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In this paper, we report on an experimental activity aimed at investigating the potential of two terrestrial remote-sensing techniques, namely, ground-based SAR (GB SAR) interferometry and terrestrial laser scanning, in order to retrieve snow-depth (SD) measurements in mountainous regions. Terrestrial laser scanning is a more consolidated technique based on the measurement of the optical (near infrared) reflectivity, and it is affected by the surface of the snow layer: a temporal data sequence allows us to estimate the absolute SD variation. Recent use of SAR interferometry to evaluate snow-mass characteristics is based on relating the measured interferometric phase shift to a change in the snow mass. Interferometric GB SAR measurements and terrestrial laser scanner scans were collected together with pointwise conventional measurements of physical snow parameters during the winters of 2005/2006 and 2006/2007. The experiment was carried out in the Wattener Lizum, a high Alpine area at about 2000-m elevation north of the main ridge of the Austrian Alps in Tyrol. Notwithstanding the difficulty of providing both lengthy data record in dry snow conditions and detailed knowledge of the observed snow characteristics, the obtained results confirmed the presence of a clearly measurable interferometric phase variation in relation to the growing height of the snow layer. A comparison of the SD maps obtained through the two techniques shows differences partly due to the different nature of the two observations. Index Terms--Ground-based microwave interferometry, snow depth (SD), terrestrial laser scanner (TLS).

Otoacoustic emissions, sounds generated by the inner ear, are widely used for diagnosing hearing disorders and studying cochlear mechanics. However, it remains unclear how emissions travel from their generation sites to the cochlear base. The prevailing view is that emissions reach the cochlear base via a backward-traveling wave, a slow-propagating transverse wave, along the cochlear partition. A different view is that emissions propagate to the cochlear base via the cochlear fluids as a compressional wave, a fast longitudinal wave. These theories were experimentally tested in this study by measuring basilar membrane (BM) vibrations at the cubic distortion product (DP) frequency from two longitudinal locations with a laser interferometer. Generation sites of DPs were varied by changing frequencies of primary tones while keeping the frequency ratio constant. Here, we show that BM vibration amplitude and phase at the DP frequency are very similar to responses evoked by external tones. Importantly, the BM vibration phase at a basal location leads that at a more apical location, indicating a traveling wave that propagates in the forward direction. These data are in conflict with the backwardtraveling-wave theory but are consistent with the idea that the emission comes out of the cochlea predominantly through compressional waves in the cochlear fluids. basilar membrane vibration | cochlear traveling wave | laser interferometer | otoacoustic emission

We introduce a new configuration for the optical head of a newly developed diffractive laser encoder system. This configuration has a high manufacturing tolerance and a high head-to-scale alignment tolerance, both of which can enhance the wider potential applicability of this newly designed laser encoder. The measurement principles of the encoder are discussed and detailed. We optimized the grating shape and analyzed the impact of the optical components and their arrangement on the measurement error. The head-to-scale alignment tolerance and the arrangement of components in the encoder were also determined. Finally, the measurement performance was evaluated and analyzed. Under nonenvironmentally controlled conditions, the measurement accuracy was found to be 37.3 nm with a standard deviation of 25.4 nm. OCIS codes: 050.1950, 230.2090, 120.0120, 230.0230.

The calming effect of oil on water has been known since ancient times. Benjamin Franklin was the first to investigate the effect, but the underlying mechanism for this striking phenomenon remains elusive. We used a miniature laser interferometer to measure the amplitude of surface waves to a resolution of [+ or -]5 nm, making it possible to determine the effect of an oil monolayer on the attenuation of capillary waves and the surface dilational modulus of the monolayer. We present attenuation data on pure water, water covered by olive oil, water covered by a fatty acid, and a water-acetone mixture for comparison. From the attenuation data at frequencies between 251 and 551 Hz, we conclude that the calming effect of oil on surface waves is principally due to the dissipation of wave energy caused by the Gibbs surface elasticity of the monolayer, with only a secondary contribution from the reduction in surface tension. Our data also indicate that the surface-dilational viscosity of the oil monolayer is negligible and plays an insignificant role in calming the waves. [DOI: 10.1119/1.2710482]

