No abstract

Optical tweezers and associated manipulation tools in the far field have had a major impact on scientific and engineering research by offering precise manipulation of small objects. More recently, the possibility of performing manipulation with surface plasmons has opened opportunities not feasible with conventional far-field optical methods. The use of surface plasmon techniques enables excitation of hotspots much smaller than the free-space wavelength; with this confinement, the plasmonic field facilitates trapping of various nanostructures and materials with higher precision. The successful manipulation of small particles has fostered numerous and expanding applications. In this paper, we review the principles of and developments in plasmonic tweezers techniques, including both nanostructure-assisted platforms and structureless systems. Construction methods and evaluation criteria of the techniques are presented, aiming to provide a guide for the design and optimization of the systems. The most common novel applications of plasmonic tweezers, namely, sorting and transport, sensing and imaging, and especially those in a biological context, are critically discussed. Finally, we consider the future of the development and new potential applications of this technique and discuss prospects for its impact on science.

No abstract

In this Letter, we show that the energy equivalent to that incident on a 4:7 m wide strip can be squeezed through a 50 nm wide slit in a metal film surrounded by grooves. This corresponds to a transmission efficiency of 9400%, which can be even further enhanced by increasing the number of grooves. We use the phase of the magnetic field to explain that the ideal slit-to-groove distance is just over half the plasmon wavelength. In addition, we also optimize the groove depth and width. Such optimized transmission enhancement is very important for near-field devices.

Single photon detectors are indispensable tools in optics, from fundamental measurements to quantum information processing. The ability of superconducting nanowire single photon detectors (SNSPDs) to detect single photons with unprecedented efficiency, short dead time, and high time resolution over a large frequency range enabled major advances in quantum optics. However, combining near-unity system detection efficiency (SDE) with high timing performance remains an outstanding challenge. In this work, we fabricated novel SNSPDs on membranes with 99.5−2.07+0.5% SDE at 1350 nm with 32 ps timing jitter (using a room-temperature amplifier), and other detectors in the same batch showed 94%–98% SDE at 1260–1625 nm with 15–26 ps timing jitter (using cryogenic amplifiers). The SiO2/Au membrane enables broadband absorption in small SNSPDs, offering high detection efficiency in combination with high timing performance. With low-noise cryogenic amplifiers operated in the same cryostat, our efficient detectors reach a timing jitter in the range of 15–26 ps. We discuss the prime challenges in optical design, device fabrication, and accurate and reliable detection efficiency measurements to achieve high performance single photon detection. As a result, the fast developing fields of quantum information science, quantum metrology, infrared imaging, and quantum networks will greatly benefit from this far-reaching quantum detection technology.

Circularly polarized electric fields incident on subwavelength apertures produce near-field phase singularities with phase vorticity AE1 depending on the polarization handedness. These near-field phase singularities combine with those associated with orbital angular momentum and result in polarizationdependent transmission. We produce arbitrary phase vorticity in the longitudinal component of scattered electric fields by varying the incident beam and aperture configuration. DOI: 10.1103/PhysRevLett.104.083903 PACS numbers: 42.25.Fx, 42.25.Gy, 42.25.Ja, 42.50.Tx Phase singularities in the electric field are locations at which the field amplitude is strictly zero. Given a fixed polarization or ''spin'', the phase integral over the transverse field components enclosing a phase singularity provides a measure of the phase vorticity or orbital angular momentum (OAM) topological charge [1,2]. The threedimensional electric field of an inhomogeneously polarized propagating electromagnetic wave produces three different types of polarization phase singularities [3], the evolution of which is studied in a rich array of literature [4]. Our understanding of phase singularities allows us to probe materials, characterize surfaces, study light propagation dynamics, and manipulate microparticles [5].Within the last decade, there have been observations of near-field phase singularities (NFPS) in the evanescent waves produced by propagating [6] and scattered [7] light. The locations of NFPS produced by chiral ''gammadion' ' [8] and spiral grating structures [9] depend on incident polarization handedness. These NFPS are connected to the extraordinary transmission of light through subwavelength slits [10], where whirlpool-like power flows and singularities in the Poynting vector are shown to exist [11,12]. Azimuthally and radially polarized vortices, beams with different polarization singularities, are transmitted through apertures with different efficiencies [13] but in spite of numerous measurements and observations of NFPS, the polarization-dependent transmission that occurs at subwavelength structures is not fully understood and light-metal interactions are neither fully optimized nor controlled.Here, we show that the polarization-dependent transmission at sub-wavelength-structured materials are concisely explained by a coupling between electromagnetic spin and OAM. ''Spin-orbit interactions'' describe the modified light propagation due to their coupling where the longitudinal component of an electric field generally plays a crucial role. It has been shown that spin-orbit interactions occur via oblique reflections and refraction [14], in wave guiding structures [15], and in the focal plane of highly focused beams [16]. In these situations, a change in either the direction of the phase vorticity or the polarization handedness results in a shift of the observed light intensity patterns.Our work explains, for the first time, that polarizationdependent NFPS describe which modes and to what extent light is transmitted through th...

