A computer code to calculate the output power and disk temperature distribution for a spinning disk laser has been developed. Calculated values agree well with experiment. The surfaces of the Nd:YAG 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, results are given for a 50 μm gap filled with He.

The spatial-mode and spectral-mode properties of a general three-mirror resonator with collinearly aligned cavity mirrors have been studied. It has been found that the resonator spatial mode can be controlled through engineering the complex reflectivity of the resonator mirrors. Further study reveals strong correlation between spatial modes and spectral modes of a three-mirror resonator. Strong spectral selectivity can be achieved with proper engineering of the spatial mode.

Producers and users of laser beam equipment have some wishes as: to have economic machines, the machines must be as small and light as possible, the power supply must be also very light and small. All mentioned desires - and other related with them - may be accomplished by an adequate efficiency of laser beam process. As we know, the first laser began with 2% efficiency. In the process of time, the efficiency increased progressive, and in this way was possible after the year 2000 to have laser weapons mounted on jet planes, including the power supply. In a laser system, there are many points where photons are lost. To reduce this losses, we must treat with the utmost care all points of the "chain" where photons could be lost. We mention: the resonance cavity - inside -, the exit from the resonance cavity, the mirrors and lenses and also other related factors. Each improvement in one of the mentioned points could contribute to the general raising of the laser machine efficiency. Authors were concerned first with some possibilities of increasing the intrinsic output of the photon beam, for definite laser active media, by applying some fields inside the resonance cavity. Such fields, characterized by nature, energy, frequency and other parameters could influence positive the efficiency of the photon beam emission.

The National Ignition Facility (NIF) is a 192 beam Nd-glass laser facility presently under construction at LLNL. When completed, NIF will produce 1.8 MJ, 500 TW of ultraviolet light making it the world's largest and most powerful laser system. NIF will be the world's preeminent facility for performing experiments for Inertial Confinement Fusion (ICF) and High Energy Density Science (HEDS). The Project, begun in 1995, is over 80% complete. The building and the beam path are essentially complete. Nearly all of the functionality of the laser subsystems has been demonstrated. NIF has demonstrated on a single beam basis that it meets its performance goals and shown the laser's precision and flexibility for pulse shaping, pointing, and timing. Beam conditioning techniques, important for target performance, were also demonstrated. The focal spot can be tailored to user specifications using phase plates. Temporal smoothing using smoothing by spectral dispersion (SSD) as well as polarization smoothing was demonstrated. The remaining work is mostly to complete the optics and install them in the beam path and complete the utilities. Presently, eight beams have been activated through the amplifiers and spatial filters to the switchyard wall. Over 150 kJ of 1ω light has been produced with just 4% of the NIF capacity activated. The Project is scheduled for completion in 2009 and plans have been developed to begin ignition experiments in 2010. This talk will provide NIF status, the plan to complete NIF, and the path to ignition.

Some peculiarities of the use of adaptive optical elements and the whole system to correct for the aberrations of high power single pulse lasers are discussed in this paper. The examples of the use of adaptive system to correct for the aberrations of some lasers are presented. As a corrector we used bimorph multi electrode deformable mirror while as a sensor - Shack-Hartmann wavefront sensor.

The ISO 11146:1999 standard has been published for 6 years and set forth the proper way to measure the M² parameter. In spite of the strong experimental guidance given by this standard and the many commercial devices based upon ISO 11146, it is still the custom to quote M² measurements without any reference to significant figures or error estimation. To the author's knowledge, no commercial M² measurement device includes error estimation. There exists, perhaps, a false belief that M² numbers are high precision and of insignificant error. This paradigm causes program managers and purchasers to over-specify a beam quality parameter and researchers not to question the accuracy and precision of their M² measurements. This paper will examine the experimental sources of error in an M² measurement including discretization error, CCD noise, discrete filter sets, noise equivalent aperture estimation, laser fluctuation and curve fitting error. These sources of error will be explained in their experimental context and convenient formula given to properly estimate error in a given M2 measurement. This work is the result of the author's inability to find error estimation and disclosure of methods in commercial beam quality measurement devices and building an ISO 11146 compliant, computer- automated M² measurement device and the resulting lessons learned and concepts developed.

Laser diode arrays oscillate in multiple spatial and longitudinal modes. Adaptive optics is the field dedicated to automatic compensation for wavefront distortion. A number of approaches are available to achieve spatial and spectral control of high power diode lasers using phase conjugate mirrors. A new method is being developed to determine phase (and hence, phase distortion) using wavelet ridge extraction. In addition, an adaptive wavelet system will be developed to cancel distortion.

The ideal adaptive optical mirror combines large aperture with high spatial and temporal resolution and a phase shift of at least 2π. Further, a simple low-cost solution is preferred. No adaptive system can perfectly fulfill all these requirements. We present a system that has the potential to reach this goal with the exception of high temporal resolution. But even with a moderate temporal resolution of one second such a system can find practical applications. For example as a laser resonator mirror that allows to modify the intensity distribution of the emission, or to correct slowly varying aberrations of optical systems. Two possible mechanisms can be used to change the optical path length of the adaptive mirror: thermal expansion of the mirror substrate or the thermally induced change of the refractive index (thermal dispersion) of a medium in front of the mirror. Both mechanisms have been shown to lead to promising results. In both cases heating was performed by irradiation of light in the active medium. The thermal dispersion based adaptive mirror is built with a thin layer of a liquid in front of a mirror. To allow a modification of the refractive index by irradiation with a diode laser at 808 nm, a suitable absorber is dissolved in the water. With chopped irradiation a resolution of 3.8 Hz at 30 % contrast is measured. This mirror has been used in a laser resonator to modify the output distribution of the laser. The thermal expansion based adaptive mirror is built with a thin layer of a silicon elastomer with a gold coated front side. We present a preparation method to produce thin films of Sylgard on sapphire. With an irradiated intensity of only 370 mW/cm² surface modulations of up to 350 nm are obtained. With a test pattern a resolution of 1.6 line-pairs per millimeter at 30 % contrast is measured. The temporal resolution is better than one second.

