Use Of Total Internal Reflection Research Articles

Attenuated Total Reflection at THz Wavelengths: Prospective Use of Total Internal Reflection and Polariscopy

Capabilities of the attenuated total reflection (ATR) at THz wavelengths for increased sub-surface depth characterisation of (bio-)materials are presented. The penetration depth of a THz evanescent wave in biological samples is dependent on the wavelength and temperature and can reach 0.1–0.5 mm depth, due to the strong refractive index change ∼0.4 of the ice-water transition; this is quite significant and important when studying biological samples. Technical challenges are discussed when using ATR for uneven, heterogeneous, high refractive index samples with the possibility of frustrated total internal reflection (a breakdown of the ATR reflection mode into transmission mode). Local field enhancements at the interface are discussed with numerical/analytical examples. Maxwell’s scaling is used to model the behaviour of absorber–scatterer inside the materials at the interface with the ATR prism for realistic complex refractive indices of bio-materials. The modality of ATR with a polarisation analysis is proposed, and its principle is illustrated, opening an invitation for its experimental validation. The sensitivity of the polarised ATR mode to the refractive index between the sample and ATR prism is numerically modelled and experimentally verified for background (air) spectra. The design principles of polarisation active optical elements and spectral filters are outlined. The results and proposed concepts are based on experimental conditions at the THz beamline of the Australian Synchrotron.

Solar Pumping of Fiber Lasers with Solid‐State Luminescent Concentrators: Design Optimization by Ray Tracing

AbstractSolar‐pumped lasers (SPLs) typically couple sunlight into the laser cavity using focusing optics and solar tracking. Luminescent solar concentrators (LSC) are an alternative, fully planar, scalable pump source that can concentrate diffuse light. For liquid LSC‐based SPLs, reflective cavities have been used to trap light and pump a Nd3+‐doped silica fiber. Here, three solid‐state LSC‐based SPL designs, in addition to the reflective cavity making use of total internal reflection, are analyzed by ray‐tracing simulations. Results are compared to a liquid LSC reference, also used for validating simulations. Substituting the liquid‐state LSC for a solid‐state LSC (with the fiber placed inside) allows a 7‐fold enhancement of the gain coefficient, corresponding to a 30‐fold enhancement of the laser output power. An additional 4‐fold increase of the output power is possible with a fiber of kilometers length. These results show a roadmap for realizing SPLs with output powers on the order of 2.8 W m−2 under terrestrial sunlight, while keeping an identical reflective cavity used for the liquid LSC design. In addition, room‐temperature operation should be possible with certain solid LSC designs, and the necessity for a reflective cavity comprised of costly dielectric mirrors may be relieved.

Conical sum-frequency generation in a bulk anomalous-like dispersion medium

We observe conical sum-frequency generation in a bulk anomalous-like dispersion medium, which is attributed to complete phase-matching of one fundamental wave and the scattering wave of the other fundamental wave. In addition, efficient sum-frequency output is achieved making use of total internal reflection with conversion efficiency of 7.9% by only one reflection. The experiment proposes a new phase-matching mode under an anomalous-like dispersion condition, which suggests potential applications in efficient frequency conversion.

Diffractive flat panel solar concentrators of a novel design.

A novel design for a flat panel solar concentrator is presented which is based on a light guide with a grating applied on top that diffracts light into total internal reflection. By combining geometrical and diffractive optics the geometrical concentration ratio is optimized according to the principles of nonimaging optics, while the thickness of the device is minimized due to the use of total internal reflection.

Fresnel analysis of Kretschmann geometry with a uniaxial crystal layer on a three-layered film

The use of total internal reflection within the prism coupling scheme is a simple approach to the generation of surface plasmon polariton waves on a metal/dielectric interface. Unfortunately, an anisotropic layer on a metallic film complicates the derivation of resonance angle. In this study, we present clear Fresnel analysis of a liquid crystal film on a metal surface. Few current simulation packages enable the analysis of multiple layers with a single anisotropic layer. The proposed formulation process is applicable to multi-layered structures.

