Combining optical trapping in a microfluidic channel with simultaneous micro-Raman spectroscopy and motion detection.

Since their invention by Ashkin optical tweezers have demonstrated their ability and versatility as a non-invasive tool for micromanipulation. One of the most useful additions to the basic optical tweezers system is micro-Raman spectroscopy, which permits highly sensitive analysis of single cells or particles. We report on the development of a dual laser system combining two spatial light modulators to holographically manipulate multiple traps (at 1064nm) whilst undertaking Raman spectroscopy using a 532nm laser. We can thus simultaneously trap multiple particles and record their Raman spectra, without perturbing the trapping system. The dual beam system is built around micro-fluidic channels where crystallisation of calcium carbonate occurs on polymethylmethacrylate (PMMA) beads. The setup is designed to simulate at a microscopic level the reactions that occur on items in a dishwasher, where permanent filming of calcium carbonate on drinking glasses is a problem. Our system allows us to monitor crystal growth on trapped particles in which the Raman spectrum and changes in movement of the bead are recorded. Due to the expected low level of crystallisation on the bead surfaces this allows us to obtain results quickly and with high sensitivity. The long term goal is to study the development of filming on samples in-situ with the microfluidic system acting as a model dishwasher

Assembly and force measurement with SPM-like probes in holographic optical tweezers

We report a high fidelity tomographic reconstruction of the quantum state of photon pairs generated by parametric down-conversion with orbital angular momentum (OAM) entanglement. Our tomography method allows us to estimate an upper and lower bound for the entanglement between the down-converted photons. We investigate the two-dimensional state subspace defined by the OAM states ±ℓ and superpositions thereof, with ℓ=1, 2, ..., 30. We find that the reconstructed density matrix, even for OAMs up to around ℓ=20, is close to that of a maximally entangled Bell state with a fidelity in the range between F=0.979 and F=0.814. This demonstrates that, although the single count-rate diminishes with increasing ℓ, entanglement persists in a large dimensional state space

Comparison of closed loop and sensorless adaptive optics in widefield optical microscopy

We report on a closed loop widefield adaptive optics, optical microscopy system in which the feedback signal is provided by backscattered light from the sample acting as a guide star. The improvement in imaging performance is compared to an adaptive optics system controlled via an image optimisation routine commonly described as sensorless adaptive optics. The samples viewed were imaged without fluorescence to ensure that photobleaching and other potential variations did not affect the comparisons in system performance though the method is equally applicable for fluorescence microscopy. The closed loop system is self-optimising for different areas of the sample, using a common reference wavefront, with the accuracy of the loop being limited by variation across the sub-aperture images induced by guide star elongation. Optimisation using an image sharpness metric gives slightly sharper images but takes significantly longer. We thus believe that both wavefront sensor based closed loop AO and metric based optimisation have a role to play in AO for microscopy and that the method of backscattered light as a guide star has a great potential in the application of AO, particularly to optical coherence tomography

Quantitative High Dynamic Range Beam Proling for Fluorescence Microscopy

Modern developmental biology relies on optically-sectioning uorescence microscope techniques to produce non-destructive in-vivo images of developing specimens at high resolution in three dimensions. As optimal performance of these techniques is reliant on the three-dimensional (3-D) intensity prole of the illumination employed, the ability to directly record and analyze these proles is of great use to the uorescence microscopist or instrument builder. Though excitation beam proles can be measured indirectly using a sample of uorescent beads and recording the emission along the microscope detection path, we demonstrate an alternative approach where a miniature camera sensor is used directly within the illumination beam. Measurements taken using our approach are solely concerned with the illumination optics as the detection optics are not involved. We present a miniature beam proling device and high dynamic range ux reconstruction algorithm that together are capable of accurately reproducing quantitative 3-D ux maps over a large focal volume. Performance of this beam proling system is veried within an optical test bench and demonstrated for uorescence microscopy by proling the low NA illumination beam of a single plane illumination microscope. The generality and success of this approach showcases a widely- exible beam amplitude diagnostic tool for use within the life sciences

Real-time optical gating for three-dimensional beating heart imaging.

We demonstrate real-time microscope image gating to an arbitrary position in the cycle of the beating heart of a zebrafish embryo. We show how this can be used for high-precision prospective gating of fluorescence image slices of the moving heart. We also present initial results demonstrating the application of this technique to 3-D structural imaging of the beating embryonic heart