This PDF file contains the front matter associated with SPIE Proceedings Volume 9194 including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

We study both theoretically and experimentally the cross-correlation function of single-ringed Laguerre-Gaussian (LG) beams, which allows us to determinate the topological charge of the beam by performing power measure-ments only. We employ a superposition of two exact copies of the original LG beam whose centroids are displaced from each other. The behaviour of the auto-correlation is studied as a function of the displacement between these two copies of the beam for different topological charges. Our results indicate that the auto-correlation is described by a polynomial function of the displacement parameter, and the number of zeros of this polynomial maintains a one to one correspondence with the topological charge. A detailed description of the experiment to perform these measurements is also provided, our experimental findings are in excellent agreement with the theory. This technique offers an alternative for measuring the content of orbital angular momentum in a beam without the need of a camera.

We generated holographic masks starting with the interference between the reference beam and the signal beam, which is diffracted by the object. We investigate additive and multiplicative combinations between conical and helical phase distributions as compound objects to be inserted in the signal beam. We explored experimentally the dynamics of the diffracted intensity patterns, in two and three dimensions, after these holographic masks are addressed onto a programmable spatial light modulator. The diffracted intensity spatial arrangement contain information about constructive parameters used for holographic masks generation and exhibit asymmetric shapes and peaks along the optical axis in all analyzed compound objects. We introduce a reading mask in the optical path and, by analyzing changes of the spatial distribution in the final diffracted intensity arrangement, is possible to read the values of the constructive parameters. The generation of these reading masks in each case is discussed.

We present a simple way of simulating Spontaneous parametric down-conversion (SPDC) by modulating a classical laser beam with two spatial light modulators (SLM) through a back projection setup. This system has the advantage of having very high photon count rates, it can simulate a large range of pump beam profiles simply by modifying the hologram on the SLM, and it can be easily converted to a SPDC setup by simply changing only two of its components without the need to perform realignment. This setup can be used to give an indication whether a SPDC experiment will be feasible in a very short amount of time.

Bessel-Gaussian (BG) modes possess unique characteristics that have been exploited in the classical world and which may also offer advantages over other modes in the quantum regime. The easily adjustable radial scale of BG modes provides a more favourable basis of orbital angular momentum (OAM) entanglement over Laguerre- Gaussian (LG) modes, where the radial dependence is often ignored. We demonstrate high-dimensional entanglement with the BG modes and show a higher fidelity than the LG modes. We use the reconstruction property of BG modes to recover the degree of entanglement of our quantum state after encountering an obstruction. By moving the obstruction along the path of propagation of the entangled photon pairs, we quantitatively show a increase in the degree of entanglement as the obstruction was moved beyond that minimum distance.

Quantum ghost imaging using entangled photon pairs has become an interesting field of investigation as it illustrates the quantum correlation between the photon pairs. We introduce a new technique using spatial light modulators encoded with appropriate digital holograms to recover not only the amplitude, but also the phase of the digital object. Down-converted photon pairs are entangled in the orbital angular momentum basis, which are typically measured using a spiral phase hologram. Thus by encoding a spiral annular slit hologram into the idler arm, and varying it radially we can simultaneously recover the phase and amplitude of the field in question. We show that there is a good correlation between the encoded field function and the reconstructed images.

We propose a 2-dimensional method for Bessel Gaussian beam azimuthal and radial decomposition using digital holograms. We illustrate the reconstruction of a Bessel Gaussian beam after encountering an obstruction. From the measured decomposition we show the reconstruction of the amplitude, phase and azimuthal index of the field with high degree of accuracy.

A long-standing question in optics has been to efficiently measure the phase (or wavefront) of an optical field. This has led to numerous publications and commercial devices such as phase shift interferometry, wavefront reconstruction via modal decomposition and Shack-Hartmann wavefront sensors. In this work we develop a new technique to extract the phase which in contrast to previously mentioned methods is based on polarization (or Stokes) measurements. We outline a simple, all-digital approach using only a spatial light modulator and a polarization grating to exploit the amplitude and phase relationship between the orthogonal states of polarization to determine the phase of an optical field. We implement this technique to reconstruct the phase of static and propagating optical vortices.

