JEOS:RP - Journal of the European Optical Society Rapid publications
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Spectral analysis of the Forel-Ule Ocean colour comparator scale.
Get PDFFrançois Alphonse Forel (1890) and Willi Ule (1892) composed a colour comparator scale, with tints varying from indigo-blue to coca-cola brown, to quantify the colour of natural waters, like seas, lakes and rivers. For each measurement, the observer compares the colour of the water above a submersed white disc (Secchi disc) with the hand-held scale of pre-defined colours. The scale can be well reproduced from a simple recipe for twenty-one coloured chemical solutions and because the ease of its use, the Forel-Ule (FU) scale has been applied globally and intensively by oceanographers and limnologists from the year 1890. Indeed, the archived FU data belong to the oldest oceanographic data sets and do contain information on the changes in geobiophysical properties of natural waters during the last century. In this article we describe the optical properties of the FU-scale and its ability to cover the colours of natural waters, as observed by the human eye. The recipe of the scale and its reproduction is described. The spectral transmission of the tubes, with belonging chromaticity coordinates, is presented. The FU scale, in all its simplicity, is found to be an adequate ocean colour comparator scale. The scale is well characterized, is stable and observations are reproducible. This supports the idea that the large historic data base of FU measurements is coherent and well calibrated. Moreover, the scale can be coupled to contemporary multi-spectral observations with hand-held and satellite-based spectrometers
On the Thompson-Wolf Experiment: a study with laser sources
Get PDFWe present a revisited study of the Thompson-Wolf experiment earlier developed in 1957, with the aim to characterize the degree of spatial coherence of a luminous source. We develop further experiments by using laser sources under various modal regimes. We analyze the experimental results
Determination of the anisotropy complex refractive indices of chicken tissues in vitro at 650 nm
Get PDFThe anisotropy complex refractive index of tissue is an important parameter in understanding the behavior of light, including its transportation in and interaction with tissues. We used the specular reflection method to investigate the anisotropy complex refractive index of chicken tissue with fibrous structures in vitro at a wavelength of 650 nm. The measurement data were highly consistent with the Fesnell equations. The results showed that the real refractive index was higher along the orientation of the fibers than along the cross section, but the imaginary refractive index was nearly identical. Furthermore, the fiber orientation was in the direction of the optic axis of the chicken tissue and the chicken tissue section was similar to a negative uniaxial crystal wafer
Sub surface damage measurements based on short coherent interferometry
Get PDFDuring the manufacturing process of glass lenses, especially the grinding step, it is important to control such parameters as shape and sub-surface damage (SSD) with high accuracy which essentially influences the duration and costs of the subsequent polishing process. Typically used methods measure the parameters only separately and suffer from limited resolution. Especially, the nondestructive measurement of SSD is a challenge for the metrology of grinded surfaces. In order to detect these parameters simultaneously, the scanning short-coherence interferometer, a method very similar to optical coherence tomography, is setup and tested at Aalen University. The lens under test is mounted on a rotation stage which can be translated in lateral direction. The sensor beam of the interferometer is focused onto the sample and can be moved along the axial direction. The precision of the depth measurements is 0.25 µm, lateral positioning accuracy is 2 µm and lateral resolution is 4 µm. The system is able to measure SSD at several positions on a lens within 10 min inside the optical workshop
On the unambiguous determination of effective optical properties of periodic metamaterials: a one-dimensional case study
Get PDFWe show how branch ambiguities in the extraction of effective parameters is arising as a direct consequence of the underlying Bloch state physics. The mutual importance of the different branches in general depends on the experimental context, and we show how the Fourier spectrum of the field inside the metamaterial can be used to access this. Different numerical examples illustrate how a predominant branch may be identified for while at higher frequency the power may be distributed over more branches. This is in particular true near band-edges and strong resonances. Extensions to two and three-dimensional metamaterial designs are discussed
Switchable photonic crystal cavity by liquid crystal infiltration
Get PDFWe report on the fabrication and optical characterization of a switchable photonic crystal nanocavity actuated by liquid crystals. This device acts as a filter presenting a transmission peak around the telecom wavelength λ = 1550 nm. Passing from the isotropic to the anisotropic (oriented crystals) state of the liquid crystals, a shift of Δλ =13 nm has been measured, which confirms the theoretical predictions obtained by finite difference time domain simulations. We have developed a photonic crystal nanocavity that can be tuned thanks to the properties of liquid crystals infiltrated in the holes of the photonic device
