Search

An analytical solution is developed for thermal stress in exponentially time decaying laser short-pulse heating of a metallic surface. Because the heating duration is short, a nonequilibrium heating model incorporating the electron kinetic theory approach is used to formulate the temperature distribution during the laser heating pulse. Thermomechanical coupling is introduced in the analysis to formulate the thermal stress field. Thermodynamic irreversibility is considered and the entropy generation rate due to heat transfer and thermal stress field is formulated during the heating process. It is found that temperature decays gradually in the surface region and becomes sharp as the distance increases towards the solid bulk. Thermal stress is compressive in the irradiated region. Thermodynamic irreversibility due to heat transfer dominates thermodynamic irreversibility because of the thermal stress field. PACS No.: 44.10.+i. Nous presentons une solution analytique pour la contrainte thermique due a une impulsion laser a decroissance exponentielle sur une surface metallique. Parce que le chauffage est de courte duree, nous utilisons un modele de chauffage hors d'equilibre incorporant la theorie cinetique des electrons afin de formuler la distribution de temperature pendant l'impulsion laser. L'introduction d'un couplage thermomecanique permet de decrire le champ de contrainte thermique. Nous tenons compte de l'irreversibilite thermodynamique et nous formulons le taux de generation d'entropie du au transfert de chaleur et au champ de contrainte thermique pendant le processus, pour trouver que la diminution de temperature qui est graduelle dans la region du chauffage devient rapide a distance. La contrainte thermique est compressive dans la region du chauffage. L'irreversibilite thermodynamique due au transfert de chaleur est plus importante que celle due a la contrainte thermique. [Traduit par la Redaction], Introduction Laser short pulse heating of metallic surfaces involves nonequilibrium energy transport in the irradiated region. Electron and lattice subsystems separate thermally because of electron temperature increases through energy absorption [...]

Phonon transport in paired aluminum and silicon thin films is considered under laser short-pulse irradiation at the aluminum film surface. The Boltzmann equation is incorporated to formulate energy transport in the films. To include a volumetric source resembling laser irradiation in the aluminum film, the Boltzmann equation is modified. Thermal boundary resistance is located at the interface of the film pair. An equivalent equilibrium temperature is introduced to assess the thermal resistance of the film during the laser heating process. The phonon temperature obtained from solution of the Boltzmann equation is compared with the findings of the two-temperature model. It is found that phonon temperature obtained from the solution of the Boltzmann equation is lower than that corresponding to the two-temperature model, which is particularly true in the surface region of the aluminum film. Phonon temperature increases gradually while, early on, the electron temperature rises and decays sharply in the surface region of the aluminum film. PACS Nos.: 44.90.+c, 63.20.-e. Nous etudions le transport de phonons dans un film mince d'aluminium et silicium, qui est generee par l'irradiation d'une courte impulsion laser sur la surface d'aluminium. Nous incorporons l'equation de Boltzmann dans la formulation de transport d'energie dans le film et nous la modifions, afin d'inclure les sources volumetriques ressemblant a l'irradiation laser dans le film. La resistance limite thermique est situee a l'interface des deux films. Nous introduisons une temperature d'equilibre equivalente pour verifier la resistance thermique du film pendant le processus de chauffage par le laser. Nous comparons les temperatures de phonon obtenues de la solution de l'equation de Boltzmann avec celles obtenues du modele a deux temperatures et trouvons que les premieres sont plus basses que les deuxiemes, ce qui est particulierement vrai dans la region du film d'aluminium. La temperature des phonons augmente graduellement, alors que celle des electrons monte et decroit brusquement autour de la surface d'aluminium au debut du processus. [Traduit par la Redaction], Introduction Laser short-pulse heating of metallic thin films results in non-equilibrium energy transport in the film. This, in turn, causes thermal separation of electron and lattice subsystems in the thin [...]

