Explore the vast range of titles available.

We present experimental results from a new scheme for magneto-optically trapping strontium monofluoride (SrF) molecules, which provides increased confinement compared to our original work. The improved trap employs a new approach to magneto-optical trapping presented by Tarbutt (2015 New J. Phys. 17 015007), which provided insight for the first time into the source of the restoring force in magneto-optical traps (MOTs) where the cycling transition includes dark Zeeman sublevels (known as type-II MOTs). We measure a radial spring constant greater than in our original work with SrF, comparable to the spring constants reported in atomic type-II MOTs. We achieve a trap lifetime ms, over longer than originally reported for SrF. Finally, we demonstrate further cooling of the trapped molecules by briefly increasing the trapping lasers' detunings. Our trapping scheme remains a straightforward extension of atomic techniques and marks a step towards the direct production of large, dense, ultracold molecular gases via laser cooling.

Recent experiments have demonstrated direct cooling and trapping of diatomic and triatomic molecules in magneto-optical traps (MOTs). However, even the best molecular MOTs to date still have density 10 −5 times smaller than in typical atomic MOTs. The main limiting factors are: (i) inefficiencies in slowing molecules to velocities low enough to be captured by the MOT, (ii) low MOT capture velocities, and (iii) limits on density within the MOT resulting from sub-Doppler heating (Devlin and Tarbutt 2018 Phys. Rev. A 90 063415). All of these are consequences of the need to drive ‘Type-II’ optical cycling transitions, where dark states appear in Zeeman sublevels, in order to avoid rotational branching. We present simulations demonstrating ways to mitigate each of these limitations. This should pave the way toward loading molecules into conservative traps with sufficiently high density and number to evaporatively cool them to quantum degeneracy.

For several decades optical tweezers have proven to be an invaluable tool in the study and analysis of myriad biological responses and applications. However, as with every tool, they can have undesirable or damaging effects upon the very sample they are helping to study. In this review the main negative effects of optical tweezers upon biostructures and living systems will be presented. There are three main areas on which the review will focus: linear optical excitation within the tweezers, non-linear photonic effects, and thermal load upon the sampled volume. Additional information is provided on negative mechanical effects of optical traps on biological structures. Strategies to avoid or, at least, minimize these negative effects will be introduced. Finally, all these effects, undesirable for the most, can have positive applications under the right conditions. Some hints in this direction will also be discussed.

We present the properties of a magneto-optical trap (MOT) of CaF molecules. We study the process of loading the MOT from a decelerated buffer-gas-cooled beam, and how best to slow this molecular beam in order to capture the most molecules. We determine how the number of molecules, the photon scattering rate, the oscillation frequency, damping constant, temperature, cloud size and lifetime depend on the key parameters of the MOT, especially the intensity and detuning of the main cooling laser. We compare our results to analytical and numerical models, to the properties of standard atomic MOTs, and to MOTs of SrF molecules. We load up to 2 × 10 4 molecules, and measure a maximum scattering rate of 2.5 × 10 6 s−1 per molecule, a maximum oscillation frequency of 100 Hz, a maximum damping constant of 500 s−1, and a minimum MOT rms radius of 1.5 mm. A minimum temperature of 730 K is obtained by ramping down the laser intensity to low values. The lifetime, typically about 100 ms, is consistent with a leak out of the cooling cycle with a branching ratio of about 6 × 10 − 6 . The MOT has a capture velocity of about 11 m s−1.

An optical trap forms a restoring optical force field to immobilize and manipulate tiny objects. A fiber optical trap is capable of establishing the restoring optical force field using one or a few pieces of optical fiber, and it greatly simplifies the optical setup by removing bulky optical components, such as microscope objectives from the working space. It also inherits other major advantages of optical fibers: flexible in shape, robust against disturbance, and highly integrative with fiber-optic systems and on-chip devices. This review will begin with a concise introduction on the principle of optical trapping techniques, followed by a comprehensive discussion on different types of fiber optical traps, including their structures, functionalities and associated fabrication techniques. A brief outlook to the future development and potential applications of fiber optical traps is given at the end.

Magneto-optical trapping (MOT) is a key technique on the route towards ultracold molecular ensembles. However, the realization and optimization of magneto-optical traps with their wide parameter space is particularly difficult. Here, we present a very general method for the optimization of molecular magneto-optical trap operation by means of Bayesian optimization. As an example for a possible application, we consider the optimization of a calcium fluoride MOT for maximum capture velocity. We find that both the X 2 Σ + to A 2 Π 1/2 and the X 2 Σ + to B 2 Σ + transition to allow for capture velocities with 24 m s −1 and 23 m s −1 respectively at a total laser power of 200 mW. In our simulation, the optimized capture velocity depends logarithmically on the beam power within the simulated power range of 25 to 400 mW. Applied to heavy molecules such as BaH, BaF, YbF and YbOH with their low capture velocity MOTs it might offer a route to far more robust MOT.