We describe a closed-loop adaptive optical system with bimorph deformable mirror to obtain good focused laser beam. This adaptive system can correct for the wavefront aberrations without any measurements of the wavefront: we use M2-meter as a sensor for the feedback. Closed-loop software allows to measure focal spot with M2-meter and then to calculate voltages to be applied to corrector. The best focal spot can be reached by use of combined method based on genetic and hill-climbing algorithms. We demonstrate the use of such a system with water-cooled bimorph deformable mirror as a wavefront corrector on CW solid state Nd:YAG 1kW CW laser system.

We introduce the results of the study of quasi-phase matched processes of self-frequency conversion in periodically poled active nonlinear crystals. The processes of self-frequency doubling and self-frequency summing have been experimentally realized and studied in periodically poled Nd:Mg:LiNbO₃ crystals in CW and Q-switched regimes. The theory of self-frequency conversion has developed. The results of theory are in good agreement with experiments.

The paper gives an algorithm for elaboration of the RF excited slab-waveguide CO₂ laser working on one chosen emission line in a pulse regime. The solution of the problem bases on an RF transversal excitation in a slab-waveguide laser structure and laser signature phenomenon. The structure gives a homogeneous distribution of the excited laser plasma along the electrodes. The plasma in the structure is stable and reproducible from the pulse to pulse comparing to conventional tube lasers, and particularly to flow dynamic lasers. On the other hand, the applied unstable kind optical resonator produces a single-mode operation by definition. It suppresses higher modes in the laser cavity. The only problem are parasitic "hooting modes" created along the waveguide direction - between electrodes. But usually they do not bring too much perturbations to a spectral contents of the laser output radiation. The problem of the one-color operation of the laser can be solved by careful selection of the laser signature. The paper shows the results of the experiments, and gives the methodology to design the CO₂ laser in a pulse regime operating on one chosen emission line. Controlled two-color and multi-color pulsed operations are also considered. The results can be applied to design lasers for the trace gas analysis around of 10 or 9 μm or other spectral devices. It can be also applied for material processing of the media sensitive for the wavelength of the laser radiation.

A new laser Doppler velocimeter employing an RF-excited CO₂ laser has been developed by using its photoacoustic effect. A change in the pressure of a discharge, induced by mixing of a returned wave with an originally existing wave inside the cavity, is employed to detect the Doppler frequency shift. We found that a Doppler frequency shift as small as 50 kHz was detected, and also a good linear relationship between the velocity and the Doppler frequency shift was obtained.

The new highly rare-earth doped triple-clad fiber design comprises a first clad next to the core of the well-known double-clad design. The added clad allows to reduce and to better control the core effective numerical aperture for achieving a highly doped large mode area amplifying fiber with a very low numerical aperture (~0.07). The triple-clad design is optimized to obtain a nearly bending insensitive fiber output while keeping excellent beam quality through proper ytterbium doping. The high ytterbium concentration allows for very high gain from a short (~1 m) fiber length which, in many applications, is required to prevent the onset of nonlinear effects such as stimulated Brillouin scattering. A polarization-maintaining 22-μm core Yb-doped triple-clad fiber was first tested. A laser slope efficiency of up to 86% with a polarization extinction ratio exceeding 24 dB and a M2 output beam quality factor below 1.1, for both laser and amplifier configurations, have been measured. Moreover, beam quality and output power were not significantly affected when coiling the fiber down to a 1.2 cm diameter, thus showing the optical robustness of the triple clad fiber design and offering the opportunity to build very compact high power fiber amplifiers and laser sources.

Tapered fibers have shown high efficiency to generate white light continua, which have many important applications such as pulse compression, spectroscopy, pump-probe measurements, and optical frequency metrology. In this paper, we discuss the principle of white light continuum generation in tapered fibers with incident pulse durations in the femtosecond and picosecond range. We are going to demonstrate some new technologies to design and improve the spectral characteristics of supercontinuum generation, which make tapered fibers very convenient for the construction of white light sources.

The use of LiNbO3 based Volume Holographic Gratings (VHGs) to provide spectrally filtered feedback to a semiconductor laser diode was documented in the mid 1980s1, however issues with long term stability had left this technology on the sidelines. Photo-sensitive glass based VHGs do not exhibit long term aging or thermal/photo bleaching effects, and therefore have enabled a new type of External Cavity Laser (ECL). This highly manufacturable "hybrid ECL/DBR" (HECL) laser utilizes precision VHGs and has been used to create high performance lasers with spectrally tailored output. Lasers with fiber coupled output powers in excess of 4.2 W and spectral line widths of less than 0.15 nm have been demonstrated. Additionally, multi-mode lasers have been developed for High Resolution Raman Spectroscopy that exhibit spectral line widths below 0.06 nm (i.e. < 1 wavenumber) with fiber coupled output power in excess of 350 mW. The use of glass based VHGs provides HECL laser wavelength stabilization of better than 0.01 nm/oC, and allows the production of lasers at virtually any wavelength between 650 nm - 2400 nm.

We propose and demonstrate an interferometric method of fabricating one-dimensional (1D) and two-dimensional (2D) periodic structures on planar substrates. The central idea of the method is to match the substrate or fiber translation velocity to that of the moving interference pattern so as to create its stationary image on the substrate or fiber. The moving interference pattern is produced by phase control of multiple interfering beams. The pitch of the structures can be changed by adjusting the frequency shifts between the interfering beams, and we demonstrate this pitch control technique in the case of interferometrically written 1D periodic structures. There is no limitation on the grating length, and grating designs can be arbitrarily complex optimized for use in both planar and fiber Bragg grating laser resonators.

Morphology-dependent resonances are observed in silicon microspheres, both in the transmission and elastic scattering spectra in the O-band. Approximately 23% of the power is coupled out at the resonance wavelength. The highest observed quality factor for the morphology dependent resonances was on the order of 10⁵. These resonances have a linewidth of 0.007 nm and a mode spacing of 0.19 nm.

