Unveiling low THz Dynamics of Liquid Crystals: Identification of Intermolecular Interaction among Intramolecular Modes

Liquid crystal based technologies have found considerably diversified uses and areas of application over the last few decades, proving to be excellent materials for tunable optical elements from visible to near-infrared frequencies. Currently, much effort is devoted to demonstrating their applicability in the far-infrared or THz spectral frequency (1 - 10 THz), where tremendous advances have been achieved in terms of broadband and intense sources. Yet a detailed understanding of the dynamics triggered by THz light in liquid crystals is far from complete. In this work, we perform broadband THz Time Domain Spectroscopy on the low-frequency modes of 4-cyano-4'-alkylbiphenyl (nCB) and 5-phenylcyclohexanes (PCH5) across different mesophases. DFT calculations on isolated molecules capture the majority of the measured response above 3 THz. In particular, the pronounced modes around 4.5 and 5.5 THz mainly originate from in-plane and out-of-plane bending of the cyano group. In contrast, the broad response below 3 THz, linked to modes of the alkyl chain, disagrees with the single molecule calculation. Here, we identify a clear intermolecular character of the response, supported by dimer and trimer calculations.Comment: 14 pages, 4 figure

Compact, simple and robust cross polarized wave generation source of few-cycle, high-contrast pulses for seeding petawatt-class laser systems

International audienceA compact and robust, dual-crystal cross polarized wave generation setup combined with a hollow waveguide filter is implemented to deliver few-cycle, high-contrast laser pulses sourced from a commercial multipass Ti:Sa amplifier. The initial 25-fs pulses with a temporal contrast of 108 are shortened to 10 fs with an improved contrast of at least 10^10. The single nonlinear stage for spectral broadening and contrast enhancement of a commercial amplifier serves as an ideal injector for petawatt-class laser systems

Diode-pumped Yb:CaF 2 multipass amplifier producing 50 mJ with dynamic analysis for high repetition rate operation

International audienceThe dynamic thermal issues of the Yb:CaF 2 crystals within a multi-tens-mJ-energy multipass amplifier operating in the 20–100 Hz repetition rate range and pumped in quasi-cw regime have been studied at different timescales. Thermal response times of the system have been precisely investigated and analyzed, for the first time to our best knowledge in such amplifiers. This study includes a dual timescale analysis: in the long-timescale (second) with direct thermography mapping and in the millisecond range with thermal lensing in a pump-probe configuration. Very atypical positive lens behavior with fluorites will also be presented and discussed. This complete analysis is used to demonstrate the capability of Yb:CaF 2 multipass amplifier systems for operating the amplifier at 20 Hz with 57 mJ and 100 Hz with 32-mJ stable regime. Indeed, high repetition rate multipass amplifier has been realized for the first time with Yb:CaF 2 and for this energy. The results have been analyzed precisely to take into account the thermal issues and excellent beam quality, with a M 2 of 1.1. The pointing stability of 20 lrad has been measured documenting the reliability of the high repetition rate mJ amplifier

High-order Harmonic Generation in Thermotropic Liquid Crystals

Thermotropic liquid crystals are versatile optical materials that exhibit a state of matter intermediate between liquids and solids. Their properties can change significantly with temperature, pressure, or other external factors, leading to different phases. The transport properties within these materials in different phases are still largely unexplored and their understanding would enable exciting prospects for innovative technological advancements. High-order harmonic spectroscopy proved to be a powerful spectroscopic tool for investigating the electronic and nuclear dynamics in matter. Here we report the first experimental observation of high-order harmonic generation in thermotropic liquid crystals in two different phase states, nematic and isotropic. We found the harmonic emission in the nematic phase to be strongly dependent on the relative orientation of the driving field polarization with respect to the liquid crystal alignment. Specifically, the harmonic yield has a maximum when the molecules are aligned perpendicularly to the polarization of the incoming radiation. Our results establish the first step for applying high-order harmonic spectroscopy as a tool for resolving ultrafast electron dynamics in liquid crystals with unprecedented temporal and spatial resolution.Comment: The paper is composed by 12 pages including references. Five images are presen

