Dielectric waveguide with periodic surface corrugation are used in distributed feedback lasers and DBR lasers. In this paper the boundary element method (BEM) has been used to analyze 2D dielectric periodic corrugated waveguides. It is a very efficient method for analysis of this type of structure. The computational method relies on the numerical solution of the integral wave equation inside the grating region. This formalism has distinct advantages over the more traditional ones, especially when the boundary conditions are imposed through a collocation (point-matching) technique. The unknown field quantities together with all the boundary conditions of the problem are explicitly incorporated in the defining equation. For the problem at hand, the boundary conditions on the longitudinal interfaces of the grating layer are functionally known because of the Floquet expansion of the fields in the uniform layers above and below it. On the other hand, the boundary conditions for the interface between the periodic unit cells are naturally provided by Floquet's theorem and continuity requirements. Thus the method can be applied in a rather straightforward way towards a rigorous solution of the periodic problem, without any a priori assumptions, within a user specified accuracy. The BEM is a natural choice for this problem because we seek the field solution only on the grating layer interfaces in order to set up a transverse resonant-type characteristic equation for propagating mode. In this paper electromagnetic field and coupling coefficient for multi- layer dielectric waveguide is calculated.

Experimental results on the realization and characterization of microspherical lasers at 1.56 micrometers with Er-doped ZBLAN glasses are presented. The lasers are excited through an evanescent wave coupling. Thresholds of 600 (mu) W have been obtained. Multimode operation has been observed with linewidths of the order of 250 KHz.

The spontaneous cooperative emission (superradiance) of initially excited two-level active centers (atoms) inside Fabry-Perot resonator was considered. With the help of numerical solution of coupled Maxwell-Bloch equations the kinetics of atomic system and output field evolution were obtained. The strong dependencies of the superradiance pulse parameters on the resonator characteristics were analyzed.

A Fourier-optical set-up within the external cavity of a commercially available broad-area laser diode to select certain transverse modes is investigated experimentally. The external cavity consists of a lens and a spatial frequency filter, the latter consisting of a reflecting slit (perpendicular to the active layer) surrounded by a darkened background. This is a Fourier-optical 4f set-up (2f plus reflection). The laser employed first is a partially antireflection coated 0.25 W 655 nm AlGaInP broad area laser. The free running laser shows non-stationary filamentation. Placing the slit directly onto the optical axis gives cw fundamental mode operation and a transverse shift of the spatial filter allows for selective excitation of higher order modes at low pump currents. Next, a highly antireflection coated 1.2 W 811 nm AlGaAs broad area laser is utilized in the 4f set-up. Selective excitation of higher order modes is achieved at high pump currents. Another approach to support fundamental mode operation uses a 2f set-up (1f plus reflection) consisting of a concave mirror at a distance f away from the laser facet. Here, the laser facet with its active region dimensions is the spatial filter. Also, the feasibility of autocatalytic mode coupling for reduction of unstable filamentation of broad-area lasers is examined experimentally.

We present a detailed analysis of the effect of volumetric and surface inhomogeneities as a source of quality-factor limitation and intracavity resonant backscattering in optical microsphere cavities of fused silica. Intrinsic scattering in microspheres is shown to be significantly inhibited as compared to standard Rayleigh scattering in the bulk material. This reassessment of fundamental losses indicates that Q-factors substantially exceeding the previously expected limit of approximately 10¹¹ can be obtained in microspheres, as soon as surface hydration is prevented. The intracavity backscattering is analyzed as a source of whispering-gallery mode splitting and resonant optical feedback in presence of a mode-matched travelling- wave coupler.

We show that the coordinate-transformed mode which is the transformation from a Gaussian profile to a uniform circular one inside a cavity, is selected through iteration of round trips, using Fox-Li simulation in a bare cavity. When the phase constraint due to cavity mirrors is predominant, the intensity profiles converge to the desired profiles.

We demonstrate a new all-optical method of moire fringe analysis for the purpose of fast wavefront detection and correction of single ultrashort light pulses. The magnitude and sense of wavefront curvature is determined by fringe orientation. Single-shot fringe processing takes place at the Fourier plane of an imaging lens with an apodized slit as the transmission filter. The curvature (directional 2^nd derivative) of the wavefront shape is obtained as an image. Results imply the possibility of fast detection and correction of single pulses.