Optical microsphere resonators, with their exceptionally low optical losses and high Q-factors, are attracting a lot of interest in integrated optics and related fields. Not being accessible by free-space beams, whispering gallery modes (WGM) of a microsphere resonator require near-field coupler devices. Efficient evanescent coupling has been demonstrated previously by using thin tapered fibres, fibre half-block couplers, angle-polished fibres and bulk prisms. In this work, we demonstrate WGM excitation in microspheres, from 8 to 15 μm in diameter, by using an integrated optics channel waveguide. Light from a tunable laser was coupled into a single mode K⁺ ion-exchanged channel waveguide formed in BK7 glass substrate. Dry borosilicate glass microspheres were dispersed on the substrate surface. Polystyrene microspheres were suspended in electrolyte water solution and confined in a closed cell on top of the waveguide. The light was coupled to the particles sitting on the waveguide surface. The scattered light was observed through the microscope. As the laser wavelength was tuned, the observed images were recorded with a CCD camera. WGM excitation was observed through the increased scattered light intensity at certain wavelengths. In the case of glass microspheres and a Ti:Sapphire tunable laser, the obtained resonance quality (Q-) factors were about 400. The resonances observed in polystyrene microspheres using a tunable diode laser had lower Q-factors and were deteriorating with decreasing particle size.

We demonstrate lasing in a cavity formed by two Mie scatterers in a dye colloidal solution. Like a Fabry-Perot cavity, the feedback mechanism for lasing is based on back scattering from each particle. Strong light amplification in between the scatterer pair not only compensate its large diffraction loss, but also help to choose the particular pair out of many scatterers in the suspension to form the laser cavity. Such cavity selection is facilitated by a careful designed cone shaped excitation geometry. Detailed experimental studies on the threshold behavior, spectral characteristic of lasing emission, and output directionality are presented. A simple theoretical model provides qualitative explanation for this lasing phenomenon.

We report on fabrication of new ultrahigh Q crystalline microcavities. Optical Q factor of (4.4±1.2)×10⁸ is achieved for Vacuum UV grade CaF₂ cavity with 100 μm in diameter. It is shown that if excimer grade crystal is used, Q factor of 5.5 mm cavity can be as high as (5.31±0.04)×10¹⁰ at laser wavelength of 1064 nm. We discuss nonlinear properties of these cavities such as Raman lasing with threshold of less than a few microwatts. Possible application in cavity quantum electrodynamics is analyzed.

By engineering the geometry of a nonlinear optical crystal, the effective efficiency of all nonlinear optical oscillations can be increased dramatically. Specifically, sphere and disk shaped crystal resonators have been used to demonstrate nonlinear optical oscillations at sub-miliwatt input power when cw light propagates in a Whispering Gallery Mode (WGM) of such a resonant cavity. In terms of both device production and experimentation in quantum optics, some nonlinear optical effects with naturally high efficiency can occult the desired nonlinear scattering process. The efficiency of second order nonlinear optical effects in ferroelectric crystals can be increased by engineering a poling structure to the crystal resonator. In this paper, I will discuss a new method for generating poling structures in ferroelectric crystal resonators called calligraphic poling. The details of the poling apparatus, experimental results, and speculation on future applications will be discussed.

Recently developed organic electro-optic materials have demonstrated large increases in activity creating a drive towards utilizing organics in ring micro-resonators and modulators. These materials allow for extremely low drive voltages and fundamental response times within the terahertz region. Present synthetic efforts have efficiently incorporated molecules with large first molecular hyperpolarizabilities, β, into macromolecular systems producing unprecedented electro-optic coefficients, r₃₃. Previously, incorporation of these large β molecules into macromolecular systems proved difficult due to phase separation or molecular aggregation within the processed films. Therefore, integration into workable devices was inconsistent and difficult. The new material systems however, have shown considerably enhanced film qualities, leading to improved device incorporation and fabrication. This paper will focus on current organic materials strategies and their incorporation into current ring micro-resonator devices and results.

We experimentally demonstrate Fano resonance line shapes tuning by using a Mach-Zehnder interferometer (MZI). We employ a silica 125-μm-size hexagonal micropillar resonator with prism coupling in one arm of the interferometer, and a phase shifter together with a variable attenuator in the other arm. Our initial experiments reveal that the resonance line shapes observed at the interferometer output are characteristically asymmetric as Fano resonances. By using the phase shifter, we controllably tune the asymmetric line shapes from near-symmetric dip to near-symmetric peak and back to near-symmetric dip. We discuss potential applications of our MZI-based microresonator resonance line shapes tuning for bio-chemical sensing.

An oxide aperture is used to confine optical modes in a micropillar structure. This method overcomes the limitations due to sidewall scattering loss typical in semiconductor etched micropillars. High cavity quality factors (Q) up to 48 000 are determined by external Fabry-Perot cavity scanning measurements, a significantly higher value than prior work in III-V etched micropillars. Measured Q values and estimated mode volumes correspond to a maximum Purcell factor figure of merit value of 72. A Purcell Factor of 2.5 is experimentally observed from a single quantum dot emitter coupled to a high Q cavity mode.

Quasiclassical approach and geometric optics allow to describe rather accurately whispering gallery modes in convex axisymmetric bodies. Using this approach we obtain practical formulas for the calculation of eigenfrequencies and radiative Q-factors in dielectrical spheroid and compare them with the known solutions for the particular cases and with numerical calculations. We show how geometrical interpretation allows expansion of the method on arbitrary shaped axisymmetric bodies.

With modern laser technologies we can cut multiple layers at once, yielding high production levels and short setup times between cutting runs. One example could be the operation of cutting the material named Nylon 66, used to manufacture automobile airbags. With laser, up to seven layers of Nylon 66 can be cut in one pass, that means high production rates on a single machine. Airbags must be precisely crafted piece of critical safety equipment that is built to very high levels of precision in a mass production environment. Of course, synthetic material, used for airbags, can be cut also by a conventional fixed blade system, but for a high production rates and a long term low-maintenance, laser cutting is most suitable. Most systems, are equipped with two material handling systems, which can cut on one half of he table while the finished product is being removed from the other half and the new stock material laid out. The laser system is reliable and adaptable to any flatbed-cutting task. Computer controlled industrial cutting and plotting machines are the latest offerings from a well established and experienced industrial engineering company that is dedicated to reduce cutting costs and boosting productivity in today's competitive industrial machine tool market. In this way, just one machine can carry out a multitude of production tasks. Authors have studied the cutting parameters for different textile materials, to reach the maximum output of the process.

