Recent progress in laser beam shaping and characterization with novel-type thin-film microoptics is presented. These novel microoptical devices offer several distinctive advantages, such as a short optical path, small angles, low roughness or multilayer design. These features allow shaping of laser beams at extreme parameters with respect to spectrum, angular distribution, intensity, or pulse duration. Particular emphasis is laid on (i) hybrid components for high-power diode laser collimation, (ii) spatio-temporal shaping of localized few-cycle wavepackets, and (iii) microoptics for the vacuum ultraviolet. For the fabrication of thin-film structures, vapor deposition with shading masks was used. To improve the efficiency of diode laser collimation, spatially variable AR coatings and integrated arrays of cylindrical microlenses were developed. Arrays of Bessel-like beams were generated from sub-10-fs Ti:sapphire laser pulses by refractive and reflective microaxicons. We further demonstrated the use of microaxicon arrays for spatially resolved autocorrelation of ultrashort pulses. Deposition and etching transfer of flat VUV-structures was studied. Finally, the generation of single-maximum nondiffracting beams by self-apodizing system design is discussed.

We extend a model of the evanescent field-coupled multi-core Yb-doped fiber laser to include fluctuations of the level populations with the goa lof determining the stability properties of collective modes. The nonlinear differential equations for light intensity, the phases of the electric fields, and the occupation number of the upper laser level of each core are integrated numerically, while, for two cores the relaxation rates, oscillation frequencies, and stability criteria are determined analytically from the set of linearized equations. For example, for two identical lasers we find the in-phase super mode to be unstable in the range 0<κ/Δβ_nl<1, where κ is the inter-guide coupling constant and Δβ_nl the non-linear change in the mode propagation constant. The system is bi-stable for |κ/Δβ_nl|>1, and we describe how switching can be performed. Besides evanescent-field coupled lasers the analysis may be applicable to other coupling mechanisms, such as external cavities, although with some caution.

In this paper we present the results of studies of a multiple-channel laser system, operating in the phase-array regime with a single output aperture. The dynamically coupled resonators of the laser use an optical phase conjugation (OPC) element for coupling the master and slave lasers, the latter being a multiple channel array.

This paper presents adaptive optical closed loop system with bimorph mirror as a wavefront corrector and Shack-Hartmann wavefront sensor to compensate for the aberrations of the high power lasers. Adaptive system can correct for the low-order aberrations in the real-time -- the frequency of corrected aberrations is less than 25 (30) Hz. The amplitude of such aberrations -- about 7 microns. These parameters are mostly determined by utilized Shack-Hartmann wavefront sensor. Number of corrected aberrations -- up to 30^th Zernike polynomial (excluding tip-tilt). We are presenting the results of the use of our adaptive system in several high-power laser systems such as ATLAS, LULI, JAERI and Beijing Institute of Physics.

We present an adaptive optical closed loop system to obtain a good focused beam. A bimorph mirror is used as a wavefront corrector and CCD camera at the focal plane of the lens is a sensor. Such adaptive system can correct for the low-order wavefront aberrations without any sophisticated wavefront sensors.

The Solid-State, Heat-Capacity Laser (SSHCL), under development at Lawrence Livermore National Laboratory (LLNL) is a large aperture (100 cm²), confocal, unstable resonator requiring near-diffraction-limited beam quality. There are two primary sources of the aberrations in the system: residual, static aberrations from the fabrication of the optical components and predictable, time-dependent, thermally-induced index gradients within the gain medium. A deformable mirror placed within the cavity is used to correct the aberrations that are sensed with a Shack-Hartmann wavefront sensor. Although it is more challenging than external correction, intracavity correction enables control of the mode growth within the resonator, resulting in the ability to correct a more aberrated system longer. The overall system design, measurement techniques and correction algorithms are discussed. Experimental results from initial correction of the static aberrations and dynamic correction of the time-dependent aberrations are presented.

