Trapping Laser Light Research Articles

Reflection mode optical trapping using polarization symmetry breaking from tilted double nanoholes.

We demonstrate reflection geometry optical trapping using double nanoholes in a metal film. Symmetry breaking of the double nanohole allows for selecting the scattered trapping laser light of orthogonal polarization to the incident beam. This orthogonal polarization light shows a few percent increase when the nanoparticle (e.g., a 20 nm polystyrene particle, or protein bovine serum albumin) is trapped. The reflection geometry simplifies the optical setup and frees up one side of the trap, which has great potential for adding microfluidics to the other side or working with opaque or highly scattering samples.

Development of a Laser Frequency Stabilization and an Optical Transmission System for the Francium Electric Dipole Moment Search

Abstract We developed a laser frequency stabilization and an optical fiber transmission system for the the francium electric dipole moment search. The absolute accuracy of a laser frequency stabilization scheme using a state-of-the-art commercial wavelength meter was 0.48 MHz at ±2 nm and -1.33 MHz at ±200 nm from calibration wavelength, respectively, and the frequency instability is below 10-9 with a standard deviation of 0.56 MHz over 60 hours. We also demonstrated that a 400 m long fiber laid between laboratories can transmit 30 mW of trapping laser light, which is sufficient for a magneto-optical trapping of francium. The polarization crosstalk in the fiber was stable at -25 dB over 12 hours of measurement.

Nanotraffic Lights: Rayleigh Scattering Microspectroscopy of Optically Trapped Octahedral Gold Nanoparticles

We demonstrate a pronounced color change in the light scattered from thermally fluctuating optically trapped octahedral gold nanoparticles (OGPs) in water using a tightly focused near-infrared laser beam. Monodispersed OGPs with an average edge length of 67 ± 6.5 nm were synthesized using a polyol method. Using dark-field microscopy, we observed successive changes of color (i.e., red → green → yellow) scattered from the trapped OGPs. We analyzed this trapping behavior by means of Rayleigh scattering microspectroscopy and concluded that pairs of OGPs trapped in the potential well interact with each other to form dimers oriented in the direction of the electric field vector of the trapping laser light. We theoretically obtained the absorption and scattering cross sections and the enhancement factors of the electric field of an OGP dimer in three different configurations by means of finite-difference time-domain calculations. The calculations suggest that the dimers become preferentially oriented in a vertex...

A remote laboratory for optical levitation of charged droplets

We present a remotely controlled experiment in which liquid droplets are levitated by a vertically aligned focused laser beam. The droplets levitate at the point where the photon pressure of the focused laser beam balances the gravitational force. The size of a trapped droplet can be measured by detecting the diffraction pattern created by the trapping laser light. The charge on the trapped droplet can thereafter be determined by observing its motion when a vertically directed electrical field is applied. This experiment allows a student to study many fundamental physics processes, such as photon pressure, diffraction of light, or the motion of charged particles in electrical fields. The complexity of the experiments and the concept studied make this suitable for advanced studies in physics. The laser power required in the experiment is about 1 W, which is a thousand times greater than the value of 1 mW at which lasers begin to be capable of causing harm to eyes; high voltages are also used. Further, the cost of the equipment is relatively high, which limits its availability to most undergraduate teaching laboratories. It thus constitutes an ideal experiment for remote control.

Wigner Function Reconstruction in Levitated Optomechanics

AbstractWe demonstrate the reconstruction of theWigner function from marginal distributions of the motion of a single trapped particle using homodyne detection. We show that it is possible to generate quantum states of levitated optomechanical systems even under the efect of continuous measurement by the trapping laser light. We describe the opto-mechanical coupling for the case of the particle trapped by a free-space focused laser beam, explicitly for the case without an optical cavity. We use the scheme to reconstruct the Wigner function of experimental data in perfect agreement with the expected Gaussian distribution of a thermal state of motion. This opens a route for quantum state preparation in levitated optomechanics.

Trapping of intense light in hollow shell

A small hollow shell for trapping laser light is proposed. Two-dimensional particle-in-cell simulation shows that under appropriate laser and plasma conditions a part of the radiation fields of an intense short laser pulse can enter the cavity of a small shell through an over-critical density plasma in an adjacent guide channel and become trapped. The trapped light evolves into a circulating radial wave pattern until its energy is dissipated.

Time-symmetry breaking in a modulated cold atom system: An ideal mean-field transition

We realize an ideal mean-field transition of time-translation symmetry in a periodically-driven atomic system. The symmetry in steady-state oscillatory atomic motions spontaneously changes with the total number of atoms due to the interplay between inter-atomic interactions which originate from the attenuation effects in the trapping laser light and thermal fluctuations. A large separation of the time scales governing the transition suppresses the spatial dependence of the system dynamics, leading to a mean-field behavior even close to the transition point.

Controlling the Position and Orientation of Single Silver Nanowires on a Surface Using Structured Optical Fields

We demonstrate controlled trapping and manipulation of single silver (Ag) nanowires in two dimensions at a surface using structured light fields generated with a spatial light modulator. The Ag nanowires are attracted toward the regions of maximal optical intensity along the surface when the trapping laser light is linearly polarized and are repelled toward the minima of optical intensity when the light is circularly polarized. For linearly polarized light, stably trapped nanowires are oriented perpendicular to the polarization direction due to a torque induced by an asymmetrical response of the nanowire to the electric field. The attractive interactions with linearly polarized trapping laser light, which is at 800 nm for all measurements, enable stable trapping and translation of Ag nanowires in the antinodes of optical gratings and in zero-order Bessel beams. Trapped nanowires can be positioned and oriented on a transparent dielectric substrate, making possible the nonmechanical assembly of plasmonic nanostructures for particular functions.

