This PDF file contains the front matter associated with SPIE Proceedings Volume 8843, including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.
A means to measure orbital angular momentum in a partially coherent beam is demonstrated by using a wavefront
folding interferometer. This interferometer allows us to study the cross correlation function of a partially coherent
vortex beam. It is shown that the cross correlation function possesses ring dislocations which are related to the
topological charge of the partially coherent vortex, exhibiting a one to one correspondence between the number of
rings and the value of the topological charge, thus providing a direct measure of the orbital angular momentum.
An alternative method to experimentally measure the topological charge of a vortex beam is presented. The method is based on the number of polarization singularities arising in the superposition of two off-axis Laguerre-Gauss beams having orthogonal polarizations. The experimental setup consists of a modified Mach-Zehnder interferometer which provides control over the polarization structure by allowing us to introduce lateral displace ments as well as relative phase variations between the two arms of the interferometer. A comparison between theoretical and experimental results is done with very good agreement. This method offers an alternative for measuring orbital angular momentum content in a beam without the need of interfering with a reference plane wave. The dynamics of polarization singularities are also studied experimentally.
Accelerating and Airy beams are of great interest in a variety of applications as they remain diffraction free while experiencing a transverse quadratic shift along propagation, transporting intensity in the transverse plane over a straight line and describing an overall parabolic trajectory in space. This work presents optical fields that transport intensity in the transverse plane over a continuum of directions arranged over a semi-circle, creating transverse intensity fluxes with a variety of shapes. We construct these beams via a superposition of a nondiffracting beam with a strong carrier wave that reproduces phase variations of the former field over the resultant intensity distribution, generating profiles with a finite and well defined propagation period. The on-demand light patterns presented here are expected to find diverse applications as Airy beams and nondiffracting beams have previously found.
We experimentally generate non-diffracting vector vortex beams by using a Spatial Light Modulator (SLM) and an azimuthal birefringent plate (q-plate). The SLM generates scalar Bessel beams and the q-plate converts them to vector vortex beams. Both single order Bessel beam and superposition cases are studied. The polarization and the azimuthal modes of the generated beams are analyzed. The results of modal decompositions on polarization components are in good agreement with theory. We demonstrate that the generated beams have cylindrical polarization and carry polarization dependent Orbital Angular Momentum (OAM).
In this work we will present two techniques for the measurement of superimposed higher-order Bessel beams. In the first technique we will outline a simple approach using only a spatial light modulator and a Fourier transforming lens to decompose the OAM spectrum of an optical field. We test this approach on symmetric and non-symmetric superpositions of non-diffracting higher-order Bessel beams. Our second procedure consists of two refractive optical elements which perform a Cartesian to log-polar coordinate transformation, translating helically phased beams into a transverse phase gradient. By introducing two cylindrical lenses we can focus each of the azimuthal modes associated with each Bessel beam to a different lateral position in the Fourier plane, while separating the radial wave-vectors in the image-plane.
We demonstrate the recording of volume phase masks in the bulk of photo-thermo-refractive glass. Recording was
produced by exposing the glass to UV radiation through binary amplitude masks. Depending on the profile of the
amplitude mask either a binary volume phase mask or a grayscale phase mask may be produced. Volume phase masks
have been used to generate Fresnel lenses, convert a Gaussian beam into higher order Hermite-Gauss and Laguerre-Gauss modes, to produce optical vortices, and to create aberration-correcting optical components.
SLMs used for spatial modulation of lasers are often used in conjunction with very narrow bandwidth laser
light where diffractive dispersion could be approximated as a constant. It is known that diffractive dispersion
is inversely proportional to wavelength and this effect can be compensated for depending on the optical set-up.
SLMs use birefringent liquid crystal (LC) pixels each with an adjustable refractive index at a specific polarization.