In this work we report on the optimization of the conversion efficiency of the harmonic generation process, by adaptive control of the wavefront of sub-10-fs light pulses, obtained by using a deformable mirror and a genetic algorithm. Sub-10-fs, 0.2-mJ energy light pulses, generated by the hollow-fiber compression technique, were focused in the gas target (argon or neon) by a 250-mm focal-length mirror. Pulse wavefront correction has been achieved by using a deformable mirror (DM) controlled by 37 actuators distributed on a honeycomb pattern of 15 mm diameter. The harmonic radiation was observed by a soft-X-ray spectrometer, with double output: time-integrated high-resolution bidimensional focal-plane image and real-time (1 kHz) intensity of a suitable spectral region. This latter signal was used as fitness parameter for the genetic algorithm; an initial population of DM configurations was initialized with random values of the actuator signals. A new generation of DM configurations is derived from ordering, selection and transformation of previous generation, up to the convergence to the fittest individual. Strong enhancement of the harmonic conversion efficiency of about one order of magnitude, as well as a significant extension of the harmonic spectrum is evident. The initial and optimal wavefronts of the fundamental beam were measured both in real time with an Hartmann sensor and off-line using a ZYGO interferometer. Using the measured beam wavefront were calculated the spatial characteristics of the fundamental beam.

Spatially resolved wavefront sensing and time-resolved autocorrelation measurement of ultrashort pulses are usually separated procedures. For few-cycle pulses with significant spatial inhomogeneities and poor beam quality, a fully spatio-temporal beam characterization is necessary. Here we report on a new concept for a joint two-dimensional mapping of local temporal coherence and local wavefront tilt based on the combination of collinear autocorrelation and Shack-Hartmann wavefront sensing. Essentially for this "wavefront autocorrelation" is a splitting of the beam into a matrix of Bessel-like sub-beams by an array of thin-film microaxicons. The sub-beams are further processed by a two-dimensional collinear autocorrelation setup. The second harmonic distribution of sub-beams at a defined distance is imaged onto a CCD camera. The nondiffractive sub-beams ensure an extended depth of focus and a low sensitivity towards angular misalignment or axial displacement. With low-dispersion small-angle refractive-reflective shapers, wavefront-sensing of Ti:sapphire laser wavepackets was demonstrated experimentally for the first time.

A pulsed excitation of the laser plasma in gas lasers creates an acoustic wave in the laser reservoir. It changes thermodynamic parameters of the laser plasma in the laser cavity like pressure, and temperature, as well, and consequently it changes the density of the laser plasma, or, in other words, the refractive index of the laser medium. Tuning laser frequency during the pulse developing is observed as a result. The measurements of the pressure, temperature, and refractive index changes in an RF pulsed excited C_O2 slab-waveguide laser are purposes of the work. The pressure changes are measured with calibrated microphones situated close to the laser plasma. The temperature changes are calculated via measured refractive index characteristics, and simple formulas linking the refractive index with the gas density. The picture of the acoustic wave propagation in the laser cavity is presented. The obtained results give the picture of the laser plasma behavior during the pulsed excitation. It leads to a single frequency pulsed laser operation design.

We demonstrate the wave-front correction of the LULI 100TW, 300 fs/30 J high power laser facility for a sequence of shots. Excellent beam focusability close to diffraction limit has been obtained using an adaptive optic system, composed of a large aperture dielectric coated deformable mirror and a home-made shearing interferometer. This correction allows to produce reproducible focal spots with Strehl ratios close to 0.9 at a repetition rate of a shot every 20 minutes, despite of wave front distortions generated by cumulative thermal effects in the large disc amplifiers.

For the past 28 years, the Laser Hardened Materials Evaluation Laboratory (LHMEL) at the Wright-Patterson Air Force Base, OH, has worked with CO₂ lasers capable of producing continuous energy up to 150 kW. These lasers are used in a number of advanced materials processing applications that require accurate spatial energy measurements of the laser. Conventional non-electronic methods are not satisfactory for determining the spatial energy profile. This paper describes a new method in which a continuous, real-time electronic spatial energy profile can be obtained for very high power, (VHP) CO₂ lasers.

A new method for computing eigenmodes of a laser resonator by the use of finite element analysis (FEA) is presented. For this purpose, the scalar wave equation [Δ + k²]E(x,y,z) = 0 is transformed into a solvable 3D eigenvalue problem by separating out the propagation factor exp(-ikz) from the phasor amplitude E(x,y,z) of the time-harmonic electrical field. For standing wave resonators, the beam inside the cavity is represented by a two-wave ansatz. For cavities with parabolic optical elements the new approach has successfully been verified by the use of the Gaussian mode algorithm. For a DPSSL with a thermally lensing crystal inside the cavity the expected deviation between Gaussian approximation and numerical solution could be demonstrated clearly.

Approximate calculations of the temperature distribution of a rotating-disk solid-state laser are presented. The surfaces of the Nd:YAG or Nd:glass rotating disk pass close to two water-cooled plates. A thin gap, filled with gas, separates each plate from the disk. For an Nd:YAG disk, temperature distributions are given for a 50 μm gap filled with He, for a 50 μm gap filled with air, and for the case in which the thermal conductivity of the Nd:YAG dominates the problem. Calculated results for an Nd:glass disk are compared with a temperature profile obtained from a rotating-disk laser.

