A holographic technique for fabricating 3D photonic crystal is presented. The key element in the fabrication system is a holographic optical element (HOE) consisting of three gratings. Used in combination with a mask, the HOE can generate four beams under single illuminating beam, and 3D lattice structures can be formed by the interference of the four beams. Holographic approach is used to make HOE, so large area lattice structures can be fabricated. Numerical simulations indicate that beam intensity ratio of central beam to outer beam is one of the factors that affects the structures fabricated in photoresist, and high diffraction efficiency of the gratings in HOE is favorable when using cw laser with relatively low power as light source. Experimental results show clear 3D lattice structures fabricated using the HOE, verifying the effectiveness of the technique. 相似文献
In recent years, optical vortex beams possessing orbital angular momentum have received much attention due to their potential for high‐capacity optical communications. This capability arises from the unbounded topological charges of orbital angular momentum (OAM) that provide infinite freedoms for encoding information. The two most common approaches for generating vortex beams are through fork diffraction gratings and spiral phase plates. While realization of conventional spiral phase plate requires complicated 3D fabrication, the emerging field of metasurfaces has provided a planar and facile solution for generating vortex beams of arbitrary orbit angular momentum. Among various types of metasurfaces, the geometric phase metasurface has shown great potential for robust control of light‐ and spin‐controlled wave propagation. Here, we realize a novel type of geometric metasurface fork grating that seamlessly combine the functionality of a metasurface phase plate for vortex‐beam generation, and that of a linear phase gradient metasurface for controlling the wave‐propagation direction. The metasurface fork grating is therefore capable of simultaneously controlling both the spin and the orbital angular momentum of light.
Fresnel diffraction on periodic gratings results in a two-dimensional periodic distribution of light intensity, also known as the Talbot effect. Here this approach is extended to the family of superimposed structures with translational symmetry, which consist of superposed spatial harmonics. The Talbot effect is demonstrated to be valid for superimposed gratings. The considered superimposed gratings provide a wide range of textures of optical super-lattices. These texture super-lattices represent a Talbot carpets with a complex motif, which can be varied by choosing structure parameters. These results provide a new functionality for structuring optical lattices and can find potential applications in a wide range of light–matter interactions. 相似文献
Gratings with subwavelength groove depth and period are frequently used in optics for various purposes. The polarization dependent diffraction characteristics of subwavelength (high frequency) gratings can only be calculated by solving Maxwell’s equations of electromagnetism. In this paper, we calculate the classical diffraction characteristics of subwavelength conducting gratings numerically, using a new high accuracy version of nonstandard finite-difference time-domain (NS-FDTD) algorithm. For the purpose of analysis, we employ a gold sinusoidal grating with light incident at a large angle. We have compared high accuracy NS-FDTD simulation results with those obtained from standard finite-difference time-domain (S-FDTD), and the finite element method (FEM) simulations. 相似文献
A new way to enhance the directional stability of laser beams with alternating intensity by fast feedback control of both linear and angular drifts has been proposed for alignment of laser beams at higher accuracy. Both linear and angular drifts of laser beams, processed through light intensity modulation and primary alignment using single-mode optical fiber (SMOF), are separated using light path arrangement and detected using phase-lock technique, and are controlled using fast feedback control mechanisms according to their detected magnitudes, so that both linear and angular drifts are suppressed to enhance the directional stability of the emitting laser beams. Theoretical analyses and preliminary experimental results indicate that the approach proposed can be used to achieve an alignment accuracy of more than 10−8 rad. 相似文献
In order to achieve interaction between light beams, a mediating material object is required. Nonlinear materials are commonly used for this purpose. Here a new approach to control light with light, based on a nano‐opto‐mechanical system integrated in a plasmonic waveguide is proposed. Optomechanics of a free‐floating resonant nanoparticle in a subwavelength plasmonic V‐groove waveguide is studied. It is shown that nanoparticle auto‐oscillations in the waveguide induced by a control light result in the periodic modulation of a transmitted plasmonic signal. The modulation depth of 10% per single nanoparticle of 25 nm diameter with the clock frequencies of tens of MHz and the record low energy‐per‐bit energies of 10−18 J is observed. The frequency of auto‐oscillations depends on the intensity of the continuous control light. The efficient modulation and deep‐subwavelength dimensions make this nano‐optomechanical system of significant interest for opto‐electronic and opto‐fluidic technologies. 相似文献
We propose a new approach to generating a pair of initial beams for a polarization converter that operates by summing up two opposite-sign circularly polarized beams. The conjugated pairs of vortex beams matched with laser modes are generated using binary diffractive optical elements (DOEs). The same binary element simultaneously serves two functions: a beam shaper and a beam splitter. Two proposed optical arrangements are compared in terms of alignment complexity and energy efficiency. The DOEs in question have been designed and fabricated. Natural experiments that demonstrate the generation of vector higher-order cylindrical beams have been conducted. 相似文献
We demonstrate superradiant conversion between a two-mode collective atomic state and a single-mode light field in an elongated cloud of Bose-condensed atoms. Two off-resonant write beams induce superradiant Raman scattering, producing two independent coherence gratings with different wave vectors in the cloud. By applying phase-matched read beams after a controllable delay, the gratings can be selectively converted into the light field also in a superradiant way. Because of the large optical density and the small velocity width of the condensate, a high conversion efficiency of >70% and a long storage time of >120 micros were achieved. 相似文献
Quartz-enhanced photoacoustic spectroscopy (QEPAS) sensors are based on a recent approach to photoacoustic detection which
employs a quartz tuning fork as an acoustic transducer. These sensors enable detection of trace gases for air quality monitoring,
industrial process control, and medical diagnostics. To detect a trace gas, modulated laser radiation is directed between
the tines of a tuning fork. The optical energy absorbed by the gas results in a periodic thermal expansion which gives rise
to a weak acoustic pressure wave. This pressure wave excites a resonant vibration of the tuning fork thereby generating an
electrical signal via the piezoelectric effect. This paper describes a theoretical model of a QEPAS sensor. By deriving analytical
solutions for the partial differential equations in the model, we obtain a formula for the piezoelectric current in terms
of the optical, mechanical, and electrical parameters of the system. We use the model to calculate the optimal position of
the laser beam with respect to the tuning fork and the phase of the piezoelectric current. We also show that a QEPAS transducer
with a particular 32.8 kHz tuning fork is 2–3 times as sensitive as one with a 4.25 kHz tuning fork. These simulation results
closely match experimental data. 相似文献