We theoretically investigate harmonic-selective enhancement by controlling the time-delayed two-color laser field. By properly controlling the delay times of the two pulses, selective enhancement of the harmonics with photon energies between 75 and 125 eV can be obtained, resulting in wavelength-tunable and bandwidth-controllable coherent extreme ultraviolet radiation. In addition, the other laser parameters' effects on the harmonic-selective-enhancement have also been investigated. PACS Nos.: 42.65Ky, 32.80Rm. Nous presentons une etude theorique de l'accroissement selectif des harmoniques en controlant le champ laser bi-couleurs a delai temporel. Elle montre qu'en controlant de facon appropriee le delai temporel entre les deux impulsions, nous pouvons obtenir un accroissement selectif des harmoniques ayant des photons d'energie entre 75 eV et 125 eV, resultant en une radiation coherente dans l'UV extreme (XUV) qui est accordable en longueur d'onde et en bande passante. Nous etudions aussi les effets des autres parametres du laser sur l'accroissement selectif des harmoniques. [Traduit par la Redaction], 1. Introduction High-order harmonic generation (HHG) as a promising extreme ultraviolet (XUV) and X-ray source as well as to generate attosecond pulses, has been intensively investigated in the last two [...]

A high-power multifrequency ultrasonic actuator is proposed and characterized. The actuator is used in many applications as a multifrequency ultrasound power generator, but also as a mirror with variable bend radius to deflect laser beams in optical applications.

The operation of positive index-guided submicrometer-ridge laser arrays (SLAs) that produced a near-diffraction-limited single-main-lobe far-field profile (FFP) is described. The SLAs have favored the lasing of in-phase array modes and have produced a near-diffraction-limited single-main-lobe FFP.

Practical laser communication is impeded by the inherent strict requirements on agile and accurate steering of the laser beam over a wide angular range that are addressed by the pointing, acquisition, and tracking (PAT) system. While the vehicle carrying the optical instrumentation is in motion, a PAT system is required to compensate for the vibrations applied to the optical platform through the proper application of advanced control laws. This paper presents a feedforward vibration rejection system interacting with an optical tracking system to successfully perform the PAT task. It features a set of inertial navigation sensors to monitor the optical platform orientation, and the optical tracker monitoring the optical alignment errors. The control effort is defined on the basis of both signals and upon amplification drives the actuators of a novel singularity-free fuill-hemisphere-range robotic manipulator supporting the optical platform. The resultant technology enables two ground vehicles navigating through a difficult terrain to maintain optical connectivity sufficient for reliable laser communication. The paper presents the development of an extended Kalman filter 'fusing' the inertial navigation sensor data, the design and implementation of the disturbance rejection/optical tracking control system, and the results of the experimental evaluation of the overall system performance.

The experimental results on laser beam guiding by a self-tightening lattice photo induced in a strontium barium niobate (SBN) photorefractive crystal is reported. The gradual transformation of the optical lattice into array of weakly coupled ones revealed significant role of induced modulation instability in the strong laser beam guiding.

A theoretical model is presented for describing the finite beams incident on reflective volume Bragg gratings. Findings reveal that the reflection of a finite beam is a convolution of the transverse beam profile and a general filter function of the Bragg grating.

The effectiveness of the wavenumber domain analysis of two-dimensional (2D) images captured by phase-sensitive laser probe systems in the characterization of RF SAW devices is studied. The wavenumber domain analysis can be usefully applied to the selective characterization of unwanted responses of RF SAW devices and also offers information like types and characteristics and the place of origin of spurious signals.

The principle of an interferometric strain/slope rosette (ISSR) is based on interference of laser beams reflected from three microindentations on a specimen surface. The ISSR can simultaneously measure the in-plane strains and the out-of-plane slopes. Ring-core cutting is a mechanical stress relief method. When used with the ISSR technique for residual stress measurement, the ring core can be made much smaller than used with the resistance strain rosette. Thus, more localized residual stresses can be measured. The theories of the ISSR/ring-core cutting method are described in this paper. Both mechanical and finite element models are developed for the incremental ring-core cutting process with the application of the ISSR technique. The stress-strain coefficients of the ISSR/ring-core method are calculated and nondimensionalized for general applications. A test example is given to demonstrate how residual stress distribution is determined by using the stress-strain coefficients and the ISSR data. [DOI: 10.1115/1.2198251]

