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A newly developed branch of ultra-high-pressure chemistry, which employs high pressure to create the necessary reaction conditions, to transform simple hydrocarbons and monochromatic light to direct the chemical reaction in selective paths, is presented. An overview of the effects that can be obtained by the combined use of pressure and laser light is depicted.

A theoretical formalism for the stabilization of the CMC-VCSEL (Concave Micromirrorcapped Vertical Cavity Surface Emitting Lasers) operation to the transverse mode is explained. A detailed numerical calculation of the mode discriminating factors is lined out.

A technique for calculating the temperature of the nonequilibrium electron distribution functions in general quantum well intersubband devices is presented. It is shown that at low current densities the electron temperature recovers the expected physical limit of the lattice temperature, and that it is a function of current density and the quantised energy level structure of the device.

A study was conducted, by using surface photovoltage spectroscopy (SPS) and normal-incidence reflectivity, to investigate a 1.3 mue m InGaAlAs/InP (001) vertical-cavity surface-emitting laser (VCSEL) structure. The result demonstrates the considerable potential of SPS for the characterization of these device structures.

The effectiveness of using the line-source laser ultrasonics to investigate circumferential waves on thin cylindrical shells is presented. The technique enables a clear recognition of the multimode wave forms in the time signals, and identifies the dispersion features of multimode circumferential waves and obtain the phase and group velocities.

A study was conducted to investigate the influence of oxide aperture size and number of top distributed Bragg reflector pairs on the performance of oxide confined vertical-cavity surface emitting lasers. The result shows that optimal performance was achieved for similar values under either static or dynamic operation.

The analysis for a realistic situation, when the high intercavity light intensity typical in vertical cavity surface-emitting lasers (VCSELs) leads to high nonequilibrium electron hole plasma densities in the modulator layers, significantly decreasing the absorption coefficient in the layer radically due to band-fitting effect, is shown. A specialized laser construction to achieve the purpose is proposed.

This study explores the relationship between laser waveforms and canopy structure parameters and the effects of the spatial arrangement of canopy structure on this relationship through a geometric optical model. Studying laser waveforms for such plant canopies is needed for the advanced retrieval of three-dimensional (3-D) canopy structure parameters from the vegetation canopy lidar (VCL) mission. For discontinuous plant canopies, a hybrid geometric optical and radiative transfer (GORT) model describing the effects of 3-D canopy structure parameters of discrete canopies on the radiation environment has been modified for use with lidar. The GORT model is first used to describe the canopy lidar waveforms as a function of canopy structure parameters and then validated using scanning lidar imager of canopies by echo recovery (SLICER) data collected in conifer forests in central Canada during the boreal ecosystem-atmosphere study (BOREAS). Model simulations show that the clumping in natural vegetation, such as leaves clustering into tree crowns causes larger gap probability and smaller waveforms for discontinuous plant canopies than for horizontally homogeneous plant canopies. Ignoring the clumping effect can result in significantly lower values for the estimated foliage amount in the profile and in turn lower estimated biomass. Because of clumping, only the gap probability and apparent vertical projected foliage profile can be directly retrieved from the canopy lidar data. The retrieval is sensitive to the ratio of the volume backscattering coefficients of the vegetation and background, and this ratio depends on canopy architecture as well as foliage spectral characteristics. Extensions of the GORT model from single-layered canopies to include multilayered ones are also explored. Index Terms--Geometric optical and radiative transfer (GORT) model, heterogeneous plant canopies, lidar waveforms.

We report on a 1.57-[micro]m wavelength singly resonant optical parametric oscillator (OPO) using a non-critically phase-matched KTP crystal intracavity pumped by an electro-optically Q-switched Nd:YAG laser. A simple model for numerical calculation of the temporal profile of the laser and signal pulses developed inside the intracavity pumped OPO (IPOPO) resonator is described. Working conditions for single-pulse and multipulse parametric oscillation are established. A single signal pulse of 8.1-mJ output energy was obtained when the laser was pumped three times above the pulsed IPOPO threshold. A pulse duration of 5.9 ns was measured at 1.5 times above threshold for the IPOPO. OCIS codes: 190.4410, 190.4970, 320.4240, 140.3580, 140.3540, 140.3360.

A 50-mJ green beam was generated at a 1-kHz repetition rate by intracavity frequency doubling of a quasi-cw laser-diode-pumped Nd:YAG laser. The green laser was used for 12-mJ fourth-harmonic beam generation with a [CsLiB.sub.6][O.sub.10] crystal. OCIS codes: 140.3480, 140.3540, 140.3610, 140.7300.

