Cyril Bourgenot

Light sheet adaptive optics microscope for 3D live imaging

We report on the incorporation of adaptive optics (AO) into the imaging arm of a selective plane illumination microscope (SPIM). SPIM has recently emerged as an important tool for life science research due to its ability to deliver high-speed, optically sectioned, time-lapse microscope images from deep within in vivo selected samples. SPIM provides a very interesting system for the incorporation of AO as the illumination and imaging paths are decoupled and AO may be useful in both paths. In this paper, we will report the use of AO applied to the imaging path of a SPIM, demonstrating significant improvement in image quality of a live GFP-labeled transgenic zebrafish embryo heart using a modal, wavefront sensorless approach and a heart synchronization method. These experimental results are linked to a computational model showing that significant aberrations are produced by the tube holding the sample in addition to the aberration from the biological sample itself.

CHOUGH: implementation and performance of a high-order 4m AO demonstrator

CHOUGH is a small, fast project to provide an experimental on-sky high-order SCAO capability to the 4.2m WHT telescope. The basic goal has r0-sized sub- apertures with the aim of achieving high-Strehl ratios (> 0:5) in the visible (> 650 nm). It achieves this by including itself into the CANARY experiment: CHOUGH is mounted as a breadboard and intercepts the beam within CANARY via a periscope. In doing so, it takes advantage of the mature CANARY infrastructure, but add new AO capabilities. The key instruments that CHOUGH brings to CANARY are: an atmospheric dispersion compensator; a 32 × 32 (1000 actuator) MEMS deformable mirror; 31 × 31 wavefront sensor; and a complementary (narrow-field) imager. CANARY provides a 241-actuator DM, tip/tilt mirror, and comprehensive off-sky alignment facility together with a RTC. In this work, we describe the CHOUGH sub-systems: backbone, ADC, MEMS-DM, HOWFS, CAWS, and NFSI.

Diamond machining of a single shot ellipsoidal focusing plasma mirror

Plasma mirrors have become an important tool in high power laser physics due to their ability to suppress laser pre-pulses and amplified spontaneous emission allowing a cleaner and sharper rising edge pulse to be focused onto a target. A PMMA ellipsoidal plasma mirror used to increase the peak intensity of a high power laser pulses before it reaches the target is presented. The ellipse has been designed to increase by a factor 3, between input and output, the F-number of the beam, inducing in theory a factor 9 gain in peak intensity. Diamond machining, which is a technique capable of producing sub-micron accuracy on steep, freeform surfaces, is an ideal process for manufacturing these types of mirrors. In this paper, we discuss the diamond machining requirements to manufacture such near diffraction limited high numerical aperture mirrors.

AO modal optimization in a live, beating zebrafish heart

We report on the combined use of heart synchronization and wavefront sensorless modal AO to enable significant improvement in image quality of a live transgenic zebrafish embryo heart, imaged with a light sheet microscope.

Closed loop adaptive optics with a laser guide star for biological light microscopy

We report on the development of a widefield microscope that achieves adaptive optics correction through the use of a wavefront sensor observing an artificial laser guide star induced within the sample. By generating this guide star at arbitrary positions and depths within the sample we allow the delivery of high-resolution images. This approach delivers much faster AO correction than image optimization techniques, and allows the use of AO with fluorescent imaging modalities without generating excessive photo-toxic damage in the sample, or inducing significant photo-bleaching in the flurophore molecules.

Adaptive optics for wide-field microscopy

We report on recent developments in the use of adaptive optics (AO) in wide-field microscopy to remove both system and sample induced aberrations. We describe progress on using both a full AO system and image optimization techniques (wavefront sensorless AO). In the latter system the determination of the best mirror shape is found via two routes. In the first an optimization algorithm using a Simplex search pattern is used with an initial random set of mirror shapes. We then explore the use of specific Zernike terms as our starting basis set. In both cases the final optimization performance is not affected by the choice of optimization metric. We then describe an open loop AO system in which the equivalent of a laser guide star is used as the light source for the wavefront sensor.

A new concept of imaging system: telescope windows

A Telescope window is a novel concept of transformation-optics consisting of an array of micro-telescopes, in our configuration, of a Galilean type. When the array is considered as one multifaceted device, it acts as a traditional Galilean telescope with distinctive and attractive properties such as compactness and modularity. Each lenslet, can in principle, be independently designed for a specific optical function. In this paper, we report on the design, manufacture and prototyping, by diamond precision machining, of 2 concepts of telescope windows, and discuss both their performances and limitations with a view to use them as potential low vision aid devices to support patients with macular degeneration.

Design, manufacture, and evaluation of prototype telescope windows for use in low-vision aids

Pixellated Optics, a class of optical devices which preserve phase front continuity only over small sub areas of the device, allow for a range of uses that would not otherwise be possible. One potential use is as Low Vision Aids (LVAs), where they are hoped to combine the function and performance of existing devices with the size and comfort of conventional eyewear. For these devices a Generalised Confocal Lenslet Array (GCLA) is designed to magnify object space, creating the effect of traditional refracting telescope within a thin, planar device. By creating a device that is appreciably thinner than existing LVA telescopes it is hoped that the comfort for the wearer will be increased. We have developed a series of prototype GLCA-based devices to examine their real-world performance, focussing on the resolution, magnification and clarity of image attainable through the devices. It is hoped that these will form the basis for a future LVA devices. This development has required novel manufacturing techniques and a phased development approach centred on maximising performance. Presented here will be an overview of the development so far, alongside the performance of the latest devices.

Resolution limits of pixellated optical components

Pixellated optical components, for example generalised confocal lenslet arrays (GCLAs), enable the design of optical devices which cannot be realised without introducing pixellation or a similar compromise. A key concern is the degradation of imaging quality due to the combined effects of diffraction, worst for smaller pixels, and the visibility of the pixels. Here we examine the effects of these two factors on image quality through use of our custom raytracer, Dr TIM. We also outline future work in developing these ideas more rigorously and applying the conclusions to more complicated devices.

Towards freeform curved blazed gratings using diamond machining

Concave blazed gratings greatly simplify the architecture of spectrographs by reducing the number of optical components. The production of these gratings using diamond-machining offers practically no limits in the design of the grating substrate shape, with the possibility of making large sag freeform surfaces unlike the alternative and traditional method of holography and ion etching. In this paper, we report on the technological challenges and progress in the making of these curved blazed gratings using an ultra-high precision 5 axes Moore-Nanotech machine. We describe their implementation in an integral field unit prototype called IGIS (Integrated Grating Imaging Spectrograph) where freeform curved gratings are used as pupil mirrors. The goal is to develop the technologies for the production of the next generation of low-cost, compact, high performance integral field unit spectrometers.