We have investigated for the first time optical feedback noise characteristics of violet laser diode (LD) and also demonstrated its noise reduction by selecting the polarization of the feedback light in a typical optical disk pick-up system using 160mW type 405 nm GaN violet LD. The polarization axes of feedback light have been selected by means of rotatable quarter-wave plate (QWP). In this method, we have attained certain noise reduction without superposition of a high frequency (HF) component on driving current, which makes the pick-up system simple and inexpensive. As a result of our experiments, by selecting the angle of QWP relative to the original polarization axis of LD, we could suppress the optical output fluctuations caused by optical feedback from external cavity to less than 20% of peak-to-peak value in our violet laser diodes. In addition, we also measured noise reduction effect by the method of HF superposition. We achieved the noise suppression by selection of feedback light polarization as good as that of HF superposition. As a consequence, our present method could be a new approach for practical and simplified industrial fabrications of inexpensive, substantially low noise optical disk pick-up systems for high power violet laser diode.

The intracavity self-frequency conversion of laser radiation in active nonlinear crystal is studied. The spatial distributions of intensities and powers of laser radiation and radiation with conversed frequency are calculated by the method of numerical simulations as functions of parameters of cavity, active nonlinear crystal and pump. The analysis is performed for periodically poled Nd:Mg:LiNbO₃ crystal taking diffraction into account.

It is possible to construct summations of Laguerre-Gaussian modes which have the appearance of a zero order fundamental Gaussian but which, in fact, have no zero order content. These examples have circulated informally as a warning against trusting a single beam profile measurement as to the indication of the modal content of a given beam. These 'non-Gaussian' Gaussian beams also turn out to be extremely revealing of the fundamental assumptions upon which all modal decompositions and modal-based beam quality measures are based upon. Due to the contrived nature of these beams, they are also subject to some very subtle but important theoretical errors. This paper will rigorously examine a 'non-Gaussian', Gaussian beam in terms of its amplitude and phase characteristics, propagation behavior, M² and what it reveals about modal decompositions and modal beam quality measures in general.

We report here the development, construction and characterization of a flashlamp pumped Cr:LiSAF rod pumping cavity designed to minimize the thermal load on the crystal. The cavity is a close coupled one with 2 Xe lamps and absorptive filters between the lamps and the Cr:LiSAF rod, and is refrigerated with cooled water. A compact and stable (g₁×g₂=0.57) resonator was designed for lasers tests and gain medium characterization, and we expected to obtain operation at 20 Hz repetition rate. Nevertheless, the thermal load minimizing design was so successful that allowed laser operation up to 30 Hz with an average power of 20 W. When operating with a 10% transmission output coupler this laser exhibited an overall laser efficiency of 0.6% under 100 J electrical pumping, and a slope efficiency of 0.8%. Under these conditions, a maximum gain per pass of 1.5 was obtained, suitable for regenerative amplifiers. To increase the gain, the intracavity filters were substituted by glass plates, resulting in a gain per pass of 3.6, adequate for multipass amplifiers. In this configuration, and operating as a laser resonator, it showed a maximum overall efficiency of 2.81% under 88 J electrical pumping with a 25% transmission output coupler, and maximum output power of 18 W at 8 Hz. A study of the thermal load on the crystal was conducted by observation of the upper laser level lifetime, and we concluded that there are no noticeable accumulated thermal effects on the Cr:LiSAF emission.

We report on observation of photorefractive effects in whispering gallery mode resonators made of as-grown lithium niobate and lithium tantalate in the near as well as far infrared. The effects manifested themselves as dynamic modification of the spectra as well as quality factors of the resonators coupled to the laser radiation.

We extract the chirp of an ultrashort laser pulse accurately in real-time using a simple modified auto-interferometric correlation (MOSAIC) technique. Through the use of our newly developed time-domain algorithm, chirp information is accessible with signal-to-noise levels approaching unity. Correction algorithms have been developed to accommodate signal distortions due to bandwidth limitations, autocorrelator misalignment, and non-quadratic detector response.

The well tested and accepted ISO standard 11146 provides the measurement procedures to characterize the propagation properties of stigmatic and simple astigmatic laser beams which are intrinsically symmetric. The beam diameters are defined by the second order moments of the power density distribution which can be measured e.g. with a CCD-camera. In this standard the second order moments are used since the knowledge of these second order moments allows the calculation of the beam properties behind aberration-free optical systems with the well known ABCD-matrices. The new ISO/FDIS 11146-2 provides a new measurement procedure to characterize general astigmatic beams which are characterized by ten independent second order moments of their Wigner distribution. We present experimental results of the characterization of general astigmatic beams which are generated by propagating a simple astigmatic beam through a cylindrical lens which is tilted with respect to the symmetry axis of the beam. These generated general astigmatic beams are characterized according to the new ISO standard ISO/FDIS 11146-2. According to this standard the twist parameter is measured by acquiring two power density distributions in the focal plane of a cylindrical lens which is orientated in horizontally and vertically focusing direction. The twist parameter is given by the difference of these two mixed spatial moments divided by the focal length of the cylindrical lens. We present a possible improvement of this measurement technique by measuring in several planes behind the cylindrical lens. The measured data of the general astigmatic beams and their derived beam properties are presented with a detailed error analysis of the data.

The second-order moments method is a standard method to characterize laser beams. All beams are described by a beam matrix, with specific mathematical properties. The geometrical classification of these beams is based on their matrix structure, or symmetry, rather than on the symmetry of beams' cross sections in freespace propagation. Accordingly, the beams can be stigmatic, simple astigmatic, or general astigmatic. On the other hand, at propagation through ABCD-type optical systems, some intrinsic properties of the beams remain invariant. Two independent invariant quantities define two classes and four types of families of beams, providing the intrinsic classification of beams, irrespective of their geometrical classification. The paper reveals the intrinsic classification of the general astigmatic beams, by determining the intrinsic class and family each general astigmatic beam matrix belongs to. First, we summarize previous results which are important to understand and to obtain the new results of this paper. This includes the beam description using two more mathematical models, one using the same beam matrix with a different order of the elements, and the other being the gaussian-Schell-model. Then we show what kind of information on the invariants we can retrieve from the mathematical properties of the different quantities used in the three beam descriptions. Finally we analyze all possible non-degenerate matrices representing general astigmatic beams (ten in all) and apply the information retrieved as described above for each of them. The final result is a list of all ten matrices representing general astigmatic beams and their intrinsic classification.

