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The pulse-buildup in miniature passively Q-switched lasers occurs in a similar time-scale as the phonon-assisted thermalization of the laser manifolds. We study how the time-dynamics of the laser is affected by the thermalization and relaxation processes using a dimensionless geometrical rate equation model for a homogeneously broadened four-level gain medium. The pulse length is found to depend strongly on the thermalization rate when the ratio of the ground-state absorption cross section of the saturable absorber to the spectroscopic emission cross section of the laser transition is small (lsim 10). Numerically calculated design curves are shown for the 1064 nm transition in Nd:YAG, and guidelines are given for applying the model to other transitions. Experimental results are used for estimating the thermalization time constant of Nd:YAG for the 1 mum transition group and the ground-state absorption cross section of the Cr4+:YAG saturable absorber crystal.

We exploit nondegenerate four-wave mixing to generate narrow-bandwidth visible light from blue to orange in microstructured optical fiber. The process is excited by nanosecond dual-wavelength pump pulses (532/1064 nm) produced by a frequency-doubled passively Q-switched Nd:YAG laser. A linearly polarized, fundamental mode signal wave is generated in the visible, accompanied by an idler wave in the near-infrared. The signal and idler wavelengths are adjustable by the design of the microstructure.

We report on generation of 946 nm laser pulses of a few nanosecond duration and up to 3.7 kW peak power from a compact diode-pumped passively Q-switched Nd:YAG laser. This power is 2.5 times as much as what previously has been obtained from this type of a laser. The short pulses with the record high peak power may be particularly attractive for laser range finding type applications.

A microcavity laser pumped by a pulsed evanescent optical wave is demonstrated. The laser radiates intense, linearly polarized light isotropically in a plane perpendicular to the axis of the cylindrical microcavity. The lasing was achieved by surrounding a small section of a glass capillary with a solution of rhodamine 6G and by coupling the pump light into the capillary wall. The laser modes are the whispering gallery modes which orbit in the capillary by total internal reflection. The laser gain is provided by the dye molecules around the capillary, where the evanescent waves of the modes spatially overlap with the evanescent part of the pump field. The lasing threshold pump energy was ∼100 nJ/pulse at a pump pulse duration of 6 ns.

We demonstrate a simple and compact laser source that directly produces a Bessel–Gauss beam. The laser resonator consists of a diode-end-pumped Nd:YAG crystal, a planar mirror, and a diffractive mirror designed to phase-conjugate only the lowest-order Bessel–Gauss beam.

We examine the idea to use self-focusing in a non-linear liquid crystal to increase the accuracy of measurements of wavefront distortions with an active Shack–Hartmann sensor. This modification should improve the measurement accuracy by two orders of magnitude.

We present a simple method to convert a Gaussian laser beam into an annular beam using a homeotropically oriented nematic liquid crystal. The method allows creation of a beam with sub-millimeter diameter and a width of a few tens of microns for a propagation distance of more than 10 mm. High spatial gradients in the radial intensity distribution make the beams promising for use in atom trapping and guiding.

A hyperspectral remote sensing instrument employing a novel near-infrared supercontinuum light source has been developed for active illumination and identification of targets. The supercontinuum is generated in a standard normal dispersion multi-mode fiber and has 16 W total optical output power covering 1000 nm to 2300 nm spectral range. A commercial 256-channel infrared spectrometer was used for broadband infrared detection. The feasibility of the presented hyperspectral measurement approach was investigated both indoors and in the field. Reflection spectra from several diffusive targets were successfully measured and a measurement range of 1.5 km was demonstrated.

The aim of this work was to develop a cost effective hyperspectral instrument and to demonstrate the acquisition of IR reflection spectra over long distances.

The application of a new microchip laser source for Raman spectral measurements is demonstrated. The performance of the device is evaluated and illustrated by Raman spectra of diamond thin films and a solid-state laser host material.

We study experimentally the spectral evolution of supercontinua in two different microstructured fibers that are pumped with nanosecond pulses from dual-wavelength sources of either 1064/532 nm or 946/473 nm output. The experimental findings are compared with simulations based on numerically solving the nonlinear Schrodinger equation. The role of cascaded cross-phase modulation processes and the group-delay properties of the fiber are emphasized and demonstrated to determine the extent of the broadening of the continua to the visible wavelengths.

Modifying the output pulses of a passively Q-switched Nd:YAG laser, operating at 1064 nm, was realized by heating the laser crystal. With the demonstrated laser setups, a 100 K temperature rise led to a more than 50% increase in the pulse energy and a more than 10% decrease in the pulse length. This method offers an effective way to tune the output of the laser without mechanical adjustment or a change of components.

