Guilmot Ernotte

Decoupling Frequencies, Amplitudes and Phases in Nonlinear Optics

In linear optics, light fields do not mutually interact in a medium. However, they do mix when their field strength becomes comparable to electron binding energies in the so-called nonlinear optical regime. Such high fields are typically achieved with ultra-short laser pulses containing very broad frequency spectra where their amplitudes and phases are mutually coupled in a convolution process. Here, we describe a regime of nonlinear interactions without mixing of different frequencies. We demonstrate both in theory and experiment how frequency domain nonlinear optics overcomes the shortcomings arising from the convolution in conventional time domain interactions. We generate light fields with previously inaccessible properties by avoiding these uncontrolled couplings. Consequently, arbitrary phase functions are transferred linearly to other frequencies while preserving the general shape of the input spectrum. As a powerful application, we introduce deep UV phase control at 207 nm by using a conventional NIR pulse shaper.

2.5 TW, two-cycle IR laser pulses via frequency domain optical parametric amplification

Broadband optical parametric amplification in the IR region has reached a new milestone through the use of a non-collinear Frequency domain Optical Parametric Amplification system. We report a laser source delivering 11.6 fs pulses with 30 mJ of energy at a central wavelength of 1.8 μm at 10 Hz repetition rate corresponding to a peak power of 2.5 TW. The peak power scaling is accompanied by a pulse shortening of about 20% upon amplification due to the spectral reshaping with higher gain in the spectral wings. This source paves the way for high flux soft X-ray pulses and IR-driven laser wakefield acceleration.

Frequency domain tailoring for intra-pulse frequency mixing

Generating mid infrared (MIR) pulses by difference frequency generation (DFG) is often a trade-off between the maximum stability given by all-inline intra-pulse arrangements and the independent control of pulse parameters with inter-pulse pump-probe like scenarios. We propose a coalescence between both opposing approaches by realizing an all-inline inter-pulse DFG scheme employing a 4-f setup. This allows independent manipulation of the amplitude, delay and polarization of the two corresponding spectral side bands of a supercontinuum source while maintaining 20 attoseconds jitter without any feedback stabilization. After filamentation in air, the broadened Ti:Sa spectrum is tailored in a 4-f setup to generate tunable MIR pulses. In this manner, 2 µm, 4.8 µJ, 26.5 fs and carrier-envelope-phase (CEP) stabilized pulses are generated in a single DFG stage.

Linearizing nonlinear optics

We demonstrate how Fourier Nonlinear Optics elegantly merges the simplicity of linear optics with the power of conventional nonlinear optics to achieve the decoupling of frequencies, amplitudes and phases in nonlinear processes.

Study of difference frequency generation and optical parametric amplification in La 3 Ga 5.5 Ta 0.5 O 14 in the femtosecond regime

Optical parametric generation in nonlinear crystals across the atmosphere transmission band II (3–5 μm) is of interest for various applications such as infrared spectroscopy or countermeasures. For an efficient parametric generation in this spectral range with well-developed ultrashort laser sources, we identified Langatate La<inf>3</inf>Ga<inf>5.5</inf>Ta<inf>0.5</inf>O<inf>14</inf> (LGT) [1]. LGT is transparent from 0.25 up to 6.5 μm and can be grown in large sizes using the Czochralski method. Its unique nonlinear coefficient d<inf>11</inf>=2.4 ± 0.4 pm/V at λ=0.67 μm as well as the refinement of the Sellmeier equations are reported in ref [1]. The study highlights the potential for LGT to generate broadband spectrum between 1.5 and 5 μm if pumped around 0.97 μm available from a Ti:Sapphire (Ti:Sa) laser.

Towards TW few-cycle IR laser pulses via FOPA

Employing 80mJ of TiSa pump energy for Frequency domain Optical Parametric Amplification (FOPA) yielded 13mJ output pulses within a two-cycle bandwidth at 1.8µm wavelength.

Frequency domain optical parametric amplification

General restrictions arising from gain-narrowing and phase-matching are circumvented by employing parametric amplification in the frequency rather than the time domain. Frequency-domain OPA has been used for amplifying few-cycle pulses and for high gain amplification.