We report on tuned-laser, pump--probe-gain, and fluorescence yield studies of the effect that crystal temperature plays on the polarized emission characteristics of Ce:LiLuF. It was found that [Sigma]-polarized emission at the 327-nm fluorescence spectra peak is characterized by smaller laser pulse buildup times, higher small-signal gains, and smaller output powers than the [Pi]-polarized 327-nm emission. We concluded that excited-state absorption (ESA) (and the resultant formation of color centers) is more severe for [Sigma]-polarized emission than for [Pi]-polarized emission in this spectral region. We postulate that the enhancement in laser performance and crystal fluorescence observed with crystal cooling is due to narrowing of the ESA absorption band that reduces the probability of ESA and color-center formation. OCIS codes: 140.0140, 140.3320, 140.3610, 140.3580, 140.6810.

By using a continuous-wave Ti:sapphire laser as a pumping source, we demonstrated a passively Q-switched Yb:YAG laser at room temperature with [Cr.sup.4+]:YAG as the saturable absorber. We achieved an average output power of as much as 55 mW at 1.03 [micro]m with a pulse width (FWHM) as short as 350 ns. The initial transmission of the [Cr.sup.4+]:YAG has an effect on the pulse duration (FWHM) and the repetition rate of the Yb:YAG passively Q-switched laser. The Yb:YAG crystal can be a most promising passively Q-switched laser crystal for compact, efficient, solid-state lasers. OCIS codes: 140.3540, 140.5680, 140.3580.

A novel system for on-line measurement of the distance from the melt pool to the lens in laser material processing is described. A spectrometer analyzes the broadband radiation that is produced at the laser-workpiece interaction zone and then focused by the effector optics in the direction of the laser source. From the influence of chromatic aberration on the detected radiation spectrum, the distance from the workpiece to the lens can be derived. An analytical calculation of the shift of the melt pool spectrum that depends on the distance between the molten zone and the focusing lens shows good agreement with the measured results. OCIS codes: 140.3390, 120.3940, 120.2830, 120.3930.

Light monitoring will serve as an intercalibration for compact muon solenoid (CMS) lead tungstate crystals in situ at the large hadronic collider, which is crucial for maintaining crystal calorimeter's subpercent constant term in the energy resolution. This paper presents the design of the CMS electromagnetic calorimeter monitoring light source and high-level distribution system. The correlations between variations of the light output and the transmittance for the CMS choice of yttrium-doped Pb[WO.sub.4] crystals were investigated and were used to study monitoring linearity and sensitivity as a function of wavelength. The monitoring wavelength was determined so that a good linearity as well as adequate sensitivity can be achieved. The performance of a custom manufactured tunable laser system is presented. Issues related to monitoring precision are discussed. Index Terms--Calibration, crystal, laser, monitoring, radiation damage.

Passive Q switching of a tunable alexandrite solid-state laser with a Cr:[Y.sub.2]Si[O.sub.5] solid-state saturable absorber is numerically studied over a major portion of the alexandrite tuning range. The theory of passive Q switching with a slowly relaxing saturable absorber is studied and utilized for evaluating the performance of the Cr:YSO Q-switched alexandrite laser system. With a typical laser configuration, a Q-switched laser pulse of 262 mJ in 23 ns is obtained. [C] 2001 Optical Society of America OCIS codes: 140.3430, 140.3540, 140.3580, 140.3600.

The U-Pb ages of fine-grained zircon separated from 2 dust-dominated soils in the eastern highlands of south-eastern Australia and measured by ion microprobe (SHRIMP) revealed a characteristic age `fingerprint' from which the source of the dust has been determined and by which it will be possible to assess the contribution of dust to other soil profiles. The 2 soils are dominated by zircon 400-600 and 1000-1200 Ma old, derived from Palaeozoic granites and sediments of the Lachlan Fold Belt, but also contain significant components 100-300 Ma old, characteristic of igneous rocks in the New England Fold Belt in northern New South Wales and Queensland. This pattern closely matches that of sediments of the Murray-Darling Basin, especially the Mallee dunefield, suggesting that weathering of rocks in the eastern highlands has contributed large quantities of sediment to the arid and semi-arid inland basins via internally draining rivers of the present and past Murray-Darling River systems, where it has formed a major source of dust subsequently blown eastwards and deposited in the highland soils of eastern Australia. Additional keywords: aeolian dust, dust deposition, dust provenance., Introduction Windblown dust contributes significantly to soil formation in many regions worldwide (Simonson 1995). In south-eastern Australia, dust is carried from the arid and semi-arid interior and deposited in the [...]