The range of the adjustable refractive index is wavelength dependent. This adds an additional SLM dependent
dispersion. Note that we distinguish between diffractive dispersion and SLM dependent dispersion. SLMs are
therefore calibrated in order to have linearly adjustable phase retardation of light incident on the pixels between
zero and two pi for a specific wavelength. It is therefore unavoidable when using the same SLM, to do beam
shaping of a source which emits multiple wavelengths or a wide bandwidth, that the device will not modulate
all wavelengths between zero and two pi. We numerically and experimentally investigate the effect of SLM
dependent dispersion on spatial modulation of light incident on a 2D SLM. We further discuss why it is possible
to modulate multiple wavelengths between zero and two pi despite SLM dependent dispersion.
Many scientific and industrial applications often require high performance optical systems utilizing spatially shaped
illumination patterns of laser beams. Precisely shaped line illumination can be used for various line scanning systems or
surface inspection devices. In order to achieve the highest resolution or superior signal to noise ratio limited by the
fundamental theory, a diffraction limited illumination optical system (e.g. <0.8 Strehl ratio) gives the narrowest
illumination line width determined by the system’s NA (Numerical Aperture) value. For high precision and in-factory
industrial applications, the Diffraction Limited Line Illumination (DLLI) needs to be controlled in three dimensional
space rapidly as the target object under the illumination may not be always aligned with respect to the illumination
system. A steerable DLLI system with three degrees of freedom (i.e. axial displacement, rotation, and tilt) is developed
using an adaptive optics system. By electronically controlling the Zernike based surface shapes of the deformable mirror,
the DLLI in free space is actively positioned and oriented with high accuracy. The geometrical optics based
mathematical model to control the Zernike modes of the deformable mirror and the performance of a bench-top proof-ofconcept
system will be presented with experimental data and analysis results.
Generation of “Laser Light Sheet” beams and linear laser spots characterized by uniform irradiance distribution is
important in various laser techniques like Particle Image Velocimetry (PIV), Laser-Induced Fluorescence (LIF),
hardening, annealing, cladding, uniform laser illumination of linear spatial light modulators. This task can be
successfully solved with using refractive beam shaping optics of field mapping type in combination with additional
optical components. Due to their unique features: low output divergence, high transmittance, flatness of output phase
front and irradiance profile, as well as extended depth of field, the refractive field mappers provide freedom in further
manipulation of intensity profile and shape of output beam. Typically design of refractive field mapping beam shapers
has circular symmetry; therefore to create linear spot shapes it is suggested to apply anamorphic optical components like
cylinder lenses, prism pairs, etc. The combined beam shaping systems allow achieving very high aspect ratio, up to
1:1000, of linear spots with simultaneous providing extended depth of field, i.e. it is possible to realize a “Laser Light
Sheet” characterized by keeping uniform intensity of linear spot over extended distance along optical axis.
This paper will describe some design basics of refractive beam shapers of the field mapping type and optical layouts for
creating linear laser spots and “Laser Light Sheet”. Examples of real implementations will be presented as well.
The structuring of functional and design metallic surfaces takes full advantage of economic, flexible and fully automated
processing techniques. Structuring by laser remelting enables totally new possibilities for structuring with individual
textures without any ablation of material or the utilization of harmful chemical etching. The functional principle requires
the superposition of three laser beams emitted from two different laser sources. For this process, a new optical system is
designed and built up which allows for the combination of cw and pulsed laser beams on a working plain. To maintain a
high degree of flexibility and automation the system allows for a high number of degrees of freedom for each individual
beam. To take full advantage of structuring by remelting for the processing of 3D surfaces, the optical system needs to be
extended. With additional optical capabilities elliptical pre-shaping can be applied to enable robust and reliable
processing. The huge amount of degrees of freedom leads to a challenging, complex optical design that is being
discussed in this work.
We describe a laboratory experiment to improve the energy-on-target for an extended object. We utilize an iterative
approach combining digital holography for detection and SLM beam shaping for object re-illumination. We developed a
technique to modify the SLM phase to prevent oversharpening of glints and other high intensity return signal points that
cause the beam to collapse to a single point with further iterations. Instead, the gain is increased as more light uniformly
hits the intended target with each iteration. We present laboratory results to verify this approach and demonstrate the
increased gain resulting from this dynamic beam-shaping.