Use of Total Internal Reflection Raman (TIR) and Attenuated Total Reflection Infrared (ATR-IR) Spectroscopy to Analyze Component Separation in Thin Offset Ink Films after Setting on Coated Paper Surfaces

The interactive behavior of ink constituents with porous substrates during and after the offset print process has an important effect on the quality of printed products. To help elucidate the distribution of ink components between the retained ink layer and the substrate, a variety of spectroscopic and microscopic analysis techniques have been developed. This paper describes for the first time the use of total internal reflection (TIR) Raman spectroscopy to analyze the penetration behavior of separated offset ink components (linseed oil, solid color pigment) in coated papers providing chemically intrinsic information rapidly, nondestructively, and with minimal sample preparation. In addition, the already widely applied technique of attenuated total reflection infrared spectroscopy (ATR-IR) was evaluated in parallel and compared. The results of the ATR-IR Raman clearly revealed an improvement in uppermost depth resolution compared with values previously published from other nondestructive techniques, and the method is shown to be capable of providing new knowledge of the setting of thin (0.25-2 μm) offset ink films, allowing the spreading and the penetration behavior on physically different paper coating surfaces to be studied.

Packaging Process for Grating-Coupled Silicon Photonic Waveguides Using Angle-Polished Fibers

A novel process for fiber-packaging submicrometer silicon waveguides is presented. The process uses fibers polished at an angle to reflect light between a horizontal core and the slightly off-vertical input and output path of a grating coupler. The necessity for a reflective coating on the fiber facet is overcome through the use of total internal reflection and a novel technique of epoxy distribution based on capillary action. Simulations of alignment tolerance are presented, along with measurements confirming the applicability of passive alignment. A peak coupling efficiency within 0.2 dB of the theoretical maximum for the grating coupler is achieved.

Composite Yb:YAG/SiC-prism thin disk laser

We report the first demonstration of a Yb:YAG thin disk laser wherein the gain medium is intracavity face-cooled through bonding to an optical quality SiC prism. Due to the particular design of the composite bonded Yb:YAG/SiC-prism gain element, the laser beam impinges on all refractive index interfaces inside the laser cavity at Brewster's angles. The laser beam undergoes total internal reflection (TIR) at the bottom of the Yb(10%):YAG thin disk layer in a V-bounce cavity configuration. Through the use of TIR and Brewster's angles, no optical coatings, either anti-reflective (AR) or highly reflective (HR), are required inside the laser cavity. In this first demonstration, the 936.5-nm diode pumped laser performed with approximately 38% slope efficiency at 12 W of quasi-CW (Q-CW) output power at 1030 nm with a beam quality measured at M(2) = 1.5. This demonstration opens up a viable path toward novel thin disk laser designs with efficient double-sided room-temperature heatsinking via materials with the thermal conductivity of copper on both sides of the disk.

Surface relief subwavelength gratings by means of total internal reflection evanescent wave interference lithography

We present the use of total internal reflection (TIR) evanescent waves for lithography purposes. In particular, we focus our attention on their singular capabilities to nano-structure surface relief gratings and the potentialities for nano-photonic device fabrication. Interference of two (or more) evanescent waves achieves periodic linear (or 2D) surface relief gratings of around 100 nm period depending on the wavelength and materials used. In contrast to common and some newer lithographic techniques, the evanescent wave does not propagate all through the film, allowing fabrication of surface profiles with maximum height features limited to around the wavelength of the exposure. Here, we present an analysis of several structures and profiles for linear gratings—many of which are not achievable with known interference photolithographic techniques—and some experimental results validating the model of evanescent wave lithography proposed. Possible applications in the field of nano-photonic devices are antireflection treatments, polarizers, diffraction gratings, micro- and nano-lens arrays, etc. We also find in the technique a great potential for other nano-technologies, as in the fabrication of field emitter arrays for displays, as templates for self-assembling structures, etc.

Total internal reflection Raman spectroscopy of barley leaf epicuticular waxes in vivo

The use of total internal reflection (TIR)-Raman spectroscopy to examine cuticular wax layers in vivo at the surface of barley leaves ( Hordeum vulgare L. cultivar Pastoral) is demonstrated. The limited penetration depth (40 nm) of the evanescent wave compared to the thickness of the wax layer eliminates problems arising from fluorescence from underlying pigments. Epicuticular wax crystals are observed to be more crystalline than the amorphous wax layer, which is analysed after removal of the wax crystals by cellulose acetate stripping. Carotenoids are detected as trace species in the cuticular waxes.

