JEOS:RP - Journal of the European Optical Society Rapid publications
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"Blue" Photonics: Optics in the Sea
Get PDFThe oceans and coastal zones of the world are vitally important resources for many aspects of human life. Their exploitation as sources of food dates back to the beginnings of civilisation, but in relatively more recent times, by comparison, our oceans have become valuable sources of energy. The oil and gas industries are well known examples of how the oceans can be exploited to provide us with our fossil fuel needs. More recently, wind, tidal and wave power are coming to the fore as we look more towards renewable sources of energy. We should also not forget the extraction of other mineral resources. However, the gathering and farming of food is still the most significant treasure that the oceans hold for us; and its control, management and sustainability are vital aspects of sea utilisation. There are many significant challenges which still face us in our drive to understand and utilise this unique environment and to exploit the natural resources contained within it. New techniques and instruments are continually being developed to help us explore and enhance our appreciation of the sea and how we depend upon it. Foremost amongst these is the increased use of optical techniques or photonics that help to us to extract information about the nature of the oceans, its constituents and its behaviour.
In this special issue of the Journal of the European Optical Society we focus on what we term “Blue†Photonics: in other words, the use and understanding of optics in the sea (and also in rivers and lakes). Such a title embraces a wide range of aspects of optics and light in the oceans from basic optical propagation through water to the design of complex instruments which enable us to measure its properties and behaviour. The chosen papers highlight major topics in photonics applied to marine science and engineering from fundamental science through marine optics, optical metrology, biological optics, environmental optics to technology and instrumentation.
A number of papers are related to the measurement of ocean water properties like the transparency measurements using the Secchi Disc (Wernand) or the colour evaluation with the Forel-Ule comparator (Wernand) and its change as a function of time (Wernand) caused by pollution or the presence of micro-organism. Another two papers deal with the development of new measurement methods and their influencing parameters. An interesting method in this area is the measurement of reflectance scattering with the application to the measurement of waves on the ocean surface (Creanor et al) as well as to the determination of solutes in the water. A complementary method is the measurement of light fluctuations in different depths under the surface giving an excellent approach to the wave evaluation (Hieronymi). The detection of micro-bubbles in the subsea environment is discussed by Zielinski et al. A new measurement method too is the Laser Line Scan method in the CW mode as well as in pulsed mode (Caimi and Dalgleish). This method increases the resolution and is robust against environmental influences and scans a larger volume. Imaging methods are another area of underwater metrology systems. Systems like the LOKI system (Schulz et al) are used to image Plankton.
The papers here act only as a primer for the vast amount of work now being undertaken in Blue Photonics and we hope that they will serve as a catalyst for increased use of optics in the sea
Concentration measurement of injected gaseous fuel using quantitative schlieren and optical tomography
Get PDFIn this paper, the quantitative schlieren method is extended to measure the concentration field of an injected gaseous fuel along several planes perpendicular to the jet axis. Background Oriented Schlieren (BOS) is used as a quantitative flow field concentration measurement based on the deflection made by features in the background pattern. The flow field which is located between the camera and the background pattern varies the intensity value of the background points in the transfer medium. The Optical flow algorithm, which is used to measure the deflection vectors in the background due to the change in index of refraction, is modified to consider the change in intensity of the background image. Optical tomography served as a tool to extract the index of refraction of the gaseous field. Mole fraction values at differentplanes perpendicular to the jet axis are obtained and displayed
Improving underwater imaging in an amplitude-modulated laser system with radio frequency control technique
Get PDFWe present the results of an experiment aimed to demonstrate the low-pass filter dependence of water backscattered power in an amplitude-modulated laser scanner for underwater 3D imaging. We also demonstrate that improvements in target imaging are obtained by allowing the device to operate in the stop-band region. A simple model is described to account for the physics underlying the effect and suggesting future experimental schemes based on demodulated detection techniques
Lasers, photon statistics, photon-correlation spectroscopy and subsequent applications