We describe a novel coherent radiation enhancement technique and its application to laser beam shaping. The technique is based on coherent transformations of the propagating radiation employing amplitude and/or phase structures, and produces localized radiation enhancements in the output plane. The described technique offers significant flexibility in generating a variety of output laser beam shapes. Employment of electronically controllable spatial light modulators in place of the phase or amplitude structures allows dynamic adjustments of the output laser beam patterns. We demonstrate the influence of various parameters on the resulting output radiation enhancements, including the effects of the shape of the propagating radiation as well as the shape and size of the phase or amplitude structures. Our results indicate that by appropriately selecting the phase and amplitude characteristics of the structures employed during the beam shaping, a significant increase in the resulting peak intensities of the shaped beams is achieved.

Optimization of the point spread function by means of sensor-less adaptive optics, based on direct imaging of the focal spot, suffers from errors due to enormous dynamic range of the focal intensity. Also, optimization algorithms based on the focal spot metrics only, are insensitive to other system parameters and can converge towrong" solutions. To improve the beam quality and the robustness of the global extremum, we have introduced dynamic feedback control of the camera sensitivity. To further increase the robustness of optimization, we introduced a regularization parameter in the form of some function of the system state, achieving its minimum together with the desired solution. Significant gain in achievable beam quality is shown in comparison with the implementation lacking those improvements. Proposed techniques are implemented in Beam Tuner software forne-tuning of laser and imaging systems with adaptive optics.

When a highly absorbing thermal medium is heated with a focused laser pump beam, diffraction ring patterns can be observed due to self-phase modulation. It is further observed that when the laser power increases, the usual self-phase modulation diffraction patterns change due to formation of a bubble inside the thermal lens created by the focused beam. This phenomenon, called thermal blooming, is the next step to selfphase modulation. A stable bubble is formed using a focused laser beam, and the bubble is characterized using holograms made with a probe beam. A 532 nm Argon-Ion laser is used as the pump and a 633 nm low power He-Ne laser is used as the probe. The thermal medium comprises a mixture of a red dye and isopropyl alcohol. To minimize the optical effects arising from convection, the focused pump is introduced vertically into the liquid sample. The recorded in-line holograms are numerically reconstructed to determine the size and 3d shape of the bubbles. Bubble sizes are monitored as a function of the pump intensity. Once formed, the bubbles can be steered by mechanically deflecting the pump beam or any other laser beam. Finally, Ag nanoparticles are fabricated, examined, and introduced into the thermal medium. The presence of nanoparticle agglomeration around the thermally generated bubbles is tested using a focused probe beam at 405 nm corresponding to the absorption peak of the Ag nanoparticles due to plasmonic resonance. This technique should prove useful in drug delivery systems using nanoparticles agglomerated around microbubbles.

In this paper, we implement an Optical Flat Comb Source generating a coherent super-channel operating at 1 Tbps using WDM-Nyquist and OFDM approaches with new flex-grid channel spacing. The new flex-grid defines WDM channel spacing having a multiple of 12.5 GHz. We compare through simulation the performance of two techniques for generating Dual Polarization-Quadrature Amplitude Modulation based on 16 (DP-16QAM), 64 (DP-64QAM) and 128 (DP-128QAM). We first study the performance of WDM-Nyquist and OFDM super-channels implementing DP- 16QAM, DP-64QAM and DP-128QAM in back-to-back scenarios in terms of receiver sensitivity and Optical Signal-to- Noise Ratio (OSNR) requirement with 12.5 GHz flex-grid spacing. We find that DP-16QAM has the best receiver sensitivity and the lower OSNR penalty compared to the other modulation formats in WDM-Nyquist system. With DP- 128QAM sensitivity as reference, we can observe a benefit of 10 dB for DP-16QAM with a BER equal to 3.8 10-3. In addition, we can observe a benefit of 12.4 dB in OSNR for DP-16QAM compared to DP-128QAM for a BER equal to 3.8 10-3. Also, we study the impact of the optical and electrical shaping filters. Finally, we investigate the performance of WDM-Nyquist and OFDM terabit system with 12.5 GHz flex-grid spacing over long-haul dispersion compensated links using Standard Single Mode Fiber (SSMF). We find that DP-16QAM is the suitable modulation format in dispersion compensated WDM-Nyquist systems using SSMF fiber. In addition, we prove that the use of Raman amplification improve the maximum reach of the super-channel by increasing the span distance between the amplifier module. Indeed, using the Raman amplification the maximum reach increase from 812 km to 955 km in a WDM-Nyquist system based on DP-16QAM with 12.5 GHz flex-grid spacing.

