I now declare that these annual reviews are a tradition! A quote seems in order here, so let us hear from Ezra Pound: But to have done instead of not doing this is not vanity To have, with decency, knocked That a Blunt should open To have gathered from the air a live tradition or from a fine old eye the unconquered flame This is not vanity. Here error it all in the not done, all in the diffidence that faltered.

The field of photothermal science and engineering has reached a level of maturity and diversity such that it is quite difficult for an individual researcher to be aware of all new and important developments, even in his or her particular domain of application. Fortunately, there exist specific publications, mostly journals, which carry the majority of research articles in a given subfield; this is true for the spectrum of activities ranging from basic physics and chemistry to novel instruments and measurement methodologies.

A model for photothermal lens signal generation in a cylindrical sample cell under constant irradiance excitation is described and tested. The model is developed with and without the assumption that the sample cell does not change temperature over the irradiation time. In both cases, the photothermal lens is predicted to be parabolic in form with a strength that is independent of sample cell radius. The predicted irradiance independence suggests that incoherent illumination can be used to perform photothermal lens spectroscopy in low-volume cells. Experimental evidence is obtained using a Xe arc lamp to perform photothermal lens spectroscopy in a 6 ?L cylindrical spectrophotometric cell. Optical filters are used to reduce the power at IR and UV wavelengths of the Xe lamp emission spectrum. This pseudo-white-light source enables indirect optical absorbance measurement independent of the absorption spectrum of the analyte. The preliminary data reported show that photothermal lens signals can be obtained using wide-spectral-bandwidth, incoherent excitation sources. Although the theoretical enhancement factor is found to be only ~0.01 for these experiments, limits of detection of the order of 30 to 300 pM pseudoisocyanine dye in ethanol solution are found. This corresponds to spectral integrated absorption detection limit from 10-4 to 10-6 au in the centimeter path length cell. These low detection limits are found even with low enhancement factors because the factors that affect the noise in the photothermal lens and conventional transmission spectroscopy signals are not the same in these experiments. The major sources of uncertainty in these detection limit estimates are knowledge of the excitation source spectrum and periodic chaotic behavior of the diode laser used as a probe of the photothermal lens. Examination of the response time of the signal reveals that thermal conductivity of the sample cell influences the characteristic signal rise and decay time constants. The radiative heat transfer model is applied to interpret measured time constants in terms of the cell thermal conductivity and thickness of the sample cell walls. The sample cell thermal conductivity determined by this method is consistent with ferrous materials.

The phase of the photoacoustic signal is of prime importance for obtaining accurate optical absorption coefficients using the photoacoustic technique. Variations in the spectrometer or the photoacoustic cell parameters between the measurement of the sample spectrum and the carbon black reference spectrum are the main source of phase shifts. We reconsider a simple model that provides an accurate description of the photoacoustic effect—including photoacoustic saturation—for thermally thick, homogeneous samples. The model includes absorption from a thin layer at the sample surface. We propose a method for optimizing the photoacoustic phase for this model. The method is based on the internal calibration at the onset of the photoacoustic saturation, and on a simple analysis of the shape of the calculated surface absorption spectrum. Optimization is illustrated with a simulated spectrum and an experimental spectrum of ethylene-propylene-rubber.

Piezoelectric photoacoustic IR spectra of mica are obtained using a Fourier transform IR spectrometer and lead zirconate titanate (PZT) as a detector. The spectra exhibit negative intensities and transmission like bands, instead of more conventional absorption bands generally observed with a gas-microphone cell. Correct spectra of mica/PZT are calculated only when the interferogram phase is constrained to the first and fourth quadrants, similar to the case in differential spectroscopy where negative intensities occur.

The application of UV photoacoustic spectroscopy to the evaluation of UV-absorbing paint additives in clear paint layers is described. This technique enables the quantitative analysis of additive concentration and aids in determining the effects due to paint processes and substrate composition changes on additive concentration. The inclusion of photoacoustic phase information is essential to offset the saturation effects that dominate these strongly absorbing samples. Two analysis techniques are evaluated, both of which partially or totally utilize the phase data. When comparisons between samples on substrates with different heat capacities are needed, the phase-only method is preferred. Otherwise, the two methods give comparable results. Using these methods, two different paint/substrate/additive systems are easily evaluated for changes in process or changes in substrate materials. The instrumentation and interpretation methods are discussed in detail.

