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

Femtosecond laser-assisted selective holding with ultra-low power for direct manipulation of biological specimens

Traditional optical tweezers techniques often rely on high-power continuous wave (CW) lasers, which can introduce unwanted thermal effects and photodamage to delicate samples. To overcome these limitations, we demonstrate femtosecond laser assisted selective holding with ultra-low power (FLASH-UP). We find that the FLASH-UP exhibits a five times greater trap stiffness than CW-OT, and can trap at lower intensities. Furthermore, we demonstrate OT of different pathogenic bacteria species and find that FLASH-UP does not impact cell motility. These results pave the way for applications in sorting, bio-sensing, in vivo cell manipulation and single cell analysis

Ellipsometric measurements by use of photon pairs generated by spontaneous parametric down-conversion

We present a novel interferometric technique for performing ellipsometric measurements. This technique relies on the use of a non-classical optical source, namely, polarization-entangled twin photons generated by spontaneous parametric down-conversion from a nonlinear crystal, in conjunction with a coincidence-detection scheme. Ellipsometric measurements acquired with this scheme are absolute; i.e., they do not require source and detector calibration.Comment: 10 pages, accepted for publication in Optics Letter

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

Media 2: Plasmonic nanotweezers: strong influence of adhesion layer and nanostructure orientation on trapping performance

Originally published in Optics Express on 23 April 2012 (oe-20-9-9591

Media 1: Plasmonic nanotweezers: strong influence of adhesion layer and nanostructure orientation on trapping performance

Originally published in Optics Express on 23 April 2012 (oe-20-9-9591

Application of quantitative second-harmonic generation microscopy to dynamic conditions

We present a quantitative second-harmonic generation (SHG) imaging technique that quantifies the 2D spatial organization of collagen fiber samples under dynamic conditions, as an image is acquired. The technique is demonstrated for both a well-aligned tendon sample and a randomly aligned, sparsely distributed collagen scaffold sample. For a fixed signal-to-noise ratio, we confirm the applicability of this method for various window sizes (pixel areas) as well as with using a gridded overlay map that allows for correlations of fiber orientations within a given image. This work has direct impact to in vivo biological studies by incorporating simultaneous SHG image acquisition and analysis

Demonstration Of An Optical-Coherence Converter

Studying the coherence of an optical field is typically compartmentalized with respect to its different physical 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 regard 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