In this work we construct coherent superpositions of Gaussian and vortex modes which can be described to occupy the complex-plane. We demonstrate how these fields can be experimentally constructed in a digital, controllable manner with a spatial light modulator. Once these fields have been generated we illustrate, with three separate techniques, how the constituent components of these fields can be extracted, namely by measuring the intensity of the field at two adjacent points; performing a modal decomposition and a new digital Stokes measurement.

Laser beam shaping is a widely used technique in many application areas, such as material processing, lithography, optical data storage, and medical procedures. In most cases a laser beam shaping system consists of conventional lenses with curved surfaces. However these lenses are bulky and their fabrication precisions are limited. In this work, we design and fabricate a lens for laser beam shaping using nanostructures. The lens is designed with traditional geometrical optical methods, using energy conservation and optical coordinate transformation algorithms. But instead of using curved surfaces to implement the lens design, we realize the designs with dielectric nanostructures. The lens is then fabricated using electron beam lithography to achieve a high precision. The fabricated lens has very low profile and is capable of fine tuning laser beams. The lens is then experimentally tested. In the experimental setup a laser beam is directed into a multimode fiber and the irradiance of the output beam irradiance profile is measured. Then the lens is placed in front of the multimode fiber and the outcome beam irradiance profile is measured again to test the effects of our laser beam shaping lens.

We present experimental results from variable output refractive beam shapers based on freeform optical surfaces. Two freeform elements in close proximity comprise a beam shaper that maps a circular Gaussian input to a circular ‘flat-top’ output. Different lateral relative shifts between the elements result in a varying output diameter while maintaining the uniform irradiance distribution. We fabricated the beam shaping elements in PMMA using multi-axis milling on a Moore Nanotech 350FG diamond machining center and tested with a 632.8 nm Gaussian input. Initial optical testing confirmed both the predicted beam shaping and variable functionality, but with poor output uniformity. The effects of surface finish on optical performance were investigated using LightTrans VirtualLab^TM to perform physical optics simulations of the milled freeform surfaces. These simulations provided an optimization path for determining machining parameters to improve the output uniformity of the beam shaping elements. A second variable beam shaper based on a super-Gaussian output was designed and fabricated using the newly determined machining parameters. Experimental test results from the second beam shaper showed outputs with significantly higher quality, but also suggest additional areas of study for further improvements in uniformity.

The polarization state of a laser has a huge bearing on the physics of laser-plasma interactions and it is often desirable to change between linear and circular. For short pulse high power lasers large beam apertures are necessary for transportation. However, in these extreme conditions transmissive birefringent polarization optics become impractical due to their delicacy and their dispersion of the laser bandwidth which will increase the pulse length, which along with large B-integrals, which arises from the transmission of the high-power beams through optics, can be detrimental to the intensity of the laser. It is therefore necessary to consider reflective optics in order to change the polarization. Modelling has been performed at the Central Laser Facility on a design of a large aperture broadband reflective waveplate suitable for short pulse laser systems.

