Two-dimensional near-wavelength microstructures have been fabricated on a copper film and a silicon wafer by femtosecond vector optical fields with different spatial polarization distribution, at a central wavelength of 800 nm, pulse duration of ∼70 fs, and a repetition rate of 1 kHz. Laser-induced ripples appear at the ablated region on silicon when the laser fluence is above the ablated threshold. When the number of the irradiated pulses increases, ripples with interspace larger than the wavelength could be observed, while the dimension of the ablated region has a slight variation. In the induced microstructures on a copper film, the microstructures in a ring have been observed under the irradiation of a few pulses. Under the irradiation of the multipulse femtosecond vector field, differently from the condition of the silicon, the induced microstructures on the metallic copper surface exhibit the anisotropic extending feature dependent on the polarization distribution of the vector field. The physics behind this unique feature is the anisotropic excitation and propagation of surface plasmon, caused by the coupling of the subsequent irradiation pulses with the existing microstructure. In this case, the surface plasmons resonance in the induced 2D microstructures is closely related to the induced grating structures on the surface.
Orbital angular momentum (OAM), as nature of optical field, has attracted considerable attention, due to its
academic interest and potential applications such as quantum information, atomic manipulation, micromanipulation
and the biosciences. The well-known OAM carried by an optical field originates from the azimuthal phase
gradient of an optical vortex field with a helical phase structure. Here we predict a novel optical OAM, which
is induced by curl of polarization. To demonstrate experimentally the above prediction, we present an idea for
creating a kind of radial-variant vector fields, which could have all local linear polarization and hybrid states of polarization (SoPs). By specifically arranging the SoPs of the vector fields, new effects and phenomena can be anticipated that can expand the functionality and enhance the capability of optical system. The generated vector fields with the radial-variant hybrid SoPs can carry such a novel OAM. Optical trapping experiments validate that the focused vector fields without any additional phase vortex, as the ring optical tweezers, exert torques to drive the orbital motion of the trapped isotropic microspheres.
We describe a convenient way to generate arbitrary vector beams by using a spatial light modulator, based on
interferometric superposition of two orthogonally polarized beams. In our constructed optical setup, the SLM is used to
produce a computer-generated holographic grating that diffracts a linearly polarized incident light into the +1st and -1st
diffraction orders with desired wavefronts. After the two diffraction beams pass through two quarter wave-plates, the
left- and right-handed circularly polarizations are yielded, respectively. Then a Rochi grating is utilized to recombine the
two beams into single one such that any desired polarization configuration is achieved. We demonstrate the versatility of
our method through optical experiment, in which a variety of polarization beams are realized. By making use of the
incident wave with helical phase, our technique can produce both cylindrically symmetric and asymmetric polarizations.
To the best of our knowledge, the experimental realization of cylindrically asymmetric polarization is reported for first
time. We also study the focal properties of vector beam through a high numerical aperture lens. Starting from
Richards-Wolf vectorial diffraction theory we calculate the focal field distribution and obtain some interesting focal
volume structures, such as flat-topped focus, doughnut focus with special dark volume structure.
A novel algorithm is proposed to reconstruct two-dimensional wave-front from differential wave-fronts measured in shearing interferometer. Two 1-dimensional estimates of object wave-front are computed using Fourier transform from differential wave-fronts, and then the 2-dimensional wave-front distribution is derived by use of least-square fitting. The algorithm is applicable to cases in which the shear amount is larger than one sampling interval, and thus alleviates the limitation on the shear amount imposed by conventional algorithms. Investigations into reconstruction accuracy and reliability are carried out by computer simulation. Optical experiments are made in a lateral shearing interferometer based on double-grating, and 3-dimensional surface profile of optical element under test are measured and presented. The analysis and discussion are also given in the final part of this article.
Several kinds of disperse-dye polymer films of the guest-host system were prepared by spin-coating method. Disperse orange 25 (DO25), disperse orange 3, disperse red 73, and disperse yellow 9 were chosen as nonlinear optical (NLO) active chromophores and polymethylmethacrylate (PMMA), polycarbonate (PC), and polyetherimide (PI) as polymer matrixes. Polymer films were poled by all optical poling or electric corona poling. The glass transition temperature (Tg), absorption spectra, rigidity, NLO properties of polymer films were characterized by means of DSC, UV-IR spectra, microhardness analyses, and NLO measurements. The all-optical poling characteristic of four kinds of NLO chromophores in PMMA matrixes systems has been investigated. DO25/PMMA has largest NLO effect. The possible explanation has been proposed. The relaxation and rigidity characteristics of DO25 doped polymer matrixes with various Tg have been studied by means of corona poling method. It is found that DO25/PI polymer films show best thermal and temporal stability and DO25/PMMA has largest NLO property. Generally, DO25/PC system has optimal tradeoff properties of NLO and stability. In addition, the second-order NLO coefficient and average electro-optic coefficient of 10wt% DO25/PMMA poled by optical poling and corona poling is determined to be around 60 and 34 pm/V, respectively.
In digital holography, holograms are digitally recorded by a CCD camera and stored in a computer’s memory. The reconstruction of the recorded wave field from the digitally stored hologram is realized numerically by the computer.123 This technique has found numerous applications, especially in 3-D microscopy,45 encryption,6 pattern recognition,7 and surface contouring.8 The process of digital holography by recording an interference pattern with a CCD array, and storing it in a computer to numerically reconstructing it can be interpreted as a coherent optical imaging system, which can be analyzed by Fourier optics and can be characterized by a point spread function (PSF). Such an analysis has been reported in recent publications written by Kreis.910 In this work, we indicate some shortages in Kreis’ analysis. At the same time we describe our new treatment and some new analytical results.
The Z-scan technique is a popular method for measuring degenerate optical nonlinearities using a single laser beam. In cases where nonlinear refraction is accomplished by storing nonlinear absorption, we report an accurate analytic method for extracting nonlinear refraction from the closed aperture Z-scan transmittance curve with the aid of the open aperture Z-scan transmittance curve. This method possesses very high accurayc, especially, in the presence of strong nonlinear absorption and/or for the larger size aperture. This method is also demonstrated on a solution of Pd(mpo)2 by the experiment.