With submillimeter size and optical Q up to approximately 10¹⁰, microspheres with whispering-gallery (WG) modes are attractive new component for fiber-optics/photonics applications and a potential core in ultra-compact high- spectral-purity optical and microwave oscillators. In addition to earlier demonstrated optical locking of diode laser to WG mode in a microsphere, we report on microsphere application in the microwave optoelectronic oscillator, OEO. In OEO, a steady-state microwave modulation of optical carrier is obtained in a closed loop including electro- optical modulator, fiber-optic delay, detector and microwave amplifier. OEO demonstrates exceptionally low phase noise (-140 dBc/Hz at 10 kHz from approximately 10 GHz carrier) with a fiber length approximately 2 km. Current technology allows to put all parts of the OEO, except the fiber, on the same chip. Microspheres, with their demonstrated Q equivalent to a kilometer fiber storage, can replace fiber delays in a truly integrated device. We have obtained microwave oscillation in microsphere-based OEO at 5 to 18 GHz, with 1310 nm and 1550 nm optical carrier, in two configurations: (1) with external DFB pump laser, and (2) with a ring laser including microsphere and a fiber optic amplifier. Also reported is a simple and efficient fiber coupler for microspheres facilitating their integration with existing fiber optics devices.

Brighter far-field pattern of a phase-locked Nd:YAG microchip laser array was obtained by the Talbot effect in a three-mirror cavity. The laterally coupled Nd:YAG microchip laser array produced a pair of spots with sharper peaks with an angular separation of (lambda) /d in its far-field, where d is the distance between the adjacent sources, indicating an out-of-phase spatial mode coupling was improved. The far- field spot size is reduced by a factor of 9.3 compared with that obtained by incoherent pile of the individual microchip laser outputs. We demonstrated that the far-field pattern is improved by enhancing the self-imaging with side mirrors which make the array source disguise an infinity. A mode selecting slit placed right after the crystal is also effective to stabilize the out-of-phase mode.

In a laser with the cavity, formed by the mirrors with thermal non-linearity, in some conditions the moving transverse spatial structures can occur. In this report, on the base of computer simulation, the analyses of dynamics of such structures have been performed for two cases: for the cavity with one non-linear mirror with dR/dT > 0 and for the conjugate cavity with two non-linear mirrors which have dR/dT of different signs. In the example of TEA-CO₂ laser with light-controlled vanadium dioxide mirrors, we have shown that in the first case intracavity interaction of radiation with the non-linear mirror makes possible the control of shape and duration of leading edge of laser pulse and laser mode composition. In the second case one can obtain the regime of directed movement of laser action region with the velocity of 5 - 50 mm/microsecond(s) , which can be used in scan laser systems. The influence of optical and thermal parameters of non-linear mirrors on the laser action dynamics is discussed.

We present the stabilization of an intracavity frequency doubled blue Nd:YAG laser. A single stripe 1 W/808 nm laser diode was used for longitudinal end-pumping of a half- monolithic Nd:YAG/KNbO₃ 473 nm microlaser. A quarter- wave plate (QWP) was used inside the cavity to suppress the large amplitude noise. An adjustment of the QWP with a rotation angle of 45 degree(s) referring to the ordinary axis of the KNbO₃ crystal resulted in a suppression of the noise in the blue laser emission.

Advanced resonator technology consisted of uniform pumping and bifocusing-compensation has been developed for rod- geometry laser-diode-pumped Nd:YAG lasers to generate laser power of > 100 W with the beam quality of M² < 1.2 in cw mode. Experimental results are explained with wave- optics calculations.

In this paper an approach of calculating the coupling losses in a coaxial (or annular) waveguide laser resonator is developed by which the computational time is considerably reduced. Computations of the coupling losses for some TE modes of an annular waveguide, as a function of mirror curvature and position, are presented in the limit of large mirror aperture. It is shown that there exist three special configurations to provide low coupling losses. The resonator properties are discussed. The calculating results are useful for design of annular waveguide laser resonators.