With any form of phase distortions there is the need to qualitatively characterize beam quality. Three different qualitative criteria are most commonly used for this purpose, each of them describing the beam with one ratio: the overlapping integral, the Strehl ratio, and the [M.sup.2] parameter. We have analyzed the interrelation of the above-mentioned criteria in the three most common types of beam quality degradation: thermal lens, electronic self-focusing, and spherical aberration. Approximate analytical expressions for all three criteria and three types of beam distortion are derived for Gaussian and super-Gaussian intensity profiles. The efficiency of characterizing those beams by various criteria is discussed. OCIS codes: 220.1000, 140.6810.

An in situ separation system, cross-type optical chromatography, is developed theoretically, and an analytic solution of the retention distance is derived. Particle trajectories in the cross-type optical chromatography are calculated for various sizes and materials of the particles and for flow velocities. Further, cross-type optical chromatography assisted by a particle beam generation system is designed. OCIS codes: 080.2710, 140.3300.

A new experimental technique is used to analyze the transient response of partially depleted SOI devices to pulsed laser irradiation. This new technique allows calibration of the deposited charge in the sensitive volume (i.e., the body region of the measured SOI transistors) and then the quantitative analysis of the device transient response. In particular 50-nm gate length SOI transistors have been tested with the pulsed laser, and their response is compared to 0.25-[micro]m partially depleted SOI transistors. The transient current and the collected charge are investigated as a function of the supply voltage for both types of SOI devices. The technology optimization for low leakage or high performance applications is shown to have large effects on the SOI device sensitivity. Index Terms--Bipolar amplification gain, charge calibration, critical charge, partially depleted SOI, pulsed laser irradiation, threshold LET.

We present the results of a laser beam passing through a turbulent medium. First we measure the geometric parameters and the spatial coherence of the beam as a function of wind velocities. A multifractal detrended fluctuation analysis algorithm is applied to determine the multifractal scaling behavior of the intensity patterns. The measurements are fitted with models used in the analysis of river runoff records. We show the surprising result that the multifractality decreases when the spatial coherence of the laser is decreased. Universal scaling properties could be applied to the spatial characterization of a laser propagating in a turbulent medium or random medium. OCIS codes: 010.3920, 030.1670, 030.7060, 290.1310.

It is proposed to use three interfering and coplanar laser beams to form the probe volume of laser Doppler systems. This allows us to obtain, for each particle crossing this probe volume, a Doppler signal whose frequency amplitude spectrum exhibits two characteristic peaks. Electromagnetic calculations and experimental validations clearly demonstrate that we can estimate simultaneously, from the analysis of these two frequency peaks, the particle position along the optical axis and one velocity component. This technique is expected to have great potentialities for velocity profile measurements in microfluidic or boundary layer flows, as well as for the sizing of spherical particles. OCIS codes: 280.3340, 120.0120, 120.3180, 290.5850, 280.2490.

A detailed study of surface laser damage performed on a nonlinear optical crystal, urea L-malic acid, using 7 ns laser pulses at 10 Hz repetition rate from a Q-switched Nd:YAG laser at wavelengths of 532 and 1064 nm is reported. The investigations reveal a direct correlation between the laser damage profile and hardness anisotropy.

Computational study of nanosecond pulse laser radiation in periodically poled LinbO3 (PPLN) crystals reveals the complex spatio-temporal evolution of the 1.064 mum fundamental harmonic (FH) and second harmonic (SH) energy fields with associated temperature fields, leading to the thermal dephasing and inhibition of second harmonic generation. (SHG). Selected PPLN conformal cooling parameters lead to the formation of a temperature-uniform quasi-phase-matching channel for a 300 mum diameter laser beam providing a high SHG efficiency.