Pulsed photoacoustic studies in solutions of C70 in toluene are made using the 532-nm radiation from a frequency-doubled Nd:YAG laser. It is found that contrary to expectation, there is no photoacoustic (PA) signal enhancement in the power-limiting range of laser fluences. Instead, the PA signal tends to saturate during optical power-limiting phenomenon. This could be due to the enhanced optical absorption from the photoexcited state and hence the depletion of the ground-state population. PA measurements also ruled out the possibility of multiphoton absorption in the C70 solution. We demonstrate that the nonlinear absorption leading to optical limiting is mainly due to reverse saturable absorption.

The application of photoacoustic spectroscopy to the study of photosynthesis in thylakoid membranes is well documented in the literature. We use various parameters to compare the quenching of variable fluorescence with the energy storage measured by photoacoustic spectroscopy to gain more information about their interrelationship. The use of thylakoid membranes and photosystem II (PSII) enriched submembrane fractions pretreated at various temperatures or exposed to photoinhibitory illumination indicates that there is a strong correlation between the photochemical quenching of variable fluorescence and that of variable thermal dissipation. However, some differences also exist that are likely due to the involvement of cyclic electron transport in both photosystem I and PSII during the formation of energy storage and to the fact that energy storage is more influenced by the reduction of the plastoquinone pool, whereas variable fluorescence depends solely on the redox state of the primary photosystem II acceptor QA .

The use of the photoacoustic technique to monitor the thermal properties of materials that can be obtained only as parts of multicomponent samples is illustrated by performing the thermal characterization of two porous materials: porous silicon obtained from n-type crystalline silicon through the spark process and that obtained through the electrochemical etching method. This nonseparative, and hence nondestructive, approach makes use of an effective thermal diffusivity treatment based on the analogy between thermal and electrical resistances, in combination with simplified compositional models for the corresponding multicomponent systems. The thermal parameters obtained are in agreement with existent studies concerning the composition of these materials. This approach offers the possibility of performing the thermal characterization of other porous semiconductors and analogous materials.

Basic data on thermal, dielectric, and IR spectral properties of cooked tortillas were investigated with the major aim to understand the role of lime, Ca(OH)2 , incorporated during the alkaline cooking process. The data are further supplemented by x-ray diffraction and texture measurements. The changes in the thermal diffusivities, measured by the photoacoustic technique, as well as the changes in texture, x-ray patterns, dielectric, and IR spectral properties are presented as a function of the lime concentration. The results show strong evidence that there is a marked concentration of lime (around 0.2%) above and below which different behavior patterns of the measured properties of tortilla were observed. In particular, the results for the dielectric constant and thermal diffusivity provide strong evidences for enhanced starch crosslinking taking place for lime content close to 0.2%.

A modified photodeflection method based on the wave optics approach is proposed for the thermal parameter measurement of volume materials and thin films. Experimental and theoretical results of the application of this method to measurements of the thermal parameters of solids are presented. It is shown that the modified photodeflection method can be used in a wide frequency range of thermal waves and provides a lower mean squared error between experimental and theoretical results in comparison with the ordinary method.

The photopyroelectric (PPE) method for thermo-optic materials investigation uses a pyroelectric sensor to measure the photothermal heating of the sample. We report on a self-calibrated PPE technique consisting of simultaneous excitation of the PPE cell at two frequencies. The corresponding signals are retrieved from the multiplexed pyroelectric response with two lock-in amplifiers. Their ratio depends only on the sensor’s specific heat and the sample’s thermal effusivity, as temperature-dependent quantities. This scheme has the advantage that it cancels out possible fluctuations of excitation intensity and of the pyroelectric coefficient. Experimental results with (NH4)HSO4 and (ND4)2TeCl6 crystals show that this feature is particularly important when studying structural phase transitions at low temperature (20 to 300 K). Finally it is found that below 240 K epoxy resin is a better coupling medium than silicon grease.

Pulse-transient IR thermography enables detection and quantification of subsurface defects. However, defect detection can be perturbed by the geometry of the part, if not planar. A method is presented that, from a single IR image recorded at the end of the thermal pulse, enables one to evaluate the shape of a nonplanar part and then apply a correction on subsequent thermograms in the time sequence to increase the reliability of defect detection. The method uses some of the concepts of the ‘‘shape from shading’’ theory from the machine vision field.

