This PDF file contains the front matter associated with SPIE Proceedings Volume 6452, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

We developed a Nd:YAG rod-based MOPA to generate high power in a radially-polarized beam. Two pump-chambers in the amplifier section produced 2.1kW @ M²=9.5, while three pump-chambers yielded 3.1kW @ M²=14. Efficiency in the last pump-chamber was 33%. Several techniques were utilized to enhance beam-quality: an azimuthally-polarized oscillator, special pump-chambers, external compensation of lower-order aberrations, and high-order aberration compensation by pairing pump-chambers.

Dynamic tuning of systems of microresonators coupled to waveguides allows a rich range of physical effects. Periodic resonator arrays can be tuned to stop and store light pulses, theoretically allowing for tunable delay devices in which the delay is limited neither by bandwidth nor by dispersion. For two-resonator systems, adjustable delays can be obtained from tuning a narrow transparency resonance. Similar behavior is also predicted in a quite different physical system, that of a single photon interacting with dynamically-tuned quantum bits.

We analyze the effect of a highly dispersive element placed inside a modulated optical cavity on the frequency and amplitude of the modulation to determine the conditions for cavity self-stabilization and enhanced gyroscopic sensitivity. We find an enhancement in the sensitivity of a laser gyroscope to rotation for normal dispersion, while anomalous dispersion can be used to self-stabilize an optical cavity. Our results indicate that atomic media, even coherent superpositions in multilevel atoms, are of limited use for these applications, because the amplitude and phase filters work against one another, i.e., decreasing the modulation frequency increases its amplitude and vice-versa. On the other hand, for optical resonators the dispersion reversal associated with critical coupling enables the amplitude and phase filters to work together. We find that for over-coupled resonators, the absorption and normal dispersion on-resonance increase the contrast and frequency of the beat-note, respectively, resulting in a substantial enhancement of the gyroscopic response. Under-coupled resonators can be used to stabilize the frequency of a laser cavity, but result in a concomitant increase in amplitude fluctuations. As a more ideal solution we propose the use of a variety of coupled-resonator-induced transparency that is accompanied by anomalous dispersion.

We report on the light transport phenomena in linear chains composed of several tens of touching spherical microcavities. A new optical mode type, namely nanojet-induced modes (NIMs) is observed. These modes result from the optical coupling of microspheres acting as a series of micro-lenses, which periodically focus propagating wave into photonic nanojets. Theoretically, formation of periodic nanojets has been predicted in Z. Chen et al., Opt. Lett. 31, 389 (2006). The chains were produced by means of the self-assembly directed by micro-flows of water suspension of polystyrene microspheres. The mean size of spheres was varied in the 2-10 micron range. To couple light to NIMs we used built-in emission sources formed by several locally excited dye-doped microcavities from the same chain. Conversion of modes emitted by the light source into the NIMs results in losses of several dB per sphere in the vicinity (first few tens of spheres) of such sources. At longer distances we found an attenuation rate as small as 0.5 dB per sphere that reveals low intrinsic propagation loss for NIMs. The NIMs have potential applications for coupling and guiding of light in compact arrays of spherical cavities with extremely high quality (Q) whispering gallery modes.

Experiments in laser physics often require more comprehensive information about a beam than can be extracted from single spatial profile measurements alone. In particular, the determination of irradiance and phase distribution at locations were measurement is difficult as well as the accurate measurement of important 2^nd order moment based beam parameters, as e.g. M², divergence or Strehl-ratio, are quite often essential for a wide class of laser applications. Here we compare Hartmann-Shack results of numerical beam propagation and parameter estimation to camera based profile measurements and the standard ISO 11146 procedure, respectively. He-Ne fundamental mode beams (with and without aberration) were investigated. For spatially coherent, high to moderate quality beams (M²<2) the numerically propagated and measured beam profiles are in good agreement and 2^nd order moment beam parameters differ by less than 5% for the standard method and Hartmann-Shack. Partial coherent beams on the other hand require information beyond Hartmann-Shack. Drawbacks and opportunities of the Hartmann-Shack technique for means of laser beam parameters are discussed.