Uniform irradiance distribution of laser spot is highly advisable in various micromachining techniques like scribing, PCB and Through-Silicon Via (TSV) drilling, repair techniques in display making technologies. Scanning over whole working field with using popular 2- and 3-axis galvo mirror scanners is another important part of microprocessing systems. Therefore, combining of beam shaping optics, converting Gaussian to flattop (uniform) laser beam profile, with scanning optical heads is an insistent technical task. To provide flattop irradiance profile it is suggested to apply field mapping refractive beam shaping optics πShaper being characterized by some important features: low output divergence, high transmittance, extended depth of field, capability to work with TEM00 and multimode lasers, as result providing a freedom in building various optical systems. De-magnifying of flattop laser beam can be realized with using imaging technique; the imaging optical system to be composed from F-theta lens of scanning head and additional collimating system to be used right after a πShaper. One of the problems in this approach is implementation of compact design of the collimating part. As a solution it is suggested to apply a specially designed Beam Shaping Unit (BSU) to be installed between a laser and a scanning head and providing: conversion from Gaussian to flattop laser beam irradiance profile, compact collimator design, and functions of laser beam adjustment and adaptation to a laser and a scanning head used in particular equipment. There will be considered design features of refractive beam shapers πShaper and BSU, examples of optical layouts to generate flattop laser spots, which sizes span from several tens of microns to millimetres. Examples of real implementations and results of material processing will be presented as well.
This paper documents the investigation of a diffuser based fiber injection system and its
successful implementation and experimental testing in a robotic industrial process. This is a new
concept based on the idea that a diffuser that has the angular radiation pattern matching the NA
of the fiber can be used to approximate the field pattern at the face of a mode filled fiber. The
research considered two approaches to this problem. The two related approaches to the problem
were developed conceptually and analytically for two predominant wavelengths of interest, 1030
nm and 532 nm. The first is an implementation that would consist of illuminating the diffuser
with a uniform spot having the same shape as the fiber core and imaging the illuminated spot
onto the fiber face. The other approach is the use of a far-field (Fourier transform) diffractive
element with a transform lens. This paper will provide an overview of the analytics and testing
of the later concept (Fourier transform) and the experimental implementation of the design to a
laser fiber coupling system to launch a 532 nm pulsed laser beam into a square core fiber optical
beam delivery system. Further detail will be shared with the experimental performance of the
design when integrated within a multi-axis robotic arm, which has six degrees of freedom. These
results will include how the fiber injection system improved laser beam stability during process
operations, in comparison to traditional simple lens injection methods.
This paper presents what the author hopes will be a novel interpretation of the integrator, and draws
unique comparisons between two types of integrator: the microlens array based imaging beam
integrator and the integrating tube, or light pipe, for which a quality factor has been derived.
Due to the restriction of the aperture effect and the aperture transverse delay, it is very difficult to get large
instantaneous bandwidth under wide scan range for conventional phased array radar. Optical controlled beam
forming network (OCBFN) technology can solve this problem. The key of the OCBFN is the optical true time
delay line network. In this paper, we propose a new differential time delay line network based on the free-space
integrated prism array technology. The new method can realize any linear time delay for the space multi-beam
radar. Furthermore, the time delay can be adjusted very easily. In order to validate the new method, we design a
4×4 differential time delay line network, and the time delay ranges from 0 ps to 100 ps.
Bessel beams belong to a class of propagation invariant, structured laser beams, and are used in various applications,
including particle micro-manipulation, optical coherence tomography, optical metrology, and high resolution
microscopy. In practice, Bessel beams are produced by optical fields with finite lateral dimensions propagating through
finite aperture optical components, such as axicons. However, field distortions and component misalignments influence
the shape of the resulting beams.
In this paper, we present the influence of the beam shape and ellipticity, beam forming optics imperfections, and
component misalignments on the shape of the resulting Bessel beams along the direction of propagation. Our results
demonstrate that even modest fabrication errors in the input field distribution or component formation can significantly
increase undesirable axial intensity oscillations in the resulting Bessel beams. Misalignments between the axicon and
incoming laser beam can additionally lead to a decrease in the maximum axial intensity of the propagating beam.