We demonstrate what we believe is the first application of the recently developed electrically pumped GaAs/A1GaAs quantum-cascade lasers in a spectroscopic gas-sensing system by use of hollow waveguides. Laser light with an emission maximum at 10.009 [micro]m is used to investigate the mid-infrared absorption of ethene at atmospheric pressure. We used a 434-mm-long silver-coated silica hollow waveguide as a sensing element, which served as a gas absorption cell. Different mixtures of helium and ethene with known concentrations are flushed through the waveguide while the laser radiation that passes through the waveguide is analyzed with a Fourier-transform infrared spectrometer. The experimentally obtained discrete ethene spectrum agrees well with the calculated spectrum. A detection threshold of 250 parts per million is achieved with the current setup. [C] 2000 Optical Society of America OCIS codes: 300.1030, 300.6260, 140.3600, 000.2107, 060.2370, 300.6390.

A high-frequency train of 5-100-ps pulses (picket fence) is proposed to improve significantly the third-harmonic frequency conversion of Nd:glass lasers that are used to generate high-contrast-shaped pulses for inertial confinement fusion (ICF) targets. High conversion efficiency of the low-power foot of a shaped ICF pulse is obtained by use of a low duty cycle, multi-gigahertz train of ~20-ps pulses with high peak power. Even with less than 10% duty cycle, continuous illumination is maintained on the target by a combination of temporal broadening schemes. The picket fence approach is analyzed, and the practical limits are identified as applied to the National Ignition Facility laser. It is found that the higher conversion efficiency allows ~40% more third-harmonic energy to be delivered to the target, potentially enabling the larger drive needed for high-yield ICF target designs. In addition, the frequency conversion efficiency of these short pulses saturates much more readily, which reduces the transfer of fluctuations at the fundamental and thus greatly improves the power stability of the third harmonic. [C] 2000 Optical Society of America OCIS codes: 190.2620, 350.2660, 320.7090, 320.7110, 320.5540.

Formation of speckled speckles in the case of biflow perfusion by partially coherent light was considered. Dependencies of statistical characteristics of low-coherence biospeckles with a small number of scatterers on the scattering properties of the flow and on the coherence length of incident light were analyzed. It was shown that the value of the Doppler bandwidth in the scattered light essentially depends on the ratio between the coherence length and the average size of the flow's inhomogeneities. A procedure for reconstructing velocity distribution in a single blood vessel was suggested. [C] 2000 Optical Society of America OCIS codes: 170.0170, 290.0290.

The lasing performance of single-cavity and double-cavity Tm,Ho:YLF lasers was measured experimentally. The maximum, single-longitudinal mode output power for the double-cavity laser was 30 mW, whereas for the single-cavity laser it was 7 mW. We determined the frequency stabilities to be 600 Hz for a single-cavity laser and 300 Hz for a double-cavity laser, by measuring the fluctuation of a self-heterodyne beat signal for a 1.5- [micro] s delay time over a 10-min integrated period. In addition, we obtained a 15-GHz frequency tuning range for the double-cavity laser by changing its cavity length under maximum stable conditions at room temperature. OCIS codes: 140.0140, 140.3070, 140.3480, 140.3570, 140.3580.

A new theoretical derivation that makes it possible to compute the performance of a quasi-three-level longitudinally pumped cw laser is proposed. This theory, which takes into account the laser wave amplification and the pump wave absorption saturation coupling, seems simpler and more accurate than what has been previously published. The model accounts for single-pass, double-pass, and resonant pumping and can be used to characterize the thermal effect in the gain medium. It is also well suited for designing and optimizing such lasers. As an example, the theory is applied to the well-known Yb:YAG gain medium. [C] 2000 Optical Society of America OCIS codes: 140.0140, 140.5680.

Nulling interferometry, a proposed technique for dimming a star relative to its surroundings by destructively interfering the light collected by two individual telescopes [Bracewell, Nature 274, 780-781 (1978); Shao and Colavita, Ann. Rev. Astron. Astrophys. 30, 457-498 (1992)], has the potential to permit the direct detection of nearby extrasolar planets. However, because of the extremely high degree of symmetry required for useful levels of starlight nulling, the technique remains in its infancy. We present results of laboratory experiments with a rotational shearing interferometer that are aimed at demonstrating the feasibility of deep nulling at the levels needed for direct planet detection. Our first results include the successful nulling of red laser light to a part in [10.sup.5] and the stabilization of the null leakage to a part in [10.sup.4]. [C] 1999 Optical Society of America OCIS codes: 260.3160, 350.1260.

The band structures, absorption coefficient due to intervalence subband transition and optical gain in mid-infrared type II InAs/GaInSb/A1Sb interband cascade lasers are determined using an eight-band k.p model. It is shown that the band structures for the A1Sb/InAs (25 angstrom)/GaInSb (34 angstrom)/A1Sb quantum well active region in a type II interband laser at 800 and 300 Kelvin are a function of an in-plane wave vector.