In both scientific and industrial laser beam applications is essential for users to know what could be expected from the laser beam. That is why analysis of the laser beam parameters is very important during laser use in various industrial and scientific applications. To describe the beam one can use a beam quality factor M² that characterizes the degree of imperfection of a laser beam. There are many methods of beam quality determination. The most common way is to use a device based on techniques described in the International Standard ISO11146 "Test methods for laser beam parameters: Beam widths, divergence angle and beam propagation factor". For example we can use M2-sensor that we design and produce in our Lab. The measurement of the beam quality factor according to ISO11146 is not a simple procedure and might take a long time. And for some applications fast beam quality determination is needed. Moreover sometimes it is not necessary to know the exact value of M², only estimation of M² is just needed. And for the beam quality estimation we suggest to use Shack-Hartmann wavefront sensor. With this sensor we can easily and fast measure the wavefront of the beam and then according to the wavefront calculate M². The comparison of two sensors is presented. Advantages and disadvantages are pointed out.

Measurement of the laser beam propagation factor M² is essential in many laser applications including materials processing, laser therapy, and lithography. In this paper we describe the characterisation of a prototype device using a cross-distorted diffraction grating known as an Image Multiplex (IMP^(R)) grating, to measure the M² value of laser beams. The advantage of the IMP^(R) grating instrument lies in its ability to simultaneously image nine positions along the beam path. This enables beam propagation parameters to be calculated both for pulsed lasers and lasers with rapidly changing propagation characteristics. This is in contrast to the scanned technique recommended by the ISO, which is relatively slow and in practice can only be easily used with cw sources. The characterisation was accomplished by comparison of results from the IMP^(R) grating device with those obtained using the accepted methodology described in the ISO 11146 series of standards through measurements conducted by the National Physical Laboratory. The scope of the work also included provision of a traceability route to international standards, and an uncertainty budget, to allow the intended user community to have confidence in measurements obtained when using the device, and to enable them to use it as part of their quality framework.

Electronic laser beam profiling is now a widely accepted method to measure the mode quality and spatial profile of a laser beam. For the most part, profiling has been limited to the unfocused or 'raw' beam, because the energy density or irradiance in the vicinity of focus is high enough to destroy almost any measurement device. Recent developments in measuring technology now enable users to make beam profiling measurements at and near the focus of many lasers. We discuss two new designs and show examples of how they function.

An adaptive optics system was developed to reduce the time taken to reach full brightness of a solid-state laser. This system was based on the translation of the end-mirror during the turn-on time of the laser. It was implemented on a simple laser configuration featuring a side-pumped Nd:YLF rod and resulted in the reduction of the transient time by a factor of 15. Several limitations such as the innate astigmatism of Nd:YLF and the inertia of the moving mirror were also observed.

In this work we present results of the given intensity distribution formation in the far-field by means of extracavity and intracavity techniques. In both cases we consider formation by means of flexible mirror composed of semipassive bimorph element. As extracavity technique we apply iterative Gerchberg-Saxton algorithm and as intracavity one we consider genetic algorithm of mirror voltage control.

Progress in laser resonators and beam control requires new criteria for laser beam characterization, especially with spatial and longitudinal modes which tend to oscillate and are critical to their role as high power pump sources in solid state lasers. Previous papers by the author (K. J. Jones, 200f), (K. J. Jones, 2006) have applied wavelet-based phase extraction and adaptive wavelets to distortion correction in laser diode arrays. Adaptive optics aim at achieving greater dynamic stability in laser systems. This investigation examines multiple spatial and longitudinal modes in diode laser arrays and applies wavelets, first to determine the phase of the oscillating modes and adaptive wavelets to minimize mode distortion.

New methods of laser metrology (interferometry and microscopy) based on applications of beams with special structures provide increased resolution and efficiency. To generate a beam with linear singularity (dark beam) we recently proposed a beam shaping method using a bi-prism-like element within the laser resonator. There we have studied resonators that are traditionally designed to oscillate on the fundamental mode designed within the range of configuration parameters, 0.5⩽G⩽1. In the present work we extend the approach and show that the choice of specific configurations, outside the above range of configuration parameters, can lead to much better results for our application. This is the case in particular for an approximately semi-concentric resonator (G ~ -1).The optimal dark beam is obtained for a bi-prism angle about twice that obtained for the earlier configurations. For this case the difference between the losses of the first odd mode and other modes is 0.12-0.15, which is adequate for oscillation on this mode in lasers with any type of active media.

Presented is a study of a coaxial, hybrid-stable-unstable resonator for high power lasers. The coaxial configuration allows the realization of the outcoupling and rear mirror in one mechanical structure with the incorporation of an axicon mirror with retroreflective characteristics as an intra-cavity folding mirror. The design of the stable direction is investigated to optimize the set-up for best beam quality and minimized alignment sensitivity. Additionally, the instable direction is examined to achieve an even heat load on the mirrors. Simulations of the laser structure are performed and compared to measurements.