Bessel beams belong to a class of propagation invariant, structured beams, and are used in a variety of applications,
including particle micro-manipulation, optical coherence tomography, optical metrology, and high resolution
microscopy. In practical applications, Bessel beams are formed by the interaction of optical fields with finite lateral
In this paper, we discuss the formation and propagation characteristics of Bessel beams based on input field distributions
defined by Laguerre-Gaussian beams of different orders. We present the influence of the beam order on the shape and
the axial intensity distribution of the resulting Bessel beams. One of the limiting factors in the applications of Bessel
beams is related to the variations in the axial intensity distribution of the produced beams. We show that the incoherent
superposition of input Laguerre-Gaussian beams of different orders can resolve the above limitation and produce Bessel
beams with uniform peak intensity distributions over an extended axial distance.
The transmittance curves describing effects important in the behavior of the diffracted fields generated by
coherent illuminated. However, when it is performed a spatial transform on a transmittance curve, this can
be done by tilting the screen, for example, the projection of a circle curve is an ellipse as result the diffraction
field is no more a smooth transformation. In this case, the boundary condition may generate regions identified
as singularities regions. In this study, we describe slit-shape transmittance whose diffraction field presented
bifurcation effects and focusing regions know as caustics. The geometric shape of the transmittance allows to
study the structure diffraction fields, where they are organized around focusing regions. We describe singularities
that corresponds to cusp caustics of codimension two and astroid caustics. In the focusing regions are produced
dislocation points on intensity pattern. In particular, in the cusp catastrophe is presented the Pearcey pattern.
The generation of singularities is studied by mean the numerical solution of the paraxial Helmholtz equation.
Recently, cylindrical vector beams have drawn considerable attention for their interesting
properties and potential applications in super-resolution optical imaging, optical trapping and
manipulating. It’s easy to obtain inhomogeneous status of polarization by designing the diffractive
optical elements particularly. With the change of the polarization of cylindrical vector beams, three dimensional (3D) flattop fields could be obtained. Numerical analysis shows that the full width at half
maximum of the proposed 3D flattop light field is nearly 5λ for axial distributions. The result shows a
potential application of the cylindrical vector beams in laser beam shaping system and laser cutting.
The focusing properties of vector beams have attracted great attention and quickly became the
subject of extensive worldwide research due to their applications in lithography, optical storage,
microscopy, material processing, and optical trapping. Focusing properties of the radially polarized
beam and generalized cylindrical vector beams in high numerical aperture system with designed pure
phase filter are analyzed in detail by using vector Debye diffraction theory. By utilizing diffractive
optical element to partly change the polarization of vector beams, the energy density of light field in the
vicinity of focus is studied by the numerical analysis. Numerical simulation result shows that optical
bubbles can be obtained by changing the composition and polarization of the incident beams. At last,
optical tweezers are constituted by two optical bubbles around the focus.
Light is capable of directly manipulating and probing molecular dynamics at its most fundamental level. One versatile
approach to influencing such dynamics exploits temporally shaped femtosecond laser pulses. Oftentimes the control
mechanisms necessary to induce a desired reaction cannot be determined theoretically a priori. However under certain
circumstances these mechanisms can be extracted experimentally through trial and error. This can be implemented
systematically by using an evolutionary learning algorithm (LA) with closed loop feedback. Most frequently, pulse
shaping algorithms operate within either the time or frequency domain, however seldom both. This may influence the
physical insight gained due to dependence on the search basis, as well as influence the speed the algorithm takes to
converge. As an alternative to the Fourier domain basis, we make use of a combined time-frequency representation
known as the von Neumann basis where we observe temporal and spectral effects at the same time.
We report on the numerical and experimental results obtained using the Fourier, as well as the von Neumann basis to
maximize the second harmonic generation (SHG) output in a non-linear crystal. We show that the von Neumann
representation converges faster than the Fourier domain when compared to searches in the Fourier domain. We also
show a reduced parameter space is required for the Fourier domain to converge efficiently, but not for von Neumann
domain. Finally we show the highest SHG signal is not only a consequence of the shortest pulse, but that the pulse
central frequency also plays a key role.
Taken together these results suggest that the von Neumann basis can be used as a viable alternative to the Fourier domain
with improved convergence time and potentially deeper physical insight.