Diffractive optics has traditionally been used to transform a parallel beam of light into a pattern with a desired phase and intensity distribution. One of the advantages of using diffractive optics is the fact that multiple functions can be integrated into one element. Although, in theory several functions can be combined, the efficiency reduces with each added function. Also, depending on the nature of each function, feature sizes could get finer. Optical lithography with its 1 μm limit becomes inadequate for fabrication and sophisticated tools such as e-beam lithography and focused ion beam milling are required. In this paper, two different techniques of fabrication of composite elements are studied. A comparison of the beams generated in both cases is presented.

Achromatic beam shapers can provide beam shaping in a certain spectral band and are very important for various laser techniques, such as, applications based on ultra-short pulse lasers with pulse width <100 fs, confocal microscopy, multicolour holography, life sciences fluorescence techniques, where several lasers in spectrum 405-650 nm are used simultaneously, for example 405-650 nm. Conditions of energy re-distribution and zero wave aberration are strictly fulfilled in ordinary plano-aspheric lens pair beam shapers for a definite wavelength only. Hence, these beam shapers work efficiently in relatively narrow, few nm spectrum. To provide acceptable beam quality for refractive beam shaping over a wide spectrum, an achromatizing design condition should be added. Consequently, the typical beam shaper design contains more than two-lenses, to avoid any damaging and other undesirable effects the lenses of beam shaper should be air-spaced. We suggest a two-step method of designing the beam shaper: 1) achromatizing of each plano-aspheric lens using a buried achromatizing surface (“chromatic radius”), then each beam shaper component presents a cemented doublet lens, 2) “splitting” the cemented lenses and realizing air-spaced lens design using optical systems design software. This method allows for using an achromatic design principle during the first step of the design, and then, refining the design by using optimization software. We shall present examples of this design procedure for an achromatic Keplerian beam shaper and for the design of an achromatic Galilean type of beam shaper. Experimental results of operation of refractive beam shapers will be presented as well.

In this paper, we use aberration theory to design a refractive laser beam shaper in the configuration of two-aspheric lenses, whose analytical equations are known, but rather complicated. Specifically, we use results from third order aberration theory to obtain the parameters of the refracting laser beam shaper from the transverse aberration, which are then used as a starting point for further optimization by using optical design software. This approach was developed during the beginning of the twentieth century, works well for systems with a low numerical aperture, and allows one to define the following parameters of an optical system: radii of curvature, indices of refraction, thicknesses or air gaps, and conic constants of second order aspheric surfaces. We shall consider surfaces of the second-order spherical and conic sections and shall consider the example of designing of a two-lens beam shaper of the Keplerian 1-to-1 telescopic design providing a theoretical flat phase front and a flat-top irradiance profile of the output beam, where the ray mapping function from the input aperture to the output aperture is known from the literature. Explicit expression for third order longitudinal aberration and the Seidel coefficients are expressed in terms beam waist and input beam geometrical parameter, indices, lens radii and conic constants.

Beam expanding is a common task, where Galileo telescopes are preferred. However researches and customers have found limitations when using these systems. A new monolithical solution which is based on the usage of only one aspherical component will be presented. It will be shown how to combine up to five monolithical beam expanding systems and to keep the beam quality at diffraction limitation. Insights will be given how aspherical beam expanding systems will help using larger incoming beams and reducing the overall length of such a system. Additionally an add-on element for divergence and wavelength adaption will be presented.

The behavior of the optical vortices with fractional topological charges in the far-field is assessed through numerical modeling and confirmed by experimental results. The generation of fractional topological charge variations of the phase within a Gaussian beam was achieved by using a liquid crystal spatial light modulator (LCoS SLM). It is shown that a laser beam carrying an optical vortex with a fractional topological charge evolves into a beam with a topological charge of integer value, specifically an integer value closer to the fractional number in the far field. A potential application of this work is for data transmission within optical telecommunication systems.

