Richard Simmonds

Adaptive slit beam shaping for direct laser written waveguides.

We demonstrate an improved method for fabricating optical waveguides in bulk materials by means of femtosecond laser writing. We use an LC spatial light modulator (SLM) to shape the beam focus by generating adaptive slit illumination in the pupil of the objective lens. A diffraction grating is applied in a strip across the SLM to simulate a slit, with the first diffracted order mapped onto the pupil plane of the objective lens while the zeroth order is blocked. This technique enables real-time control of the beam-shaping parameters during writing, facilitating the fabrication of more complicated structures than is possible using nonadaptive methods. Waveguides are demonstrated in fused silica with a coupling loss to single-mode fibers in the range of 0.2 to 0.5 dB and propagation loss <0.4 dB/cm.

Three dimensional laser microfabrication in diamond using a dual adaptive optics system

Femtosecond laser fabrication of controlled three dimensional structures deep in the bulk of diamond is facilitated by a dual adaptive optics system. A deformable mirror is used in parallel with a liquid crystal spatial light modulator to compensate the extreme aberrations caused by the refractive index mismatch between the diamond and the objective immersion medium. 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.

Modelling of multi-conjugate adaptive optics for spatially variant aberrations in microscopy

Adaptive optics has been implemented in a range of high-resolution microscopes in order to overcome the problems of specimen-induced aberrations. Most implementations have used a single aberration correction across the imaged field. It is known, however, that aberrations often vary across the field of view, so a single correction setting cannot compensate all aberrations. Multi-conjugate adaptive optics (MCAO) has been suggested as a possible method for correction of these spatially variant aberrations. MCAO is modelled to simulate the correction of aberrations, both for simple model specimens and using real aberration data from a biological specimen.

Uniform Lying Helix Alignment on Periodic Surface Relief Structure Generated via Laser Scanning Lithography

The main drawback in the exploitation of the chiral-flexo-electro-optic effect is that it relies on a texture, the Uniform Lying Helix (ULH), which is unstable when the cholesteric is sandwiched between spatially uniform aligning surfaces (UASs). It has been shown that the ULH can be promoted by periodic (horizontal/vertical) anchoring conditions or by the presence of periodic polymeric walls. Here we show that periodic surface relief structures can also promote the formation of a stable ULH texture. The surface relief structure was created by curing an ultraviolet curable material via a two-photon excitation laser-lithography process. The process allows sub-micron resolution and flexibility in creating the topographic relief.

Effects of aberrations and specimen structure in conventional, confocal and two-photon fluorescence microscopy.

Specimen‐induced aberrations cause a reduction in signal levels and resolution in fluorescence microscopy. Aberrations also affect the image contrast achieved by these microscopes. We model the effects of aberrations on the fluorescence signals acquired from different specimen structures, such as point‐like, linear, planar and volume structures, when imaged by conventional, confocal and two‐photon microscopes. From this we derive the image contrast obtained when observing combinations of such structures. We show that the effect of aberrations on the visibility of fine features depends upon the specimen morphology and that the contrast is less significantly affected in microscopes exhibiting optical sectioning. For example, we show that point objects become indistinguishable from background fluorescence in the presence of aberrations, particularly when imaged in a conventional fluorescence microscope. This demonstrates the significant advantage of using confocal or two‐photon microscopes over conventional instruments when aberrations are present.

Development of integrated mode reformatting components for diffraction-limited spectroscopy.

We present the results of our work on developing fully integrated devices (photonic dicers) for reformatting multimode light to a diffraction limited pseudo-slit. These devices can be used to couple a seeing limited telescope point spread function to a spectrograph operating at the diffraction limit, thus potentially enabling compact, high-resolution spectrographs that are free of modal noise.

Active and adaptive optical methods for rapid fabrication of 3D photonic structures

We outline recent research into the application of adaptive optical techniques to the laser fabrication of threedimensional structures with sub-micrometer precision. Aberration correction can be implemented using deformable mirrors or liquid crystal spatial light modulators (LCSLMs). The correction ensures that the quality of the laser focus is maintained when focussing at depth into a material with high refractive index. Flexible parallel fabrication methods have been implemented using a LCSLM through both holographic beam shaping and an addressable microlens array. Applications have been shown in a range of high index materials, including diamond, lithium niobate and glasses.

Dual adaptive optics system for laser processing of diamond

Laser fabrication depth in diamond is limited by refractive index mismatch induced aberrations that can be corrected by using adaptive optics; we demonstrate a dual active element system that considerably extends practical fabrication depth.

Parallel laser microfabrication of three-dimensional structures corrected for optical aberrations

An adaptive optical element is employed to generate multiple fabrication spots while also compensating for any optical aberration present in the system. We present rapid diffraction limited optical fabrication in a range of interesting substrates.

Dual adaptive optics system for 3D laser fabrication in high refractive index media

Laser fabrication depth is limited by refractive index induced focussing aberrations. We correct these using dual adaptive optical elements that considerably extend fabrication depth in materials including diamond, fused silica and lithium niobate.