It has previously not been possible to measure eardrum vibration of human subjects in the region of auditory threshold. It is proposed that such measurements should provide information about the status of the mechanical amplifier in the cochlea. It is this amplifier that is responsible for our extraordinary hearing sensitivity. Here, we present results from a laser Doppler vibrometer that we designed to noninvasively probe cochlear mechanics near auditory threshold. This device enables picometer-sized vibration measurements of the human eardrum in vivo. With this sensitivity, we found the eardrum frequency response to be linear down to at least a 20-dB sound pressure level (SPL). Nonlinear cochlear amplification was evaluated with the cubic distortion product of the otoacoustic emissions (DPOAEs) in response to sound stimulation with two tones. DPOAEs originate from mechanical nonlinearity in the cochlea. For stimulus frequencies, [f.sub.1] and [f.sub.2], with [f.sub.2]/[f.sub.1] = 1.2 and [f.sub.2] = 4-9.5 kHz, and intensities [L.sub.1] and [L.sub.2], with [L.sub.1] = 0.4[f.sub.2] + 39 dB and [L.sub.2] = 20-65 dB SPL, the DPOAE displacement amplitudes were no more than 8 pm across subjects (n = 20), with hearing loss up to 16 dB. DPOAE vibration was nonlinearly dependent on vibration at [f.sub.2]. The dependence allowed the hearing threshold to be estimated objectively with high accuracy; the standard deviation of the threshold estimate was only 8.6 dB SPL. This device promises to be a powerful tool for differentially characterizing the mechanical condition of the cochlea and middle ear with high accuracy. cochlea | hearing loss | laser interferometer | middle ear

A four-point bending setup, when combined with a single- or double-beam laser interferometer can be used to measure the electrical and electrochemical characteristics of piezoelectric thin films, used in microelectromechanical systems (MEMS) devices. The method proved to be extremely useful, as it can measure the important characteristics of the films, including their dielectric coefficient, as well as their large signal electrical polarization.

A novel, double-beam common-path laser interferometer is developed to measure the longitudinal ([d.sub.33]) piezoelectric coefficient thin films and the results are compared with the values obtained by Berlincourt and laser scanning vibrometer methods. The results have shown that, for thin-film samples, the [d.sub.33]f values obtained from the Berlincourt method are larger than those obtained from the interferometer and vibrometer methods.

Stabilization of laser frequency to interferometers with a large time delay in one arm is of significant interest to space-based gravitational wave detectors such as the Laser Interferometer Space Antenna. A recently proposed technique allows a control bandwidth larger than the inverse delay time to be achieved. We present experimental results demonstrating laser frequency stabilization to an optical fiber delay line. A control bandwidth approximately 50 times the inverse delay time is demonstrated.

Surface waves on fluids with wavelengths in the millimeter range are known as capillary waves. Surface tension determines the propagation and dispersion of capillary waves while gravity plays a minor role. We describe a simple method for generating standing capillary waves of known frequency on water and introduce a novel noncontact technique based on laser interferometry to measure the wavelength of capillary waves with great precision. The data gives the dispersion relation of capillary waves and provides an accurate method for determining the surface tension of fluids. [DOI: 10.1119/1.2215617]

A technique based on superresolution by digital holographic microscopic imaging is presented. We used a two dimensional (2-D) vertical-cavity self-emitting laser (VCSEL) array as spherical-wave illumination sources. The method is defined in terms of an incoherent superposition of tilted wavefronts. The tilted spherical wave originating from the 2-D VCSEL elements illuminates the target in transmission mode to obtain a hologram in a Mach-Zehnder interferometer configuration. Superresolved images of the input object above the common lens diffraction limit are generated by sequential recording of the individual holograms and numerical reconstruction of the image with the extended spatial frequency range. We have experimentally tested the approach for a microscope objective with an exact 2-D reconstruction image of the input object. The proposed approach has implementation advantages for applications in biological imaging or the microelectronic industry in which structured targets are being inspected. OCIS codes: 090.0090, 100.6640, 110.0180.

A finite-element study of acoustic interactions in capacitive microfabricated ultrasonic transducers (CMUTs) and experimental results obtained by laser interferometry measurements is reported. The good agreement found between finite element modeling results and optical displacement measurements demonstrates that acoustic interactions through the liquid represent a major source of cross coupling in CMUTs.