The iridescence colors of abalone shell arise from Bragg diffraction of light from the layers of the nacre. The thickness of the aragonite nacre tiles is locally regular but varies during the growth cycles of the shell and this can give rise to complex color play. In Paua shell (Haliotis iris) and in H. fulgens (particularly the muscle scar shell) the thickness of the nacre tiles varies from 0.25(3) to 0.39(3) [micro]m, but locally the thickness is constant within domains of hundreds of tiles. Other species such as H. laevigata and H. rufescens are similar, but their tile thicknesses range from 0.35(4) to 0.52(4) [micro]m. In all species, the color displayed changes with observation angle and is due to layer diffraction. In H. iris and H. fulgens, the colors displayed encompass the complete visible spectrum; color hues are pure and are well-defined first-order diffraction colors. Shells of the other species display red and green, but not blue colors. The colors are rendered most vividly where dark organic growth layers are formed. These absorb or scatter light and enhance the iridescence colors. The origin and nature of the diffraction colors are compared with those observed in labradorite and opal. The degree of regularity in tile thickness needed to allow diffraction colors to be generated is modeled using pearl (sheet nacre) and abalone shell (columnar nacre) as examples. The wavelength dispersion is proportional to the product of the squares of the refractive indices of the material, the normalized standard deviation of the thickness, and the order of the diffraction color. For this reason, only first-order diffraction color is seen from shells.

A new device concept based on coherent processing of optical signals and allowing generation of ultrafast all-optical functions is presented. The device is modeled by rate equations and its functionality is demonstrated by studying the re-amplification and re-shaping (2R) regeneration of a 30-GHz signals in detail.

Continuous-wave (CW) as well as pulsed-laser-emission from a midinfrared IV-VI vertical-cavity surface-emitting laser (VCSEL) at 1.8K is presented. The results on the linewidth and the emitted power of CW and pulsed laser emission from PbSe VCSEL at 8 (mu)m are discussed.

The surface photovoltage (SPV) effect and its temporal profiles in a GaAs-GaAsP superlattice (SL) are measured by core-level photoelectron spectroscopy with the combination of synchrotron radiation and laser. The findings show that the SL with high-doping surface layer is suitable for the spin-polarized electron source without the SPV effect.

By variational approach, we analyze the characteristics of beam propagation through a cubic optical nonlinear medium using a laser beam that has a transverse elliptic Gaussian profile. The analytic solution to the normalized transmittance at the center of the far field as a function of medium position and the beam characteristics is obtained and compared with the numerical simulation, which is realized by a combination of algorithms. We also analyze the peak-valley transmittance difference as a function of medium length, ellipticity, and astigmatism. The relationship between peak-valley normalized transmittance difference of the z-scan trace and aperture size or the slit width are obtained. Meanwhile, the comparison of z-scan characteristics with an elliptic Gaussian beam with those using a circular symmetric Gaussian beam is made.

A new principle of lidar--radar is theoretically and experimentally investigated. The proposed architecture is based on the use of an rf modulation of the emitted light beam and a direct detection of the backscattered intensity. Use of a radar-processing chain allows one to obtain range and Doppler measurements with the advantages of lidar spatial resolution. We calculate the maximum range of this device, taking into account different possible improvements. In particular, we show that use of a pulsed two-frequency laser and a spatially multimode optical preamplification of the backscattered light leads to calculated ranges larger than 20 km, including the possibility of both range and Doppler measurements. The building blocks of this lidar--radar are tested experimentally: The radar processing of an rf-modulated backscattered cw laser beam is demonstrated at 532 nm, illustrating the Doppler and identification capabilities of the system. In addition, signal-to-noise ratio improvement by optical preamplification is demonstrated at 1.06 [micro]m. Finally, a two-frequency passively Q-switched Nd:YAG laser is developed. This laser then permits two-frequency pulses with tunable pulse duration (from 18 to 240 ns) and beat frequency (from 0 to 2.65 GHz) to be obtained.

Laser-induced incandescence applied to a heterogeneous, multielement reacting flow is characterized by temporally resolved emission spectra, time-resolved emission at selected detection wavelengths, and fluence dependence. Two-pulse laser measurements are used to further probe the effects of laser-induced changes on the optical signal. Laser fluences above 0.6 J/[cm.sup.2] at 1064 nm initiate laser-induced vaporization, yielding a lower incandescence intensity, as found through fluence-dependence measurements. Spectrally derived temperatures show that values of excitation laser fluence greater than this value lead to superheated plasmas with temperatures well above the vaporization point of carbon. The temporal evolution of the emission signal at these fluences is consistent with plasma dissipation processes, not incandescence from solidlike structures. Two-pulse laser experiments reveal that other material changes are produced at fluences below the apparent vaporization threshold, leading to nanostructures with different optical and thermal properties.