We present a self-starting Nd:YAG laser-oscillator with cavity formed by refractive index gratings and gain gratings accompanying population gratings which are induced in the laser crystal by generating beams themselves. The spatio- temporal and spectral characteristics of the laser including two Nd:YAG-amplifiers, a saturable absorber and a Sagnac interferometer are investigated. The laser-oscillator with a nonlinear mirror has displayed self-adaptivity to strong thermally induced intracavity distortions. Generation of single mode beams with up to 60 W average power and near- diffraction limited quality has been achieved.

A concept for a grating surface emitting semiconductor laser with a lenslike medium that causes divergence along the lateral direction is described. In principle, the output beam can be diffraction limited. A second-order grating is fabricated with straight teeth which are perpendicular to the directions of propagation of the beams along the laser axis. The constant radius of curvature of the mode results in the matching of the reflected beam with the laser mode. The output beam will exhibit mild astigmatism which can easily be corrected. The astigmatism is the same for the waves traveling in both directions. The divergence of the mode discourages the breakup of the counterpropagating beams into filaments. Surface emission decreases the optical intensity of the laser mode and can essentially eliminate the output power through the facets. This type of laser is a candidate for high power operation.

We have developed an extremely stable phase conjugate single-mode laser diode array with unique spatial and temporal coherence properties. The laser is based on a novel concept of frequency selective phase conjugate feedback. A laser diode array is coupled to the phase conjugate feedback system that comprise a rhodium doped BaTiO₃ crystal, a Fabry-Perot etalon, and a spatial filter. This feedback system forces the laser diode array to operate in a single spatial and a single longitudinal mode. In comparison with the free running laser diode array, the coherence length is increased significantly and the output is close to the diffraction limit. More than 80% of the total energy provided by the free running laser diode array can be extracted from this single-mode laser system.

In this paper we focus on the impact of planar microcavity structures on the spontaneous emission times and bandwidths of light emitting diodes. We compare microcavity and non- microcavity devices and show that the light extraction is ten times more efficient for the microcavity devices, while the small-signal modulation bandwidth remains unchanged. Bandwidths in excess of 1 GHz are obtained. The power- bandwidth figure of merit for the microcavity devices is thus of the order of ten times greater than for the non- microcavity devices. The role of photon-recycling on the bandwidth is investigated. It is found that no major reduction in the bandwidth occurs due to recycling for devices up to 85 micrometers in diameter.

Theoretical and experimental investigations are carried out to investigate the possible improvements of beam quality and electro-optical efficiency of high-power CO₂ laser devices which are equipped with aspherical end mirrors. The experiments were performed at output power levels up to 10 kW and high resonator Fresnel numbers up to 10. Compared to standard unstable resonators the electro-optical efficiency can be improved by 50%. At an output power up to 1 kW the beam quality achieved with aspherical resonator mirrors is improved significantly compared to spherical stable resonators. Resonator simulations on the basis of the Fox and Li algorithm show that multi-mode operation is the main problem with aspherical resonators at high output power.

The maximum power range over which a laser resonator supports stable oscillation is mainly determined by the (thermal) material consists of the active medium and by the cooling scheme. The power range for stable fundamental-mode operation can be shifted to higher powers with special cavity designs and intra-cavity optics but the width of the stability range will be unaffected. Moreover, increasing the pump intensity in the active medium also aggravates the aspheric components of the thermally induced distortions. It is therefore of major importance to analyze these thermal effects when developing novel resonators. We present investigations on thermally induced distortions and on a novel multi-rod laser cavity, known as the variable- configuration resonator (VCR). The thermal effects have been studied both numerically and experimentally. We present a comparison of various pumping and cooling schemes. It is found that composite rods provide the most effective cooling for end-pumped lasers. The VCR was developed to scale the power range of fundamental-mode lasers. Due to its capability to run either as a Fabry-Perot resonator or as a ring cavity it overcomes the stability problems associated with conventional multi-rod resonators and allows for a novel Q-switching technique.