Photothermal measurement techniques offer the possibility to determine thermal properties on and below the sample’s surface. Thus, subsurface thermal inhomogeneities such as defects, buried structures, and continuous profiles of thermal parameters become accessible by photothermal means. Our special interest is focused on the quantitative characterization of material modifications in near-surface layers that are induced by thermal (such as hardening) or mechanical (such as grinding) treatments of the surface as well as the reconstruction of a subsurface structure’s depth, size, and defect strength. Altogether, these investigations are aimed to develop photothermal techniques toward a true quantitative and noncontact inspection method for the nondestructive evaluation of opaque solids.

We study theoretically and experimentally the ability of photothermal techniques to thermally characterize the anisotropic materials whose principal axes are not contained at the sample surfaces. We first determine the thermal diffusivity tensor when the directions of the principal axes are known. Inversely, we calculate the directions of the principal axes in a sample whose thermal diffusivities are given. Measurements validating our theory are presented for a sample of pyrolytic graphite (PG), which has a high anisotropy, by means of two photothermal techniques: IR radiometry and the mirage effect.

Laser-induced, frequency-scanned IR photothermal radiometry was used to investigate the thermophysical properties of the paper on which several genuine and counterfeit British (£10) and U.S. ($50, $100) currency bills were printed. The radiometric photothermal amplitudes and phases were further compared with a theoretical model, which yielded simultaneous quantitative measurements of the thermal diffusivities and conductivities of the bills. Both statistical and single-specimen results demonstrated the excellent thermophysical resolution of the technique with prospects for its use in the nonintrusive, on-line identification of counterfeit banknotes.

Ultrasonic Lamb waves are generated in 90 µm thin copy paper with a Q-switched low-power Nd:YAG laser and detected with an Ar+ laser Doppler interferometer. This noncontact method enables one to determine two elastic constants (C44 or C55) that are related to the compressive strength of the paper by matching the measured high frequency limit of the phase velocity of the a0 mode with that predicted by orthotropic plate theory. The method is also used to measure the phase velocity of the nondispersive fast mode and infer the corresponding elastic constants (C11 and C22), which are directly related to the tensile strength of the paper. Although excellent agreement is obtained with orthotropic plate theory and also with independent measurements made with contact transducers, the results must be taken cautiously because interferometric measurements made simultaneously on the opposite side of the sample showed clearly the unexpected antisymmetric nature of the fast mode, thus showing the limitation of the orthotropic model when applied to paper.

The coupled equations for pressure and temperature that describe the photoacoustic effect are solved for a laser-irradiated droplet surrounded by a second fluid to determine the effects of heat conduction and viscosity on the emitted ultrasonic wave. A numerical method of solving the coupled equations is used to give frequency domain expressions for the photoacoustic wave emitted by the droplet. The results show that the range of diameters over which the solution to the wave equation remains valid is quite large, and that deviations from the wave equation solution in experimentally recorded photoacoustic waveforms is not expected until the diameter of the droplet is so small as to approach the viscous or thermal heat conduction lengths of the fluid.

Recently, porous silicon has been extensively studied due to its luminescence properties and some interesting features for micromechanical technology, characteristics that have led to a wide range of applications, from electro-optical devices to IR radiation detectors and gas sensors. It is therefore very important to obtain a complete description of this material, measuring its optical, electronic, and thermal properties. Following an introduction of the production process of porous silicon and its main physical and morphological characteristics, a review is presented of the possible applications of photothermal and photoacoustic techniques for the measurement of optical absorption and electronic and thermal transport properties.

The development of various methods for the investigation of transport phenomena in solids has attracted much attention. The photoacoustic method is a valuable tool in the study of various processes in semiconductors and electronic devices. Especially for the characterization of thermal and carrier transport processes in semiconductors, the transmission detection configuration is available for many applications. That the photoacoustic frequency transmission technique as a valuable tool in the study of carrier transport processes of the semiconductor is shown. The photoacoustic spectra of wide bandgap semiconductors (Siwafers, Ge and GaAs), narrow bandgap semiconductors (InSb, PtSb2) and thin amorphous semiconductor (GeSe) films are measured as a function of modulation frequency.