We report on a compact UV-laser with a short pulse length of 1.9 ns at 236 nm. A passively Q-switched quasi-three-level Nd:YAG laser at 946 nm acts as the pump source. UV pulses are produced by two consecutive single-pass frequency doubling events, the first one from IR to blue with a BIBO crystal and the second one from blue to deep-UV with a beta-BBO crystal. Conversion efficiency from 946 nm to 473 nm is 28% and from blue to UV 7%. Average power for UV is 7.6 mW with a energy and peak power of 230 nJ, and 120 W respectively.

Ferroelectric domain inversion has been demonstrated in BaMgF(4) . Transparency has been measured to140nm, and no change in transmission was measured under 157-nm irradiation for1.1x10(9) shots at 2mJ/cm(2) per pulse. First-order quasi-phase-matched generation of 157 nm is predicted by use of grating periods as long as 1.5mum. This material should permit shorter-wavelength chi((2)) frequency-mixing processes than with any other crystalline material.

We demonstrate the use of a miniature gain-switched Ti:Sapphire laser for efficient generation of visible supercontinuum light in a highly nonlinear microstructured optical fiber. This allows for a compact setup that puts out nanosecond pulses of light that cover the spectral range from 410 to 1300 nm. It offers a low-cost alternative to the mode-locked-laser-pumped systems as a source of visible supercontinuum light.

Light sources with a broad spectral output and diffraction limited beam quality have a wide variety of present and future applications. A few of particular interest are hyperspectral laser radar for environmental monitoring, active hyperspectral imaging for detection and identification of objects, and speckle-free illumination. With the exception of systems based on amplified femto- or picosecond lasers, which are large and extremely complicated, pulse energies from supercontinuum laser sources have been limited to

Summary form only given. We report cascade laser action at 1.4 /spl mu/m and 3.9 /spl mu/m in 10% Ho:BaY/sub 2/F/sub 8/ (Ho:BYF) pumped by a Q-switched, frequency-doubled Nd:YAG laser at 532 nm. At this high concentration we measured an absorption coefficient of 2.42 cm/sup -1/ for polarization parallel to the b-axis, which is adequate for end pumping.

The development of the Cr-doped colquiriite laser crystals, LiCaAlF/sub 6/ (LiCAF), LiSrAlF/sub 6/ (LiSAF), LiSrGaF/sub 6/ (LiSGaF) and LiCaGaF/sub 6/ (LiCaGaF) started with LiCAF. In this paper the optical and laser properties and growth and thermo-optic properties of these materials are studied.

An attractive approach for building high-power laser systems is to use laser arrays with many lower power array elements. In order to achieve high brightness from these laser arrays, beam combining techniques must be employed. We are developing a beam combining technique, spectral beam combining, which is robust and has the potential to beam combine arrays with many array elements. In spectral beam combining, the various laser array elements operate at slightly different wavelengths which an then spatially overlapped. We have made proof-of-principle demonstrations of spectral beam combining on one-dimensional laser arrays with fiber and with semiconductor array elements and shown beam combining of up to 11 array elements in these initial experiments. Simple scaling laws dictate that the maximum number of gain elements in the array is proportional to the available optical gain bandwidth and the size of the system. Using typical numbers for fibers and diode arrays, it can be shown that it should be possible to combine 10's to 100's of array elements. Experiments to scale the number of array elements, understand key issues such as cross-talk, and increase efficiency are on-going.

Miniature gain-switched lasers, pumped by passively Q-switched microchip lasers, provide robust sources of nanosecond and subnanosecond pulses at diverse wavelengths from the ultraviolet to the mid infrared.

Summary form only given. Here, we report on ferroelectric domain inversion in BaMgF/sub 4/ (BMF). This material has transparency to

Summary form only given. We believe we report the first demonstration of high-power GaInSb-InAs type-II QW lasers incorporating GaInAsSb absorber layers. To ensure good carrier transport from the absorber layers to the active wells, the absorber layers were inserted between each active well region.

Mid-infrared optically pumped semiconductor lasers (OPSLs) are presently being investigated for a variety of commercial and military applications. Active regions in such optically pumped lasers must meet the dual requirements of high gain and low loss at mid-IR wavelengths, combined with sufficient absorption of the optical pump at shorter wavelengths for efficient power conversion. In this paper we report the successful growth, fabrication, and characterization of high-performance OPSLs that employ novel active regions consisting of combinations of GalnAsSb integrated-absorber layers with type-II GaInSb/InAs quantum well regions. With 1.85-µm optical pumping at 85 K, OPSLs with such active regions have exhibited a peak output power of 2.1 W at 3.9 pm, improved beam quality, power conversion efficiency of ∼8%, and characteristic temperatures of ∼47 K.

