Characterization of organic crystals for second-harmonic generation

Area of Science:

• Nonlinear optics
• Materials science
• Organic crystal engineering

Background:

• Second-harmonic generation (SHG) is crucial for frequency conversion in optics.
• Inorganic crystals commonly used for SHG exhibit limitations at longer infrared (IR) wavelengths (1300-2000 nm).
• Organic materials optimized for terahertz (THz) generation show potential for efficient SHG in the IR spectrum.

Purpose of the Study:

• To evaluate the second-harmonic generation (SHG) performance of three efficient organic terahertz (THz) generator crystals.
• To compare the SHG capabilities of DAST, DSTMS, and PNPA with a standard inorganic SHG material (beta-barium borate).
• To identify advanced organic materials for efficient IR wavelength conversion.

Main Methods:

• Characterization of second-harmonic generation (SHG) efficiency.
• Utilizing organic crystals: DAST (trans-4-[4-(dimethylamino)-N-methylstilbazolium] p-tosylate), DSTMS (4-N,N-dimethylamino-4'-N'-methylstilbazolium 2,4,6-trimethylbenzenesulfonate), and PNPA ((E)-4-((4-nitrobenzylidene)amino)-N-phenylaniline).
• Testing with infrared (IR) pump wavelengths ranging from 1200 to 2000 nm.

Main Results:

• DAST, DSTMS, and PNPA crystals demonstrated significantly higher SHG efficiency compared to beta-barium borate (BBO).
• The organic materials effectively generated SHG light at longer IR wavelengths where BBO is less efficient.
• Performance was validated across the technologically relevant 1200-2000 nm IR range.

Conclusions:

• Efficient organic THz generators (DAST, DSTMS, PNPA) are highly effective for second-harmonic generation (SHG) at longer IR wavelengths.
• These organic crystals represent a significant advancement over conventional inorganic materials for IR-based SHG applications.
• The findings pave the way for new optical devices utilizing efficient frequency conversion in the infrared spectrum.