Two noncontact laser-based heterodyne techniques, photothermal heterodyne (PTH) and photoluminescence heterodyne (PLH), are introduced and applied to processing and quality control in silicon wafer manufacturing. The crystallographic characteristics of processinduced defects in silicon wafers are suitable for the application of PTH and PLH techniques, which are demonstrated on selected examples from different steps of silicon wafer production. Both PLH and PTH techniques meet the demand for nondestructive and on-line-suitable measurement in the semiconductor industry.

quantitative analysis of linear temperature-dependent coupled thermoelectronic diffusion waves in the generation of the laserinduced IR photothermal radiometric signal from a photoexcited, plasmawave- dominated, semi-infinite semiconductor Si wafer is presented. The strong coupling between the (usually assumed decoupled) carrier and thermal wave transport equations is accounted for explicitly and the range of violation of the Vasil’ev-Sandomirskii condition is studied. Thermoelectronic coupling is found to degrade the sensitivity of the plasmaoriginating IR radiometric signal in high-quality process Si substrates at elevated background temperatures and high modulation frequencies, with the exception of highly degenerate plasmas

The application of photothermal interferometry and near-field thermal lensing as analytical tools in liquids is described. Using the transverse setup, the smallest detection volumes are achieved. The setups of both sensor systems are miniaturized, so adjustment and external influences are minimized. The sensitivities of both systems are demonstrated with the textile dye Reactive Red as an analyte.

A novel thermal wave based pyroelectric thin film solid state sensor shown to be capable of responding to H2 gas flows in N2 or in air under ambient temperature and pressure conditions is described. The new sensor exhibits an extremely wide detection dynamic range: 100% to 25 ppm hydrogen in nitrogen, and a 10 to 90% signal rise time of approximately 10 s, limited by the inertia of the gas delivery system. The extended dynamic range is achieved through two complementary operating mechanisms, resulting in a thermophysical and a chemical response at high and low H2 concentrations, respectively.

An external cavity diode laser is constructed and shown to have stable, narrow-linewidth operation around 840 nm. Based on this laser and a photoacoustic detector, a gas monitoring system capable of measuring absorption coefficients as low as 10-8 cm-1 is developed. The continuous (mode-hop-free) tuning range of the laser is found to exceed 100 GHz, which makes possible the spectrally resolved detection of water vapor absorption lines. The photoacoustic cell with the external cavity diode laser as a light source offers great potential for the development of a portable, automated gas detection system.

The expectation minimum (EM) principle is a new method of inverse problem theory that can be used to obtain stable solutions to first-kind Fredholm integrals. The EM principle uses the addition of noise to a basis of model vectors that are related to the experimental data by a multilinear discrete model. The experimental data are projected onto this randomized basis set and solution vectors for individual data projections are recovered by any one of a number of standard algorithms. The solutions are averaged arithmetically to obtain a stable estimate of the minimum error solution by expectation. It is shown from theory that the presence of noise in the model basis provides a method of regularization of the problem. Examples applicable to the problem of source localization in inverse heat conduction are examined. When factorization methods are used to recover the solution vectors corresponding to each data projection, the solutions recovered by the EM principle are shown to quantitatively converge to the zero-order uniform Tikhonov regularized solutions. When a stepwise projection method is used in lieu of factorizations, the recovered solutions agree nearly quantitatively with the solutions recovered using the autocorrelation method of linear filtering derived via a modified form of the Yule-Walker equations. The resolution and robustness of the EM solutions in this second case are greatly superior to those obtained by the autocorrelation method. The ultimate accuracy and resolution of the EM solutions in this latter case is limited by the noise in the model basis. Through appropriate sampling methods, the noise in the model basis may be set as low as three orders of magnitude below the noise on the experimental data. This gives an enormous improvement in performance over the previous methods of solution using regularization.

The interaction of UV laser radiation with optical coatings is investigated by a pulsed two-probe-beam photothermal technique. UV laser damage resistance studies on LaF3/MgF2, Al2O3/SiO2 , HfO2/SiO2 multilayer stacks are performed at ? = 248 nm and t520 ns. By investigating the relationship of the number of high-low (HL) pairs and the substrate material, optical and thermal coating properties are shown to be responsible for UV single-shot laser damage. The damage threshold of selected samples is influenced by the deposition technique. The influence of the bandgap energy of typical UV thin film oxide materials on the damage is investigated. Furthermore, multishot damage measurements on LaF3/MgF2 high-reflection multilayer coatings reveal the accumulation of laser energy in the predamage range and lead to an increase in absorption.

The photodeflection method is able to characterize the propagation losses in optical waveguides. The theory of the transverse configurations in air and in situ is reviewed. The procedure to determine the propagation loss coefficient is widely discussed. The experimental results on two different Ti:LiNbO3 and glass channel waveguides are in good agreement with theory.

