We review recent research using amorphous electrooptic (EO) polymers for generation and detection of broadband
terahertz radiation (0.3 THz -30 THz). The advantages of amorphous EO polymers over other materials for broadband
THz generation (via optical rectification) and detection (via EO sampling) include a lack of phonon absorption (good
transparency) in the THz regime, high EO coefficient and good phase-matching properties, and, of course, easy
fabrication (low cost). Our ~12-THz, spectral gap-free THz system based on a polymer emitter-sensor pair is an
excellent demonstration of the advantages of the use of EO polymers. This system has been employed as a wideband
spectrometer to study dielectric materials in the THz regime.
We report on the application of poled electro-optic (EO) polymer films in a gap-free, broadband terahertz (THz) system. Using polymer films consisting of 40% Lemke/60% APC (LAPC) as an emitter-sensor pair and a Ti:sapphire regenerative laser pulse amplifier operated at 800-nm-wavelength, we generated and detected transient THz waves, via the optical rectification and EO effect, respectively. We obtained ~12-THz bandwidth from this system with no absorption gaps. The absence of resonant absorption gaps normally seen in THz systems based on crystalline EO materials is attributed to the amorphous form of the polymer films, making our EO polymer emitter-sensor pair advantageous over EO crystals in a gap-free, broadband THz time-domain-spectroscopy (THz-TDS) system. A model has been developed to simulate the spectrum from THz systems and the simulation results were compared with the experimental results. We also report our experiments and simulations for the pulsed THz waves generated by a EO polymer film consisting of 40% DCDHF-6-V/60% APC (DAPC) and detected either by an 80-μm ZnCdTe or a 2-mm ZnTe sensor, with 1300-nm-wavelength pulses from an optical parametric amplifier (OPA). In addition, with the help of our model, we propose employing a wavelength tuning technique to achieve good phase-matching for polymer emitter/sensor pairs, which should lead to very broad bandwidth.
Electro-optic (EO) polymers are promising materials to be used as THz emitters and sensors due to their high nonlinear coefficients and good phase-matching conditions. We demonstrate efficient THz generation from an 80 μm thick EO polymer emitter which is equivalent to that of a 1000 μm thick ZnTe standard. Also, this kind of EO polymer allows a generation up to 20 THz with ultra-short laser pulses. We have observed resonance-enhanced THz generation in another kind of EO polymer composite near its absorption maximum. Due to a sharp resonance of the EO coefficient near the absorption maximum of the material, the amplitude of THz field generated from a 3.1 μm thick film of this composite is 15% larger than that from a 1000 μm thick ZnTe standard. The estimated EO coefficient of this composite at 800 nm is over 1200 pm/V.
The dual nature of Lemke-e allow us to write both permanent and erasable holographic gratings in the same storage volume. In the presence of a triplet excited sensitizer, Lemke-e undergoes a photochemical reaction allowing the storage of permanent photochromic holographic gratings. At wavelengths longer than the triplet state of the sensitizer, the composite behaves photorefractively, allowing the storage of erasable holograms in the same location as previously stored permanent photochromic holograms. Photochromic gratings can be written in less than one minute while photorefractive gratings can be written in less than one second. The photochromic gratings have a dark lifetime of several days. Storage times, write times, read cycles and multiplexing results are also presented.
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