Low-dimensional ordered arrays of dielectric particles can possess bound optical modes having an extremely high quality factor depending on the material used. If these arrays consist of metal particles, then they cannot have a high quality factor because their light absorption restricts performance. In this paper we address the following question: can bound modes be formed in dielectric systems where the absorption of light is negligible? Our investigation of circular arrays of spherical particles within the framework of the multisphere Mie scattering theory using the simplest dipolar-like approach shows that (1) high quality modes in an array of 10 or more particles can be attained at least for a refractive index n_r > 2, so optical materials like TiO₂ or GaAs can be used; (2) the most bound modes have nearly transverse polarization perpendicular to the circular plane; (3) in a particularly interesting case of TiO₂ particles (rutile phase, n_r = 2.7), the quality factor of the most bound mode increases almost by an order of magnitude with the addition of 10 extra particles, while for particles made of GaAs the quality factor increases by almost two orders of magnitude with the addition of ten extra particles. The consideration of higher multipole contributions has demonstrated that the error of the dipolar approach does not exceed one percent if the refractive index n_r is greater than 2. Minimum acceptable disordering not affecting the quality factor is studied.

It is explained how FEMLAB / COMSOL Multiphysics can be configured to calculate, the frequencies, electromagnetic-field patterns, mode volumes, filling factors, radiation losses ... of the whispering-gallery modes of axisymmetric microresonators. The method exploits COMSOL's ability to accept the definition of solutions to Maxwells equations in so-called 'weak form'. As no transverse approximation is imposed, it remains accurate even for so-called quasi-TM and -TE modes of low, finite azimuthal mode order, as are relevant to applications in non-linear/quantum optics. The method's utility is exemplified by simulating various microresonators in the form of dielectric toroids and disks.

Comprehensive microcavity laser models should account for several physical mechanisms, e.g. carrier transport, heating and optical confinement, coupled by non-linear effects. Nevertheless, considerable useful information can still be obtained if all non-electromagnetic effects are neglected, often within an additional effective-index reduction to an equivalent 2D problem, and the optical modes viewed as solutions of Maxwell's equations. Integral equation (IE) formulations have many advantages over numerical techniques such as FDTD for the study of such microcavity laser problems. The most notable advantages of an IE approach are computational efficiency, the correct description of cavity boundaries without stair-step errors, and the direct solution of an eigenvalue problem rather than the spectral analysis of a transient signal. Boundary IE (BIE) formulations are more economic that volume IE (VIE) ones, because of their lower dimensionality, but they are only applicable to the constant cavity refractive index case. The Muller BIE, being free of 'defect' frequencies and having smooth or integrable kernels, provides a reliable tool for the modal analysis of microcavities. Whilst such an approach can readily identify complex-valued natural frequencies and Q-factors, the lasing condition is not addressed directly. We have thus suggested using a Muller BIE approach to solve a lasing eigenvalue problem (LEP), i.e. a linear eigenvalue solution in the form of two real-valued numbers (lasing wavelength and threshold information) when macroscopic gain is introduced into the cavity material within an active region. Such an approach yields clear insight into the lasing thresholds of individual cavities with uniform and non-uniform gain, cavities coupled as photonic molecules and cavities equipped with one or more quantum dots.

In parallel to a stand-alone microsphere resonator and a planar ring resonator on a wafer, the liquid core optical ring resonator (LCORR) is regarded as the third type of ring resonator that integrates microfluidics with state-of-the-art photonics. The LCORR employs a micro-sized glass capillary with a wall thickness of a few microns. The circular cross section of the capillary forms a ring resonator that supports the whispering gallery modes (WGMs), which has the evanescent field in the core, allowing for repetitive interaction with the analytes carried inside the capillary. Despite the small physical size of the LCORR and sub-nanoliter sensing volume, the effective interaction length can exceed 10 cm due to high Q-factor (10⁶), significantly improving the LCORR detection limit. The LCORR is a versatile system that exhibits excellent fluid handling capability inherent to capillaries and permits non-invasive and quantitative measurement at any location along the capillary. Furthermore, the LCORR uses the refractive index change as a transduction signal, which enables label-free detection. Therefore, the LCORR is a promising technology platform for future sensitive, miniaturized, lab-on-a-chip type sensors. In this paper, we will introduce the concept of the LCORR and present the theoretical analysis and the experimental results related to the LCORR sensor development.

