Raman Spectroscopy is a fast, rugged analytical technique based on the Raman Effect. When monochromatic light encounters matter, most of the scattered light has the same wavelength as the incident light. However, a small fraction of the scattered light is shifted in a different wavelength by the molecular vibrations and rotations in the sample. The representation of this shifted light is called Raman spectrum, and contains many sharp bands characteristics of the sample, allowing its identification without ambiguity.
In this communication, a fuzzy logic system to recognize Raman spectra of artistic pigments is presented. The identification is based on the comparison between an unknown spectrum, and pattern spectra. Frequently the comparison is made by the spectrospist by visual inspection, but this is slow and imprecise. In order to mitigate this problematic, a system based on the fuzzy logic technique to identify Raman spectra is presented. The methodology consists on implementing the comparison with the Correlation. However, a Raman spectrum is inevitably affected by noise which introduces ambiguity into the correlation values. Fuzzy Logic provides a simple way to draw conclusions from imprecise data. The fuzzy identification system is based on the following statement: when the correlation between the unidentified and the pattern is enough high, the analysed pigment is recognized as the pigment which corresponds to this pattern.
The membership functions, which characterize the fuzzy sets at the input (Correlation) and output (Identified/ Not_Identified) of the system, and the inference mechanism suitable for the problem, are chosen.
The great utility of Raman spectroscopy in molecular identification of pigments is well known. Furthermore, the incorporation of fiber optical technology has brought new advantages as compactness, security, weight and price reduction of lasers, and accessibility to analysed object. This is possible thanks to the recent notch and interferential filters, which almost eliminate, respectively, the Rayleigh frequency and both the self Raman spectrum of the fibre and laser plasma frequencies. However, the last has a great dependency on the filter spectral width. In this work, the important role that the quality of the interferential filter plays in the specific case of pigments identification is experimentally shown. Lead yellow pigments (stannate, antimoniate, ternary...) provide very important examples due to the coincidence between a fundamental Raman band of the pigment and some residual plasma frequencies.
We focus on the noise characteristics of semiconductor lasers from a theoretical point of view. More precisely, we investigate the possibility of reducing amplitude noise in single-mode semiconductor lasers by forcing emission of sub-Poissonian light. Starting from a statistical laser model based on the photon density matrix equation (master equation) applied to a saturable medium, we have derived a fundamental condition for semiconductor lasers yielding to amplitude noise reduction. However, practical results reveal that sub-Poissonian light emission could only be achieved in the limit by specially designed semiconductor laser structures such as microcavity lasers. On the other hand, conventional bulk lasers must be disregarded as suitable sources for sub-Poissonian light emission.
In this communication we focus on the potential use of travelling wave semiconductor laser amplifiers as high-speed all-optical inverters. Although semiconductor amplifiers suffer from saturation and crosstalk effects which can degrade the device performances required in some applications, we show here that both phenomena can be induced in order to produce optical transference and inversion of the information between two channels in a direct-detection system.
In this communication, analytical expressions for the oscillation threshold pump power and the lasing efficiency of an erbium-doped fiber laser are derived from well-known equations that describe the amplification process in erbium-doped fibers. These expressions show the dependence of both the oscillation threshold pump power and the lasing efficiency on the cavity length. As a design criteria, an optimum fiber length is derived from the analytical expressions by maximizing the ratio between the lasing efficiency and the oscillation threshold pump power. Finally, theoretical results are given for the case of an erbium-doped fiber ring laser together with numerical calculations obtained by means of computer simulations.
In this communication, one looks at the influence of the saturation
process over the statistical fluctuations (signal to noise ratio) of the
optical power at the output of a travelling wave semiconductor optical
amplifier (TWOA) . The statistical behaviour of this device is described
starting from the photon density matrix equation. The obtained theoretical
results, both for the noise figure and for the signal to noise ratio, allow to
take out some conclusions about noise behaviour in the non-linear light
amplification process.
This paper presents the advantages to be gained from the use of unwished
transitory peak appeared at the output of a Fabry-Perot optical amplifier when
it is switched frorr a low to high state. Simulations and numerical results
show the possibility of achieving reshaping and contrast improvement of
optical incident pulses. Potential applications of this bistable laser
amplifier as untimed regenerative repeater under certain conditions are
finally discussed.
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