Terahertz generation and optical characteristics of P-BI

Valdivia‐Berroeta, Gabriel A.; Heki, Larry K.; Jackson, Erika W.; Tangen, Isaac C.; Bahr, Charles B.; Smith, Stacey J.; Michaelis, David J.; Johnson, Jeremy A.

doi:10.1364/ol.44.004279

Cited by 19 publications

(28 citation statements)

References 25 publications

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“…Compared to the inorganic standard 1.0‐mm‐thick (110) ZnTe crystal in the optimal configuration for this crystal, the 0.15‐mm‐thick PFB‐CBS crystal in EXP1 and EXP3 configurations at the rotation angle of 45° exhibits an order of magnitude higher peak‐to‐peak THz electric field (see Figure 4b,c). This optical‐to‐THz frequency conversion efficiency of PFB‐CBS crystals based on off‐diagonal optical nonlinearity has been previously only achieved with benchmark organic nonlinear optical crystals using diagonal optical nonlinearity 15,20,42,43…”

Section: Resultsmentioning

confidence: 96%

“…In optical‐to‐THz conversion processes,8,9 benchmark organic nonlinear optical crystals simultaneously achieve high optical‐to‐THz conversion efficiency and broad bandwidth by using a diagonal optical nonlinearity from the nearly parallel alignment of nonlinear optical chromophores 10–16. For example, compared to widely used inorganic electro‐optic ZnTe crystals, organic ionic nonlinear optical crystals exhibit one order of magnitude higher THz generation efficiency, and over two times broader bandwidth, with an upper cut‐off frequency of >5 THz 17–20. This is possible in organic crystals due to their large diagonal component of macroscopic second‐order optical nonlinearity, and good phase matching between optical pump and generated THz waves 10…”

Section: Introductionmentioning

confidence: 99%

“…Most state‐of‐the‐art organic THz generators are based on optical configurations using a diagonal optical nonlinearity of benchmark organic crystals 10–20. The use of an off‐diagonal component of optical nonlinearity has rarely been investigated 21,22.…”

Section: Introductionmentioning

confidence: 99%

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X‐Shaped Alignment of Chromophores: Potential Alternative for Efficient Organic Terahertz Generators

Lee

Kim

Jazbinšek

et al. 2020

Advanced Optical Materials

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Efficient broadband organic terahertz (THz) generators using X‐shaped alignment of the nonlinear optical chromophores, as an alternative to the parallel alignment of chromophores in benchmark organic crystals, are reported. All the developed six organic benzothiazolium crystals exhibit an isomorphic X‐shaped alignment of chromophores, resulting in an unprecedentedly large off‐diagonal optical nonlinearity (>100 × 10−30 esu), which presents one of the largest off‐diagonal optical nonlinearity of organic crystals. The benzothiazolium crystals exhibit efficient broadband THz wave generation employing the off‐diagonal optical nonlinearity, in contrast to the present state‐of‐the‐art organic THz generators that mostly utilize diagonal optical nonlinearity. For using off‐diagonal and diagonal optical nonlinearities, the polarization of the optical pump is perpendicular and parallel, respectively, to the polar axis of crystals. In addition to a large THz wave generation efficiency with one order of magnitude higher peak‐to‐peak THz electric field than that generated in a 1.0‐mm‐thick inorganic benchmark ZnTe crystal, the benzothiazolium crystals generate broadband THz spectra with an upper cut‐off frequency of near 8 THz, and the absence of strong absorption dimples in the range of 0.5−4 THz. Therefore, the X‐shaped alignment of chromophores presents an interesting potential alternative for efficient broadband organic THz generators.

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Section: Resultsmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

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X‐Shaped Alignment of Chromophores: Potential Alternative for Efficient Organic Terahertz Generators

Lee

Kim

Jazbinšek

et al. 2020

Advanced Optical Materials

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“…To keep the overall molecular ordering features of the low‐bandgap mother crystal, the newly designed wide‐bandgap crystals need to provide very similar intermolecular interactions (in this work, including interionic interactions) and similar space filling characteristics (i.e., maintaining the van der Waals volume of the constituting cations and anions). [ 17b,23a ]…”

Section: Resultsmentioning

confidence: 99%

“…Following this concept, the so‐called “low‐bandgap approach”–introducing highly nonlinear optical low‐bandgap chromophores into crystals–has been widely investigated. [ 7a,b,17,20–23 ]…”