We present the results of a cw diode-pumped Nd:YV[O.sub.4] laser oscillator based on a self-starting adaptive gain-grating resonator. Adaptive laser operation has been demonstrated with 12-W output for 37 W of diode pumping, producing a TE[M.sub.00] mode that compensates for thermal aberrations. The issue of the finite aperture of the amplifier is discussed, and a design that incorporates an intracavity lens is used to improve the collection efficiency with severe thermal lensing at high pump powers. The powers of the beams involved in the resonator are compared with theory and are found to be in good agreement. Spectral and temporal behavior of the adaptive laser is investigated, and very interesting behavior is shown, including self-induced temporal modulation dynamics and a switching between a narrowband and a broad bandwidth of operation.

Experimental demonstration of a no-moving-parts free-space wavelength-multiplexed optical scanner (W-MOS) is presented. With fast tunable lasers or optical filters and planar wavelength dispersive elements such as diffraction gratings, this microsecond-speed scanner enables large several-centimeter apertures for subdegree angular scans. The proposed W-MOS design incorporates a unique optical amplifier and variable optical attenuator combination that enables the calibration and modulation of the scanner response, leading to any desired scanned laser beam power shaping. The experimental setup uses a tunable laser centered at 1560 nm and a 600-grooves/mm blazed reflection grating to accomplish an angular scan of 12.92[degrees] as the source is tuned over an 80-nm bandwidth. The values for calculated maximum optical beam divergance, required wavelength resolution, beam-pointing accuracy, and measured scanner insertion loss are 1.076 mrad, 0.172 nm, 0.06 mrad, and 4.88 dB, respectively. OCIS codes: 120.5800, 050.1950, 170.2150.

A vertical-cavity surface-emitting laser based bidirectional free-space optical interconnect has been implemented to interconnect two printed circuit boards. A total of 512 clustered channels with a density of 2844 channels/[cm.sup.2] are transmitted over a distance of 83 mm. The optical interconnect is a combination of refractive microlenses and diffractive minilens relays. OCIS codes: 200.2610, 200.4650, 220.4830, 200.4880, 250.7260, 350.3950.

Two methods are presented for the amplitude and phase recovery of optical beams with rotational symmetry. These are the tomographic method based on the ambiguity function and the one-step wavefront recovery based on the measurement of a phase-space distribution closely related to the Wigner distribution function. The results obtained from these two methods are compared, and the appropriateness of using either one of them for specific situations is discussed. OCIS codes: 100.0100, 100.2020, 140.0140, 140.3460.

A new kind of laser beam, called a decentered elliptical Gaussian beam (DEGB), is defined by a tensor method. The propagation formula for a DEGB passing through an axially nonsymmetrical paraxial optical system is derived through vector integration. The derived formula can be reduced to the formula for a fundamental elliptical Gaussian beam and a decentered Gaussian beam under certain conditions. As an example application of the derived formula, the propagation characteristics of a DEGB in free space are calculated and discussed. As another example we study the properties of a generalized laser beam array constructed by use of a DEGB as the fundamental mode. OCIS codes: 140.3300, 140.3290.

A decrease in the depolarization ratio by more than one order of magnitude by use of a recently proposed Faraday mirror (FM) in comparison with the traditional FM has been demonstrated experimentally. At a high average laser power, the possibility of an increase in the accuracy of compensation of depolarization in the active element by means of a [lambda]/4 plate with both the traditional and the novel FM is shown. OCIS codes: 260.1440, 140.3580, 230.3810.

Equations that describe the photobleaching of photochromic layers illuminated by Gaussian laser beams are given. The photochromic samples are made of thionine, triethanolamine, and polyvinyl alcohol and follow simple kinetics law. Spatial absorbance and time-dependent power transmittance are well described by the developed equations. The model is used to calculate the Gaussian dimension of helium-neon laser beams from kinetics data. OCIS codes: 260.5130, 090.2900.