We report on a side-pumped and passively mode-locked all- solid-state laser. The laser consists of an astigmatically compensated resonator with a saturable Bragg reflector to achieve mode locking and a Brewster-cut Nd:YVO₄ rod, which is side-pumped by a diode-laser bar. At 17 W of pump power a fundamental-mode average output power of 4.4 W was attained. Pulses as short as 33 ps have been measured at pulse repetition rates of 235 MHz and 440 MHz. When synchronously pumping an optical parametric oscillator (OPO), these pulse durations lead to wide cavity length detuning tolerances and a comparatively narrow spectral bandwidth of < 15 GHz which is very suitable for applications such as molecular spectroscopy and pollutant detection. A pump depletion of 78% and 1 W of signal output power between 1461 nm and 1601 nm were obtained from an OPO based on periodically poled lithium niobate.

The overview of the works on the intracavity laser beam control and formation of different types of lasers are presented in this paper. Also, the design of the different types of the bimorph correctors for the low-order aberrations compensation is discussed. An example of the efficiency of the use of the bimorph mirror to change the output excimer laser beam profile is given.

Experimental and theoretical investigations of self-pumped phase-conjugate (SPPC) resonators with four-wave mixing (FWM) in diode-pumped amplifiers are presented. A model that uses a transient treatment of FWM (in one-pass or two-pass geometries) allows us to analyze the temporal dynamics and the energy characteristics of these resonators in both injected and self-starting configurations. The influence of the input energy in the injected case, and the influence of the output coupler reflectivity and diode pump energy in the self-starting case are analyzed. In the self-starting case, the SPPC resonators demonstrate self-adaptive compensation of phase distortions and produce a TEM₀₀ mode in a single-longitudinal-mode pulse by dynamic gain-grating formation with a reasonable optical-optical efficiency.

Flashlamp pumped oscillators utilizing Nd:Cr:GSGG or Nd:YAG rods were stabilized against varying levels of thermal focusing by use of a Variable Radius Mirror (VRM). In its simplest form, the VRM consisted of a lens followed by a concave mirror. Separation of the two elements controlled the radius of curvature of the reflected phase front. Addition of a concave-convex variable-separation cylindrical lens pair, allowed astigmatism to be corrected. These distributed optical elements together with a computer controlled servo system formed an adaptive optic capable of correcting the varying thermal focusing and astigmatism encountered in a Nd:YAG confocal unstable resonator (0 - 30 W) and in Nd:Cr:GSGG stable (hemispherical or concave- convex) resonators so that high beam quality could be maintained over the entire operating range. By utilizing resonators designed to eliminate birefringence losses, high efficiency could also be maintained. The ability to eliminate thermally induced losses in GSGG allows operating power to be increased into the range where thermal fracture is a factor. We present some results on the effect of surface finish (fine grind, grooves, chemical etch strengthening) on fracture limit and high gain operation.

The quantum noise limits of a semiconductor laser with dispersive loss are examined theoretically and experimentally. Using optical feedback from Cs vapor as a dispersive loss element we demonstrate almost 6 orders of magnitude reduction in the linewidth, to a 44 Hz level, and 1.9 dB amplitude noise squeezing below the standard quantum noise limit.

Multipath resonators are well known as optical delay lines. By many zick-zack rays between two mirrors large optical path lengths can be obtained. This passive system can be converted into a laser oscillator by closed ray paths and a Nd:YAG crystal at one mirror. Optical pumping occurs by directly coupled diodes at the reflection points. Very efficient (more than 40% optical/optical) and compact systems up to 20 W, with the beam propagation factor m² < 3 were generated. Q-switching and internal frequency doubling were also demonstrated. The fundamental physics of this system including the transverse mode-locking at the degeneration points of the resonator was investigated, experimentally and theoretically.

The thulium-doped ZBLAN fiber laser is emitting visible radiation through an upconversion process which allows for the generation of hundreds of milliwatts of output power at 480 nm. The main features of this laser are presented and analyzed on the basis of an equation rate analysis. Cross- relaxation processes are shown to play an important role in the dynamical evolution of the population levels. The problem of the onset of a photo-induced absorption in the fluoride-glass matrix is also addressed in connection with its detrimental effects on laser operation. Practical solutions to this problem are explored.

