Photonex - Active & Adaptive Optics

The 18th of October 2011 was held the Active & Adaptive Optics conference as part of the PHOTONEX Exhibition & Conference. The event took place at the Ricoh Arena in Coventry, UK

The conference programme is avaible here.
Presentations are available either by directly clicking on the title (below) and can also be downloaded from this link. Documents are restricted to registered users only.

Nanometric 3D tracking in live-cell biology using wavefront sensors
Alan Greenaway
School of Engineering and Physical Sciences, Heriot Watt University, UK
Two techniques derived from adaptive optics in astronomy can be combined to facilitate very-high resolution depth measurement in microscopy. The background principles and some recent results will be described, charting progress toward our objective to track single molecules and vesicles or other organelles in living cells with ~10nm accuracy.
Adaptive phase compensation for ultracompact confocal endomicroscopy
Alex J. Thompson1, Yuhong Wan2, Carl Paterson1, Mark A. A. Neil1, Chris Dunsby1 and Paul M. W. French1
1. Department of Physics, Imperial College London, UK
2. Institute of Information Photonics Technology and College of Applied Sciences, Beijing University of Technology, China
Fluorescence endomicroscopes employ fibre optics along with miniaturized scanning and focusing mechanisms to allow microscopic investigation of remote tissue samples. At present there are two common methods used for confocal endomicroscopy, which have been applied to both clinical diagnosis and small animal imaging for biomedical research. In this talk I will review the current methodology and present a novel approach to laser scanning endomicroscopy which requires no moving parts and can be implemented without the need for any distal scanners or optics, permitting extremely compact endoscopic probes to be developed. Our technique utilizes a spatial light modulator to correct for phase variations across a fibre imaging bundle and then to encode for arbitrary wavefronts at the distal end of that fibre bundle. Thus, it is possible to realize both focusing and beam scanning at the output of the fibre bundle with no distal components. Here we present proof of principle results illustrating three-dimensional scanning of the focal spot as well as exemplar images of a United States Air Force resolution test chart.
Widefield AO microscopy based on image sharpness optimization in a sensorless and sensored configuration
Cyril Bourgenot, Christopher D. Saunter, John M. Girkin, Gordon D. Love
Department of Physics, Durham University, South Road, Durham DH1 3LE (United Kingdom)
Effects such as refraction index mismatch and sample induced aberrations limit the imaging resolution of optical microscopy and, in particular, optical sectioning methods such as confocal or multi-photon microscopes in deep biological samples. The use of adaptive optics (AO) in such cases can allow a partial correction of these aberrations and an improvement of the image quality (resolution and contrast for example) leading to a deeper penetration in the sample. Most of these systems used an optimization algorithm in some form to determine the aberration correction required, and this continues to be the general situation though this has recently come to be termed “sensorless” correction. We report on recent developments in the use of AO in wide-field microscopy to remove both system and sample induced aberrations. Two configurations have been studied. First we describe a sensorless configuration where the optimization relies on image sharpening metric techniques used with a simplex search algorithm. We compare the optimization efficiency based on 5 commonly used image sharpness metrics and discuss the advantage of guiding the search with deformable mirror shapes based on low order Zernike polynomials. Then we describe a closed loop configuration with a wavefront sensor where the aberration is measured via the help of a probe laser beam working at 633nm, reflected either on the microscope slide or on the sample.
Closed loop adaptive optics in fluorescence microscopy
Michael Shaw1, Carl Paterson2
1. National Physical Laboratory, Hampton Road, Teddington, Middlesex, TW11 0LW, UK
2. The Blackett Laboratory, Imperial College, London SW7 2BW, UK
