Vincent Couderc

White-light supercontinuum generation in normally dispersive optical fiber using original multi-wavelength pumping system

We report on the experimental demonstration of a white-light supercontinuum generation in normally dispersive singlemode air-silica microstructured fiber. We demonstrate that the simultaneous excitation of the microstuctured fiber in its normal and anomalous dispersion regimes using the fundamental and second harmonic signals of a passively Q-switched microchip laser leads to a homogeneous supercontinuum in the visible range. This pumping scheme allows the suppression of the cascaded Raman effect predominance in favor of an efficient spectrum broadening induced by parametric phenomena. A flat supercontinuum extended from 400 to 700 nm is achieved.

Non-linear optical properties of chalcogenide glasses measured by Z-scan

Abstract To explore the potentialities of chalcogenide glasses for ultrafast optical switching, the non-linear refractive indices of different compositions are measured. Several binary glasses in the [Ge–Se] system, As2S3 and As2Se3 glasses, as well as ternary glasses in the [Ge–Se–As] system have been characterized. Non-linear measurements have been performed by the Z-scan technique, at different intensities, with the picosecond pulses emitted by a 10 Hz Q-switched mode-locked Nd-YAG laser at 1064 nm, in adequate conditions to characterize ultrafast non-linearities. Non-linear refractive indices as high as 22×10 −18 m 2 / W have been obtained in the ternary system. In the case of As2S3 and As2Se3 glasses, a significant variation of the value of the non-linear index of refraction with the laser intensity has been observed which is attributed to a fifth order non-linearity.

Quantitative CARS Molecular Fingerprinting of Single Living Cells with the Use of the Maximum Entropy Method

This work was supported by the SENTAN project (Program-S) of the Japan Science and Technology Agency (JST). H. Kano gratefully acknowledges financial support from the Precursory Research for Embryonic Science and Technology (PRESTO) program of JST. The authors thank C. Onogi for providing the spontaneous Raman spectrum of yeast mitochondria, Leukos and Horus Laser companies for technical support, and Dr. F. Omura and H. Yomo (Suntory Co., Ltd.) for providing us with the yeast sample. We gratefully acknowledge J. Ukon (HORIBA, Ltd.) for assisting in the collaboration between the Japanese and French groups.

Observation of quadratic spatial solitons in periodically poled lithium niobate

We report what are to our knowledge the first observation and characterization of quadratic spatial solitons in periodically poled lithium niobate (PPLN). Using a Nd:YAG (1064-nm) source, we observed self-trapped solitary-wave propagation over more than six diffraction lengths as a result of the cascaded quadratic nonlinear process. Low-threshold operation (5-kW peak power) was measured for the quasi-phase-matched PPLN structure designed for frequency doubling.

Visible supercontinuum generation controlled by intermodal four-wave mixing in microstructured fiber.

We present an experimental and numerical study of supercontinuum generation extended in the visible part of the spectrum by using a selective optical coupling of the pump wave in the largely anomalous dispersion regime. The broadband frequency generation is induced by an initial four-wave mixing process that converts the pump wave at 1064 nm into 831 nm anti-Stokes and 1478 nm Stokes wavelengths. Phase matching is ensured on such a large frequency shift thanks to a microstructured multimodal fiber with a specific design. Continuum generation is therefore enhanced around the two generated sidebands.

Ultrabroadband multiplex CARS microspectroscopy and imaging using a subnanosecond supercontinuum light source in the deep near infrared

Subnanosecond supercontinuum (SC) has been generated by a 1,064 nm microchip laser combined with a photonic crystal fiber. The ultrabroadband (>2,000 cm(-1)) SC has facilitated multiplex coherent anti-Stokes Raman scattering (CARS) microspectroscopy in the spectral range from 1,000 to 3,000 cm(-1) with lateral and depth spatial resolution of 0.9 and 4.6 microm, respectively. A clear CARS image of a Nicotiana tabacum L. cv. Bright Yellow 2 cell has been obtained with high vibrational contrast.

Characterization of a 50-Ω Exposure Setup for High-Voltage Nanosecond Pulsed Electric Field Bioexperiments

An exposure system for a nanosecond pulsed electric field is presented and completely characterized in this paper. It is composed of a high-voltage generator and an applicator: the biological cuvette. The applied pulses have high intensities (up to 5 kV), short durations (3 and 10 ns), and different shapes (square, bipolar). A frequency characterization of the cuvette is carried out based on both an analytical model and experimental measurements (S11) in order to determine its matching bandwidth. High voltage measurements in the time domain are performed. Results show that the cuvette is well adapted to 10-ns pulses and limited to those of 3 ns. The rise/fall times of the pulses should not be less than 1.5 ns. In addition, numerical calculation providing voltage distribution within the cuvette is performed using an in-house finite-difference time-domain code. A good level of voltage homogeneity across the cuvette electrodes is obtained, as well as consistency with experimental data for all the applied pulses.

Ultra wide band supercontinuum generation in air-silica holey fibers by SHG-induced modulation instabilities.

Second harmonic generation in an air-silica microstructured optical fiber pumped by subnanosecond pulses is used in order to initiate modulation instability processes in normal and anomalous dispersion regimes. This allows us to generate an ultra wide and flat supercontinuum (350-1750 nm), covering the entire transparency window of silica and exhibiting a singlemode transverse profile in visible range.

Label-free tetra-modal molecular imaging of living cells with CARS, SHG, THG and TSFG (coherent anti-Stokes Raman scattering, second harmonic generation, third harmonic generation and third-order sum frequency generation)

We have developed a new multimodal molecular imaging system that combines CARS (coherent anti-Stokes Raman scattering), SHG (second harmonic generation), THG (third harmonic generation) and multiplex TSFG (third-order sum frequency generation) using a subnanosecond white-light laser source. Molecular composition and their distribution in living cells are clearly visualized with different contrast enhancements through different mechanisms of CARS, SHG, THG and TSFG. A correlation image of CARS and TSF reveals that the TSF signal is generated predominantly from lipid droplets inside a cell as well as the peripheral cell wall.

Kilovolt, Nanosecond, and Picosecond Electric Pulse Shaping by Using Optoelectronic Switching

This letter describes subnanosecond electric pulse generation and shaping. The optoelectronic switching of silicon semiconductor devices embedded in a frozen wave generator is obtained in the linear regime. Control of the switching delay time, combined with power modulation of the optical gating signals, enables temporal and spectral pulse shaping. In this way, monocycle nanosecond and/or picosecond pulses with balanced or unbalanced positive and negative components and square electrical pulses with adjustable duration are obtained.