Nowadays the power of lasers with diffraction beam quality is on significant rise. But it is not easy to achieve ideal quality because of severe undesired distortions. Under different forms of distortion the beam shows different behavior. With any form of distortions there is the need to qualitatively characterize the beam quality. Three various qualitative criteria are most commonly used for this purpose, each of them describing the beam with one ratio: overlapping integral, Strehl ratio, and M² parameter. All these criteria are well-known and frequently used in the literature, though the problem of their interrelation has never been discussed. In this paper we have analyzed the above mentioned criteria and have researched their interrelations in 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 shapes. The efficiency of characterizing those beams by various criteria is discussed.

To assign a diameter to a beam profile which does not feature an actual perimeter presents a formidable problem. Traditionally, different beam diameter criteria are used which, however, depending on the beam profile, may yield drastically different results. The second moment method has been standardised by ISO, however, it also has some limitations. While a certain diameter criterion may have advantageous properties for instance for describing the propagating beam, it may not be appropriate for other 'applications' such as scaling the thermal damage threshold or for calculating the power that passes through an aperture. We discuss the latter two on the basis of some example profiles which show that the second moment diameter is in these cases not an appropriate parameter. For laser safety, where the exposure limit for the eye (MPE) is stated as a function of what could be referred to as the 'thermal beam diameter', a diameter criterion is needed that yields a correct value for this parameter for any arbitrary size and shape of the beam profile at the retina. A procedure is proposed that can be applied to determine a 'thermal damage parameter' for a given beam profile. This procedure is checked against thermal model calculations of the damage threshold. It is also shown that the power that passes through an aperture (such as the pupil of the eye) can be seriously underestimated when using the second moment diameter for non-Gaussian beams.

Diode laser systems have been established for material processing and pumping solid state lasers in the recent years, due to flexibility, efficiency and lifetime. In the meantime, diode laser bars with an output power of more than 120 W and a beam parameter product less than 70 mm mrad are available (see fig. 1). Depending on the optical system an energy density in focus of more then 10⁶ Wcm^-2 can be achieved. But for several applications like hardening metal surfaces or welding thin blanks/plates the output power is insufficient. To increase optical output power several diode laser bars are arranged vertically and/or horizontally. With these so called stacks an optical output power of more than 4 kW can be achieved. Due to the incoherent beam coupling the beam parameter product is increased at the same rate. But the energy density or intensity in focus is rather less than constant. Other applications, e. g. welding or marking, require higher intensities, which can not be achieved with diode lasers. For these applications diode pumped solid state laser are mostly applied.

This day and age in the laser community we find a couple of coexisting and simultaneously competing approaches for the characterization of spatial laser beam properties. Around the well-established Method of Second Order Moments, described in full detail in the new ISO-Standard 11146/1-2-3, such methods are arranged like determination of Wigner Distribution Function, Hartmann-Shack wavefront sensor or decomposition of the beam into its transversal modal components. Each of mentioned methods has its own amenities, depending on specific demands and boundary conditions. To compare these approaches with each other with very high accuracy, it would be extremely helpful to have access to a set of ETALONs for different pure or composite transversal modes. Diffractive Optical Elements (DOEs) open a promising possibility to generate and to establish such ETALONs working later in different labs and under different conditions in a very reliable and reproducible manner. We present first results of considerations about designing, manufacturing and testing ETALONs for pure and for composite Gauss-Hermite modes.

On the basis of the irradiance-moments formalism, four matrices are proposed whose elements, defined for any partially coherent field, are closely related with the second-order measurable parameters handled in the ISO standard 11146. These matrices are shown to exhibit a number of properties concerning the orientation of the transverse beam profile. This behavior is described by the rotation of the principal axes of the field around its propagation axis. In addition, a new parameter is introduced in terms of the above matrices, which is invariant through rotationally-symmetric first-order optical systems.

Several overall parameters are introduced to characterize the linear or circular polarization content of a non-uniformly totally polarized beam over the region of its wavefront where the irradiance is significant. These parameters are determined from the values of the Stokes parameters. Experimental examples are also given to check both, the physical meaning of the proposed parameters and the validity of the measurement procedure.

The case of two identical and coaxial Gaussian beams is studied in order to consider the effects of diffraction in spatial beam characterization.

In the context of lifetime of optics in laser systems in space, spot size dependencies of laser induced damage thresholds have been investigated. The measurements were performed with two different Nd:YAG laser systems at 1064 nm with pulse durations of 8 and 50 ns and repetitition rates of 10Hz and 3kHz, respectively. The effective beam diameter was varied in the range of a few microns up to some tens of millimetres using several focussing optics. In preparation of the experimental analysis, simulations have been performed to determine the difference of the linear evaluation algorithm and a more sophisticated theoretical description of the damage threshold. Correspondence of simulated and experimental results should reveal information concerning the applicability of small spot sizes to standardized damage tests.

Driven by the increasing demands on optical components for DUV lithography, a system for angle resolved as well as total scatter measurements (ARS and TS respectively) at 193 nm and 157 nm has been developed at the Fraunhofer Institute in Jena. Extremely low background scattering levels of 10^-6 for the TS measurements and more than 12 orders of magnitude dynamic range for ARS have been accomplished. The variety of components to be measured extends from super-smooth substrates with sub-nanometer roughness to multilayer systems with pronounced nanostructures. Examples are presented for scatter analysis of DUV dielectric multilayers as well as for roughness analysis of super-smooth EUV mirrors.

We have tested a technique for characterizing optical substrates using high sensitivity of the constant of nonlinear refraction to the structural and compositional homogeneity of the material. The technique consists in two steps: first the substrate is positioned in the focal region of a lens where the signal of the nonlinear phase shift is maximal and, second, the substrate is scanned in directions transverse to the propagation direction of the probe laser beam. The measured variations are proportional to variations in the nonlinear phase shift across the substrate and reflect distribution of parameters that contribute into the nonlinear phase shift, including the absorption coefficient and substrate thickness. This technique can be used for mapping trace amounts of impurities, dopants and inclusions as well as varying external/boundary conditions in glass substrates, liquid crystals, and other materials. As an example, we have visualized subtle changes inflicted on a holographic glass by UV exposure.

