Ultrafast Non Linear Optics in liquid Crystals – UNLOC

The first phase of the project consists in developing the platform for ultrafast nonlinear optics. It can be seen as an extension of the SOFTLITE facility, towards higher peak intensity, shorter pulses and other spectral range. It relies on characterization of the newly acquired high-average power femtosecond source (PHAROS, Light Conversion), delivering 1030nm, 6W, 190fs and pulses with tunable repetition rate between 1kHz and 1MHz. In the framework of UNLOC, post-compression of this source, e.g. pulse shortening through self-phase modulation, will be setup in order to reach a shorter pulse regime (< 40 fs pulse duration), and thus higher peak intensity pulses will be available. The acquisition of an optical parametric amplifier is also contemplated.
In a second phase, the scientific investigations will be conducted with the novel platform on various LC and PRC samples. The LC samples will be realized by the project team, who has all the technical skills and equipment for practical realization of LC devices in various mesophases and different architecture (electrical driving, thickness, doping agent….). In regards to PRC, we already have in the laboratory several crystals of SBN, LiNbO3:Fe and KNbO3:Fe. If needed, other samples can be easily acquired (see e.g. Rainbow Photonics).

- Single-shot chromatic dispersion measuring device
- New method of nonlinear spectroscopy, based on the measurement of the transient carrier frequency shift during a degenerated non resonant effect
- Temporal dynamics and spectroscopy of the tensor terms Chi3 of nematic liquid crystals
- Study of the damaging mechanisms of freely suspended films of nematic liquid crystals in the femtosecond regime

We expect to extent the fundamental knowledge about nonlinearity of soft matter through our performed ultrafast spectroscopy experiments. Moreover, potential applications include the nonlinear shaping of femtosecond pulses as well as the nonlinear tailoring of the considered medium. Although highly innovative, this project is low-risk, considering the complementary expertise of the coordinator’s team and our recent and promising results related to linear ultrafast optics in liquid crystals.
At the end of the project, a novel experimental facility dedicated to ultrafast nonlinear optics will be fully operational at InPhyNi. Furthermore, we will have acquired the know-how to handle and quantify ultrafast nonlinear optics in liquid crystals and photo-refractive crystals. This know-how will lead to the development and fiabilization of the next generation of liquid-crystal based devices for ultrafast technology. The project will then strengthen the French position at the forefront of the international competition for this emerging research field.

1. « Broadband Spectral Domain Interferometry for Optical Characterization of Nematic Liquid Crystals », V. M. di Pietro and A. Jullien, Applied Sciences (2020).
« Ultrafast nonlinear spectroscopy of nematic liquid crystals via transient frequency-shift detection », E. Neradovskaia, G. Cheriaux, C. Claudet and A. Jullien, to be submitted

Ultrafast nonlinear optic is currently employed in femtosecond lasers technology and gathers numerous powerfull techniques to gate or modulate the optical signal in the frequency, time or space domain. Current nonlinear media are crystals and gas.
Liquid crystals intrinsically exhibit very interesting optical properties: a large birefringence, a wide spectral range of transparency and, above all, the possibility of modifying their optical properties through the molecular reorientation induced by an electric or magnetic field. Most common mesophases of liquid crystals have been widely studied for light manipulation. However, despite their exceptional optical properties, the applications of liquid crystal cells to the direct manipulation of ultrashort optical pulses trains have remained occasional so far.
In the framework of the LABCOM SOFTLITE between the OCL group of Institut de Physique de Nice (INPHYNI) and FASTLITE company, we have recently started a novel research activity, devoted to the linear manipulation and spectro-temporal shaping of ultrashort pulses with devices based on liquid crystals. For the two last years, we have disclosed the use of thick nematic liquid crystal cells for ultrafast applications. These investigations have simultaneously opened a novel application field for ultrafast instrumentation as well as provided a new insight of liquid crystals dynamics, through the detection of unexpected collective molecular motions. A natural extension of this research consists in investigating the ultrafast nonlinear properties of liquid crystals.
In the framework of the UNLOC project, we propose to extend our ultrafast facility with the implementation of a more energetic and shorter femtosecond source, in order to deeply investigate ultrafast nonlinear optics in liquid crystals. Although liquid crystals in two different phases (nematic and cholesteric) remain the targeted medium, we also plan to extend our expertise to photo-refractive crystals, whose properties for ultrafast optics hasn’t been studied so far. Using ultrashort pulses presents two main advantages. On one hand, it gives access to the ultrafast nonlinear temporal dynamics in the nonlinear medium. On the other hand, the facility will enable to reach high peak power and high average power, facilitating the excitation of third-order, or even higher, nonlinear processes.
We expect to extent the fundamental knowledge about nonlinearity of soft matter through our performed ultrafast spectroscopy experiments. Moreover, potential applications include the nonlinear shaping of femtosecond pulses as well as the nonlinear tailoring of the considered nonlinear medium.
At the end of the project, a novel experimental platform dedicated to ultrafast nonlinear optics will be fully operational at INPHYNI. Furthermore, we will have acquired the know-how to handle and quantify ultrafast nonlinear optics in liquid crystals. This know-how will lead to the development and fiabilization of the next generation of liquid-crystal based devices for ultrafast technology. The project will then strengthen the French position at the forefront of the international competition for this emerging research field. The UNLOC project will undoubtedly strengthen the coordinator’s research thematic at INPHYNI and will reinforce her scientific independence.