Er³⁺/Yb³⁺ co-doped phosphate glass microsphere lasers have been studied under pumping by a fiber taper at 1480 nm. Whispering Gallery Mode laser spectra were analyzed for different sphere diameters. The gain spectrum is calculated for the transition ⁴I_13/2 → ⁴I_15/2 around 1550 nm. Red-shift effect on the wavelengths of both fluorescence and laser spectra is experimentally observed when the pump power is increased, originating from thermal effects. We showed coupling effect between microspherical laser and an external cavity made by a metallic mirror. We observed line shift to lower wavelengths due to optical feedback effect.

A resonator has been manufactured using a photonic crystal at K_u band frequencies. The photonic crystal has a face centered cubic Bravais lattice structure. In the transmission measurements, the photonic crystal displayed a directional bandgap with a lower band edge of 13.0 GHz, an upper band edge of 21.5 GHz, and a center frequency of 17.25 GHz. The corresponding stop bandwidth center frequency ratio is 50%. The maximum rejection at the band center is 35 dB. The unit cell rejection ratio is 7 dB per unit cell. The resonance has a quality factor of 200, and a maximum transmission peak of -5 dB.

The evolution of optical networks calls for denser channel grids and increased number of channels. Additionally, there is a system architecture benefit to eliminate the banks of DFB lasers that act as light sources for individual channels, and use instead a single multi-wavelength source. We have demonstrated a compact multi-wavelength optical source (MWS) for 12.5 GHz DWDM. At least 16 channels are observed within 3 dB optical power bandwidth with optical spectrum contrast ratio exceeding 28 dB. The source is based on a coupled opto-electronic oscillator (COEO) with an optical whispering gallery mode (WGM) microresonator. Free spectral range of the resonator determines the spacing of the optical channels in the MWS. The spacing can be scaled up or down depending on design requirements. The resonator is robustly packaged and fiber pigtailed. In the RF domain the MWS acts as oscillator with operational frequency of 12.5 GHz.

We report on our recent results concerning fabrication of high-Q whispering gallery mode (WGM) crystalline resonators, and discuss some possible applications of lithium niobate WGM resonators in nonlinear optics and photonics. In particular, we demonstrate experimentally a tunable third-order optical filter-fabricated from the three metalized resonators; and report observation of parametric frequency doubling in a WGM resonator made of periodically poled lithium niobate (PPLN).

Faraday optical isolator is used in laser systems with amplifiers to protect master oscillator from reflected and backscattered amplified light. The main part of FOI is a magnet system with magneto-optical glass. For traditional magnet systems of two or several alternative toroidal magnets it was shown that with growth of inner radius length and mass increase. Besides that axial magnetic field of such systems does not exceed remanence of magnetic material. The goal of this paper was to solve this problem by constructing Faraday optical isolator on the base of multisector permanent magnets, the practical realization of magnets with non-uniform magnetization. On the base of those magnets, spherical and toroidal permanent magnet systems were constructed. For toroidal systems constructed on the base of multisector magnet with inner and outer radiuses r1 = 0.6 cm, r2 = 3.6 cm, length l = 1 cm and remanence of magnetic material B = 12 kOe axial magnetic field H = 14.4 kOe was calculated. For spherical systems constructed on the base of the same magnet axial magnetic field H = 19.6 kOe was calculated. The research of toroidal and spherical multisector magnet systems showed that they can be used for constructing of compact Faraday optical isolators.

We present an Adaptive Optics (AO) system for the control of geometrical fluctuations in a laser beam based on the interferometric detection of phase front. By comparison with the usual Shack-Hartmann based AO system, we show that this technique is of particular interest when high sensitivity and high band-pass are required for correction of small perturbations like, for instance, the control of the input beam of gravitational waves interferometric detectors.

Sometimes it is important to know the kind of laser and also the nature of the active media where the photons are produced, mainly when the photon source is situated at long distance from the target, and you can have information, only from the photons. The authors considered many ways of theoretical and applied research, using models for different types of lasers. High-speed and high-accuracy applications in processing trend to increase in the field of some important applications like laser beam welding and laser beam cutting. Some time the source presents inconstant parameters, and so, the measurements must be made in a relative short interval of time. The study requires problems like: space resolved analysis -- the calculation of the average intensity distribution; time resolved analysis of the beam power, position or diameter. The statistical analysis that can be performed allow an estimation of the uniformity of laser pulses. The short-term stability of the laser beam sources is very important, because in the most cases we must do the analysis of a short time pulse. Some methods, proposed by scientists until now, are not overall applicable in all cases. For that, the authors proposed a new and more complete method.