All laser components can withstand a limited intensity of optical radiation and the measurement of laser-induced damage thresholds (LIDT) is required. In the case of repetitive pulses the LIDT measurements should be performed according ISO 11254-2 standard. This procedure is time consuming and puts a high requirement on human resources. In order to speed up the LIDT measurements with a minimal human resource we developed the automated station for LIDT measurements according ISO-11254-2 standard. In this paper we overview the main parts of this automated station and present the results of LIDT measurements with repetitive pulses. In order to control the LIDT measurements, software based on LabView programming package was created. The LIDT software controls experimental sample positioning in X and Y directions, laser pulse energy attenuation and shutter. It also automates damage detection and performs statistical analysis. The program recognizes damage by detecting scattered light from damaged surface. The input of sample and laser beam technical parameters is required to start the measurements. The minimal distance between test sites on the sample surface is calculated automatically, and the surface area is divided in to a hexagonal matrix. The program also chooses the laser pulse train energy for each test site. The program also allows fast damage inspection by translating the sample under the Nomarski microscope. After completion of measurement and damage inspection, the program automatically generates the measurement report.

We report the absorption and scattering losses measurements in IR range by high average power tunable radiation of optical parametric oscillator (OPO) based on a periodically poled lithium niobate (PPLN) pumped by a diode-pumped, Q-switched TEM₀₀ mode Nd:YVO₄ laser operated at 1064 nm.

That National Ignition Facility (NIF) at Lawrence Livermore National Laboratory (LLNL) will be the world's largest and most energetic laser. It has thousands of optics and depends heavily on the quality and performance of these optics. Over the past several years, we have developed the NIF Optics Inspection Analysis System that automatically finds defects in a specific optic by analyzing images taken of that optic. This paper describes a new and complementary approach for the automatic detection of defects based on detecting the diffraction ring patterns in downstream optic images caused by defects in upstream optics. Our approach applies a robust pattern matching algorithm for images called Gradient Direction Matching (GDM). GDM compares the gradient directions (the direction of flow from dark to light) of pixels in a test image to those of a specified model and identifies regions in the test image whose gradient directions are most in line with those of the specified model. For finding rings, we use luminance disk models whose pixels have gradient directions all pointing toward the center of the disk. After GDM identifies potential rings locations, we rank these rings by how well they fit the theoretical diffraction ring pattern equation. We perform false alarm mitigation by throwing out rings of low fit. A byproduct of this fitting procedure is an estimate of the size of the defect and its distance from the image plane. We demonstrate the potential effectiveness of this approach by showing examples of rings detected in real images of NIF optics.

Electra is a repetitively pulsed, electron beam pumped Krypton Fluoride (KrF) laser at the Naval Research Laboratory that is developing technologies to meet the Inertial Fusion Energy (IFE) requirements for durability, efficiency, and cost. Electra has demonstrated single shot and rep-rate laser energies as an oscillator exceeding 700 J with 100 ns pulsewidth at 248 nm. Peak output of 731 J laser energy in single shot operation demonstrates a total pulse intrinsic efficiency of 8.3%, and an intrinsic efficiency during the flat-top region of 9.6%. Improvements in the window transmissivity from the present 93% to excimer grade fused silica with anti-reflection coatings on both sides could provide up to 17% enhancement of the output intensity, and likewise for the efficiency. The Electra KrF gain measured in 4 positions of the laser aperture in an amplifier configuration demonstrates near field uniformity. In addition, the amplifier and oscillator results are qualitatively consistent in the pressure dependence on KrF yield. A quantitative Rigrod analysis and comparison is provided at the peak oscillator yield conditions for both, oscillator and amplifier, configurations. Continuous operation of the KrF laser at 300 J has lasted for 2.5 hours without failure at 1 Hz. Successful operation at 5 Hz with 400 J per pulse output has occurred in bursts of 100 seconds. In all of these runs the laser pulse waveform is extremely consistent from the first shot to the last.

Laser produced plasma EUV source is the candidate for high quality, 115 W EUV light source for the next generation lithography. Cost effective laser driver is the key requirement for the realization of the concept as a viable scheme. A CO₂ laser driven LPP system with a Xenon droplet target is therefore a promising light source alternative for EUV. We are developing a high power and high repetition rate CO₂ laser system to achieve 10 W intermediate focus EUV power. High conversion efficiency (CE) from the laser energy to EUV in-band energy is the primarily important issue for the concept to be realized. Numerical simulation analysis of a Xenon plasma target shows that a short laser pulse less than 15 ns is necessary to obtain a high CE by a CO₂ laser. This paper describes on the development of a CO₂ laser system with a short pulse length less than 15 ns, a nominal average power of a few kW, and a repetition rate of 100 kHz, based on RF-excited, axial flow CO₂ laser amplifiers. Output power of 1 kW has been achieved with a pulse length 15 ns at 100 kHz repletion rate in a small signal amplification condition with P(20) single line. The CO₂ laser system is reported on the conceptual design for a LPP EUV light source, and amplification performance in CW and short pulse using RF-excited axial flow lasers as amplifiers. Additional approach to increase the amplification efficiency is discussed.

Properties of plasma produced in volume nanosecond high-pressure discharge and plasma formation conditions under elevated pressure in various gases in a gap with a cathode having small curvature radius have been investigated. The not local criterion for runaway electrons generation is proposed.

Discharge and laser parameters in mixtures of SF₆ with H₂ and D₂ are studied using inductive and LC-generators. Excitation pulse parameters providing ultimate performance of discharge non-chain HF- and DF-lasers are determined. Processes affecting efficiency of the lasers are discussed. Ultimate intrinsic efficiency η_int of the HF and DF lasers up to 10 % and 7%, respectively, was realized in the SF₆-H₂ (D₂) mixtures. Electrical efficiency of the lasers up to η0 =6,4% with the output up to 1,5 J was demonstrated for the first time.