A diffraction theory of the mirage effect is derived for the case of impulse excitation of a thin planar heat flux source located at the surface of an irradiated solid sample. A Fresnel diffraction theory is derived to predict optical deflection and diffraction of a probe laser beam directed over the surface of the sample, through an adjacent fluid phase. A closed-form analytical expression for the perturbed electric field distribution of a probe beam intersecting a 1-D mirage element is derived and used to compute beam profile changes, changes in the beam’s central moment, and point differences in the intensity change measured in the detector plane. Photothermally induced changes in the probe beam’s central moment are found to give a robust measure of the photothermal deflection effect and are substantially insensitive to photothermal diffraction. Photothermally induced diffraction effects are resolved by computing point changes in the probe beam intensity. The photothermal deflection effect is found to give a maximum sensitivity with the mirage region centered at the waist of the probe beam and detection in the far field. The photodeflection effect dominates the mirage signal when the thermal diffusion length of the mirage element is comparable to or greater than the probe beam radius. Photothermal diffraction effects are significant when the thermal diffusion length is much smaller than the probe beam radius and when detection occurs in the near field. With far-field detection using a bicell, photothermal diffraction effects are, in general, significant only at early times past excitation. A quantitative correction for the diffractive effect is possible using the current theory.

A special configuration based on two successive acoustooptic interactions in uniaxial crystals with two noncollinear acoustic waves is presented. It leads to two angularly split wavelengths from a multiline laser beam with independent acousto-optic efficiencies. General expressions of the angular deviation and the spectral bandwidth are derived. Since the application concerns the restitution of colored images, a novel combination of wavelengths using the blue primary at 458 nm is investigated for trichromatic color matching. Numerical computations have been drawn for paratellurite. A practical separator using the slow shear wave in paratellurite is designed, and experimental results for the independent separation of 514- and 458-nm wavelengths of an Ar laser are reported.

A silicon-based, surface micromachined, deformable mirror device for optical applications requiring phase modulation, including adaptive optics and pattern recognition systems is described. The mirror will be supported on a massively parallel system of electrostatically controlled, interconnected microactuators that can be coordinated to achieve precise actuation and control at a macroscopic level. Several generations of individual actuators as well as parallel arrays of actuators with segmented/continuous mirrors have been designed, fabricated, and tested. Deflection characteristics and pull-in behavior of the actuators have been closely studied. Devices have been characterized with regard to yield, repeatability, and frequency response. An electromechanical model of the system has been simulated numerically using the shooting method, and good correlation with experimental results has been obtained. A twenty-channel parallel control scheme has been developed and implemented on a segmented mirror array.

The design and simulated performance characteristics of narrow band-induced transmission infrared filters in the wavelength range of 2000 to 4500 nm are presented. These dielectric-spacer-metal-spacerdielectric (D-S-M-S-D) filter structures are composed of Si as high index dielectric (D) and Al2O3 as low index dielectric (D) or spacer (S) and Al as the metal (M). Typically, a total of 10, 12, or 13 layers are required with an aluminum layer in the middle of the filter stack. The bandwidth of these filters is in the range of 20 to 25 nm. Rejection of these filters in the long wavelength range is very good. The effect of thickness errors on the performance of filters has been analyzed. Based on the numerical simulation of an actual fabrication process, the permissible tolerance for process monitoring is investigated. Numerical simulations show that a high production yield may be obtained if the reflectance errors are kept within ±0.1% during process monitoring in the manufacture of these filters.

The effect of controlled aliasing in synthetic Fresnel holograms is investigated with the aid of image distribution diffracted from the aperture of the element. The intensity fluctuation of the images distorted by aliasing is predicted by considering optical phase errors from the pixel areas of an aperture of synthetic Fresnel holograms.

A push-broom imaging camera with time expansion, selected for its ability to generate images with high resolution and high radiometric signal, is described for accurate site certification from space. The system providing the high-resolution imaging requires a sensor with an increased dwell time to generate a high radiometric signal. This may be accomplished by pointing the camera at each pixel for a longer interval of time than that available due to the sensor motion in the push-broom imaging configuration. This is referred to as push-broom imaging with time expansion. The use of the camera with time expansion may be applicable to any remote sensing imaging problem that requires simultaneously high spatial resolution and a high level of radiometric signal. For surveying a Martian landing site, it is necessitated by the imaging from an autonomous orbiting sensor whose speed is determined by its orbit and the planet’s mass.