We demonstrate an all solid state, red, green and blue laser. Pr:YLF pumped by a frequency doubled Cr:LiSGaF laser produces pulsed output in the visible region of the spectrum.

Noncritical temperature-tuned phase-matching and large nonlinear coefficients make potassium niobate an attractive material for frequency doubling tuneable near-infrared radiation. We have mounted a KNbO 3 crystal intracavity in an argon ion pumped, continuous wave Ti:Sapphire ring laser to increase the power level of the second harmonic. Wavelength selection at the fundamental frequency is accomplished with a birefringent filter. By using the crystal orientation that defines the d 32 coefficient of KNbO 3 we have obtained a blue second harmonic output tuneable from 425-445 nm. The laser is also characterized by the narrow linewidth of the Ti:Sapphire ring oscillator and good temporal stability. A continuous wave, frequency doubled Ti:sapphire laser is well suited to excite the resonance Raman spectrum in heme proteins with strong absorption bands in the range of 400 to 450 nm. We demonstrate the feasibility of such a setup for Raman studies of ligand binding to myoglobin. The Raman bands yield information on the reaction dynamics and on conformational changes near the linkage between the heme and the protein. In particular, a shift of the stretch frequency of the iron- histidine bond with high pressure may be attributed to a protein conformational change.

Fluorophospates and fluorovanadates are efficient solid state laser materials with promising new applications, especially for diode pumping of microchip lasers. High quality, low loss Nd doped Sr 5 (PO 4 ) 3 F, Ca 5 (PO 4 ) 3 F, Sr 5 (VO 4 ) 3 F and Ca 5 (VO 4 ) 3 F crystals were grown by the Czochralski technique. The lattice vibrations of the host material are studied by polarized Raman spectroscopy. The Raman active modes are determined by the irreducible representations of the space group of the crystal, and they provide insight to the crystal symmetry and chemical bonding. In all four compounds the internal and external vibrations are separated in the Raman spectra indicating that the internal binding of the (PO 4 ) -3 and (VO 4 ) -3 tetrahedra is different from the other ionic forces in the crystals. The group of internal modes in the fluorovanadates is shifted to lower frequencies by more than 100 cm -1 compared with the fluorophosphates, though the x-ray structures are isomorphous. In addition there are remarkable changes in intensity, which may be attributed to interaction among the tetrahedral subunits in the hexagonal unit cell. The substitution of Sr for Ca causes frequency shifts in the vibrational modes. These are discussed with respect to the mass effect and changes in the coupling strength due to the differences between alkaline-earth cation binding and oxygen binding in the tetrahedral subunits. A comparison of the various substitutions makes assignments of the vibrational modes possible.

We present the concept and both the experimental and computational study of a simple supercontinuum light source emitting at temporally highly stable output powers. The principle of the light source is based on a standard pulsed supercontinuum source combined with fiber-based dispersive time-stretching. This approach allows for tailored spectral emission in the visible at a power stability of below 1%. Furthermore, the computation indicates that highly stable light emission with this concept does not necessarily require highest possible input pulse repetition rates and longest dispersive fiber lengths.

A simple and efficient method to convert a Gaussian laser beam into a nearly non-diverging Bessel-like beam or into a thin-walled hollow beam is described. The optical system used for the beam conversion consists of a thin liquid-crystal cell and one or two lenses. At certain parameter values, self-focusing of a Gaussian beam directly results in the formation of a narrow Bessel-like beam, and, if an additional lens is used to collimate the self-focused beam, the collimated beam shows an accurate ring-shaped profile.

We present a simple and efficient method to convert a Gaussian laser beam into a Bessel-like beam with a long and narrow focal line by using a nematic liquid crystal with a high third-order nonlinearity.

The influence of high pressure on the heme protein conformation of myoglobin in different ligation states is studied using Raman spectroscopy over the temperature range from 30 to 295 K. Photostationary experiments monitoring the oxidation state marker bands demonstrate the change of rebinding rate with pressure. While frequency changes of vibrational modes associated with rigid bonds of the porphyrin ring are

The laser reported in this work has a gain medium pumped directly with an evanescent optical wave. Bright disk laser radiation is observed to propagate isotropically in a plane perpendicular to the capillary axis.