Optical vector beams arise from point to point spatial variations of the electric component of an electromagnetic field over the transverse plane. In this work, we present a novel experimental technique to generate arbitrary vec- tor beams, and provide sufficient evidence to validate their state of polarization. This technique takes advantage of the capability of a Spatial Light Modulator to simultaneously generate two components of an electromagnetic field by halving the screen of the device and subsequently recombining them in a Sagnac interferometer. Our experimental results show the versatility and robustness of this technique for the generation of vector beams.
We experimentally generated superpositions of higher-order Bessel beams that possess no global orbital angular momentum (OAM), yet exhibit an angular rotation in their intensity profile as the field propagates. The digital holograms encoded on a spatial light modulator (SLM), used for generating such fields, consist of two annular rings of unequal radial wave-vectors where each ring is encoded with an azimuthal mode of equal order but opposite charge. We present experimentally measured angular rotation rates for some example superposition fields, which are shown to be in good agreement with that predicted theoretically. Introducing a second SLM and a Fourier transforming lens, we demonstrate a simple approach to perform an azimuthal decomposition of our generated optical fields. Bounding the match-filter to an annular ring, of varying radius, we are able to perform a scale-independent azimuthal decomposition of our initial field. From the measured weightings of the azimuthally decomposed modes we show reconstruction of the cross-sectional intensity profile and OAM density of our initial field.
Phase-only spatial light modulators are now ubiquitous tools in modern optics laboratories, and are often used to
generate so-called structured light. In this work we outline the use of a phase-only spatial light modulator to achieve full complex amplitude modulation of the light, i.e., in amplitude and phase. We outline the theoretical concept, and then illustrate its use with the example of the laser beam shaping of Gaussian beams into flat-top beams. We quantify the performance of this approach for the creation of such fields, and compare the results to conventional lossless approaches to flat-top beam generation.
The statistical distributions of phase values in computer-generated holograms produced with iterative algorithms
are studied. Useful relationships between the parameter values applied in the iterative technique used for their
generation and measured performance are provided.
We present a method to calculate the 2-dimensional complex angular spectrum required to produce a Helmholtz-
Gauss (HzG) beam with an arbitrary intensity profile. Using an iterative Fourier transform algorithm, we find
numerical solutions for several instances of spectra and we reproduce the corresponding beams by encoding the
resulting on a spatial light modulator. We verify the experimental results and compare them to the computer
model of their propagation to excellent agreement. We quantitatively asses the fidelity of the produced beams
and their expected extended propagation properties as HzG beams. Our method can be used to produce an arbitrary beam with the same extended invariance range characteristic of HzG beams.
We demonstrate on-demand production and optical manipulation of submicron-sized hydrosomes, water drops
in an immiscible medium. We use optical trapping techniques to induce the controlled fusion of multiple drops
and study the dynamics of small amounts of reagent encapsulated within the hydrosomes.
We detail a method for the accurate encoding of complex wavefields in low-cost, off-the-shelf spatial light modulators
capable of amplitude modulation. We assess the accuracy of our encoding scheme by producing a collection
of arbitrary nondiffracting beams and evaluating their propagation characteristics when compared to those predicted
by the theoretical model. The angular spectra of the beams produced using this approach is also measured and found consistent with theory.
We make use of a spatial light modulator to implement a phase-shifting interferometric method to determine the
topological charge of multiple singularities embedded in the transverse phase of singular beams. This method
allows us to discern between closely spaced singular points and elucidate the dynamics of optical vortices as their
charge is increased continually. The transverse phase of beams with a determined phase profile are analyzed
used this technique, yielding the precise location of multiple singularities as well as the value of their topological
charge. We use apply this method to accurately map the phase and study the transit of vortices across fractional
Bessel beams during their continuous order upconversion.
Optical trapping is a flexible and noninvasive technique that allows for the manipulation of single dielectric particles. Conventional single and multiple beam laser traps however, are limited by the amount of trapping sites that can be embedded in their wave field with a sufficiently high intensity gradient. We make use the interference of multiple beams and total internal reflection to couple an extended evanescent optical field to a large number of particles in a 2-D periodical landscape. The particles are confined and manipulated by modifying the spatial parameters of the landscape. We ultimately intend to use this technique for the parallel fusion of multiple pairs of microscopic droplets to investigate the dynamics of micro-reactions.
