Transmissive liquid crystal light-valve for near-infrared applications

Synthesis, Mesomorphism and the Optical Properties of Alkyl-deuterated Nematogenic 4-[(2,6-Difluorophenyl)ethynyl]biphenyls

The synthesis and characterization of new deuterated liquid crystal (LC) compounds based on phenyl tolane core is described in this paper. The work presents an alternative molecular approach to the conventional LC design. Correlations between molecular structure and mesomorphic and optical properties for compounds which are alkyl-hydrogen terminated and alkyl-deuterium, have been drawn. The compounds are characterized by mass spectrometry (electron ionization) analysis and infrared spectroscopy. They show enantiotropic nematic behavior in a broad temperature range, confirmed by a polarizing thermomicroscopy and differential scanning calorimetry. Detailed synthetic procedures are attached. Synthesized compounds show a significantly reduced absorption in the near-infrared (NIR) and medium-wavelength infrared (MWIR) radiation range, and stand as promising components of medium to highly birefringent liquid crystalline mixtures.

Femtometer displacement resolution with phase-insensitive Doppler sensing

The measurement of extremely small displacements is of utmost importance for fundamental studies and practical applications. One way to estimate a small displacement is to measure the Doppler shift generated in light reflected off a moving object, converting a displacement measurement into a frequency measurement. Here we show a sensitive device capable of measuring μHz/Hz Doppler frequency shifts corresponding to tens of femtometer displacements for a mirror oscillating at 2 Hz. While the Doppler shift measured is comparable to other techniques, the position sensitivity is orders of magnitude better, and operates over several orders of magnitude of Doppler frequency range. In addition, unlike other interferometric techniques, our device is phase insensitive, making it unusually robust to noise.

Continuously tunable femtosecond delay-line based on liquid crystal cells

We introduce a new device for group and phase delay steering of femtosecond pulse trains that makes use of cascaded, electrically driven, nematic liquid-crystal cells. Based on this approach we demonstrate a continuously tunable optical delay line. The simple collinear implementation with no moving parts enables to shape the achievable temporal range with sub-femtosecond accuracy. By appropriately choosing the bias voltages applied to the cascaded cells, the imparted group delay can be made either positive or negative and precisely adjusted. Moreover, independent control of the group delay and the phase of femtosecond pulses is demonstrated.

Infrared sensitive liquid crystal light valve with semiconductor substrate

A liquid crystal light valve (LCLV) is an optically controlled spatial light modulator that allows recording of dynamic holograms. Almost all known LCLVs operate in the visible range of the spectrum. In the present work we demonstrate a LCLV operating in the infrared. The interaction of signal and pump waves is studied for different applied voltages, grating spacings, and intensities of the recording beams. A fourfold amplification of the weak signal beam is achieved. The amplitude of the refractive index modulation Δn=0.007 and nonlinear coupling constant n₂=-1  cm²/W are estimated from the experimental results. External phase modulation of one of the recording beams is used for a further transient increase of the signal beam gain.

Adaptive holographic interferometer at 1.55 μm based on optically addressed spatial light modulator

We report the realization of an adaptive holographic interferometer based on two-beam coupling in an optically addressed liquid crystal spatial light modulator operating at 1.55-μm. The system allows efficient phase demodulation in noisy environment and behaves as an optical high-pass filter, with a cut-off frequency of approximately 10 Hz, thus filtering slow phase disturbances (due to, for example, temperature variations or low frequency fluctuations) and keeping the detection linear without the need of heterodyne or active stabilization.

Hybrid organic-inorganic materials for novel photonic applications

This novel joint feature issue on "Hybrid organic-inorganic materials for photonic applications" in Applied Optics and Optics Materials Express comprises 14 papers on liquid crystals, polymers, photoconductive materials, and gratings and filters. It is hoped that this feature issue encourages and stimulates further research into hybrid materials with enhanced linear and nonlinear optical properties, their mechanisms of operation, and their applications.