Mid-infrared frequency domain optical parametric amplifier.

We report on an optical architecture delivering sub-120 femtosecond laser pulses of 20 µJ tunable from 5.5 µm to 13 µm in the mid-infrared range (mid-IR). The system is based on a dual-band frequency domain optical parametric amplifier (FOPA) optically pumped by a Ti:Sapphire laser and amplifying 2 synchronized femtosecond pulses each with a widely tunable wavelength around 1.6 and 1.9 µm respectively. These amplified pulses are then combined in a GaSe crystal to produce the mid-IR few-cycle pulses by means of difference frequency generation (DFG). The architecture provides a passively stabilized carrier-envelope phase (CEP) whose fluctuations has been characterized to 370 mrad RMS.

Design and fabrication of dispersion controlled highly nonlinear fibers for far-detuned four-wave mixing frequency conversion.

We report on the conception, fabrication and characterization of a new concept of optical fiber enabling a precise control of the ratio between the 2nd and 4th-order of chromatic dispersion (respectively ß2 and ß4) at 1.55 µm which is at the heart of the Four-Wave-Mixing (FWM) generation. For conventional highly nonlinear fiber the sensitivity of this ratio to fiber geometry fluctuations is very critical, making the fabrication process challenging. The new design fiber reconciles the accurate control of chromatic dispersion properties and fabrication by standard stack and draw method, allowing a robust and reliable method against detrimental fluctuations parameters during the fabrication process. Experimental frequency conversion with FWM in the new design fiber is demonstrated.

High-power amplified spontaneous emission pulses with tunable coherence for efficient non-linear processes.

We report on a detailed study of an amplified spontaneous emission source operated in a pulsed regime with particular attention paid to the influence of high-intensity chaotic temporal events on the generation of nonlinear processes. To this aim, we have developed a monolithic high-power fiber system delivering partially coherent pulses of adjustable coherence. We also have demonstrated a non-linear method to characterize the stochastic properties of the source mitigating the bandwidth limitation of linear techniques. Measured parameters of the source for various configurations are presented. An enhanced classical model has been established to reproduce the statistical properties of the source and predict the behaviour when exciting non-linear processes. Finally, a non-linear process (second harmonic generation) is investigated comparing the efficiency when the process is pumped by a pulsed beam with maximal and low coherence.

Single-shot phase-matching free ultrashort pulse characterization based on transient absorption in solids.

The frequency-resolved optical switching (FROSt) method developed for ultrashort pulse characterization is implemented for single-shot measurements. In this basic demonstration, the delay axis of the spectrogram is spatially encoded by the pump beam having a small incident angle with the photoexcited material. We present the calibration procedure for spectrograms acquired in single-shot and the temporal characterization of 44 fs pulses with central wavelength at 800 nm both in scanning and single-shot FROSt configurations. The retrieved pulses are compared by means of the root-mean-square field error. Finally, the pulses are propagated through a known dispersive material to measure the added group-delay dispersion.

High-power widely tunable ps source in the visible light based on four wave mixing in optimized photonic crystal fibers.

We present a detailed study on the generation of widely tunable visible light through four wave mixing in specifically designed micro-structured fibers. The fiber's properties are optimized for an efficient conversion to the visible and near infrared with a combined tunability from 620 to 910 nm of a picosecond Yb-doped tunable source for biomedical applications.

Study of middle infrared difference frequency generation using a femtosecond laser source in LGT.

We demonstrate phase-matched difference frequency generation in the emerging nonlinear crystal La3Ga5.5Ta0.5O14. Tunable wavelengths between 1.4 and 4.7 µm are generated by using femtosecond sources. We also report on the measurements of the optical damage threshold in the femtosecond regime and on the nonlinear refractive index n2.

100 kHz Yb-fiber laser pumped 3 µm optical parametric amplifier for probing solid-state systems in the strong field regime.

We report on a laser source operating at 100 kHz repetition rate and delivering 8 µJ few-cycle mid-IR pulses at 3 µm. The system is based on optical parametric amplification pumped by a high repetition rate Yb-doped femtosecond fiber-chirped amplifier. This high-intensity ultrafast system is a promising tool for strong-field experiments (up to 50 GV/m and 186 T) in low ionization potential atomic and molecular systems, or solid-state physics with coincidence measurements. As a proof of principle, up to the sixth harmonic has been generated in a 1 mm zinc selenide sample.