We introduce a definition of group velocity for a system with a discreet spectrum and apply it to a linear resonator. We show that a positive, negative, or zero group velocity can be obtained for light propagating in the whispering gallery modes of a microspherical resonator. The associated group delay is practically independent of the ring-down time of the resonator. We demonstrate "stopped light" in an experiment with a fused silica microsphere.

An optical microfiber with the diameter significantly less than the radiation wavelength ~ 1 micron is often called a nanofiber (NF). The fundamental mode of a NF consists primarily of an evanescent field propagating in the ambient medium outside a NF. Any deformation of a NF changes the evanescent field. If a NF is thin enough, even a very small deformation may cause dramatic changes of the evanescent field structure. The simplest types of deformation of a uniform NF are bending and tapering. The structure of evanescent field and optics of radiation loss in bent uniform microfibers is understood quite well. It is determined by an effective potential barrier terminated by a caustic surface, which separates the tunneling and classically allowed regions. Tunneling through the barrier determines the radiation loss. Alternatively, for an adiabatically tapered microfiber, called a nanotaper (NT), a similar potential barrier of finite width cannot be introduced. Instead, the radiation loss in a NT takes place in small neighborhood of focal circumferences of the evanescent field, while a NT is lossless elsewhere. More specifically, for a NT, the mentioned caustic surface becomes complex and can intersect real space along certain lines only. These lines are the focal circumferences where the radiating modes and the guiding mode are split off. As examples, conical and biconical NTs with characteristic shapes are considered. The theoretically predicted interference between the guiding and radiating components of the evanescent field are confirmed by the beam propagation method (BPM) numerical modeling. The derived analytical expressions for radiation loss are in a good agreement with BPM calculations. Finally, a simple estimate formula for radiation loss of a NT is suggested.

We demonstrate biochemical detection based upon specific binding of untagged analytes to modified surfaces of high-Q optical microresonators with whispering-gallery (WG) modes. Extremely small absolute amounts of bound analyte, down to 0.25 fmol of streptavidin, are detected via displacement of the resonance frequencies of the WG modes. The sensitized microresonators are dry and storable, and the flow cell sensor design lends itself to cheap, expendable fabrication.

Numerical studies of the vector electromagnetic fields in plano-concave microresonators have recently revealed that a photonic analogue of spin-orbit coupling can occur in paraxial geometries. Laguerre-Gauss modes with circular polarization are then no longer the correct eigenstates, even if the resonator is axially symmetric. A crucial role in this effect is played by the presence of a boundary (e.g., a Bragg mirror) whose reflectivity at non-normal incidence is polarization-dependent. Aiming for an analytical treatment that can incorporate both form birefringence and non-paraxiality, we explore the Born-Oppenheimer method as an alternative to the paraxial approximation. The conditions for the validity of these two approaches are different, but in a regime where they overlap we show that all the major results of paraxial theory can also be derived from the Born-Oppenheimer method. We discuss how this new approach can incorporate the Bragg stack physics in a way that can overcome the limitations of paraxial theory.

Photonic molecules, named by analogy with chemical molecules, are clusters of closely located electromagnetically interacting microcavities or "photonic atoms". As two or several microcavities are brought close together, their optical modes interact, and a rich spectrum of photonic molecule supermodes emerges, which depends both on geometrical and material properties of individual cavities and on their mutual interactions. Here, we discuss ways of controllable manipulation of photonic molecule supermodes, which improve or add new functionalities to microcavity-based optical components. We present several optimally-tuned photonic molecule designs for lowering thresholds of semiconductor microlasers, producing directional light emission, enhancing sensitivity of microcavity-based bio(chemical)sensors, and optimizing electromagnetic energy transfer around bends of coupled-cavity waveguides. Photonic molecules composed of identical microcavities as well as of microcavities with various degrees of size or material detuning are discussed. Microwave experiments on scaled photonic molecule structures are currently under way to confirm our theoretical predictions.

We present the results of studies on small photonic microtube structures of less than 10 microns diameter. A new technique based on vacuum assisted filtration is used to produce the microtube resonantors. Whispering gallery modes are probed through the photoluminescence emission from the glass material forming the cavity. We observe resonances with polarized emission having quality factors up to 3000. These microresonator structures exhibit a large evanescent field which makes them interesting for potential photonic applications.