This work examines the problem of foreground/background extraction when stereoscopic image information is available. A two-stage algorithm is proposed, followed by postprocessing for the estimation of the global motion in the scene and the identification of moving objects. At the first stage, an estimate of the 2-D global motion in the scene is formed which then serves as an initial estimate for the algorithm for a robust 3-D global motion estimate. The 3-D global motion estimation procedure is interleaved with a procedure for removal of the outlier vectors from the initial set of training vectors. Postprocessing of the foreground/background map produced results in an improved motion detection mask, which may then be used for 3-D motion compensation.

The fuzzy C-means (FCM) algorithm has two major problems for the codebook design: tremendous memory requirement and intensive computation. This paper presents two codebook design algorithms based on FCM. The first algorithm overcomes the storage problem with the use of the codebook, rather than the membership matrix in FCM, to initiate and terminate the algorithm. A fast version is presented to further solve the computation problem. The fast algorithm partitions a training set into several classes and then the first algorithm is applied to each class separately. Experimental results show that both new algorithms achieve better picture quality. Furthermore, the fast algorithm is obviously faster than LBG and FCM.

Generation of two synchronized high-voltage discharges at a 200-Hz repetition rate by rotating a suitably configured circular dielectric plate between two pairs of spark gap electrodes is reported. The delay between the discharges could be varied from less than a microsecond to more than a millisecond by locating the electrodes of the spark gaps judiciously with respect to the passing holes of the dielectric plate. The performance of the device has been tested by switching a total of 2.5 kW power on two identical dummy loads resembling a typical transversely excited (TE) laser in terms of resistance. Operation of the switch in the triggered mode has been achieved by use of an optical sensor. The test on a real transversely excited atmosphere (TEA) CO2 laser load was limited to a 50-Hz repetition rate. Inadequate cooling of the laser gas mixture and the accumulation of discharge products led to arcing beyond this pulse repetition frequency.

An analysis is performed to obtain explicit closed-form expressions for the output power, threshold pump power, and the optimum length of an erbium-doped Fabry-Pe´ rot cavity fiber laser. To verify the validity of the model, we used an electron cyclotron resonance plasmaenhanced chemical vapor deposition apparatus to deposit dielectric thin films on one fiber end to change the reflectance of a cavity mirror, while monitoring the reflectance in situ. We also varied the active fiber length and compared the measured values of output power and threshold pump power with the theoretically predicted values. Good agreement between theory and experiment was obtained.

Many optical fiber sensors designed to recover quasi-static strain fields in the presence of significant temperature changes have been reported in recent years. A general theoretical analysis of the influence of systematic errors associated with the measurement process is presented and applied to a range of techniques that are of current interest in the literature. The performances of measurement methods based on Bragg grating sensors, polarization-maintaining Fabry–Pe´ rot interferometers, combined dual-mode interference/polarimetry sensors, and dispersive Fourier transform spectroscopy measurements are contrasted with respect to the influence of measurement error, calibration error, cross talk, and engineering practicality.

A fringe projector based on a low-cost spatial light modulator has been used to measure the shapes of discontinuous objects. By changing the fringe phase and the fringe pitch, a sequence of wrapped phase maps can be acquired at different sensitivities. This sequence can then be converted to a surface profile by the recently proposed method of temporal unwrapping rather than by a conventional spatial unwrapping approach. The main advantages are that the method is simple and robust, and that objects with surface discontinuities are profiled as easily and accurately as smooth ones. The absolute distance from the camera to an object is measured at each pixel independently of the other pixels in the image. In addition to accurate measurement of surface shape, one possible application may therefore be as a 3-D robot vision system. A simple calibration procedure is described which avoids the need for accurate positioning of the camera and projector and which takes account of instrumental artifacts. A measurement accuracy better than 1/1000 of the field of view has been achieved. A number of practical applications of the technique are illustrated.

The development of ‘‘smart’’ materials and structures has been underway for several decades. These intelligent materials and structural systems typically incorporate internal mechanisms for sensing, signal processing, and actuation. Future applications will likely include civil infrastructure monitoring, biomedicine, aerospace, hydrospace, and other uses where periodic self-examination and adaptability may be important. In the field of smart structures and materials, scientists often disagree on what makes materials or structures ‘‘intelligent.’’

This PDF file contains the editorial “Diode Lasers and Photonic Integrated Circuits” for OE Vol. 36 Issue 02