Optical traps formed in hollow-core fibers (HCFs) can overcome several limitations of conventional free-space optical tweezers. One of the key issues is to load particles from free space into the hollow core with high efficiency, in which process the capture dynamics of the particles in front of the HCF endface plays an important role. In this work, a comprehensive model of the trapping and capture process of the dielectric particles in front of HCF is established by taking into account the features of the fiber modes and the motional parameters of the particles. Stable capture positions are predicted based on analytical calculations of optical forces, and the dependencies of the equilibrium axial trapping position on the beam numerical aperture, the fiber core and particle diameters are provided. In addition, the trajectories and the capture dynamics of the particles are studied by solving the equation of motion for the particles under the impact of optical forces, predicting feasible parameter ranges of the initial amplitude and direction of particle launch velocity for achieving successful particle capture in front of HCF. The results can provide guidance for further improving the particle-loading efficiencies of the HCF-based optical traps, which may find applications of flying particle sensors and long-range particle binding in HCFs.

Results of spectroscopy experiments using the 5P3/2→6P3/2 electric dipole forbidden transition in cold rubidium atoms are presented. Production of this forbidden transition is detected by observing the emission of the 420 nm fluorescence photons that result from the decay of the 6P3/2 state into the ground state. The experiments are performed under the steady state operation conditions of a magneto-optical trap (MOT), and thus provide non-perturbing information on the atom-light system. The hyperfine structure of the 6P3/2 level is completely resolved, and the fluorescence peaks show the expected Autler–Townes (AT) splitting of the emission lines. This hyperfine structure is used to calibrate the frequency scale of all spectra recorded. A combination of this absolute frequency scale and an expression for the AT profile allows an absolute determination of the effective Rabi frequency and detuning of the MOT. The behavior of these AT doublets is studied as a function of frequency detuning and also as a function of the trapping light intensity. The experiments also take full advantage of the strong polarization dependence of the relative intensities of the hyperfine fluorescence components. This study results in a sensitive probe of the relative populations of the magnetic sublevel projections relative to the trapping magnetic field gradient. An almost isotropic population distribution was found, but small deviations from isotropy could be determined with this electric dipole forbidden probe.

Coordinated cell function requires a variety of subcellular organelles to exchange proteins and lipids across physical contacts that are also referred to as membrane contact sites. Such organelle-to-organelle contacts also evoke interest because they can appear in response to metabolic changes, immune activation, and possibly other stimuli. The microscopic size and complex, crowded geometry of these contacts, however, makes them difficult to visualize, manipulate, and understand inside cells. To address this shortcoming, we deposited endoplasmic reticulum (ER)-enriched microsomes purified from rat liver or from cultured cells on a coverslip in the form of a proteinaceous planar membrane. We visualized real-time lipid and protein exchange across contacts that form between this ER-mimicking membrane and lipid droplets (LDs) purified from the liver of rat. The high-throughput imaging possible in this geometry reveals that in vitro LD–ER contacts increase dramatically when the metabolic state is changed by feeding the animal and also when the immune system is activated. Contact formation in both cases requires Rab18 GTPase and phosphatidic acid, thus revealing common molecular targets operative in two very different biological pathways. An optical trap is used to demonstrate physical tethering of individual LDs to the ER-mimicking membrane and to estimate the strength of this tether. These methodologies can potentially be adapted to understand and target abnormal contact formation between different cellular organelles in the context of neurological and metabolic disorders or pathogen infection.

Optical traps, utilizing a laser to confine and manipulate microscopic particles, are widely employed in various scientific applications. We propose a miniaturized dual-beam fiber optical trap for acceleration sensing. It comprises two counter-propagating beams’ output from a customized pair of single-mode fiber pigtailed focusers (SMFPF). We investigate the correlation between the misalignment and the coupling efficiency of the SMFPF pair. By maximizing the coupling efficiency, the optimal alignment is achieved. A multimode fiber (MMF) is introduced to collect and transmit side-scattered light of a trapped microsphere for motion detection. By analyzing the experimental output signal, we acquire displacement information of the trapped microspheres under both aligned and misaligned conditions. This paper provides a simple and practical solution for the alignment of dual beams and the integration of the optical traps’ levitation and detection structure, which lay a solid foundation for the further miniaturization of dual-beam optical traps.