Demonstration of an optical-coherence converter

Studying the coherence of an optical field is typically compartmentalized with respect to its different optical degrees of freedom (DoFs) -- spatial, temporal, and polarization. Although this traditional approach succeeds when the DoFs are uncoupled, it fails at capturing key features of the field's coherence if the DOFs are indeed correlated -- a situation that arises often. By viewing coherence as a `resource' that can be shared among the DoFs, it becomes possible to convert the entropy associated with the fluctuations in one DoF to another DoF that is initially fluctuation-free. Here, we verify experimentally that coherence can indeed be reversibly exchanged -- without loss of energy -- between polarization and the spatial DoF of a partially coherent field. Starting from a linearly polarized spatially incoherent field -- one that produces no spatial interference fringes -- we obtain a spatially coherent field that is unpolarized. By reallocating the entropy to polarization, the field becomes invariant with regards to the action of a polarization scrambler, thus suggesting a strategy for avoiding the deleterious effects of a randomizing system on a DoF of the optical field.Comment: 7 pages; 6 figure

Locked entropy in partially coherent fields

We introduce a taxonomy for partially coherent optical fields spanning multiple degrees of freedom (DoFs) based on the rank of the associated coherence matrix (the number of non-zero eigenvalues). When DoFs comprise two spatial modes and polarization, a fourfold classification emerges, with rank-1 fields corresponding to fully coherent fields. We demonstrate theoretically and confirm experimentally that these classes have heretofore unrecognized different properties. Specifically, whereas rank-2 fields can always be rendered separable with respect to its DoFs via a unitary transformation, rank-3 fields are always non-separable. Consequently, the entropy for a rank-2 field can always be concentrated into a single DoF (thus ridding the other DoF of statistical fluctuations), whereas some entropy is always 'locked' in one DoF of a rank-3 field

Realization of high-dynamic-range broadband magnetic-field sensing with ensemble nitrogen-vacancy centers in diamond

We present a new magnetometry method integrating an ensemble of nitrogen-vacancy (NV) centers in a single-crystal diamond with an extended dynamic range for monitoring the fast changing magnetic-field. The NV-center spin resonance frequency is tracked using a closed-loop frequency locked technique with fast frequency hopping to achieve a 10 kHz measurement bandwidth, thus, allowing for the detection of fast changing magnetic signals up to 0.723 T/s.This technique exhibits an extended dynamic range subjected to the working bandwidth of the microwave source. This extended dynamic range can reach up to 4.3 mT, which is 86 times broader than the intrinsic dynamic range. The essential components for NV spin control and signal processing such as signal generation, microwave frequency control, data processing and readout are integrated in a board-level system. With this platform, we demonstrate broadband magnetometry with an optimized sensitivity of 4.2 nT-Hz-1/2. This magnetometry method has the potential to be implemented in a multichannel frequency locked vector magnetometer suitable for a wide range of practical applications such as magnetocardiography and high-precision current sensors.Comment: 18 pages, 9 figure

0 Polarization-entangled twin-photon ellipsometry

The high accuracy required in traditional ellipsometric measurements necessitates the absolute calibration of both the source and the detector. We demonstrate that these requirements can be circumvented by using a nonclassical source of light, namely, a twin-photon polarization-entangled source that produces type-II spontaneous parametric down-conversion, in conjunction with a novel polarization interferometer and coincidence-counting detection scheme. Our scheme exhibits two features that obviate the requirements of a calibrated source and detector. The first is the twin-photon nature of the source; we are guaranteed, on the detection of a photon in one of the arms of the setup, that its twin will be in the other, effectively serving as calibration of the source. The second is that the polarization entanglement of the source serves as an interferometer, thereby alleviating the need for calibrating the detector. The net result is that absolute ellipsometric data from a sample may be obtained. We present preliminary experimental results showing how the technique operates

Plasmonic Optical Trapping in Biologically Relevant Media

<div><p>We present plasmonic optical trapping of micron-sized particles in biologically relevant buffer media with varying ionic strength. The media consist of 3 cell-growth solutions and 2 buffers and are specifically chosen due to their widespread use and applicability to breast-cancer and angiogenesis studies. High-precision rheological measurements on the buffer media reveal that, in all cases excluding the 8.0 pH Stain medium, the fluids exhibit Newtonian behavior, thereby enabling straightforward measurements of optical trap stiffness from power-spectral particle displacement data. Using stiffness as a trapping performance metric, we find that for all media under consideration the plasmonic nanotweezers generate optical forces 3–4x a conventional optical trap. Further, plasmonic trap stiffness values are comparable to those of an identical water-only system, indicating that the performance of a plasmonic nanotweezer is not degraded by the biological media. These results pave the way for future biological applications utilizing plasmonic optical traps.</p></div

Schematic of the experimental setup.

<p>The experimental setup consists of a laser source (LS) coupled into the sample (S) by the microscope objective (OBJ) and dichroic mirror (DM). The sample inset shows a SEM image of the 425-nm array BNAs and the dotted-yellow line depicts the approximate focal spot diameter; scale bar is 1 . The condenser lens (COND) collects forward-scattered light from the trapped particle and the quadrant photodiode (QPD) detects Brownian fluctuations about the trap center. White-light illumination (WLI) provides visualization of particles on the CCD camera. The inset depicts the rotational rheometer geometry (not to scale) for the viscosity measurements. The measured torque <i>M</i> is due primarily to the simple shear flow in the thin gap between the inner rotor and outer stator. The shear viscosity is calculated from the measured torque and angular velocity .</p

Conventional optical tweezer stiffness.

<p>Measured trap stiffness for the various media using a conventional optical tweezer. Error bars represent standard error in determination.</p

Viscosity measurement results.

<p>Experimentally measured viscosity data at 25C for the various media at 7.4 and 8.0 pH (red and black curves, respectively). Note the BC media is unstable at 8.0 pH and is therefore not included.</p