We propose theoretically and demonstrate experimentally a method for generation of beams of light possessing large angular momenta. The method utilizes cylindrical optical waveguides as well as whispering gallery mode resonators that efficiently transform a plane electromagnetic wave into truncated Bessel beams. Generation of the high order beams with well defined angular momenta is demonstrated.

We show that a glass micro-sphere resonator can be used as a wavelength-selective mirror in fiber lasers. Due to their high quality-factor (Q ~10⁸), microsphere resonators possess a narrow reflection bandwidth. This feature enables construction of single-frequency fiber lasers even when the cavity is long. We also propose and demonstrate an active Q-switched fiber laser using a high-Q micro-sphere resonator as the Q-switching element. The laser cavity consists of an Er-doped fiber as the gain medium, a glass micro-sphere reflector (coupled through a fiber taper) at one end of the cavity, and a fiber Bragg grating reflector at the other end. The reflectivity of the micro-sphere is modulated by changing the gap between the micro-sphere and the fiber taper. Active Q-switching is realized by oscillating the micro-sphere in and out of contact with the taper. Nonlinear effects (such as stimulated Raman lasing) were also observed in our setup at relatively low pump powers.

We have investigated bound modes in finite linear chains of dielectric particles of various lengths, interparticle spacing and particle materials. Through a unique application of the multisphere Mie scattering formalism, we have developed numerical methods to calculate eigen-optical modes for various arrays of particles. These numerical methods involve the use of the multisphere scattering formalism as the entries in N×N matrices where N represents the number of particles in the chain. Eigenmodes of these matrices correspond to the eigen-optical modes of interest. We identified the eigenmodes with the highest quality factor by the application of a modified version of the Newton-Raphson algorithm. We found that convergence is strong using this algorithm for linear chains of up to several hundreds of particles. By comparing the dipolar approach with the more complex approach which utilizes a combination of both dipolar and quadrupolar approaches, we demonstrated that the dipolar approach has an accuracy of approximately 99%. We found that the quality factor Q of the mode increases with the cubed value of the number of particles in chain in agreement with the previously developed theory, the effects of disordering of particle sizes and inter-particle distances will be discussed.

It is presented a new method that allows real-time measurement of the laser beam quality from a single lateral image of a beam propagating in a scattering medium. The development of this method involved studies of an adequate scattering medium and the design of an image acquisition optical system. Comparing with traditional methods, this new method is faster and less exhaustive, providing multiple beam diameters measurements with the same (or even better) accuracy from a unique image in real time. For a single mode HeNe laser beam, it was obtained the value M² = 1.1 ± 0.1.

We have been developing the vacuum ultraviolet (VUV) light sources and novel applications using such short wavelength emission sources. High quality amorphous Si thin films were successfully produced at room temperature as a result of photo-dissociation of SiH₄ gas by using an Ar₂* excimer lamp irradiation at 126 nm. To enhance such novel VUV processing applications, a compact VUV amplifier at 126 nm was developed by use of the optical-field-ionization (OFI) electrons. The gain-length product around 5 was obtained as a result of the optical feedback by using a VUV mirror. This amplifier was operated in a table-top size with a high repetition rate up to several kHz, which should be appropriate for any process applications. We also describe the schematic concept of the ultrashort pulse high-intensity VUV laser system at 126 nm with a pulse width of 100 fs.

We demonstrate the selective modal oscillation behavior of Random Lasing (RL) by using a one-dimensional RL model. This calculation model consists of "one-dimensional scattering model", rate equations, and "cavity term". Using this model, we investigate how the number and the kinds of modes change as the "randomness" of the medium changes. Calculation results indicate that there exists the region of "randomness" where the dynamics of emission spectrum shows selective modal oscillations: certain modes strongly oscillate and shape of the emission spectrum drastically changes.

The paper describes the results of investigations of optical phenomena on an RF excited slab-waveguide CO₂ laser. The experiments are performed in two optical arrangements: two-mirror resonator and three-mirror one. The main purpose of the experiments is to check possibilities to observe the optical phenomena using a microphone. The laser plasma is modulated with a self-mixing signal in the three-mirror resonator. The response of the microphone is observed and analyzed. Detection of the laser signature phenomenon with the microphone is experimentally considered. The experiments are done at cw regime of the laser. The investigations are performed at pulse operation of the laser, as well. The response of the microphone is analyzed. It is checked how the laser pulse is reconstructed at a profile of the microphone signal. The output laser pulse with a mapped laser signature in the laser pulse profile is compared to the microphone signal shape. The presence of the laser signature at the acoustic signal is investigated.