Section: Introductionmentioning

confidence: 99%

Wide‐Bandgap Organic Crystals: Enhanced Optical‐to‐Terahertz Nonlinear Frequency Conversion at Near‐Infrared Pumping

Kim

Han

et al. 2020

Advanced Optical Materials

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Enhanced terahertz (THz) wave generation is demonstrated in nonlinear organic crystals through refractive index engineering, which improves phase matching characteristics substantially. Unlike conventional low‐bandgap nonlinear organic crystals, the newly designed benzimidazolium‐based HMI (2‐(4‐hydroxy‐3‐methoxystyryl)‐1,3‐dimethyl‐1H‐benzoimidazol‐3‐ium) chromophore possesses a relatively wide bandgap. This reduces the optical group index in the near‐infrared, allowing better phase matching with the generated THz waves, and leads to high optical‐to‐THz conversion. A unique feature of the HMI‐based crystals, compared to conventional wide‐bandgap aniline‐based crystals, is their remarkably larger macroscopic optical nonlinearity, a one order of magnitude higher diagonal component in macroscopic nonlinear susceptibility than NPP ((1‐(4‐nitrophenyl)pyrrolidin‐2‐yl)methanol) crystals. The HMI‐based crystals also exhibit much higher thermal stability, with a melting temperature Tm above 250 °C, versus aniline‐based crystals (116 °C for NPP). With pumping at the technologically important wavelength of 800 nm, the proposed HMI‐based crystals boost high optical‐to‐THz conversion efficiency, comparable to benchmark low‐bandgap quinolinium crystals with state‐of‐the‐art macroscopic nonlinearity. This performance is due to the excellent phase matching enabled by decreasing optical group indices in the near‐infrared through wide‐bandgap chromophores. The proposed wide‐bandgap design is a promising way to control the refractive index of various nonlinear organic materials for enhanced frequency conversion processes.

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Designing Non‐Centrosymmetric Molecular Crystals: Optimal Packing May Be Just One Carbon Away

Valdivia‐Berroeta

Jackson

Kenney

et al. 2019

Adv Funct Materials

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Molecular nonlinear optical (NLO) crystals feature important advantages compared to inorganic counterparts, such as low dielectric constants, ultrafast response times, and large electro‐optic coefficients. Conjugated push–pull chromophores connecting electron‐donating with accepting groups are often employed in the design of these crystals. However, associated large molecular dipole moments induce antiparallel or centrosymmetric conformations in the solid‐state, which leads to NLO inactivity. The cation–anion hydrogen bond interactions of a hydroxy‐piperidino electron donor group are combined with increased van der Waals volume effects induced by an ethyl modification of the electron‐accepting moiety. This produces non‐centrosymmetric packing in the organic salt EHPSI‐4NBS ((E)‐1‐ethyl‐2‐(4‐(4‐(hydroxymethyl)piperidin‐1‐yl)styryl)‐3,3‐dimethyl‐3H‐indol‐1‐ium 4‐nitrobenzenesulfonate). Converting a methyl group into ethyl changes the packing symmetry in the molecular crystal to switch on NLO activity. This behavior is attributed to the increased size of the ethyl group, which pushes apart the van der Waals contacts of the cation that lead to centrosymmetric packing in the methyl derivative. To test the NLO properties of EHPSI‐4NBS, THz generation experiments are performed at 1200 nm pump wavelength. Spectral amplitude similar to DAST ((E)‐4‐(4‐(dimethylamino)styryl)‐1‐methylpyridin‐1‐ium tosylate) crystal is observed with generation profile from 0 to 3.8 THz.

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Terahertz generation and optical characteristics of P-BI

Cited by 19 publications

References 25 publications

X‐Shaped Alignment of Chromophores: Potential Alternative for Efficient Organic Terahertz Generators

X‐Shaped Alignment of Chromophores: Potential Alternative for Efficient Organic Terahertz Generators

Wide‐Bandgap Organic Crystals: Enhanced Optical‐to‐Terahertz Nonlinear Frequency Conversion at Near‐Infrared Pumping

Designing Non‐Centrosymmetric Molecular Crystals: Optimal Packing May Be Just One Carbon Away

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