KNbO₃ yields very high non-linear coefficients. This material is attractive and widely used for the frequency doubling of cw and quasi cw near infrared laser sources. However it is not commonly used for pulsed applications. Frequency doubling of a pulsed high peak power titanium doped sapphire (Ti:S) laser with KNbO₃ has been investigated. Close to 60% conversion efficiencies have been obtained in external cavity single shot operation. Factors limiting the conversion efficiency in a repetitive mode and with longer crystals have been identified. Quadrature second harmonic generation technique has been shown to overcome some of these limitations compared to single crystal technique. First experimental results for frequency doubling the Nd:YAG and Nd:YAlO ⁴F_3/2-⁴I_9/2 laser transition in the pulsed nanosecond regime with KNbO₃ are also presented.

The performance of end-pumped YAG and YVO₄ lasers in fundamental mode operation (M² < 1.1) is reviewed and the physical limits of TEM₀₀ output power is discussed. By using special resonator configurations, end-pumped lasers can be designed to provide high-power, excellent beam quality, and high-efficiency in spite of the large phase distortions commensurate with the strong aberrated thermal focusing. A 35 W infrared Nd:YVO₄ laser was developed with a quantum efficiency of 94%, defined as a percentage of 1064 nm photons generated per quantity of absorbed 809 nm pump photon. A Q-switched end-pumped Nd:YAG laser provides an average output power greater 15 W in a polarized TEM₀₀ mode with 29% optical efficiency at 1064 nm. External frequency doubling and tripling of this laser resulted in maximum output powers of 8.8 W and 4.2 W, respectively.

We describe recent, energetics performance results on the engineering preamplifier module (PAM) prototype located in the front end of the 1.8 MJ National Ignition Facility laser system. Three vertically mounted subsystem located in the PAM provide laser gain as well as spatial beam shaping. The first subsystem in the PAM prototype is a diode pumped, Nd:glass, linear, TEM₀₀, 4.5 m long regenerative amplifier cavity. With a single diode pumped head, we amplify a 1 nJ, mode matched, temporally shaped (approximately equals 20 ns) seed pulse by a factor of approximately 10⁷ to 20 mJ. The second subsystem in the PAM is the beam shaping module, which magnifies the gaussian output beam of the regenerative amplifier to provide a 30 mm X 30 mm square beam that is spatially shaped in two dimensions to pre- compensate for radial gain profiles in the main amplifiers. The final subsystem in the PAM is the 4-pass amplifier which relay images the 1 mJ output of the beam shaper through four gain passes in a (phi) 5 cm X 48 cm flashlamp pumped rod amplifier, amplifying the energy to 17 J. The system gain of the PAM is 10¹⁰. Each PAM provides 3 J of injected energy to four separate main amplifier chains which in turn delivers 1.8 MJ in 192 frequency converted laser beams to the target for a broad range of laser fusion experiments.

We demonstrate a novel intensity noise suppression configuration which combines laser injection locking and electronic feedback. We use two feedback loops which together suppress the intensity noise of the injection locked laser to 4 dB above the quantum noise limit.

The results of the investigation of the beam quality of the high-power industrial CO₂ laser are presented. As a result of this investigation, a scheme of the modified stable-unstable resonator is proposed, that uses only reflective mirrors. In this scheme, the plane of the unstable telescopic resonator is transverse to the flow of the discharge chamber. In the plane parallel to the electrodes, this scheme represents a single-mode stable resonator. High efficiency of this resonator and high beam quality have been pointed out.

Diffraction analysis of the formation of low losses, large beam width and high far-field intensity peak value of the given super-gaussian fundamental modes by means of intracavity controlled mirror is presented. Such mirror is a water-cooled bimorph flexible one having four controlling electrodes. Analysis has confirmed the possibility to form various intensity distribution inside laser cavity and at the output of the stable resonators of industrial CW CO₂ and YAG:Nd³⁺ lasers. Distortions of the given intensity distributions caused by thermal deformations of the resonator mirrors is taken into account. It is shown the possibility to compensate partially for such distortions with the help of the intracavity controlled mirror. Experimental formation of the super-gaussian fundamental modes of the 4th and 6th orders of the industrial CW CO₂-laser with stable resonator by means of the intracavity flexible mirror is shown. The increase of power of the formed fundamental modes up to 10% and the enlarging of the peak intensity in the far-field zone in 1.6 times in the comparison with the traditional gaussian TEM₀₀ mode of the same resonator are observed.

