Xuemei Zheng

Broadband and gap-free response of a terahertz system based on a poled polymer emitter-sensor pair

We present a terahertz (THz) system based on a poled electro-optic (EO) polymer emitter-sensor pair for the generation and detection of broadband electromagnetic pulses free of spectral gaps. The gap-free THz spectrum obtained from the system is attributed to the amorphous form of the EO polymer films. Using ∼50-fs laser pulses centered at ∼800nm, a ∼100-μm thick emitter, and a ∼180-μm thick sensor, the observable bandwidth is ∼12THz. We also present an experimental study, in a systematic manner, on the effect of phase mismatch in the polymer emitter-sensor pair.

Comparison of parallel-plate and in-plane poled polymer films for terahertz sensing

We have performed calculations and measurements of the efficacy of two poling geometries of poled electro-optic (EO) polymer films for use in sensing terahertz (THz) radiation via EO sampling. Taking reflective and absorptive losses into consideration, we find that a parallel-plate (PP) poled film has a sensitivity maximum when oriented at 55 degrees to the incident probe and THz beams. In addition, we show that our in-plane (IP) poled polymer films are comparable in sensitivity to PP-poled films and discuss the potential for improving IP-poled polymer devices.

Terahertz science and applications based on poled electro-optic polymers

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.

Terahertz Probing of Carrier Dynamics in Hg-Based High- Temperature Superconducting Thin Films

We report on our investigation of time-resolved carrier dynamics in a Hg-based high-temperature superconducting film (Hg-Ba-Ca-Cu-O), using optical excitation and THz probing. The observed picosecond time-scale photoresponse suggests the material’s potential applications for high-speed photodetectors.

Application of poled electro-optic polymer films in a gap-free broadband terahertz system

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.

Generation and Detection of Gap-Free Broadband Terahertz Radiation Using Poled Polymer Films

We present a terahertz generation and detection system using poled electro-optic polymer films as the terahertz emitter and sensor, respectively. The system provides > 10 THz gap-free spectrum band.

Terahertz Spectroscopic Studies and Molecular Modeling of the Far-Infrared Properties of Electro-Optic Polymers

We present far-infrared spectra obtained through terahertz spectroscopy of electro-optic polymers and compare those measurements with molecular modeling simulations of the spectra in the 0-5 THz region.

Terahertz Science and Applications Based on Electro-optic Polymer Films

We review our work using electro-optic polymer films to generate and detect terahertz (THz) radiation. We demonstrate a THz system with a gap-free, wideband response > 12 THz. An OPA based system is also described.