Laser ultrasound is a technique used for the ultrasonic inspection of composites during manufacturing of advanced jet fighters. With this technique laser interferometry is used to detect ultrasonic displacements generated by a laser. In theory, the signal-to-noise ratio is proportional to the square root of the collected detection light. In practice, laser phase noise limits the signal-to-noise ratio above a certain collected light level. Two techniques are presented to decrease effects due to laser noise. In one technique the dual-cavity Fabry-Perot currently used is replaced by an interferometer based on a photerefractive crystal. The other technique has a high-finesse Sagnac cavity that filters the phase noise from the detection laser. Experimental results demonstrate that these two techniques significantly reduce limitations due to laser noise. OCIS codes: 120.3180, 120.4290, 120.2230, 190.7070.

A laser shearing interferometer (LSI) was used to make spatially and temporally resolved measurements of the electron density profile in an imploding z pinch. Experiments were conducted on the 0.7-MA/250-ns Hawk machine, the 2.5-MA/100-ns ACE-4 machine, and the 3.8-MA/190-ns Double Eagle machine. Time and space resolved measurements of the current and plasma density are needed for better understanding of the implosion dynamics and stagnation physics of z pinches. The electron density profile can be obtained using an LSI. The LSI passes a short pulse, collimated laser beam across the imploding z pinch, which distorts the laser wavefront. The maximum wavefront distortion occurs where the density gradient is highest, such as across the current sheath. After passing through the pinch, the distorted wavefronts are split into two beams that are laterally displaced relative to one other. This shearing causes interference between these two wavefronts and produces an interferogram, from which the plasma density profiles are derived. In the experiments, a 150-ps laser pulse was split into two pulses with an interpulse delay of several tens of nanoseconds. This pulse pair gave two snap shots of the electron density profiles during the 100-300-ns implosions. From these interferograms, electron densities and implosion velocities of the imploding plasmas were derived, the current sheath was observed, and the plasma ionization states, growth rates, and wavelengths of instabilities were estimated. The results motivate construction of an upgraded instrument with four or more frames and with an added laser polarimetry measurement (Faraday rotation) capability to obtain both electron and current profiles. Index Terms--Plasma, plasma measurements, plasma refraction, shearing interferometry.

The differential laser interferometry method and its application for measuring the thermal expansion of samples is described. The thermal expansion of single-crystal Al(sub 2)O(sub 3) (corundum) was measured up to 1000 K with the differential laser-interferometer. The changes in the distance between two faces of a stepped shape sample are measured. The main feature of the apparatus is simultaneously monitoring two fringe signals that are 90 degrees out of phase. This improvement of the basic laser-interferometer allows us to remotely measure the thermal expansion of minerals with high precision. The overall sensitivity with which we can detect changes in length is about 1/100 of the wavelength of the He-Ne laser (1/100 of 0.6328 x 10(super -6) m). After adjusting for errors caused by heat, the thermal expansion data measured with the differential laser-interferometer are in good agreement with previous reports. Use of this apparatus allows the investigation of the high-temperature thermodynamic properties of important rock-forming minerals.

We present the very first experiment allowing in situ observation of surface evolution during very high electric field application. This has been achieved by soft ([Lambda] = 21.2 nm) X-ray laser Fresnel two-mirror interferometry. The surface under study was a niobium planar cathode opposite to a stainless steel blade-like anode. The applied field range on the cathode was F [approximately equal to] O to 50 MV/m. The interferograms were single shots of 80 ps duration, allowing to probe the surface morphology quasi-instantaneously. The delay between two shots was 20 min while the electric field was kept on. The comparison of successive interferograms gives the Nb surface evolution over [approximately]2 h. Thus, we observed the appearance of defects of [approximately] 3 nm high and their evolution with time. These may be the precursors of the minute breakdown which occurred later on. This technique thus makes it possible to detect the preliminary stages of a discharge.

A scanning receiver with a bandwidth of 40 GHz has been demonstrated. The system uses temporal scanning of a fiber Fabry-Perot etalon to analyze the microwave sidebands on an optical carrier. A proof-of-concept system has been measured, and a conversion efficiency of 280 mV/mW has been obtained at 10 GHz, giving an unamplified RF sensitivity of -2 dBm. The RF resolution is 90 MHz within the 40-GHz scan range. A theoretical analysis of the system is presented and mprovements and limitations are discussed. While the performance of the initial all-optical system is not comparable to high-performance microwave receivers, it is believed that the potential for system improvements exists. Index Terms - Fabry-Perot interferometers, microwave receivers, photonic signal processing.