To improve the beam properties of a short-pulse KrF excimer laser (FWHM < 3.8 ns) with a low number of roundtrips (2...3) and limited magnification (< 5), unstable resonator designs have been developed. Resonators containing mirrors with super-Gaussian reflectivity distributions of different super-Gaussian orders have been investigated theoretically by beam propagation method as well as experimentally by measuring the near- and far-field beam profiles. Mirrors with radially varying multilayer systems have been fabricated by mask-shaded vacuum deposition of dielectric layers with planetary rotation of the substrate. It has been demonstrated that the (delta) -factor of the laser can be significantly improved with compact resonator configurations. For a resonator length of 400 mm, a beam spot size on the output coupler of 2 w equals 1.6 mm and a magnification of M equals 5, the optimum operation characteristics has been found for a super-Gaussian order of about k equals 10. Compared with a plane-parallel system, the (delta) -factor was enhanced by a factor of up to 7. The characteristic beam parameter M² (times-diffraction- limited-factor) could be reduced in x- and y-directions by factors of 4 and 2, respectively. The experimental results are in good agreement with our theoretical predictions.

Piezo-mounted fiber-grating output coupler is proposed as a tuning element in an Er³⁺-doped fiber laser. Tuning range in excess of 2 nm has been obtained in the vicinity of 1.57 micrometers . Such a tuning element is both compatible with wavelength modulation spectroscopy (WMS) and fiber laser intra-cavity spectroscopy (FLICS). CO leak detection was demonstrated using both geometries. (Delta) (alpha) of 9 X 10^-4 were measured with WMS while FLICS did not lead to the expected increase of sensitivity.

Hermite-Gaussian, Laguerre-Gaussian and complex Hermite- Gaussian modes are solutions of the paraxial wave equation. Using an astigmatic optical system each type of beams can be transformed into the others. This allows a generation of complex Hermite-Gaussian modes with twist whose propagation behavior is investigated in detail.

The laser interferometric gravitational wave detection by means of a long-baseline laser interferometer has been promoted in Japan. To obtain higher sensitivity for detect gravitational wave, high-quality mirrors and the high-power laser with high frequency-stability are important. In this paper our improvement of high-quality mirrors through development of high-precision measurement and the frequency stabilization of the injection-locked laser was reported.

We establish the distinction between free-space Bessel beams (the so-called `diffraction-free beams') and the guided modes of circular cylindrical geometry whose radial profiles take the form of Bessel functions. We explain why these two types of optical beams have different dispersion relations. A free-space Bessel beam can be produced by illuminating a mask with a single transparent ring placed at the focus of a lens; such a beam has group and phase velocities that are equal and larger than c, the speed of light in vacuo. We examine the propagation of polychromatic Bessel beams that can be produced when short pulses are illuminating a mask with one transmission ring; spectral modulation, temporal breakup and loss of fringe visibility can take place under such circumstances. Polychromatic Bessel beams are shown to constitute wave packets whose spatio-temporal field distributions are invariant upon propagation in vacuo; these wave packets have the shape of a double cone, and are sometimes called `X-pulses'. We present experimental evidence of loss of fringe visibility when very short pulses are used to generate such conical wave packets. The coherent superposition of multiple monochromatic Bessel beams can lead to a self-imaging phenomenon along the propagation axis when the spatial frequencies of the Bessel beams in the radial direction are properly selected. We specify the conditions for temporal self-imaging when a polychromatic single Bessel beam propagates in a dispersive medium. Spatio-temporal self-imaging is also possible when multiple polychromatic Bessel beams are propagated in a dispersive medium. We also examine the longitudinal fields associated to Bessel beams and conical wavepackets, and evaluate their suitability for partial acceleration.