ABSTRACT
Fermentation of cocoa is a key process to obtain aromatic chocolate products from raw cocoa beans. Hitherto, the levels of fermentation in cocoa are determined using destructive techniques, for example by a cut-test to manually observe the colour inside the beans, or by quantifying ammonia nitrogen (NH3) in the cocoa powder. In this paper, we present the use of Terahertz hyperspectral imaging as a new way to non-destructively analyse and detect fermented cocoa beans. The study analysed two sets of twenty-two cocoa bean samples with different levels of fermentation from two producers in Brazil. A correlation between fermentation conditions and the outcome results of their THz measurements was observed.
Subject(s)
Cacao , Chocolate , Brazil , Fermentation , Hyperspectral ImagingABSTRACT
Attainable levels of signal-to-background ratio (SBR) in Raman spectroscopy of biological samples is limited by the presence of endogenous fluorophores. It is customary to remove the ubiquitous fluorescence background using postacquisition data processing. However, new approaches are needed to reduce background contributions and maximize the fraction of the sensor dynamical range occupied by Raman photons. Time-resolved detection using pulsed lasers and time-gated measurements can be used to address the signal-to-background problem in biological samples by limiting light detection to nonresonant interaction phenomena with relaxation time scales occurring on sub-nanosecond time scales, thereby excluding contributions from resonant phenomena such as fluorescence. A time-gated Fourier-transform spectrometer was assembled using a commercially available interferometer, a single channel single-photon avalanche diode and time tagging electronics. A time gate of 300 ps increased the signal-to-background-ratio of the 1440 cm-1 Raman band from 36% to 69% in an olive oil sample hereby demonstrating the potential of this approach for autofluorescence suppression.
Subject(s)
Interferometry , Spectrum Analysis, Raman , Lasers , Photons , Spectrometry, FluorescenceABSTRACT
All-fiber ns-pulsed visible laser at λ=521 nm is realized by frequency doubling an Yb-doped fiber laser with a periodically poled silica fiber. A 50-mW second-harmonic (SH) output power is produced that is over 6-orders of magnitude greater than previous results obtained with poled fibers in the visible spectral range. The normalized conversion efficiency of 0.3%/W is to date the largest demonstrated with poled fiber technology. Furthermore, 21% conversion efficiency is achieved for the doubling of 8-ps pulses from a neodymium-doped yttrium vanadate solid-state laser. The advances are made possible by the precision and flexibility offered by using the continuous periodic UV erasure, as opposite to photolithographic methods, for the fabrication of over 20-cm-long χ(2)-gratings for quasi-phase matched SH generation.
ABSTRACT
We report a PM all-normal, all-in-fiber passively mode-locked laser operating at 1030 nm. The main pulse shaping mechanism is provided by a tilted chirped-FBG. The laser delivers nanojoule range highly chirped pulses at a repetition rate of about 40 MHz. The FWHM of the optical spectrum is up to 7.8 nm leading to sub-500 fs compressed optical pulses. The influence of the filtering bandwidth and the output coupling ratio has been investigated.
Subject(s)
Fiber Optic Technology/instrumentation , Lasers , Equipment Design , Equipment Failure AnalysisABSTRACT
The generation of 236 mW of second-harmonic power in a 32-cm-long periodically poled silica fiber, corresponding to an average conversion efficiency of 15.2+/-0.5%, is reported. This represents the highest normalized second-harmonic conversion and the highest average second-harmonic power ever reported for a periodically poled silica fiber, to our knowledge. The enhancement is attributed to an improved design of the specialty twin-hole fiber and the extension of the nonlinear interaction length.