Applications of high-power lasers are very important, especially for cutting and welding. As it is known, laser-beam characteristics have not constant value in time. So we may have suitable testing methods which allow us to determine the principal beam characteristics. The testing methods have to be very accurate, very efficient and in the same time very short as duration. We must apply a 3-dimensional intensity analysis, to the photonic beam we are studying. The number of industrial applications of lasers is increasing. An important thing is to know the optical characteristics of the laser that we study. Only the complete knowledge of the laser parameters allows controlling the process. For each laser system is very important to know the parameters i.e. their dynamic, in order to establish the correct performances. The correct information about the beam is not always possible to obtain. Various physical models help to understand the behavior of the laser beam. The best is if we have complete quantitative information about the photon beam. The definition of the beam diameter is not standardized. In order to do a comparison between different lasers, it is important to know the method that was applied to determine the beam diameter.

Thermal nonlinearity can produce oscillatory instability in optical microspheres. We analyze theoretically the conditions of observations of this regime and demonstrate it experimentally. The observed curves are well compared with results of numerical modelling. In pure fused silica with low absorption thermal oscillations are suppressed due to concurrency with Kerr nonlinearity. We also describe for the first time experimentally observed slow and irreversible thermooptical processes in microspheres.

Laser beam could be applied to act in optical media, to build different spatial images. The operation could be made direct by copying an image or through a C.D. The successive points could be realized with relatively high speed, like 10³-10⁵ points per second. Each point represents practically a machining operation done by the laser beam. In most cases, energy transfer is made not in a plane, but in a volume, and this requires moving the focal point in positions required by the image we want to create. This is a sequentially operation, made point by point following a definite order, but in the same time, because the image is spatially, we have to adapt also other parameters of the optical system, for each considered point. The energy required for each point of the image must be the same, because all the micro spheres representing a “point” of the image must have the same volume. In this way we could realize a coherent spatial image. From the experimental research we made, we have learnt that is important to build a model for the energy transfer to optical media, in order to have a good quality for the work we have to do.

The impurities into the volume of a material appear while the elaboration process of the considered material. If a material is non-homogenous, even if we machine this material by means of a classical technology we could remark some differences in the machining process like cutting, drilling a.s.o. even in the process of welding. The impurities may be gaseous or solid. Each kind of impurity has another effect for the classical tool, or for a non-traditional tool i.e. a kind of concentrated energy. Each kind of medium has another reaction versus laser beam, because each medium has other physical characteristics. The modifications of characteristics require modifications of photon beam parameters. Not any laser equipment is prepared to react correct to any kind of material, representing the impurity. To have a high quality machining process, we must know the nature-kind of the impurity, and in the same time, we must assure such components, which are able to react and correct to all kind of impurities which laser beam will meet. The recently generation of lasers are correct gifted, in order to work with materials presenting all kind of impurities.

We stabilized the high voltage (HV) excited CO₂ laser to the center of the gain curves using a photoacoustic effect generated from the laser itself. A commercial condenser microphone is located in the plasma free region. This detects pressure waves occurring in the plasma free region when laser radiation is absorbed. The signal from the microphone is used to control a feedback circuit to stabilize the frequency and power of the laser radiation. The frequency stability is estimated to be better then 3X10^-8.

The increased use of high power Semiconductor lasers for industrial applications has created a demand for accurate, detailed beam profiling devices. Current technology, however, limits the use of conventional beam profiling instruments to about 1.5 kW. We will discuss a novel method of profiling high power YAG (1064 nm) industrial lasers up to 4kW in average power and 30 mm in raw beam diameter, using a camera-based, computer operated beam-profiling device. The new instrument is portable and employs conventional optics to attenuate and reduce the raw beam, and is designed to be used in an industrial environment.

Micro-domes based on a combination of metallic and dielectric multilayer mirrors are studied using a fully vectorial numerical basis-expansion method that accurately accounts for the effects of an arbitrary Bragg stack and can efficiently cover a large range of dome shapes and sizes. Results are examined from three different viewpoints: (i) the ray-optics limit, (ii) the (semi-) confocal limit for which exact wave solutions are known, and (iii) the paraxial approximation using vectorial Gaussian beams.