Adaptive optics techniques offer the potential to correct system and sample induced wavefront aberrations in a range of optical microscopes, enabling fast, diffraction limited imaging inside complicated objects such as biological specimens. Direct wavefront sensing in such systems is often challenging and many existing approaches rely on indirect image based wavefront sensing or optimisation of the adaptive element using image quality metrics. However, these methods often have limitations in terms of speed and specimen light exposure. We have developed a stage scanning confocal / epifluorescence microscope which incorporates a Shack-Hartmann wavefront sensor and a continuous facesheet piezoelectric deformable mirror. This system has been used to investigate the use of artificial fluorescent ‘guide stars’ to allow direct wavefront sensing and closed loop adaptive optics correction for imaging a variety of objects.
Registration and selection of AO-corrected fundus images
Nicholas Devaney and Gomathy Ramaswamy
Applied optics group, School of Physics, National University of Ireland, Galway, Ireland
Adaptive optics allows retinal images to be obtained with unprecedented spatial resolution. However, as with other applications of AO, the quality of the correction fluctuates randomly, and it may be beneficial to select the best quality images for further processing. There will also be residual tip-tilt, and the retinal images need to be carefully registered. We have investigated the application of several measures of image quality to sequences of images obtained with the rtx1 AO system from Imagine Eyes. The spatio-temporal behavior of the image quality is also examined. We present the results of 2-stage registration, in which registration using template matching is followed by tracking of individual photoreceptors (cones).
Almost real-time imaging through horizontal turbulence
G. Vdovin, M. Loktev, O. Soloviev and S. Savenko
Flexible Optical BV, Polakweg 10-11, 2288GG, Rijswijk, The Netherlands
We report on the results of our experiments on the horizontal path imaging through turbulence. Our approach consists in simultaneous registration of multiple frames through a number of uncorrelated optical paths, followed by image post-processing employing the method of iterated projections on a convex set. Multiple optical paths are created by adaptable segmentation of the system pupil, where the number of segments is the function of the strength of turbulence. We also report on the applicability of adaptive optics for horizontal path imaging. Finally, we present experimental results of adaptable multi-frame horizontal-path imaging for object at distances from 0.5 to 8 km at different turbulence conditions.
Optimal techniques for the detection of exoplanets
Nicholas Devaney1, Daniel Burke1, É. Thiebaut2
1. Applied optics group, School of Physics, National University of Ireland, Galway, Ireland
2. CRAL, Observatoire de Lyon, St. Genis-Laval, France
One of the great challenges for astronomical Adaptive Optics is the detection of extrasolar planets in direct images. It requires very precise correction of aberrations, and rejection of light from the central star by factors of at least 105. This is greatly complicated by residual speckle, due to uncorrected aberrations. Knowledge of the spatial and spatio-temporal statistics of the residuals can be incorporated into algorithms which provide optimal detection. We have examined the performance of the optimal linear detector, referred to in the literature as the Hotelling observer. We have also developed an approach which exploits the wavelength-dependence of the PSF to allow rejection of the stellar light in the images i.e. without using a coronograph. Combining these approaches will provide a powerful tool for the post-processing of images from instruments which are being developed for exo-planet detection.
Dual adaptive optics system for laser processing of diamond
Richard D. Simmonds1, Patrick S. Salter1, Alexander Jesacher2 and Martin J. Booth1
1. Department of Engineering Science, University of Oxford, Parks Road, Oxford, OX1 3PJ, United Kingdom
2. Division of Biomedical Physics, Innsbruck Medical University, Müllerstraße 44, 6020, Innsbruck, Austria
Laser material processing with short pulsed laser beams has been widely used for submicron scale fabrication. In diamond, the high focal intensity transforms the material into a graphite-like phase from which three-dimensional structures can be fabricated. The fidelity of fabrication depends strongly on the quality of the focal spot, which is impaired by the extreme aberrations arising from the refractive index mismatch between the diamond (n=2.4) and the objective immersion medium (n=1.5). They lead to distortion of the focus, in particular an elongation along the optic axis, and a reduction in its intensity. As a consequence, the accuracy of fabrication is compromised. As one focuses deeper into the substrate, the aberrations increase in magnitude.
