RESUMO
One of the most effective ways of generating terahertz (THz) radiation involves the conversion of short-pulsed IR or visible laser light into THz pulses at significantly lower frequencies. This conversion can be accomplished using organic crystals with nonlinear optical crystal (NLO) properties for IR to THz conversion through optical rectification. Due to the high refractive indices of organic crystals, pump laser light as well as generated THz radiation is lost from reflections at crystal surfaces. Here we report a structure composed of a layered series of materials with intermediate refractive indices designed to reduce reflective losses and improve the THz generation from organic crystals. This structure increases the transmission coefficients for both infrared pump input and THz output. We combine simple theoretical calculations with experimental data to show that a structure composed of materials with intermediate refractive indices can be used to increase generated THz intensity by nearly 50%.
RESUMO
We present the structural and THz generation characteristics of the molecular salt crystal (E)-2-(4-(dimethylamino)styryl)-1,1,3-trimethyl-1H-benzo[e]indol-3-ium iodide (P-BI) using optical rectification with IR pump wavelengths. P-BI shows a peak-to-peak field â¼6 times greater than inorganic crystal GaP, and a broader THz spectrum. Data were obtained from 0-6 THz showing a significant dip in generation at 1.8 THz, similar to what has been observed with the THz generation crystal DAST at 1 THz. We characterized the power dependence of P-BI at different IR wavelengths, with optimal THz generation at the 1550-nm pump wavelength. To model THz generation as a function of P-BI crystal thickness, we measured the THz complex refractive index and the IR group index; modeling shows that imperfect phase matching leads to spectral narrowing centered at â¼2.5 THz as the crystal thickness is increased. P-BI could provide a useful alternative to inorganic THz generation crystals such a GaP.