Get PDFA review is given of developments in the theory and application of the quantum statistics of visible-light photons, particularly of scattered laser light, over the fifty years since Maiman's publication of the first working laser. Some introductory pre-laser historical background to photon statistics is included and details are given of research and commercial developments in the field conducted in the author's laboratory in the UK over the period. The resulting emergence of photon statistics and photon-correlation spectroscopy as widely used techniques for non-invasive measurements of diffusion and velocity in many present-day areas of science and industry is described
Mechanical forces exerted by a dipole emitter on an interface
Get PDFMechanical forces exerted by an emitting dipole on the interface between
two media with different dielectric susceptibilities are found for different distances between the dipole and the interface. Estimations of the force are given based on known values of molecular polarizabilities for inelestic processes such as Raman scattering and fluorescence including those that occur near metal structures
High resolution displacement detection with speckles : accuracy limits in linear displacement speckle metrology
No full textWe propose a simple measurement setup in reflection and a movement evaluation procedure based on a two dimensional recording of subjective speckle images. Averaging of cross correlation functions is used to determine translations. We show experimentally a 10 nm precision on a 50 µm measurement range with respect to systematical errors. An image library is shown to extend the range of measurements. Limitations are given and documented improvements are predicted to result in accuracy better than 5 nm over a range of 150 µm
Coupled-resonator optical waveguides: Q-factor influence on slow-light propagation and the maximal group delay
Get PDFCoupled-resonator optical waveguides hold potential for slow-light propagation of optical pulses. The dispersion properties may adequately be analyzed within the framework of coupled-mode theory. We extend the standard coupled-mode theory for such structures to also include complex-valued parameters which allows us to analyze the dispersion properties also in presence of finite Q factors for the coupled resonator states. Near the band-edge the group velocity saturates at a finite value v_g/c \propto \sqrt{1/Q} while in the band center, the group velocity is unaffected by a finite Q factor as compared to ideal resonators without any damping. However, the maximal group delay that can be envisioned is a balance between having a low group velocity while not jeopardizing the propagation length. We find that the maximal group delay remains roughly constant over the entire bandwidth, being given by the photon life time of the individual resonators
Ocean colour changes in the North Pacific since 1930.
Get PDFIn this paper we present an analysis of historical ocean colour data from the North Pacific Ocean. This colour is described by the Forel-Ule colour index, a sea colour comparator scale that is composed of 21 tube colours that is routinely measured since the year 1890. The main objective of this research is to characterise colour changes of the North Pacific Ocean at a timescale of decades. Next to the seasonal colour changes, due to the yearly cycle of biological activity, this time series between 1930 and 1999 might contain information on global changes in climate conditions. From seasonal independent analyses of the long-term variations it was found that the greenest values, with mean Forel-Ule scale ((FU) Ì…) of 4.1 were reached during the period of 1950-1954, with a second high ((FU) Ì… = 3) in the period 1980-1984. The bluest ocean was encountered during the years 1990-1994. The data indicate that after 1955 a remarkable long bluing took place till 1980
How short are ultra short light pulses? (looking back to the mid sixties)
Get PDFWith the arrival of mode locking for Q-switched lasers to generate ultra short light pulses, a method to measure their expected time duration in the psec range was needed. A novel method, based on an intensity correlation measurement using optical second harmonic generation, was developed. Other reported approaches for the same purpose were critically analysed. Theoretical and subsequent experimental studies lead to surprising new insight into the ultra fast temporal behaviour of broadband laser radiation: Any non mode locked multimode emission of a laser consists of random intensity fluctuations with duration of the total inverse band width of emitted radiation. However, it was shown, that with mode locking isolated ultra short pulses of psec duration can be generated. This article summarizes activities performed in the mid sixties at the University of Berne, Switzerland
Spatiotemporal underwater light field fluctuations in the open ocean
Get PDFThe light availability in the upper layer of the open sea is subject to strong fluctuations due to focusing of surface waves. This paper shows measurements of downwelling spectral irradiances as well as spatiotemporal light field patterns along the water column. Results are interpreted with respect to diverse surface waves. Direct wind develops capillary and small gravity waves that affect the light regime only up to circa 5 m water depth. At high seas and below 5 m depth, light fluctuations can be described more accurately in terms of sea state parameters such as wave height and period, rather than wind speed. Between 3 m and 25 m water depth, waves with significant heights of 1.5 m to 2.5 m provoke the strongest intensity fluctuations. In general, fluctuation amplitudes decrease and periods extend with water depth where the coefficient of variation, CV, is in average four times higher above 2 m compared to 25 m water depth