Why the first laser worked as designed (and is still kicking today)
Get PDFTheodore Maiman, the inventor of the laser, was both a physicist and an engineer. One can speculate that this combination of backgrounds was the main reason for the successful design, construction, and demonstration of the ruby laser in May 1960. The reasons for this success - as stated by Maiman in discussions with the present author - include some basic rules of elegant engineering design: understand what you want to make, understand the physics behind it, understand the nature of the materials to be used for fabrication, and finally, be a minimalist – simplify. Even now, the elegance and simplicity of the design of the first laser is evident upon viewing. The following text will try to gather and clarify all the components necessary for an invention such as the laser, classified by Nature magazine as one of twenty one most important inventions of twentieth century
Volumetric multiple optical traps produced by Devil's lenses
Get PDFWe propose the use of a new diffractive optical element coined Devil's Vortex-Lens (DVL) to produce optical tweezers. In its more general form it results as the combination of a Devil’s lens and a helical vortex phase mask. It is shown that under monochromatic illumination a DVL generates a focal volume with several concatenated doughnut modes that are axially distributed according to the self-similarity of the lens. The orbital angular momentum associated to each link in the chain is investigated
Performance considerations for continuous-wave and pulsed laser line scan (LLS) imaging systems
Get PDFExtended range underwater optical imaging techniques can be classified into one of two broad categories; those which use synchronously scanned narrow source and receiver paths to restrict both back-scattered and forward-scattered light reaching the receiver (continuous-wave laser line scan); and those which use pulsed sources and time-gating to remove back-scatter noise (pulsed laser line scan and pulse-gated laser line scan). Laser line scan systems are observed to perform at up to 5 to 6 optical attenuation lengths, but greater standoff distances are desirable for seabed imaging using the growing fleet of autonomous underwater vehicles (AUVs). Currently, a moderate physical separation between laser and receiver is necessary to reject near-field multiple back-scatter, which imposes restrictions on AUV miniaturization. Recent experiments and theoretical modeling reveal that significant imaging improvements are possible over the existing continuous-wave laser line scan systems (LLS), by using a pulsed-gated version of the LLS (PG-LLS). However, the use of such a technique has a greater advantage in reducing the overall form factor over conventional LLS imaging system, as well as providing greater depth-of-field. In this paper, we present experimental results comparing both LLS and PG-LLS systems for several source-receiver separations and standoff distances. These results compare favorably with images obtained from validated LLS image simulation tools, and indicate the potential for reducing the source-receiver separation and therefore the system size
50th anniversary of the laser
Get PDFOn July, 7, 1960 a press conference at Huyghes announced that Maiman had assembled and put into operation the first laser. It was the very pulsed ruby laser that everybody knows today. The announcement came as a bomb. Nobody expected
that in an unknown laboratory, new to the race to build a laser, this result could be obtained. It was such an unexpected result that many still today mantain that the true laser was discovered at Bell by Shawlow. This result was achieved through a long story which passed by the Townes maser and many tentative experiments and discussions both in the USA and Soviet Union. In this special issue we present a collection of papers which provide further information as to what happened after Einstein introduced the concept of stimulated emission.
The first paper is a short paper by Townes on the development of the physics of microwaves following the creation of the maser. When the laser came on the stage one of its properties was the inherent coherence of the emitted light. Emil Wolf’s contribution enlights the early days of coherence to which he so much contributed and the very timely first Rochester Conference which was held on June 27-29, 1960 a few days before the Times announcement of the Maiman achievement. Important contributions were given by Soviet Scientists and, Svetlana Lukishova’s contributions helps us understand the work of Valentin Fabrikant which was mostly unknown to western scientists. At the end of his life, Maiman went to Vancouver in Canada and Andrew H. Rawicz gives his testimoniancy of his friendship there. Coherence and
the statistical properties of laser light were much studied and we have two exceptional papers by Roy Pike and Jan Perina discussing these arguments. The issue also contains three more papers presenting some earlier achievements in the construction of multiquantumwell laser (M. L. Dotor, P. Huertas, P. A. Postigo, D. Golmayo and F. Briones), the first measurements on very short pulses (H. P. Weber and R. Dandliker) and spatial coherence (D. P. Barato and M. L. Calvo)