We experimentally demonstrate that a femtosecond frequency comb laser can be applied as a tool for longdistance measurement in air. Our method is based on the measurement of cross correlation between individual pulses in a Michelson interferometer. From the position of the correlation functions, distances of up to 50 m have been measured. We have compared this measurement to a counting laser interferometer, showing an agreement with the measured distance within 2 m (4 ϫ 10 −8 at 50 m). © 2009 Optical Society of America OCIS codes: 320.7100, 320.2250, 320.1590 Traditional techniques for long-distance measurements are often based on optical interferometry when the demands on accuracy rise. Most of these interferometric techniques rely on incremental measurements of phase accumulation. A priori knowledge of the distance to be measured is required or a complex multiwavelength system may be needed. In 2004, Ye [1] proposed a simple scheme for measuring long distances in space with a stabilized femtosecond frequency comb. The scheme is based on a Michelsontype interferometry with optical interference between individual pulses. The technique proposed by Ye has been demonstrated for interferometric measurement of short displacement [2,3]. The main advantage of applying a frequency comb for distance measurement is the large range of nonambiguity, which is determined by the cavity length of the pulsed laser, ranging from about 30 cm to 3 m. It is thus not necessary to rely on incremental measurement of the optical phase. The ambiguity is easily overcome by, e.g., a laser distance meter. The stabilized frequency comb has been applied as a source in various distance measurement schemes [4,5]. In this Letter, we demonstrate distance measurements of up to 50 m in air by analyzing the cross correlation between pulses emitted from a stabilized frequency comb source. We have implemented a model of pulse propagation in air to account for the effect of air dispersion on the measured cross-correlation functions. The measurement results obtained with the frequency comb and a conventional counting laser interferometer are compared.A mode-locked Ti:sapphire laser is the frequency comb source, with both the repetition frequency and the carrier-envelop offset (CEO) frequency referenced to a cesium atomic clock (Fig. 1). The pulse duration is 40 fs, and the repetition rate f r is locked at approximately 1 GHz, corresponding to a pulse to pulse distance l pp = c / ͑n g f r ͒ of 30 cm. Here c is the speed of light in vacuum and n g is the group refractive index at the center wavelength. The CEO frequency f 0 is fixed at 180 MHz. The center wavelength of the pulses is 815 nm, with an FWHM of about 20 nm. After collimation the beam is sent to a Michelson interferometer. One part of the beam is reflected by a hollow corner cube mounted on a piezoelectric transducer (PZT) along the short reference arm. The length of the short arm can be scanned by a translation stage. The other part of the beam is reflected by two mirrors and propagates along...

Abstract:The application of wire grid polarizers as efficient polarizing beam splitters for visible light is studied. The large differences between the transmissivity for different polarizations are explained qualitatively by using the theory of metallic wave guides. The results of rigorous calculations obtained by using the finite element method are compared with experiments for both classical and conical mount. Furthermore the application of wire-grid polarizers in liquid crystal on silicon display systems is considered.