The range-dependent overlap between the laser beam and the receiver field of view of a lidar can be determined experimentally if a pure molecular backscatter signal is measured in addition to the usually observed elastic backscatter signal, which consists of a molecular component and a particle component. Two methods, the direct determination of the overlap profile and an iterative approach, are presented and applied to a lidar measurement. The measured overlap profile accounts for actual system alignment and for all system parameters that are not explicitly known, such as actual laser beam divergence and spatial intensity distribution of the laser light. OCIS codes: 010.0010, 010.3640, 120.0120, 120.0280, 280.0280, 280.3640.

Two-dimensional distribution of the ground-state NO molecules density was investigated using laser-induced fluorescence (LIF) technique in a dc positive streamer corona reactor (needle-to-plate electrode geometry) during NO removal from a flue gas simulator (NO/air). NO density in the corona discharge reactor was monitored under the steady-state dc corona discharge condition. It was found that NO molecules density decreased due to the corona discharge processing not only in the discharging region but also in the upstream vicinity of the discharge. Index Terms--DC positive streamer corona, ground-state NO molecule, laser-induced fluorescence, NO removal.

Degenerate four-wave mixing (DFWM) line shapes and signal intensities are measured experimentally in well-characterized hydrogen-air flames operated over a wide range of equivalence ratios. We use both low (perturbative) and high (saturating) beam intensities in the phase-conjugate geometry. Resonances in the A (super 2)(SIGMA)(super +) -X (super 2)II (0,0) band of OH are probed with multiaxial-mode laser radiation. The effects of saturation on the line-center signal intensity and the resonance linewidth are investigated. The DFWM signal intensities are used to measure OH number densities in a series of near-adiabatic flames at equivalence ratios ranging from 0.5 to 1.5. Use of saturating pump intensities minimizes the effects of beam absorption, providing more-accurate number density measurements. The saturated DFWM results are in excellent agreement with OH absorption measurements and equilibrium calculations of OH number density. The polarization dependence of the P(sub 1)(2) and R(sub 2)(1) resonances is investigated in both laser intensity regimes. There is a significant change in relative reflectivities for different polarization configurations when saturated.

The spatial impulse response of antenna-coupled infrared detectors with dimensions comparable with the wavelength is obtained from a two-dimensional scan of a tightly focused C[O.sub.2]-laser beam. The method uses an experimental setup with submicrometer resolution and an iterative deconvolution algorithm. The measured spatial response is compared with numerically computed near-field distributions of a dipole antenna, with good agreement.

Laser-induced-damage thresholds (LIDT's) with various types of vitreous silica at 1064, 532,355, and 266 nm are investigated. At 1064 nm no difference in the LIDT was observed in any sample. At 1064-355 nm the wavelength dependence of the LIDT of synthetic fused silica (SFS) can be described well by the relation [I.sub.th] = 1.45[[Lambda].sup.0.43], where [I.sub.th] is the LIDT in J/[cm.sup.2] and [Lambda] is the wavelength in nanometers. At 266 nm, however, LIDT's were smaller than half of the calculated value from the relation above. This difference can be explained by the damage mechanism; at 266 nm two-photon absorption-induced defects lower the LIDT as in the case of KrF-excimer-laser-induced defects, whereas at longer wavelengths the two-photon process does not occur. LIDT's of fused quartz (FQ) at 532 and 355 nm and that of SFS containing [approximately]1000 ppm of Cl and no OH at 355 nm were a little lower than those of the other SFS's. This lower LIDT may be related to the absorption of metallic impurities in FQ and dissolved [Cl.sub.2] molecules in SFS. At 266 nm, on the other hand, LIDT's of FQ's were higher than those of most SFS's.