Adaptive optics can be used to compensate these aberrations, thus restoring the focal spot fidelity and the quality of the fabricated features. We describe a dual adaptive optics fabrication system based around an amplified titanium sapphire laser, incorporating both a liquid crystal spatial light modulator and a deformable mirror. It is shown that aberration compensation is essential for the generation of controlled micron-scale features at depths greater than 200 μm, and the dual adaptive optics approach demonstrates increased fabrication efficiency relative to experiments using a single adaptive element.
Adaptive optics in 3D microfabrication of photonic devices
Patrick Salter1, Alexander Jesacher2, Richard Simmonds1 and Martin Booth1
1. Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, United Kingdom
2. Division of Biomedical Physics, Innsbruck Medical University, Müllerstraße 44, 6020, Innsbruck, Austria
A liquid crystal spatial light modulator (SLM) is used for beam shaping in the fabrication of photonic devices by a femtosecond laser. The SLM is used to both correct for aberrations and shape the wavefront to create a desired intensity distribution at focus. In the fabrication of waveguides in fused silica, the beam shaping creates a structure with circular crosssection that is well mode matched to single mode optical fibres. The SLM also allows for parallelization of the writing through the generation of multiple fabrication foci from the incident beam, thus reducing processing times. It is additionally possible to correct for depth dependent spherical aberration arising from an interface where there is a change in refractive index, generating potential for three dimensional waveguide circuits. These circuits may find application in fields such as quantum optics or astrophotonics.
Development of a high resolution bimorph deformable mirror for free-space optical communications
Christophe Boulet, Mike Griffith, L.C. Laycock, Andrew McCarthy
BAE SYSTEMS (Operations) Ltd Advanced Technology Centre, West Hanningfield Road, Great Baddow, Chelmsford, Essex CM2 8HN, UK
We describe the development of flexi-circuit addressed, high resolution Bimorph Deformable Mirror (BDM) suitable for a satellite-to-ground optical communications link. In the first phase, the base of one of our existing 37 element mirrors was modified to enable integration onto a commercially available tip-tilt stage whilst keeping the mass similar to that of a standard mirror substrate. Evaluation demonstrated that there was no degradation in performance as a result of the mass reduction and integration. In the current phase, a 100 element BDM with a 10mm optical aperture suitable for integration onto a bespoke tip-tilt platform has been designed and assembled. The results of initial tests are presented.
'Smarter' Ultrafast Lasers with intracavity deformable mirror
Nikolaus Klaus Metzger
School of Physics and Astronomy, University of St Andrews, UK
An Yb:KYW mode-locked laser with an intracavity deformable mirror is used to demonstrate cavity self-optimization via a computer-controlled feedback loop. An algorithm optimizes the deformable mirror surface towards an optimum for the mode-locked operation of the laser. Furthermore dynamic spectral phase design and control is implemented and evaluated. With this laser it is possible to achieve linear, quadratic and cubic phase characteristics with a maximum phase change of 0.7 radians at the wings of the spectral components of the ultrashort pulses. This novel cavity design could have major impact in the operational regime of few-cycle lasers because it offers the prospect of compensating the higher orders of dispersion that cannot be controlled satisfactorily by prisms alone.
Development of MEMS micromirrors for intracavity laser control
W Lubeigt, R. Bauer and D. Uttamchandani
Centre for Microsystems and Photonics, University of Strathclyde, Department of Electronic and Electrical Engineering, 204 George Street, Glasgow G1 1XW
High reflectivity (HR), electrostatic MEMS micromirrors have the potential to Q-switch Nd:based laser cavities [Lubeigt et al. Opt. Express 19 2011]. This talk will present the latest development of a range of novel electrostatic micromirrors for intracavity laser temporal control. Most notably, a 2D array of micromirrors was incorporated inside a Nd:YAG laser cavity. The development of suitable HR coatings for implementation inside high power (output power>1W) laser systems will also be discussed.

The technical committee was comprises of:
Dr Nicholas Devaney, NUI Galway, Ireland
Dr Leslie Laycock, BAE Systems, UK
Dr Carl Parterson, Imperial College London, UK

The Adaptive Optics Sug-Group thanks the authors for making their presentations available online.