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1. Intense THz Generation with New Organic NLO Crystal NMBA

   https://doi.org/10.1002/adom.202302402  

   Ludlow, Daisy JH; Palmer, Bruce_Wayne H; Green, Natalie K; Ho, Sin‐Hang Enoch; Wayment, Coriantumr Z; Kelleher, Brenan M; Barlow, Connor D; Rollans, Olivia N; Hunter, Brittan P; Rader, Claire; et al (January 2024, Advanced Optical Materials)

   Abstract Large crystal growth and characterization of the optical and terahertz (THz) properties of organic nonlinear optical (NLO) crystal NMBA (4‐Nitro‐4′‐methylbenzylidene aniline) is presented. The reported method of crystal growth consistently produces high‐quality single crystals. The THz generation efficiency and optical properties of NMBA to other THz generation crystals including BNA and MNA are compared. The low THz absorptions that make NMBA an ideal source for THz time‐domain spectroscopy are highlighted. 

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2. Optical Rectification from Next Generation Organic THz Generation Crystals

   https://doi.org/10.1364/FIO.2022.JW5B.22  

   Green, Natalie K.; Palmer, Bruce Wayne; Rader, Claire; Ho,; Zaccardi, Zac; Ludlow, Daisy J.; Lutz, Matthew J.; Alejandro, Aldair; Nielson, Megan F.; Valdivia-Berroeta, Gabriel A.; et al (January 2022, Frontiers in Optics + Laser Science 2022)

   We recently developed new organic nonlinear optical crystals for THz generation. We report the optical and THz properties of PNPA and MNA and discuss how they pave the way for the future of THz spectroscopy. 

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3. Custom terahertz waveforms using complementary organic nonlinear optical crystals

   https://doi.org/10.1364/OL.474343  

   Rader, Claire; Nielson, Megan_F; Knighton, Brittany_E; Zaccardi, Zachary_B; Michaelis, David_J; Johnson, Jeremy_A (November 2022, Optics Letters)

   Organic nonlinear optical (NLO) crystals are among the most efficient (>1%) terahertz (THz) radiation generators. However, one of the limitations of using organic NLO crystals is that the unique THz absorptions in each crystal make it difficult to obtain a strong, smooth, and broad emission spectrum. In this work, we combine THz pulses from two complementary crystals, DAST and PNPA, to effectively fill in spectral gaps, creating a smooth spectrum with frequencies out to 5 THz. The combination of pulses also increases the peak-to-peak field strength from 1 MV/cm to 1.9 MV/cm. 

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4. Improved Generation of Terahertz Light through Heterogeneous Multi‐Layered Organic Crystal Structures

   https://doi.org/10.1002/adom.202502694  

   Alejandro, Aldair; Petersen, Paige K; Ludlow, Daisy_J H; Holland, Kayla M; N'diaye, Fatoumata; Manwaring, Tanner W; Biggs, Megan F; Michaelis, David J; Johnson, Jeremy A (October 2025, Advanced Optical Materials)

   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. 

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5. Improved Terahertz Output from Layered Organic Crystal Structures

   https://doi.org/10.1364/CLEO_AT.2023.JW2A.53  

   Ludlow, Daisy J.; Alejandro, Aldair; Petersen, Paige K.; Holland, Kayla M.; N’diaye, Fatoumata; Manwaring, Tanner; Michaelis, David J.; Johnson, Jeremy A. (January 2023, CLEO 2023)

   We have improved the THz output and damage threshold of yellow organic THz generation crystals by fusing them to sapphire and using liquid crystals as index matching fluid to reduce reflective losses. 

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