We have been developing a high average-power laser system for science and industry applications that can generate an output of 20 J per pulse at 10-Hz operation. Water-cooled Nd:glass zig-zag slab is pumped with 803-nm AlGaAs laser-diode modules. To efficiently extract energy from the laser medium, the laser beam alternately passes through dual zig-zag slab amplifier modules. Twin LD modules equipped on each slab amplifier module pump the laser medium with a peak power density of 2.5 kW/cm². In high power laser system, thermal load in the laser medium causes serious thermal effects. We arranged cladding glasses on the top and bottom of the laser slab to reduce thermal effects.

We developed the elemental technologies to construct a 500-W thin disk regenerative amplifier for EUV application. We obtained the well-polarized CW output of over 900 W without any compensation optics of the birefringence error. The extinction ratio of output was over 1:140. We developed and installed the water-cooled Pockels cell into the CW laser cavity to act as a polarization rotator by applying a DC-voltage to the cell. We confirmed that the cooled cell did not create distinguished birefringence and thermal lensing over 900-W operation. The deforming of thin-disk at high power operation was estimated by using a commercial M² meter. We optimized the cavity configuration from the estimation results to obtain high beam quality. After the optimization, the M² values kept up to 3.5 until the output reached to 400 W. At the 100-W output, the M² in vertical and horizontal plane were 1.47 and 1.43, respectively.

The Penn State Electro-Optics Center will be installing a 10 kW fiber laser at its Northpointe, PA facility in Fall 2005. This presentation will discuss the facility's capabilities and introduce three planned experiments that will utilize the high power near 1μm. The first experiment will be in the area of laser charring effects with semi-transparent composite materials. Previous work had been limited due to spot size requirements and limited available power. The new laser will enable effects testing up to levels of several hundred W/cm². The second application will be damage testing of optical coatings. Coating damage continues to be a major obstacle in the development of HEL systems. The new facility at the EOC will allow us to test optical coating damage at fluence relevant to HEL systems. A third planned application is the demonstration of a low-cost, non-coherent beam combiner. The combiner design will be discussed with preliminary results and plans for range testing at an underground mine location.

We have demonstrated the measurements of attenuation constant of a multi-mode fiber (300μm core diameter and 1km length) at 1070nm. The observed attenuation constant was below 0.7dB/km. The laser power of 5kW was coupled into the 1km fiber at 1070nm. The overall transmittance was 85 %. We observed the first Raman stokes in the transmitted laser spectrum. We demonstrated concrete cutting with a 4kW fiber laser at 1070nm. The demonstrated slab thickness was 100mm. This technique can be extended to thick concrete slabs more than 1m without laser power increasing.

Acoustic waves, generated in solids by irradiation of a surface with powerful laser pulses, are widely used to study mechanical, thermal and elastic properties of materials. Application of this technique to MEMS technology will open new insights into fabrication and characterization but will require understanding of acoustic wave generation in small-sized objects. To that end, acoustic wave generation was studied in thin (10-50 μm) metal and semiconductor foils (including Mo, Si, W, Ni, Ta, Au) back-side irradiated by nanosecond IR and UV laser pulses over a range of peak intensities. Both interferometric techniques and capacitance transducers were employed for detection of surface displacements in the foils. By varying the peak laser power over a wide range of intensities (1-500 MW/cm²) detection of the transition from a thermoelastic to a laser-plasma driven shock-wave mechanism for acoustic wave generation was possible. Measurements show that this transition is accompanied by a dramatic change in the waveform of the generated shock-wave and that this waveform differs for various materials and foil thicknesses. Since thin foils were studied, the longitudinal and shear waves were experimentally indistinguishable, making the observed waveform very complex. Moreover, at higher peak laser powers, mechanical vibrations at resonance frequencies of the thin foils can occur and further complicate the analysis. Nevertheless, the observed phenomena can be described in the framework of a simplified theoretical model and can be used for materials testing in different applications.

Time dependent, three-dimensional simulations of chemical oxygen-iodine laser and related flowfields are performed to elucidate the influence of unsteady fluid dynamics upon laser performance.

Generation of singlet oxygen metastables, O₂(a¹Δ), in an electric discharge plasma offers the potential for development of compact electric oxygen-iodine laser (EOIL) systems using a recyclable, all-gas-phase medium. The primary technical challenge for this concept is to develop a high-power, scalable electric discharge configuration that can produce high yields and flow rates of O₂(a) to support I(²P_1/2->²P_3/2) lasing at high output power. This paper discusses the chemical kinetics of the generation of O₂(a) and the excitation of I(²P_1/2) in discharge-flow reactors using microwave discharges at low power, 40-120 W, and moderate power, 1-2 kW. The relatively high E/N of the microwave discharge, coupled with the dilution of O₂ with Ar and/or He, leads to increased O₂(a) production rates, resulting in O₂(a) yields in the range 20-40%. At elevated power, the optimum O₂(a) yield occurs at higher total flow rates, resulting in O₂(a) flow rates as large as 1 mmole/s (~100 W of O₂(a) in the flow) for 1 kW discharge power. We perform the reacting flow measurements using a comprehensive suite of optical emission and absorption diagnostics to monitor the absolute concentrations of O₂(a), O₂(b), O(³P), I₂, I(²P_3/2), I(²P_1/2), small-signal gain, and temperature. These measurements constrain the kinetics model of the system, and reveal the existence of new chemical loss mechanisms related to atomic oxygen. The results for O₂(a) production at 1 kW have intriguing implications for the scaling of EOIL systems to high power.

Singlet delta oxygen O₂(a¹Δg) (SDO) production in a slab discharges ignited in oxygen gas mixtures was experimentally studied. An influence of gas mixture content and input electric power on SDO yield was analyzed. In self-sustained RF slab discharge SDO yield of 10±5% was measured by comparison luminescence intensity of SDO going from a chemical generator and SDO generated in electric discharge. SDO yield of 7.2% was measured by intracavity laser spectroscopy method. It was demonstrated that the choice of electrodes material is very important. Experiments on SDO production in slab non-self-sustained discharge with external ionization by repeating high-voltage pulses were carried out. SDO concentration was measured by the method of intracavity laser spectroscopy. The measured concentration of SDO was about 1.5 10¹⁶ cm^-3, with SDO yield of ~10.6%. A development of electric discharge oxygen-iodine laser with SDO production in long electrodes slab discharge is discussed.