A laser beam delivery system is presented, consisting of a high power Neodymium :YAG Diode Pumped Solid State DPSS laser, a complete vision processing system for seam tracking, custom electronics consisting of firmware developed especially for this application, processing head, integrated beam shaping optics and an all optical compact actuator to steer the high power laser beam to a target substrate. Delivery of <800W average power was successfully delivered to the target substrate with a homogenous rectangular beam profile. Beam steering resolutions of <3μm were achieved and target tracking accuracies were 50μm, limited by the vision system. Development of custom software was required to interpret system latency and vision system deviations encountered under production conditions. The system has been in serial manufacture since Dec2013.

We consider a problem of direct synthesis of the laser beam with predetermined intensity distribution, by means of intracavity adaptive optics. The mathematical formulation of the problem is reduced to the study of the solutions of the resonator equation, expressed in terms of the field amplitudes and phases inside the resonator, and the parameters of resonators that includes the deformable mirror. It is shown that, with some assumptions, the shape of the deformable mirror can be expressed as a function of the output intensity distribution. The results of direct numerical simulations agree with the obtained analytical estimates. Experimental verification is in progress.

Unstable canonical resonators can possess eigenmodes with a fractal intensity structure [Karman et al., Nature 402, 138(1999)]. In one particular transverse plane, the intensity is not merely statistically fractal, but self-similar [Courtial and Padgett, PRL 85, 5320 (2000)]. This can be explained using a combination of diffraction and imaging with magnification greater than one. Here we show that the same mechanism also shapes the intensity cross-section in the longitudinal direction into a self-similar fractal, but with a different magnification. This results in three-dimensional, self-similar, fractal intensity structure in the eigenmodes.

This study demonstrates hysteresis loop and pattern formation in a Nd:YVO4 laser at 1064nm (⁴F_3/2 →4I1 _1/2) and 1342nm (⁴F_3/2→⁴I_13/2) with an intracavity electro-optic periodically poled lithium niobate (EO PPLN) Bragg modulator by using a T-type cavity configuration. Based on these dual wavelengths sharing population inversion in the same upper energy level to lase, the transmission, Tp, of EO PPLN was chosen as the controlling parameter to explore the dynamics of dualwavelength competition. A hysteresis loop occurred when the extracting efficiencies of dual wavelength were near equivalent. When the pump power was 9.0 W, the hysteresis loop was observed in the region of the transmission of PPLN between Tp=64.88% to Tp=84.47%. The slope efficiencies were 25.96 and 3.92% and the thresholds were 2.5 and 3.5 W for the wavelengths of 1064 and 1342 nm, respectively. The width of the hysteresis loop increased when the pump power increased. Moreover, the hysteresis loop accompanied with the variation of the pattern formation. A high-order transvers mode was easily observed at 1342 nm light, but a simple spot existed for 1064 nm light. Apparently, the role of gain competition is worthy to deeply explore.

We report a coherent combining of four slab laser amplifiers with high beam quality. The long strip laser beam is reshaped into a square beam using adjustable beam expander which removes the enormous astigmatism aberration. A filling ratio of 90% is achieved by two-dimensional splicing. A compact optical system with high sampling frequency is designed to detect the pointing direction of lasers. Fast steering mirror (FSM) driven by piezoelectric ceramics is applied in laser stabilizing. Thanks to the closed loop pointing control, the root mean square error of the optical axis is significantly reduced to be less than 2 microradians. The piston phases of the lasers are locked by an active phase control system based on Field Programmable Gate Array (FPGA) using stochastic parallel gradient descent (SPGD) algorithm. When the total output power of four lasers is 400W, the in-phase peak intensity of the far field spot is increased by a factor of 3.8, reaching 95% of the ideal case. The beam quality of the combined beam is improved by CBC from 1.52x diffraction limit (DL) to 1.26x DL. When the output power is increased to 805W, the phase locking and pointing control still work stably. The results suggest that CBC of solid-state lasers with higher energy could be achieved by using the techniques presented here.