Towards an integrated optical single aerosol particle lab

We present a manipulation and characterization system for single airborne particles which is integrated onto a microscope slide. Trapped particles are manipulated by means of radiation pressure and characterized by cavity enhanced Raman spectroscopy. Optical fibers are used to deliver the trapping laser light as well as to collect the Raman scattered light, allowing for a flexible usage of the device. The system features a sample chamber which is separated from an aerosol-flooded injection chamber by means of a light guiding glass-capillary. The coupling of this device with an aerosol optical tweezers setup to selectively load its trapping sites is demonstrated. Finally, a route towards chip-integrated handling and processing of multiple particles is shown and the first results are presented.

Electric-field-dependent dynamic polarizability and state-insensitive conditions for optical trapping of diatomic polar molecules

Selection of "magic" trapping conditions with ultracold atoms or molecules, where pairs of internal states experience identical trapping potentials, brings substantial benefits to precision measurements and quantum computing schemes. Working at such conditions could ensure that detrimental effects of inevitable inhomogeneities across an ultracold sample are significantly reduced. However, this aspect of confinement remains unexplored for ultracold polar molecules. Here, we present means to control the AC Stark shift of rotational states of ultracold polar molecules, when subjected to both trapping laser light and an external electric field. We show that both the strength and relative orientation of the two fields influence the trapping potential. In particular, we predict "magic electric field strengths" and a "magic angle", where the Stark shift is independent of the DC external field and rotational states of the molecule.

Optical Trapping and Two-Photon Exitations of Quantum Dots

Individual colloidal quantum dots can be optically trapped and manipulated by a single infrared laserbeam operated a low laser powers [Jauffred et al. Nano letters 2008 (10)] and the spring constant of the force, exerted by the harmonic optical trap on a quantum dot, have been found to be of the order of 10−4 pN/nm. We measured the optical trapping strength of individual colloidal quantum dots with different emission wavelenghts (from 525 nm to 800 nm) and different physical sizes, with the result that these diverse quantum dots have identical trapping capabilities. Furthermore, we show that the trapping laserlight can also act as a source for two-photon excitation of the trapped quantum dots, thus eliminating the demand for an excitation light source in addition to the trapping laser beam.

Optical tweezers with millikelvin precision of temperature-controlled objectives and base-pair resolution

In optical tweezers, thermal drift is detrimental for high-resolution measurements. In particular, absorption of the trapping laser light by the microscope objective that focuses the beam leads to heating of the objective and subsequent drift. This entails long equilibration times which may limit sensitive biophysical assays. Here, we introduce an objective temperature feedback system for minimizing thermal drift. We measured that the infrared laser heated the objective by 0.7 K per watt of laser power and that the laser focus moved relative to the sample by approximately 1 nm/mK due to thermal expansion of the objective. The feedback stabilized the temperature of the trapping objective with millikelvin precision. This enhanced the long-term temperature stability and significantly reduced the settling time of the instrument to about 100 s after a temperature disturbance while preserving single DNA base-pair resolution of surface-coupled assays. Minimizing systematic temperature changes of the objective and concurrent drift is of interest for other high-resolution microscopy techniques. Furthermore, temperature control is often a desirable parameter in biophysical experiments.

Photoassociation spectroscopy of ultracold Cs below the 6P1/2 limit.

We have performed high precision photoassociation spectroscopy of ultracold cesium gas. Using trap-loss fluorescence detection and controlling the background cesium pressure we were able to photoassociate atoms into excited states of ultracold molecules with large detunings up to 56 cm(-1) below the Cs(6S(1/2)) + Cs(6P(1/2)) atomic asymptote. Vibrational progressions are assigned to 0(g)(-), 0(u)(+), and 1(g) long-range states. By fitting the spectral data to the LeRoy-Bernstein expression, the effective coefficients of the leading long-range interactions and the vibrational quantum number at dissociation are obtained. In addition we have observed spectral perturbations between states of the same symmetry belonging to different asymptotes (6P(1/2) and 6P(3/2)). The perturbations are manifested through irregular vibrational level spacings and are especially pronounced in the 0(u)(+) symmetry. Many observed rotational levels indicate d- and higher partial wave contributions to the photoassociation cross section in the presence of trapping laser light, while spectral regions with only weak features suggest nodes in the lower state wave functions corresponding to the two ground state atoms asymptote.

Comparison of the cold-collision losses for laser-trapped sodium in different ground-state hyperfine sublevels.

We have measured the cold-collision loss rates of laser-trapped Na atoms in each ground-state hyperfine sublevel. The laser intensity dependence for the [ital F]=1 sublevel agrees with a simple theory and we establish experimentally that hyperfine-level-changing collision losses are absent as expected. We observed hyperfine-level-changing collisions in the [ital F]=2 sublevel but the dependence of the loss-rate constant on laser intensity disagrees with simple theories. Unexpected behavior observed for total trapping laser light intensity between 4 and 12 mW/cm[sup 2] may be a consequence of the sub-Doppler cooling in the [ital F]=2 trap.

Observation of second harmonic generation from optically trapped microscopic LiNbO 3 particle using Nd:YAG laser

Optical trapping of a microscopic LiNbO3 particle is demonstrated using a single beam from a CW Nd:YAG laser at 1.064 μm for the first reported time. The simultaneous generation of a second harmonic wave from the LiNbO3 particle induced by the trapping laser light itself is also confirmed by the emission spectrum at 532 nm and by its intensity variation that is almost proportional to the square of the input Nd:YAG laser power ranging from several milliwatts to 40 mW.