Oxygen-iodine lasers that utilize electrical or microwave discharges to produce singlet oxygen are currently being developed. The discharge generators differ from conventional chemical singlet oxygen generators in that they produce significant amounts of atomic oxygen. Post-discharge chemistry includes channels that lead to the formation of ozone. Consequently, removal of I(²P_1/2) by O atoms and O₃ may impact the efficiency of discharge driven iodine lasers. In the present study we have measured the rate constants for quenching of I(²P_1/2) by O(³P) atoms and O₃ using pulsed laser photolysis techniques. The rate constant for quenching by O₃, 1.8x10^-12 cm³ s^-1, was found to be a factor of five smaller than the literature value. The rate constant for quenching by O(³P) was 1.2x10^-11 cm³ s^-1. This was six times larger than a previously reported upper bound, but consistent with estimates obtained by modeling the kinetics of discharge-driven laser systems.

Heterogeneous iodine cluster formation has been identified as the responsible factor resulting in large iodine titration requirements for Boeing's first high Mach number nitrogen ejector nozzle. A solution employing geometrically produced aerodynamic heating in the flow was envisioned to break up these clusters. Horizontal and vertical wire arrays (cluster busters) placed downstream of the nozzle exit plane (NEP) have been shown to significantly reduce the optimal iodine titration and to greatly improve the power extraction efficiency of the Chemical Oxygen-Iodine Laser utilizing this first generation ejector nozzle.

The NCl-I laser has been demonstrated using HN₃ as a fuel with a combustor to produce chlorine atoms. In this paper, we discuss the possibility of producing NCl(a¹Δ) from the auto-decomposition of NCl₃. This would eliminate the requirement for a combustor. We present the results of experiments and kinetic modeling designed to understand the basic physical processes in this system. The NCl-I laser operates using only gaseous species, eliminating the need for heterogeneous gas liquid reactions such as used in COIL chemical lasers. The lasing species is the same as in COIL, simplifying the scaling process since many optical, tracking and propagation problems have been demonstrated in other programs.

We discuss experimental results from spectroscopic and kinetic investigations of the reaction sequence starting with NCI₃ + H. Through a series of abstraction reactions, NCI (a¹Δ) is produced. We have used sensitive optical emission diagnostics and have observed both [NCI(a¹Δ)]and [NCI(b¹Σ)] produced by this reaction. Upon addition of HI to the flow, the reaction of H + HI produced iodine atoms that were pumped to the excited I(²P_1/2) state, and we observed strong emission from the I atom ²P _1/2 -> ²P_3/2 transition at 1.315 μm. With a tunable diode laser we probed the I atom transition and observed significant transfer of population from ground state (²P_3/2) to the excited state (²P_1/2) and have observed optical transparency within the iodine atom energy level manifold.

An extensive development of high power lasers for military and civilian applications has resulted in several highly successful laser systems based on chemical lasers. These lasers have some undesirable features, most notably their use of dangerous chemicals and excessive size. Alternative laser systems such as solid state, fiber lasers and semiconductor lasers have not achieved the necessary powers and beam quality. In this paper we present the results of our work on optically pumped cesium vapor laser development. We demonstrated efficient cesium laser operation at wavelength 894 nm with diode laser pumping. The measured optical efficiency was more than 32% with an overall electrical to optical efficiency of 15%. With an improved cavity design and narrowband pump source we have demonstrated Cs laser with slope efficiency of 81% and overall optical efficiency of 63%. This laser can be scaled to higher powers by increasing the volume of the active medium and number of narrowband pump diode lasers.

A rectangular negative branch off-axis hybrid resonator was coupled to a 10-kW class Chemical Oxygen-Iodine Laser (COIL). Various schemes of geometrical coupling between resonator and gain medium were investigated. The extracted power was 6.6 kW and reached about 70% of the output power for the COIL device in an optimized conventional stable resonator configuration. Experimentally measured margins for the sensitivity of resonator setup and alignment were found in close agreement with numerical calculations. Power density distributions were measured in the near field and in the far field. The divergence of the emitted laser beam in the unstable direction was lower than 2 times diffraction limited.

In an electric discharge Oxygen-Iodine laser (ElectricOIL), the desired O₂(a¹Δ) is produced using a low-to-medium pressure electric discharge. The discharge production of atomic oxygen, ozone, and other excited species adds higher levels of complexity to the post-discharge kinetics which are not encountered in a classic purely chemical O₂(a¹-Δ) generation system. Mixing effects are also present. In this paper we present post-discharge modeling results obtained using a modified version of the Blaze-II gas laser code. A 28 specie, 105 reaction chemical kinetic reaction set for the post-discharge kinetics is presented. Calculations were performed to ascertain the impact of a two stream mixing mechanism on the numerical model and to study gain as a function of reactant mass flow rates. The calculations were compared with experimental data. Agreement with experimental data was improved with the addition of new kinetics and the mixing mechanism.

A novel subpicosecond pulse radiolysis experimental system has been developed in Terawatt Ultrafast High Field Facility (TUHFF) at Argonne National Laboratory. TUHFF houses a 20 TW Ti:sapphire laser system that generates 2.5 nC sub-picosecond pulses of 4-25 MeV electrons at 10 Hz using laser wakefield acceleration. The system has been optimized for chemical studies. The subpicosecond electron pulses were used to generate hydrated electrons in pulse radiolysis of liquid water. Preliminary transient absorption spectroscopy data with picosecond resolution is presented.

Methane hydrate is a energy resource distributed even in the resource-less countries such as Japan and India. The energy is necessary to extract the methane from the methane hydrate and COIL is the unique solution for the extraction tool, because fuels of COIL can be produced from the natural energy without the fossil energy resources. The experimental results of laser light-methane hydrate interaction, multi kW laser light transmission through 1 km optical fiber, and the estimation of the extracted methane by radiation of the multi hundreds kW COIL output on the methane hydrate layer, will be reported.