Brett A. Patterson

Design of a static Fourier-transform spectrometer with increased field of view

We present several novel designs of static Fourier-transform spectrometers based on Wollaston prisms. By numerical modeling we show the increased field of view that can be obtained when an achromatic half-wave plate is included between the prisms or when prisms fabricated from positive and negative birefringent materials are combined. In addition, we model how a single Wollaston prism with an inclined optic axis produces a fringe plane localized behind its exit face, thus enabling the design of a static Fourier-transform spectrometer based on a single Wollaston prism.

An ultra-compact static Fourier-transform spectrometer based on a single birefringent component

Abstract The development of a static Fourier-transform spectrometer based on a single Wollaston prism, two polarizers and a compact 2D detector array is discussed. The Wollaston prism is of a modified configuration so that for an extended light source the interferogram fringes are localised just behind the exit face of the prism. This leads to an ultra-compact design for a Fourier-transform spectrometer (mounted within a 40 mm cube) that has a resolution of approximately 230 cm −1 and an angular acceptance of ±5°.

Dynamic closed-loop system for focus tracking using a spatial light modulator and a deformable membrane mirror

A dynamic closed-loop method for focus tracking using a spatial light modulator and a deformable membrane mirror within a confocal microscope is described. We report that it is possible to track defocus over a distance of up to 80 microm with an RMS precision of 57 nm. For demonstration purposes we concentrate on defocus, although in principle the method applies to any wavefront shape or aberration that can be successfully reproduced by the deformable membrane mirror and spatial light modulator, for example, spherical aberration.

Static Fourier-transform ultraviolet spectrometer for gas detection

We report the design, construction, and evaluation of a static Fourier-transform ultraviolet spectrometer. The spectrometer is based on Wollaston prisms that form an interferogram in the spatial domain, which is recorded with a detector array. We demonstrate the application of the spectrometer to gas detection. Using a deuterium light source, we measured a detection limit, with a 1-s integration time, for hydrogen sulfide and sulfur dioxide, corresponding to 0.2 ppm over a 5-m path length.

Wide field of view, ultracompact static Fourier-transform spectrometer

The development of a novel static Fourier-transform spectrometer based on two Wollaston prisms, two polarizers, and a compact two-dimensional detector array is described. The wavelength calibration is fixed by the geometry of the prisms and the detector array and is therefore inherently stable. The Wollaston prisms are fabricated from materials with opposite sign of birefringence which gives a significantly increased field of view compared with existing Wollaston prism based Fourier-transform spectrometers. The spectrometer operates in the visible region of the spectrum, has a resolution of 350 cm−1, an aperture of 6×4.6 mm, and a field of view of ±10°. The optical assembly is interfaced to a laptop computer resulting in a rugged, portable instrument with no moving parts.

Detection Of Benzene And Other Gases With An Open-Path, Static Fourier-Transform UV Spectrometer

Releases of benzene and other gases have been detected and quantified using a novel optical, open-path instrument based on a deuterium light source and a static Fourier-transform spectrometer. The spectrometer uses Wollaston prisms to form an interferogram in the spatial domain that is recorded by use of a detector array. The instrument is designed to operate in the ultraviolet region of the spectrum between 200 and 270 nm, which coincides with strong absorption features in the spectra of many gases of environmental and health interest. Using the instrument with a 5-s measurement period provides a path-integrated concentration sensitivity to benzene of 2 parts in 10(6) times meter, which corresponds to a 20-parts in 10(9) detection limit over a typical path length of 100 m.

Use of optimisation algorithmic techniques with active optics for aberration correction in optical sectioning microscopy

Confocal techniques allow the user to achieve optically sectioned images with significantly enhanced axial and improved lateral resolution compared to widefield methods. Unfortunately, as one images more deeply within a sample, sample induced aberrations lead to a significant reduction in image resolution and contrast. Using adaptive optic techniques, we report on the effectiveness of a number of algorithms for removing sample induced aberrations. The viability and efficiency at a number of fitness parameters used in the optimisation routines is also considered.

Biophotonics at Strathclyde University; working at the photonics/life science interface

We review recent developments in photonics research at Strathclyde University motivated by applications in biomedicine. Areas covered include novel sources for microscopy, micro-pixellated light emitting diodes, microlasers and microoptics.

Confocal and multiphoton microscopy for imaging at depth in living tissue

The desire to image with sub micron resolution at ever increasing depths into living samples is providing optical physicists with the latest in a long line of challenges presented by life science researchers. The advent of confocal, and subsequently multiphoton microscopy, has opened up exciting new possibilities but simultaneously posed new challenges. As one images ever more deeply into the sample, the optical properties of the tissue distort the image significantly lowering the resolution and, in the case of multiphoton imaging in particular, decreasing the fluorescence yield as the excitation volume rises. The recent use of active optical elements has shown a way forward in restoring high contrast high resolution images at depth. However, significant issues on the actual shape required on such an element are as yet unresolved. We report on two recent advances in this area. The first is the use of a range of optimisation algorithms to restore the optical point spread function and hence improve the image quality at depth. The second is a radically new approach incorporating two active elements, a slow spatial light modulator and a fast deformable mirror, to actively lock up the system. We report on the latest advances in active image compensation where conections at over 5OOmicrons into the sample have been made using a combination of deformable mirrors and spatial light modulators.

Open-path UV Fourier-transform gas monitor with no moving parts

New legislation requiring the monitoring and reduction of polluting gases in both Europe and the USA has increased the demand for reliable and affordable open-path monitoring systems, suitable for hazardous area operation. We report on the research and development of a UV Fourier-transform spectrometer-based system for open-path monitoring of both hazardous and environmental gases. The device has no moving parts and is designed for unattended operation. Laboratory tests have successfully detected the presence of and differentiated between and present in a 1 m test cell down to 1.0 ppm.m levels. The real-time response of the system allows for the use of maximum entropy modelling to predict the size and location of a gas leak. Initial field tests with open-air gas releases of and have verified this. The multiple-gas feature of the instrument allows for additional possible applications with regards to environmental monitoring.