Low coherence interferometry (LCI) methods have been investigated for the detection of damage on coated and
uncoated airfoils in advanced gas turbines, and in particular methods for implementing LCI for in situ inspection using
borescope-type instrumentation. The work reported in this paper includes design of prototype instrumentation and some
test results, as well as results using commercial instruments obtained on TBCs. LCI techniques can provide significant
advance over currently employed visual inspection of gas turbine airfoils. The instrumentation provides a significant
advance over currently employed visual inspection of gas turbine airfoils. For instance, with thermal barrier coatings
(TBCs), these techniques allow the detection and quantification of incipient spalls, delamination, and changes in TBC
porosity which typically go unnoticed with visual inspection methods. The methods are well suited for use with
borescopes and thus provide a large potential to be developed into commercial optical diagnostics instruments for use
during maintenance and inspection of on-wing airfoils in advanced gas turbines.
There exists a vast range of optical techniques that have been under development for solving complex measurement
problems related to gas-turbine machinery and phenomena. For instance, several optical techniques are ideally suited for
studying fundamental combustion phenomena in laboratory environments. Yet other techniques hold significant promise
for use as either on-line gas turbine control sensors, or as health monitoring diagnostics sensors. In this paper, we briefly
summarize these and discuss, in more detail, some of the latter class of techniques, including phosphor thermometry,
hyperspectral imaging and low coherence interferometry, which are particularly suited for control and diagnostics
sensing on hot section components with ceramic thermal barrier coatings (TBCs).
Thermally assisted electro-luminescence may provide a means to convert heat into electricity. In this process, radiation
from a hot light-emitting diode (LED) is converted to electricity by a photovoltaic (PV) cell, which is termed
thermophotonics. Novel analytical solutions to the equations governing such a system show that this system combines
physical characteristics of thermophotovoltaics (TPV) and the inverse process of laser cooling. The flexibility of having
both adjustable bias and load parameters may allow an optimized power generation system based on this concept to
exceed the power throughput and efficiency of TPV systems. Such devices could function as efficient solar thermal,
waste heat, and fuel-based generators.
It has been proposed recently that thermally assisted electroluminescence may in principle provide a means to convert solar or waste heat into electricity. The basic concept is to use an intermediate active emitter between a heat source and a photovoltaic (PV) cell. The active emitter would be a forward biased light emitting diode (LED) with a bias voltage, Vb, below bandgap, Eg (i.e., qVb < Eg), such that the average emitted photon energy is larger than the average energy that is required to create charge carriers. The basic requirement for this conversion mechanism is that the emitter can act as an optical refrigerator. For this process to work and be efficient, however, several materials challenges will need to be addressed and overcome. Here, we outline a preliminary analysis of the efficiency and conversion power density as a function of temperature, bandgap energy and bias voltage, by considering realistic high temperature radiative and non-radiative rates as well as radiative heat loss in the absorber/emitter. From this analysis, it appears that both the overall efficiency and net generated power increase with increasing bandgap energy and increasing temperature, at least for temperatures up to 1000 K, despite the fact that the internal quantum yield for radiative recombination decreases with increasing temperature. On the other hand, the escape efficiency is a crucial design parameter which needs to be optimized.
Bacteriorhodopsin (bR) is a small protein containing the chromophore retinal, and resides in the membrane of the Halobacterium salinarium. When the retinal absorbs a photon, a cycle of structural changes is triggered resulting in a cross-membrane proton transfer, which is used to generate energy for the organism. Many studies have been conducted to elucidate the dynamical structure - optical property relations, and the overall mechanism of photo-induced proton transport in bR is now well understood. On the other hand, site selective mutagenesis allows engineering of the original ("wild-type") bR, such that the protein can be made sensitive to specific chemicals or biological structures that consequently induce changes in the proton-transport. As such, bR provides a unique molecular platform onto which various functional elements can be built: peptide receptors for molecular recognition of pathogens (e.g. viruses, cancer cells, spores, bacteria, bio-toxins), fluorescent tags (using the inherent optical transduction mechanism of bR), and chemical anchors for capturing target cells. In particular, the stability of bR in extreme environments (pH range of 1 - 11, temperatures up to 110 °C) allows for optical detection under a large range of environmental conditions. In this paper we present and discuss experimental data of several bR mutants and their potential as chemical and biological sensors. In particular, the optical changes associated with metal ligand binding are discussed for two mutants, 170C and 169C/96N, as well as the optical changes associated with streptavidin-coated beads bound to bR with strep II tags inserted in the E/F loop.