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Endogenous and exogenous fluorescence emission from biological samples encodes complementary information. Here we report, to the best of our knowledge, the first results from an optical imaging platform with interleaved excitation and detection of exogenous and endogenous fluorescence from tissue samples using a single flexible multimode fiber that delivers the excitation beam and collects the emitted light. A custom-built reflective optical chopper wheel with synchronized rotation temporally multiplexes an autofluorescence lifetime imaging apparatus with an intensity-based fluorescence module tailored to imaging green fluorescent protein. We demonstrate the functionality of such platform imaging dyes of varying fluorescence signatures and resolving cellularized areas on bio-engineered tissue constructs.

Tissue engineers utilize a battery of expensive, time-consuming and destructive techniques to assess the composition and function of engineered tissues. A nondestructive solution to monitor tissue maturation would reduce costs and accelerate product development. As a first step toward this goal, two nondestructive, label-free optical techniques, namely multispectral fluorescent lifetime imaging (FLIm) and time-resolved fluorescence spectroscopy (TRFS), were investigated for their potential in evaluating the biochemical and mechanical properties of articular cartilage. Enzymatic treatments were utilized to selectively deplete cartilage of either collagen or proteoglycan, to produce a range of matrix compositions. Samples were assessed for their optical properties using a fiber-coupled optical system combining FLIm and TRFS, their biochemical and mechanical properties and by histological staining. Single and multivariable correlations were performed to evaluate relationships among these properties. FLIm- and TRFS-derived measurements are sensitive to changes in cartilage matrix and correlate with mechanical and biochemical assays. Mean fluorescence lifetime values extracted from FLIm images (375-410 nm spectral band) showed strong, specific correlations with collagen content (R2 = 0.79, p < 0.001) and tensile properties (R2 = 0.45, p = 0.02). TRFS lifetime measurements centered at 520 nm (with a 5 nm bandwidth) possessed strong, specific correlations with proteoglycan content (R2 = 0.59, p = 0.001) and compressive properties (R2 = 0.71, p < 0.001). Nondestructive optical assessment of articular cartilage, using a combination of FLIm- and TRFS-derived parameters, provided a quantitative method for determining tissue biochemical composition and mechanical function. These tools hold great potential for research, industrial and clinical settings.

This paper reports a handheld multiphoton fluorescence microscope designed for clinical imaging that incorporates axial motion compensation and lateral image stabilization. Spectral domain optical coherence tomography is employed to track the axial position of the skin surface, and lateral motion compensation is realised by imaging the speckle pattern arising from the optical coherence tomography beam illuminating the sample. Our system is able to correct lateral sample velocities of up to approximately 65 μm s

Fluorescence Lifetime Imaging (FLIm) was used to study the zonal and depth-dependent changes in the structure, and biochemistry of bovine articular cartilage to evaluate its potential for nondestructively measuring cartilage health.

We present the first results from a hybrid fluorescence lifetime imaging and optical coherence tomography platform using a double clad fiber.

Laser spectroscopy experiments are often conducted with a probe that does not significantly alter the medium’s properties. For a two-level atom a clear measure of the strength of a probe beam in terms of the saturation intensity is known. We show that for a multilevel atom the situation is very different, and the effects of optical pumping are crucial to understanding the opacity of the medium. We present a simple theoretical analysis for Doppler-broadened spectroscopy of alkali metals on the D2 line that emphasizes the importance of the transient nature of the population dynamics, and the crucial role of the distribution of the times of flight of atoms through the probe beam. Experimental results are obtained with room temperature rubidium vapor probed by an extended-cavity diode laser and confirm our theoretical prediction.

In this paper, we demonstrate, both numerically and experimentally, a method for the detection of defects on structured surfaces having optically unresolved features. The method makes use of synthetic reference data generated by an observational model that is able to simulate the response of the selected optical inspection system to the ideal structure, thereby providing an ideal measure of deviation from nominal geometry. The method addresses the high dynamic range challenge faced in highly parallel manufacturing by enabling the use of low resolution, wide field of view optical systems for defect detection on surfaces containing small features over large regions.