Diode-pumped 99 fs Yb : CaF2 oscillator

International audienceWe demonstrate the generation of 99 fs pulses by a mode-locked laser oscillator built around a Yb:CaF2 crystal. An average power of 380 mW for a 13 nm bandwidth spectrum centered at 1053 nm is obtained. The short-pulse operation is achieved thanks to a saturable absorber mirror and is stabilized by the Kerr lens effect. We investigated the limits of the stabilization process and observed a regime slowly oscillating between mode locking and Q switching

Genome-Wide Association Study in BRCA1 Mutation Carriers Identifies Novel Loci Associated with Breast and Ovarian Cancer Risk

BRCA1-associated breast and ovarian cancer risks can be modified by common genetic variants. To identify further cancer risk-modifying loci, we performed a multi-stage GWAS of 11,705 BRCA1 carriers (of whom 5,920 were diagnosed with breast and 1,839 were diagnosed with ovarian cancer), with a further replication in an additional sample of 2,646 BRCA1 carriers. We identified a novel breast cancer risk modifier locus at 1q32 for BRCA1 carriers (rs2290854, P = 2.7×10-8, HR = 1.14, 95% CI: 1.09-1.20). In addition, we identified two novel ovarian cancer risk modifier loci: 17q21.31 (rs17631303, P = 1.4×10-8, HR = 1.27, 95% CI: 1.17-1.38) and 4q32.3 (rs4691139, P = 3.4×10-8, HR = 1.20, 95% CI: 1.17-1.38). The 4q32.3 locus was not associated with ovarian cancer risk in the general population or BRCA2 carriers, suggesting a BRCA1-specific associat

Home range and habitat use of feral hogs in Congaree National Park, South Carolina

Feral hogs (Sus scrofa) are a widespread exotic species that currently occur in most states within the United States and are common throughout the southeastern United States. We radio-collared and tracked feral hogs from April 2005 to November 2006 in Congaree National Park (CNP), South Carolina, USA. The CNP is one of the largest and most intact tracts of old-growth, bottomland hardwood forest remaining in the United States. We measured home range size and determined habitat use for male and female hogs. The mean (± SE) home range sizes for male hogs (n = 7) and female hogs (n = 9) were 218 ± 43 ha and 191 ± 31 ha, respectively. These home range estimates are relatively small compared to estimates from other studies of feral hogs. Habitat use models indicated that high use areas for hogs included habitat types best characterized as bottomland hardwoods and that hog locations were distributed in a relatively uniform manner throughout the study area within CNP. The small home ranges and habitat use patterns we observed suggest that habitat quality in CNP is good for feral hogs. Radio-collared hogs also moved readily between park and private lands. Thirteen of 23 collared hogs were found on private lands adjacent to CNP at least once. At least eight of the 23 collared hogs were shot and killed by hunters and one of these was taken on CNP land. If control of hogs in CNP were a goal of resource managers, then it would likely succeed or fail based in large part on the incorporation of adjacent private lands into the program

57-mJ 20-Hz multipass laser amplifier based on Yb:CaF 2 crystals (orale)

International audienceWe are presenting a 57 mJ multipass amplifier based on Yb:CaF 2 operating at 20 Hz. Special attention has been given to the thermal measurement and management in order to push it to the 100 Hz regime

Unveiling Low THz Dynamics of Liquid Crystals: Identification of Intermolecular Interaction among Intramolecular Modes

Liquid crystals have found a wide area of application over the last few decades, proving to be excellent materials for tunable optics from visible to near-infrared frequencies. Currently, much effort is devoted to demonstrating their applicability at THz frequencies (1–10 THz), where tremendous advances of broadband and intense sources have been achieved. Yet, a detailed understanding of THz-triggered dynamics in liquid crystals is incomplete. Here, we perform broadband THz time domain spectroscopy on 4-cyano-4′-alkyl-biphenyl (nCB) and 5-phenylcyclohexanes (PCH5) across mesophases. Density functional theory calculations on isolated molecules capture the majority of the response. In particular, the pronounced modes around 4.5 and 5.5 THz mainly originate from bending modes of the cyano group. In contrast, the broad response below 3 THz, linked to modes of the alkyl chain, disagrees with the single molecule calculation. Here, we identify a clear intermolecular character of the response, supported by dimer and trimer calculations.ISSN:1520-6106ISSN:1520-5207ISSN:1089-564