Fourier-transform profilometry (FTP) and data-dependent system profilometry (DDSP) are the two major phase-extraction methods that use a single interferogram. The difficulty in verifying surface profiles obtained by these methods is that the exact spot on an actual surface cannot be measured with two different instruments. An interferogram regeneration procedure is developed to solve this problem. The surface profile is then extracted from the regenerated interferogram by both FTP and DDSP. Comparisons of the actual surface profile with the extracted surface profiles show that both methods perform equally well in measuring the root mean square and the center line average, but only DDSP is able to reproduce the detailed surface profile of the reference surface.

A new method has been demonstrated for absolute-length measurements of a long-baseline Fabry-Perot cavity by use of phase-modulated light. This method is based on determination of a free spectral range (FSR) of the cavity from the frequency difference between a carrier and phase-modulation sidebands, both of which resonate in the cavity. Sensitive response of the Fabry-Perot cavity near resonant frequencies ensures accurate determination of the FSR and thus of the absolute length of the cavity. This method was applied to a 300-m Fabry-Perot cavity of the TAMA gravitational wave detector that is being developed at the National Astronomical Observatory, Tokyo. With a modulation frequency of [approximately] 12 MHz, we successfully determined the absolute cavity length with resolution of 1 [[micro]meter] (3 x [10.sup.-9] in strain) and observed local ground strain variations of 6 x [10.sup.-8]. OCIS codes: 120.2230, 120.3180, 120.3940, 120.5060.

We have studied the history of vibration and demonstrate a laser-based noncontact interferometric vibration sensor. The sensor promises the measurement of microdisplacement by using a Fabry-Perot cavity formed between a partially coated gradient-index lens and a movable reflector. Displacement is determined by the detection of interference fringes caused by phase modulation within the cavity. The sensor was tested in conjunction with both multimode and single-mode fiber transmission. Calibration with multimode fiber produced a fringe-contrast function that decreased monotonically with displacement. This calibration allowed at least 30 fringes to be discriminated, giving a displacement resolution of 0.034 [[micro]meter] across a range of 10.2 [[micro]meter]. Dynamic tests demonstrated a working range of at least 3.74 [[micro]meter] at frequencies as high as 2 kHz. Similar tests in which single-mode fiber was used indicated a dynamic working range of at least 4.29 [[micro]meter].

Conventional Mach-Zehnder interferometer configuration is modified to enhance its stability from the vibrations. To study the effects of vibrations on the Mach-Zehnder interferometer, we used spectral interference fringes from a broadband nanosecond dye laser source. We observed an improvement in the stability of the interferometer by a factor of 3.

In this experiment, the frequency separation between two longitudinal He-Ne laser modes is studied. A description is given of the physics that causes a change in the frequency separation when the modes are observed at various positions in the gain profile. The frequency separation is measured with a fast photodetector in combination with a counter as a function of the mode intensity ratio. The intensity ratio is monitored with a scanning Fabry-Perot interferometer. For a scan of the two modes through the gain profile, a frequency separation change of [approximately]30 kHz was observed.

Laser interferometry is used for the first time to measure plasma electron density along the slow wave structure (SWS) wall during microwave generation in a vacuum, long pulse, high power backward-wave oscillator (BWO). The University of New Mexico long pulse backward-wave oscillator, which displays the characteristic pulse shortening phenomenon, is investigated in these studies. Although pulse shortening is observed across a wide class of high power microwave devices, its origin is not definitively understood. Many hypotheses suggest that the unintentional introduction of plasma into the interaction region near the walls of the SWS is one of several likely causes of pulse shortening in intense electron beam-driven slow wave devices. This article presents initial measurements of the line-integrated, temporally resolved plasma density between an intense, relativistic, annular electron beam and SWS walls for a variety of radiated microwave peak power levels. Line-integrated electron densities, , between 9[multiplied by][10.sup.15] and 2.4[multiplied by][10.sup.16] [cm.sup.-2] for radiated microwave powers between 20 and 120 MW have been measured. The two main sources of the measured electron density are postulated to be i) plasma generated from the cutoff neck due to beam scrape off, and ii) material removed and ionized from the SWS walls during microwave generation. Index Terms - Backward-wave oscillator, high power microwave generation, Michelson laser interferometry, plasma diagnostics, pulse shortening.

