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It is shown that an aberrated wavefront incident upon a Fabry-Perot optical cavity excites higher order spatial modes in the cavity, and that the spectral width and distribution of these modes is indicative of the type and magnitude of the aberration. The cavities are purely passive and therefore frequency content is limited to that provided by the original light source, unless time-varying content is introduced. To illustrate this concept, spatial mode decomposition and transmission spectrum calculation are simulated on an example cavity; the effects of various phase delays, in the form of two basic Seidel aberrations and a composite of Zernike polynomial terms, are shown using both Laguerre-Gaussian and plane wave incident beams. The aggregate spectral width of the excited cavity modes is seen to widen as the magnitude of the phase delay increases.

While there are innumerable devices that measure temperature, the nonvolatile measurement of thermal history is far more difficult, particularly for sensors embedded in extreme environments such as fires and explosions. In this review, an extensive analysis is given of one such technology: thermoluminescent microparticles. These are transparent dielectrics with a large distribution of trap states that can store charge carriers over very long periods of time. In their simplest form, the population of these traps is dictated by an Arrhenius expression, which is highly dependent on temperature. A particle with filled traps that is exposed to high temperatures over a short period of time will preferentially lose carriers in shallow traps. This depopulation leaves a signature on the particle luminescence, which can be used to determine the temperature and time of the thermal event. Particles are prepared-many months in advance of a test, if desired-by exposure to deep ultraviolet, X-ray, beta, or gamma radiation, which fills the traps with charge carriers. Luminescence can be extracted from one or more particles regardless of whether or not they are embedded in debris or other inert materials. Testing and analysis of the method is demonstrated using laboratory experiments with microheaters and high energy explosives in the field. It is shown that the thermoluminescent materials LiF:Mg,Ti, MgB 4 O 7 :Dy,Li, and CaSO 4 :Ce,Tb, among others, provide accurate measurements of temperature in the 200 to 500°C range in a variety of high-explosive environments.

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Thermoluminescent LiF:Mg,Ti (TLD-100) microparticle sensors are demonstrated to record the thermal history of the region near a detonated high explosive. Microparticles were gamma-irradiated to fill their charge-carrier traps and then exposed to the detonation of 20 g of a plastic bonded explosive formulation containing HMX and Al particles at a test distance of approximately 22 cm from the center of the detonation. The thermal history was reconstructed by measuring the thermoluminescent signature of the traps and matching it to appropriate models. The trap populations derived from luminescence measurements and modeling indicate that the particles experienced a maximum temperature of 240 • C, then cooled to 1 • C above ambient temperature within 0.4 seconds. The resulting glow curve intensity is calculated to match the observed postdetonation signal to 3% averaged over the comparison values used for reconstruction.

It is well known that thermal gradients penetrating deep into a material can preserve a memory of the temperature history of the surface. To date, this concept has been largely applied in the earth sciences, but there are many applications where a memory of rapid thermal events would be useful. For example, multiple layers of thermoluminescent films could serve as temperature sensors that indicate temperature versus depth in a microfabricated structure. As an advance toward this goal, this paper examines the effect of nonuniform temperature profiles on the thermoluminescence of heterogeneous multilayers. A Nd:YAG laser is used to create a known thermal event and apply pulses of heat energy of varying duration to a metalized thermoluminescent multilayer composed of LiF:Mg,Ti and CaF2:Dy. The thermoluminescence of the system is measured before and after the applied laser pulse. To model the process, a finite-difference time-domain method is used to calculate the dynamic heat transfer, and the temperature distribution is plugged into a first order kinetics model of the thermoluminescence of each film to get a final luminescent intensity. A thermal contact conductance between the critical layers is also introduced. Dynamic temperatures in durations of hundreds of milliseconds are resolved with the technique, and simulation curves match experimental measurements to within 6% at 250 ms.

The thermal history of a material with initially filled trap states has been probed using the thermoluminescence of microparticle sensors. Mg2SiO4:Tb,Co particles with two thermoluminescence peaks have been heated using microheaters over a 230 • C to 310 • C range for durations of less than 200ms. The effect of maximum temperature during excitation on the intensity ratio of the peaks is compared with first-order kinetics theory and shown to match within an average error of 4.4%.

Germanium is one of the most commonly used materials in the longwave infrared ( λ ∼ 8 − 12 µ m ), but ironically, its absorption coefficient is poorly known in this range. An infrared photothermal common-path interferometry system with a tunable quantum cascade pump laser is used to measure the absorption coefficient of > 99.999 % pure undoped germanium as a function of wavelengths between 9 and 11 µm, varying between about 0.15 and 0.45 c m − 1 over this range.