The interferometry of reversed and non-reversed spectra,

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Near-resonant holographic interferometry and absorption measurements of seeded atomic species in a flame

The development of near-resonant holographic interferometry techniques for use on flows seeded with atomic species is described. A theoretical model for the refractivity that is due to the seed species is outlined, and an approximation to this model is also described that is shown to be valid for practical regimes of interest and allows the number density of the species to be determined without knowledge of line-broadening effects. The details of quantitative number density experiments performed on an air-acetylene flame are given, and a comparison with an alternative absorption-based experiment is made. (C) 2004 Optical Society of America.

OH concentration and temperature measurements by use of near-resonant holographic interferometry

Near-resonant holographic interferometry is demonstrated to measure temperature and species concentration in a two-dimensional steady premixed air-acetylene flame. A peak temperature of (2600 +/- 100) K and a peak OH number density of (9.6 +/- 0.3) X 10(22) m(-3) are obtained, consistent with the expected values for such a flame. These values are determined by recording interferograms with a laser assumed sufficiently detuned from line center so that pressure and temperature broadening can be ignored. The results are thus obtained without making prior assumptions on the temperature or pressure of the flame beyond the existence of thermal equilibrium. (C) 2004 Optical Society of America.

Extended-range, low coherence dual wavelength interferometry using a superfluorescent fibre source and chirped fibre Bragg gratings

We describe an all-fibre, passive scheme for making extended range interferometric measurements based on the dual wavelength technique. The coherence tuned interferometer network is illuminated with a single superfluorescent fibre source at 1.55 µm and the two wavelengths are synthesised at the output by means of chirped fibre Bragg gratings. We demonstrate an unambiguous sensing range of 270 µm, with a dynamic range of 2.7 × 10 5.

Fibre Bragg grating sensor interrogation using an acousto-optic tunable filter and low-coherence interferometry

We describe how an acousto-optic tunable filter can be used to both demultiplex the signals from multiple fibre Bragg grating sensors and simultaneously provide wide bandwidth signal demodulation in a system using interferometric wavelength shift detection. In an experimental demonstration, the approach provided a noise limited strain resolution of 24.9 n epsilon Hz(-1/ 2) at 15 Hz.

Transversal and longitudinal images from the retina of the living eye using low coherence interferometry

An optical coherence tomography (OCT) system to produce both longitudinal and transversal images of the in vivo human eye is presented. For the first time, OCT transversal images collected from the living eye at 50-µm depth steps show details unobtainable with the state-of-the-art scanning laser ophthalmoscope. Images of up to 3×3?mm are produced from the retina in less than a second. For images larger than 1.6×1.6?mm, a path modulation is introduced by the galvanometric scanning mirror and is used as an effective phase modulation method.

Extended range interferometry using a coherence tuned synthesised dual wavelength technique with multimode fibres

We describe in the letter a technique for making extended-range interferometric measurements with a coherence multiplexed system by means of a variation on the dual-wavelength technique. The interferometer is illuminated with a single source and the two wavelengths are synthesised at the output by means of an interference filter.

An analysis of progressive addition spectacles lens design by the use of interferometry

Progressive addition spectacle lenses (PALs) have now become the method of choice for many presbyopic individuals to alleviate the visual problems of middle-age. Such lenses are difficult to assess and characterise because of their lack of discrete geographical locators of their key features. A review of the literature (mostly patents) describing the different designs of these lenses indicates the range of approaches to solving the visual problem of presbyopia. However, very little is published about the comparative optical performance of these lenses. A method is described here based on interferometry for the assessment of PALs, with a comparison of measurements made on an automatic focimeter. The relative merits of these techniques are discussed. Although the measurements are comparable, it is considered that the interferometry method is more readily automated, and would be ultimately capable of producing a more rapid result.

Extended-range, low coherence dual wavelength interferometry using a superfluorescent fibre source and chirped fibre Bragg gratings

We describe an all-fibre, passive scheme for making extended range interferometric measurements based on the dual wavelength technique. The coherence tuned interferometer network is illuminated with a single superfluorescent fibre source at 1.55 μm and the two wavelengths are synthesised at the output by means of chirped fibre Bragg gratings. We demonstrate an unambiguous sensing range of 270 μm, with a dynamic range of 2.7 × 105.

Fibre Bragg grating sensor interrogation using an acousto-optic tunable filter and low-coherence interferometry

We describe how an acousto-optic tunable filter can be used to both demultiplex the signals from multiple fibre Bragg grating sensors and simultaneously provide wide bandwidth signal demodulation in a system using interferometric wavelength shift detection. In an experimental demonstration, the approach provided a noise limited strain resolution of 24.9 nε Hz -1/2 at 15 Hz. © 2007 IOP Publishing Ltd.

Transversal and longitudinal images from the retina of the living eye using low coherence interferometry

An optical coherence tomography (OCT) system to produce both longitudinal and transversal images of the in vivo human eye is presented. For the first time, OCT transversal images collected from the living eye at 50-µm depth steps show details unobtainable with the state-of-the-art scanning laser ophthalmoscope. Images of up to 3×3?mm are produced from the retina in less than a second. For images larger than 1.6×1.6?mm, a path modulation is introduced by the galvanometric scanning mirror and is used as an effective phase modulation method.