研究目的
Investigating the optically-induced thermal nonlinear effect in a nematic liquid-crystal cell through weak light-absorption by the ITO coating of an infrared pulsed femtosecond laser.
研究成果
The study demonstrates an optically-induced thermal nonlinearity in a thick nematic liquid-crystal cell, enabling control of the extraordinary and ordinary indices up to the isotropic phase transition. The process is characterized by high fidelity and stability, opening new prospects for spatial shaping devices and defining the operating wavelength range for ultrafast liquid-crystal based electro-optic applications.
研究不足
The study is limited by the specific characteristics of the ITO coating and the LC cell used, which may affect the generalizability of the findings. Additionally, the spatial resolution of the thermal gradient is better than 100 μm, which may limit applications requiring finer resolution.
1：Experimental Design and Method Selection:
The study involves the use of a nematic liquid-crystal (E7) cell with ITO coating to investigate the thermal nonlinear effect induced by an infrared femtosecond laser. The experiment measures the refractive index and thermal gradients as a function of laser intensity.
2：Sample Selection and Data Sources:
The main LC cell used is home-made with conductive windows from Thorlabs, composed of a 5 mm thick AR-coated BK7 substrate with a thin layer of ITO optimized for the spectral range 1050–1650 nm.
3：List of Experimental Equipment and Materials:
The femtosecond laser (TOPTICA) produces a 40 fs pulses train, with a high repetition rate of 80 MHz and a spectral bandwidth centered at λ0 = 1.55 μm. The LC-cell transmission is 75% in the considered spectral range.
4：55 μm. The LC-cell transmission is 75% in the considered spectral range.
Experimental Procedures and Operational Workflow:
4. Experimental Procedures and Operational Workflow: The laser beam, after passing through the LC-cell, exhibits a spatial deformation after about 10 cm of propagation. An iris is used to select the central part of the beam and the transmission is measured for various configurations.
5：Data Analysis Methods:
The refractive index variation is estimated from the number of rings observed, and the thermal gradient is calculated from the refractive index variation.
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