We investigate theoretically and experimentally the propagation characteristics of the Helical Hermite-Gauss
beams corresponding to the helical Ince-Gauss beams in the limit of infinite ellipticity. Particular attention is
paid to the transverse irradiance structure, the orbital angular momentum density, and the vortex distribution.
A beam shaping method based on the superposition and unwinding of vortex beams is proposed. This method allows for the continuous tuning of the orbital angular momentum content and longitudinal intensity distribution of the beam. We provide with a closed expression for the orbital angular momentum content of a general
superposition of vortex beams and find its relation to the functional parameters of the beams. We compare our theoretical predictions with experimental results with excellent fidelity.
We demonstrate phase conjugation by means of degenerate four-wave mixing from a colloidal crystal. The nonlinear medium is provided by a periodic spatial refractive index grating created in a colloidal suspension of dielectric microparticles trapped in the intensity distribution of two nearly copropagating interfering laser beams. Phase conjugation is achieved for a probe beam carrying orbital angular momentum as evidenced by the inversion of the topological charge of a phase singularity within the beam. The e ciency and nonlinear parameters of the colloidal crystal as well as its lattice properties are measured and compared to theoretical predictions and previous experimental work.
A novel method for tuning the orbital angular momentum (OAM) content of a vortex beam is presented. This
approach makes use of the shaping of the odd and even components of the helical phase profile associated to
the vortex. A relative azimuthal shift of the components results in the harmonic variation of the magnitude
of the OAM density of the beam. We calculate the OAM content and show that for a beam with a vortex of
topological charge m, the OAM per photon per unit length can be tuned continuously from (formula available in manuscript). We also
observe the experimental propagation of the beam and compare the propagation parameters to our theoretical
We present the experimental generation and characterization of each one of the four fundamental families of Helmholtz-Gauss beams: cosine-Gauss beams, stationary and helical Mathieu-Gauss beams, stationary and traveling parabolic-Gauss beams, and Bessel-Gauss beams. Both the transverse intensity profile and power spectrum that each one of the beams exhibits upon propagation is observed and compared to the theoretical model with good quantitative agreement. Emphasis is made on the fact that each of the four families of HzG beams is complete and orthogonal, and thus of fundamental relevance.
We observe the orbital motion of particles in the Mie regime as they are trapped within the multiringed transverse field of a rotating Helical Mathieu light beam. The observed motion results as angular momentum is transferred to the particles from the orbital component of this novel light beam. Mathieu Beams present nondiffracting features within a limited distace are suitable for a variety of applications in optical manipulation where guiding and rotation of particles is required. Dynamic variables of the motion of the particles such as angular velocity and acceleration are measured and compared to the theoretical predictions from numerical simulation.
The term Helmholtz-Gauss beam refers to a field whose disturbance at the plane z =0 reduces to the product of the transverse field of an arbitrary nondiffracting beam (i.e. a solution of the two-dimensional Helmholtz equation) and a two-dimensional Gaussian function. In this work, the transverse shape and the propagation of Helmholtz-Gauss beams is experimentally studied for the four fundamental orthogonal families of Helmholtz-Gauss beams: cosine-Gauss beams, Bessel-Gauss beams, stationary and helical Mathieu-Gauss beams, and stationary and traveling parabolic-Gauss beams. The power spectrum of the Helmholtz-Gauss beams is also recorded and its intensity distribution is assessed. Potential applications are discussed.
Propagation of light beams with apparent nondiffracting properties have intrigued the scientific community since they were introduced. In this talk we will introduce the fundamentals of nondiffracting beams and discuss the dynamics of optical vortices embedded in the new two families of nondiffracting beams we have recently discovered, Mathieu and parabolic beams.
Recently, a new class of nondiffracting beams has been demonstrated theoretically. Namely, Parabolic nondiffracting optical wavefields constitute the last member of the family of fundamental nondiffracting wavefields. Additionally, the existence of a new class of parabolic traveling waves associated to these wavefields has been demonstrated along the same lines. We have succeeded in demonstrating experimentally the fundamental odd and even parabolic wavefields in the laboratory. In this work, we present and discuss the experimental generation of higher-order parabolic nondiffracting wavefields. Because these fields show a complex structure, their generation relies in the successful construction of the field.
A novel experimental arrangement to produce high-order Bessel beams is proposed. The system is based on the decomposition of the even and odd spatial components of the Bessel beam. The reconstruction is made with a Mach-Zender interferometer. The original annular squeme of Durnin is used to generate each component of the Bessel beam. The main advantage of our setup is that the annular transmittances have only discrete changes of phase.