We propose and analyze a new type of resonator in an annular geometry which is based on a single defect surrounded by radial Bragg reflectors on both sides. Unlike conventional, total internal reflection based ring resonators, this structure supports modal fields with very low azimuthal number (large radial k-vector component). We show that the conditions for efficient mode confinement are different from those of conventional Bragg waveguiding in a rectangular geometry. To realize tight confinement of the light in the defect, chirped gratings are required. Compared to a conventional resonator, the new resonator exhibits larger FSR and lower losses making it suitable for both telecom and sensing applications. In addition, the resonance wavelength and Q factor of the device are very sensitive to environmental changes, and thus provide ideal observables for sensing applications. Annular Bragg resonators with several unique geometries have been fabricated in an InGaAsP multi-quantum-well membrane. The spectral properties of the resonators have been investigated through analysis of photoluminescence induced by pulsed optical excitation.

At present, many researchers in the leading laser-building companies are involved in solving the problem of creation of high-power industrial lasers. This is conditioned both by increasing demand of industry for such sort of laser devices and by significant achievements in studies of the moderate-power lasers. Besides the high average power, the output beam of a commercial laser must have a small divergence (close to the diffraction limit) and a minimized beam jitter (not higher than the divergence). As is well known, the increase of the average output power of a laser operating in a repetitively-pulsed mode, is accompanied, practically inevitably, by increasing divergence and yawing of the output beam. This universal tendency (Such a dependence of changing specified parameters) is basically caused by instabilities in the laser active media at higher level of pumping and, in this connection, by a less efficient heat removal from the active medium and degradation of optical quality of the active media and resonator components during its operation. Similar problems also arise when the average output power is increased in a straightforward way by direct scaling of the laser systems. In this report, we describe an original configuration of the unstable resonator intended for a high-power repetitively-pulsed laser comprised of several laser heads of moderate power. We show that the beam divergence and yawing of such a powerful laser remain practically at the level of appropriate parameters for the moderate-power lasers, whereas the average output power increases proportionally to a number of the laser heads used.

In this paper we discuss different configurations of experiments where two nanoemitters are coupled through exchange of photons via shared cavity modes. We introduce an experimental setup where we combine microspheres as optical resonators with the techniques of scanning confocal and scanning near-field microscopy. The emission of fluorescence light from a single nanoemitter in high-Q whispering-gallery modes is demonstrated. Also first experiments with a novel type of stable active nanoprobe are reported. These results demonstrate the feasibility of experiments where optical modes mediate interactions between few quantum emitters in a controlled manner.

An extended-cavity resonator with an aspheric third mirror aligned collinear to a standing-wave two-mirror resonator is studied. A number of benefits of this new cavity design such as improved mode selectivity and mode shaping were predicted by simulation. An experiment was performed with a Nd:YVO₄ laser system. With an optimized aspheric third mirror, this three-mirror solid-state laser has an experimentally measured modal discrimination of 1.43 and oscillates in the designed fundamental Gaussian mode. The M² of the cavity mode was measured to be 1.02. Applications of aspheric feedback mirrors in other advanced laser resonators are also briefly discussed.

Microring resonators can serve as key elements in the realization of engineerable photonic media. A sequence of resonators coupled to an optical waveguide can be viewed as an optical transmission line with highly controllable dispersive and nonlinear properties, similar to those of photonic crystals or gratings. We have constructed and characterized several optical micro-ring resonators with scale sizes of the order of 10 microns. These devices are intended to serve as building blocks for engineerable linear and nonlinear photonic media. Light is guided vertically by an epitaxially grown structure and transversely by deeply etched air-clad sidewalls. In this work, we chose to construct ring resonators in AlGaAs and probe them at a photon energy below the half-gap of the material. Our motivation for this choice was to maximize the ultrafast bound (Kerr) nonlinearities resulting from virtual transitions while minimizing the two-photon contribution to carrier generation. We report on the spectral phase transfer characteristics of such resonators. We also report the observation of a pi-radian Kerr nonlinear phase shift accumulated in a single compact ring resonator evidenced by all-optical switching between output ports of a resonator-enhanced Mach-Zehnder interferometer.

The self-focusing of elliptically polarized gaussian beam in isotropic gyrotropic medium with spatial dispersion of nonlinearity has been investigated numerically. Along with the effects predictable by traditional self-focusing theories the new peculiarities of the self-focusing have been found which cannot be described in principle by the aberrationless approximation theory. The dynamics of the light beam cross-section polarization state distribution changes in a process of the beam propagation have been investigated.