Extensive and systematic time-resolved measurements of the electron density in an ArF laser discharge were performed using an accurate two-wavelength laser interferometry. The electron density dependences and laser output power on the Ar and F2 fractions in Ar-F2-He mixture and on the Ne-He mixing ratio in Ar-F2-He-Ne mixture were examined. A comparison of experimental results with computer simulation results was conducted.

We develop a regularized phase-tracking (RPT) technique to unwrap phase maps. The phase maps that can be unwrapped with this new method may be bounded by arbitrarily shaped boundaries. Moreover, the RPT unwrapper has a higher noise robustness than previously reported phase-unwrapping schemes.

An experiment was performed to determine the laser-induced loading characterization using numerical and experimental calculations derived from the velocity interferometer system for any reflector (VISAR) velocimetry technique. There were two numerical calculations used in simulating the mechanism of laser irradiation and shock wave propagation. The pressure amplitudes were evaluated using aluminum, molybdenum, copper and tantalum. Results revealed that VISAR interferometry was an effective technique in identifying ablation pressure and the loading temporal shape.

A Fizeau interferometer utilizes a multimode laser as a light source for testing thin transparent plate samples. As a result of multimode linear laser operation, interference fringes are obtained only when the optical path difference between two surfaces is equal to twice a multiple of the laser's effective cavity length. For three parallel surfaces, we can either adjust their separations or select a laser such that only two of the three surfaces meet the requirement of twice a multiple of the laser's effective cavity length. Key words: Fizeau interferometer, optical testing, phase-shift interferometry, laser diode, glass disk

A simple technique based on a Fizeau interferometer to measure the absolute phase shift on reflection for a Fabry-Perot interferometer dielectric stack mirror is described. Excellent agreement between the measured and predicted phase shift on reflection was found. Also described are the salient features of low-order Fabry-Perot interferometers and the demonstration of a near ideal low-order (1-10) Fabry-Perot interferometer through minimizing the phase dispersion on reflection of the dielectric stack. This near ideal performance of a low-order Fabry-Perot interferometer should enable several applications such as compact spectral imagers for solid and gas detection. The large free spectral range of such systems combined with an active control system will also allow simple interactive tuning of wavelength agile laser sources such as C[O.sub.2] lasers, external cavity diode lasers, and optical parametric oscillators. Key words: Fizeau interferometery, phase-shift measurement.

Here the variation of a liquid-film thickness at small Reynolds numbers is discussed. The film thickness measurement by laser interferometry corresponds to the liquid flowing on the inner surface of a small-bore glass tube. An adequate theoretical background for the techniques used in this experiment is discussed to demonstrate the capability of the experimental technique. An advantage of this method is that it shows the shape of the thin film on the inner surface of the vertical tube at a point in a horizontal cross section. The results obtained from this experiment show that the flow of liquid films on vertical surfaces is inherently unstable and three dimensional even at a Reynolds number smaller than 1.

Measurements were made on the metal axial acceleration and interface velocity of impedance-matching salt crystals using Fabry-Perot laser interferometry by detonating triaminotrinitrobenzene (TATB)-based charges. The ultrafine TATB became the bases for the investigation of the von Neumann spike state, reaction rates and the reaction product equation of state in the ignition and growth detonation reactive flow model. The data derived were found consistent with other estimates for carbon-rich explosives, which took account of the carbon condensation processes.

The worldwide endeavor to build long baseline laser interferometers to detect and study gravitational radiation is well under way. In the German-British GEO600 project, it is proposed to pass the sidebands induced on the light by an electro-optic phase modulator through a Fabry-Perot optical cavity used in transmission, called a mode cleaner. This can be achieved when the phase modulation frequency is matched to the first longitudinal-mode frequency of the mode cleaner cavity so that both carrier and sidebands are transmitted. The primary function of the mode cleaner is to reduce the geometry fluctuations associated with the light, and thus any such noise induced by the modulation process is also suppressed. We present the results of an experiment that investigates the feasibility of passing modulation sidebands through an optical cavity and the factors limiting its success. In particular, we show that it is possible to avoid introducing excess noise associated with the transmitted sidebands, provided that certain experimental criteria are satisfied. The research was carried out on a prototype mode cleaner cavity built and tested at Glasgow University but which is similar to the equivalent apparatus planned for GEO600. Key words: Gravitational waves, modulation, mode cleaner.