Based on the birefringence of the laser crystal and cavity design, a simple method directly generate radially and azimuthally polarized laser beams with a c-cut Nd:GdVO4 in a three-element cavity. The experimental results reveal that the transformations of polarization are observed by tuning cavity length with hundreds of micrometer. The slope efficiency is maintained up to 36.7% and output power reaches up to 1.34 W with the pump power of 5 W. The degree of polarizations can be greater than 92.2% for both of azimuthally and radially polarized beams. By considering the extraction efficiency from pump energy with the condition of changing the cavity length for o-ray and e-ray, mechanism of polarization transformation in the laser is discussed.

In this work we construct coherent superpositions of Gaussian and vortex modes which can be described to occupy the complex-plane. We demonstrate how these fields can be experimentally constructed in a digital, controllable manner with a spatial light modulator. Once these fields have been generated we illustrate, with three separate techniques, how the constituent components of these fields can be extracted, namely by measuring the intensity of the field at two adjacent points; performing a modal decomposition and a new digital Stokes measurement.

The intensity distributions of self-focusing dual Airy beams are studied analytically by means of their statistical moments. Closed form expressions are derived that allow the determination of the focal shift through two different criteria; the first one is based on the second moment of the intensity whereas the second takes advantage of the beams symmetry to employ encircled-power calculations for defining the focus. Our results confirm the existence of a focal shift as expected, and show an effective quadratic dependence on the truncation parameter of the Airy beams.

In this work we theoretically study the possibilities for controlling the propagation of beams and pulses by modifying their coherence distributions. Theoretical models for partially coherent fields that have non-uniform coherence functions instead of the typical Schell-model correlations are introduced and the propagation of the fields is studied by numerical simulations for example cases. It is shown that extraordinary propagation-induced changes, such as self-focusing and laterally shifted intensity maxima, can be obtained with suitable initial coherence distributions. Our results imply that tailoring of the coherence properties could offer a novel alternative way to shape and control optical fields.

We analyze the effect of atmospheric turbulence on the propagation of multiplexed Laguerre Gaussian modes. We present a method to multiplex Laguerre Gaussian modes using digital holograms and decompose the resulting field after encountering a laboratory simulated atmospheric turbulence. The proposed technique makes use of a single spatial light modulator for the generation of superimposed beam and a second spatial light modulator and a CCD camera for the modal decomposition. The obtained results demonstrate how sensitive the Laguerre Gaussian beams are to atmospheric distortions.

High-capacity data transmission has been implemented using single channel optical systems. This technique is limited and soon it will be unable to fulfill the growing needs for higher bit rate data transmission. Hence multi-mode transmission has been recently given attention as a potential solution to the current problems. In this context, we demonstrate a method of multiplexing laser modes using spatial light modulators (SLMs). In our proposed technique, we use Laguerre Gaussian (LG) modes, which form a complete basis set; hence multi-mode masks can be created by taking a linear combination of the LG modes. Since LG modes are characterised by two degrees of freedom, the azimuthal index ` and radial index ρ, this allows for multi-dimensional states. There are however some experimental challenges which include the sensitivity of the setup to misalignment, that leads to mode-coupling. It is also important that the injected modes ha a uniform power spectrum so that are weighted equally. The size of the multi-modes is highly dependent on the resolution of the SLM.

We show both, experimentally and analytically, generation of bottle beam by uniaxial crystal, in the case optical axis of a uniaxial crystal tilted with respect to axis of a beam. Intensity and polarization structure of a bottle beam experiences dramatic changes. At the angle of 3.5 deg. closed three dimensional structure, of initially circularly polarized beam, breaks. Both analytically and experimentally, we demonstrate that if the beam initially linearly polarized, it structure changes faster than in the case of circular polarization and two focuses of bottle beam “switch” positions. We experimentally, generate arrays of tilted bottle beams with a uniaxial crystal.

In this paper we present the Optical Vortex Scanning Microscope (OVSM) in which the new scanning method induced by vortex lens movement is introduced. This method allows to scan the sample in a simple way. The behavior of the vortex position at the sample plane and phase retrieval algorithm is discussed. The new experimental results confirming the progress in the OVSM building are presented.