We take advantage of the Raman soliton self-frequency shift experienced during the propagation in an anomalous
dispersive photonic crystal fiber in order to continuously tune the central frequency of ultrashort pulses. We discuss the
fiber properties to be favored to obtain high power spectral densities and we carry out an extensive experimental study of
the properties of the frequency shifted pulses in terms of spectral, autocorrelation, and RF spectrum measurements.
We perform multiplex coherent anti-Stokes Raman scattering (CARS) micro-spectroscopy with a picosecond pulsed laser and a broadband supercontinuum (SC) generated in photonic crystal fiber. CARS signal stability is achieved using an active fiber coupler that avoids thermal and mechanical drifts. We obtain multiplex CARS spectra for test liquids in the 600-2000 cm−1 spectral range. In addition we investigate the polarization dependence of the CARS spectra when rotating the pump beam linear polarization state relative to the linearly polarized broad stokes SC. From these polarization measurements we deduce the Raman depolarization ratio, the resonant versus nonresonant contribution, the Raman resonance frequency, and the linewidth.
We investigate a compact, stable and broadband multiplex Coherent anti-Stokes Raman Scattering (CARS) source for
micro-spectroscopy. By pumping an adapted photonic crystal fiber, we generate the broadband Stokes pulses required for
multiplex CARS measurements. The CARS signal stability is provided by an active fiber coupling, avoiding therefore
the thermal or mechanical drifts. With only a few nanojoule for pump and Stokes pulses energies, we demonstrate on test
liquids the capability of the source to generate multiplex CARS spectra in the 600-2000 cm-1 spectral range.
In the aim of describing the thermo-mechanical behaviour of a thin-film filter, simplified models have been studied. An
easy way is to determine the evolution of the optical properties of each layer composing the stack, and thus to derive the
features change at the component level. Therefore, the knowledge of physical parameters describing each material, such
as the coefficient of thermal expansion, the thermo-optic coefficient, the Poisson's ratio and the elasto-optic coefficients,
is required. The main challenge is to evaluate these parameters at a single layer level. We propose here a new optical
method, based on the analysis of the thermal behaviour of two dedicated Fabry-Perot (FP) structures including a thin
disk of the material under study. In parallel, we show through modelling, that we can determine the physical properties
of this material with a high accuracy, only by measuring the shift of FP resonance wavelengths. However, we have to
take into account the mechanical deformation of the Fabry-Perot structures induced by the thin-film deposition process
as well as its evolution with the temperature change (thermal stresses). In this goal, we carried out an accurate study of
the thermo-mechanical behaviour of our interferometric structures by using a Finite Element Method.
The wavelengths associated to the transmission peaks of a Fabry-Perot etalon are directly connected with its optical
thickness. As a consequence, any change in the physical thickness or the refractive index of the cavity has a direct
influence on the value of these specific wavelengths. This property can be used to determine the thermal characteristics,
like the coefficient of thermal expansion or the thermo-optic coefficient, of some materials. However, to be efficient, this
method needs a very high accuracy in the determination of these resonant wavelengths. We developed a dedicated
measurement set-up, combining a tunable laser source around 850 nm and a high precision wavelength meter to
determine with accuracy better than 0.2 pm the resonant wavelengths of a Fabry-Perot etalon. We use a temperature
stabilized chamber to avoid temperature fluctuations or, on the contrary, to apply a deterministic temperature change at
the cavity level. We describe the structure of our bench and present the results obtained on BK7 windows as well as on
an optically contacted ULE Fabry-Perot with silver coatings.
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