The phenomenon of stepwise creep has been discovered and studied earlier for unoriented polymers by a new laser interferometer method. This same technique has been used for studying long-term mechanical properties of UHMWPE gel-spun fibers of various draw ratios. A variability of creep rate has been observed. The creep rate variability has been characterized by two parameters: the typical period of deformation increment, with enhanced deformation rate (step), and the variability (inhomogeneity) of the deformation rate over a deformation interval. Despite a large scatter of data, at least three levels of deformation steps could be derived: (i) microns, (ii) tens of microns, (iii) hundred and more microns. The larger levels of deformation steps decrease with increasing draw ratio. Their dependence on strain is not observed. The creep rate variability significantly depends on the creep strain. First, it increases with strain and then decreases just prior to rupture. The effect of draw ratio on creep rate variability is not significant. It is assumed that the creep rate variability is a cooperative deformation. It is suggested that interfibrillar slip and slip between fibrillar layers occurs via a slip-stick motion making a significant contribution to total deformation. The mechanism does not change with draw ratio., INTRODUCTION By efforts of many polymer scientists over the last two decades, highly oriented gel-spun UHMWPE fibers with extreme short-term mechanical properties (Young's modulus and strength) have been produced both [...]

A novel signal processing scheme for detecting distance and velocity signals simultaneously is demonstrated. In this method, a frequency-modulated diode laser is used to illuminate a dual-channel Michelson interferometer with two orthogonal output signals. The distance and the velocity signals then exist on the beat frequencies of the output interferometric signal. Two interferometric output signals with a quadrature phase shift are used to adjust the gating time period of frequency counters for beat-frequency measurement. The distance and velocity signals can thus be obtained from the counting number within the gated-in time period.

This paper addresses the servo design for a real-time, laser-tracking, three-dimensional (3-D), position measurement system. The 3-D measurement system uses two sets of tracking mirrors to shine laser beams toward the measurement point. By examining the angles of these mirrors, one can calculate the position of this point. The servo loop in the measurement system corrects the mirror orientations by continuously checking and compensating the offset between the out going laser beam and the beam reflected from a retro-reflector attached to the measurement point. To achieve high speed and high accuracy measurement, the tracking servo system has to compensate for the highly nonlinear nature of the system and maintain the laser beams close to the measurement point. This paper derives the relationship between the tracking angle rotations and the measured beam offsets. By including this relationship in the system model, the linear [H.sub.[infinity]] optimization technique can be applied for controller synthesis. All the design specifications are then directly implemented.

Two methods and an experimental setup for the measurement of spacing of diffraction gratings have been developed. These methods depend on interferometric measurements at different wavelengths of the angles of diffraction beams from the grating to be measured. A lower limit for the measured spacing is the half-wavelength of laser radiation. The results of spacing measurements of approximately 0.28, 0.39, and 0.50 [[micro]meter] are presented. Key words: Diffraction grating, interferometry, groove spacing measurement, metrology.

A laser Doppler interferometer was built for the precise measurement of intraocular optical distances in humans and chicks. A technique using Purkinje images was developed to position the chick's eye reproducibly. A computer algorithm for the objective analysis of the interference signal and determination of the optical distances is presented. The precision of this noncontact interferometric method for measuring the cornea-retina distance is better than [+ or -]20 [[micro]meter].

Extraction of biotinylated peptides by streptavidin magnetic beads has been directly coupled to the MALDI-TOF mass analysis. The elution of peptides from the beads is achieved by first mixing the beads with the MALDI matrix solution and removing, after a few minutes, the beads with a magnet; then, the matrix solution containing the biotinylated peptide is directly mass analyzed by MALDI. Three examples are presented to show the capabilities of this procedure to detect biotinylated peptides present at very low concentrations in complex mixtures. Detection limits of less than 100 fmol can be achieved. Such a coupling strategy is of great interest to investigate peptide/protein interactions.

Effective analysis of the sequence of peptides using matrix-assisted laser desorption/ionization (MALDI) tandem ion trap mass spectrometry requires efficient mass isolation and the ability to induce extensive sequence-specific fragmentation. The present paper describes a new excitation scheme, which we term red-shifted off-resonance large-amplitude excitation (RSORIAE), that can deposit higher amounts of internal energy in ions than is feasible with conventional resonant excitation. The new method provides an effective means for inducing fragmentation of MALDI-produced peptide ions with m/z values up to 3500. Prior to excitation, it is necessary to isolate ions of interest with high efficiency. We demonstrate that isolation efficiencies of >95% can be achieved by careful design of the rf scan functions used during ion isolation. In particular, sudden transitions in the amplitude of the rf field (from low to high amplitudes) must be avoided. The combined improvements in the efficiency for ion isolation and the efficacy of ion activation make MALDI tandem ion trap mass spectrometry a practical tool for the characterization of proteins with high sensitivity.