A hollow fiber composed of a glass capillary tube and a metal thin film upon the inside of the tube is proposed for the delivery of ArF-excimer laser light. From theoretical analysis, aluminum is chosen as the metal layer. A thin aluminum film is deposited by metallorganic chemical-vapor deposition, with dimethylethylamine alane employed as the source material. Measured loss spectra in vacuum-ultraviolet and ultraviolet regions and losses for ArF-excimer laser light show the low-loss property of the aluminum-coated fiber at the 193-nm wavelength of ArF-excimer laser light. The straight loss of the 1-m long, 1-mm-bore fiber is 1.0 dB.

A theoretical analysis of a thermal defocusing optimal limiter's performance in a transient environment is presented. The situation occurs when the duration of the laser pulse is comparable to the time of the acoustic transit. The analysis, which used space- and time-dependent refractive index changes to calculate the nonlinear pulse change experienced by the pulse as it travels through the medium, supports the idea that the performance of the optical limiter is dependent on the laser pulse's duration.

A study of the time evolution of the transversal modes contained in a TEA CO2 laser cavity has been conducted via the analysis of the time-varying beam quality factor of the emitted pulse. The study reveals a substantial change in the beam quality factor during the pulse evolution stage. The results, when interpreted based on the appearance of a specific mode and its growth process, suggest an evolution by the laser cavity modes towards an almost stationary behavior.

This paper proposes a beamforming scheme for suppressing coherent interference with an array of arbitrary geometry. The scheme first uses estimates of the source directions to construct a transformation, which removes the desired signal while retaining the coherent interference. Optimum beamforming is then performed on the transformed data containing only interference and noise to produce the maximum output signal-to-interference-plus-noise ratio (SINR). Analysis and numerical results demonstrate that the proposed complementally transformed beamformer significantly outperforms the conventional multiply constrained minimum variance (MCMV) beamformers. Index Terms - Adaptive arrays.

A study was conducted to examine the lasing properties of a circular grating-coupled surface-emitting laser (GCSEL's) with an integrated focusing outcoupler. Results show that GCSEL's are lasing in mutually incoherent and near-orthogonal quasi-linear distributed Bragg reflector elements, rather than the ideal clean circular modes. This behavior is observed to effect the degradation of the focused spot quality.

In laser projection systems the observer in the far field of the image points on the screen will recognize serious speckle noise. There are many methods to reduce or eliminate speckles in the near field by reducing or eliminating temporal or spatial coherence of the laser. But for the far field it is hardly possible to change the coherence properties of laser sources so that speckles will disappear. We propose a new method for eliminating speckles in the far field by using a diffractive optical element. The intensity modulation depth in the far-field speckle pattern can be reduced to a few percent while good beam quality is preserved.

The far-field pattern of an onboard laser transmitter was measured with a transatmospheric optical link with a distance of [approximately]33,000 km between the satellite and the optical ground station. The far-field pattern was acquired with a new method used to analyze statistically downlink irradiance data obtained at the ground station. The statistical tracking and pointing characteristics of the transmitter were taken into account in estimating downlink irradiance, assuming that there were no atmospheric scintillation effects. The peak directive gain of the downlink laser beam was 104.3 dB. The beam width (full width at half-maximum) was 28.5 x 17.5 [micro]rad. These results were consistent with the results from a laboratory test undertaken before launch of the satellite.

An algorithm is presented for calculating the phase difference that is obtained with rapid-switching, double-pulsed holographic interferometry. Imperfect switching between reference beams in between two laser pulses causes a distortion in the phase-stepped interferograms that results in erroneous phase calculation when conventional phase-calculating algorithms are used. Instead of estimating the error that is involved, an extra step is added to a more conventional algorithm such as Carre's algorithm, so that this leakage effect is compensated for. Thus the desired phase difference is found. Also, a measure is found for excluding unreliable calculations, based on the light intensities and phase steps for each pixel and the leakage ratios. OCIS codes: 090.2880, 120.2650, 120.5050.

To improve the frequency-doubling efficiency in type II second-harmonic generation (SHG), a fundamental walkoff-compensated SHG scheme was geometrically analyzed and its usefulness was experimentally demonstrated in a 12-mm length of KTiOPO4 with 20% power enhancement and in a 10-mm length of LiB3O5 with double enhancement. OCIS codes: 190.2620, 190.4160.