Negative curvature fibre (NCF) guides light in its core by inhibiting the coupling of core and cladding modes. In this work, an NCF was designed and fabricated to transmit ultrashort optical pulses for multiphoton microscopy with low group velocity dispersion (GVD) at 800 nm. Its attenuation was measured to be0.3 dB m(-1) over the range 600-850 nm and the GVD was -180 ± 70 fs(2) m(-1) at 800 nm. Using an average fibre output power of ∼20 mW and pulse repetition rate of 80 MHz, the NCF enabled pulses with a duration of200 fs to be transmitted through a length of 1.5 m of fibre over a tuning range of 180 nm without the need for dispersion compensation. In a 4 m fibre, temporal and spectral pulse widths were maintained to within 10% of low power values up to the maximum fibre output power achievable with the laser system used of 278 mW at 700 nm, 808 mW at 800 nm and 420 mW at 860 nm. When coupled to a multiphoton microscope, it enabled imaging of ex vivo tissue using excitation wavelengths from 740 nm to 860 nm without any need for adjustments to the set-up.

To address the challenge of sample motion during in vivo imaging, we present a fibre-coupled multiphoton microscope with active axial motion compensation. The position of the sample surface is measured using optical coherence tomography and fed back to a piezo actuator that adjusts the axial location of the objective to compensate for sample motion. We characterise the system's performance and demonstrate that it can compensate for axial sample velocities up to 700 µm/s. Finally we illustrate the impact of motion compensation when imaging multiphoton excited autofluorescence in ex vivo mouse skin.

To address the challenge of sample motion during in vivo imaging, we present a handheld multiphoton microscope with active motion compensation. We demonstrate the system's ability to compensate motion in ex vivo mouse skin.

Current international standardisation effort in the field of areal surface texture measurement includes the development of a series of documents describing the nominal characteristics of, and calibration methods for, areal surface topography measuring instruments. Technical committee ISO/TC 213/WG 16, which is directly involved in developing such documents, identified, based on the fact that all areal surface topography measuring instruments produce 3D data sets of points [1], a set of metrological characteristics applicable to all these instruments regardless of their design or operation. Metrological characteristics are input quantities, in a measurement model, that can be measured directly [2], generally using calibrated material measures, and make an immediate contribution to the measurement uncertainty associated with the measured coordinates provided by the instrument. The set of metrological characteristics includes: measurement noise; residual flatness; amplification and linearity of the scales; squareness of the axes; and resolution. In two previous papers, methods to determine measurement noise and residual flatness [3] and amplification, linearity and squareness of the axes [4] were presented. A full paper on the determination of resolution is under review at the time of writing [5] and this work is also summarised here.

We report two novel techniques for cooling and rotating Bose-Einstein condensates in a dilute rubidium vapour that highlight the control and versatility afforded over cold atom systems by time-averaged adiabatic potentials (TAAPs). The intrinsic loss channel of the TAAP has been successfully employed to evaporatively cool a sample of trapped atoms to quantum degeneracy. The speed and efficiency of this process compares well with that of conventional forced rf-evaporation. In an independent experiment, we imparted angular momentum to a cloud of atoms forming a Bose-Einstein condensate by introducing a rotating elliptical deformation to the TAAP geometry. Triangular lattices of up to 60 vortices were created. All findings reported herein result from straightforward adjustments of the magnetic fields that give rise to the TAAP., Comment: The first two authors contributed equally to this work

We report the experimental realization of a versatile ring trap for ultracold atoms. The ring geometry is created by the time-averaged adiabatic potential resulting from the application of an oscillating magnetic bias field to a rf-dressed quadrupole trap. Lifetimes for a Bose-Einstein condensate in the ring exceed $11\mathrm{s}$ and the ring radius was continuously varied from $50 \ensuremath{\mu}\text{m}$ to $262 \ensuremath{\mu}\text{m}$. An efficient method of loading the ring from a conventional time-averaged orbiting potential trap is presented together with a rotation scheme which introduces angular momentum into the system. The ring presents an opportunity to study the superfluid properties of a condensate in a multiply connected geometry and also has applications for matter-wave interferometry.

A large range of high-value manufactured parts require structures to be produced over large areas (metres squared) at high-resolution (micrometres and smaller). Such manufacturing puts demands on the metrology that is required to assure product quality. High-speed, in-line metrology solutions are required to operate over large ranges with high-resolution. In this review, the use of optical super-resolution techniques to enhance the dynamic range of surface topography measuring instruments to allow them to be used in high dynamic range manufacturing scenarios will be highlighted. A brief discussion of optical super-resolution will be given, followed by a presentation of applications that may be able to benefit from optical super-resolution techniques, from the fields of microelectronics, structured surfaces and roll-to-roll manufacturing.