks. Prelimenary experimental results show that this device permits the management of the spectral power of a WDM stream with an attenuation range of 6 dB.

In-plane switching of cholesteric liquid crystals for visible and near-infrared applications.

We have investigated the in-plane switching of cholesteric liquid crystals for reflective wavelength shifters for visible and near-infrared applications. These devices are based on the elongation of the cholesteric pitch by an electric field perpendicular to the helical axis. The transmission notch-reflection peak position can be tuned continuously to a longer wavelength (redshift) by application of an in-plane electric field.

Template synthesis of nanophase mesocarbon.

Templating techniques are used increasingly to create carbon materials with precisely engineered pore systems. This article presents a new templating technique that achieves simultaneous control of pore structure and molecular (crystal) structure in a single synthesis step. With the use of discotic liquid crystalline precursors, unique carbon structures can be engineered by selecting the size and geometry of the confining spaces and selecting the template material to induce edge-on or face-on orientation of the discotic precursor.

Deuteron NMR study of molecular ordering in a holographic-polymer-dispersed liquid crystal.

Using deuteron nuclear magnetic resonance (NMR) and dynamic light scattering, we study the orientational order and dynamics of a BL038-5CB liquid-crystal mixture in a holographic polymer dispersed liquid-crystal material (HPDLC) as used for switchable diffractive optical elements. At high temperatures, where the liquid crystal is predominantly in the isotropic phase, the HPDLC deuteron NMR linewidth and transverse spin-relaxation rate T-12 are two orders of magnitude larger than in the bulk. The analysis shows that the surface-induced order parameter in HPDLC is significantly larger than in similar confining systems and that translational diffusion of molecules in the surface layer is at least two orders of magnitude slower than in the rest of the cavity.