Sum-Frequency Spectroscopy of Surfactant Monolayers at the Oil−Water Interface

A new experimental arrangement is described for acquiring sum-frequency (SF) spectra from surfactants at the oil−water interface. The key features of this approach are the stabilization of a thin oil film between a sapphire prism and an aqueous phase and the use of total internal reflection to enhance the total signal and discriminate against signals from other interfaces in the system. With this new methodology, the first SF vibrational spectra of surfactant monolayers at an alkane−water interface were obtained. Surface tensiometry was used to characterize the monolayers further. The structure of monolayers of the cationic surfactant hexadecyltrimethylammonium bromide (CTAB) at the hexadecane−water interface was determined by sum-frequency spectroscopy (SFS) and compared with monolayers of CTAB at the air−water interface. At low concentrations, CTAB/hexadecane showed the expected features in the C−H stretching region, characteristic of a conformationally disordered monolayer. As the bulk concentration approached the critical micelle concentration, the spectra changed to one characteristic of a more ordered, upright conformation. Ellipsometric measurements supported this conclusion. This qualitative structural change is not observed in analogous monolayers at the air−water interface or CCl4−water interface or in surfactant solutions in contact with a hydrophobic solid surface.

Low-loss ultrabroadband 90 degree optical rotator with collinear input and output beams.

An achromatic device to rotate optical polarization by 90 degrees is described. This is based on a series of reflecting surfaces that rotates incoming light about the optical axis and translates it such that the exiting light is collinear. Polarization rotation is achieved by rotation of the optical beam, as opposed to the more common approach of phase retardation by use of birefringent elements. For broadband operation from the UV to the near infrared, the device was constructed by use of total internal reflection in three fused-silica glass components. Losses are minimized with interstitial surfaces designed to be angled close to Brewster's angle.

Polarization dependence of diffraction gratings that have total internal reflection facets

The total internal reflection (TIR) grating is an integrated optical diffraction grating designed to achieve high efficiency for the retrodiffracted order by use of total internal reflection twice within a groove of the grating rather than by use of metalized grooves. Numerical calculations are presented for both TE and TM polarizations of incident light. When the TIR grating was used in the -mth-order Littrow mount with m > 13, the diffraction efficiency was found to decrease linearly with 1/m. The polarization dependence of the retrodiffraction efficiency exceeds 3 dB for TIR gratings formed in silica glass (n = 1.5) but is very small for gratings with InP-based technology (n = 3.2).

Internal reflection sensors with high angular resolution

We discuss the use of total internal reflection for the production of sensors with high angular resolution. These sensors are intended for measurement of the angle between a sensor's axis and the direction to a source of radiation or reflecting object. Sensors of this type are used in controlling the position of machine parts in robotics and industry, orienting space vehicles and astronomic devices in relation to the Sun, and as autocollimators for checking angles of deviation. This kind of sensor was used in the Apollo space vehicle some 20 years ago. Using photodetectors with linear and area CCD arrays has opened up new application possibilities for appropriately designed sensors. A generalized methodology is presented applicable to a wide range of tasks. Some modifications that can improve the performance of the basic design are described.

Rectangular and L-shaped GaAs/AlGaAs lasers with very high quality etched facets

GaAs/AlGaAs semiconductor lasers with very high quality etched facets have been fabricated. Laser facets are formed by the chemically assisted ion beam etching technique with SiO2 as the etch mask. The threshold current densities of lasers produced with this technique are almost identical to comparable lasers with one etched and one cleaved facet. L-shaped lasers, which make use of total internal reflection, have also been fabricated. The threshold current density of L-shaped lasers is similar to that of rectangular lasers with comparable cavity length.

Fabrication of diffractive–reflective optical interconnects for infrared operation based on total internal reflection

Diffractive-reflective optical interconnects (DROIs) for optical chip-to-chip interconnection were introduced in a 1988 paper. In this paper we demonstrate the use of total internal reflection for guiding the light. inside the glass plate. The required holographic grating couplers were produced by expoiting the wavelength change from blue light recording to red light reconstruction. Several types of fan-out DROI have been made in dichromated gelatin.