The present paper explores the coupling of a matrix-assisted laser desorption/ionization (MALDI) ion source with an ion trap mass analyzer, with particular emphasis on the development of methods for improving the efficiency of ion trapping and ejection. A technique is described for directly measuring, for the first time, the trapping efficiency of peptide ions produced in a remote external MALDI ion source. The technique was used to devise an improved scheme for trapping, which yielded efficiencies as high as 39%. An improved understanding of the resonant ejection process led us to a new resonant ejection parameter set that increased the ejection efficiency by 1 order of magnitude over more conventionally used parameter sets and allowed for marked improvements in the mass resolution of ions with m/z > 2500. The presently described improvements in the efficiencies of ion trapping and ejection together with improved methods for isolating and fragmenting ions (Qin, J.; Chait, B. T. Anal. Chem., following article in this issue) lay the foundation for highly sensitive MALDI ion trap mass spectrometry of proteins (Qin, J.; et al. Anal. Chem. 1996, 68, 1784-1791).

The nonlinear index of refraction in a resonant region has been determined by the use of a fiber-based Mach-Zehnder interferometer to measure the temporal fringe shift between two signals. The measurement technique is direct and does not require additional amplitude information for the extraction of the nonlinear index of refraction. This technique has been used to measure the temporal response of an InGaAsP semiconductor optical amplifier at 1.313 [[micro]meter].

A full-field, time-resolved interferometric method for the characterization of sparse, polydisperse spray systems is reported. The method makes use of the angular intensity oscillations in the wide-angle forward-scatter region. A pulsed laser is used to illuminate a planar sheet through the spray, which is imaged, out of focus, from the 45 [degrees] direction. The image consists of a set of out-of-focus spots, each of which represents an individual droplet, and superimposed on which is a set of fringes corresponding to the angular intensity oscillations of that droplet. Macrophotographic recording with high-resolution digitization for image analysis provides a full-field capability. The spatial frequency of fringes on each spot in the image plane is dependent on the diameter of the corresponding droplet in the object plane, and a simple geometric analysis is shown to be appropriate for the calculation of the spatial frequency of fringes as a function of droplet size. Images are analyzed automatically by a software suite that uses Gaussian blur, Canny edge detection, and Hough transforms to locate individual droplets in the image field. Fringe spatial frequency is then determined by least-squares fitting to a Chirp function. The method is applicable to droplets with diameters in the range of several millimeters to several hundred millimeters and number densities of up to [10.sup.3] to [10.sup.4]. The accuracy of the method for droplet-size determination has been evaluated by measurements of monodisperse aerosols of known droplet size, and measurements of droplet-size distribution in a polydisperse aerosol produced by a gasoline fuel injector are also presented. An extension of the method, using high-speed photography to measure two components of velocity in addition to size and position, is discussed. A two-wavelength approach may also offer the capability to measure the concentration of model fuel additives in droplets, and the results of a feasibility study are described.

A differential laser interferometer/vibrometer is given, based on Doppler's principle and phase/frequency decoding algorithm to measure steady-state and dynamic behavior of mechanical systems on a nanometer scale. The motion of flying sliders with respect to the disk can be measured by this method. The measurement of the nonmember displacement, differential and displacement velocity by this method is accurate.

Experiments conducted inside and outside the bad-cavity regime of a HeNe 3.39-micron laser measured quantum limited linewidth. They showed an increase in linewidth proportional to nonuniformity of the intracavity intensity distribution as described by the longitudinal Petermann K-factor. The effects of the bad cavity can be separated from nonuniformity effects. The changes in population dynamics associated with the altered electron density when the power is changed via the discharge current needs further research.

A new method for estimating displacement in GaAlAs laser diodes without sign ambiguity involves a laser diode feedback interferometer that yields the displacement values by measuring the backreflection from the diode surface. The measurement is done in a single interferometric channel at a resolution of 1.2-m and at nominal feedback levels to derive a two-level hysteresis in the amplitude modulated signal. The experimental results correlate well with theoretical explanations.