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Abstract Yellow organic crystals, like BNA, MNA, and NMBA, can be used to generate terahertz (THz) pulses of light through optical rectification of infrared ultrafast laser pulses. When producing THz with these organic crystals, one needs to consider that 1) their damage thresholds are low due to having low melting points and 2) Fresnel reflection losses due to multiple interfaces reduce the efficiency of the generated THz output. In this work, new heterogeneous multi‐layer “sandwich” structures are developed with these yellow organic crystals by 1) fusing them to sapphire plates to permit the crystal to withstand higher laser fluences and 2) using an index‐matching fluid (liquid crystal MBBA) to decrease Fresnel reflection losses and improve the THz output. It is shown that the sapphire plates increase the damage threshold of these yellow organic crystals by a factor of two or more, thus allowing the crystals to generate higher THz electric fields. Furthermore, it is shown that the THz light output efficiency increases by assembling the yellow crystals into multi‐layered sandwich structures. For some yellow organic crystals, the sandwich structures increase the THz intensity by more than a factor of two. 

N-Benzyl-2-methyl-4-nitroanaline (BNA) is currently the industry standard for terahertz generation at 800 nm using organic materials. We developed four derivatives of BNA by replacing a hydrogen atom on the benzyl substituent with either a fluorine (F-BNA), a methoxy group (MeO-BNA), a cyano group (CN-BNA), or a methyl group (Me-BNA). X-ray diffraction measurements confirmed that all derivatives were crystallized in the same space group as BNA (Pna21). The THz generation capability of F-BNA is higher than that of BNA, with the maximum Fourier amplitude increasing by an average of 14% when pumped with wavelengths of 800, 1250, and 1550 nm. The damage threshold of F-BNA was also found to be higher than that of BNA, increasing by a factor of 1.14. The phase matching of F-BNA and BNA was found to be comparable. The increased THz output is, therefore, likely due to the higher induced nonlinear polarization, molecular hyperpolarizability, and closer molecular packing of F-BNA compared to BNA.